CARDIOMYOPLASTY - PROBABLE MECHANISM OF EFFECTIVENESS USING THE PRESSURE-VOLUME RELATIONSHIP

The mechanism of effectiveness of cardiomyoplasty was evaluated in the setting of chronic left ventricular dysfunction in terms of the press ure-volume relationship. The distal branches of the left coronary arte ry were ligated in 12 sheep. Seven sheep died and the 5 survivors unde rwent cardiomyoplasty using a left latissimus dorsi graft 10 to 12 wee ks later. These muscle grafts were then electrically conditioned for 2 months. The systemic pressure and cardiac output were not different b etween the postinfarction and postcardiomyoplasty period with the pace maker off or on. However, the pressure-volume loops were altered by ca rdiomyoplasty in all 5 animals. Emax, which is an index of ventricular contractility, increased after cardiomyoplasty from 2.66 +/- 0.92 to 4.59 +/- 1.73 mm Hg/mL (mean +/- the standard deviation; p < 0.05), bu t did not change between the pacemaker off and on situations. The pres sure-volume area, which strongly correlates with myocardial oxygen con sumption, decreased after cardiomyoplasty (1,932 +/- 615 mm Hg ml), co mpared with before cardiomyoplasty (3,776 +/- 1,201 mm Hg mL) (p < 0.0 5), but did not change between pacemaker off and on. The probable mech anism responsible for the effectiveness of cardiomyoplasty is an ''act ive'' support or constraint of the damaged myocardium by the latissimu s dorsi and the prevention of further ventricular dilation. This sugge sts that left ventricular systolic function can be augmented by cardio myoplasty, but that it is a secondary mechanism of action.