[Cardiac resynchronization therapy: when the pacing site really matters].

Cardiac resynchronization therapy has been one of the major qualitative advances made in the treatment of heart failure in recent decades, and it strongly underlines the relationship between heart mechanics, hemodynamic function, and electrophysiology. Since the 1980s a number of clinical and experimental studies have shown that abnormalities in intraventricular conduction, associated or not with delays in atrioventricular conduction, can adversely affect hemodynamic performance through the discoordination of cardiac contraction.1 Over the last 20 years, researchers (especially in Europe) have explored the extraordinarily simple yet original hypothesis that mechanical discoordination caused by delays in electrical conduction can be reverted by atrioventricular electrical stimulation. This should improve the hemodynamics of the failing heart in patients with refractory heart failure, left ventricular dysfunction, and intraventricular conduction abnormalities.2,3 The first clinical studies, which were initially designed to determine the mechanism of action of this technique, showed that in the latter subgroup of patients electrical stimulation of the left ventricle corrected intraventricular dyssynchrony, improved the values of acute hemodynamic variables, increased systolic efficiency, and optimized diastolic function without increasing the heart rate or the consumption of oxygen by the myocardium.4,5 Later, large scale clinical trials gradually showed that cardiac resynchronization therapy was safe, that a percutaneous approach was technically possible, that it improved patients’ functional status and quality of life, that it reduced the number of hospitalizations, and that it inversely remodeled the left ventricle–a powerful prognostic predictor of heart failure.6-8 The inverse remodeling achieved was found to be similar in its magnitude to that obtained with betaadrenergic blockers,8 and that it was associated with a Cardiac Resynchronization Therapy: When the Pacing Site Really Matters