[Refractory heart failure. Multisite stimulation].

The pathophysiological background of cardiac resynchronization therapy is represented by the intraventricular conduction delay such as left bundle branch block, present in about one third of patients with dilated cardiomyopathy. Intraventricular conduction block, with or without atrioventricular delay, adversely influences ventricular function due to unsynchronized contraction and is associated with a poor prognosis. Contractile dyssynchrony and abnormal atrioventricular delay can be corrected by non-conventional stimulation modalities such as left ventricular pacing or biventricular pacing associated with preexcitation to restore the physiological atrioventricular timing. Over the last decade several studies have reported the short- or long-term favorable effects of resynchronization therapy on the left ventricular function and remodeling, the quality of life, the functional capacity, the adrenergic activity, and the reduced rehospitalization rate. The most significant results have been reported in patients with a QRS duration > or = 150 ms, while the InSync Italian Registry has shown improvement even in patients with a QRS duration < 150 ms as well as in patients with atrial fibrillation. On the basis of such data it may be argued that the activation sequence of the different walls of the left ventricle is likely more important than the QRS duration. Inclusion criteria commonly used in the published or ongoing trials are: moderate to severe congestive heart failure (NYHA functional class III-IV) on optimized pharmacological treatment; left ventricular ejection fraction < or = 35%; left ventricular diastolic diameter > 60 mm; end-diastolic mitral regurgitation; no need of conventional pacing. While with regard to the surrogate endpoints the results of published trials are very encouraging, we do not yet know whether resynchronization therapy prolongs the life expectancy of patients with heart failure. Studies able to provide important answers to these problems are near completion. In the meanwhile, in agreement with the guidelines of the European Society of Cardiology, it seems prudent to employ such a therapy only in case of patients satisfying the above-mentioned criteria.