14879762-EKG.ppt

7/16/2019 14879762-EKG.ppt

http://slidepdf.com/reader/full/14879762-ekgppt 1/94

Electrocardiogram

Hanan Fathy

2008

7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


Pacemaker = sinoatrial node

Impulse travels across atria

Reaches AV node

Transmitted along interventricular septum inBundle of His

Bundle splits in two (right and left branches)

Purkinje fibres

7/16/2019 14879762-EKG.ppt


Overall

direction

of

cardiac

impulse

7/16/2019 14879762-EKG.ppt


• An EKG is a method of measuring,

displaying and recording the electrical

activity of a heart

• Electrical stimuli is amplified to create

a “rhythm strip” by a machine thatconsistently produces representations

of the heart‟s electrical activity

7/16/2019 14879762-EKG.ppt


• Bipolar Leads - leads have one

positive and one negative

• Limb Leads - Leads I, II, and III• Lead II is most common due to

ability to visualize P wave

– Lead I = left arm + and right arm - – Lead II = left leg + and right arm -

– Lead III = left leg + and left arm -

7/16/2019 14879762-EKG.ppt


• Augmented LimbLeads

–

Leads aVR, aVL, aVF – Utilizes the four limb

leads

– Heart is the focal point

–

Current flows fromheart outward toextremities

– EKG machine mustboost amplification due

to positions of theseleads

7/16/2019 14879762-EKG.ppt


• Chest Leads

– Called precordial or vector

[V] leads

– Look at horizontal or transverse plane

– Proper placement is

important for correct

interpretation – Should be measured each

time pads placed

7/16/2019 14879762-EKG.ppt


• 6 are chest electrodes• Called V1-6 or C1-6

• 4 are limb electrodes

– Right arm R ide

– Left arm Your

– Left leg Green

– Right leg Bike

– Remember

• The right leg electrode is a

neutral or “dummy”!

7/16/2019 14879762-EKG.ppt


Precordial (chest) leads

• V1⇒Right bundle branch system

• V2⇒Right anterior surface

• V3⇒Right anterior septal surface

• V4⇒Left anterior surface

• V5⇒Left ventricle

• V6⇒

Lateral surface

7/16/2019 14879762-EKG.ppt


ECG machines can run at 50 or 25 mm/sec.

Major grid lines are 5 mm apart, at standard

25 mm/s, 5 mm corresponds to .20 seconds.Minor lines are 1 mm apart, at standard 25

mm/s, 1 mm corresponds to .04 seconds.

Voltage is measured on vertical axis.

Standard calibration is 0.1 mV per mm of

deflection.

7/16/2019 14879762-EKG.ppt


• Arrhythmia: Abnormal rhythm

• Baseline: Flat, straight, isoelectric

line

•

Waveform: Movement away from thebaseline, up or down

• Segment: A line between waveforms

• Interval: A waveform plus a segment

• Complex: Combination of several

waveforms

7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


• The excitation begins atthe sinus (SA) node and

spreads along the atrial

walls

• The resultant electricvector is shown in yellow

• Cannot propagate across

the boundary between atriaand ventricle

• The projections on Leads

I, II and III are all positive

7/16/2019 14879762-EKG.ppt


Direction of impulse (axis)

Towards t

electrode

= positive

deflection

Away from

theelectrode

= negative

deflection

7/16/2019 14879762-EKG.ppt


Electrophysiology

7/16/2019 14879762-EKG.ppt


Cardiac Current Flow

7/16/2019 14879762-EKG.ppt


Cardiac Current Flow

7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


• If the heart rate is regular

– Count the number of large squares betweenR waves

• i.e. the RR interval in large squares

• Rate = 300

RR

e.g. RR = 4 large squares

300/4 = 75 beats per minute

7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


If the rhythm is irregular it may be better to estimate the rate using the rhythm

strip at the bottom of the ECG (usually

lead II)

The rhythm strip is usually 25cm long

(250mm i.e. 10 seconds)If you count the number of R waves on

that strip and multiple by 6 you will get

the rate

7/16/2019 14879762-EKG.ppt


I s the rhythm regular?

