Single-lead electrocardiogram (ECG) showing lead V5 in type II sinoatrial block

There is a 3:2 SA block, resulting in group beating of pairs of sinus beats. The P-P interval during the pause has a duration (1840 msec) that is approximately equal to two P-P cycles (920 msec); this finding distinguishes this arrhythmia from type I SA block in which the pause duration is less than that of two P-P cycles. There may be some sinus variability, as in this case, due to sinus arrhythmia and possibly to baroreceptor responses to varying diastolic filling intervals.

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.