The wearable cardioverter defibrillator: Still without a compelling indication

Abstract

The wearable cardioverter defibrillator (WCD) has recently been introduced as a therapy to reduce mortality in patients presumed to be at increased risk for sudden arrhythmic death. Its efficacy appears to be implied by its proven ability to detect and defibrillate ventricular tachycardia/ventricular fibrillation (VT/VF). However, the currently available data on the WCD is non-randomized and comes from several reports of single center experiences, and reviews of post market release, often vendor supported, registry data. In the absence of randomized trials, the effect of the WCD on patient survival cannot be determined. The mere ability to shock terminate VT/VF by the WCD does not suffice to assume a reduction in mortality when used in large patient populations. These severe limitations have been acknowledged in the recent AHA science advisory report [1], providing a "tentative interim framework" resulting in mostly class II b recommendations ("treatment may be considered") with only level C support ("consensus opinion by experts only"). This contrast sharply with AHA class I recommendations ("treatment should be considered") with level A support ("multiple clinical randomized trials") for the implantable cardioverter defibrillator (ICD).The WCD is being heavily advertised to temporarily "protect" patients presumed at increased risk for arrhythmic death (primary prevention), in particular patients early after acute myocardial infarction (MI) or with newly diagnosed dilated cardiomyopathy. In these patient populations, several randomized trials with the implantable ICD [2-4] failed to show mortality reduction and these patients remain temporarily ineligible for device implantation for a period of 40 days (early after acute MI) or 90 days (newly diagnosed dilated cardiomyopathy). In practical terms, these time periods serve to allow for optimizing medical therapy, which often results in improvement of cardiac function with subsequent removal from ICD eligibility. The actual mortality risk, and in particular the risk of sudden arrhythmic death, and thus the utility of the WCD during these waiting periods is not well established.Clinical research has shown an increased risk of sudden death in patients early after acute MI. One of the largest trials, addressing this clinical issue, was the VALIANT trial [5], it randomized 14,609 patients after acute MI with reduced LV function and/or clinical heart failure to valsartan, captopril, or both. During 2.4 year follow up, 2,800 deaths were observed, of which 1067 were classified as either sudden death (N= 903) or resuscitated cardiac arrest (n= 104). The median time to event occurrence was 180 days, but 580 events occurred within the first 30 days (event rate 1.4%), suggesting a possible role for defibrillator therapy early after acute MI. However, two trials [2,3] in a total of 1,572 patients early after acute MI with reduced LV function and additional risk markers, randomized to medical therapy with or without ICD implantation, failed to show a reduction in overall morta...