The easiest way to tell is to take a sheet of paper and line up one edge with the tips of

the R waves on the rhythm strip.

Mark off on the paper the positions of 3 or 4R wave tips

Move the paper along the rhythm strip so thatyour first mark lines up with another R wavetip

See if the subsequent R wave tips line upwith the subsequent marks on your paper

7/16/2019 14879762-EKG.ppt


Interpretation of ECG

Normal heart rhythm has consistent R-R interval.

Mild variations due to breathing also normal.

7/16/2019 14879762-EKG.ppt


Sinus Rhythm

– Definition:Cardiac impulse originates from thesinus node. Every QRS must be preceded by a P

wave.

– (This does not mean that every P wave must befollowed by a QRS – such as in 2nd degree heart

block where some P waves are not followed by a

QRS, however every QRS is preceded by a Pwave and the rhythm originates in the sinus node,hence it is a sinus rhythm. It could be said that itis not a normal sinus rhythm)

7/16/2019 14879762-EKG.ppt


Sinus arrhythmia

• There is a change in heart rate depending on the phase of respiration

• Q. If a person with sinus arrhythmia inspires,what happens to their heart rate?

• A. The heart rate speeds up. This is because oninspiration there is a decrease in intrathoracic

pressure, this leads to an increased venous returnto the right atrium. Increased stretching of the

right atrium sets off a brainstem reflex(Bainbridge‟s reflex) that leads to sympatheticactivation of the heart, hence it speeds up)

• This physiological phenomenon is more apparent

in children and young adults

7/16/2019 14879762-EKG.ppt


Sinus bradycardia

• Rhythm originates in the sinus node

• Rate of less than 60 beats per minute

Sinus tachycardia

• Rhythm originates in the sinus node

• Rate of greater than 100 beats per minute

7/16/2019 14879762-EKG.ppt


• Step 1: Are there P waves?

• Step 2: Are there QRS complexes?

• Step 3: Are the P waves and QRS complexes related?

7/16/2019 14879762-EKG.ppt


Example 1

• STEP 1.

–Are there P waves?

7/16/2019 14879762-EKG.ppt


Example 1 Continued

• Are there P waves?

– Yes, P waves are easily identifiableand regular in rate.

7/16/2019 14879762-EKG.ppt


Example 1 Continued

• STEP 2.

– Are there QRS complexes?

7/16/2019 14879762-EKG.ppt


Example 1 Continued

• STEP 2.

– Yes there are normal, narrow, QRS

complexes.

7/16/2019 14879762-EKG.ppt


Example 1 Continued

• STEP 3

– Are they related, 1:1?

7/16/2019 14879762-EKG.ppt


Example 1 Continued

• STEP 3

– Are they related, 1:1?• Yes, there is one P wave for every QRS.

•This is called a sinus rhythm

7/16/2019 14879762-EKG.ppt


Example 2

• Follow steps 1-3 as demonstrated in Ex.1.

• This is also a sinus rhythm.

• Note: The P waves are smaller, yet their regularity in

relation to the QRS complexes gives them away.

7/16/2019 14879762-EKG.ppt


Example Three

• Following the same steps, this one doesn‟tmatch up!?!?

7/16/2019 14879762-EKG.ppt


Example 3 continued

• Step 1 – Are there P waves?

• Yes,

– Note: notice the dotted arrows indicate thelocation of P waves buried in the strongerelectrical activity of the QRS complexes.

7/16/2019 14879762-EKG.ppt


Example 3 Continued

• STEP 2

– Are there QRS complexes?

•Yes, there are normal, narrow

QRS complexes.

7/16/2019 14879762-EKG.ppt


Example 3 Continued

• STEP 3.

– Are they related?

• NO, they are both regular in shape and rate, but

there is no relation between them.

– This shows a Complete Heart Block, also called a

3rd degree block.

