A 34-year-old man was admitted to our hospital because his implantable cardioverter-defibrillator (ICD) frequently began delivering shocks while the patient was conscious. Five years ago, the patient was implanted with a Medtronic single-chamber ICD for early repolarization pattern (ERP) symptomatic of probable arrhythmic syncope. His 12-lead ECG at ICD implantation showed a J-point elevation of 2 mm in more than two adjacent leads with notching on terminal QRS complex (Fig 1). There had been no recurrence of ventricular arrhythmia since implantation.
The ICD was programmed with a conditional zone over 200 beats per minute, a shock zone over 220 beats per minute. Sensitivity was programmed to 0.4 mV. Pacing lead impedance was 589 Ohm and shocking lead impedance was 50 Ohm.
He experienced an ICD shock in December 2022. Device interrogation revealed high frequency oversensing on the ventricular channel, interpreted as ventricular fibrillation by the ICD. Twenty shock at 34-J was delivered…(Fig 2)
The ventricular impedance lead was more than 3000 ohms. (Fig 3)
The chest X-ray was requested (Fig 4).