"SANKALP" CP-6, Indra Vihar Kota (Rajasthan), India 324005

“On” or “Off” pump coronary artery bypass grafting (CABG)

A glance at the history of the development of Coronary Artery Bypass Surgery (CABG) throws up the interesting finding that the first milestones were without cardiopulmonary bypass (CPB) support. Off-pump CABG (OPCAB), having predated On-pump surgery, has had a roller coaster ride for want of a clean, still and bloodless field, culminating in the introduction of CABG on CPB (On-pump) by Favaloro in 1967. This development profoundly “democratised” the CABG procedure in that now a broad number of surgeons could achieve better and reproducible results with considerably more optimum operating conditions. The initial enthusiasm for On-pump CABG gradually gave way to concerns regarding its safety, especially with regard to complications arising from CPB, and not CABG per se. Foremost of these relate to microembolic showering during manipulation of the aorta and neurocognitive dysfunction. In addition, CPB triggers a whole-body inflammatory response caused by contact activation of the complement cascade. This leads to multiple organ dysfunction affecting the kidneys, liver, lungs, brain and heart itself.1Studies published over a decade and a half ago questioned the safety of On-pump CABG. The proportion of patients recovering without any complication was found to be only 64.3%.2 In addition, health insurance data and data from clinical studies showed that 10.2% did not leave the hospital within 14 days after the operation and 3.6% of the patients were discharged to a non-acute care facility.3 These and other observations, pari passu with the development of mechanical and pharmacological organ stabilizers and intracoronary shunts, resurrected OPCAB in the early 1990s.

As regards surgical technique, the actual suture anastomosis of the vessels follows the same technique both in On- and Off-pump surgery. The difference is that unlike On-pump surgery, where the heart is arrested by means of cardioplegia, in Off-pump surgery the area of interest is kept immobile with the help of organ stabilizers while the anastomosis is being performed. Pharmacologic agents like short-acting beta-blockers (e.g. Esmolol) or Adenosine are used in conjunction with these mechanical stabilizers to achieve the goal of a relatively motionless field. Exposure of the heart is aided by retraction devices like the “Starfish”, which lift up the apex from the pericardial cavity . Retraction can also be achieved by means of folded sponges placed in the pericardial sac to lift the heart, or by pericardial hitching sutures. Distal coronary perfusion is maintained by means of flexible intracoronary shunts introduced into the coronary vessel prior to commencement of the anastomosis . Although these devices are designed for one-time use, they may be reused after ETO sterilization. This assumes importance as far as cost-containment in a country like India is concerned, giving a further fillip to Off-pump surgery.

Numerous large observational studies and small randomized controlled trials (RCT) have been published in the past 18 years suggesting benefits from OPCAB. Among these are, a reduction in stroke, duration of post-operative ventilation, need for reoperation, bleeding, wound infection, renal failure, post-operative length of stay4 and decreased atrial fibrillation and inotrope requirement.5 A major study published in 2001 (the Octopus trial), showing no major differences in cardiac, neurological and neuropsychological outcomes in patients operated On- and Off-pump was also a shot in the arm for Off-pump surgery.6 However, as with any new technique, initial enthusiasm was somewhat dampened by reports of incomplete revascularization using OPCAB.

The most recent comparison study of the two techniques is the CABG Off or On pump revascularization study (CORONARY Study) published in March this year.The trial randomized 4752 patients undergoing CABG to Off-pump or On-pump groups. There was no significant difference seen in the primary end-points of death, MI, stroke, or new renal failure requiring dialysis at 30 days.

The investigators thus struck a middle path by recommending either of the two techniques based on patient factors, provided the surgeon was competent in both. For example, if a patient had renal dysfunction or a heavily calcified aorta, OPCAB would be preferred.

Much like the proverbial see-saw, a 1-year follow-up angiographic study of the ROOBY cohort was reported this year by Hattler at the AHA Congress in Orlando. He revealed that Off-pump patients had a lower saphenous vein patency than On-pump, but a similar arterial graft patency rate, leading to less effective revascularization. Grover in an editorial tried to reconcile the difference between the ROOBY and CORONARY trial findings.The latter involved only surgeons experienced in Off-pump surgery, whereas the ROOBY trial also had trainees as operating surgeons. On a conservative note however, he cautioned that any firm conclusions would have to await long term follow-up results.

Training of surgeons in OPCAB techniques has been an issue as it requires a great deal of focus and enthusiasm, apart from safety concerns. However, even this issue has been laid to rest by a recent study from the Bristol Heart Institute that Off-pump surgery is not only safe and reproducible, but the technique can be taught effectively and safely to trainees with clinical outcomes unrelated to either the level of supervision or the seniority of the trainees.

The final frontier for the Off-pump coronary surgeon remains the patient with left main disease as well as those with severely depressed LV function. Here too, lower mortality and complication rates have been demonstrated.OPCAB has been validated with results quite similar to the CORONARY trial in left main stem disease also. Murzi et al showed that OPCAB was associated with lower in-hospital mortality (0.5% vs. 2.9%; p = 0.001) and morbidity in terms of stroke, renal dysfunction and pulmonary complications/infections.But the biggest bugbear of OPCAB, viz. fewer grafts (2.7 ± 0.7 vs. 3 ± 0.7; p = 0.001) and lower rate of complete revascularization (88.3% vs. 92%; p = 0.04) continue to remain. On multivariate analysis, CPB was confirmed to be an independent predictor of in-hospital mortality (OR 5.74; p = 0.001). The countervailing pros and cons negating each other lead to similar survivals at 1.5 and 10 years, a fact validated by Cheng et al.OPCAB has also been shown to give superior results in patients with chronic kidney disease.

The International Society for Minimally Invasive Cardiothoracic Surgery (ISMICS) recommendations state that the use of Off-pump bypass reduces perioperative morbidity, neurocognitive dysfunction and hospital length of stay and should be considered especially in high-risk patients, for example, those with severe ascending aortic calcification, liver disease, renal insufficiency or other systemic processes that may be exacerbated by CPB, in order to reduce morbidity and mortality.

 

A balanced approach has been advocated by the American Heart Association in their 2011 Guidelines.Based on available data, the guidelines contend, both approaches are reasonable, with certain factors tilting the balance one way or the other. For example, the oft-quoted instance of a patient with a heavily diseased aorta being more amenable to Off-pump surgery. The European Guidelines (2010) on the other hand make no mention of Off-pump surgery, stating instead that over 70% of bypass surgeries worldwide are conducted On-pump (perhaps a diplomatic way of making an undiplomatic point!).

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