10 Common Heart Diseases: ECG Changes & Images

1. ST-Elevation Myocardial Infarction (STEMI)

• ST elevation ≥ 1 mm in two or more contiguous leads (convex/tombstone morphology)
• Reciprocal ST depression in opposite leads (very characteristic)
• Hyperacute T waves - tall, peaked T waves in the earliest phase
• Pathological Q waves develop after infarction (>40 ms wide, >25% of R wave height)
• T-wave inversions evolve over hours-days
• Lead localization: Inferior STEMI = II, III, aVF | Anterior STEMI = V1-V4 | Lateral STEMI = I, aVL, V5-V6

ECG Image - Inferior STEMI:

(Source: LITFL ECG Library - ST elevations in leads II, III, aVF with reciprocal changes in aVL)

2. Atrial Fibrillation (AF)

• Absent P waves - replaced by fine, irregular fibrillatory baseline (f-waves)
• Irregularly irregular RR intervals - the hallmark
• Narrow QRS (unless aberrant conduction or bundle branch block)
• Ventricular rate varies: rapid (~100-160 bpm in uncontrolled AF), normal, or slow

ECG Image - Atrial Fibrillation:

(Source: LITFL ECG Library - Atrial Fibrillation - Note absent P waves, irregular baseline, irregularly irregular QRS complexes)

3. Ventricular Tachycardia (VT)

• Wide QRS complexes (≥ 120 ms), often bizarre morphology
• Rate 100-250 bpm, usually regular
• AV dissociation - P waves marching through at a slower independent rate (pathognomonic when visible)
• Capture beats and fusion beats (Dressler beats) - hallmark features
• Concordance in precordial leads (all positive or all negative)
• Left axis deviation (usually)

ECG Image - Ventricular Tachycardia:

(Source: LITFL ECG Library - Regular wide complex tachycardia)

4. Complete (Third-Degree) AV Block

• Complete AV dissociation - P waves and QRS have no fixed relationship
• P waves march at a faster rate than QRS complexes (atrial rate > ventricular rate)
• Escape rhythm is slow: junctional escape (40-60 bpm, narrow QRS) or ventricular escape (20-40 bpm, wide QRS)
• PR interval varies randomly
• First-degree AV block: PR > 200 ms only
• Mobitz II: sudden dropped beats without PR lengthening (most dangerous 2nd degree type)

ECG Image - Complete Heart Block:

(Source: LITFL ECG Library - P waves (arrows) dissociated from slow wide QRS escape rhythm)

5. Acute Pericarditis

• Stage 1 (hours-days): Diffuse concave-up ST elevation in nearly all leads (except aVR and V1) + PR segment depression (best in leads II, V6), with PR elevation in aVR
• Stage 2 (within 1 week): ST and PR return to baseline, T-wave flattening
• Stage 3: Diffuse T-wave inversions after ST normalizes
• Stage 4: ECG normalization (may take weeks)

ECG Image - Acute Pericarditis:

(Source: ECG Waves - Pericarditis - Note diffuse concave ST elevations without reciprocal depressions)

6. Left Ventricular Hypertrophy (LVH)

• Voltage criteria (Sokolow-Lyon): S in V1 + R in V5 or V6 ≥ 35 mm
• Cornell criteria: R in aVL + S in V3 > 28 mm (men), > 20 mm (women)
• Left axis deviation
• ST depression + T-wave inversions in lateral leads (I, aVL, V5-V6) = "strain pattern" (most specific finding)
• Broad, notched P wave (P mitrale) from associated left atrial enlargement
• Wide QRS (may exceed 110 ms)

ECG Image - LVH:

(Source: LITFL ECG Library - Tall lateral R waves with lateral ST depression/T inversion strain pattern)

7. Wolff-Parkinson-White (WPW) Syndrome

• Short PR interval < 120 ms (bypasses AV nodal delay)
• Delta wave - slurred upstroke at the beginning of the QRS (pre-excitation of ventricular myocardium)
• Wide QRS > 120 ms (fusion of normal + pre-excited conduction)
• Pseudo-ST changes and T-wave inversions secondary to abnormal depolarization
• During tachycardia: narrow QRS (orthodromic AVRT) or wide QRS (antidromic AVRT or AF with pre-excitation)

ECG Image - WPW:

(Source: LITFL ECG Library - Short PR interval, delta wave slurring at QRS onset, wide QRS complex)

8. Hypertrophic Cardiomyopathy (HCM)

• LVH voltage changes (tall R waves, deep S waves)
• Deep, narrow Q waves ("dagger Q waves") in lateral and inferior leads (I, aVL, V5-V6, II, III, aVF) - due to septal hypertrophy
• ST depression and T-wave inversions in lateral leads
• Giant negative T waves in the apical variant (Yamaguchi syndrome, V3-V5)
• Left axis deviation
• Atrial fibrillation in advanced disease
• Pre-excitation pattern may coexist

9. Pulmonary Embolism (PE)

• Sinus tachycardia - most common finding (~40% of PE)
• S1Q3T3 pattern - deep S wave in lead I, Q wave + T-wave inversion in lead III (present in ~20%, not specific)
• Right bundle branch block (RBBB) - new or incomplete
• Right axis deviation
• T-wave inversions in V1-V4 (right ventricular strain pattern - most specific)
• P pulmonale (tall, peaked P waves > 2.5 mm in II) from right atrial strain
• Atrial fibrillation or flutter
• Electrical alternans if associated with pericardial effusion

ECG Image - Pulmonary Embolism:

(Source: LITFL ECG Library - S1Q3T3 pattern with right heart strain changes)

10. Long QT Syndrome (LQTS) / Torsades de Pointes

• Prolonged QTc interval: QTc > 450 ms (men), > 460 ms (women) by Bazett formula
• T-wave morphology abnormalities: notched, bifid, or broad T waves
• U waves may be prominent
• QTc > 500 ms = high risk of Torsades

• Polymorphic VT - QRS complexes that "twist" around the isoelectric baseline
• Axis changes every 5-20 beats (waxing and waning amplitude)
• Initiated by a long-short RR sequence (R-on-T phenomenon)
• May be self-terminating or degenerate to VF

ECG Image - Torsades de Pointes:

(Source: LITFL ECG Library - Characteristic "twisting" QRS morphology around the isoelectric baseline)

Quick Reference Summary Table

• LITFL ECG Library - comprehensive free ECG examples
• ECG Waves (ecgwaves.com) - detailed ECG teaching with case-based learning
• Harrison's Principles of Internal Medicine 22E - Myocardial Ischemia and Infarction chapter
• Tintinalli's Emergency Medicine - Electrocardiography section

Note: ECG interpretation must always be correlated with clinical history, symptoms, and other investigations. If some images don't render due to external hosting, click the source links above to view them directly on LITFL or ECGwaves.