Systematic Reading Order
- Rate — 300 divided by number of large squares between R waves
- Rhythm — regular or irregular; P wave before every QRS?
- Axis — Lead I and aVF both positive suggests normal axis
- P waves — present, normal shape?
- PR interval — normal 120-200 ms
- QRS complex — width (<120 ms normal) and shape
- ST segment — elevated or depressed?
- T waves — inverted, peaked, hyperacute?
- QT interval — use the QTc calculator
STEMI Criteria
- ST elevation 1mm or more in 2 contiguous limb leads, or 2mm or more in 2 contiguous precordial leads
- New left bundle branch block with high suspicion of ischemia
- Posterior MI: ST depression in V1-V3 with tall R waves — confirm with posterior leads V7-V9
- Reciprocal ST depression in the opposite territory supports a true STEMI over a mimic
T Wave Changes to Know
- Hyperacute T waves — tall, broad; an early ischemia sign that can precede ST elevation
- T wave inversion — ischemia, NSTEMI, or evolving infarction
- Peaked T waves — think hyperkalemia, not ischemia
Red Flags: STEMI Equivalents
Wellens syndrome: biphasic or deeply inverted T waves in V2-V3, in a patient whose chest pain has resolved. Signals critical proximal LAD stenosis.
de Winter pattern: upsloping ST depression with tall, symmetric T waves in the precordial leads — also indicates proximal LAD occlusion without classic ST elevation.
Both patterns carry urgency similar to a classic STEMI. Don't rule out major occlusion just because ST elevation is absent.
Hypertrophy
- Left ventricular hypertrophy (LVH) — Sokolow-Lyon criteria: S wave in V1 + R wave in V5 or V6 ≥35mm. Often accompanied by left axis deviation and a "strain" pattern (ST depression with T wave inversion in the lateral leads)
- Right ventricular hypertrophy (RVH) — right axis deviation, dominant R wave in V1, and right atrial enlargement (peaked P waves in II) are supportive clues
Voltage criteria alone are insensitive but reasonably specific — a positive result is meaningful, but a negative result doesn't rule out hypertrophy, especially in obesity or significant lung disease.