EKG lab

EKG readings

Th t b f ll 12 l d d d d l b ll d There must be a full 12 leads recorded and labelled plus a rhythm strip, usually from lead II.The baseline must be stable and not wandering The baseline must be stable and not wandering. Leads must be well attached, even if it means shaving a hairy chest a hairy chest. There should be little interference from skeletal muscle. The patient must be relaxed and comfortable. muscle. The patient must be relaxed and comfortable. There should be a square wave calibration to show that 1mV is equivalent to 1cm in height. q gSpeed should be 25mm/sec. Hence 1 large square is 200msec and 1 small square is 40msec. q

EKG interpretation: look at five areas, in order, on each EKG.

RateRhythm (Intervals)AxisH t hHypertrophyInfarct

LIMB LEAD I:Right arm -> left arm

LIMB LEADaVR: right arm

CHEST LEADS V1-V6LIMB LEAD II:Right arm -> left leg

LIMB LEADaVL: left arm

LIMB LEAD III:Left arm -> left leg

LIMB LEADaVF: left leg (foot)Left arm -> left leg

Rhythm strip

a e t eg ( oot)

y p

Rh h d RRhythm and RateAre there P waves? Are they regular? D d QRS? Does every one precede a QRS? Is the PR interval constant? What is the PR interval? The PR interval should be between 120 and 240 msec (3 to 6 small The PR interval should be between 120 and 240 msec (3 to 6 small squares)

Ventricular rateVentricular rateCount the number of R waves over 15 large squares (3 seconds) and multiply by 20. To be slightly more accurate count the number of R waves over 30 large squares (6 seconds) and multiply by 10.

Normal EKG

A positive wave form (QRS mainly above the baseline) results from the wave of depolarization moving towards the positive end of the lead.

e g e.g. A negative waveform (QRS mainly below the baseline) is when a wave of depolarization is moving away from the positive electrode (towards the

ti d f th l d) negative end of the lead). EKG paper has 1 millimeter small squares - so height and depth of wave is measured in millimeters.

10 mm = 1.0 mVolt Horizontal axis is time.

0.04 seconds for 1 mm (1 small box).

Positive QRS in Lead I.Negative QRS in Lead aVR

0.2 seconds for 1 large box = 5 small boxes = 5 x .04 seconds.

Negative QRS in Lead aVR.R wave = 7-8 mm high in Lead I = 7-8mV.QRS wave = 0.06 seconds long in Lead I.

PQRS

T 7.0mV

0.2sec0.5mV 0.06sec

Rate calculationMemorize the number sequence:Memorize the number sequence:

300, 150, 100, 75, 60, 50, 40

-if the QRS lands on a heavy line – count the next as 300

Mathematical method:Use this method if there is a regular bradycardia, i.e. - rate < 50. If the distance between the two R waves is too long to use the common method, use the g ,approach: 300/[# large boxes between two R waves].

Count number of large boxes between first and second R waves=7.5. 300/7.5 large boxes = rate 40boxes = rate 40.

Six-second method:Count off 30 large boxes = 6 seconds (remember 1 large box = 0.2 seconds, so 30 l b 6 d ) Th h b f R R i l i i d large boxes = 6 seconds). Then, count the number of R-R intervals in six seconds and multiply by 10. This is the number of beats per minute. This is most useful if you have an irregular rhythm (like atrial fibrillation) when you want to know an average rate.

Count 30 large boxes, starting from the first R wave. There are 8 R-R intervals within 30 boxes Multiply 8 x 10 = Rate 80within 30 boxes. Multiply 8 x 10 = Rate 80.

Estimating rate - quizEstimating rate quiz

RhythmRhythmA reasonable way to group arrhythmias is in four general groups. groups. 1. Irregular rhythms2. Escape & premature beatsp p3. Ectopic beats4. AV blocks

RhythmRhythm

QRS is narrow (normal).

If the beat is ventricular in origin, the QRS is wide and bizarre because it doesn't come down the normal pathway.

QRS is wide.

Group 1: Irregular rhythmsA) Sinus arrhythmia.

45 100 b/ ig y

rate = 45-100 b/minif the rate varies a lot over the strip, this term is used.P waves and P-R intervals are all identical because they originate from the i d sinus node.

Sinus rate may vary normally a bit (increase with inspiration, decrease with expiration)

i i ti t t h t i l ti l t di t i th d llinspiration – stretch receptors in lung stimulate cardiac centers in the medulla

QRS is normal

S h h P d l l h Sinus arrhythmia: P waves are not identical in spacing along the strip.

B) Wandering atrial pacemaker.- pacemaker discharges from different atrial locations - the clue here is the P waves are of varying shape and differing PR intervalsintervals. -PR interval is measured from the beginning of the the P wave to the beginning of the QRS - if the atrial pacemaker location varies it will take different lengths of p gtime to get to the ventricle - resulting in different PR intervals. -also called multifocal atrial tachycardia.

