Fully Compensatory Pause: Post-Ectopic SA Depression

Report:

Sinus rhythm 80/min 1

Left atrial abnormality (LAA) 2

SVEB with (fully) compensatory pause 3

Atrial-sensing ventricular pacing with 100% capture 4

Comment:

The SVEB, probably of atrial origin, causes a fully compensatory pause – exactly the length of the two preceding sinus cycles and only almost imperceptibly less than the length of the two succeeding sinus cycles. It’s easy to measure here using the ventricular pacing spikes.

The reason for this is that the sinus node becomes depressed, temporarily, when prematurely discharged by the atrial ectopic beat. Although the latter resets the SA node the pause may be fully compensatory or even longer if the post-ectopic SA depression is pronounced. In this case, the sinus escape following the SVEB is obviously longer than the normal sinus cycle.

The pacemaker is a red herring here: surprising number of students state that the pause is (fully) compensatory because of the pacemaker! Others, more “knowledgeable”, go for rate hysteresis, which cannot be diagnosed where, like here, the pacemaker follows the native rhythm.

Fig 80. 75 year old man in CCU , with a permanent pacemaker. He is feeling unwell.