This 28-year-old woman received a Biotronik Lumax 540 VR-T single chamber defibrillator after an episode of aborted sudden cardiac death; programming of an enhanced T wave suppression, maximal sensitivity 0.5 mV. An event report (yellow color) was issued in the context of supraventricular tachycardia (SVT).
Telecardiology tracing
The 3 channels available are 1) the markers with the time intervals, 2) the shock channel (FF = far field) between the coil of the RV lead and the pulse generator, and 3) the right ventricular (RV) sensing channel.
This tracing illustrates the limits of the programming implemented in the patient of the previous tracing. In this young patient, enhanced T wave suppression had been systematically programmed to limit the risk of delivery of inappropriate therapy due to T wave oversensing. The wide variability of the ventricular electrograms’ amplitude present on this tracing is noteworthy, and the spontaneous, low-amplitude, ventricular signals occurring after higher-amplitude electrograms were not sensed, because, as mentioned earlier, the sensing level hinges on the amplitude of the preceding QRS. This explains the high likelihood of undersensing low-amplitude signals falling after high-amplitude electrograms. This undersensing is highly worrisome, as an accurate detection of all arrhythmias is an indispensable prerequisite for the delivery of therapies. The sensitivity programmed at 0.5 mV leaves little room for the reprogramming of a higher sensitivity. We reprogrammed to a standard programming and tested induction of VF to verify the reliability of sensing.
