Objectives: We sought to compare the short- and long-term clinical effects of atrial synchronous pre-excitation of one (univentricular) or both ventricles (biventricular), that provide cardiac resynchronization therapy (CRT).
Background: In patients with heart failure (HF) who have a ventricular conduction delay, CRT improves systolic hemodynamic function. The clinical benefit of CRT is still being investigated.
Methods: Forty-one patients were randomized to four weeks of first treatment with biventricular or univentricular stimulation, followed by four weeks without treatment, and then four weeks of a second treatment with the opposite stimulation. The best CRT stimulation was continued for nine months. Cardiac resynchronization therapy was optimized by hemodynamic testing at implantation. The primary end points were exercise capacity measures. Data were analyzed by two-way repeated-measures analysis of variance.
Results: The left ventricle was selected for univentricular pacing in 36 patients. The clinical effects of univentricular and biventricular CRT were not significantly different. The results of each method were pooled to assess sequential treatment effects. Oxygen uptake during bicycle exercise increased from 9.48 to 10.4 ml/kg/min at the anaerobic threshold (p = 0.03) and from 12.5 to 14.3 ml/kg/min at peak exercise (p < 0.001) with the first treatment, and from 10.0 to 10.7 ml/kg/min at the anaerobic threshold (p = 0.2) and from 13.4 to 15.2 ml/kg/min at peak exercise (p = 0.002) with the second treatment. The 6-min walk distance increased from 342 m at baseline to 386 m after the first treatment (p < 0.001) and to 416 m after the second treatment (p = 0.03). All improvements persisted after 12 months of therapy.
Conclusions: Cardiac resynchronization therapy produces a long-term improvement in the clinical symptoms of patients with HF who have a ventricular conduction delay. The differences between optimized biventricular and univentricular therapy appear to be small for short-term treatment.