Symptomatic Bigeminy Due to Trigeminy

Report:

Sinus rhythm 80/min 1

Blocked SVEBs, trigeminal 8

A-sensing ventricular pacing throughout 1

Comment:

Not surprisingly, the pacemaker was blamed. It was programmed to pace at 60/min, with a sleep mode of 50/min during night hours. There was no rate hysteresis. The escape cycles appeared unduly long, projecting a heart rate of 42/min and producing an overall rate of 55/min.

These escapes were of course sinus escapes; the pacemaker was only doing what it was programmed to do, viz. to follow sinus P waves at 0.18” AV intervals. The sinus escape beats are delayed by the so-called post-ectopic sino-atrial depression, which is a mouthful increasingly replaced by slightly unsatisfactory but punchier overdrive suppression. The cause of this depression (or suppression) is easily seen, once sought: it wrinkles every second T wave and even stands out clearly in its own right in lead 1. The sinus P wave escapes exactly one second after the blocked P’ wave – just beating the pacemaker at the latter’s programmed rate of 60/min. The P wave must be slightly, imperceptibly faster than its artificial counterpart, which remains invisible since no atrial pacing takes place (atrial-looking spikes in the short cycles at the beginning of the trace are artefactual). [! XE "Overdrive suppression" \t "See post-ectopic sino-atrial depression" !]

Fig 107. 73 year old man with permanent DDD pacemaker, admitted to CCU for bradycardia.