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Ann Thorac Surg 1996;62:1294
© 1996 The Society of Thoracic Surgeons
DR NOEL L. MILLS (New Orleans, LA): I thank Doctor Carrel and co-authors for the opportunity to review their manuscript. They have compared retrospectively and in a nonrandomized fashion two groups of patients with one ITA versus two ITA grafts. They are to be applauded for their effort in pursuing the question: "Are two IMA grafts better than one?" However, I do not think this study offers any final answer, and here is why.
The first reason is the time frame-When do SVGs fail? At 8 years, which is the maximum follow-up time in this study, the SVGs are just beginning to enter the high-attrition zone. Only after 10 years or more would one expect the ITAs to show the effects of their resistance to atherosclerosis compared with an atherosclerosis-prone SVG.
The second concerns the anatomy of the coronary arteries. Ninety-five percent and more of the LADs are a single sizable vessel. Not so with the RCA system, and I use the word systemas opposed toartery.There is a whole spectrum of RCA distal anatomy, from a single, small posterior descending branch, to a sizable posterior descending branch, to an array of vessels supplying the inferior left ventricle. To be meaningful, such a study must be designed to take this variable anatomy into account.
The third reason is coronary artery pathology. We all know there is a definite propensity for atherosclerosis to occur at the origin of the posterior descending. From the manuscript it appears all right ITA grafts were anastomosed to the RCA. The posterior descending is never mentioned. What about patients whose RCA systems had a stenosis of the posterior descending and several sizable inferior ventricular branches?
The fourth reason is competition for flow. A 50% stenosis in the conduit portion of a 2.5-mm RCA will compete fiercely with a right ITA that is 2.5 mm at the distal anastomosis. Flow is 1/resistance, and resistance is directly proportional to graft length. We have learned also that the longer RGEA grafts must be to a very tightly stenosed or occluded vessel. A right ITA to a 50% to 70% stenosed RCA system is asking for trouble from competition for flow when one plugs in the formula for graft flows.
In summary, Dr Carrel and associates' data show a significantly poorer reintervention-free survival in the unilateral ITA versus bilateral ITA group, that is, 84% versus 95%. Likewise, recurrence of angina was less likely in the bilateral group (16%) than in the unilateral ITA group (21%)-not yet significant, but I propose that it would be significant with time as more SVGs fail.
Doctor Carrel and associates note in the manuscript that other authors have found a lower patency rate for right ITAs than for left ITAs. I would love to see the patients in this study with anatomically matched SVGs versus right ITAs to sizable posterior descending arteries followed up for beyond 15 to 17 years, as reported by Galbut and Fiore and quoted in this manuscript. A clear, statistically sound benefit was found for bilateral ITA grafts. Bilateral ITA use must be tailored to anatomic and pathologic principles.
DR CARREL: Thank you very much, Dr Mills, for your pertinent comments. I think we were well aware at the time we designed this study that the time frame would not give definitive results concerning the real benefits of bilateral ITA grafting, exactly because SVGs just begin to fail at 8 years postoperatively. Interestingly, it seems that the bypass grafts to the RCA system do not exhibit a behavior identical to that of conduits to the LAD, for instance. In 1992, the Cleveland Clinic Foundation showed some results from late angiography of the right ITA on the RCA system. Independent of whether the right ITA had been grafted in situ or as a free graft, the patency rate was significantly inferior to that for the left ITA to the left descending branch. The patency rate varied between 69% and 76% for the right ITA and was more than 90% for the left ITA.
Regarding the anatomy of the RCA system, all patients in this series had a single anastomosis to the RCA, placed proximally to the bifurcation of this vessel. In more than 80% of the patients, the RCA had been described as the dominant vessel.
Concerning the incidence of distal lesions in the RCA system, I am pretty sure that all surgeons on our team have examined visually and by palpation the bifurcation of the RCA to exclude the presence of any significant lesion that might not have appeared clearly on the coronary angiogram.
Finally, it has not been our policy to use a right ITA to bypass a large and only moderately stenosed RCA. In our opinion, a moderate stenosis should be considered as a relative contraindication to revascularization with an ITA graft. Because we have been interested in the "internal thoracic artery malperfusion syndrome," we assess the free flow only when it seems clear that a low-flow situation exists. Otherwise, visual assessment provides enough information for experienced surgeons.
Related Article
Ann. Thorac. Surg. 1996 62: 1289-1294.
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