Long-term multicenter experience with a second-generation implantable pacemaker-defibrillator in patients with malignant ventricular tachyarrhythmias. The Guardian Multicenter Investigators Group

Telectronics Pacing Systems, Denver, Colorado.

A second-generation implantable pacemaker-cardioverter-defibrillator was evaluated in 200 patients with sustained ventricular tachycardia, ventricular fibrillation or prior cardiac arrest. The device permits demand ventricular pacing for bradyarrhythmias and for long QT interval or tachycardia suppression, uses programmable (3 to 30 J) energy shocks for conversion of ventricular tachycardia and ventricular fibrillation and is used with conventional pacing and defibrillation leads. Ventricular tachycardia/fibrillation recognition is based on the ventricular electrogram rate and requires reconfirmation before shock delivery. Two hundred patients (mean age 62 years, mean left ventricular ejection fraction 36%) were enrolled and followed up for 0 to 23 months (mean 12). Epicardial lead system implantation was performed with use of an anterolateral thoracotomy (38%), median sternotomy (26%) and subxiphoid (20%) or subcostal (16%) approach. Perioperative mortality rate was 5.5% (all nonarrhythmic deaths). Implant defibrillation threshold ranged from 3 to 30 J (mean 15), with initial programmed shock energy ranging from 3 to 30 J (mean 22). Ventricular tachycardia/fibrillation sensing threshold ranged from 0.7 to 1.8 mV (median 1) and the tachycardia detection interval from 288 to 416 ms (median 320). Reprogramming of implant variables was necessary for reliable electrographic sensing (54 patients), programmed shock therapy (61 patients) and tachycardia detection rate (63 patients). Device activation for potential shock delivery occurred in 111 patients (55.5%) with actual shock delivery after ventricular tachycardia/fibrillation reconfirmation in 66 patients (33%). During follow-up study, there was a 1% arrhythmia mortality rate, 6.5% cardiac mortality rate and 10.5% total mortality rate. This study demonstrates that the programmable implantable pacemaker-cardioverter-defibrillator is effective in preventing arrhythmic death, yet reduces patient exposure to repeated shock therapy. Reprogramming is usually necessary during follow-up for optimal function.

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