Hemodynamic effects of different pacing ratios in chronic dynamic double cardiomyoplasty

Background. Dynamic cardiomyoplasty is being used clinically worldwide, and evaluated by a clinical trial (phase III) in the United States. Some centers stimulate the skeletal muscle wrap with every heart beat (1:1 [muscle:heart]), whereas others use every other heart beat (1:2). Recent concern over the possible deleterious effects of too-frequent stimulation of the muscles motivated the attempt to evaluate, in a canine model of chronic, double cardiomyoplasty, the effects of two different pacing ratios on several hemodynamic parameters of interest. Methods. Double cardiomyoplasty was performed using both latissimus dorsi muscles in 11 dogs. Fatigue resistance was achieved using the clinical transformation protocol. At a final experiment, acute cardiac failure was induced by administration of propranolol. Hemodynamic measurements of eight physiologic variables were averaged over complete pacing cycles, including the nonpaced beat at a 1:2 pacing ratio. Results. The net effects of latissimus dorsi muscle stimulation at each of two pacing ratios were compared using nonparametric statistics. With the exception of left ventricular pressure (p = 0.0262) and its first derivative, dP/dt (p = 0.0099), there was no significant difference between hemodynamic performance at the two pacing ratios. Conclusions. In this canine model, pacing every other beat produces hemodynamic results that are statistically similar to pacing every beat. Less frequent stimulation of the latissimus dorsi muscle may preserve its function and improve clinical results without compromising hemodynamic benefit.