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Ann Thorac Surg 1997;64:35-36
© 1997 The Society of Thoracic Surgeons
DR CONSTANTINE MAVROUDIS (Chicago, IL): This was an excellent presentation of a very controversial topic in a relatively small group of patients. The issue is clearly important because of the significant problems that occur with anticoagulation in children. Also important is the risk of cerebral thromboembolism over time in patients who are not treated with Coumadin, which of course fuels the controversy. The difficulty is in planning a prospective clinical study to determine the comparative efficacy of antiplatelet therapy versus Coumadin therapy. Because such a study has not been and is unlikely to be performed, studies such as this one take on added importance. In those patients who underwent reoperation and replacement of an existing prosthetic valve, did you find surrounding tissue ingrowth, either above or below the valve, that might have interfered with valve function and contributed to clot formation? Under these circumstances, both antiplatelet therapy and Coumadin therapy would be ineffective, which could confound any results. Also, how do you manage patients with prosthetic heart valves who are taking aspirin and dipyridamole and have a stroke? Do you convert them to Coumadin therapy? Thank you, I enjoyed this paper.
DR BRADLEY: Thank you very much for your comments. The problem of pannus formation is obviously a significant one. However, it is difficult to obtain accurate information on its incidence in the absence of reoperation. We do not have any specific information on pannus formation in the patients who are in this series. The one comment that I can make is in reference to the three episodes of valve thrombosis that we observed. All three of these episodes were treated successfully with lytic therapy, which indicates that at least a significant portion of the thrombosis was due to thrombosis per se and not to pannus formation in these particular patients.
The 2 patients who had thromboembolic events while taking aspirin and dipyridamole crossed over to Coumadin.
As Dr Mavroudis has mentioned, the significant limitation of this study is the small number of patients, particularly in the aspirin and dipyridamole group. This was compensated for somewhat by the fact that we have a reasonably large total number of patient-years of follow-up, even in the aspirin and dipyridamole group. One attempt to address this limitation was the literature analysis, which pooled information from a larger number of patients with more patient-years of follow-up. In the absence of a prospective, randomized study, which would be very difficult to put together, I think that ongoing follow-up of the patients in all these series is the best that we are going to be able to do.
DR JOHN H. CALHOON (San Antonio, TX): Doctor Bradley, that was a lovely paper. I would like to echo some of Dr Mavroudis' comments, and add one that you may have answered. Did you have any frozen valves that required reoperation because of the kind of pannus that he described? It sounds like you were able to get them to all free up with thrombolytics.
I also have a couple of other points. This looked like an older group of patients for kids. Do you use, with such good results, the Ross procedure in the smaller kids, or will you start using it?
Anecdotally, having operated on a couple of patients who were taking ticlopidine, we find that they do not clot very well after operation. It seems to be a great antiplatelet agent. Do you have any experience or knowledge of that being used in lieu of or in addition to aspirin and dipyridamole?
This was really a beautifully presented paper.
DR BRADLEY: Thank you very much. We did not have any incidence of valves that were frozen by pannus alone, so again I cannot comment on that particular problem. We also have no experience with the use of ticlopidine.
It is the preference of our group, and particularly so in recent years, to use valve repair rather than replacement in the mitral position. In the aortic position, we prefer valve repair. When that is not possible, we use either the pulmonary autograft or, in select circumstances, aortic homografts for valve replacement. Nonetheless, there are situations in which none of these possibilities can be carried out successfully. I think there still will remain, therefore, a small number of patients who require valve replacement with mechanical valves, and this study was aimed specifically at deciding how to manage these patients.
DR ROSS M. UNGERLEIDER (Durham, NC): I just have a quick question, and I think Dr Calhoon alluded to this. With the greater emphasis now on using pulmonary autografts or homografts in the aortic position, I suspect that in the future we will see mechanical valves being used more frequently in the mitral position in children. I wonder whether you looked at your data, and the outcomes in particular, and separated the outcomes into adverse outcomes related to the position of the valve. Was there a difference in the outcomes related to the aortic versus mitral position? And, in looking at the data that way, can you make recommendations regarding the anticoagulation regimens depending on the position of the valve?
Thank you again for your excellent paper.
DR BRADLEY: Thank you very much for your comments. We did specifically break the data down into two groups according to whether the aortic or the mitral valve had been replaced. Not only were there no detectable differences in either thromboembolism or bleeding complications, but the rates were essentially identical in the two groups, and we therefore pooled the two groups in all these analyses.
DR CHRISTOPHER J. KNOTT-CRAIG (Oklahoma City, OK): It seems to me that your conclusions are controversial. If the complications are that much lower in the aspirin and dypiridamole group, how strongly do you feel about converting all those patients taking Coumadin to therapy with aspirin and dipyridamole? That is my first question.
My second question concerns patients with valve thrombosis. How do you decide how long to allow the cardiologists to attempt to resolve the clots with lytic agents, and what dosages are required for that?
And finally, when we use Coumadin in patients, the Coumadin dosage varies with the size of the patient, and we use the international normalized ratio to standardize this. Are you dosing all the patients receiving aspirin and dipyridamole with a uniform dosage, or do you titrate the dosage against their size?
DR BRADLEY: Thank you for your questions. The conclusions from our data are that the thromboembolism rates are very similar between the two groups, and that the bleeding rates appear to be somewhat less with aspirin and dipyridamole than with Coumadin. The data available in the literature indicate that rates of both these complication are indistinguishable between the two treatment regimens. I would not conclude from this information that aspirin and dipyridamole are better than Coumadin, but merely that the two regimens cannot be distinguished on the basis of current information.
Lytic therapy was used in 3 patients with valve thromboses. All these patients had reasonable hemodynamics on presentation and, therefore, were candidates for lytic therapy rather than reoperation. The courses of lytic therapy lasted 24 to 48 hours. Indications for declaring lytic therapy a failure were hemodynamic deterioration or failure of normal valve function (assessed clinically and by echocardiography) to return after 48 hours of therapy.
In regard to the dosage of the medications, in the early years of the study, Coumadin usually was dosed to maintain prothrombin times about 1.5 times normal. More recently, it has been dosed to maintain international normalized ratios around 2.5 to 3. Aspirin and dipyridamole dosing has been fairly standardized, and we use about 5 mg•kg-1•d of aspirin and about 6 mg•kg-1•d of dipyridamole in three divided doses.
DR KIT V. AROM (Minneapolis, MN): I have one question. It seems to me that in the Coumadin group, the incidences of hemorrhage and thrombosis are higher in the adult population. Can you explain why?
DR BRADLEY: The lower thromboembolism rates observed in children compared with adults may be due to hemodynamic differences. Compared with adults, children have higher heart rates and lower rates of atrial arrhythmias and depressed ventricular function. These differences may make children less susceptible to thromboembolism than adults. Lower bleeding rates may relate to the adequacy of anticoagulation, an issue on which we do not have completely accurate information.
DR AROM: What year did you first use the international normalized ratio instead of the prothrombin time level? Was it recently or in the middle of your study?
DR BRADLEY: The international normalized ratio became adopted fairly routinely about 4 or 5 years ago. Some of our patients are followed up by cardiologists in outlying centers, and I cannot exactly answer when they adopted the international normalized ratio.
DR AROM: The prothrombin time ratio is not as reliable as the international normalized ratio.
Related Article
Ann. Thorac. Surg. 1997 64: 30-34.
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