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Ann Thorac Surg 2000;69:1730-1731
© 2000 The Society of Thoracic Surgeons
DR MICHAEL J. MACK (Dallas, TX): President Kouchoukos, Dr Pairolero. I would like to congratulate Dr Kshettry on his presentation and acknowledge the pioneering work of the Minneapolis group in cardiac surgery. I appreciate Dr Kshettry forwarding me a copy of his manuscript for review prior to this meeting.
Evaluation of any new procedure begins first with historical analysis, then registries followed by the design of this study, that is, comparison of contemporaneous cohorts. Further validation includes matched cohorts and the most rigorous controlled, prospective, randomized trials. I would propose that on the basis of the design and methodology of this study, the conclusions of no benefit or minimal benefit are premature.
What are the possible reasons that no greater benefit could be demonstrated from off-pump surgery? It is possible there really is no significant benefit, or there really is a benefit, and this will become more evident with time. There are only 135 patients in the off-pump group. With a low incidence of complication in both groups, power analysis would indicate the necessity of a larger study group to demonstrate differences between the two groups. The predicted risk was higher in the off-pump group, but the mortality results are not risk adjusted. Without risk adjustment the outcomes are not strictly comparable. It is also possible that high-risk subgroups that would receive benefit were not examined. Indeed, Dr Arom from your group recently presented a paper demonstrating a benefit from OPCAB in high-risk patients. If the groups that were most likely to receive benefit were examined independently, perhaps greater benefit could be defined.
Another conceivable reason is that the outcomes in both groups benefited from the selection of high-risk patients into off-pump surgery. If off-pump surgery is indeed most beneficial in high-risk patients, then improved outcomes in both groups would be expected. It may also have been too early in the learning curve to achieve the benefits of a new operation. Examination of results while surgeons are still on the learning curve may be a premature analysis. Indeed, the fact that one can eliminate cardiopulmonary bypass and have no increase in complications while on the learning curve I think is a positive. It may also be that the wrong end points to demonstrate benefit were examined. The real potential benefits of off-pump surgery may be in the potential for improving neurocognitive outcomes. In view of the fact that this is a retrospective nonrandomized study, the results have to be reviewed with caution.
It may be that different statistical tools would show different outcomes. These results were analyzed by univariate statistical methods. In a population with multiple variables impacting potential outcomes, a stepwise logistic regression analysis may have shown different results.
We examined our results of multivessel bypass in 8,700 patients, 513 off pump. Stepwise logistic regression analysis identified the use of cardiopulmonary bypass to be an independent risk factor for mortality. The Emory group has also shown that the pump is an independent predictor of mortality. On the basis of these comments, I would ask Dr Kshettry the following questions.
One, are your current results still the same as reported in this series, now 10 months old, now that your group has larger volumes to analyze and your surgeons are further along the learning curve? Two, do you have risk-adjusted results since the off-pump group tended toward higher risk and have you looked at results in high-risk subgroups? Three, have you examined neurocognitive outcomes in your patients?
I would suggest caution interpreting conclusions, either positive or negative, until prospective randomized studies or outcomes analysis in larger populations are performed.
Once again, I congratulate Dr Kshettry on an excellent presentation and thank the Society for the opportunity of discussing this paper.
DR DIMITRI NOVITZKY (Tampa, FL): At the University of South Florida, we have operated 530 patients off bypass. This is a routine operation at the Tampa VA. We have compared 205 off bypass versus 204 on bypass. We have found that the group off bypass had significantly higher preoperative risk regarding carotid disease, worse heart failure, more emergent procedures, and more preoperative intraaortic balloon pumps. The operative time was significantly shorter for the off-pump group. The off-bypass group had 2.9 versus 3.2 grafts on bypass. The off-bypass group required fewer blood product transfusions. The postoperative stay in the ICU was reduced by 0.6 days and the length of stay in hospital was reduced by 1.2 days. We followed the patients for 6 months and we looked at the readmission rates. The readmissions were reduced from 14% to 4%. The true cost for the off-bypass group was reduced by $5000.00 per patient.
We do intermittent controlled hypotensive anesthesia whenever we bypass the obtuse marginal. We also perform cardiac herniation into the right pleural cavity whenever a graft is required to the circumflex territory. This facilitates the cardiac manipulation and renders a more complete revascularization of the obtuse marginal branches.
I do not understand why you use partial heparinization. This may activate clotting within the patient at the time of surgery. I also believe that full heparinization should be done in these patients. Thank you.
