Ventricular Tachycardia Recognized as Ventricular Fibrillation by an ICD Due to Double Counting of the QRS Complex

A case of ventricular tachycardia misdiagnosed as ventricular fibrillation due to double counting of the tachycardia’s wide QRS complex in an implantable cardioverter defibrillator (ICD) recipient is presented. As a result, an inappropriate shock was delivered by the device instead of anti-tachycardia pacing. Reprogramming of the detection criteria in a less sensitive manner resolved the problem. I n T R o d u C T I o n Appropriate and reliable detection of ventricular tachyarrhythmias is crucial for determining effective and safe interventions of implantable cardioverter defibrillators (ICD). Inappropriate shocks delivered by ICDs are an increasingly recognized complication, many cases have been reported and availability of stored electrograms allows correct interpretation of ICD failures. We report a case in which a sustained ventricular tachycardia (VT) was falsely characterized as ventricular fibrillation (VF), due to double counting of the VT’s QRS complex, resulting in inappropriate shock delivered by the device, instead of anti-tachycardia pacing (ATP) therapy.