Case report: Masked premature ventricular contractions and Intradevice interaction causing ventricular Arrythmias.

An implantable cardioverter-defibrillator (ICD) intended to prevent malignant arrhythmias can, in rare cases, precipitate them. We report a 44-year-old man with cardiac sarcoidosis who suffered recurrent polymorphic ventricular tachycardia (VT) and ventricular fibrillation (VF) due to an intradevice timing interaction. Premature ventricular contractions (PVCs) fell within the ICD's post-atrial pacing ventricular blanking period and went undetected ("masked"), resulting in ventricular pacing during the vulnerable period (R-on-T), which triggered VT/VF. Reprogramming the device from DDD to VVI mode prevented further arrhythmias. This case highlights the importance of individualized ICD programming to avoid device-induced arrhythmias.