DR JAMES R. JUDE (Miami, FL): This is an excellent presentation, but my question is what do you mean by learning curve and does anyone here want to be part of a learning curve if you are the patient. Is there a morbidity or a mortality associated with it? Question two is, what is the incidence of conversion from doing reoperation off pump to having to convert to on pump?
DR CURTIS C. QUINN (Milwaukee, WI): My question is, your length for both on pump and off pump seemed a little bit long. In your off-pump cases did your anesthesiologists try to modify any of their techniques to allow for early or even intraoperative extubation, and did you try to streamline the mobilization of your off-pump cases to get them home sooner? We extubate the majority of our OPCAB patients in the operating room and our length of stay is 4.5 days.
DR GIOVANNI SPEZIALI (Morbegno, Italy): I have two questions. The first one is, is there a difference in the percentage of patients who received total arterial revascularization between the two groups; and the second question is, did you measure cardiac index during the time the heart was lifted out of the chest, because when we did that, we saw an important, sustained reduction in cardiac index. Thank you.
DR KSHETTRY: Thank you, Dr Mack. We acknowledge your contribution to the field of minimally invasive cardiac surgery and our group has followed many of your leads.
The purpose of this review was not to recommend or discourage one technique over another one. I think it was to look honestly where we stand right now after doing beating heart surgery for the past 4 years. Our cardiac surgery database has information on close to 800 patients who have undergone beating heart surgery. However, when one looks at the data many patients get mixed together; high risk and low risk are there. In the initial experience, the number of grafts performed per patient were lower as compared to the middle of 1997 onwards when multivessel bypasses were done. In most of the information in the literature on results of off-pump bypass, the mean number of grafts has been low, 2.1 to 2.7 per patient. If you look at The Society of Thoracic Surgeons data for patients in the low-risk group, the mortality risk is between 0 and 5%, and the mean number of grafts are 3.4.
The purpose of this study was to compare patients who are getting more or less the same number of grafts (more than three grafts per patient) on or off pump with similar mortality risk (2.3% vs 2.7%). It is true that the learning curve of a new procedure will improve with experience; nevertheless, if we have not done so in the past 4 years, I don’t know how long it will take us complete the learning curve. Coronary artery bypass is one of the most commonly done procedures. The other concern has been what is the reproducibility factor? Most of the coronary bypass surgery is not done in ivory towers. It is done in various sized community hospitals. Can these results be duplicated?
From our group, Dr Arom reported a larger number of off-pump patients. The only thing we could see that was different and significant were patients who were in the highest risk category with mortality risk more than 5% benefited having their coronary revascularization done with an off-pump technique. I think that as the technique matures and more information comes along, we won’t be surprised that the patients who are the sickest are the best candidates to have this technology offered to them.
There was a question about the learning curve and conversion of patients undergoing off-pump CABG. In this group there were no conversions. In part this may be due to patient selection; patients with good distal targets were selected initially, and as we are doing more OPCABG, a small percentage of patients are being converted to cardiopulmonary bypass if we find that technically the anastomosis is difficult.
Another question was length of stay. We have participated in the state of Minnesota in a statewide database looking at all the hospitals performing cardiac surgery, and the average length of stay has been 7.1 to 7.2 days. Many of our older patients come from outside the Twin Cities, and it becomes difficult to get them home sooner.
Difference between arterial grafts? I think our philosophy for total arterial revascularization is based upon patient age. We offer that to a younger age group, patients younger than 60 years of age. I think that it is reflected in the philosophy of the practice. Most of the patients in this review were older than 65 years of age, so the total arterial revascularization numbers were small.
Another question we have looked at while performing off-pump bypass is what happens to the cardiac index during elevation? As a matter of fact we have, and we hope to be presenting, this information very soon. We have used a continuous cardiac output monitor in selected patients while performing a posterior anastomosis. Even though the blood pressure has been pretty adequate by inotropic support, however, the average cardiac index has been 1.4 liters per minute. Maybe over the years beating heart surgery experience will teach us that coronary artery bypass may not require cardiopulmonary bypass, but that does not mean that coronary artery bypass requires no circulatory assistance.
Thank you.
This article has been cited by other articles:
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  P.-G. Chassot, P. van der Linden, M. Zaugg, X. M. Mueller, and D. R. Spahn Off-pump coronary artery bypass surgery: physiology and anaesthetic management{dagger} Br. J. Anaesth., March 1, 2004; 92(3): 400 - 413. [Abstract] [Full Text] [PDF]
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