Effects of Simultaneous and Optimized Sequential Cardiac Resynchronization Therapy on Myocardial Oxidative Metabolism and Efficiency

Introduction: Cardiac resynchronization therapy (CRT) can improve left ventricular (LV) hemodynamics and function. Recent data suggest the energy cost of such improvement is favorable. The effects of sequential CRT on myocardial oxidative metabolism (MVO2) and efficiency have not been previously assessed. Methods and Results: Eight patients with NYHA class III heart failure were studied 196 ± 180 days after CRT implant. Dynamic [11C]acetate positron emission tomography (PET) and echocardiography were performed after 1 hour of: 1) AAI pacing, 2) simultaneous CRT, and 3) sequential CRT. MVO2 was calculated using the monoexponential clearance rate of [11C]acetate (kmono). Myocardial efficiency was expressed in terms of the work metabolic index (WMI). P values represent overall significance from repeated measures analysis. Global LV and right ventricular (RV) MVO2 were not significantly different between pacing modes, but the septal/lateral MVO2 ratio differed significantly with the change in pacing mode (AAI pacing = 0.696 ± 0.094 min−1, simultaneous CRT = 0.975 ± 0.143 min−1, and sequential CRT = 0.938 ± 0.189 min−1; overall P = 0.001). Stroke volume index (SVI) (AAI pacing = 26.7 ± 10.4 mL/m2, simultaneous CRT = 30.6 ± 11.2 mL/m2, sequential CRT = 33.5 ± 12.2 mL/m2; overall P < 0.001) and WMI (AAI pacing = 3.29 ± 1.34 mmHg*mL/m2*106, simultaneous CRT = 4.29 ± 1.72 mmHg*mL/m2*106, sequential CRT = 4.79 ± 1.92 mmHg*mL/m2*106; overall P = 0.002) also differed between pacing modes. Compared with simultaneous CRT, additional changes in septal/lateral MVO2, SVI, and WMI with sequential CRT were not statistically significant on post hoc analysis. Conclusion: In this small selected population, CRT increases LV SVI without increasing MVO2, resulting in improved myocardial efficiency. Additional improvements in LV work, oxidative metabolism, and efficiency from simultaneous to sequential CRT were not significant.