Intracardiac Electrograms (IEGM) and Catheter Positions
Presenter
Presentation Notes
AN EP study uses surface ECGs and intracardiac electrograms (IEGMs) to assess and characterize the cardiac activation and conditions. Recall that a surface ECG represents the electrical activity of the entire heart. It is the sum of all of the action potentials of all of the cardiac cells. Thus an ECG provides information about the sequence of cardiac depolarization and repolarization across the entire heart. An intracardiac EGM represents electrical activity in a localized area of the heart – specifically, between two closely spaced electrodes (bipolar electrode pair) or a single unipolar electrode (with a reference located some distance away) that lie near or come into contact with the endocardial tissue. The electrodes record electrical signals at the precise moment a depolarization wave passes by. The point of the most negative slope of a unipolar recording is the point at which the electrical activity is passing under the electrode. In general, only the rapid depolarization phase (Phase 0) of the cardiac tissue is recorded. Thus an EGM provides precise, localized information in the immediate vicinity of the intracardiac electrodes.
2
Unipolar Recording
Catheter with the positive electrode placed in the heart
V1 lead used for the negative
(reference) pole
+
-
Presenter
Presentation Notes
Unipolar recording: With unipolar recording, the electrogram is recording between a single electrode on a catheter placed in the heart and a reference pole outside of the heart. That reference pole is often either the V1 lead, right leg lead or Wilson’s Central Terminal which is within the 12 lead ECG or EP computer recording system. The recording takes place between the positive electrode, which is that single electrode placed in the heart and the negative pole which is the reference. Because unipolar recording encompasses a rather large area there is occasionally the tendency to record some noise on the electrogram because when the reference is placed on the chest the electrical activity given off by the lungs and chest muscle can create that noise. Thus a unipolar recording is more prone to pick up far field signals.
3
Bipolar Recording
Presenter
Presentation Notes
Bipolar recording: With bipolar recording, the electrogram is recording between a pair of closely spaced electrodes within the heart in contact with the endocardium. One electrode will be positive (+) and the other negative (-) and the recording essentially is made up of only the activity that occurs between those two electrodes. Activity between those electrodes that is moving in the direction of the positive electrode will create a positive deflection and that activity moving away from the positive electrode will create a negative deflection. Because a bipolar recording sees only what occurs between those closely spaced positive and negative electrodes, it is less prone than unipolar recording to pick up noise on the signal. Thus there is less far field influence.
4
Bipolar Electrograms
5
Bipolar Electrogram Construction
- = Uni 1
Uni 2
Uni1 (+) – Uni2 (-) = Bipolar
Unipolar Bipolar
+ +
- -
Bipole
Uni-distal
Uni-proximal
Presenter
Presentation Notes
Bipolar versus unipolar recording The bipolar electrogram reflects the voltage potential difference between the two poles. The bipolar electrogram is the algebraic difference between the two unipolar electrograms and is as below: Bipolar = uni(+) – uni (-) Since when recording a bipolar electrogram (for example with an ablation catheter), the distal electrode is negative (because you use that electrode to either pace and/or ablate) and the proximal electrode is positive. This may be reversed depending on the situation when using diagnostic catheters. Thus the electrograms will be near mirror images of each other, only one will be slightly delayed in time.
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Bipolar signal construction
(Signal 1 + Noise) – (Signal 2 + Noise) = Signal 1 – Signal 2
t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t1 t2 t3 t4 t5 t6 t7 t8 t9
Differential amplifier
+ -
Presenter
Presentation Notes
Bipolar signal construction: This slide breaks down the bipolar electrogram into the two unipolar recordings from the positive and negative electrodes of the bipolar pair after the negative recording has been flipped positive. The yellow triangles represent noise. Then signal 2 is subtracted from signal 1 to obtain the resultant bipolar recording. t1 will have one positive block (1-0=1) t2 will have 2 positive blocks (2-0=2) t3 will have 2 positive blocks (3-1=2) t4 will have 0 blocks (2-2=0) t5 will have 1 positive blocks (4-3=1) t6 will have 1 positive blocks (3-2=1) t7 will have 2 negative blocks (1-4=-3) t8 will have 3 negative blocks (0-3=-3) t9 will have one negative block (0-1=-1) t10 will have 0 blocks (2-2=0) t11 will have 0 blocks (1-1=0)
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Bipolar EGMs
E1
E2
Bi
Presenter
Presentation Notes
Animation of the formation of a bipolar recording from the two unipolar recordings: This animation demonstrates the effects of a differential amplifier, and high pass filtration. First both unipolar electrograms are flipped positive and E2 is overlaid on E1 and those components of the electrogram that are numerically the same (regardless of the polarity) are subtracted, leaving only the difference between the two electrograms remaining. In this case since E2 is slightly delayed after E1, there will be a difference for the atrial signal. However, since both E1 and E2 would detect the ventricular far-field signal essentially at the same time, those two ventricular components will cancel each other out. The remainder of the signal is what is then subjected to filtering to remove the lower frequencies. In this example it is subjected to a 30 Hz highpass filter Then the resultant signal is flipped positive. The resulting trace then represents only what occurred between the electrodes and is your bipolar recording.
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Electrophysiology of the cardiac muscle cell
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Affect of the Direction of Activation on the Electrogram
Direction of Activation and its Influence on the Bipolar ECG
- +
Presenter
Presentation Notes
Direction of Activation and its Influence on the Bipolar ECG: If the activation is moving toward the positive electrode from a proximal site (in the positive electrode to negative electrode direction), the initial deflection may be positive (but small) and will be followed by a large negative deflection as the activation moves away from the positive pole towards the negative pole of the bipolar pair. There may also be a small positive deflection at the end as the impulse travels away distally from the pair (far field). Thus, if that initial deflection is positive it may mean the impulse is coming from a proximal site. However, this is usually no easy to determine, and unipolar recording is more useful for that.
Direction of Activation and its Influence on the Bipolar ECG
- +
Presenter
Presentation Notes
Direction of Activation and its Influence on the Bipolar ECG: If the activation is moving toward the positive electrode from a distal site (in the negative electrode to positive electrode direction), the initial deflection may be negative (but small) and will be followed by a large positive deflection as the activation moves toward the positive pole and away from the negative pole of the bipolar pair. There may also be a small negative deflection at the end as the impulse travels away distally from the positive electrode of the pair (far field). Thus, if that initial deflection is negative, it may mean the impulse is coming from a distal site. However, this is usually no easy to determine, and unipolar recording is more useful for that.
Direction of Activation and its Influence on the Bipolar ECG
- +
A B C
Presenter
Presentation Notes
Direction of Activation and its Influence on the Bipolar ECG: If the activation is moving perpendicular to the bipolar electrode orientation, there will be a biphasic waveform with an initial positive deflection as it travels close to the positive electrode in a perspective view (since recordings see through the positive electrode) and then a negative deflection as it travels away from the positive electrode. If directly perpendicular, the positive and negative components will be equal in amplitude. However, if it comes in at an angle the size of the positive and negative components will vary. The more the activation is moving towards the positive electrode in the negative to positive pole direction, the larger the initial positive deflection and smaller the following negative deflection will be. The more the activation is moving towards the negative electrode in the positive to negative pole direction, the smaller the initial positive deflection and larger the following negative deflection will be. The largest positive amplitude will occur when the activation is moving toward the positive pole parallel to the orientation of the bipolar pair. The largest negative amplitude will occur when the activation is moving toward the negative pole parallel to the orientation of the bipolar pair.
