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

Background. Optimal clinical stimulation for skeletal muscle cardiac assist systems (such as dynamic cardiomyoplasty) is not clearly defined. The pres sure-generating capacity of canine skeletal muscle ventricles (SMVs) at a v ariety 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 e lectrical conditioning. Pressure generation and time to develop peak pressu re were determined using a distensible mandrel. Results. Higher preloads resulted in increased pressure generation; conditi oned SMVs generated significantly less pressure than unconditioned SMVs. In creasing stimulation frequency from 20 to 50 Hz increased pressure-generati ng capacity; increases beyond 50 Hz did not result in further increases. Ti me to 90% peak pressure was least at 10 HZ and 65 Hz. Conclusions. Higher stimulation frequencies and preloads result in a more q uickly contracting muscle, which generates more pressure. Midrange stimulat ion 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. (C) 2001 by The Society of Thoracic Surg eons.