MECHANISMS OF CARDIOMYOPLASTY - COMPARATIVE EFFECTS OF ADYNAMIC VERSUS DYNAMIC CARDIOMYOPLASTY

Background. The apparent paradox seen in patients who have undergone d ynamic cardiomyoplasty and shown substantial clinical and functional i mprovements with only modest hemodynamic changes may be due to inappro priate end points chosen for study, a result of incomplete understandi ng of mechanisms involved. The purpose of this study was to compare th e relative role of the passive ''girdling effect'' and the dynamic ''s ystolic squeezing effect'' of the wrapped muscle in cardiomyoplasty. M ethods. The control group of 6 dogs underwent 4 weeks of rapid pacing (250 beats/min) to induce severe heart failure followed by 8 weeks of observation without rapid pacing. The trajectory of recovery in hemody namics and cardiac dimensions was followed with echocardiography and S wan-Ganz catheters. In the ''adynamic'' cardiomyoplasty group (n = 4), the left latissimus dorsi muscle was wrapped around the ventricles an d allowed to stabilize and mature for 4 weeks. This was followed by ra pid pacing and recovery as in the control group. In the ''dynamic'' ca rdiomyoplasty group (n = 3), the same protocol for the adynamic group was followed except that a synchronizable cardiomyostimulator was atta ched to the thoracodorsal nerve of the muscle wrap. This allowed the l atter to be transformed during the rapid-pacing phase and permitted dy namic squeezing of the muscle wrap to be generated by burst stimulatio n synchronized with cardiac contraction in a 1:2 ratio. Results. Basel ine data were comparable in all groups prior to rapid pacing. After 4 weeks of rapid pacing, the left ventricular ejection fraction was high er in the adynamic (27.0% +/- 3.9%; p < 0.05) and dynamic (33.3% +/- 2 .3%; p < 0.02) cardiomyoplasty groups compared with controls (18.8% +/ - 8.3%). Similarly, ventricular dilatation in both systole and diastol e was less in the adynamic (51.8 +/- 8.7 mt, [p < 0.002] and 38.2 +/- 7.2 mt [p < 0.001], respectively) and dynamic (62.0 +/- 7.2 [p < 0.02] and 41.3 +/- 3.5 mt [p < 0.005], respectively) cardiomyoplasty groups compared with controls. In the dynamic group, on and off studies were carried out after cessation of rapid pacing while the heart was still in severe failure, and they demonstrated a systolic squeezing effect in stimulated beats. Only this group recovered fully to baseline after 8 weeks. Conclusions. By reducing myocardial stress, both the passive girdling effect and the dynamic systolic squeezing effect have comple mentary roles in the mechanisms of dynamic cardiomyoplasty. (C) 1998 b y The Society of Thoracic Surgeons.