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Unipolar Electrograms
14
unipolar
The influence of any active cell upon the unipolar recording is inversely proportional to the distance between the cell and the electrode
AP
Influence of individual cells on the Unipolar Electrogram
Because activation propagates from cell-to-cell, active cells are organized along a wave “front”
Consequently, the unipolar electrogram is a summation of membrane currents
Presenter
Presentation Notes
Influence of individual cells on the Unipolar Electrogram: The influence of any active cell upon the unipolar recording is inversely proportional to the distance between the cell and the electrode.
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Unipolar versus Action Potential
Presenter
Presentation Notes
Unipolar versus the Action Potential: It can be mathematically shown that the unfiltered unipolar recording is correlated with a scaled version of the monophasic action potential at the electrode. The scale factor is determined by the degree of influence that wavefront propagation has on the potential near the electrode. This is simply the far-field effect and it scales inversely with distance away from the recording site. In practical terms, this creates a smoother recording than the monophasic action potential, as observed in the figure. Note that the unipolar recording is inverted from the monophasic recording because the unipolar potential is measured in the extracellular fluid, while the action potential is measured across the cell membrane. Also note the phase reversal in the middle of the unipolar recording which comes from the relative approach and retreat of the propagating wavefront as it passes under the electrode. Note that the most negative slope of the unipolar recording (maximum –dV/dt) corresponds to phase 0 (depolarization phase) of the action potential. Thus it corresponds to the time when the majority of the Na+ channels have opened causing that rapid depolarization.
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Comparison of Bipolar versus Unipolar Recording
17
Unipolar recordings measure an amplified version of voltage at a single electrode (E1) and retain both near and far field signal components
Bipolar recordings measure the amplified difference between two unipolar electrodes (E1 - E2), which reduces common-mode noise and far-field signal components
E1 E2
Comparison of Unipolar versus Bipolar Recording
Presenter
Presentation Notes
Unipolar versus bipolar: Unipolar recordings measure an amplified version of the voltage at a single electrode (E1) and retain both near and far field signal components. Thus, unipolar recordings tell you whether activation is approaching or receding and can guide the doctor towards a focus of an activation. For a uniformly propagating wave in an ideal medium, the signal at E2 is the same as the signal at E1, except that it is slightly delayed in time. This is a special case found only in a propagating medium Bipolar recordings measure the amplified difference between two unipolar electrodes (E1 - E2), which reduces the common-mode noise and far-field signal components. Since the propagation wavefront is essentially uniform as it moves along the myocardium, electrodes E1 and E2 should record essentially the same unipolar waveform but only delayed in time as stated above. Thus the difference between those two unipolar recordings which represents the bipolar recording, expresses the change in the waveform from E1 to E2. Bipolar recordings do not give much information on how a propagation wave is flowing and instead mainly only give you timing information (i.e., the doctor will search for the earliest bipolar recording to find a focus of an activation).
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Unipolar versus Bipolar
Bipolar recordings approximate a measure of the rate-of-change of the wavefront
This measure is approximate because cardiac wavefronts do not propagate uniformly and the medium is not ideal
E1 E2
Presenter
Presentation Notes
Unipolar versus bipolar: Bipolar recordings approximate a measure of the rate-of-change of the wavefront. This measure is approximate because cardiac wavefronts do not propagate uniformly and the medium is not ideal. It can also be mathematically shown that unfiltered bipolar recordings measure the rate-of-change of the wavefront in the idealized textbook case. Therefore in practice, bipolar recordings approximate a measure of the rate-of-change of the wavefront. This measure is approximate because cardiac wavefronts do not propagate uniformly and the medium is not ideal. However, it is a very good approximation. The unfiltered unipolar recording is correlated with the wavefront itself, while the unfiltered bipolar recording is correlated with wavefront change. Thus, the unipolar recording gives information on the wavefronts approach and retreat, whereas the bipolar only expresses the change from E1 to E2 and thus can only be used for timing.
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Propagating Activation Wavefront
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Propagating Activation Wavefront
Depol. toward positive electrode Positive Signal
Repol. toward positive electrode Negative Signal
Depol. away from positive electrode Negative Signal
Repol. Away from positive electrode Positive Signal
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Comparison of the Filtered and unfiltered Unipolar and Bipolar Recordings
•Note the peak negative slope indicated by the arrow in the unfiltered unipolar recording corresponds to the indicated negative peak in the highpass-filtered unipole, confirming the approximation to rate-of-change.
Presenter
Presentation Notes
Waveforms – Comparison: To graphically integrate and summarize these concepts, an unfiltered unipolar recording is displayed at the top, followed by a 32 Hz, highpass-filtered unipole, followed by an unfiltered bipole, and finally a 32 Hz, highpass-filtered bipole at the bottom. Waveforms – Unipolar unfiltered and unipolar filtered (32Hz) Note the peak negative slope indicated by the arrow in the unfiltered unipolar recording corresponds to the indicated negative peak in the highpass-filtered unipole, confirming the approximation to rate-of-change. In a sheet of uniformly conducting tissue, the maximum negative slope (−dV/dt) of the signal coincides with the arrival of the depolarization wavefront directly beneath the electrode.
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•Note the brief occurrence of the zero slope (arrow) in the unfiltered unipole which corresponds with the zero-crossing and phase-reversal of the highpass-filtered unipole. It also corresponds to the zero crossing of the unfiltered bipole and the most positive peak of the filtered (32Hz) bipole.
Comparison of the Filtered and unfiltered Unipolar and Bipolar Recordings
Presenter
Presentation Notes
Waveforms – Unipolar unfiltered and unipolar filtered (32Hz): Note the brief occurrence of the zero slope indicated by the arrow in the unfiltered unipole. This point corresponds to the indicated zero-crossing and phase-reversal of the highpass-filtered unipole. It also corresponds to the zero crossing of the unfiltered bipole and the most positive peak of the filtered (32Hz) bipole.
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Physical basis of electrograms - Summary
– The unipole records the perspective-view of the wavefront Wavefront = summation of the action potentials over space and time Action potential = generated by membrane ion currents
– The bipole records the derivative (slope) of the unipole
– Bipolar recording (spatial) and the highpass filter (temporal) are correlated, and have a lower sensitivity to low frequencies (slow conduction) and higher sensitivity to high frequencies (fast conduction)
Unipolar versus Bipolar Recording
Presenter
Presentation Notes
Unipolar versus bipolar recording: Physical basis of electrograms - Summary The unipole records the perspective-view of the wavefront Wavefront = summation of the action potentials over space and time Action potential = generated by membrane ion currents The bipole records the derivative (slope) of the unipole Bipolar recording (spatial) and the highpass filter (temporal) are correlated, and have a lower sensitivity to low frequencies (slow conduction) and higher sensitivity to high frequencies (fast conduction)
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25
26
27
Problems influencing the signal fidelity: – Signal to noise ratio – Distortion of the signal
To limit these a properly designed amplification system with filters is required
Noise
Signal Filtering
Presenter
Presentation Notes
Filtering: When detecting and recording the ECG signals, there are two problems that influence the fidelity of the signal. Signal to noise ratio Ratio of the energy in the ECG signal to the energy of the noise Noise = electrical signals that are not part of the wanted ECG signal. Distortion of the signal Relative contribution of any frequency component in the ECG signal should not be altered To limit these 2 conditions a properly designed amplification system with filters is required
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Amplifier
High Pass Filter
Low Pass Filter
Isolation Amplifier
The Amplifier increases the amplitude of the signals (often up to a factor of 10000).
