ECG: Axis and Rhythm
Beyond intervals, determining the electrical axis and evaluating rhythm strip regularity are the next steps in systematic ECG analysis.
1. Determining Electrical Axis
| Lead I | aVF Lead | Axis Result |
|---|---|---|
| Positive (Up) | Positive (Up) | Normal (0° to +90°) |
| Positive (Up) | Negative (Down) | Left Axis Deviation |
| Negative (Down) | Positive (Up) | Right Axis Deviation |
2. Systematic Rhythm Checklist
- Regularity: Are R-R intervals consistent? (Irregularly irregular = A-fib).
- P Waves: Are they present? Do they precede every QRS? Are they uniform?
- Narrow vs. Wide QRS: QRS <0.12s suggests supraventricular origin; QRS ≥0.12s suggests ventricular origin or bundle branch block.
Pathology Board Hint: For axis deviation, think about hypertrophy. Left Axis Deviation is classically seen in Left Ventricular Hypertrophy (LVH) and LBBB. Right Axis Deviation is common in Right Ventricular Hypertrophy (RVH), pulmonary disease, or RBBB.