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Ann Thorac Surg 1997;64:1746
© 1997 The Society of Thoracic Surgeons

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Invited Commentary

Invited Commentary

Department of Cardiac Surgery, University of Melbourne, Austin Campus, Studley Rd, Heidelberg, Victoria 3084, Australia

See also page 1742.

Inotropes commonly have different central and peripheral actions. In patients with a low output syndrome, the question arises whether to select a drug because of its central positive inotropic action or because of its peripheral (which includes the internal mammary artery) vasodilative properties. The peripheral action of commonly used inotropes varies widely; for example, some have - or ß-mimetic activity and others produce vasodilatation through phosphodiesterase III inhibition. Prevention of graft spasm and promotion of vasodilatation through drugs acting either directly on the smooth muscle cells or indirectly on the endothelium are believed to be important in promoting graft flow and possibly in preventing early graft occlusion. Surgical technique, inappropriate pharmacologic preparation, or graft ischemia may cause changes in a graft, making it vulnerable to the subsequent development of intimal hyperplasia and atherosclerosis.

Coronary artery bypass graft flow, however, is dependent on the mean blood pressure and the resistance of the myocardial arteriolar bed, as well as on the vasomotor status of the graft. The mean systolic blood pressure has been shown to be a major determinant of internal mammary artery flow [1]. In selecting an inotrope for a patient with an internal mammary artery graft, it is tempting to focus on its peripheral actions. However, its central effects may be more important. This article by Cracowski and colleagues shows that there is no significant difference in the vasodilative properties of dobutamine, enoximone, and epinephrine in the doses used. Therefore, the choice of inotropes should depend logically on their ability to produce the desired cardiac output and mean blood pressure, rather than on their effects on the internal mammary artery graft.

Reference

1. Beavis RE, Mullany CJ, Cronin KD, et al. An experimental in vivo study of the canine internal mammary artery and its response to vasoactive drugs. J Thorac Cardiovasc Surg 1988;95:1059–66.

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