Ann Thorac Surg 1996;62:1396
© 1996 The Society of Thoracic Surgeons
Invited Commentary
Invited Commentary
Guo-Wei He, MD, PhD
Department of Surgery University of Hong Kong, Grantham Hospital 125 Wong Chuk Hang Rd Aberdeen, Hong Kong
See also page 1392.
The high patency rate of the internal mammary artery (IMA) has greatly promoted its use as an arterial graft for coronary artery bypass grafting. The IMA is a living conduit and responsive to circulating vasoactive substances. It is a small artery; therefore, any depreciation in its diameter may lead to clinical problems and even affect its long-term patency. In recent years, the reactivity of the IMA is a topic that has gained considerable research interest and the findings from numerous studies on the topic, including those conducted by my colleagues and myself, have been published. Blood flow in a vessel depends on the pressure gradient, the diameter, and the hemodynamic characteristics of the blood (eg, viscosity). The direct action of a vasoconstrictor on a vessel is to reduce the diameter of the vessel and therefore to reduce the flow. However, other factors also play a role in determining the flow. Therefore, any findings from studies on a vasoconstrictor must be carefully applied in the clinical setting. In addition, the interaction between vasoactive substances is complex and the clinical situation is more complicated than that created in the laboratory setting. Therefore, the finding in the present study that the IMA in hypertensive patients is more reactive to 5-HT1 agonists may not have a direct bearing on the long-term patency of the IMA graft, as Yildiz and associates imply. There is no report of the patency rate of IMA grafts in hypertensive patients being less than that in normotensive patients. In fact, they are essentially the same. Therefore, the results from this study should not be simply interpreted to mean that there is a contraindication to the use of the IMA in hypertensive patients.
A few years ago, I proposed a "law of the IMA"-that the contractility of the IMA at the distal section increases toward the end (reference 6 in Yildiz and associates' article) and the bifurcation has an even higher contractility (reference 5 Yildiz and associates' article). This was demonstrated in our experiments. I therefore suggested that the best way to avoid the IMA spasm is not to use the distal section and the bifurcation for grafting. This may also improve the long-term patency, because it has been reported that the patency rate is low for the IMA bifurcation when it is used for grafting ([3] in Yildiz and associates' article). In my own practice and on the basis of communications with other surgeons, this concept is well accepted and IMA spasm is not a problem if the distal end is trimmed off, as I originally proposed. In the study performed by Yildiz and associates, the response of the IMA distal section tended to be higher than that in the proximal segment, although the difference did not reach statistical significance. The study did not use a normalization procedure, which could provide information about the diameter of the IMA at a certain pressure, and therefore Yildiz and associates could not normalize the contractile force to 5-HT1 agonists by the diameter. If they had done this, the study findings would have been enhanced by more significant statistics. Nevertheless, the findings provide some evidence that supports my previous observations.
Sumatriptan is a 5-HT1 agonist that is prescribed for the treatment of migraine. The observations in this study may provide some basis for the cautious use of this drug in these patients. However, if the distal end is not used for these patients, it may be unnecessary to worry about the use of such drugs.
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Hypertension Increases the Contractions to Sumatriptan in the Human Internal Mammary Artery
- OGuzhan Yildiz, Sertaç Çiçek, Ilknur Ay, Ufuk Demirkiliç, and Meral Tuncer
Ann. Thorac. Surg. 1996 62: 1392-1395.
[Abstract]
[Full Text]
