EDITORIAL

To Pump or Not to Pump: A Surgeon’s View on Randomization
25 Years Later

Alex Zapolanski, MD
Alex Zapolanski, MD
Historia magistra vitae est. Cicero, Tusculanas, 2 A look at the historical evolution of coronary bypass surgery is helpful in understanding the dilemma facing cardiac surgeons today. What is the ideal technique to achieve the best surgical revascularization? Favaloro and Johnson popularized coronary bypass surgery using ventricular fibrillation and intermittent anoxic arrest.1 During the early years, the operation enjoyed variable results. Cleveland, Milwaukee, and a few other centers delivered consistently good outcomes. This success was a function of sound judgment in patient selection, but perhaps more importantly, precise and expeditious surgical technique. It took many years for coronary surgery to become uniformly safe. The introduction of crystalloid and blood cardioplegia in the 1970s and 1980s leveled the playing field. These techniques allowed surgeons the luxury of operating on an arrested heart, reducing the time constraints and myocardial protection problems related to intermittent anoxic arrest. Later, the incorporation of retrograde cardioplegia enhanced myocardial protection and made arresting the heart even less of an issue. The introduction of the single cross-clamp technique is credited with a reduction in neurological injury, achieving further improvement in what is perhaps the most devastating complication of heart surgery.2 In spite of these changes, the best results achieved by surgeons collectively was a leveling of the mortality rate for coronary bypass to 2.9% until 1999. In the last three years, mortality has dropped to 2.6%, coinciding with a modest increase in the volume of off-pump surgery.3 Have cardiac surgeons reached a plateau in their ability to deliver better results in coronary surgery? Can we overcome the persistent risks associated with previous stroke, severely depressed pulmonary function, renal insufficiency, and extensive peripheral vascular disease? Can we circumvent dealing with a calcified ascending aorta? Is off-pump surgery the key to further improvement in the results, and if so, are we all responsible for incorporating this technique in our armamentarium? The development of beating heart surgery in South America and Europe was slowly adopted in the United States.4–6 Any new technique always has the disadvantage of taking surgeons out of their comfort zone. A conservative establishment frequently challenges innovators and early adopters.7 We have seen this in the past with the slow adoption of the use of the internal thoracic artery. It took more than fifteen years for surgeons to concede and accept the procedure when a definitive paper demonstrated its unquestionable benefit.8 Today the Society of Thoracic Surgeons considers the use of the internal thoracic artery a marker of quality improvement.9 Mitral valve repair surgery is another example of the slow adoption of a new technique in the United States that had been long established in Europe. Over the last few years, OPCAB destabilized the “leveled playing field” provided by the cardioplegic techniques of the 1970s and 1980s. Few publications, including some randomized trials, have shown no difference in results between OPCAB and conventional coronary bypass.10–13 The fact that a procedure is shown not to be better in a selected group of randomized patients does not mean that the results are applicable to the majority of patients. While randomized trials intend to eliminate bias in the treatment selection, they do not eliminate a bias in the inclusion in the trial. The recent randomized trial reported in the New England Journal of Medicine concludes that patency rates are lower in off-pump surgery.14 While the paper is supposed to be valid by its randomized nature, it fails to address two very important issues. First, the authors claim that the surgeons’ skills were not a factor in their results. Their on-pump patency rate was excellent. In turn, the assumption is made that their skills would be maintained while operating on the beating heart. This is probably not valid, as operating on the beating heart requires different expertise. In addition, they admit that the learning curve for the procedure is substantial and may be longer than they anticipated. Secondly, did both surgeons have equal experience with off-pump surgery prior to embarking on the trial? The institution performed only 98 OPCAB procedures prior to the study, yet it is unclear whether the surgeons had equal experience with this procedure. This paper provides an opportunity to recall an excellent editorial written by Floyd Loop twenty-five years ago regarding randomized trials: “Variation in surgical skill and judgment often are unappreciated or ignored; yet, perhaps these variables may greatly affect results.”15 The human component of a sophisticated technical procedure is more difficult to control in a trial than the precise dosages of a drug.16 Loop also emphasized the value of time and experience. Using the data from the Australian National Heart Foundation as an example, he showed that it took a significant increase in volume and experience for the mortality rate to decrease from 5.5% to 2.4%. The idea of randomizing OPCAB and on-pump procedures is particularly complicated. The decision to perform a coronary bypass on or off-pump is ultimately made after the pericardium has been opened and the situation assessed. Vessel graftability based on size and/or location (i.e., deep intramyocardial artery) and tolerance to cardiac manipulation are essential factors to determine its feasibility. How can we randomize a surgeon’s judgment? As an alternative, a study could involve only surgeons who are extremely experienced with OPCAB, those capable of performing the majority of their cases on the beating heart, and in doing so, their judgment becomes somewhat neutralized. Yet surgeons who learned and adopted the technique out of the conviction that OPCAB is superior to on-pump, would be hard pressed to participate in such a trial. An attempt to randomize introduces a certain form of “experimentation,” stated Loop, assigning patients to an ultimately poor risk group. An example of this is patients who were assigned to medical therapy in 1972 to prove that left main obstruction was a highly lethal form of atherosclerosis.15 How could one possibly commit a patient with a calcified/porcelain aorta to an on-pump coronary bypass today? The use of the “no-touch” technique in the diseased aorta, avoiding cardiopulmonary bypass in patients with renal disease, the strict control of fluid overload, and the minimization of the inflammatory response in patients with poor pulmonary function are sensible intraoperative decisions. They are supported by adequate documentation, yet not formally randomized. Many publications have demonstrated the disadvantages of extracorporeal circulation. Patients whose renal function is compromised pre-operatively,17 patients with calcified ascending aortas,18,19 and patients with depressed pulmonary function20 benefit from an off-pump approach. Norman Cousins stated, “Wisdom consists of the anticipation of consequences.” Even in these days of evidence-based medicine, it is not necessary to have a randomized trial to avoid cannulating or clamping a grossly calcified aorta. Where is the logic of flooding the lungs of patients with severely depressed pulmonary function or exposing those with elevated creatinine to the hypotensive and non-pulsatile effect of cardiopulmonary bypass? In these circumstances, on-pump coronary surgery not only does not make sense, it is probably suboptimal practice, and potentially actionable. The implementation of a new technique entices surgeons to think about the effort/benefit ratio. Coronary bypass surgery has achieved a level of safety and efficacy that seems hard to improve upon. The commitment and dedication required from us to learn off-pump techniques to attain minor improvements appears to be disproportional to the gain. A similar situation is encountered with the addition of a second arterial conduit in coronary surgery. Time consumption, and perhaps the technical challenge, preclude surgeons from complicating an operation for a benefit that will not be realized for years to come, as the surgeon is removed in time and space from the patient by the time the veins fail. Yet, there is a difference in the case of OPCAB as the surgeon is faced with the consequences of his/her intraoperative decisions the next day. This brings us back to Loop’s remarks from 1979: “Today there is no excuse for high morbidity and mortality in elective coronary arterial bypass surgery. The stakes are too high for the patient and the referring physician to allow myocardial revascularization to be performed by the surgeon who operates occasionally.” This concept can be easily extrapolated to OPCAB today. It cannot be performed occasionally. With the development of new techniques today, we are in the process of accomplishing Dr. Loop’s vision. He predicted that “Within our lifetime, elective open heart surgery will be performed with negligible or even no mortality rates in many centers.”15
References
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