ECG InterpretationECG Interpretation

DefinitionDefinition Test that records the electrical

activity of the heart Measure:

Rate and regularity of heartbeats Size and position of the chambers Presence of any damage to the heart Effects of drugs or devices used to

regulate the heart Systemic condition that gives effect

to the heart

How does it work?How does it work? The heart is a muscle with well-

coordinated electrical activity, so the electrical activity within the heart can be easily detected from outside of the body.

After the appropriate leads are attached to the body, a heated stylus moves upward with positive voltage and downward for negative voltage.

• On the moving heat-sensitive paper, voltage is traced out.

ECG leadECG lead Electrodes used to measure

electrical activity of the hearts 2 basic types

Bipolar leads (standard limb leads) utilize a single positive and a single negative electrode between which electrical potentials are measured. 

Unipolar leads (augmented leads and chest leads) have a single positive recording electrode and utilize a combination of the other electrodes to serve as a composite negative electrode.

Limb lead (bipolar)Limb lead (bipolar)

I

II III

+/-

+

-

Extremity lead (unipolar)Extremity lead (unipolar)

Menggunakan terminal sentral sebagai titik nol

Precordial leadPrecordial lead

The Normal Conduction SystemThe Normal Conduction System

ECG TerminologyECG Terminology

P wave : the sequential activation (depolarization) of the right and left atria

PR interval: time interval from onset of atrial depolarization (P wave

QRS complex: right and left ventricular depolarization (normally the ventricles are activated simultaneously)

QRS duration: duration of ventricular muscle depolarization

PP interval: duration of atrial cycle (an indicator or atrial rate)

RR interval: duration of ventricular cardiac cycle (an indicator of ventricular rate

QT interval: duration of ventricular depolarization and repolarization

Normal ECGNormal ECG P wave

Width < 0.12 s Height < 0.3 milliVolt Always positive in lead II, negative in

aVR PR interval

From the start of P wave to the start of QRS

Normal duration 0.12 – 0.20 s QRS complex

Width 0.06 – 0.12 s (~ 0.10 s) Length varies among leads Q first negative deflection R first positive deflection S negative deflection after R

ST segment From the end of S to the start of T Normal : iso-electrical

T wave Positive in lead I, II, V3 – V6 and

negative in aVR

Normal ECGNormal ECG

Basic interpretationBasic interpretation

Rate Rhythm

Axis P wave morphology

PR interval QRS complex morphology ST segment morphology

T wave morphology U wave morphology

QTc interval

Determining the Heart RateDetermining the Heart Rate Rule of 300

300/[number of large boxes between two R waves]. only works for regular rhythms !!

300/7.5 large boxes = rate 40

Six second methods Count the number of R-R intervals in six seconds and multiply by 10 Useful for irregular rhythm average rate

There are 8 R-R intervals within 30 boxes. Multiply 8 x 10 = Rate 80

Determining the RhythmDetermining the Rhythm Source of depolarization

Sino-atrial (SA) node: sinus rhythm Depending on rate can be sinus bradicardi or sinus tachycardia

Non-sinus: atrial/ventricular rhythm (see arrhythmia section)

Sinus rhythm criteria P wave always followed by QRS complex

Normal ECGNormal ECG

AxisAxis

Defleksi positif Defleksi negatif

ECG abnormalitiesECG abnormalities

Hypertrophy Ischemia/infarct

Arrhythmia

HypertrophyHypertrophy

Right atrial enlargement Tall, peaked p wave

Left atrial enlargement Widening p wave, M-shape, notched Deep, negative component p wave in V1

Ventricular HypertrophyVentricular Hypertrophy

LVH (sokolow, Lyon) S di V1 + R di V5 atau V6 > 35 mm R di V5 atau V6 > 26 mm R + S di lead precordial > 45 mm

RVH R/S di V1 > 1 atau R/S di V6 < 1

R in V5 > 26 mm

R/S in V1 > 1 or R/S in V6 < 1

Infarct / IschemiaInfarct / Ischemia Evolution of MI

Hyperacute T wave changes - increased T wave amplitude and width; may also see ST elevation

Marked ST elevation with hyperacute T wave changes (transmural injury)

Pathologic Q waves, less ST elevation, terminal T wave inversion (necrosis)

