IMPROVED EFFICIENCY OF ENERGY-TRANSFER TO EXTERNAL WORK IN CHRONIC CARDIOMYOPLASTY BASED ON THE PRESSURE-VOLUME RELATIONSHIP

Objective: Cardiomyoplasty is a surgical procedure to support the fail ing heart, in which a burst-stimulated latissimus dorsi muscle flag is transposed and wrapped around the ventricles. The effect of dynamic c ardiac compression, implemented as cardiomyoplasty, on left ventricula r performance remains controversial; the mechanism by which clinical s ymptoms are improved remains unclear. To investigate the mechanism for improvement of patients' symptoms, it is important to evaluate the ef fects of cardiomyoplasty on left ventricular energetics and on left ve ntricular systolic and diastolic function. We therefore evaluated the efficiency of energy transfer from the native pressure-volume area to external work under conditions of 1:3 skeletal muscle burst pacing in an animal model with chronic heart failure. Methods: In seven Merino-W ether sheep, cardiomyoplasty was performed after stable heart failure was induced by staged coronary embolizations (ejection fraction < 35%) . Hemodynamic assessment including the assessment of the pressure-volu me relationship was performed 8 weeks after cardiomyoplasty when the l atissimus dorsi muscle was fully trained. Instantaneous left ventricul ar pressure and volume were measured with a catheter-tipped manometer and a conductance catheter during steady-state conditions and after a transient inferior vena cava occlusion, The effect of dynamic cardiac compression on left ventricular systolic function was assessed by comp aring pre-assisted and assisted beats and on diastolic function by com paring assisted and post-assisted beats. Result: The slope of the end- systolic pressure-volume relationship decreased by 30.5% +/- 27.8% (p = 0.02) during assisted beats. However, left ventricular pump performa nce improved by increasing stroke volume and external work by 35.9% +/ - 36.0% (p = 0.03) and 9.7% +/- 6.8% (p = 0.03), respectively, resulti ng in a reduction of the volume intercept. As a result, the end-systol ic pressure-volume relationship shifted to the left. The efficiency of energy transfer from the native pressure-volume area to the overall e xternal work improved by 7.6% +/- 8.2% (p = 0.03), Cardiomyoplasty did not affect the time constant of left ventricular isovolumic pressure decline or the maximal rate of pressure decay, which suggested that ca rdiomyoplasty did not affect left ventricular relaxation. Conclusions: Dynamic cardiac compression in the form of cardiomyoplasty enhanced l eft ventricular pump performance without interrupting left ventricular filling. The ratio of energy transfer from the native pressure-volume area to the overall external work suggests a myocardial oxygen-sparin g effect of cardiomyoplasty.