Filtering The leads record the raw electrical potential data and send it to the amplifier.
The high-pass filter removes any base line drift or physiologic noise by cutting off anything below a set value.
An isolation amplifier isolates the circuit from the patient (this can be done by transmitting the signals optically).
The low-pass filter removes any environmental noise by cutting off anything above a certain value.
The resultant signal is either the surface EKG or intracardiac signals of interest.
Presenter
Presentation Notes
Filtering: Recording systems include a system to filter out any unwanted signals that are picked up by the leads and only let the desired signal to enter. Below is the system: The leads record the raw electrical potential data and send it to the amplifier. The raw ECG data has extremely weak signals ranging from 0.5 mV to 5.0 mV, plus a DC component of up to 300 mV caused by the electrode-skin contact and a common-mode component of up to 1.5 V, caused by the potential created between the electrodes and the ground. The useful bandwidth of a 12 lead ECG signal can range from 0.5 Hz to 50 Hz, for standard monitoring, up to 1 kHz for late-potential measurements. The standard clinical ECG application has a bandwidth of 0.05 Hz to 100 Hz. In order to enlarge the R-wave to about 0.5 – 1 V, the signal needs to be amplified by an amplifier. The Amplifier increases the amplitude of the signals (often up to a factor of 10000). The data is then passed on to the filters. To remove the low-frequency noise, a high-pass filter can be used. The signal first enters the high-pass filter where it removes any base line drift or physiologic noise by cutting off anything below a set value. For the surface ECG leads, the corner frequency of the filter should be between 0.03 to 0.1 Hz, and for bipolar and unipolar intracardiac recordings it is usually between 0 and 32Hz. The signal then enters an isolation amplifier which isolates the circuit from the patient (this can be done by transmitting the signals optically). The signal then enters the low-pass filter where it removes any environmental noise by cutting off anything above a certain value. The resultant signal is either the surface EKG or intracardiac signals of interest with all unwanted noise removed.
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Surface ECG signals are concentrated in the bandwidth between 1Hz - 80Hz. Intracardiac ECG signals are
concentrated in the bandwidth between 15 - 60Hz High Resolution ECG signals are
concentrated between a bandwidth of 0.05Hz - 300Hz
Filtering
Presenter
Presentation Notes
Filtering: Most of the energy in the standard ECG signals is concentrated in a bandwidth between 1Hz - 80Hz. Intracardiac ECG signals are concentrated within a bandwidth of about 15-60Hz. High resolution ECG signals are concentrated between a bandwidth of 0.05Hz - 300Hz in order to acquire as many signal frequencies as possible.
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Filtering
Presenter
Presentation Notes
Signal Filtering. If we want to use an amplifier to enlarge the signal, we need to make sure that the amplifier has a suitable bandwidth to cover the frequency range of the desired signal. Since the raw data of the ECG signal is a mixture of useful signals and some noise, and since the frequency range of the signal is different from that of the noise, we can use filters to separate the useful signals from the noise. The normal surface ECG waveform is from 0.1 Hz to 250 Hz, and depolarization recorded from the intracardiac recording is considered to be from 15-60 Hz. A number of different kinds of noise can interfere with the recordings Noise from: Respirations causing baseline drift = < 0.3 Hz Electrode movement (surface) or contact noise resulting in shifts in the baseline (baseline drift) caused by changes in the electrode-skin impedance = < 0.3 Hz Skeletal (electromyogram – EMG) noise = frequency range (1 – 5000 Hz), AC power line noise = 50/60 Hz Electromagnetic interference from other electronic devices, with the electrode wires serving as antennas Noise coupled from other electronic devices, usually with high frequencies
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ECG data filtered with 60Hz Notch Filter
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Frequency (f)
Mag
nitu
de
unfiltered ECGfiltered ECG
Filtering
Presenter
Presentation Notes
Signal filtering: The noise from respirations and electrode movement are different from the ECG and thus can be filtered out by the high-pass filter The skeletal (EMG) noise can be reduced by requiring the subject to maintain motionless during the recording. The AC noise (50 or 60 Hz) can be filtered out by a 50/60Hz notch filter. The P-wave and T-wave mainly contain frequencies below 60 Hz and the R-wave also mainly contains frequencies below 60 Hz but can contain some frequencies beyond 60 Hz. Thus, the notch filter may have an effect on the morphology.
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Filtering – Lowpass Filter Lowpass Filter
V
f cutoff frequency
(250 - 500 Hz)
(Passes LF)
A lowpass filter allows lower frequencies to pass through while reducing higher frequencies, relative to an upper cutoff frequency. In conventional electrophysiology, this cutoff (corner) frequency is typically in the range of 250 to 500 Hz.
Corner Frequency
Pass-band Stop-band
Presenter
Presentation Notes
Filtering – Lowpass Filter: A bandpass filter is made up of a lowpass and highpass filter. A lowpass filter allows lower frequencies to pass through while reducing higher frequencies, relative to an upper cutoff frequency. In conventional electrophysiology, this cutoff frequency (also called the corner frequency) is typically in the range of 250 to 500 Hz. Thus anything lower than that cut off passes and anything higher is reduced. Since the normal range of frequencies that make up the cardiac depolarization are from 15-60Hz, the lowpass filter has no effect on the morphology of electrogram in the recording.
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Filtering
Lowpass Filter
V
f cutoff freq
(250 - 500 Hz)
(Passes LF)
Highpass Filter
V
f cutoff freq
(30 - 32 Hz)
repol depol
Highpass Filter
V
f cutoff frequency (30 - 32 Hz)
(Passes HF)
The highpass filter is the exact opposite of the lowpass filter in which higher frequencies are now allowed to pass through while reducing lower frequencies, relative to a lower cutoff (corner) frequency, which is typically 30 Hz.
Corner Frequency
Pass-band Stop-band
Presenter
Presentation Notes
Filtering – Highpass Filter: The second component of a bandpass filter is the highpass filter. A highpass filter is the exact opposite of a lowpass filter and allows higher frequencies to pass and reduces low frequencies, relative to the lower cutoff frequency (also called the corner frequency), which is usually about 30Hz. Thus it allows anything over 30Hz to pass and reduces anything below that. Since the normal range of frequencies that make up the cardiac depolarization are from 15-60Hz, the highpass filter will have a big effect on the morphology of the electrogram in the recording, since it will eliminate the low frequencies.
•The highpass reduces signal components related to physiologic noise, i.e., repolarization. Thus the intent of these filter settings is to allow signal components related to depolarization to pass.
•The lowpass section of the bandpass filter is intended to reduce environmental noise.
Presenter
Presentation Notes
Bandpass Filtering: When the two filters are combined, we have a bandpass filter that allows a band of frequencies to pass through in the range between about 30 and 500 Hz. Filtering- “Physiological”: The highpass section is intended to reduce signal components related to repolarization, conventionally regarded as physiologic noise. The practical intent of these filter settings is to allow signal components related to depolarization (15-60Hz) to pass through the filter. Filter – “Environmental”: The lowpass section of the bandpass filter is intended to reduce environmental noise.
