ECG Characteristics for Diagnosing Cardiac Conditions

Introduction to ECG Diagnosis

• The American College of Cardiology recommends looking for wide QRS complexes (>120 ms) occurring earlier than expected, without preceding P waves, followed by a compensatory pause, to diagnose Premature Ventricular Beats (PVCs) 1
• The American College of Cardiology suggests that multiple PVCs (>2,000 in 24 hours) warrant comprehensive cardiac evaluation including echocardiography and CMR to exclude cardiomyopathy 1, 2

Atrial Fibrillation Diagnosis

• The American College of Cardiology states that atrial fibrillation shows irregularly irregular RR intervals with absent P waves, replaced by chaotic fibrillatory waves best seen in leads V1, II, III, and aVF 1, 3
• The American College of Cardiology recommends measuring ventricular rate over 6 seconds and multiplying by 10 for average rate in atrial fibrillation 3

STEMI Diagnosis

• The American College of Cardiology and the European Society of Cardiology state that STEMI requires ST elevation at the J-point in two or more contiguous leads: ≥0.1 mV in all leads except V2-V3, where thresholds are higher and age/sex-dependent 5, 6
• The American College of Cardiology recommends obtaining an ECG within 10 minutes of presentation and repeating every 15-30 minutes if initially non-diagnostic for STEMI 6

Hypertrophic Obstructive Cardiomyopathy (HOCM) Diagnosis

• The European Heart Journal suggests that HOCM shows deep, narrow Q waves in lateral and inferior leads, giant inverted T waves in precordial leads, and voltage criteria for left ventricular hypertrophy 8
• The European Heart Journal recommends focusing on lateral leads (I, aVL, V5-V6) for Q waves and ST-T changes, and V2-V4 for giant T wave inversion in HOCM 8

Bundle Branch Blocks Diagnosis

• The American College of Cardiology states that Right Bundle Branch Block (RBBB) shows QRS ≥120 ms with RSR' pattern ("M-shaped") in V1-V2 and wide S waves in lateral leads I, aVL, V5-V6 3, 2
• The American College of Cardiology recommends looking for broad, notched R waves in lateral leads (I, aVL, V5-V6) and deep S waves in V1-V2, without Q waves in lateral leads, to diagnose Left Bundle Branch Block (LBBB) 3, 2

Acute Pericarditis Diagnosis

• The American College of Cardiology and the European Heart Journal state that acute pericarditis shows diffuse ST elevation with upward concavity (saddle-shaped) in multiple leads, accompanied by PR depression, without reciprocal ST depression 5, 6, 7
• The American College of Cardiology recommends looking for widespread ST elevation with upward concavity in leads I, II, aVL, aVF, V2-V6, and PR depression in most leads except aVR, to diagnose acute pericarditis 5, 6, 7

Brugada Syndrome Diagnosis

• The American College of Cardiology and the European Heart Journal suggest that Brugada syndrome Type 1 pattern shows coved ST elevation ≥2 mm in V1-V2 with downsloping ST segment and inverted T wave, often with right bundle branch block 2, 8, 4
• The American College of Cardiology recommends recording V1-V2 in the 4th intercostal space and considering recording V1-V2 in the 2nd intercostal space to unmask the Brugada pattern 2, 4

Hyperkalemia and Hypokalemia Diagnosis

• The European Heart Journal states that hyperkalemia creates peaked, narrow-based "tented" T waves initially, progressing to widened QRS, flattened P waves, and potentially Brugada-like patterns in severe cases, but this section is ignored as per instructions.
• The European Heart Journal suggests that hypomagnesemia causes QT prolongation, prominent U waves, and predisposes to torsades de pointes, with changes most evident in precordial leads 4

Hypermagnesemia Diagnosis

• The European Heart Journal states that hypermagnesemia produces prolonged PR and QT intervals with widened QRS, though ECG changes are less specific than other electrolyte disorders 4