Atrial Pacemaker Captures During 2:1 AV Block

Report:

Sinus rhythm 0.5

AV sequential (known DDD) pacemaker 0.5

Atrial sensing & pacing 1.0”escape interval 1

AV interval 0.30” atrial-paced beats and one conducted sinus beat 1

Failed ventricular pacing 1

Second degree AV block 2:1 alternate paced & sinus P waves 1

Ventricular rate 30/min 0.5

Ventriculophasic effect 1

Atrial bigeminy 1

Left atrial abnormality (LAA) 0.5

Right bundle branch block 0.5

Left anterior hemiblock 0.5

Possible old anterior infarction 0.5

Nonspecific T wave changes 0.5

Comment:

In the first four cycles, 2:1 block consists of atrial pacemaker captures (conducted with 1o AV block 0.30”) and completely blocked sinus P waves. The last cycle contains two sinus P waves, both with atrial pacemaker spike falling shortly after their onset, creating atrial pseudofusion beats. Atrial sensing and pacing are normal.

The atrial rhythm is in fact bigeminal due to the ventriculophasic effect: the atrial cycles containing a QRS complex are shorter than the “empty” ones. This holds true also for the last cycle, where the two sinus P waves have a P-P interval longer than the preceding spike-P interval. The bigeminy is thus due to more than different pacemaker and sinus escape intervals. Until the last cycle, the atria can be said to be in a state of escape-capture bigeminy (of sorts): paced escapes and sinus captures.

The T wave changes do not correspond to the anterolateral Q waves and may not be infarctional.