28-year-old woman implanted with a Lumax 540 VR-T single-chamber ICD for resuscitated sudden death; systematic programming of an enhanced T wave suppression to limit the risk of inappropriate therapy due to T wave oversensing in the presence of an R wave of modest amplitude (3 mV); event report (yellow color) in the setting of the recording of a SVT.
3 channels are available; the markers with the time intervals, the shock channel (FF: far field) between the ventricular lead coil and the pulse generator, the right ventricular sensing channel (RV).
In this young patient, an enhanced T wave suppression had been systematically programmed to limit the risk of inappropriate therapy due to T wave oversensing. She presented poor ventricular sensing with R waves measured between 3 and 4 mV at rest explaining a change in the programmed sensitivity (from 0.8 to 0.5 mV). On this tracing, there is a great variability in the amplitude of the ventriculograms. The absence of sensing of spontaneous low-amplitude ventricular signals occurs after a higher-amplitude signal. It should be reminded that the sensing level adapts to the amplitude of the previous QRS. This explains the high probability of undersensing low-amplitude signals occurring after a high-amplitude signal. This undersensing in sinus rhythm is highly worrisome, since a correct sensing of the arrhythmia is an essential prerequisite for the delivery of any therapy. The programmed sensitivity value leaves very little margin. It is possible to return to a standard programming or to reprogram with enhanced VF sensing. In this patient, an induction procedure seems indispensable to validate proper sensing in VF. In case of doubt, repositioning of the right ventricular lead may be necessary.
