Lawton, Jennifer S. MD; Damiano, Ralph J. Jr MD
From the Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St. Louis, MO USA.
Accepted for publication December 17, 2009.
Disclosure: Ralph J. Damiano, Jr., MD is a consultant for Medtronic, Inc., Minneapolis, MN USA.
Address correspondence and reprint requests to Jennifer S. Lawton, MD, Division of Cardiothoracic Surgery, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8234, St. Louis, MO 63110 USA. E-mail: firstname.lastname@example.org.
Less than one third of all coronary artery bypass (CABG) operations in the United States are performed without cardiopulmonary bypass. The reduced morbidity (atrial fibrillation, red blood cell transfusion, inotrope requirement, respiratory infection, release of myocardial enzymes, and inflammatory mediators) with off-pump CABG has been documented in randomized trials comparing off-pump with on-pump CABG, and off-pump CABG is recommended to reduce duration of ventilation, hospital and intensive care unit stay, and resource utilization by the Consensus Statement of ISMICS.1 In this Consensus Statement, adequate surgeon experience is included as an important factor in obtaining similar graft patency to on-pump CABG. In the recent New England Journal of Medicine publication that has gained significant media attention, Shroyer et al2 concluded that patients who underwent off-pump CABG had worse composite outcomes and poorer graft patency at 1 year follow-up when compared with patients who underwent on-pump CABG. However, it is important to put this conclusion in perspective and not discard a valuable surgical technique without a careful analysis of this study.
Shroyer et al2 randomized 2203 patients to on- or off-pump CABG at 18 VA medical centers. Patients were almost exclusively men (99.4% in the off-pump group and 99.5% in the on-pump group), excluding one very important high-risk group of patients (women) who have been documented to benefit from off-pump CABG. Surgeons included in the study performed a minimum of 20 off-pump procedures (median of 50) before the trial. Sixteen of the 18 centers had cardiothoracic surgery trainees who performed 55.4% of the off-pump surgeries and 64% of the on-pump surgeries as the primary surgeon. The most important flaw of this trial was the relative lack of experience of the surgeons, particularly with the off-pump technique. Completion of only 20 off-pump surgeries should not be considered as adequate progress on the learning curve to participate in a randomized trial and certainly not adequate to be teaching trainees with even less experience. This result is similar to a previous study that demonstrated decreased graft patency (at 3 months) in patients who underwent off-pump CABG compared with on-pump CABG.3 In this randomized study of 104 patients, the surgeons had only 2 years experience and had performed <100 cases (13% of all cases during the 2 years.) using the off-pump technique.3 In an editorial commenting on this study, MacGillivray and Vlahakes4 noted that, “off pump CABG is a highly demanding procedure with a long learning curve that surgeons should attempt only after mastering conventional CABG.” Therefore, cardiothoracic trainees are not the best primary surgeons in a randomized study of a technically demanding procedure. Interestingly, in the Shroyer et al study, a sensitivity analysis with stratification of surgeon experience into >50 or ≤50 prestudy cases showed no significant difference in the primary 30-day and 1-year composite outcomes.
The correct take-home message for surgeons from this study is not that off-pump CABG is worse than on-pump CABG. In our opinion, this study showed that off-pump CABG is not for every surgeon, and it is not for every patient. Off pump CABG clearly has a learning curve for the surgeon. It is technically more challenging, and appropriate patient selection must be learned. Knowing when to safely convert to on-pump CABG because of exposure issues, bleeding, or hemodynamic instability is critical to obtaining good results. Methods to improve visibility of target vessels and the appropriate use of intracoronary shunts are also learned with experience. The learning curve includes the ability of the surgeon to work with the anesthesiologist to provide support when appropriate. Teaching these methods to residents may be accomplished with the use of intracoronary shunts or with the use of cardiopulmonary bypass (performing surgery on pump with the heart beating) to provide hemodynamic support during longer anastomosis times.
The learning curve for off-pump CABG has been estimated to be >200 cases, with an evolution of selection criteria for off-pump cases with increasing experience.5 Song et al emphasized the importance of appropriate patient selection during the learning curve to avoid compromise of excellent outcomes while technical proficiency develops. In the Shroyer report, the high rate of conversion to on-pump CABG (12.4%) and the higher rate of incomplete revascularization in the off-pump group strongly testify to the inexperience with off-pump techniques and inappropriate randomization. The rate of conversion in experienced off-pump surgeons is ∼1%.6 Patients in the Shroyer et al report who underwent conversion to the alternative surgical method remained in the intent to treat group. A 12% conversion rate to on pump in the off-pump group would also increase the rate of unfavorable outcomes in this group as conversion to on pump is typically a poor prognostic indicator (conversion is often urgent and in the face of hemodynamic compromise).6–9 Interestingly, when the authors removed patients who underwent conversion to the alternative surgical method, the 1-year primary end point was not statistically different between the groups. Furthermore, no significant differences in survival between groups were noted.
