Fine Ventricular Fibrillation Therapy Assurance Algorithm Failure From Low-Amplitude Far-Field Signals: Precision Sensing Strategy.

BACKGROUND: The VF Therapy Assurance (VFTA) algorithm in Abbott implantable cardioverter-defibrillators (ICDs) enhances detection of fine ventricular fibrillation by utilizing far-field signals when near-field sensing is inadequate. However, this algorithm may paradoxically trigger inappropriate ICD therapy in certain electrogram phenotypes. CASE SUMMARY: A 53-year-old man with a cardiac resynchronization therapy-defibrillator for nonischemic cardiomyopathy presented after an ICD shock during light housework. Device interrogation revealed stable supraventricular tachycardia at 160 beats/min with low-amplitude far-field signals on the Coil-Can vector, triggering VFTA activation. This collapsed all detection zones into a single therapy zone, disabled supraventricular tachycardia discriminators, and delivered an inappropriate shock after only 6 beats meeting ventricular fibrillation criteria. The sensing vector was reprogrammed from Coil-Can to Tip-Can, with no recurrent inappropriate therapy on follow-up. DISCUSSION: Low-amplitude far-field signals can inappropriately activate VFTA, leading to zone collapse and discriminator suspension during supraventricular tachycardia, resulting in unwarranted therapy delivery. TAKE-HOME MESSAGE: Targeted sensing vector reprogramming may mitigate VFTA-mediated inappropriate shocks while preserving the algorithm's intended benefit for fine ventricular fibrillation detection.