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Ann Thorac Surg 2003;76:977
© 2003 The Society of Thoracic Surgeons

Correspondence

Dynamic cardiomyoplasty reduces myocardial oxygen consumption

Yoshio Misawa, MDa, Katsuo Fuse, MDa

a Division of Cardiovascular Surgery, Jichi Medical School, 3311-1 Yakushiji, Minami-kawachi, Tochigi 329-0498, Japan

e-mail: tcvmisa{at}jichi.ac.jp

To the Editor:

Kawaguchi and associates [1] reported an interesting issue concerning dynamic cardiomyoplasty. In their heart failure model, cardiomyoplasty increased stroke volume and ejection fraction of the left ventricle, although it had no effect on end-systolic pressure, pressure–volume area, or external work of the left ventricle. Oxygen consumption was derived directly from the left main coronary artery blood flow and the coronary sinus blood flow in their sheep model of dynamic cardiomyoplasty. They showed a reduction in myocardial oxygen consumption and concluded that their findings provided a rationale for reverse remodeling of a failing heart using direct mechanical compression. These results have many implications regarding the mechanisms of dynamic cardiomyoplasty. Blood flow to an ischemic heart from wrapped latissimus dorsi muscle grafts was recognized in a patient of ours [2]. However, in their nonischemic models, blood flow from the graft to the myocardium would have been extremely limited. Therefore, their data must reveal the real myocardial oxygen consumption.

We [3] hypothesized that in cardiomyoplasty, after a latissimus dorsi muscle graft has been wrapped around the heart, the static girdling effect preventing left ventricular dilatation and the myocardial-sparing effect reducing left ventricular wall stress improve impaired hemodynamic conditions. In a model of adynamic cardiomyoplasty where dilation of the left ventricle paced by rapid stimulation of 250 beats per minute was delayed, we [4] achieved a hemodynamic effect. In a clinical study, we [2] also found that the hemodynamic effects after dynamic cardiomyoplasty may depend on the quality and quantity of the latissimus dorsi muscle grafts. The postmortem examinations of 5 of our patients indicated that preservation of latissimus dorsi muscle graft integrity may be important for the success of dynamic cardiomyoplasty. For the sparing effect, the muscle graft must play the role of a mass mimicking myocardium. The latissimus dorsi graft wrapping the left ventricle can be considered induced neo-myocardium, although the blood flow to the neo-myocardium is supplied by the thoracodorsal artery. According to Laplace’s law, the thicker the wall of the left ventricle, the lower the wall stress on the left ventricle. As wall stress is lowered, myocardial oxygen demand is also lowered.

We believe that the data presented by Kawaguchi and associates [1] support our hypothesis of a myocardial-sparing effect rather than an effect of direct mechanical compression after dynamic cardiomyoplasty. The reduction in myocardial oxygen consumption results from the reduced wall stress on the left ventricle.

References

  1. Kawaguchi O., Huang Y.F., Yuasa T., Shirota K., Carrington R.A.J., Hunyor S.N. Cardiomyoplasty reduces myocardial oxygen consumption: implications for direct mechanical compression. Ann Thorac Surg 2002;74:1092-1097.[Abstract/Free Full Text]
  2. Misawa Y., Mott B.D., Lough J.O., Chiu R.C.J. Pathologic findings of latissimus dorsi muscle graft in dynamic cardiomyoplasty: clinical implications. J Heart Lung Transplant 1997;16:585-595.[Medline]
  3. Misawa Y., Chiu R.C.J., Kamisawa O., Hasegawa T., Fuse K. Dynamic cardiomyoplasty in 1995. Jpn J Artif Organs 1996;25:749-752.
  4. Mott B.D., Oh J.H., Misawa Y., et al. Mechanisms of cardiomyoplasty: comparative effects of adynamic versus dynamic cardiomyoplasty. Ann Thorac Surg 1998;65:1039-1045.[Abstract/Free Full Text]




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