| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||
Ann Thorac Surg 1997;64:1262
© 1997 The Society of Thoracic Surgeons
DR STEVEN R. GUNDRY (Loma Linda, CA): It is a pleasure to discuss this paper, and I thank the authors for giving me their manuscript in a timely fashion for review.
As you have just heard, Carrier and associates have presented a select group of extremely well patients, with 90% of these patients having ejection fractions of 0.40 or better. Indeed, only 50% of the patients had unstable angina, whereas 50% of the patients were actually operated on for stable angina. Thirty percent to 40% of the patients presented in this series had single- or double-vessel disease rather than triple-vessel disease. Cross-clamp times were remarkably short in these groups, about 46 minutes in each group.
With regard to cross-clamp times in ischemia, as was reported to this group 2 years ago, our experiments in dead hearts suffering 45 minutes of ischemia and then undergoing transplantation could find no difference in need for inotropic support or for enzyme release even when these hearts were completely warmly ischemic for 45 minutes. Thus, this cross-clamp period is an extremely short period in which to look for a difference between groups.
Interestingly enough, each group received the identical amounts of cold blood cardioplegia, but I noticed that the retrograde group was delivered retrograde cardioplegia with an autoinflating balloon catheter. First of all, as Menasché and Laks have both pointed out, autoinflating balloon catheters lose at least 30% of a delivered dose backward through the catheter without delivery to the myocardium. So what Carrier and associates have shown is that two thirds of a retrograde dose, compared with a full antegrade dose, gives equal protection. One might argue in this day of cost savings that we need one-third less of retrograde cardioplegia than antegrade cardioplegia to obtain the same results.
Second, Carrier and associates in their manuscript report that they have to hold the cannula in place and seal the coronary sinus during delivery of retrograde cardioplegia. Did the time spent to do this, which was several minutes for each dose, significantly lengthen their relative cross-clamp time in the retrograde group? And if a catheter with a manually inflated balloon, where this was not necessary, was used, would the cross-clamp times in the retrograde group go down accordingly?
Third, Carrier and associates show no difference in enzyme release and correlate this with no difference in myocardial ischemia. And yet from their data there were twice as many myocardial infarctions in the antegrade group, there were twice as many patients with high CK levels in the antegrade group than in the retrograde group, and all balloon pumps in this extremely well group of patients were used in the antegrade group and none were used in the retrograde group.
Finally, Dr Carrier, do you have any examples of physiologic outcomes in these patients? In other words, were serial cardiac outputs looked at to determine whether there was a difference in these groups, and have you subsequently looked at long cross-clamp times and done similar comparisons?
DR CHRISTIAN T. CAMPOS (Boston, MA): My question concerns the statistical power of this study. The outcome events that Carrier and associates measured should be relatively rare in patients with preserved left ventricular function undergoing coronary artery bypass. Have you performed a power analysis? If the power of this study is less than 80%, and I suspect that it is, then the proper conclusion from these data should not be that retrograde cardioplegia confers no advantage but rather that this study was too small to detect it. Such small, but still important, differences may not matter in patients with normal ventricular function, but may be important in patients undergoing emergency operations or in patients with poor ventricular function in whom we believe retrograde cardioplegia offers a significant advantage.
DR YVES LOUAGIE (Mont-Yvoir, Belgium): I would like to have some precision concerning the type of grafts used for revascularization because I believe this is a critical issue. Indeed it has been demonstrated that patients undergoing predominantly arterial revascularization were better with retrograde cardioplegia in cases of three-vessel disease with an occluded left anterior descending artery and in cases of significant left main stem disease [1].
DR CARRIER: I thank Dr Gundry for his interesting comments, and I recognize his work in the retrograde perfusion method. To answer some of his questions, the cross-clamp time was identical in the two groups. And I do not think that changing the kind of catheter we put in the coronary sinus will change this much. And in fact, as you all know, it does not take much longer to put this catheter in.
Obviously it was a selected group of patients. And for a higher risk group, like redo coronary bypass grafting, we also use the retrograde approach. But I think that for the more usual coronary artery bypass patients, even those with a lower ejection fraction, we do not see much difference between the antegrade and the retrograde approach.
As for the cardiac output and the hemodynamic status of these patients, it was very much the same in the two groups.
Now, for the power analysis, this study was done to evaluate the possibility of doing a major randomized trial with the clinical end point as the primary end point. The study was constructed to be able to show a decrease in troponin T levels of more than 30% to 40%, which we have shown in a previous trial comparing warm with cold blood cardioplegia. But with the results that we have, we do not believe that it will be worthwhile to do a major randomized trial with clinical end points as the primary end point of this study, mainly because we believe that the difference will be worthless.
Now, as to the kind of patients, 95% of these patients had an IMA graft, on the left anterior descending artery as well as two other saphenous vein grafts. But I must admit that even when we do perform complete arterial revascularization we do not change our mode of cardioplegia administration.
To add also another comment, in this group, 46 patients had significant left main coronary artery disease, and even in this subgroup analysis there are absolutely no differences in terms of the results, clinically as well as with the enzyme release. So we feel confident that there is no major difference in using antegrade versus retrograde blood cardioplegia in the usual coronary artery bypass grafting patients except if it is at higher risk, like in a redo operation.
Reference
Related Article
| ||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