– Can the Heart effectively pump blood if the Atria

and Ventricles are not working together?

7/16/2019 14879762-EKG.ppt


Supraventricular tachycardias• These are tachycardias where the impulse

is initiated in the atria (sinoatrial node,atrial wall or atrioventricular node)

• If there is a normal conduction pathway

when the impulse reaches the ventricles, anarrow QRS complex is formed, hencethey are narrow complex tachycardias

• However if there is a conduction problemin the ventricles such as LBBB, then a

broad QRS complex is formed. Thiswould result in a form of broad complextachycardia

7/16/2019 14879762-EKG.ppt


Atrial FibrillationFeatures:

• There maybe tachycardia

• The rhythm is usually irregularly

irregular • No P waves are discernible – instead

there is a shaky baseline

– This is because there is no order to atrialdepolarisation, different areas of atriumdepolarise at will

7/16/2019 14879762-EKG.ppt


Atrial Fibrillation

7/16/2019 14879762-EKG.ppt


Atrial flutter

Features:

• There is a saw-tooth baseline which

rises above and dips below theisoelectric line

• This is created by circular circuits of depolarisation set up in the atria

7/16/2019 14879762-EKG.ppt


Cardiac Rhythm: Supraventricular NORMAL SINUS RHYTHM Impuses originate at S-A node at normal rate

SINUS TACHYCARDIA Impuses originate at S-A node at rapid rate

All complexes normal, evenly spaced

Rate > 100/min

SINUS TACHYCARDIA

Impuses originate at S-A node at rapid rate

All complexes normal, rhythm is irregular

- >

7/16/2019 14879762-EKG.ppt


Cardiac Rhythm: Supraventricular

ATRIAL FLUTTER Impulses travel in circular course in atria – No interval between T and P

Rapid flutter waves, ventricular response irregular

ATRIAL FIBRILLATION Impuses have chaotic, random pathways in atria

Baseline irregular, ventricular response irregular

7/16/2019 14879762-EKG.ppt


Cardiac Rhythm: Ventricular PREMATURE VENTRICULAR CONTRACTION A single impulse originates at right ventricle

Time interval between normal R peaksis a multiple of R-R intervals

VENTRICULAR TACHYCARDIA Impulse originate at ventricular pacemaker – odd/wide QRS complex - often due to myocardial infarction

Wide ventricular complexes

Rate> 120/min

7/16/2019 14879762-EKG.ppt


Cardiac Rhythm: Ventricular VENTRICULAR FIBRILLATION Chaotic ventricular depolarization – ineffective at pumping blood – death within minutes

Rapid, wide, irregular ventricular complexes

PACER RHYTHM Impulses originate at transvenous pacemaker

Wide ventricular complexes preceded by pacemaker spike

Rate is the pacer rhythm

A i i S i d

7/16/2019 14879762-EKG.ppt


Activation Sequence DisordersA-V BLOCK, FIRST DEGREE

Atrio-ventricular conduction lengthened

P-wave precedes each QRS-complex but PR-interval is > 0.2 s

A-V BLOCK, SECOND DEGREE

Sudden dropped QRS-complex

Intermittently skipped ventricular beat

B dl b h Bl k

7/16/2019 14879762-EKG.ppt


Bundle-branch Block RIGHT BUNDLE-BRANCH BLOCK

QRS duration greater than 0.12 s

Wide S wave in leads I, V5 and V6

V i l T h di

7/16/2019 14879762-EKG.ppt


Ventricular Tachycardia

• Usually secondary to infarction

• Circuits of depolarisation are set up indamaged myocardium

• This leads to recurrent earlyrepolarisation of the ventricle leadingto tachycardia

• As the rhythm originates in the

ventricles, there is a broad QRScomplex

• Hence it is one of the causes of a broad complex tachycardia (along

with supraventricular tachycardia with

V i l fib ill i

7/16/2019 14879762-EKG.ppt


Ventricular fibrillation

• Completely disordered ventricular

depolarisation

• Not compatible with a cardiac

output

• Results in a completely irregular

trace consisting of broad QRS

complexes of varying widths,

heights and rates

7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


Elements of the tracing

7/16/2019 14879762-EKG.ppt


Elements of the tracingP wave

– Magnitude and shape,

– e.g. P pulmonale, P mitrale

PR interval (start of P to start of QRS)

– Normal 3-5 small squares, 0.12-0.2s

Pathological Q waves?

