Excerpt

A 64-year old man with left ventricular non-compaction cardiomyopathy (NCC) [1], left ventricular ejection fraction of 15%, and a CRT-D device in place was admitted to our Emergency Department because of multiple sequential syncopal episodes. Patient was found to have recurrent episodes of transient ventricular fibrillation (VF) (Fig. 1, panel a) and underwent cardiopulmonary resuscitation by the rescue team. Interrogation of the device showed multiple episodes of transient VF which were not shocked by the device because of undersensing of the underlying ventricular arrhythmia on the right ventricular lead and which required external defibrillation (Fig. 1, panel b, black arrow). Remote monitoring the day before the mentioned clinical event showed satisfactory sensing levels in both ventricles. This lack of correlation between the sensed sinus R-wave and the sensed ventricular signals in VF is not surprising since it has been demonstrated to be poor. Patient was on heart failure medications and was not on any anti-arrhythmic drugs. VF undersensing has been already described in the literature [2]. We believe that, in this case, the underlying cardiomyopathy has played a determinant role in the undersensing of VF. The nature of this cardiomyopathy has caused, in our opinion, a dramatic reduction of the QRS voltage during VF in the right ventricle; indeed, the voltage of VF electrograms in the left ventricle was high enough to allow a normal left ventricular sensing. Patients with NCC should therefore undergo defibrillation threshold (DFT) test after implantation of the ICD, both in primary and secondary prevention. In case of undersensing of VF during defibrillation testing, where possible, it is recommendable to sense the ventricular chamber which gives better margins of sensing, all along the life of the device or at least during a ventricular arrhythmia [3]. Subcutaneous defibrillators can also potentially assure a better recognition of VF, in case of no need of pacing and with the necessity to perform DFT test after the implantation.

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