Unexpected pacing..

Trace category: 

Hello everybody,

Here is a VT tracing misinterpreted as SVT because of the chamber onset discrimination algorithm. Nothing special except the following sequence (4 and 5th ventricular events):


The 4th ventricular event is sensed and marked "-" (discrepancy between the current interval which is fast and the average of the 4 last intervals). Immediately after, we see a AP at the sensor rate which is followed by a BIV stimulation (BP) within the vulnerable period of the ventricular cycle. The atrial pacing interval is not altered by the PVC which is expected to trigger a PVARP.

Does somebody have an explanation for that?

Thank you,


I have some news from the SJM tech department:

"While the VS marker is shifted slightly to the left of the A Pace, both events occur functionally simultaneously and while the device detects and marks the Ventricular Sense event it is unable to complete the processing to reset the brady pacing timing. "

The device behaves as if the PCV occurred during the post AP ventricular blanking except that the PVC is not after the AP... This sequence must be a very rare occurrence. It should not be a problem for CRT where short AV delays are programmed but I wonder what could happend with a DR device programmed with a long AV delay (VIP for example).

Many thanks to SJM for the explanation.