Masked Premature Ventricular Contractions and Intradevice Interaction Causing Ventricular Fibrillation

Implantable cardioverter-defibrillators (ICD) are indicated for patients with cardiomyopathies to reduce their risk of sudden cardiac death from both ventricular tachycardia (VT) and ventricular fibrillation (VF). ICDs and biventricular ICDs can, however, be proarrhythmic, especially when pacing into a scar. We describe 2 cases of patients with frequent premature ventricular contractions (PVCs) who developed recurrent polymorphic VT/VF due to interaction between PVC timing and blanking periods, leading to R-on-T ventricular pacing following pseudo-pseudofusion.