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Ann Thorac Surg 2001;72:1336-1342
© 2001 The Society of Thoracic Surgeons

Original article: cardiovascular

Physiologic characteristics of canine skeletal muscle: implications for timing skeletal muscle cardiac assist devices

George V. Letsou, MDa,b,c,d, James F. Hogan, BSEEa,b,c,d, Charles C. Miller, III, PhDa,b,c,d, John A. Elefteriades, MDa,b,c,d, David Francischelli, MSa,b,c,d, John C. Baldwin, MDa,b,c,d, Hazim J. Safi, MDa,b,c,d

a Department of Cardiothoracic and Vascular Surgery, University of Texas Medical School-Houston, Houston, Texas, USA
b Yale Medical School, New Haven, Connecticut, USA
c Dartmouth Medical School, Dartmouth, New Hampshire, USA
d Medtronic, Inc, Minneapolis, Minnesota, USA

Accepted for publication June 11, 2001.

Address reprints requests to Dr Letsou, University of Texas Medical School-Houston, 6410 Fannin, Suite 450, Houston, TX 77030
e-mail: george.v.letsou{at}mail.uth.tmc.edu

Background. Optimal clinical stimulation for skeletal muscle cardiac assist systems (such as dynamic cardiomyoplasty) is not clearly defined. The pressure-generating capacity of canine skeletal muscle ventricles (SMVs) at a variety of preloads and stimulation frequencies was examined as was time for SMVs to develop peak pressure.

Methods. SMVs were analyzed just after construction and after 3 months of electrical conditioning. Pressure generation and time to develop peak pressure were determined using a distensible mandrel.

Results. Higher preloads resulted in increased pressure generation; conditioned SMVs generated significantly less pressure than unconditioned SMVs. Increasing stimulation frequency from 20 to 50 Hz increased pressure-generating capacity; increases beyond 50 Hz did not result in further increases. Time to 90% peak pressure was least at 10 HZ and 65 Hz.

Conclusions. Higher stimulation frequencies and preloads result in a more quickly contracting muscle, which generates more pressure. Midrange stimulation frequencies of 30 Hz provide optimal muscle strength and minimize time to develop peak pressure. Initiation of contraction should begin before the time maximal pressure is desired.






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Copyright © 2001 by The Society of Thoracic Surgeons.