Sinoatrial Block | Reference Guide

EKG Features

Rate: Normal or slow
Rhythm: Irregular when SA block occurs
P Wave: Normal
PR Interval: Normal (0.12-0.20 sec)
QRS: Normal (0.06-0.10 sec)

In sinoatrial block, the impulse is delayed or blocked on the way to the atria. This creates a dropped beat which is a multiple of the P-P interval. After the dropped beat, the rhythm continues regularly. There are three types of SA blocks, based upon the length of the delay.
External Source: http://connects.catalyst.harvard.edu/Profiles/display/Concept/Sinoatrial%20Block
Harvard Med School Catalyst