QRS complex

– Magnitude, duration and shape

– 3 small squares or 0.12sduration

ST segment

– Should be isoelectric

T wave

– Magnitude and direction

QT interval (Start QRS to end of T)

– Normally < 2 big squares or

0.4s at 60bpm

– Corrected to 60bpm

– (QTc) = QT/RR interval

7/16/2019 14879762-EKG.ppt


Further work

• Check out the various quizzes / games

available on the Imperial Intranet

• Get doctors on the wards to run through a

patient‟s ECG with you

7/16/2019 14879762-EKG.ppt


Case Study of Beau

• Beau is an 11 y/o 45 lb. Male Australian

Shepard.

• Physical exam: see overhead• Beau presents with a moderate, chronic, nocturnal

cough with mild dyspnea. Secondary exam also

reveals a pounding irregular heartbeat and Grade 4

murmur.

• Electrocardiogram was ordered in addition to other

tests. Result:

Point of Origin Name

7/16/2019 14879762-EKG.ppt


Point of Origin Name

• SA Node- Sinus rhythm

– Causes regular, rounded P waves, and normal,narrow QRS complexes

• Atria-Atrial rhythm

– Causes irregularly shaped P waves, but still

normal, narrow QRS complexes

• AV Node-Junctional rhythm

– Normal, narrow QRS complexes with no P

waves

• Perkinjie Fibers- Ventricular rhythm

– No P waves, and irregular, wide QRS

complexes

7/16/2019 14879762-EKG.ppt


• The axis can be though of as the

overall direction of the cardiac

impulse or wave of depolarisation of the heart

• An abnormal axis (axis deviation) cangive a clue to possible pathology

7/16/2019 14879762-EKG.ppt


A normal axis

can lie

anywhere

between -30

and +90degrees

or +120

degrees

according to

some

An axis falling

outside the normal

range can be left

axis deviation

right axisdeviation

or extreme

axis

deviation

7/16/2019 14879762-EKG.ppt


• Wolff-Parkinson-Whitesyndrome can cause both Leftand Right axis deviation

A useful mnemonic:

“RAD RALPH the LAD from VILLA”

R ight Axis Deviation

R ight ventricular hypertrophy

Anterolateral MI

Left Posterior Hemiblock

Left Axis Deviation

Ventricular tachycardia

Inferior MI

Left ventricular hypertrophy

Left Anterior hemiblock

The P wave

7/16/2019 14879762-EKG.ppt


The P wave

The P wave represents atrial depolarisation

It can be thought of as being made up of two separate waves due to

right atrial depolarisation and left atrial depolarisation.

Which occurs first?

Right atrial depolarisation

right atrial depolarisation

Sum of

right and

left waves

left atrial depolarisation

The P wave

7/16/2019 14879762-EKG.ppt


The P wave

Dimensions

• No hard and fast rules

Height

– a P wave over 2.5mm should arouse suspicion

Length

– a P wave longer than 0.08s (2 small squares) shouldarouse suspicion

The P wave

7/16/2019 14879762-EKG.ppt


The P waveHeight

• A tall P wave (over 2.5mm) can be called P pulmonale

• Occurs due to R atrial hypertrophy

• Causes include: – pulmonary hypertension,

– pulmonary stenosis

– tricuspid stenosis

normal P pulmonale

>2.5mm

The P wave

7/16/2019 14879762-EKG.ppt


The P waveLength

• A P wave with a length >0.08 seconds (2

small squares) and a bifid shape is called

P mitrale

• It is caused by left atrial hypertrophy and

delayed left atrial depolarisation • Causes include:

– Mitral valve disease

– LVH

normal P mitrale

The PR interval

7/16/2019 14879762-EKG.ppt


The PR interval

The PR interval is measured between

the start of the P wave to the start of the QRS complex

(therefore if there is a Q wave before

the R wave the PR interval is measured

from the start of the P wave to the start

of the Q wave, not the start of the R wave)

The PR interval

7/16/2019 14879762-EKG.ppt


The PR interval corresponds to thetime period between depolarisation

of the atria and ventricular

depolarisation.

