What does the "pause" in sinus arrest indicate on an ECG?

The "pause" in sinus arrest on an ECG is indicative of a failure of the SA node to initiate a heartbeat. This pause occurs when there is an interruption in the normal rhythmic pacing of the heart, specifically when the primary pacemaker, the SA node, does not generate an impulse. Typically, the SA node sends out electrical signals that trigger the heart's contractions, maintaining a regular heart rate. When a sinus arrest takes place, it generally results in a transient cessation in these signals, leading to a noticeable pause on the ECG tracing. This may manifest as a gap in the rhythm, marking the absence of expected P waves and subsequent QRS complexes during the arrest period.

In contrast, other options focus on mechanisms that do not specifically relate to the initiation of impulses by the SA node. A blockage in the His-Purkinje system would not cause a pause due to failure in the SA node but rather would lead to delayed or absent transmission of impulses; rapid heart rate alterations would not signify a pause, and myocardial ischemia typically presents with changes in the ST segment or T waves rather than a straightforward pause in the rhythm. Thus, the identification of a pause due to a sinus arrest is pivotal for understanding underlying rhythms and potential cardiac issues linked to