C) Atrial fibrillation.You will frequently see this arrhythmia. there are no P waves, only irregular or wavy baseline there are no P waves, only irregular or wavy baseline. the QRS complexes are irregularly spaced, therefore it is included under irregular rhythms.

Group 2: Escape & Premature beatsescape beat is latepremature beat is earlyp yAtrial escape

Different appearing and late P wave wave.

Ventricular escapeNo P, wide, bizarre QRS.-An

i k fi l ventricular escapeectopic pacemaker fires early before the next scheduled beat.

Premature atrial i

ventricular escape

contraction"PAC", early and differently shaped P wave, narrow QRS.

Premature ventricular contraction-No P, wide bizarre QRS.No P, wide bizarre QRS. -PVCs that occur three (3) or more in a row is called ventricular tachycardia

ltif l PVC (diff t h )-multifocal PVCs (different shapes),

PVCPVC PVC

Group 3: Ectopic[150-250] Paroxysmal tachycardia p p[250-350] Flutter[350+] Fibrillation

Paroxysmal supraventricular t h di t l t d ttachycardia: note accelerated rate and narrow QRS complexes.

Ventricular tachycardia: note fast rate and wide bizarre QRS.

Atrial flutter: “sawtooth” pattern prior to QRS complexes.

Ventricular fibrillation: erratic and wavy baseline.

Group 4: AV blocks(occur in three (3) degrees, like skin burns; third degree is the worst).

1st degree-PR interval > 0.2 seconds (1 large box), each P is followed by a QRS. -PR interval is measured from the beginning of the P wave to the beginning of the QRS.

Figure 19: The PR interval is approximately 0 28Figure 19: The PR interval is approximately 0.28 seconds.

dropped QRS

2nd degree block - type 1

increased time between P and QRS start

2nd degree block - type 1-Also called "Wenkebach". -PR interval gets progressively longereach beat until finally a QRS is "dropped" (missing).

Figure 20: Note the increasing PR interval before the QRS is dropped then the cyclebefore the QRS is dropped, then the cycle is repeated.

2nd degree block - type 2-Also called "Mobitz II".-Look out! A more serious conduction problem than Type 1problem than Type 1.-PR intervals are constant and a QRS is "dropped" intermittently.

Figure 21: Note the dropped QRS after the second and sixth P wave in lead II (the rhythm strip).

P waveDropped QRS P wave Dropped QRSpp Q

Normal PR interval

3rd degree blockThe atrial rate is independent of the ventricular rate (P wave and QRS march out separately separately. The clue here is no relationship at all of the P-R intervals. The P-R interval is constantly changing, the QRS is usually wide and bizarre because it is ventricular origin.

Figure 22: Note the P waves and QRS waves are independent of each other.

P P P PP

IntervalsIntervalsAn interval is a portion of the baseline and at least one wave. We measure an interval on the horizontal axis in seconds seconds. The PR, QRS, and QT are the intervals which should be routinely scanned on each ECG. For measuring intervals, look at the widest form in any lead.

Figure 23: Intervals.

PR interval (beginning of P wave to the beginning of the next QRS). Q )

Normally, < 0.2 seconds or one large box.If it is >0.2 seconds, it is a first degree block.

Figure 24: Note the prolonged PR interval (.28 seconds), especially at the second beat.seconds), especially at the second beat.

•QRS interval (beginning of Q to the end of the S wave) should be < .12 seconds (< 3 small boxes). •If QRS is > 0.12sec, check for bundle branch block.

Fi 25 RBBBFigure 25: RBBB.

0.04sec x 20 = 0.8sec

Bundle Branch BlockRight bundle branch block occurs as a congenital anomaly or is associated with volume overload in the g g yright ventricle. Left bundle branch block is almost always pathological, reflecting disease of the left ventricle. Right bundle branch block produces a prolonged QRS, usually about 160 msecs or 4 small squares Left bundle branch block produces a longer QRS, usually around 200 msec with a more square pattern than RBBB. The changes are best seen in the lateral V leads.

If QRS is > 0.12 and RR occurs in the left chest leads (V5-V6), this indicates a left bundle branch block.

Figure 26: LBBBFigure 26: LBBB.

EKG lab: in class labEKG lab: in class lab

Estimate the rhythm of this stripWhat condition is this??

FOR EACH OF THE FOLLOWING STRIPS – diagnose the condition and justifyyour diagnosesy g

FOR EACH OF THE FOLLOWING STRIPS – diagnose the condition and justifyyour diagnosesyour diagnoses

THESE STRIPS ARE BLOCKS – what type are they?? e.g. 1st, 2nd or 3rd??