Electrocardiogram showing Mobitz type I (Wenckebach) atrioventricular block

Single-lead electrocardiogram showing Mobitz type I (Wenckebach) second-degree atrioventricular block with 5:4 conduction. The characteristics of this arrhythmia include: a progressively increasing PR interval until a P wave is not conducted (arrow), a progressive decrease in the increment in the PR interval, a progressive decrease in the RR interval, and the RR interval that includes the dropped beat (0.96 s) is less than twice the RR interval between conducted beats (0.53 to 0.57 s).

Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright.