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Ann Thorac Surg 2000;69:1317-1318
© 2000 The Society of Thoracic Surgeons
a Department of Cardiac Anesthesiology, University of Western Ontario, London, Ontario, Canada
b Cerebral Blood Flow Laboratory, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
Address reprint requests to Dr Murkin, Department of Anesthesiology, London Health Sciences Centre, University Campus, 339 Windermere Rd, London, ON N6A 5A5, Canada
Just a few short years ago, in 1996, we suggested in an Editorial in The Annals, a relatively novel concept for the time: "Neurobehavioral tests are tools to improve outcome after cardiac surgery" [1]. Since then, there has been a flurry of activity in this area with many publications demonstrating that prevention of both macro and micro embolization results in less evidence of brain injury after cardiopulmonary bypass (CPB). That this should be so, at this the end of "The Decade of the Brain," is fitting. That attention is being drawn ever more closely to the challenge of decreasing postoperative central nervous system (CNS) injury, is necessary if cardiovascular surgery is to continue to evolve. That a definitive answer to the question, "Does off-pump coronary artery bypass (OPCAB) result in a lower incidence of brain injury than conventional coronary artery bypass grafting (CABG)?" is not as yet available, however, is not surprising.
Increasingly, neuroprotection is becoming an important consideration in the adoption of new methods or equipment in cardiac surgery. However, in interpreting the results of various behavioral measures of brain function (neuropsychological, neurobehavioral, neurocognitive, neurologic, etc), there are many confounds that can give rise to these data being misinterpreted, misapplied, or inappropriately analyzed, in a way that makes the outcome difficult to interpret relative to the efficacy of the technique or technology in question.
There appears to be a pattern or evolution whenever a new surgical technique is introduced. There is initially the advocacy position, followed by the testimonials, then the battle between the new zealots (with my eyes alone I can see it is better!) and the old school (if it ain’t broke, don’t fix it). Fortunately, in the debate pitting off-pump surgery versus on-pump surgery, we are entering the next stage where appropriate scientific methods and large clinical trials begin to burn away the fog generated by the initial small early studies.
In a recent editorial, Ali and Large [2] advocated the initiation of a well-powered multicentered trial comparing outcomes after conventional coronary artery bypass grafting (CABG) versus beating heart surgery (OPCAB). We applaud this initiative. This may well be an achievable goal for this year’s "Outcomes" meeting, to be held May 24 to 28, 2000 in Key West, Florida (www.outcomeskeywest.com). One focus of "Outcomes 2000" will be the role of OPCAB relative to CABG where the pros and cons of these approaches will be debated by Drs Denton A. Cooley and Michael J. Mack. This debate will be preceded by a discussion of experimental and statistical methods that are most appropriate in order to detect meaningful differences in outcomes after on-pump versus off-pump surgery. Two satellite symposia on minimally invasive cardiac surgery (MICS II) and advances in perfusion technology (PICS) will immediately follow on Sunday, May 28, expanding upon these and related topics.
Ali and Large also raised a number of other issues that are of considerable import to those involved in the management of cardiac surgical patients. They noted the recent publication in the Annals of the Proceedings from the "Outcomes 99" meeting focusing on neuropsychological injury after cardiac surgery [3]. While many of these issues were discussed at that meeting, their commentary faulted the meeting for not discussing two important new studies from the UK and Canada. Unfortunately, of these studies neither that of Taggart and associates [4] nor that of Murkin and colleagues [5] had been published at the time of "Outcomes 99" in May 1999. These studies will be the focus of much attention in the upcoming "Outcomes 2000" meeting, however.
In considering the apparently divergent results of the studies by Taggart and associates [4] and Murkin and colleagues [5] comparing conventional CABG versus beating heart surgery, it should be recognized that neither group has claimed their results as conclusive, but rather as preliminary, and hopefully, provocative. Neither study was randomized. Neither employed other surgical cohorts. Both were small. Based in part on these limitations, our clinical investigative groups have recently been awarded funding (Medical Research Council of Canada, MOP-37914; National Institutes of Health, NS-327242) for large scale, prospective, randomized studies comparing beating heart surgery with conventional and "best practice" CABG. The Canadian study will additionally incorporate a noncardiac surgical cohort, as well as a nonhospitalized control group, in order to address confounds raised by exposure to major surgery and anesthesia.
As to the relative efficacy of revascularization with CABG versus OPCAB, the cited results of Calafiore and colleagues [6], reporting an overall angiographic graft patency rate of 89.8% for internal mammary artery to left anterior descending (LAD) coronary artery, has been superseded by their more recent report. In 67 patients undergoing revascularization with two or more arterial grafts, they demonstrated an angiographic patency rate of 98.9% for LAD [7]. Among other things, this illustrates the learning curve associated with any new procedure, as well as the subsequent introduction and utilization of myocardial stabilizer devices. Of interest, however, is the comment of Calafiore and associates that these results were achieved in a population with a greater number of high-risk patients in comparison with a study cohort undergoing conventional CABG, yet perioperative morbidity was similar. Ongoing advances in stabilizer technology and innovations in surgical approach will likely continue to narrow the gap between these various complementary approaches to surgical coronary revascularization. Will it really be the healthiest, or rather, the sickest patients who will in fact benefit most?
In their comment that the CPB machine is perhaps not the sole culprit in negative outcomes after CPB, Ali and Large have considerable support. The role of diverse factors such as aortic atheroma, concomitant cerebrovascular disease, and transfusion of cardiotomy suction blood have all been identified in various studies, as well as being featured topics in prior "Outcomes" meetings.
Much work has already gone into improving patient outcomes after CPB, with clinical adoption of various techniques and equipment modifications being accelerated by the results derived from studies of CNS sequelae, studies that have led the way in the introduction and widespread acceptance of CPB equipment modifications such as arterial line filtration and membrane oxygenators, and may well shortly lead to a reconsideration of the ubiquitous use of unprocessed cardiotomy suction blood during CPB. Management techniques such as alpha-stat pH control during moderately hypothermic CPB have been predicated upon a knowledge of cerebral physiology, and patient outcomes tested and verified using cognitive testing such as that alluded to by Ali and Large. These studies led very directly to the convening of an open invitational Consensus Conference. An initial attempt to bring some consistency to the study of postoperative neurocognitive dysfunction, this resulted in the publication of a Consensus Statement outlining suggested minimum guidelines for cognitive and neurological testing in this population [8].
Further, the increasing recognition of the role played by aortic atheroma, and the innovative steps taken to minimize this risk including epiaortic scanning and the potential for intraaortic filtration, are all currently undergoing large-scale, prospective evaluations employing CNS outcomes as primary endpoints. Understanding the mechanisms of CNS injury, or some of them at least, enables potential cerebroprotective strategies to be assessed, and the outcomes after CPB to continue to be improved. The series of "Outcomes" meetings to which Ali and Large alluded represents one attempt to provide a focused scientific forum for these issues and their discussion.
The importance of these studies was that the attention focused on organ systems other than the heart, which engendered a new appreciation for whole patient outcomes. The specific goals of coronary surgery remain unchanged: to provide the safest and most effective means of coronary revascularization; what was added, however, was a new regard for other factors that can influence the overall success of the operation. Given the subsequent progressive increase in patient ages and the increasing acuity of their comorbidity at time of operation, such a broadened perspective has proven essential in decreasing various adverse sequelae of cardiac surgery. Further trials are necessary to confirm the various preliminary observations suggesting OPCAB may be especially beneficial in high-risk patient groups.
The primary goal of the "Outcomes" meetings is to focus attention on issues related to CNS sequelae of cardiac and vascular surgery. As coorganizers, we believe we have in fact been very successful to date in achieving this goal. The very fact that the "Outcomes" forum has been the focus of an editorial in Annals supports this view; it speaks for itself. We have been gratified to see that issues raised in Poster/Discussion sessions, and at poolside, at previous "Outcomes" meetings have stimulated the scientific curiosity of various groups. Several groups have subsequently undertaken, and either have in progress, or have published, studies dealing with some of these issues, eg, aortic cannulation strategies, lidocaine as a potential cerebroprotectant. Such issues may also be the focus of formal debate at a subsequent "Outcomes" meeting, as is the case this year with OPCAB versus conventional CABG.
We must always remember that we are dedicated as scientists and clinicians to bringing the best practice possible to our patients. We do not believe there is one best, universal surgical approach that will be applicable to all coronary revascularization patients. We need to identify which patients will benefit most from what procedure. We do believe that the "Outcomes" meetings can and do serve to stimulate further interest in these issues. By highlighting current studies and in providing a scientific forum encouraging open discussion, in some cases they may even serve to stimulate the development of multicenter collaborative studies. Some or all of these various endpoints have resulted from previous "Outcomes" meetings. Let us hope that this might happen again this year. This would be a highly successful "Outcome."
References
This article has been cited by other articles:
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  G. Bolotin, Y. Domany, L. de Perini, I. Frolkis, O. Lev-Ran, N. Nesher, and G. Uretzky Use of Intraoperative Epiaortic Ultrasonography To Delineate Aortic Atheroma Chest, January 1, 2005; 127(1): 60 - 65. [Abstract] [Full Text] [PDF]
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 G. K. Peel, S. C. Stamou, M. K. C. Dullum, P. C. Hill, K. A. Jablonski, A. S. Bafi, S. W. Boyce, K. R. Petro, and P. J. Corso Chronologic distribution of stroke after minimally invasive versus conventional coronary artery bypass J. Am. Coll. Cardiol., March 3, 2004; 43(5): 752 - 756. [Abstract] [Full Text] [PDF]
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 S. C. Stamou, K. A. Jablonski, A. J. Pfister, P. C. Hill, M. K.C. Dullum, A. S. Bafi, S. W. Boyce, K. R. Petro, and P. J. Corso Stroke after conventional versus minimally invasive coronary artery bypass Ann. Thorac. Surg., August 1, 2002; 74(2): 394 - 399. [Abstract] [Full Text] [PDF]
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 M. A. Borger and V. Rao Temperature Management During Cardiopulmonary Bypass: Effect of Rewarming Rate on Cognitive Dysfunction Seminars in Cardiothoracic and Vascular Anesthesia, March 1, 2002; 6(1): 17 - 20. [Abstract] [PDF]
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J. A. Macoviak, J. Hwang, K. L. Boerjan, and D. D. Deal Comparing dual-stream and standard cardiopulmonary bypass in pigs Ann. Thorac. Surg., January 1, 2002; 73(1): 203 - 208. [Abstract] [Full Text] [PDF]
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N. Trehan, M. Mishra, O. P. Sharma, A. Mishra, and R. R. Kasliwal Further reduction in stroke after off-pump coronary artery bypass grafting: a 10-year experience Ann. Thorac. Surg., September 1, 2001; 72(3): S1026 - 1032. [Abstract] [Full Text] [PDF]
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 S. C. Stamou, P. C. Hill, G. Dangas, A. J. Pfister, S. W. Boyce, M. K.C. Dullum, A. S. Bafi, P. J. Corso, and B. Silver Stroke After Coronary Artery Bypass : Incidence, Predictors, and Clinical Outcome Editorial Comment: Incidence, Predictors, and Clinical Outcome Stroke, July 1, 2001; 32(7): 1508 - 1513. [Abstract] [Full Text] [PDF]
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