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Filtering
V
f ~16 Hz ~64 Hz
32 Hz
Subtle point about highpass section:
• The bandpass filters actually exhibit a gradual response to frequency, as shown in the figure, rather than an idealized, straight-line response
• Frequencies below 16Hz (green), are reduced enough by the filter that they are essentially insignificant. • At frequencies approximately twice the cutoff frequency (in this case 64 Hz) there is a range of frequencies
above this point in which the response of the filter is fairly flat and the signal components are passed through essentially unchanged.
Presenter
Presentation Notes
Filter - highpass: Frequencies below this point, shown in the green region, are reduced enough by the filter that they are essentially insignificant. Filter – “64Hz” Note that there is another important characteristic of this filter at a frequency approximately twice the cutoff frequency, in this case 64 Hz. Note that there is a range of frequencies above this point in which the response of the filter is fairly flat and the signal components are passed through essentially unchanged.
36
V
f ~16 Hz ~64 Hz
approximates the derivative
Subtle point about highpass section:
Depolarization
Filtering
• The red line shows a special filter response which computes the time-derivative of the signal. • The gradual response of the highpass filter between 16 to 64 Hz is a reasonable approximation
of the rate-of-change for signal components that fall into that range of frequencies. • The majority of the signal energy related to depolarization falls between 15-60 Hz. Thus unipolar
recordings made with a highpass filter set at 32 Hz are correlated with wavefront change. Note both the highpass filtered unipole and the unfiltered bipole are both correlated with wavefront change.
Presenter
Presentation Notes
Filter – Highpass: The subtle aspect of this filter occurs in the region between these two frequencies (16Hz and 64Hz). The red line indicates a special kind of filter response which computes the time-derivative of the recorded signal. Therefore, the gradual response of the highpass filter between 16 and 64 Hz is a reasonable approximation of the rate-of-change for those signal components in the recording that fall into that range of frequencies. The majority of the intracardiac signal energy related to depolarization falls between about 15 and 60 Hz. This means that unipolar recordings made with a highpass filter set at 32 Hz are correlated with the wavefront change. Note that both the highpass filtered unipole and the unfiltered bipole are both correlated with wavefront change.
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Clinical use of Unipolar Recording
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wavefront receding “QS”
“RS”
“R”
50% – 50% approaching &
receding
wavefront approaching
Schematic Representation of RA
• early “QS”
• mid “RS”
• late “R”
Stimulation of HRA portrays endocardial breakthrough from the SA node network with
typical waveform morphologies:
Expected Electrogram Progression
A
B
C
Presenter
Presentation Notes
Electrogram progression: In this all of the activation is moving away from the recording site since the activation begins there and spreads down. There is no activation moving toward that electrode. Thus, since all activation is moving away, the ECG morphology will be entirely negative. This is called a “QS” morphology pattern. In this case the activation wavefront from “A” is moving toward the recording electrode, thus the initial deflection will be positive. Then the activation passes it and moves away toward the IV resulting in a second component of the electrogram that is negative. This is called an “RS” morphology pattern and occurs when activation approaches and then recedes from a recording site. This site is located at the IVC where the myocardium ends. Thus no activation can occur below it. Therefore that electrode only sees the activation approaching it resulting on only a positive deflection. This is called an “R” morphology pattern. This is also seen with far-field sensing.
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Sinus Rhythm
SA Node
“QS”
Actual Electrogram Progression
A
B
C
Presenter
Presentation Notes
Actual electrogram progression: These next 3 figures display an unfiltered unipolar animation of activation in the right atrium (RA) during sinus rhythm. The first slide shows the activation begin at the sinus node region and travel away from that site resulting in a “QS” pattern. In the second figure, the activation moves toward and them away from the electrode located in the mid-lateral region resulting in an “RS” pattern. In the third figure now all activation moves toward the electrode placed at the RA_IVC junction and stops resulting in an “R” pattern.
40
Sinus Rhythm
Mid Lateral
“QS”
“RS”
A
B
C
Actual Electrogram Progression
Presenter
Presentation Notes
Use the previous slide notes. This picture is attached to slide 41.
41
Sinus Rhythm
IVC Junction
“QS”
“RS”
“R”
A
B
C
Actual Electrogram Progression
Presenter
Presentation Notes
Use the notes in slide 41. This picture is attached to slide 41.
42
Large mass or distance = Large
amplitude
R Wave Amplitude is Dependent on the Amount of Myocardium Involved
Large mass myocardial recruitment
Small mass myocardial recruitment
Large mass or distance = Large
amplitude
43
Amplitude of the ECG is effected by the size of the Myocardium
Presenter
Presentation Notes
This slide shows an animation of the previous slides.
44
Dead
Diseased
Healthy
1. If the tissue is diseased it will exhibit low-frequency low amplitude electrograms, but if healthy it will have high frequency high-amplitude electrograms
2. With a set distance between the two electrodes of the bipolar ECG, you can see the activation time and thus it tells you conduction speed
Myocardial Characteristics and the Bipolar ECG
45
Rapid conduction such as with myocardial recruitment post-exit results in a narrow
duration
R Wave Width is Dependent on the Conduction Speed
Narrow R Wave Wide R Wave
Slow conduction across diseased or
deep tissue results in a wide duration
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1
CL
1
2
3
4
Unipolar Recording: Circus Movement
2 4
3
The red loop represents one cycle length (CL) of the tachycardia
CL Start
CL End
1
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1
CL
1
Unipolar Recording: Circus Movement
The red loop represents one cycle length (CL) of the tachycardia
CL End
CL Start 1 1
• The electrogram is a result of the activation from “A” and “B”
• “A” = activation moving toward the electrode
• “B” = activation moving away from the electrode B A
A
B
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Normally an arrhythmia focus has a negative deflection resulting in a QS Pattern, but that is not always true
Q wave (qs-RS) pattern
• QS Pattern at the arrhythmia focus site
• A qs-RS pattern can occur when: • There is a preferential pathway from the
arrhythmia focus • Activation proceeds from a low to high
current generating region • There is myocardium exhibiting
anisotropic conduction
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Unipolar Recording: Within Small Conducting Channel
* Breakout site with large and rapid activation
Preferential pathway from the arrhythmia focus – Two components of
activation occur: Slow confined
conduction Rapid myocardial
breakout conduction
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Double Potentials
51
2
Bipolar ECG Unipolar ECG
Double Potentials
* 1
3
Barriers to conduction Turn around
point
Turn around point = end of a fixed or functional barrier such as scar tissue (fixed) or the crista terminalis (functional)
52
Double Potentials
Presenter
Presentation Notes
This slide illustrates the double potential at the block site (CT)during AFL. Please point to 1. The far field and the near field components 2. The slop of the far field components are stiffer then the near field component , which indicate almost simultaneous conduction , while the near field component indicate sequential activation. 3. RA 9 electrogram is from the most proximal pair of the duo deca 4. The duo deca catheter is on the anterior side of the CT
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2
Bipolar ECG Unipolar ECG
Double Potentials
* 1
3
Barriers to conduction
Area of slow conduction
54
Flatline Between Double Potentials
＋ ＋ ＋
＋ ＋ ＋
*
*
* Slow conduction zone (SCZ)
SCZ
SCZ
55
Double Potentials Double potentials are indicative of a line of
block Crista terminalis is an important anatomical
and functional barrier in atrial flutter Lines of block are either fixed or functional
(anisotropy) Atriotomy sites and the Eustachian ridge are
examples of fixed lines of block Evidence exists that block in the region of the
crista terminalis during atrial flutter is a form of functional conduction block
56
Anisotropic Myocardial Activation
57
Anisotropic Myocardial Activation
Results in a qs-RS Pattern
Presenter
Presentation Notes
The arrow facing down is coming towards “b” but not as large as that of the arrow moving away toward “a” so it is just a little negative total.
