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An unusual case of implantable cardioverter-defibrillator inhibition

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Clinical record

A 34-year-old woman with an implantable cardioverter-defibrillator (ICD) for mitral valve prolapse and non-sustained ventricular tachycardia presented for clinical and device review on a background of intermittent palpitations associated with syncope since the age of 22 years.

At that time, an echocardiogram showed mild left ventricular dysfunction and moderate mitral regurgitation. After careful consideration of the risks and benefits, the patient underwent ICD implantation for primary prevention. A Maximo VR 7232 single chamber ICD (Medtronic) was implanted with a Sprint Quattro Secure 6947 active fixation lead (Medtronic) positioned in the right ventricular apex, and defibrillation threshold testing performed after implantation was successful. Device programming was set to ventricular pacing and sensing mode (VVI mode) with a lower rate of 30 beats/min. Therapy settings were programmed with a ventricular tachycardia monitor zone of 200–250 beats/min and a ventricular fibrillation zone of > 250 beats/min with 35 J shock therapy. On follow-up, device function proved to be normal.

At review, the patient noted that an alarm sound was being emitted from her ICD. She had been well otherwise, with no record of arrhythmic events seen on device interrogation, and no device alerts or alarms. She described a continuous alarm sound (suggesting to us that the device…