ECG

ECG manifestations of chamber enlargement:

A-Left atrial enlargement:

a. P wave duration equal or more than 0.12 sec.

b. Notched, slurred P wave in lead I and II (P mitrale).

c. Biphasic P wave in lead V1 wit ha wide ,deep and negative terminal component.

d. Mean P wav axis shifted to the left ( between +45 to – 30 degree ).

B-Right atrial enlargement:

a. P wave duration equal or less than 0.11 sec.

b. Tall, peaked T wave equal or more than 2.5 mm in amplitude in lead II,III or aVF (P pulmonale).

c. Mean P wave axis shifted to the right( more than +70 degree).

C-Left ventricular enlargement :

a. "Voltage criteria":

1-R or S wave in limb lead equal or more than 20mm

2-S wave in V1,V2 or V3 equal or more than 30mm

3-R wave in V4,V5 or V6 equal or more than 30mm.

b. Depressed ST segment with inverted T waves in lateral leads(strain pattern ;more reliable in the absence of digitalis therapy.

c. Left axis of -30 degree or more.

d. QRS duration equal or more than 0.09 sec.

e. Time of onset of the intrinsicoid deflection ( time from the beginning of the QRS to the peak of the R wave ) equal or more than 0.05 sec in lead V5 or V6.

D-Right ventricular enlargement :

a. Tall R waves over the right precordium and deep S waves over the left precordium ( R:S ratio in lead V1 > 1.0)

b. Normal QRS duration (if no bundle branch block)

c. Right axis deviation.

d. ST-T "strain" pattern over the right precordium.

e. Late intrinsicoid deflection in lead V1 or V2.

ECG manifestations of bundle branch block (BBB):

A-Left bundle branch block :

a. QRS duration equal or more than 0.12 sec.

b. Broad , notched or slurred R wave in lateral leads( I, aVL , V5,V6 )

c. QS or rS pattern in the anterior precordium.

d. Secondary ST-T wave changes ( ST and T wave vectors are opposite to the terminal QRS vectors).

e. Late intrinsicoid deflection in lead V5 and V6.

B-Right bundle branch block:

a. QRS duration equal or more than 0.12 sec.

b. Large R' wave in lead V1( rsR' ).

c. Deep terminal S wave in lead V6.

d. Normal septal Q wave.

e. Inverted T wave in lead V1 ( secondary T wave changes ).

f. Late intinsicoid deflection in lead V1 and V2.

ECG manifestations of fascicular blocks:

A-Left anterior fascicular block:

a. QRS duration equal or more than 0.10 sec.

b. Left axis deviation ( -45 degree or greater ).

c. rS pattern in lead II, III and aVF.

d. qR pattern in lead I and aVL.

B-Left posterior fascicular block:

a. QRS duration equal or more than 0.10 sec.

b. Right axis deviation ( +90 degree or greater ).

c. qR pattern in lead II,III ands aVF.

d. rS pattern in lead I and aVL.

e. Exclusion of other causes of right axis deviation ( COPD, RVH, lateral MI ).

Localization of myocardial infarction:

Infarct location Leads depicting primary ECG changes Likely vessel * involved

Inferior II,III,aVF RCA

Septal V1-V2 LAD

Anterior V3-V4 LAD

Antero-septal V1-V4 LAD

Extensiveanterior I,aVL,V1-V6 LAD

Lateral I,aVL,V5-V6 CIRC

High Lateral I, aVL CIRC

Posterior ** Prominent R in lead V1 RCA or CIRC

Right ventricular*** ST elevation in lead V1,and more specifically, V4R in the setting of inferior infarction RCA

*this is a simple generalization, variations occur.

** Usually in association with inferior or lateral infarctions.

***Usually in association with inferior infarctions.

Some observations on abnormal rhythms:

Remember: A slow regular ventricular rhythm might be due to :

1-Sinus bradycardia.

2-Complete AV block with idioventricualr rhythm.

3-Normal sinus rhythm with 2:1 AV block.

4-Normal sinus rhythm with 2:1 SA block (very rare).

5-Atrial flutter with high grade 4:1 AV block.

6-Sinus default with idionodal escape rhythm.

7-Sinus default with idioventricualr escape rhythm.

Remember: Causes of IRREGULAR ventricular rhythm:

1-Atrial fibrillation.

2-frequent and irregularly occurring atrial and or ventricular extrasystoles.

3-Atrial flutter with second degree AV blockand varying AV conduction ratios.

4-Paroxysmal atrial tachycardia with variable second degree AV block .

5-Marked respiratory sinus arrhythmia.

"SLOW' atrial fibrillation:

Slow atrial fibrillation usually reflects treatment with digitalis ; or in the absence of digitalis therapy , a structural nodal disease ( sick sinus syndrome ).A more correct description is " atrial fibrillation with slow or diminished ventricular response".

