ICD therapy: 'the sickest benefit the most...': what about the less sick?

Implantable cardioverter defibrillators (ICDs) have been proven to be highly efficacious in protecting very high-risk cardiac patients from sudden cardiac death and hence enhancing their overall survival. Furthermore, several post hoc sub-study analyses seem to indicate that ICD benefit is predominant in the patients with the highest risk, particularly with depressed left ventricular function. This, in turn, has led some clinicians to question the benefit of ICD therapy in relatively healthy, i.e. 'less sick', patients. As these interpretations come entirely from the sub-group analyses of the completed ICD prospective studies, it is important to examine more profoundly the study design, length of follow-up, and outcomes of these studies. Such analysis identifies three primary reasons why the conclusion that 'less sick' patients benefit less from ICD therapy may be erroneous: (i) the relatively short follow-up time of the studies (ended as soon as ICD therapy benefit became manifest); (ii) high 'crossover rate' from control to ICD therapy; and (iii) predominance of study endpoints (deaths) in the 'sickest' patients. The results of several studies, including the most recent and largest ICD study-SCD-Heft-and sub-group analyses of 'healthier' patient cohorts in several studies, support the benefit of ICDs in this group of patients, provided the follow-up time is sufficiently long.