Does reception of appropriate shocks from the implantable cardioverter defibrillator affect survival?

The implantable cardioverter defibrillator has become an important therapeutic modality for treatment of life-threatening ventricular tachyarrhythmias. Recent reports have suggested that patients who receive appropriate shocks from this device have an inordinately high overall mortality, and questioned the extent of benefit these patients derive from the implant. This report analyzed the survival among 184 patients who received the implantable cardioverter defibrillator to assess survival differences between patients who received appropriate shocks versus those who did not. At a mean follow-up of 24 +/- 18.7 months, 68 patients received an appropriate shock from their device while 116 did not receive an appropriate shock. Overall survival of the entire population was quite similar to those published by others. There was no significant difference between overall survival of patients who received an appropriate shock versus those who did not. However, there was a statistically significant difference in sudden death mortality. The group of patients that received appropriate shocks included all five sudden deaths. This observation suggested that sudden death in this population was likely due to ventricular tachyarrhythmias rather than strictly bradycardia or asystole. The "benefit" of the device to the entire population was also assessed by estimating survival after receipt of the first appropriate shock. Using this approach, an estimated 10% of patients died without receiving an appropriate shock. In other words, ultimately, 90% of patients were expected to benefit from the device. This survival curve, which initiated only after receipt of the first appropriate shock was fairly similar to those estimated from conventional methods. Therefore, survival after receipt of an appropriate shock was comparable to overall survival and there was no significant difference between survival of patients who received appropriate shocks and those who did not.