A normal PR interval is between

0.12 and 0.2 seconds ( 3-5 small

squares)

The PR interval

7/16/2019 14879762-EKG.ppt


If the PR interval is short (less than

3 small squares) it may signify thatthere is an accessory electrical pathway between the atria and the

ventricles, hence the ventriclesdepolarise early giving a short PR interval.

One example of this is Wolff-Parkinson-White syndrome wherethe accessory pathway is called the

bundle of Kent.

Depolarisation begins at

7/16/2019 14879762-EKG.ppt


Depolarisation begins at

the SA node

The wave of

depolarisation spreads

across the atria

It reaches the AV node

and the accessory bundle

Conduction is delayed as

usual by the in-built delay

in the AV node

However, the accessory

bundle has no such delay

and depolarisation begins

early in the part of the

ventricle served by thebundle

As the depolarisation in this part of the ventricle

does not travel in the high speed conduction

pathway, the spread of depolarisation across the

ventricle is slow, causing a slow rising delta wave

Until rapid depolarisation

resumes via the normal

pathway and a more normal

complex follows

The PR interval

7/16/2019 14879762-EKG.ppt


If the PR interval is long (>5 small

squares or 0.2s):

If there is a constant long PR interval

1st degree heart block is present

First degree heart block is a longer

than normal delay in conduction at the

AV node

The PR interval

7/16/2019 14879762-EKG.ppt


• If the PR interval looks as though it is

widening every beat and then a QRScomplex is missing, there is 2nd degree heart

block, Mobitz type I. The lengthening of

the PR interval in subsequent beats is

known as the Wenckebach phenomenon

• (remember (w)one, Wenckebach, widens)

• If the PR interval is constant but then thereis a missed QRS complex then there is 2nd

degree heart block, Mobitz type II

Th PR i t l

7/16/2019 14879762-EKG.ppt


The PR interval

• If there is no discernable

relationship between the P waves

and the QRS complexes, then 3rd

degree heart block is present

Heart block (AV node block)

7/16/2019 14879762-EKG.ppt


ea t b oc ( V ode b oc )

Summary

• 1st degree

– constant PR, >0.2 seconds

• 2nd degree type 1 (Wenckebach)

– PR widens over subsequent beats then a QRSis dropped

• 2nd degree type 2

– PR is constant then a QRS is dropped

• 3rd degree

– No discernable relationship between p wavesand QRS complexes

The Q wave

7/16/2019 14879762-EKG.ppt


QAre there any pathological Q waves?

• A Q wave can be pathological if it is: – Deeper than 2 small squares (0.2mV)

and/or

– Wider than 1 small square (0.04s)

and/or

– In a lead other than III or one of the leads thatlook at the heart from the left (I, II, aVL, V5and V6) where small Qs (i.e. not meeting thecriteria above) can be normal

Normal if in

I,II,III,aVL,V5-6

Pathological

anywhere

The QRS height

7/16/2019 14879762-EKG.ppt


Q g

• If the complexes in the chest

leads look very tall, consider leftventricular hypertrophy (LVH)

• If the depth of the S wave in V1added to the height of the R wave

in V6 comes to more than 35mm,

LVH is present

QRS width

7/16/2019 14879762-EKG.ppt


Q

• The width of the QRS complex should be less than 0.12 seconds (3 small

squares)

• Some texts say less than 0.10 seconds

(2.5 small squares)

• If the QRS is wider than this, itsuggests a ventricular conduction

problem – usually right or left bundle

branch block (RBBB or LBBB)

