P-wave

Left atrial enlargement: negative portion of P-wave in lead V1 of ≤0.1 mV depth and duration of ≥0.04 seconds

Right atrial enlargement: peaked P-wave in leads II and III or V1 of ≥0.25 mV amplitude

QRS complex

QRS axis deviation: right 120° or more or left −30° to −90°

Increased voltage: amplitude of R-wave or S-wave in a standard lead of ≥2 mV, S-wave in lead V1 or V2 of ≥3 mV, or R-wave in lead V5 or V6 of ≥3 mV

Pathological Q-waves: duration ≥0.04 seconds, or ≥25% of the height of the ensuing R-wave, or QS pattern in two or more leads

Right or left bundle branch block with QRS duration of ≥0.12 seconds

R or R’ wave in lead V1 ≥0.5 mV in amplitude and R/S ratio of ≥1

ST-segment, T-waves, and QT-interval

ST-segment depression, T-wave flattening, or inversion in two or more leads

Prolongation of heart rate-corrected QT interval of >0.44 seconds in males and >0.46 seconds in females

Rhythm and conduction abnormalities

Premature ventricular beats or more severe ventricular arrhythmias

Supraventricular tachycardias, atrial flutter, or atrial fibrillation

Short PR interval (<0.12 seconds) with or without ‘delta’ wave

Sinus bradycardia with resting heart rate ≤40 beats/minute

First- (PR 0.21 seconds), second-, or third-degree atrioventricular block