Normal rate = 60-100 beats per minute.

Bradycardia <60

Tachycardia >100

Normal sinus rhythm—

With junctional rhythm, there is loss of P waves and rate is 40-60 beats per minute.

With ventricular rhythm the rate is 20-40 beats per minute.

QRS complex in leads I and aVF are positive indicates axis is normal.

QRS complex up in lead I and down in lead aVF indicates left axis deviation—think left anterior fascicular block, left ventricular hypertrophy, inferior wall myocardial infarction.

QRS complex down in lead I and up in lead aVF indicates right axis deviation—think right ventricular hypertrophy, acute right heart strain (e.g., massive pulmonary embolism), left posterior fascicular block.

Normal PR = 0.12-0.20 sec (three to five small boxes).

Normal QRS = ≤0.10sec (≤2.5 small boxes).

QTc should be <440 msec (less than half of RR interval).

Corrected QT = QT interval divided by the square root of (RR interval).

In right atrial enlargement, the initial component of part of the P wave is prominent (>2.5 mm) in lead II.

In left atrial enlargement, there is a large terminal downward deflection in lead V1 and the terminal component of part of the P wave is prominent.

Inspect for Q waves, bundle branch blocks, and ventricular hypertrophy.

Significant Q waves are >25% of QRS height and duration >0.04 sec. Q waves indicate necrosis and may be due to old infarct. They remain for the lifetime of the patient.