Effectiveness of implantable cardioverter defibrillators and cardiac resynchronization therapy in heart failure.

Randomized trials and observational data have consistently demonstrated the benefit of ICDs for primary prevention of SCD in patients with HF and LVSD or secondary prevention in patients with a history of prior ventricular arrhythmias or aborted SCD, most of whom have HF. Secondary and post hoc analyses of trial data, as well as observational data, generally suggest that ICD therapy is effective in most selected subpopulations, such as the elderly and patients with NYHA class IV HF symptoms, but some studies suggest that ICDs may not be as effective in women and those with severe comorbidities, such as ESRD. Although there is limited evidence for an incremental benefit achieved with dual-chamber compared with single-chamber ICDs, the former devices are placed almost twice as frequently in the United States. Finally, observational data have recently shown that ICD procedural outcomes are improved when the device is placed by an electrophysiologist and at a high-volume hospital. More recently, clinical trials have demonstrated that cardiac resynchronization therapy improves quality of life and lowers rates of HF hospitalization in patients with symptomatic HF, LVSD, and a prolonged QRS complex already receiving optimal medical management; recent trial results have also suggested a mortality benefit with CRT in this population. In addition, recent trial data suggest that CRT reduces nonfatal events among mildly symptomatic patients (NYHA class I-II); however, the cost-effectiveness of CRT in this population remains unclear. As with ICDs, secondary and post hoc analyses of trial data as well as observational data suggest that CRT remains effective in most selected subpopulations, including stable NYHA class IV patients, the very elderly, and women. Recent observational work has suggested that CRT may not benefit patients with an RBBB QRS morphology to the same extent as those with an LBBB pattern, although because more conclusive studies are currently lacking, the guidelines do not tailor the recommendations based on QRS morphology. In summary, ICDs, CRT-P, and CRT-D represent important and effective treatment modalities for select patients with HF. Additional investigation is required to better determine which patient populations most benefit from these cardiac devices and which device, implanting physician, and hospital characteristics optimize outcomes with these cardiac devices.