Critical appraisal of the use of cardiac resynchronization therapy beyond current guidelines.

Cardiac resynchronization therapy (CRT) is an effective treatment for patients with drug-refractory, chronic heart failure. Multiple single-center and multicenter studies have shown significant reductions in left ventricular (LV) volumes and an increase in LV systolic function. More importantly, CRT reduces mortality and morbidity during long-term follow-up. Current guidelines consider CRT as a Class I indication for heart failure patients in New York Heart Association (NYHA) functional class III to IV with depressed LV ejection fraction <or=35% and a wide QRS complex (>or=120 ms). However, the benefits of this therapy could possibly be extended to selected subgroups of patients who do not fulfill these criteria. These subgroups include patients with mildly symptomatic heart failure and patients with a narrow QRS complex (<120 ms). Results from recent multicenter controlled clinical trials including heart failure patients in NYHA functional class I to II or with a narrow QRS complex are equivocal. Although expanding CRT to patients with a narrow QRS complex seems currently not likely, the benefits of CRT in mildly symptomatic patients are more evident. Perhaps attenuation of disease progression will prove to be a successful new treatment strategy in heart failure patients in the future. In addition, multimodality cardiac imaging will allow optimizing responder rate in patients undergoing CRT according to current guidelines.