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Ann Thorac Surg 1999;67:1344
© 1999 The Society of Thoracic Surgeons
a Department of Human Anatomy and Cell Biology, University of Liverpool, Liverpool L69 3GE, United Kingdom
Invited commentary
In cardiomyoplasty (CMP), the latissimus dorsi muscle (LDM) of one side (usually the left) is mobilized as a pedicled graft, wrapped around the ventricles, conditioned to render it fatigue-resistant, and activated in synchrony with the cardiac cycle. Originally it was anticipated that the muscular wrap would assist the patient’s heart by actively squeezing the ventricles during each systole. The current consensus is that the benefits derive mainly from a girdling action of the muscle, which reduces wall stress and prevents, or even reverses, the trend to further enlargement. Furuta and coworkers, in an attempt to achieve the original objective of beat-to-beat systolic assistance, have tried a configuration that involves the LDMs of both sides.
In the normal procedure, the tendinous insertion of the LDM is transferred from the humerus to the ribs. Radiographic examination has confirmed that contraction of the free (unwrapped) portion of the LDM tends to pull the heart toward this attachment. Adding a wrap from the contralateral LDM reduces this tendency by providing a balancing force. The two muscles produce better coverage, particularly of a pathologically enlarged heart, and appearances suggest that the oppositely directed forces would be more effective in compressing the ventricles (but see subsequent discussion). Although this idea is not new in itself, the authors have adopted a novel symmetrical configuration in which the two muscles are crossed and attached behind the heart. They show, in acute experiments during propanolol-induced failure, that such a configuration is much more effective hemodynamically than a single left CMP, although more rigorous proof would require the order of the single and double CMPs to be randomized.
The acute results are impressive but are they likely to persist in the longer term? Certainly not to this extent. The muscles must be conditioned to provide the necessary fatigue resistance, and this will result in some loss of power. More importantly, the benefits of the authors’ configuration are realized only if the muscular wraps can slide freely over each other and over the epicardial surface. As adhesions develop between all these surfaces, such movement will be resisted by shear forces, dissipating the energy that can be transferred from the free portions of the LDMs to the heart. In simple terms, it will be as if the two LDMs are anchored at the front of the heart. Contraction within the portions of the muscles in contact with the heart will continue to have an effect, but the situation will be closer to that of a conventional CMP. So does double CMP have a future as a clinical procedure? The LDM is less straplike in human patients than in the dog. Bilateral wraps would be bulky in the relatively shallow thoracic cavity of humans and might have some passive hemodynamic effects after closure of the chest. Use of the second muscle would add substantially to the duration of the procedure and the subsequent discomfort of the patient. On the other hand, there may be a net advantage, particularly for patients with biventricular failure. We await the results of the authors’ long-term experiments with interest.
Related Article
Ann. Thorac. Surg. 1999 67: 1339-1344.
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