The Nature of the Game

Implantable cardioverter defibrillators (ICDs) reduce mortality among appropriately selected patients who have survived an episode of life-threatening ventricular arrhythmia (secondary prevention) or are at risk for ventricular arrhythmia (primary prevention).1-7 Attention has increasingly focused on primary prevention since survival from out-ofhospital cardiac arrest remains abysmal. The remarkably reproducible success of ICDs to prevent sudden cardiac death in high-risk populations has resulted in modest clinical acceptance of device therapy for mortality benefit. However, large-scale “indications” trials in increasingly unrefined patient populations have nurtured a peculiar intellectual dissatisfaction among astute observers that relates to the troubling matter of optimal patient selection. At the center is an unsubstantiated, but commonly held clinical bias (hunch), which presupposes that primary prevention patients have less absolute need for life-saving therapies and, therefore, are potentially “overtreated” on a population basis. “Overtreatment” in this situation means not only did the patients receive an expensive therapy that they never really needed, but they were also placed at risk for painful shocks due to inappropriate therapies for supraventricular tachycardia (SVT). This issue is important because one of the principal limitations of ICD therapy is the physical and psychological discomfort associated with high-voltage shocks. A direct correlation between poor quality-of-life scores and shocks has been described in ICD trials of primary8 and secondary9,10 prevention. Relatively little is known regarding the incidence and characteristics of appropriate and inappropriate therapies between primary and secondary prevention patients. Wilkoff et al.11 reported primary prevention patients had a significantly higher percentage of device-classified ventricular fibrillation (VF, 40%) versus secondary (14%) prevention patients in MIRACLE ICD. Further, the median cycle lengths (CL) of true ventricular rhythms was significantly shorter in primary versus secondary prevention patients (303 ± 53 vs 367 ± 54 msec). However, because a fast ventricular tachycardia (VT) zone was not used in MIRACLE ICD, it is likely that many episodes of potentially pace-terminable rapid monomorphic VT were detected as VF. Additionally, 44% of patients in the primary prevention group had nonischemic dilated cardiomyopathy (NDCMP) and no history of sustained VT or syncope, and, therefore, did not meet existing guidelines for ICD therapy during the time period the study was conducted. This patient population has a lower event rate