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Ann Thorac Surg 1997;64:657-658
© 1997 The Society of Thoracic Surgeons
DR HARTZELL V. SCHAFF (Rochester, MN): I congratulate Dr Sundt and his colleagues on their very good results in managing a difficult group of patients. Many of you may not know that Dr Sundt was raised in Rochester, Minnesota, where his father was Head of Neurosurgery at Mayo Clinic and a world expert in cerebrovascular disease. We take an almost paternal pride in his presentation and professional achievements.
There are really two important points to this study. The first is the outcome of patients who have aortic valve replacement after coronary artery bypass grafting, and the second is how these results might influence our management of patients with mild or moderate aortic stenosis undergoing coronary revascularization. These data from Washington University suggest that the risk of reoperation for aortic valve replacement is no higher than that of primary operation for aortic valve replacement and coronary artery bypass, but this is not consistent with results of other larger studies, nor is it intuitive.
Two other large published studies, one from our institution and the other from the Texas Heart Institute, suggest that the operative mortality of patients undergoing aortic valve replacement after coronary artery bypass is higher than that for a primary operation. These two studies include patients operated on earlier than those in the present review, and this leads to the first question. Were the patients included in this study all of the patients who had late aortic valve replacement at Barnes-Jewish Hospital, and if not, would inclusion of patients before 1985 have altered your results and conclusions?
There are several reasons why we believe that patients having aortic valve replacement after coronary bypass would be expected to have an operative mortality higher than that of a primary procedure. First, age is increased, especially when compared with the age of patients having isolated coronary artery bypass, not a group of patients having simultaneous operation. Second, there are inherent difficulties with management of these patients because of the frequent presence of atherosclerosis in the vein grafts, advanced native-vessel disease, and inclusion of patients who are graft dependent. In addition, in our experience, patients who have late aortic valve replacement often have senescent aortic stenosis and an increased risk of aortic atherosclerosis.
When we see the improved results Dr Sundt presented, we must look for differences in patient selection, improved techniques, or both. Were there patients in your series with aortic valve stenosis later after coronary artery bypass who were refused operation? Asked another way, do you have any information on patients with this clinical presentation who were not referred for operation by your cardiologists?
I hope you will comment on the management of patent grafts at the time of reoperation, especially internal mammary artery grafts. Was there any consistent approach to myocardial protection that might have resulted in the good outcomes you achieved?
Finally, I have a point about inferences from the study. This is, perhaps, the most important issue from this presentation. You have concluded that if operative mortality for late aortic valve replacement is the same as for primary operation, we should have a rather high threshold for valve replacement at the time of the primary operation. However, to establish this, one needs to analyze outcome of patients with mild aortic stenosis having coronary artery bypass and ask what is the incremental risk of adding aortic valve replacement. In our estimate, the risk of adding aortic valve replacement to primary elective coronary artery bypass is low, certainly less than 6%. If that is the experience at Barnes-Jewish Hospital, would you change your conclusions?
I applaud your results, but differ with your conclusions.
DR JOHN J. COLLINS JR (Boston, MA): I think my colleagues and I may have been among the earliest to recommend in an absolute fashion that patients with any degree of aortic stenosis, that is, any gradient across the aortic valve, should have simultaneous aortic valve replacement with coronary bypass. I will clarify the reason that we made such a recommendation. It relates to the difference in the natural history of operated coronary artery disease and unoperated "mild" aortic stenosis. Aortic stenosis of any degree, if it is of a degenerative nature, progresses to critical obstruction about 4 to 5 years after coronary bypass, on average. Patients then return for valve replacement with well-functioning coronary grafts in many instances. This need of early reoperation can be avoided by aortic valve replacement at the time of coronary artery bypass grafting. Regardless of whether the risk of reoperation is low, it is a considerable inconvenience to require two operations when one would have been sufficient.
DR SAFUH ATTAR (Baltimore, MD): I congratulate Dr Sundt and his colleagues for an excellent presentation. My first question pertains to the use of blood in the primary and reoperative procedures. Did you compare blood loss in the primary operations versus that in the reoperative procedures? Second, what was the rate of reoperation? Third, were any of the deaths related to bleeding?
DR SUNDT: I very much appreciate Dr Schaff's kind remarks. We agree that the result reported here was not intuitive, and all of us were surprised by it.
You asked several specific questions. First, would inclusion of patients seen before 1985 have changed the result? I do not know the answer to that question, as our database extends back only to 1985. As the preponderant cause of death was myocardial failure, however, it may not be fair to compare operations performed during different eras, if you will, of myocardial management. Although inclusion of patients seen earlier might have altered the result, I am not certain that it would be relevant to current practice.
Second, although all of the patients operated on during the study interval were included in the study, I do not know the number of patients who were either refused surgical intervention after surgical consultation or were not offered such intervention at the discretion of the clinical cardiologist involved. This is one of the inherent limitations of such a retrospective study, and I appreciate your highlighting this point.
Third, as regards patent grafts and myocardial protection, our general approach is to replace grafts more than 7 to 10 years old and grafts that have angiographically significant atherosclerosis. Patent internal mammary arteries are routinely dissected out and controlled with a bulldog clamp. Currently myocardial protection is most commonly accomplished with cold blood cardioplegia, although this was not a uniform practice over the entire study interval. Similarly, retrograde cardioplegia is employed increasingly commonly now, but was not early in the study.
You point out that inferences regarding the optimal management of mild aortic stenosis at the time of primary coronary bypass grafting are problematic given this study population. I agree that this is not the ideal control group; optimally we should compare patients with mild aortic stenosis having bypass grafting who do and do not undergo valve replacement to determine the increased risk of valve replacement itself. This is a limitation shared by most of the other studies, and it is a critical one. You asked if the addition of valve replacement were to add a mortality rate of less than 6%, would we change our conclusions. This is, of course, entirely contingent on the percentage of patients expected to progress to hemodynamically significant aortic stenosis. If the operative mortality rate were to double for primary coronary bypass from 3% to 6% and if less than half of the patients would progress to hemodynamically significant aortic stenosis, routine valve replacement would impose an inappropriate burden of risk on the group as a whole.
Doctor Collins, thank you very much for your comments. We know that your group early recognized the importance of this very difficult clinical question. Your point, I think, also touches on Dr Schaff's final question regarding the appropriate study group. Again, a critical issue is the expected rate of progression of the aortic stenosis in this population of patients and the percentage of patients who would be expected to undergo such progression. This can really be answered only with a prospective, randomized study.
Doctor Attar, data concerning blood loss and blood product use were not compared between the primary and repeat surgical groups. All of the deaths in the reoperative group were secondary to myocardial failure, and none were related to bleeding. The rate of reoperation was actually lower in the reoperative group than in the primary group, although this did not approach significance.
Related Article
Ann. Thorac. Surg. 1997 64: 651-657.
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