Basic and Advanced Electrocardiography
Rate, rhythm, axis, intervals, morphology
Read every ECG in a fixed order so nothing is skipped: rate (300 ÷ large boxes between R waves, or 1500 ÷ small boxes; count complexes in a 6-second strip and multiply by 10 when the rhythm is irregular), rhythm (P before every QRS, regular), axis (leads I and aVF), intervals (PR 0.12–0.20 s, QRS <0.12 s, QT corrected for rate), then morphology - P waves, QRS amplitude and precordial progression, ST segment at the J point, T and U waves.
Candidates are expected to know: left ventricular hypertrophy (S in V1 + R in V5/V6 ≥ 35 mm; Cornell R aVL + S V3), bundle branch block patterns, fascicular blocks and axis deviation, first-, second- and third-degree AV block, chamber enlargement, and localization of ST elevation (inferior II/III/aVF; anterior V1–V4; lateral I/aVL/V5–V6).
Traps: measure QT in the lead with the longest interval using the tangent method and exclude a fused T-U wave; the machine's QTc is only a starting point. LVH, digoxin and early repolarization all produce ST-T changes that mimic ischemia. Upsloping ST depression is common with tachycardia and is less specific than horizontal or downsloping depression. Always compare with prior tracings when available.
Rule of thumb: measure ST deviation 60–80 ms after the J point; ≥1 mm in two contiguous limb leads or ≥2 mm in precordial leads is the standard exercise criterion.