COMBAT--conventional versus multisite pacing for bradyarrhythmia therapy: rationale of a prospective randomized multicenter study.

COMBAT is a prospective, multicenter, randomized, blinded clinical study, with crossover design. The main objective is the comparative evaluation of atrio-biventricular versus conventional atrioventricular stimulation (atrio and right ventricle) in patients with heart failure and bradycardia as the primary indication for pacemaker implantation. After successful atrio-biventricular system implantation, patients will be randomized into two groups: group A--atrioventricular conventional pacing and group B--atrio-biventricular pacing. Both groups will be programmed in DDD mode with AV delay optimized by echocardiogram. After 3 months, New York Heart Association functional class, ventricular arrhythmia density and complexity, echocardiography outcomes, 6-min hall walk distance, quality of life and peak oxygen consumption will be assessed in all patients. Then, all patients will crossover to the other pacing regimen, with an additional AV delay adjustment by echo. Patients will be followed up for another 3 months at the end of which all evaluations will be repeated. Patients will then crossover back to their original pacing regimen for a further 3 months. At the end of this 9-month period, patients will be reprogrammed according to their optimal pacing regime. In an extended follow-up, patient survival will be evaluated after 24 months of the optimal pacing therapy.