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Ann Thorac Surg 2002;73:1696
© 2002 The Society of Thoracic Surgeons
a Alliance of Cardiac, Thoracic and Vascular Surgeons, 2501 Citico Avenue, Chattanooga, TN 37404, USA
b Division of Cardiothoracic Surgery, Medical University of South Carolina, Strom Thurmond Research Building, 114 Doughty St, Suite 625, Charleston, SC 29403, USA
To the Editor
We appreciate the comments by Drs Rosenfeldt and Esmore regarding the use of calcium-channel antagonists for the prevention of radial artery spasm, which can occur when this conduit is used in coronary artery bypass grafting procedures. At present, there is little quantitative clinical data clearly supporting the use of a specific calcium-channel antagonist as a preventive strategy for postoperative radial artery spasm. Nevertheless, the most widely used calcium-channel antagonist for this purpose today is diltiazem hydrochloride. When delivered systemically, diltiazem can cause substantial alterations in myocardial conduction and contractility, which may not be advantageous in the postoperative setting. The large number of patients in whom the radial artery was used as a conduit for coronary artery bypass grafting by the authors from Australia further emphasizes the importance of considering factors that may potentially precipitate spasm of this vessel in the postoperative period.
Accordingly, our study [1] examined the concentration-dependent effects of norepinephrine or endothelin on radial artery vasoconstriction. Both of these neurohormones induced a sustained vasoconstrictive effect on radial artery segments. We next examined the relative effects of the calcium-channel antagonists diltiazem, nifedipine, and amlodipine besylate to interrupt the neurohormonally mediated radial artery vasoconstriction. Whereas all of these calcium-channel antagonists were effective, amlodipine attenuated radial artery vasoconstriction to the greatest degree. Amlodipine is of a unique structural class and demonstrates a high degree of vascular selectivity and a prolonged half-life. Because of its vascular selectivity, amlodipine has been safely used in the setting of compromised ventricular function.
It is of interest that Drs Rosenfeldt and Esmore use diltiazem in the radial artery preparation solution rather than in a solution for systemic administration. We concur that the use of selective receptor antagonists in the preparation of the radial artery in vitro may be of clinical utility. For example, pretreatment with an endothelin receptor antagonist may be useful in preventing early postoperative radial artery vasospasm. However, future controlled clinical trials employing different treatment strategies in which the relative incidence of radial artery vasospasm is quantified through the use of perfusion studies, angiography, or both will be necessary. We have demonstrated that neurohormonal factors contribute to radial artery vasospasm, but it must be recognized that flow characteristics within the radial artery can also influence this postoperative phenomenon [2]. Thus, future pretreatment strategies will need to consider the multifactorial causes of postoperative radial artery vasospasm.
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