Sinus pause/arrest is defined by which of the following findings?

• A. SA node stops firing; P waves do not march out
• B. P waves march out from the previous beat
• C. The R-R irregularity is due to respiration
• D. There are no P waves due to atrial fibrillation

Answer: (A)

Sinus pause/arrest happens when the SA node fails to generate an impulse for a period, causing a pause in atrial activity. On the ECG you see a longer-than-normal interval with no P waves during that pause because no atrial depolarization is occurring. When the pause ends, a secondary pacemaker may take over and produce the next beat, which can have a different P-wave morphology or no P wave if the escape rhythm is junctional. This absence of P waves during the pause is the key feature indicating SA node inactivity. In contrast, sinus arrhythmia shows normal SA node firing with RR variation due to respiration, and atrial fibrillation shows no discrete P waves with an irregularly irregular rhythm.