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Utility of Unipolar Recording Allows the recording of detailed
electrogram information from the distal electrode of the ablation catheter – Confirmation of the earliest activation site (QS
pattern) – Analysis of the ST segment reveals the
degree of tissue contact – Presence of ST elevation after ablation
confirms the tissue has been ablated ST elevation: reflects myocardial tissue damage
Presenter
Presentation Notes
Utility of Unipolar recording; In actual ablation procedures, the unipolar recording can offer the doctor an excellent additional tool to better confirm an ideal site to apply a radiofrequency energy application. If you are using unipolar recording, the electrode will be positive. When recording everything is seen through the positive electrode. If activation moves toward the positive electrode, the electrogram recording will be positive. If the activation has passed the electrode and is traveling away from it, a negative deflection is produced. Thus, the electrogram gives a sense of the wavefront propagation. Unipolar recording also allows the recording of detailed electrogram information from the distal electrode of the ablation catheter which can help the doctor..: Confirm the earliest activation site (QS pattern) Analyze the ST segment revealing the degree of tissue contact Observe the presence of ST elevation after ablation confirming the tissue has been ablated ST elevation: reflects myocardial tissue damage These concepts will be explained in the following pages.
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Utility of Unipolar Recording Confirmation of the earliest activation site (QS pattern)
QS Pattern
rS Pattern
1 2
3
4
1-2
3-4
Presenter
Presentation Notes
Utility of unipolar recording: By locating the site with a QS pattern, it will confirm the earliest activation site. Look at the example in the figure: See that bipolar electrode pair 1-2 records the earliest activation (i.e. the potential occurs before the potential recorded by electrode pair 3-4). Assuming that that site recorded by electrode pair 1-2 is the earliest site found in the heart, then the bipolar pair 1-2 tell you that the true site of the origin is located somewhere between electrodes 1 and 2. If the spacing between those electrode is narrow such a 2mm which it usually is on an ablation catheter, it will most likely be accurate enough for most purposes, however, if the spacing is wider such as 5mm, it would not be very accurate since it could occur anywhere within that 5mm and a standard ablation lesion is only 4mm in diameter. Thus, bipolar recording is used to only tell the activation sequence. That is, it tells which site has the earliest activation. However, with bipolar recording, you do not know which electrode of the bipolar recording pair is closest to the site of earliest activation. Now look at the unipolar recording of each of the 4 electrodes. You now see that electrode 1 has a QS pattern meaning that the activation starts there and electrode 2 has an rS pattern meaning it is away form the origin and activation is traveling toward it (i.e. a small “r” wave indicates activation is moving toward it). You will also note that in the electrograms recorded by electrode 3 the “r” is even bigger than the “r” in electrogram 2, and in electrogram 4 the “r” is even bigger. Thus, this shows that the further you are from the origin of the activation, the larger the “r” wave will be and as you get closer and closer it will get smaller and smaller until you reach the site of origin where only a QS will be recorded. Therefore, unipolar recording can tell us which electrode is at the earliest site of activation (QS pattern). If an “r” wave is present and the doctor moves the catheter in a certain direction and he/she notices that the “r” wave is getting smaller, it tells the doctor that he/she is getting closer to the origin. However, an “r” wave does not always mean you are away from the origin of the activation. It may mean that the origin is more epicardial. See the next page.
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Unipolar versus Bipolar
*
Endocardium
Epicardium
+
Presenter
Presentation Notes
Unipolar versus Bipolar: However, an “r” wave does not always mean you are away from the origin of the activation. It may mean that the origin is more epicardial or deep in the myocardium. In this example the activation travels toward the electrode from deep in the myocardium resulting in an initial “r” wave. This is more common in the left ventricle where the myocardium is thick.
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Pre-ablation: strong tissue contact
ST elevation
Utility of Unipolar Recording
Analysis of the ST segment reveals the degree of tissue contact
ST elevation: reflects myocardial tissue damage
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Presenter
Presentation Notes
Utility of unipolar recording: During unipolar recording you can determine if you have good tissue contact by seeing if you have ST elevation as in this slide. The ST elevation means you are pressing the catheter tip hard against the myocardium and thus you have good tissue contact (ST elevation reflects myocardial tissue damage). That will result in a much more efficient radiofrequency energy application.
62 Pre-ablation Post-ablation ST segment changes (elevation): Post-ablation
Utility of Unipolar Recording ST segment elevation post-ablation confirms the tissue has been damaged, thus the tissue has been ablated
Presenter
Presentation Notes
Utility of unipolar recording: ST Segment elevation post-ablation means the tissue has necrosed, and thus the ablation was effective. This gives the doctor immediate feedback that the ablation application was effective. Without this, the doctor can only assume the application was effective, where as with unipolar electrogram monitoring the doctor can see the tissue has been ablated.
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SVC
HEART
IVC
Ablation catheter
Reference electrodes
Record unipolar recording between the distal electrode of the ablation catheter (or the electrodes on the CS catheter) and one of the reference electrodes in the IVC
HRA
Unipolar Catheters
Presenter
Presentation Notes
Unipolar catheters: Add a more realistic picture showing the placement if the reference electrodes in the IVC. The Wilson central terminal introduces substantial electrical noise, and using the IVC reference electrode as an alternative to the Wilson central terminal will reduce the electrical noise. The amplifier left set in a bipolar configuration, but the negative input is a fir distance from the heart chambers (in the IVC). The distal electrodes of the unipolar catheter are positioned at either the high right atrium, His bundle region or right ventricular apex. If the unipolar catheter has two electrodes, one can be used for unipolar recording and the other for unipolar pacing if desired.
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HIS
CS catheter with electrodes all positive (Uni 1-10)
Reference electrode is negative
Utility for determining the best ablation site in WPW PQS Pattern; Recording multiple
simultaneous unipolar recordings
Utility of Unipolar Electrogram Recording
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Presenter
Presentation Notes
Unipolar recording using an internal reference electrode: In this picture simultaneous multipolar recording from a coronary sinus catheter is being performed using the reference electrode on the shaft of the special catheter called a “unipolar catheter” because it has a reference electrode to use for unipolar recording.
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Waveform during pacing & sinus rhythm
Bi
Uni
65
Presenter
Presentation Notes
Unipolar recording using an internal reference electrode: The electrograms on the left show unipolar recordings during pacing and those on the left show the unipolar recordings during sinus rhythm. Notice how clean the electrograms are during pacing when an IVC reference electrode is used. When the surface leads are used for the reference this is not always the case. The EPMEd Systems EP Workmate computer uses an intracardiac electrode for the reference instead of V1 or Wilson’s Central Terminal as most EP computers normally use. Thus, if an IVC reference electrode is used for the Wokmate’s reference signal, it will result in clearer recordings than if the His or CS electrodes are used as the reference. Also, for prolonged procedures unipolar catheters with their IVC reference electrodes provide cleaner continuous recordings than if V1 is used as the reference.
