Left ventricular ejection fraction for sudden death risk stratification and guiding implantable cardioverter-defibrillators implantation

Current guidelines for use of implantable cardioverter-defibrillators (ICDs) for primary prevention of sudden death in patients with coronary disease and nonischemic dilated cardiomyopathy are based primarily on ejection fraction (EF) <30%-35%. The origin of this is based on EF as the common variable in several randomized clinical trials evaluating the ability of ICDs to reduce mortality. However, although low EF identifies one patient population at relatively increased risk for sudden death, there are a number of limitations to use of EF as the primary indication for ICD. Patients with low EF are not uniform with regard to other prognostic markers, and not all are at high risk for sudden death. Conversely, although patients with EF >35% as a group are at lower risk for sudden death, these patients are not uniform with regard to other prognostic variables. A variety of tests, including measures of reduced repolarization reserve and measures of altered sympathetic/parasympathetic balance, have identified patients with EF >35% at relatively high risk for sudden death. One explanation for this "disconnect" is that there is no evidence of any direct mechanistic link between low EF and mechanisms responsible for ventricular tachyarrhythmias.