- AIMS: Biventricular (BiV) pacing and left univentricular (LUV) pacing can each produce clinical benefits in heart failure. The impact of modern refinements in pacing optimization on the relative benefits of these two modes is unknown. We aimed to compare these two modes in patients with heart failure, using Echo-based optimization of each pacing mode. METHODS AND RESULTS: Paired data were collected on 18 patients (age 72 +/- 8 years; 16 male) with refractory heart failure symptoms, sinus rhythm, and LBBB with QRS duration>120 ms. Patients were randomized to an initial 8 weeks of either BiV or LUV pacing, followed by 8 weeks of the other mode, in a blinded cross-over design. Echocardiography was used to optimize atrioventricular delay for both modes and right ventricular-left ventricular offset for BiV mode. Peak oxygen consumption (baseline 13.6 +/- 2.7; BiV 15.8 +/- 3.0; LUV 15.2 +/- 3.1 mL/kg/min), 6 min walk distance (baseline 258 +/- 47; BiV 290 +/- 63; LUV 287 +/- 69 m), and scores on SF36 health questionnaire (baseline 41.5 +/- 16.8; BiV 58.6 +/- 19.6; LUV 51.8 +/- 21.3) did not differ between BiV and LUV modes. New York Heart Association class was significantly better in BiV than in LUV mode (P < 0.01). CONCLUSION: In this pilot study, we found no differences in major clinical outcome measures between the two modes of resynchronization.