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Peculiarities of Unipolar Recording
A B
Soejima, et al., J Cardiovasc Electrophysiol, Vol. 16, pp. 1017-1022, September 2005
Presenter
Presentation Notes
Peculiarities of unipolar recording: A QS pattern is an indication that the electrode of a mapping catheter is located at the focal site of an arrhythmia, however, a QS complex can often be recorded not just at that site, but in an area sometimes even larger than a centimeter in diameter. Thus, a QS pattern should not be your only tool to look for to guide the ablation. A QS pattern may also be recorded when the mapping electrode is floating in the chamber and is not in contact with the myocardium. If that is the case, the unipolar electrogram will have a slower initial negative slope which suggests that the electrogram is a far-field signal, because the electrode in not in contact with the tissue and is some distance from the myocardium. See Fig. A in which the unipolar recording from electrode 2 (Uni 2) has a slower negative slope than that from electrode 1 (Uni 1). That means that electrode 2 is not in contact with the myocardium. Thus, careful scrutiny of the unipolar electrograms is required when you find a QS pattern over a wide area. If you do record a QS pattern and are not sure if it is due to poor contact or not, you can do unipolar pacing to see if you capture the myocardium. If you do, you have good contact. You can then use bipolar recording to more precisely find the site of earliest activation and also see if it has a rapid negative deflection in the unipolar signal. Sometimes low amplitude potentials can be recorded in the bipolar recordings, but not in the minimally filtered unipolar recordings, because it gets obscured by the far-field component of the unipolar electrogram. In Figure B, you can see that in the bipolar recording (Bipolar 1-2), a very low amplitude potential is recorded just prior to the onset of the QRS in the surface leads, but not as notable in the minimally filtered unipolar recording (Uni 1). However, in the high pass filtered unipolar recordings (Uni HP 1), that potential is much more evident. Also, you will note that it can be observed in Uni HP 1, but not in Uni HP 2 meaning that electrode 2 is away from the site. One of the biggest things to be aware of with unipolar recording is the effect the far-field recording of the depolarization of tissue far from the recording site can have on the resulting electrogram. In normal myocardial tissue the maximum negative slope generally represents the local depolarization. However, if the tissue is diseased such as with a scar from an infract, the amount of viable tissue under the electrode placed on the scar in comparison to that of the viable tissue around the scar may be small. Thus, it would result inn a large far-field signal that would obscure the small local potential. Thus, minimally filtered unipolar recording is not so useful for scar tissue, and instead a 30Hz filtered unipolar recording should be used along with the bipolar recording. That will eliminate the far-field signals. Although a QS pattern may not always mean it is at the focus, an rS pattern usually means you are definitely away form the focus. *Stevenson WG and Soejima, K. J Cardiovasc Electrophysiol, Vol. 16, pp. 1017-1022, September 2005
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Catheter Positions and Their Recordings
68
QRS Complex )
P-R Interval
P-Wave
Relationship of the Surface 12 lead Electrogram to the Activation Sequence
Presenter
Presentation Notes
Relationship of the Surface 12 lead Electrograms to the Activation Sequence: P wave – the P wave represents the atrial activation as activation travels from the sinus node to just before entering the AV node. PR interval – the PR interval represents the activation as it slowly travels through the AV node to just before the activation breaks out into the ventricles. QRS complex – the QRS complex is the activation of the right and left ventricles.
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V Wave = CS (LBB) & RVa (RBB)
His potential = His
A-Wave = HRA
Relationship of the Intracardiac Electrogram to the Activation Sequence
Presenter
Presentation Notes
Relationship of the intracardiac electrogram to the activation sequence: Intracardiac recordings record only the activation in the small area in the local proximity of the electrode on the catheter that is being used for the recording. This is unlike the 12 lead recordings which represent the entire activation of the heart. Thus the following potentials or waves are recorded: A wave – the A wave represents the atrial activation at the site the catheter is located in right or left atrium. In a standard EP study the HRA catheter is used to record the A wave from the high right atrium near the sinus node. His potential – the His potential is recorded by the His (HBE) catheter which is straddling the tricuspid valve. It represents the activation as it leaves the AV node and rapidly travels past the electrode on the His bundle. V wave – the V wave is recorded usually by the RVA catheter located in the apex of the right ventricle (RV) and the His catheter located on the His with its tip in the (RV) complex is the activation of the right and left ventricles. If an ablation catheter is placed in the RV it too will record a V wave.
Intracardiac EGM recordings – Catheter Placement: In the standard electrophysiology study (EPS) procedure, 4 catheters are generally inserted and placed in the high right atrium (HRA), coronary sinus (CS), His region (HIS) and right ventricular apex (RVA). If an ablation procedure is to be performed, one more catheter called the ablation catheter is inserted. Below are the locations where the 4 catheters used in the EPS are placed. High right atrium (HRA): positioned in the right atrial appendage His bundle electrogram (HBE or HIS): positioned with the tip electrodes crossing the tricuspid annulus and a few millimeters on the ventricular side of the tricuspid annulus, and the proximal electrodes on the atrial side of the tricuspid annulus. The best His potential recording is a few millimeters into the ventricular side of the tricuspid annulus. Coronary Sinus (CS): positioned in the coronary sinus between the left atrium and left ventricular and covers anywhere from the left posteroseptal region to the left anterior region depending on how deep it is placed in the CS. Right ventricular apex (RVA): positioned in the right ventricular apex. An alternative location can be the right ventricular outflow tract (RVOT) Characteristic recordings will be made as the wavefront propagates across the recording pairs or unipolar recording electrodes. Those recordings are then compared in terms of relative timing of those various catheters around the heart.
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Catheter Types Steerable Fixed Curve
Presenter
Presentation Notes
Catheter types: Electrophysiology catheters come in either a fixed curve or steerable curve version. Ablation catheters in general are all steerable curve versions. Fixed curve – these curves have a predetermined curve suited for the particular anatomical location they were meant to be positioned at. Steerable curve – these curves when undeflected are straight, but as the curve is deflected, it will take a particular shape suited for the particular anatomical location it was meant to be positioned at. Being deflectable (steerable), it allows for more fine tuning of the location for better stability and recording. There are a variety of handle types as well and they are as below: Plunger type – this is a push-pull mechanism where when you push the plunger up distally, the catheter will deflect. When you pull back on the plunger, the catheter straightens. This type is most common, but the movement tends to be jerky, however, it can easily make quick movements. Also the thumb can tire, thus, the so called “numb thumb syndrome”. These types have the auto-locking feature where when the catheter is deflected, the curve will stay in that deflected position and will not try to return to the straight position. (IBI, Biosense Webster, Bard, EPT) Rotational type – by rotating a knob on the handle the catheter will deflect. This allows for much finer movements for more detailed mapping. However, it does not allow for quick movements when desired. This also has the auto-lock feature. (St. Jude Medical, AF Division) Swivel type – these have a knob that you swivel to make the catheter deflect. These are often bi-direction types. They do not have the auto-lock feature and require a locking mechanism. (EPT) Slide type – these have knobs on the handle that are slid up and down to deflect and straighten the curve. They often also have a feature to allow the know to be rotated as well making the curve deflect off plane. These also may or may not have an auto-lock feature and may require a locking mechanism. (Medtronic, Bard) m
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ATRIAL DEPOLARIZATION
Intracardiac Electrograms –HRA Catheter
Presenter
Presentation Notes
HRA catheter – intracardiac electrograms: The HRA catheter is placed in the lateral wall of the high right atrium, near the junction of the SVC and as close to the SA node as possible. Because the HRA catheter is so high in the Right Atrium, far removed from the ventricles, and theoretically at least the atria are isolated from the ventricles, the signal it senses will be atrial in nature and not include a ventricular component. Accordingly, the atrial signal will be somewhat aligned with the surface P-wave since both represent atrial depolarization. With 10mm spacing and filter settings in a range of 30-100HZ, some far field may be recorded resulting in V waves as well. However, in general no V waves should be recorded. When trying to discern electrograms, the A waves from the HRA catheter recordings (as are the P waves from the surface ECGs) are a good reference to determine what is an atrial potential on the other recording channels (i.e. His, CS and RVA).
