Optimizing muscle-to-cardiac timing for aortomyoplasty.

A new surgical approach to support failing hearts is known as aortomyoplasty-a technique in which the latissimus dorsi muscle is wrapped around the aorta and stimulated during cardiac diastole to provide chronic diastolic counterpulsation. We hypothesized that the timing of muscle contraction within the cardiac cycle effects the amount of diastolic augmentation during counterpulsation. In dogs (n = 9, 20-25 kg), the effect of muscle-to-cardiac timing on hemodynamic outcome of aortomyoplasty was measured. Muscle stimulation was initiated at the dicrotic notch and stimulus durations were systematically increased. Mean diastolic aortic pressure was maximized when stimulation terminated at the ensuing R-wave. Peak left-ventricular pressure was minimized when muscle stimulation terminated before the ensuing R-wave. The endocardial-viability ratio (a ratio of aortic diastolic pressure augmentation to left-ventricular pressure reduction) was maximized when stimulus terminated at the ensuing R-wave. Muscle-to-cardiac timing influences the effectiveness of counterpulsation during aortomyoplasty.