Single Lead Dual-Chamber Pacing

Report:

Ventricular pacemaker rhythm 90/min (top strip) 2

Atrial pacemaker rhythm 90/min (bottom strip) 2

Switch from ventricular to atrial pacing with decreased output 6

Comment:

The report, as written above, appears correct. However, two things are against it: the nurses’ observation that the lead did not change and the obviously larger pacemaker spike in the top strip, all at the same rate on the same lead.

It turned out that with increased atrial lead output it started pacing the ventricles (and, by inference, the atria, whose P waves were flat in L2 anyway and would now be masked by the broad paced QRS). The strips below illustrate (i) that the pacemaker is a dual one, and the ventricle is paced by the atrial lead (top) and (ii) that increasing the spike amplitude converts the pacing from atrial to ventricular49. The top strip had ventricular spikes added (DDD mode) to show which lead is pacing the ventricles. Of course, the same appearance would result from reversing A & V leads, but this was specifically excluded.