Pathologic Q waves, T wave inversion (necrosis and fibrosis)

Pathologic Q waves, upright T waves (fibrosis)

•I, aVL, V5•V2-V4

Arrhythmia Arrhythmia

ClassificationSupraventrivular arrythmia

Sinus pause or arrest, SA block, PAC, atrial flutter, atrial fibrillation, etc

Ventricular arrythmia PVC, VT, torsade de pointes, VF, etc

AV conduction abnormalities AV block, WPW syndrome, etc

RhythmRhythm

Rhythm Guidelines: Check the bottom rhythm strip for regularity, i.e. - regular,

regularly irregular, and irregularly irregular. Check for a P wave before each QRS, QRS after each P. Check PR interval (for AV blocks) and QRS (for bundle

branch blocks). Check for prolonged QT. Recognize "patterns" such as atrial fibrillation, PVC's,

PAC's, escape beats, ventricular tachycardia, paroxysmal atrial tachycardia, AV blocks and bundle branch blocks

BlocksBlocks SA node block

Failure of the SA node to transmit an impulse Complete pause of 1 beat ("skipped beat")

AV node block Block which delays the electrical impulse as it

travels between the atria and the ventricles in the AV node

Presented by PR interval

Blocks…Blocks… 1st degree AV block

PR interval greater than 0.2 seconds (200ms or 1 large box)

2nd degree AV block Type I (Wenckebach) PR interval gets longer (by shorter

increments) until a nonconducted P wave occurs Type II (Mobitz) PR intervals are constant until a

nonconducted P wave occurs

Blocks…Blocks…

3rd degree AV block Complete block of signals from the atria to the

ventricles complete dissociation between the timing of the P-waves and the QRS complexes

Bundle branch blocksBlocks within the ventricular bundlesWide QRS complexConsist of

Right ventricular bundle branch block Left ventricular bundle branch block Left anterior fasicular block Left posterior fasicular block

Blocks…Blocks…

RBBBRBBB Complete

QRS duration > 0.12 s rSR’ in lead V1-V2 Slurred S wave in lead I, aVL,

V5-V6 Down sloping of ST segment

and T wave inversion in lead V1-V2

Incomplete rSR’ complex in lead V1 QRS duration of 0.12 s or less R or S waves are not broad or

slurred Normal QRS axis

LBBBLBBB Complete

QRS duration > 0.12 s Bizarre, wide rS or QS complex in lead V1 Wide R wave in lead V6, sometimes plateu or M-

shaped Discordant T wave Absence of normal septal Q wave in lead I, aVL, V6

LAFBLAFB Criteria

QRS duration < 0.12 Left axis deviation more than -45 degrees qR wave in leads I, aVL Small rS complex in leads II, III, aVF

LPFBLPFB

CriteriaQRS duration < 0.12 sRight axis deviation > +110 degreesSmall r wave and large S wave in leads I, aVLSmall q waves in inferior leadsNo other explanation for RAD (ex. RVH,

COPD, lateral myocardial infarction)

Supraventricular ArrythmiaSupraventricular Arrythmia Premature atrial contraction

Single or repetitive, unifocal or multifocal

Atrial fibrillation Atrial activity is poorly defined; may see course or fine

undulations or no atrial activity at all Ventricular response is irregularly irregular

Supraventricular…Supraventricular… Atrial flutter

Regular atrial activity with a "clean" saw-tooth appearance The ventricular response may be 2:1, 3:1 (rare), 4:1, or

irregular

Paroxysmal supraventricular tachycardia Arise from structure above his bundle Reciprocating tachycardias because they utilize the mechanism of reentry

Ventricular ArrythmiaVentricular Arrythmia Premature ventricular contraction

May be unifocal, multifocal or multiformed Occur as isolated single events or as couplets, triplets, and salvos (4-

6 PVCs in a row ~ brief VT) R-on-T PVCs vulnerable to ventricular tachycardia or fibrillation

Ventricular tachycardia Sustained (lasting >30 sec) vs. nonsustained Monomorphic (uniform morphology) vs. polymorphic vs. Torsade-de-

pointes

Ventricular…Ventricular…

Ventricular fibrillation Chaotic, wide, ventricular tachyarrythmia with

grossly irregular morphology No consistent identifiable QRS complexes