Shroyer et al provided 1-year angiographic follow-up on 669 patients in the off-pump group and 666 patients in the on-pump group. Graft patency was significantly lower in the off-pump group, largely because of differences in the patency of saphenous vein grafts. There was no statistically significant difference between patency in the left internal mammary grafts. Similar to findings in multiple randomized and nonrandomized trials, patients in the off-pump group required fewer red blood cell transfusions when compared with patients in the on-pump group. However, there was no difference in the hospital length of stay between off-pump and on-pump groups. This comparison is not valuable in the VA population as typical insurance constraints on hospital length of stay are nonexistent in VA hospitals.
Randomized trials between off-pump and on-pump surgery performed by experienced off-pump surgeons have documented similar graft patency, cardiac outcomes, and completeness of revascularization.10 In addition, a large study of propensity matched patients (N = 12,812) who underwent off-pump and on-pump CABG documented similar survival at 10 years between groups, as well as significant morbidity and mortality advantages with off-pump CABG for the high-risk group of women who typically have an operative mortality of twice that of men when CABG is performed on pump.11
Off-pump CABG also is not for every patient. Experience guides appropriate selection with important considerations including the need to perform multiple or sequential grafts on the lateral wall, intramyocardial vessels, small target vessels, diffusely diseased and calcified vessels, comfort with stabilization techniques, and patient body habitus. In addition, not all patients can or should be randomized to either method. Instead, the procedure should be tailored to the patient.
Off-pump CABG provides real benefit to, particularly in high-risk patients, those with end-stage renal disease, or at high-risk for neurologic injury, women, porcelain, or calcified aorta prohibiting cross clamping, significant pulmonary disease, hepatic dysfunction, or bleeding disorders. It is vital that this technique remain part of our armamentarium as cardiothoracic surgeons. These benefits can be achieved in experienced hands, and we must critically evaluate comparisons of outcomes in light of this fact.
1. Puskas J, Cheng D, Knight J, et al. Off-pump versus conventional coronary artery bypass grafting: a meta-analysis and consensus statement from the 2004 ISMICS Consensus Conference. Innovations. 2005;1:3–27.
2. Shroyer AL, Grover FL, Hatler B, et al; for the Veterans Affairs Randomized On/Off Bypass (ROOBY) Study Group. On-pump versus off-pump coronary-artery bypass surgery. N Engl J Med. 2009;361:1827–1837.
3. Khan NE, De Souza A, Mister R, et al. A randomized comparison of off-pump and on-pump multivessel coronary-artery bypass surgery. N Engl J Med. 2004;350:21–28.
4. MacGillivray TE, Vlahakes GJ. Patency and the pump-the risks and benefits of off-pump CABG. N Engl J Med. 2004;350:3–4.
5. Song HK, Peterson RJ, Sharoni E, et al. Safe evolution towards routine off-pump coronary bypass: negotiating the learning curve. Eur J Cardiothorac Surg. 2003;24:947–952.
6. Reeves BC, Ascione R, Caputo M, et al. Morbidity and mortality following acute conversion from off-pump to on-pump coronary surgery. Eur J Cardiothorac Surg. 2006;29:941–947.
7. Jin R, Hiratzka LF, Grunkemeier GL, et al. Aborted off-pump coronary artery bypass patients have much worse outcomes than on-pump or successful off-pump patients. Circulation. 2005;112:I332–I337.
8. Edgerton JR, Dewey TM, Magee MJ, et al. Conversion in off-pump coronary artery bypass grafting: an analysis of predictors and outcomes. Ann Thorac Surg. 2003;76:1138–1142.
9. Patel NC, Patel NU, Loulmet DF, et al. Emergency conversion to cardiopulmonary bypass during attempted off-pump revascularization results in increased morbidity and mortality. J Thorac Cardiovasc Surg. 2004;128:655–661.
10. Puskas JD, Williams WH, Mahoney EM, et al. Off-pump vs conventional coronary artery bypass grafting: Early and 1-year graft patency, cost, and quality of life outcomes. A randomized trial. JAMA. 2004;291:1841–1849.
11. Puskas JD, Kilgo PD, Lattouf OM, et al. Off-pump coronary bypass provides reduced mortality and morbidity and equivalent 10-year survival. Ann Thorac Surg. 2008;86:1139–1146.
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