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Ann Thorac Surg 2001;71:1736-1737
© 2001 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Wayne State University School of Medicine, Detroit, Michigan, USA
Address reprint requests to Dr
Stephenson, Cardiothoracic Surgery, Suite 2102, Harper Professional
Building, 3990 John R St, Detroit, MI 48201
As Originally Published in 1993: Skeletal Muscle Ventricles: Left Ventricular Apex to Aorta Configuration
Huiping Lu, MD, Robert Fietsam, Jr, MD, Robert L. Hammond, MD, Hidehiro Nakajima, MD, Frank W. Mocek, MD, Gregory A. Thomas, MD, Renato Ruggiero, MD, Hisako Nakajima, MD, Michael Colson, MS, and Larry W. Stephenson, MD
Division of Cardiothoracic Surgery, Department of Surgery, Wayne State University, Detroit, Michigan, and Medtronics, Inc, Minneapolis, Minnesota
Abstract—Skeletal muscle ventricles (SMVs) were constructed from the latissimus dorsi muscle in 6 dogs. After 3 weeks of vascular delay followed by 6 weeks of 2-Hz continuous electrical conditioning, a valved conduit was placed between the left ventricular apex and the SMV and a second valved conduit, between the SMV and the aorta. The SMV was stimulated to contract during diastole at a 1:2 ratio with the heart. The SMV pumped 47% of the systemic blood flow initially (0.73 ± 0.23 versus 1.54 ± 0.42 L/min) and 40% after 3 hours. Skeletal muscle ventricle stimulation resulted in a 58% increase in mean diastolic pressure initially (52 ± 9 to 82 ± 11 mm Hg; p < 0.05) and a 73% increase (45 ± 7 to 78 ± 8 mm Hg) after 3 hours of continuous pumping. This was associated with a 68% increase in the endocardial viability ratio initially and a 63% increase at 3 hours. The systolic tension-time index decreased by 26% initially and 25% at 3 hours. This study indicates that the SMV configuration of left ventricular apex to aorta may be particularly suitable for left ventricular assist.
Updated in 2001
Our laboratory has focused on using muscle in the form of an autogenous blood pump, called a skeletal muscle ventricle (SMV), for heart assist.
SMV aorta-aorta counterpulsator
Our most reproducible long-term SMV model for chronic left heart assist is connected to the aorta with a bifurcated conduit and the aorta ligated between the two limbs of the conduit [1]. Initially continued heart assistance was demonstrated for over 2 years. However, SMV rupture and thromboembolism remained significant complications. In an effort to minimize thromboembolism, the inner surface of the SMV was successfully seeded with endothelial cells and this layer was retained while the SMV pumped in circulation [2]. But, using a pericardium lining for the blood-contacting surface essentially eliminated the incidence of both rupture and thrombosis; as a result, we have had SMVs pump blood in circulation as aortic counterpulsators for over 4 years [3]. Although our best long-term success has occurred with the aorta-aorta configuration, it has not been the most hemodynamically efficient model.
SMV left ventricular (LV) apex-to-aorta assist
Previous acute studies by others used unconditioned muscle in a LV-to-aorta configuration so that the blood was routed from the LV apex to the muscle pump and then to the aorta [4, 5]. Computer and electrical modeling have demonstrated the superiority of the LV-to-aorta configuration for heart assist [6, 7]. Based on these studies, Lu and associates performed acute studies with conditioned skeletal muscle ventricles connected from the apex of the LV to the SMV with a valved conduit and a second valved conduit connected from the SMV to the descending aorta [8]. Over a 3-hour period, sustained augmentation of diastolic pressure occurred, associated with significant LV unloading. These SMVs pumped between 40% and 47% of systemic blood flow; this is in comparison with 20% to 27% of systemic flow pumped by SMVs in either an aorta-aorta or left atrial-aortic configuration.
Recently, we reported a series of SMVs where 6 of 10 animals survived between 72 and 249 days [9]. Thromboembolism occurred in 4 of the 10 dogs. In this study, passive flow through the SMV circuit was 26% of total blood flow. The SMV pumped 40% of total flow at 33 Hz and a 1:2 ratio, and 43% at 50 Hz and a 1:2 ratio with the heart. LV stroke work was decreased 56% at 33 Hz and 64% at 50 Hz. The SMV was able to generate 51% of the stroke work of the native, unassisted LV.
One of the 10 dogs was still alive after 228 days in circulation at the time of that report. Since then, the dog was electively sacrificed after 1 year in circulation. A flow-pressure trace obtained at 1 year in circulation is shown in Figure 1. The degree of assist in regards to diastolic augmentation, LV unloading, as well as the amount of blood pumped by the SMV are comparable with the initial values.
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With the aorta-aortic counterpulsator, more than 90% should function effectively beyond 1 year as a prerequisite to clinical studies. This model has been tested in an acute heart failure setting using propranolol over several hours. This model is now being tested with chronic heart failure.
The SMV LV apex-to-aorta model is the most effective model from a hemodynamic standpoint that we have tested. Although several animals survived with this model for between 6 months and 1 year, the morbidity and mortality in this model must be reduced, and then testing during chronic heart failure is necessary.
References
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