QRS width

7/16/2019 14879762-EKG.ppt


QRS widthIt is then useful to look at leads V1 and V6

• If left bundle branch block is present, theQRS complex may look like a „W‟ in V1 and/or an „M‟ shape in V6

• If right bundle branch block is present,there may be an „M‟ in V1 and/or a „W‟in V6

• This can be remembered by themnemonic:

• WiLLiaM MaRR oW

QRS width

7/16/2019 14879762-EKG.ppt


QRS width

• If LBBB is present, it is verydifficult to interpret the followingST segment

• If there is new onset LBBB, it mayrepresent an MI

• Bundle branch block is causedeither by infarction or fibrosis(related to the ageing process)

The ST segment

7/16/2019 14879762-EKG.ppt


The ST segment• The ST segment should sit on the isoelectric

line

• It is abnormal if there is planar (i.e. flat)

elevation or depression of the ST segment

• Planar ST elevation can represent an MI or

Prinzmetal‟s (vasospastic) angina

• Planar ST depression can represent

ischaemia

Th ST t

7/16/2019 14879762-EKG.ppt


The ST segment

• If the ST segment is elevated butslanted, it may not be significant

• If there are raised ST segments inmost of the leads, it may indicate

pericarditis – especially if the ST

segments are saddle shaped. Therecan also be PR segment depression

Myocardial infarction

7/16/2019 14879762-EKG.ppt



• Within hours: – T wave may become peaked

– ST segment may begin to rise

• Within 24 hours: – T wave inverts (may or may not persist)

– ST elevation begins to resolve

– If a left ventricular aneurysm forms, ST

elevation may persist

• Within a few days:

– pathological Q waves can form and usually

persist


7/16/2019 14879762-EKG.ppt



• The leads affected determine the

site of the infarct

• Inferior II, III, aVF

• Anteroseptal V1-V4

• Anterolateral V4-V6, I, aVL

• Posterior Tall wide R and ST↓ inV1 and V2

Acute Anterior MI

7/16/2019 14879762-EKG.ppt


ST elevation

Inferior MI

7/16/2019 14879762-EKG.ppt


ST elevation

The T wave

7/16/2019 14879762-EKG.ppt


The T wave

• Are the T waves too

tall? – No definite rule for

height

– T wave generally

shouldn‟t be taller than half the size of

the preceding QRS

– Causes:

• Hyperkalaemia

• Acute myocardial

infarction

The T wave

7/16/2019 14879762-EKG.ppt


The T wave

• If the T wave is flat, it may indicatehypokalaemia

• If the T wave is inverted it mayindicate ischaemia

The QT interval

7/16/2019 14879762-EKG.ppt


The QT interval

• The QT interval is measured from the start

of the QRS complex to the end of the Twave.

• The QT interval varies with heart rate

• As the heart rate gets faster, the QTinterval gets shorter

• It is possible to correct the QT intervalwith respect to rate by using the followingformula:

– QTc = QT/√RR (QTc = corrected QT)

The QT interval

7/16/2019 14879762-EKG.ppt


The QT interval

• The normal range for QTc is 0.38-

0.42

• A short QTc may indicate

hypercalcaemia

• A long QTc has many causes

• Long QTc increases the risk of developing an arrhythmia

The U wave

7/16/2019 14879762-EKG.ppt


The U wave

• U waves occur after the T wave

and are often difficult to see

• The are thought to be due to

repolarisation of the atrial

septum

• Prominent U waves can be a sign

of hypokalaemia,

hyperthyroidism

C St d f B

7/16/2019 14879762-EKG.ppt


Case Study of Beau

• EKG reveals a Sinus Arrhythmia, – Beaus heart is “firing off” PrematureAtrial Contractions, “PAC‟s.

• Potentially indicative of atrialenlargement, or other heart irritability,which may or may not be related toBeau’s cough and current presentation.

7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


7/16/2019 14879762-EKG.ppt


Documents

14879762-EKG.ppt