10 Most Common Heart Diseases & Their ECG Findings

1. 🫀 ST-Elevation Myocardial Infarction (STEMI)

• ST-segment elevation ≥1 mm in ≥2 contiguous leads (convex/tombstone morphology)
• Hyperacute T-waves (tall, peaked) — earliest sign
• Reciprocal ST depression in opposing leads
• Pathological Q waves develop within hours (necrosis marker)
• Lead localization: V1–V4 = anterior (LAD); II, III, aVF = inferior (RCA); I, aVL, V5–V6 = lateral (LCx)

2. 🫀 Non-ST Elevation ACS / Unstable Angina (NSTEMI/UA)

• ST-segment depression (horizontal or downsloping) — most common
• T-wave inversions — symmetric, deep (especially lateral leads)
• Wellens' syndrome (critical LAD stenosis): biphasic or deeply inverted T-waves in V2–V3 with no ST elevation
• No pathological Q waves (no transmural necrosis)
• Normal ECG possible in up to 5% of NSTEMIs

3. 🫀 Atrial Fibrillation (AF)

• Absent P waves — replaced by fine irregular fibrillatory (f) waves, best seen in V1
• Irregularly irregular RR intervals — the hallmark finding
• Narrow QRS (unless aberrant conduction or pre-existing BBB)
• Rate may be: controlled (<100 bpm) or rapid ventricular response (>100 bpm)

4. 🫀 Complete (Third-Degree) AV Heart Block

• Complete AV dissociation — P waves and QRS complexes are completely independent
• Regular P-P intervals and regular RR intervals, but no fixed PR relationship
• Slow escape rhythm: narrow QRS (junctional, 40–60 bpm) or wide QRS (ventricular, 20–40 bpm)
• P waves "march through" QRS complexes without conducting

5. 🫀 Left Ventricular Hypertrophy (LVH) / Hypertensive Heart Disease

• High-voltage QRS: Sokolow-Lyon criteria — S in V1 + R in V5/V6 ≥35 mm
• Cornell criteria: R in aVL + S in V3 ≥28 mm (men) / ≥20 mm (women)
• LV strain pattern: ST depression + T-wave inversion in I, aVL, V5–V6
• Left axis deviation
• Caused by: hypertension, aortic stenosis, HCM

6. 🫀 Ventricular Tachycardia (VT)

• Wide complex tachycardia (QRS >120 ms) at rate 100–250 bpm
• AV dissociation — P waves independent of QRS (pathognomonic of VT)
• Fusion beats and capture beats (strong VT indicators)
• Concordance across precordial leads (all positive or all negative)
• Axis deviation (often northwest axis)
• Brugada criteria help distinguish VT from SVT with aberrancy

7. 🫀 Wolff-Parkinson-White (WPW) Syndrome

• Short PR interval (<120 ms) — rapid conduction via accessory pathway (Bundle of Kent)
• Delta wave — slurred, slow upstroke at the beginning of QRS
• Wide QRS complex (>120 ms) due to ventricular pre-excitation
• Secondary ST/T-wave changes (discordant to QRS)
• Can mimic STEMI or LBBB; risk of sudden death with AF

8. 🫀 Pulmonary Embolism (PE) / Acute Cor Pulmonale

• S1Q3T3 pattern — S wave in lead I, Q wave in lead III, T-wave inversion in lead III (classic but only ~20% sensitive)
• Sinus tachycardia — most common finding
• Right heart strain: T-wave inversions in V1–V4
• Incomplete/complete RBBB — sudden right ventricular pressure overload
• Rightward axis deviation

9. 🫀 Left Bundle Branch Block (LBBB)

• Wide QRS (≥120 ms)
• Broad, notched ("M-shaped") R waves in I, aVL, V5–V6
• Deep rS or QS pattern in V1
• Absence of septal Q waves in lateral leads
• Discordant ST/T changes (ST and T in opposite direction to QRS)
• New LBBB + chest pain = STEMI equivalent (Sgarbossa criteria apply)

10. 🫀 Pericarditis

• Stage 1: Diffuse, saddle-shaped (concave) ST elevation in most leads; PR depression (hallmark); ST elevation in aVR is absent/depressed
• Stage 2: ST returns to baseline; T-waves flatten
• Stage 3: T-wave inversions (widespread)
• Stage 4: Normalization
• Key distinction from STEMI: diffuse (not regional), concave elevation, PR depression, no reciprocal changes (except aVR)

Quick Reference Summary Table

Clinical tip: Always interpret ECGs in the clinical context. A single ECG finding rarely makes a diagnosis alone — correlate with history, symptoms, and other investigations.