Paced Bigeminy in PAT with Block

Report:

Atrial tachycardia 146/min with block 2

100% paced atrial-sensing ventricular rhythm 97/min 3

Escape-capture bigeminy 5

Comment:

This is a visually striking trace, with regular atrial tachycardia resulting in bigeminal paced ventricular rhythm. The mechanism of this is as follows: in each couplet, the second beat is 0.16” after an atrial wave, since the programmed pacing AV interval is 0.16”. He next P wave is ignored, being within the 0.31” PVARP. The third P wave is also ignored, as the ventricular escape spike falls immediately after it or even on its terminal portion: the ventricle is activated by its own spike rather than the P wave, whose sensed AV delay is 0.16”. That third P wave also accounts for no atrial pacing spikes appearing in this tracing.

The escape interval is relatively short at 0.72” because this is a rate-responsive, DDDR unit. The ventricular rate is, as expected, 2/3 of the atrial rate. This case was the first reported case of paced-escape – paced-capture bigeminy59. Another is in this Volume (Case 110).