R wave in V5-V6 + S wave in V1-V2 > 35 mm

 R wave in lead I + S wave in lead III > 25 mm

 R wave in V1 ≥ 7 mm

 R/S wave ratio in V1 > 1

 P wave total width of > 0.12 sec (3 small boxes) in the inferior leads, usually with a double-peaked P wave

 Terminal portion of the P wave in lead V1 ≥ 0.04 sec (1 small box) wide and ≥ 1 mm (1 small box) deep

 P-wave height in the inferior leads (II, III, and aVF) ≥ 2.5 to 3 mm (2.5 to 3 small boxes) (Fig. 3-1)

 First-degree heart block: The PR interval is a fixed duration of more than 0.20 seconds.

 Second-degree heart block: In Mobitz type I (Wenckebach) block, the PR interval increases until a P wave is nonconducted (Fig. 3-2). The cycle then resets and starts again. Mobitz type I second-degree heart block is sometimes due to increased vagal tone and is usually a relatively benign finding. In Mobitz type II block, the PR interval is fixed and occasional P waves are nonconducted. Mobitz type II second-degree heart block usually indicates structural disease in the atrioventricular (AV) node or His-Purkinje system and is an indication for pacemaker implantation.

 Third-degree heart block: All P waves are nonconducted, and there is either a junctional or ventricular escape rhythm. To call a rhythm third-degree or complete heart block, the atrial rate (as evidenced by the P waves) should be faster than the ventricular escape rate (the QRS complexes). Third-degree heart block is almost always an indication for a permanent pacemaker.

 Acute myocardial infarction (MI) due to thrombotic occlusion of a coronary artery

 Prinzmetal angina (variant angina), in which there is vasospasm of a coronary artery

 Cocaine-induced MI, in which there is vasospasm of a coronary artery, with or without additional thrombotic occlusion

 Pericarditis, in which there is usually diffuse ST segment elevation

 Left ventricular aneurysm

 Left bundle branch block (LBBB)

 Left ventricular hypertrophy with repolarization abnormalities