Remember: Common causes of bigeminal rhythm:

1-alternate ventricular extrasystoles( the commonest cause ).

2-alternate atrial or nodal extrasystoles.

3-any form of 3:2 AV block.

4-atrial flutter with alternating 4:1 and 2:1 AV block.

Remember: Absent P wave might be due to :

1-SA block.

2-Atrial fibrillation.

3-Severe hyperkalemia.

4-AV nodal rhythm ( the P wave might be hidden within the QRS complexes).

Remember: A long PAUSE interrupting a regular rhythm might be caused by:

1-a dropped beat as a result of 2nd degree AV block.

2-a dropped beat as a result of SA block.

3-a blocked or non conducted atrial extrasystole.

NB: extrasystoles occur PREMATURELY , escape beats occur LATE.

NB: when the PR interval becomes progressively shorter, AV dissociation is usually present.

Remember: Paroxysmal atrial rhythm (tachycardia, paroxysmal or flutter fibrillation ) in a young person without obvious evidence of cardiac disease rises the possibility of :

1-Thyrotoxicosis.

2-WPW syndrome.

3-Lone atrial fibrillation .

Remember: TALL symmetrical T waves in the precordial leads might be due to :

1-acute subendocardial ischemia , injury or infarction.

2-recovering inferior wall myocardial infarction.

3-hyperacute phase of anterior wall myocardial infarction.

4-Prinzmetal 's angina.

5-true posterior wall myocardial infarctions.

6-hyperkalemia.

Remember: Generalized LOW voltage might be due to :

1-incorrect standardization.

2-emphydema.

3-marked obesity or thick chest wall.

4-pericardial effusion.

5-myxedema.

6-hypopituitarism.

7-Cardiac Amyloid.

8-Severe cardiomyopathy

9-Global Myocardial iscehmia.

Remember: Acute rheumatic frequently associated with :

1-sinus tachycardia.

2-non paroxysmal AV nodal tachycardia( idionodal tachycardia).

3-prolonged PR interval.

4-2nd degree AV block .

5-prolonged QT interval.

NB: it is NEVER associated with 3rd degree AV block

Some ECG finding in heart diseases:

Mitral stenosis:

1-atrial fibrillation

2-RVH ,right axis deviation

3-P mitrale, P pulmonale

Mitral reflux:

1-P mitrale

2-atrial fibrillation

3-left ventricular "diastolic" overload

4-RVH, Right axis deviation.

Tricuspid stenosis:

1-VERY TALL right atrial P wave in standard lead II.

2-1st degree AV block

3-normal QRS axis

Hypertensive heart disease:

1-left atrial P wave

2-left ventricular "systolic " overload

Arrhythmias associated with HYPERthyroidism:

1-sinus tachycardia

2-atrial extrasystoles

3-paroxysmal atrial tachycardia

4-paroxysmal atrial flutter

5-paroxysmal atrial fibrillation

6-idionodal tachycardia

7-paroxysmal nodal tachycardia

NB: Ventricular rhythms are NOT usually associated with hyperthyroidism unless there is a cardiac DECOMPENSATION.

Pulmonic styenosis:

1-P congenitale

2-right ventricular systolic overload

3-right axis deviation

Tricuspid atresia:

1-left axis deviation

2-left ventricular dominance

NB: MOST cases of cyanotic congenital heart disease are associated with RIGHT ventricular dominance and RIGHT axis deviation ; tricuspid atresia is a notable exception .

Ebstein's anomaly:

1-TALL peaked P waves in standard lead II

2-RBBB with small amplitude QRS complexes

3-WPW syndrome type B, ie the QRS complex is negative in the right precordial leads

4-paroxysmal supra-ventricular tachycardia

Mirror image dextro-cardia:

1-Inverted P waves in standard lead I

2-all other deflections –QRS complex and T wave- are also negative in standard lead I.

2-This lead now resembles a normal lead aVR.

3-the normal appearances of standard leads II and lead III are interchanged .

4-the QRS complexes are tallest in the right precordial leads –V1 and V2- and diminished progressively towards the left.

Limb lead reversal:

This will manifest as a mirror image dextro-cardia but the precordial lead complexes are NORMAL.

Anomalous left coronary artery:

When the left coronary artery arises from the pulmonary artery ,the ECG reflects the pattern of ANTERO-LATERAL myocardial infarction, viz pathological q waves, raised coved ST segments and inverted T waves in standard lead I and aVL and the left precordial leads.

Causes of SA block:

SA block is a rare ECG finding and might be caused ny:

1-marked sinus bradycardia

2-marked sinus arrhythmia

3-highly trained young athletes

4-digitalis toxixity

5-ureamia

6-hypokalemia

7-sick sinus syndrome

1st degree AV block is associated with:

1-coronary artery disease

2-acute rheumatic carditis

3-Beta blockers

4-digitalis

5-cardiomyopathy