Effects of dilation with a balloon catheter on the endothelium of the internal thoracic artery.

Controlled dilation of the internal thoracic artery with a balloon catheter has been reported to effectively treat intraoperative arterial spasm. It has been shown in laboratory animals that dilation of the internal thoracic artery at prescribed shear force levels will not cause intimal damage. Using scanning electron and light microscopy, we have examined the effects of calibrated balloon dilation on the endothelium of the human internal thoracic artery. In 10 patients with bilateral internal thoracic artery grafting, the artery was dilated with a Fogarty IMAG balloon catheter (Baxter Healthcare Corporation, Edwards Division, Santa Ana, Calif.) that was withdrawn at tensions of 20 or 30 gm. Arterial segments and nondilated control specimens were prepared for scanning electron microscopy. The intimal surface of each internal thoracic artery was evaluated by assigning a score (from 0 to 3) to 10 examined scanning electron microscopy fields; subsequently the arterial tissue was viewed by light microscopy with paraffin-embedded sections stained for elastic tissue. Arteries were obtained from three additional patients so that the microscopic appearance of the arteries could be observed after rough manipulation or removal of the balloon without shearing. The results of this study are as follows: (1) By scanning electron microscopy, dilated internal thoracic arteries yielded consistently higher scores than the control arteries, reflecting severe, tension-dependent alterations of the endothelium, which included marked desquamation of endothelial cells, with extensive areas of complete denudation and pronounced attachment of platelets to these areas; (2) endothelial injury occurred by inflation alone, without shearing by the inflated balloon; (3) by light microscopy, the internal thoracic arteries showed (a) fenestrations of the internal elastic lamina with occasional transmigration of smooth muscle cells through these gaps and (b) foci of intimal thickening without overt atherosclerotic lesions. We conclude that the endothelium of human internal thoracic arteries is highly vulnerable to balloon dilation, which can severely injure the intimal surface. For this reason we prefer not to include this procedure in our protocol for preparing the internal thoracic artery.