INTERVALS

Prolonged PR

PR > 200ms or > 1 big box
e.g. AV block, hypermagnesemia, hyperkalemia

Shortened PR

PR < 120ms or < 3 small boxes
e.g. Wolff-Parkinson White syndrome, Long-Ganong-Levine syndrome

Widened QRS

QRS > 120ms or > 3 small boxes
e.g. any aberrant ventricular beat, bundle branch block, intraventricular conduction delay

Narrow (normal) QRS

QRS ≤ 120ms or ≤ 3 small boxes
e.g. any beat conducted down the His-bundle branch-Purkinje system

Prolonged QT

QT > 1/2 of RR’ or > 460ms
e.g. inherited or acquired long QT syndrome, hypokalemia, hypomagnesemia, hypocalcemia, ICH

Shortened QT

QT < 360ms
e.g. short QT syndrome, hypercalcemia, hypothermia