ANALYSIS OF CARDIAC ASSISTANCE BY LATISSIMUS-DORSI CARDIOMYOPLASTY WITH A TIME-VARYING ELASTANCE MODEL

Objective: The clinical use of skeletal muscle cardiomyoplasty is limi ted because of its inadequate haemodynamic benefits. To facilitate exp erimental and clinical efforts to improve the efficacy of this techniq ue, a mathematical model was proposed and its validity was tested in a cute experiments. Methods: The model was based on the assumption that the skeletal muscle wrapped around the heart behaves as a time varying elastance that is connected in series with another time varying elast ance representing the native heart. From this model two predictions we re made: (1) Skeletal muscle augments the contractility of the heart b y increasing the slope (Ees) of the end systolic pressure-volume relat ion; (2) time varying elastance of the skeletal muscle chamber (E(s)(t )) can be estimated from that of the assisted heart. These predictions were examined in experiments. In nine anaesthetised, open chest dogs, preconditioned latissimus dorsi muscle was transposed to wrap the hea rt. Left ventricular pressure (catheter tipped micromanometer), and vo lume (conductance catheter) were measured while reducing the preload b y vena caval occlusion to evaluate Ees with 1:2 (stimulation:heart bea t ratio) stimulation of the skeletal muscle. Results: With the stimula tion of latissimus muscle, the end systolic pressure-volume relation w as linear and Ees increased from 8.6(SEM 2.4) to 11.9(SEM 3.4) mm Hg.m l-1. Estimated E(s)(t) reflected the stimulation pattern and could acc ount for the mechanism of the cardiac assistance. Conclusions: Skeleta l muscle cardiomyoplasty improved the haemodynamic variable (Ees) as p redicted by.a mathematical model.