Canine Skeletal Muscle Ventricles: Functional Assessment Using the Pressure-Volume Plane

Abstract

In five dogs, skeletal muscle ventricles (SMVs) were constructed from the latissimus dorsi muscle, and placed within the thoracic cavity. After a 3-week delay period, SMVs were electrically preconditioned with 2-Hz continuous stimulation for 6 weeks. At a second procedure, SMVs were connected to a mock-circulation system, and performance was evaluated according to pressure-volume relationships at three different SMV contraction rates (33, 54, and 97 per min) and three stimulation protocols (25, 43, and 85 Hz) under varying loading conditions. Under appropriate conditions of afterload, the end-diastolic pressure-volume relation of SMVs was comparable with that of the cardiac ventricles, although SMVs were less compliant. At higher burst stimulation frequencies, SMV compliance was increased. Compliance was not affected by varying the rate of SMV contraction. End-systolic elastance, a reflection of contractility, appeared to be constant for each SMV, in contrast to cardiac ventricles, and was not influenced by changes in burst stimulation frequency or contraction rate. In this study, SMVs were capable of a level of stroke work 180% of that of the native right ventricle (RV) at rest (0.397 +/- 0.047 x 10(6) ergs) and 37% of that of the left ventricle (LV) at rest (0.298 +/- 0.61 x 10(6) ergs), at 33 contractions per minute (CPM), 25-Hz burst frequency, and physiological preload, but this level could not be sustained at higher contraction rates. Nevertheless, power output (SMV stroke work x contraction rate) was maximal at 97 CPM. These findings demonstrate important function differences between pumping chambers constructed from conditioned skeletal muscle, and those composed of cardiac muscle, which must be considered when using skeletal muscle ventricles for cardiac support or replacement.