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H
Intracardiac Electrograms –His Catheter
A V H A V H A V H A V
ATRIAL DEPOLARIZATION HIS BUNDLE DEPOLARIZATION
VENTRICULAR DEPOLARIZATION
Presenter
Presentation Notes
His catheter - intracardiac Electrograms: The His catheter is located with the distal tip across the tricuspid annulus lying several millimeters on the ventricular side. The more proximal pair or pairs of electrodes will lie closer and closer to the atrial side with the proximal pair likely in the atrium. Since the catheter lies on the His bundle with part in the atrium and part in the ventricle, then you should be able to record an atrial (A) wave, ventricular (V) wave and His potential (H). If a pair of electrodes lies in the ventricle past the tricuspid annulus, possibly no A wave can be recorded from that pair of electrodes or the A wave will be smaller as in the diagram here. Thus you may have only a His and V wave and no A wave or a small A wave, His and V wave. If the proximal pair of electrodes is lying on the atrial side of the tricuspid annulus, depending on how far from the ventricle and His region, no or a very small His potential may be recorded. Thus, you will have a large A wave, either no or a small His wave, and a smaller V wave. If due to the location of the electrode pairs, you have only a His and V wave recorded from the distal pair of electrodes and only a large A wave, small V wave and no His recorded from the proximal pair, in order to measure what we call the AH interval, you will need to use the A wave from the proximal pair and the His from the distal pair to make that measurement. Thus, neither the proximal or distal pairs could record all three potentials (A, H and V) for the measurement in such an example. The His catheter is used to evaluate AV and VA conduction properties. The AH interval represents conduction from the lower atrium to the His. Therefore, the His catheter is excellent for evaluating AV node conduction. If the AH interval prolongs, that means conduction is slowing in the AV node.
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ATRIAL DEPOLARIZATION VENTRICULAR DEPOLARIZATION
Intracardiac Electrograms –CS Catheter
A V A V A V A V
Presenter
Presentation Notes
CS catheter-intracardiac electrograms: Since the CS catheter lies between the left atrium and left ventricle, it will record activity from the left atrium (A) and left ventricle (V). It thus is excellent for evaluating conduction from the left atrium to the left ventricle which normally can only occur through the AV node. Thus, since conduction slows in the AV node, there should be a delay between the A waves and V waves as is seen in this diagram. If the patient had a left sided accessory pathway (abnormal connection between the atrium and ventricle which allows direct conduction between them without a delay) then there would be no or a very short delay noted at the pair of electrodes close to the site of that accessory pathway.
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CS EGM
Presenter
Presentation Notes
The CS catheter helps to evaluate the conduction between the left atrium (LA) and ventricle (LV). “A” waves (atrial potentials) and “V” waves (ventricular potentials) can be recorded from the CS catheter, since it lies in the CS which runs along the AV sulcus. Usually a decapolar catheter is used for CS recording, so 5 bipolar recordings can be recorded (CS1-2 to CS9-10). Occasionally a doctor will do unipolar recording and have 10 CS channel recordings. The above example shows conduction via an accessory pathway (AP). The pair of electrodes closest to that AP (CS1) has a narrower AV interval than the rest of the CS electrode pairs. If there was no AP, all of the AV intervals recorded from the CS catheter would be essentially the same as in the previous figure.
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1 Wider
Narrow
Wider
The general location of a left sided AP can be located by bracketing the AP using the CS electrograms.
• Intervals between the “A” and “V” waves, or vice versa, is wide-narrow-wide • Determines the general location of the AP • In the case above that is CS2-3
Special Uses of the CS: Catheter: Bracketing Left-Sided Pathways
Presenter
Presentation Notes
Bracketing left-sided pathways (Partially described in slide 115): The general location of a left sided AP can be located by bracketing the AP using the CS electrograms. In this case you try to find an electrogram sequence in which the interval between the “A” and “V” waves, or vice versa, goes from a wide interval then narrow interval and back to a wide interval. This shows that the general location of the AP is between the 2 wide intervals, which is around the narrowest interval. In the case above that is CS2-3. To confirm this you can push the CS catheter deeper into the CS to see the narrowest pair shift to CS3-4.
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V V
RVA catheter recording
VENTRICULAR DEPOLARIZATION
Intracardiac Electrograms –RVA Catheter
Presenter
Presentation Notes
RVA catheter-intracardiac electrograms: Since the RVA catheter lies with the distal tip in the RV apex far from the right atrium, it will record only a ventricular (V) potential. Since it is close to the breakout site of RV activation, it normally will record the earliest ventricular activation of the four standard catheters (HRA, His, CS and RVA). This catheter is the proxy for the right ventricle. When trying to discern electrograms the V wave from the RVA catheter recordings (as are the R waves from the surface ECGs) are a good reference to determine what is a ventricular potential on the other catheter recordings.
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Normal Activation Sequence as Seen from the Intracardiac
Recordings
79
Electrogram Recordings - correlation with surface ECG
Between dashed lines = A wave Between solid lines = V wave Between dashed & solid lines = H
potential if from the His catheter
Presenter
Presentation Notes
Electrogram recordings - correlation with surface ECG: The HRA trace correlates with early atrial activation; The HIS trace correlates with late atrial, AV Nodal and early His Purkinje activation; The RVA trace correlates with the early activation of the ventricles. Collectively, the surface and intracardiac traces reveal greater detail than either type alone. Knowing this relationship, the various intervals that express the various conduction times in the heart can be measured. These measurements will be explained in the following sides.
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Normal Activation Sequence
Earliest A wave
Earliest v wave
Presenter
Presentation Notes
Normal activation sequence in respect to the intracardiac catheters (HRA, His, CS and RVA): Atrial activation – You will note all the atrial activation (A waves) falls under the P wave on the surface ECG. The atrial activation occurs in the following order: HRA Proximal His Distal His Proximal CS Mid CS Distal CS Ventricular activation – You will note all the ventricular activation (V waves) falls under the V wave on the surface ECG. The ventricular activation occurs in the following order: RVA Sometimes the RVA electrogram can have the same timing as the distal His electrogram depending on the placement. If the RVA catheter is positioned far from the right ventricular breakout site, the activation time from the breakout site to the RVA may be the same as that to the His. However, normally the RVA is earlier than the His. Distal His Proximal His The proximal His can have a very close timing to the proximal CS depending on how far into the right ventricle the proximal electrodes are inserted. If they are a few millimeters in it may have the same timing. Distal CS Mid CS Proximal CS The above is normal activation. If the activation is anything other than this, than it may indicate an arrhythmia or conduction abnormality.
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Intracardiac EGM recordings – Catheter Placement
Presenter
Presentation Notes
Activation Sequence in the Surface Leads I, aVF and V1, and the intracardiac electrograms: This animation shows the depolarization of the atria and ventricles. Click on the picture for the animation and once you start it you can click on pause and step through the activation step by step with the arrow keys to see the sequence of activation in relation to the catheters.
