Significance of missing telemetered markers in implanted cardioverter-defibrillators

We report three patients with St Jude ICDs (St. Jude Medical, Sylmar, CA, USA) where some aspect of the marker channel was missing.

Two cases were caused by the simultaneous occurrence of two distinct cardiac or device events that affected the proper delivery of markers by the telemetry system. Inability of the devices to sequentially process these events resulted in incomplete transmission of telemetry data to the programmers and caused missing markers in the telemetry recordings. In the third case, sensed atrial interference resulted in a short period of atrial asynchronous pacing, which prevented the delivery of a sensed atrial marker coincident with an atrial electrogram. This atrial electrogram by virtue of its timing would have otherwise been sensed outside the atrial refractory period.

The perplexing recordings of the three patients should not be interpreted as representing true pacemaker malfunction.