RIGHT LATISSIMUS-DORSI CARDIOMYOPLASTY IMPROVES LEFT-VENTRICULAR FUNCTION BY INCREASING PEAK SYSTOLIC ELASTANCE (E(MAX))

Background Dynamic cardiomyoplasty remains a promising but poorly unde rstood surgical modality for selected patients with dilated cardiomyop athy. Despite encouraging clinical results, objective evidence of enha nced ventricular function using traditional indexes (cardiac output, e jection fraction, and dP/dt) has been difficult to document after card iomyoplasty. Several investigators have suggested that cardiomyoplasty acts partly by unloading the left ventricle. These indexes all depend somewhat on loading conditions, however, and might not detect such an interaction. The time-varying elastance model provides an index of co ntractility, E(max), that is relatively insensitive to changes in load ing conditions. We applied this model to study the effect of right lat issimus dorsi cardiomyoplasty on left ventricular function in an acute canine model. Methods and Results Five dogs underwent acute cardiomyo plasty using untrained right latissimus dorsi muscle. Instrumentation included Millar pressure transducers in the left ventricle and aortic root, an electromagnetic flow probe around the ascending aorta, and a volume conductance catheter in the left ventricle. A cuffed nerve elec trode around the thoracodorsal nerve and a right ventricular sensing l ead were connected to a Medtronic Cardiomyostimulator (5 V, 30 Hz, 1:1 synchronization). Transient caval occlusions were performed with the stimulator both off and on to calculate E(max) and the slope of the en d-systolic pressure-volume relationship (E(es)). Turning the stimulato r on significantly increased peak systolic elastance (E(max)) and end- systolic elastance (E(es)) in all five dogs by an average of 56% and 7 8%, respectively (P<.05). End-diastolic volume and end-systolic volume decreased by 18% and 28%, respectively (P<.05). All other measured he modynamic parameters, including peak left ventricular pressure, mean a rterial pressure, cardiac output, stroke volume, stroke work, ejection fraction, preload-recruitable stroke work, and dP/dt, did not change significantly. Conclusions These results show that, in this acute cani ne model, right latissimus dorsi cardiomyoplasty significantly improve s left ventricular function while decreasing left ventricular volumes. The results are consistent with the theory that cardiomyoplasty incre ases contractility while unloading the ventricle by decreasing end-dia stolic volume. This increase in E(max) despite inconsistent changes in other indexes underlies the importance of using load-insensitive inde xes of ventricular function when studying cardiomyoplasty.