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P-A
A-H
H-V
Baseline Electrogram Recording Measurements
ST segment
PR segment
P wave
NORMAL RANGE
PA (IACT) - 20-60 msec
AH - 50-130 msec
His - 10-25 msec
HV - 35-55 msec
Presenter
Presentation Notes
Baseline electrogram recording measurements: The following intervals are recorded from the 12 Lead ECG: The P wave represents the activation of the right and left atrium. If there is a conduction delay between the atria or an intra-atrial conduction delay, the P wave will become wide. If the P wave during an arrhythmia looks different then the normal sinus P wave, then the atrial activation is not from the sinus node. If the P wave is notched, there is most likely a delay between the right and left atria. If the P wave is inverted, it means the activation is most likely originating from the isthmus or tricuspid valve region. If the P wave is biphasic, it means there is a intra-atrial reentrant circuit such as atrial flutter. The normal width of the P wave = 0.10 sec or 100ms. The PR Interval is the conduction time from the sinus node all the way down to the Purkinje fibers. It is measured from the beginning of the P wave to the point of the first negative or positive deflection of the QRA complex. It is the point where the QRS first leaves the baseline. The normal range for the PR interval = 0.12-0.2 sec or 120-200 msec. The P-R interval may exceed 0. 20 sec in some normal individuals such as well-conditioned young adults with high vagal tone and normalization of the P-R interval during exercise. The PR segment is the interval between the end of the P wave to the beginning of the QRS. It is the time from when conduction enters the AV node and travels down to the Purkinje fibers. The normal value of the PR segment = 0.03-0.06 sec or 30-60 msec. The QRS is the conduction time from the beginning of the activation of the ventricular myocardium to the end of that activation. It is measured from the point the QRS complex first leaves the baseline to the point where it returns to baseline. The normal range for the QRS complex = 0.04-0.10 sec or 40-100 msec. The QT interval is the time from the beginning of ventricular activation to the end of ventricular repolarization. It is measured from the beginning of the QRS (first negative or positive deflection from baseline) to the end of the T wave. At normal heart rates, the QT length is abnormal if it is greater than 0.40 sec for males and 0.44 sec for females (but is heart rate dependent). However, in general the QT interval is prolonged if it is more than half the R-R interval. An exception to this general rule is when there is a rapid heart rate (greater than 100 beats/minute). In such a case, the QT interval measurements have little clinical significance, and it is not necessary to make a precise measurement of the QT interval. The important thing is only whether or not the QT interval is normal or prolonged. Optimal measurement of the QT interval is difficult because of the lack of a standardized method and lack of data on the best method to adjust for the heart rate. Hypercalcemia can cause QT shortening but this is very difficult to diagnose clinically. Extreme QT prolongation (greater than 0.60 sec or 600 msec) predisposes the patient to arrhythmias, and although a QT interval of at least 500 msec has been correlated with a higher risk of torsades de pointes, there is no established threshold below which prolongation of the QT interval is considered free of a proarrhythmic risk. The risk of torsades de pointes should be assessed in patients who are about to begin taking any QT-prolonging medications. Causes of QT prolongation are: Type 1A antiarrhythmic agents (quinidine, procainamide, disopyramide, etc.) and tricyclic antidepressants and phenothiazines. Hypokalemia, hypocalcemia or hypomagnesemia Stroke, intracerebral or brainstem bleeding, seizures, comas, etc. Bundle branch block infarction, and ischemia Reliable information on the proper use of QT-prolonging medications is scarce. The ST segment is measured from the end of the QRS (J point) to the beginning of the T wave. The normal value = 0.08 sec or 80 msec. However, this is heart rate dependent. ST segment elevation is determined by looking at the baseline just before the QRS and seeing if it is higher or not.
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Display Sweep Speed
50mm/sec 200mm/sec
The EP doctor uses different paper speeds to analyze the data. The faster the speed (100-200mm/sec), the more details he can see. The slower the speed (25-50mm/sec), the easier to see the overall picture or induction of an arrhythmia. The doctor will switch back and for between the various speeds. The 12 lead uses 25 mm/second.
Presenter
Presentation Notes
Display sweep speed: This is another example of sweep speeds. The EP doctor uses different paper speeds to analyze the data. The faster the speed (100-200mm/sec), the more details he can see. The slower the speed (25-50mm/sec), the easier to see the overall picture or induction of an arrhythmia. The doctor will switch back and for between the various speeds. You can see in this example how much easier it is to determine the A, H and V potentials at 200mm/sec than at 50mmm/sec.
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Intracardiac recordings can reveal more than the Surface ECG
Presenter
Presentation Notes
Intracardiac recordings can reveal more than the Surface ECG: The real etiology of a particular 12 lead ECG strip can not easily be determined by the 12 lead ECG itself. It is not until you look at the intacardiac electrograms that you realize what the real etiology is. In the example here the 12 lead ECG shows 1st degree heart block (P-R interval >0.20 sec.), but the etiology of the increase in the P-R interval can not be determined by this strip alone. Placing a catheter in the high right atrium (HRA) and His positions may be helpful in determining what tissue(s) is (are) contributing to the delay (prolonged PR interval). See the next few slides for possible etiologies of the 1st degree heart block.
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Intracardiac recordings can reveal more than the Surface ECG
Presenter
Presentation Notes
Intracardiac recordings can reveal more than the Surface ECG: By measuring the time it takes an impulse to travel from one point to another inside the heart, you can determine from where a particular problem arises. This assists in making a “differential diagnosis” (figuring out what something is by ruling out what it is not). In this scenario, the surface lead show a prolonged PR interval. However, if you look at the P wave, you see it is very wide. You also notice that the intraatrial conduction time (IACT) is also prolonged. A wide P wave and prolonged IACT means there is some kind of intraatrial conduction delay. You also note that the AH and HV intervals are normal meaning conduction in the AV node and His-Purkinje systems is normal. Thus the 1st degree AV block in this case was caused by an intraatrial conduction delay.
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Intracardiac recordings can reveal more than the Surface ECG
Presenter
Presentation Notes
Intracardiac recordings can reveal more than the Surface ECG: It is important to make the correct differential diagnosis, since one etiology might not be much cause for alarm. As in this example, a first degree block that is seen due to a longer than normal AH interval might not warrant any intervention. It only means that conduction in the AV node is slowing. Any intraatrial conduction delay can be ruled out by the normal IACT and P wave duration. However, the prolonged AH interval does conform the etiology is a conduction delay in the AV node. Such an AV node delay is usually not of concern and can be caused by antiarrhythmic drugs such as digoxin.
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Intracardiac recordings can reveal more than the Surface ECG
Presenter
Presentation Notes
Intracardiac recordings can reveal more than the Surface ECG: However, a certain etiology may be of great concern. In this example, the IACT, P wave duration and AH interval are fine, but the HV interval is prolonged. First degree AV block due to a long HV interval indicates that there is serious conduction system disease that almost invariably leads to complete heart block. Patients diagnosed as having this condition warrant the implantation of a permanent pacemaker. This differential diagnosis is critical for the appropriate treatment of the patient. If only the 12 lead had been used to diagnose the disease in this patient, the HV prolongation may have been missed. Thus, the intracardiac electrograms are of great value in diagnosing conduction abnormalities.
