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ECG Abnormalities - A Systematic Overview

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1. Cardiac Enlargement and Hypertrophy

Atrial Abnormalities

• Right atrial overload: Tall, peaked P waves (≥2.5 mm), historically called "P-pulmonale"
• Left atrial overload: Biphasic P wave in V1 with a broad negative component, OR a broad (≥120 ms), often notched P wave in limb leads ("P-mitrale"). This can also occur with interatrial conduction delays even without true enlargement.

Ventricular Hypertrophy

• Left ventricular hypertrophy (LVH): Increased QRS amplitude directed leftward and posteriorly; ST-segment depression and T-wave inversions in leads with prominent R waves (strain pattern). Common voltage criteria: S in V1 + R in V5/V6 >35 mm.
• Right ventricular hypertrophy (RVH): Rightward QRS axis; tall R in V1 (R, RS, or qR complex); T-wave inversions in right precordial leads. Associated with pulmonary hypertension, pulmonic stenosis.

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2. Bundle Branch Blocks and Intraventricular Conduction Defects

• Left anterior fascicular block: axis more negative than -45° (marked left axis deviation) - most common cause of marked left axis deviation in adults
• Left posterior fascicular block: axis more rightward than +110-120° (rare as isolated finding)

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3. Myocardial Ischemia and Infarction

ST-Segment Elevation MI (STEMI)

• Transmural ischemia shifts the ST vector toward the epicardium → ST elevation in overlying leads
• Earliest sign: tall, peaked "hyperacute" T waves
• Evolution over hours to days: ST elevation → T-wave inversions → Q waves

Non-ST Elevation / Subendocardial Ischemia

• Subendocardial ischemia shifts the ST vector toward the ventricular cavity → ST depression in precordial leads + ST elevation in aVR
• T-wave inversions without ST elevation

Pathological Q Waves

• Width ≥40 ms or depth ≥25% of R-wave height indicates prior transmural infarction
• Exception: septal Q waves in V5-V6 are normal (small, narrow)

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4. Arrhythmias and Conduction (Rate/Rhythm Abnormalities)

By Heart Rate

• Tachycardia (>100 bpm): Sinus tachycardia, SVT, atrial flutter/fibrillation, ventricular tachycardia, ventricular fibrillation
• Bradycardia (<60 bpm): Sinus bradycardia, sick sinus syndrome, junctional rhythm

AV Conduction Blocks

Atrial Fibrillation

• Absent P waves, irregularly irregular rhythm, fibrillatory baseline
• Narrow QRS unless aberrant conduction

Ventricular Tachycardia

• Wide QRS (>120 ms), rate >100 bpm, AV dissociation
• Fusion beats and capture beats are diagnostic

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5. Metabolic and Drug-Induced Changes

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6. Other Notable Abnormalities

Brugada Pattern

• Right bundle branch block morphology + ST elevation in V1-V3 (coved or saddleback type)
• Associated with sudden cardiac death risk; inherited channelopathy

QT Prolongation

• QTc >440 ms in men, >460 ms in women (Bazett formula)
• Risk of torsades de pointes and sudden death
• Causes: congenital LQTS, drugs, electrolyte disturbances, hypothermia

Pericarditis

• Diffuse ST elevation (concave/"saddle-shaped") in multiple leads + PR depression
• No reciprocal changes (unlike MI), no Q waves

Low QRS Voltage

• Peak-to-trough QRS ≤5 mm in all limb leads and/or ≤10 mm in chest leads
• Causes: pericardial effusion, pleural effusion, COPD, cardiac amyloid, anasarca

Electrical Alternans

• Beat-to-beat alternation in QRS amplitude (and sometimes T waves)
• Classic finding in large pericardial effusion with cardiac tamponade

Pulmonary Embolism (Acute Cor Pulmonale)

• Sinus tachycardia (most common)
• S1Q3T3 pattern (deep S in I, Q and inverted T in III)
• Right axis deviation, new RBBB, atrial fibrillation

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Summary Table of Key ECG Abnormalities

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