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Ann Thorac Surg 2001;72:1343
© 2001 The Society of Thoracic Surgeons

Invited commentary

George J. Magovern, Jr, MDa, Dennis R. Trumble, MSa

a Department of Cardiothoracic Surgery, Allegheny General Hospital, 320 East North Ave, Pittsburgh, PA 15212, USA

e-mail: gmagover{at}wpahs.org

This study offers several interesting insights regarding the application of skeletal muscle as an auxiliary means to pump blood. Dr Letsou and his colleagues confirm once again that stimulation parameters are of critical importance to the proper function of any muscle-powered system and that changes in contractile dynamics due to conditioning must be taken into consideration when attempting to coordinate muscle contractions with the heart. An important case in point is their finding that conditioned skeletal muscle ventricles can, in some instances, require over 0.3 seconds to reach peak force generation. Unless this delay is taken into account, trained muscles could inadvertently be made to contract at precisely the wrong time in the cardiac cycle, thereby doing more harm than good.

While proper timing of the burst stimulus is certainly a key factor to consider here, it is also important to note than there are other plausible reasons for the lack of improved ejection fraction seen in cardiomyoplasty (CMP) trials to date. Poor muscle perfusion leading to fibrosis and subsequent loss of muscle viability is one likely culprit. Another is the fact that wrapped skeletal muscle is simply not an efficient means of transfering contractile energy to the bloodstream—as evidenced by the low pressure generation (55 mm Hg) maintained by conditioned skeletal muscle venticles in this study. It is, in fact, quite possible that disappointing clinical CMP results have more to do with ischemic effects of muscle mobilization and poor muscle mechanics than suboptimal stimulation settings. All three elements however, are likely culpable to some degree and measures should be taken to mitigate these factors.

It is for these reasons that we continue to pursue efforts to harvest energy from in situ latissimus dorsi muscle. The advantages of using this powerful muscle in its natural anatomic position are twofold. First, its intercostal blood supply can be left intact, thereby avoiding the ischemic insult endemic to muscle-wrap procedures. Second, the natural mechanical efficiency of the muscle is maintained, greatly increasing overall energy transfer capacity. The down-side is that a mechanical prosthesis is needed to collect and transmit this energy, yet, we believe this approach offers the best chance to overcome power supply problems that have plagued implantable blood pump technology from its inception. Skeletal muscles are marvelously efficient, adaptable engines with tremendous potential to effect long-term cardiac support—how best to tap this endogenous energy source however, remains an important lesson to be learned.


Related Article

Physiologic characteristics of canine skeletal muscle: implications for timing skeletal muscle cardiac assist devices
George V. Letsou, James F. Hogan, Charles C. Miller, III, John A. Elefteriades, David Francischelli, John C. Baldwin, and Hazim J. Safi
Ann. Thorac. Surg. 2001 72: 1336-1342. [Abstract] [Full Text] [PDF]




This Article
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Right arrow Articles by Trumble, D. R.
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