I. What is ECG?
Electrocardiography (ECG) is a non-invasive test that records the electrical activity of the heart via surface electrodes. It is essential for the diagnosis of arrhythmias, ischemia, infarction, electrolyte disturbances, and structural heart diseases.
II. Standard 12-Lead ECG Setup
- Limb Leads (6 total):
- Bipolar: I, II, III
- Augmented unipolar: aVR, aVL, aVF
- Chest Leads (6 total): V1–V6
III. Steps in ECG Interpretation
- Rate
- Normal: 60–100 bpm
- Tachycardia: >100 bpm
- Bradycardia: <60 bpm
- Rhythm
- Regular vs irregular
- Sinus rhythm = P wave before each QRS, regular PR interval
- P wave
- Atrial depolarization
- Abnormal in atrial enlargement or ectopic atrial rhythm
- PR interval (0.12–0.20 sec)
- Prolonged = 1st-degree AV block
- Short = pre-excitation (e.g., WPW)
- QRS complex (< 0.12 sec)
- Widened in bundle branch block, ventricular rhythm
- Axis deviation:
- Left axis: -30° to -90° → LVH, LBBB
- Right axis: +90° to +180° → RVH, PE
- ST segment
- Elevation: acute MI, pericarditis
- Depression: ischemia
- T wave
- Inversion: ischemia, PE
- Peaked: hyperkalemia
- Flattened: hypokalemia
- QT interval (QTc)
- Prolonged: risk of Torsades de Pointes
- Shortened: hypercalcemia