A 37-year-old man with type I Brugada syndrome and successful reanimation from cardiac arrest underwent implantation of a Virtuoso VR single chamber ICD for secondary prevention, and VF induction at the end of the procedure.
1 : VF induction by T wave shock (not shown); 2 :Ventricular undersensing resulting in delayed detection (alternating FS-VS) and therefore delayed capacitor charge; 3 : Detection of VF (FD : the programmed VF criterion is met : 18/24); 4 : Abandonment of therapies by the operator; 5 : The recording of electrograms is interrupted; 6 : A manual backup DC shock is delivered by the programmer; 7 : Ventricular paced (VP) rhythm has returned.
During this induction, the operator noted considerable ventricular undersensing due to a wide variability in the amplitude of the ventricular signal interfering with the device’s automatic sensitivity control. The failure to detect the low amplitude VF signals occurred after a higher amplitude signal. Recall that the detection level fits the amplitude of the preceding QRS. Because of the risk of delayed treatment, the operator proceeded with the delivery of a manual shock. In this patient, the 3.2 mV ventricular sensing in sinus rhythm was insufficient. The lead was moved from the apex of the right ventricle to a high septal position, a site that allowed reliable sensing to 5.6 mV. On subsequent induction VF was accurately sensed and effectively terminated by a 20-J shock.
Episode of induced VF; abandonment of therapies after user intervention due to undersensing of the tachyarrhythmia; sensitivity programmed to 1.2 mV
