Restratification at time of implantable cardioverter defibrillator replacement.

Based on the results of several large, randomized, clinical trials, implantable cardioverter defibrillators (ICDs) have become a ‘‘gold standard’’ therapy in prevention of sudden cardiac death. Under current guidelines, ICDs are implanted in patients who survived cardiac arrest or hemodynamically unstable ventricular tachycardia, as well as in primary prevention, mainly for those with ischemic or nonischemic cardiomyopathy with left ventricular ejection fraction (LVEF) 35%, New York Heart Association functional class II/III, optimal pharmacotherapy, good life expectancy, and no identifiable reversible causes of low LVEF. Current guidelines do not distinguish between patients implanted de novo and those undergoing elective battery replacement. No doubts exist about the need to replace ICD in secondary prevention patients; however, a debate continues on how to approach subjects implanted in primary prevention referred for elective replacement due to battery depletion. Despite decades of clinical experience, no consensus exists on how to stratify the risk of sudden cardiac death. The current approach, in which low LVEF is considered the only risk stratifier, is far from optimal. A substantial number of ICD recipients who are eligible for a device replacement have never developed arrhythmia requiring ICD therapy. As evidenced by randomized trials and ICD registries, only 20% to 30% of patients implanted for primary prevention receive appropriate ICD shocks. Therefore, at the time of generator replacement physicians have to face 2 problematic groups of patients: a) those who have never had appropriate therapy but still present low LVEF qualifying them for an ICD, and b) those who have never had ICD shocks and at the time of replacement present with improved LVEF falling beyond ICD indications criteria. Patients who have not received any antiarrhythmic therapy most probably constitute a group of subjects who were ‘‘too healthy’’ or ‘‘too sick’’ for ICD implantation. There is an ongoing debate on how to stratify the risk of sudden cardiac death and better identify patients with low LVEF who develop ICD-treatable arrhythmia. Even though a plethora of noninvasive risk markers such as electrocardiogram and imaging techniques, laboratory tests, and simple bedside tests has been investigated, no