Haemodynamic considerations in the design of a skeletal muscle ventricle.

Skeletal muscle ventricles (SMVs) configured to operate as diastolic counterpulsators show promise as cardiac assist devices. In four pigs, SMVs were connected to the aorta by a single-limbed conduit and activated during every third cardiac diastole. During the assisted beats, mean diastolic aortic pressure increased by 30.3 +/- 2.2%, peak diastolic aortic pressure increased by 38.5 +/- 2.7%, the endocardial viability ratio increased by 42.3 +/- 3.4%, and mean left anterior descending coronary artery flow increased by 61.6 +/- 4.5%. Although there are major advantages to making the connection to the aorta by a single-limb conduit, the lack of separation between inlet and outlet means that such devices must be designed carefully to avoid thrombogenesis under chronic conditions. Design rules were developed for this configuration, based on earlier in vitro studies. They addressed the problem of stasis by promoting the development of a propagating vortex that travels the length of the ventricle and ensured proper exchange of blood with the circulation by limiting the volume of the connecting conduit. An SMV compatible with these rules was connected in a pig. At elective termination 1 week later, activation of the SMV increased peak diastolic pressure by 20.1% and reduced left-ventricular stroke work in the post-assisted beat by 10.1%. The SMV was free from thrombus.

Skeletal muscle ventricles: full versus half aortic ligation.

BACKGROUND: Skeletal muscle ventricles have been shown to provide effective aortic diastolic counterpulsation in an experimental model. Construction has included full ligation of the thoracic aorta. The authors sought to determine if these muscle pumps could function effectively without fully ligating the aorta. METHODS: Skeletal muscle ventricles were constructed in two groups of dogs. Group 1 had their aortas fully ligated (n = 10) while group 2 had their aortas narrowed by 50% (n = 10). The animals were followed for 10 weeks. RESULTS: There was no significant difference in femoral diastolic augmentation at implant or at 10 weeks (19.1% +/- 9.9% in group 1 [full ligation] versus 16.3% +/- 10.2% in group 2 [half ligation] p = 0.502). Survival to 10 weeks was significantly better in group 1 (full ligation). Nine of 10 animals in this group survived versus 4 of 10 in group 2 (p = 0.019). Two animals survived in the half ligation group with effective augmentation and without thrombus formation. CONCLUSION: Both models produce effective diastolic counterpulsation. Survival was decreased in this model using half ligation, and survival without complication was observed in 2 of 10 animals. Currently the overall results are better with the full aortic ligation model. However, design modifications will probably result in an effective model of diastolic counterpulsation without full aortic ligation.