CRT-D use in heart failure: too little or too much?

Cardiac resynchronization therapy (CRT) is a new therapy for patients with symptomatic heart failure (HF) resulting from systolic dysfunction. Numerous clinical investigations have demonstrated that in selected patients with ventricular dyssynchrony, CRT improved left ventricular function, functional status, and left ventricular ejection fraction (LVEF). Randomized clinical trials showed that in patients already on optimal medical therapy, CRT reduced morbidity and all-cause mortality. On the basis of the inclusion criteria and the results of these CRT trials, CRT is currently recommended, both in Europe and in the USA, for patients with NYHA functional Class III or IV heart failure, a LVEF 35%, and a QRS duration 160 ms (or 120 ms with other evidence of ventricular dyssynchrony) who are receiving chronic optimal medical therapy. However, several issues still remain unresolved: in particular, the benefit of CRT therapy has not been established in patients with mild HF (NYHA Class I or II), atrial fibrillation, minor conduction abnormality, or pacemaker dependence. In addition, 20-30% of patients do not respond to CRT. Considering that CRT is an invasive and costly procedure, identification of patients most likely to benefit from CRT is clearly a research priority.