Is it time to dump the pump for coronary artery bypass surgery?
Admittedly, the vast majority of these publications can justifiably be criticized as small retrospective series of carefully selected patients with at-best imperfect control groups. But buried in these data is some highly persuasive evidence.
For example, an analysis of the large Society of Thoracic Surgeons database concluded that risk-adjusted operative mortality and major complication rates were at least 20% lower with OPCAB. A separate analysis of the Veterans Affairs hospital database also concluded these rates were significantly lower with OPCAB. And several studies have documented less neurologic impairment following OPCAB, compared with conventional CABG.
There have been three well-conducted randomized, controlled trials to date of OPCAB versus on-pump CABG. Collectively these studies--from the Netherlands, the United Kingdom, and our own study at Emory University--enrolled 879 patients. A metaanalysis of the three showed the rate of any transfusion was 41% with on-pump surgery, compared with 20.6% with OPCAB.
Now if everything else was absolutely equal and one operation offered half the risk of transfusion as another, that would constitute a compelling argument. But in fact, OPCAB piled on additional significant advantages: less myocardial injury, as reflected in myocardial serum enzyme levels of only half the levels in the on-pump group, and a 1-full-day shorter postoperative hospital length of stay.
Moreover, operative mortality was 0.9% with on-pump surgery, compared with 0.2% with OPCAB. The acute MI rate was 3.6% with on-pump CABG, compared with 2.7% with OPCAB. And the stroke rate in OPCAB patients was reduced by half. While none of the differences in these infrequent events reached statistical significance because of small sample size, the trend is consistent.
At this point, virtually any coronary artery bypass I can construct on-pump I can also construct in the same way with beating heart surgery. In our Emory study, the number of grafts performed per patient and the index of completeness of revascularization were the same for on-and off-pump CABG (J. Thorac. Cardiovasc. Surg. 125:797-808, 2003).
NO Dr. Norman Shumway, an influential figure who trained two generations of heart surgeons, was fond of saying, "The pump is your friend."
Well, the pump is still your friend. And that's not going to change in the foreseeable future. Regardless of OPCAB's ultimate role--still very much unsettled--the vast majority of cardiac surgical procedures other than perhaps stand-alone CABG are always going to require some sort of bypass. You cannot replace an aortic or mitral valve without putting the patient on bypass and interrupting the circulation. The same holds true for all operations within the ventricle, major aortic surgery, heart transplantation, and most congenital heart disease procedures.
As for OPCAB, I know some excellent surgeons around the world who now do 99% of their CABGs off-pump. And there are other equally fine surgeons who vow they will never do an off-pump procedure. Some of them find ethically unacceptable the thought of subjecting their first 50 or so OPCAB patients to suboptimal results as they learn the nuances of OPCAB, particularly when there is a time-proven, remarkably successful, and consistently reproducible alternative in the form of on-pump surgery.
I'll concede that OPCAB appears to result in a decreased transfusion requirement, shorter length of stay, and a reduction in the short-term postoperative neurocognitive disturbances. But the real question regarding these often-subtle neurocognitive deficits associated with use of the cardiopulmonary bypass machine is whether they persist long-term.
But the evidence is unequivocal that emergency conversion from OPCAB to on-pump surgery is associated with a marked increase in major complications.
But if OPCAB is the optimal approach, why are only 22% of all CABG procedures in the United States done off pump? I think the answer is that most surgeons are awaiting convincing evidence from randomized, controlled trials that OPCAB offers advantages in the hands of all surgeons, not just the minority who were early adopters of OPCAB and who may possess special skills.
OPCAB has seen rapid development of heart-stabilizing devices and other advances, but on-pump cardiac surgery isn't standing still, either. Pending improvements in cardiopulmonary bypass include smaller perfusion circuits, improved bio-material surfaces, better membranes for oxygenation, and perhaps the use of biosensor technology to improve hemostasis. There is also some hope that aggressive prevention of serious anemia during and after surgery might reduce neurocognitive deficiencies.
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|Title Annotation:||off-pump coronary artery bypass|
|Publication:||Internal Medicine News|
|Date:||Jul 15, 2004|
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