Off-Pump Versus On-Pump Coronary Artery Bypass Grafting in ...

James M. Brown, MD, Robert S. Poston, MD, James S. Gammie, MD, Marcello G. Cardarelli, MD, Kimberly Schwartz, CRNFA, Jo Ann H. Sikora, CRNP, Susan Yi, CRNP, Richard N. Pierson III, MD, and Bartley P. Griffith, MD Division of Cardiac Surgery, University of Maryland Medical Center, Baltimore, Maryland

Background. Debate continues between on-pump or off-pump approach for coronary artery bypass grafting (CABG). We used off-pump coronary artery bypass grafting (OPCAB) as a tool within a decision-making algorithm driven by the patient-related factors of coronary anatomy and comorbidity. Our analysis presents this decision algorithm and describes outcomes using this approach. Methods. From January 2000 to December 2003, 592 consecutive patients undergoing isolated CABG were assigned by one surgeon to a technique: on-pump CABG or OPCAB according to (1) anatomy and (2) predicted risk. Anatomic factors against OPCAB were target vessel size less than 1.25 mm, calcification, poor quality, intramyocardial location, and multiple stenoses. Given that OPCAB could be performed safely, patients in the moderate risk range, ie, those elderly with multiple comorbidities, were preferentially treated using OPCAB.

Results. The OPCAB group had higher predicted 30day mortality compared with the on-pump CABG group, consistent with the protocol’s intent. However, morbidity and mortality were similar between on-pump CABG and OPCAB. The OPCAB patients received the same number of internal mammary artery grafts but fewer distal grafts. Mortality and observed to expected ratios were favorable for both groups and below those The Society of Thoracic Surgeons’ predicted for OPCAB. Conclusions. Matching surgical strategy to patientrelated factors and needs resulted in excellent outcomes. Our data support the use of a protocol based on patient characteristics to drive the surgeon’s choice between an on-pump CABG or OPCAB approach. As such, OPCAB can be viewed as a tool to be used by the surgeon developing a best practice in treating coronary artery disease. (Ann Thorac Surg 2006;81:555– 61) © 2006 by The Society of Thoracic Surgeons

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Given that the trial design for a prospective and randomized study requires by nature exclusion criteria and competing analysis attempting to show differences between treatments, our study design took a different approach. It was directed at the question of which technique was best suited for a given patient treated by the cardiothoracic surgeon. In this study we assigned patients to an off-pump approach on the basis of patientrelated characteristics of coronary anatomy and comorbidities. Our central hypothesis was that, first, off-pump coronary artery bypass grafting technique should be applied to patients in whom it could be performed safely and effectively on the basis of coronary angiography. Second, it should be applied to those patients who had significant comorbidities because these patients are the ones who from the standpoint of the practicing cardiothoracic surgeon would most likely derive incremental risk-reduction benefit from an off-pump approach.

revious studies comparing conventional coronary artery bypass grafting to off-pump coronary artery bypass grafting have answered some questions, yet created others. This work has included prospective randomized trials [1–16], retrospective analysis of large databases [17–19], and clinical series [20 –28]. Although several prospective randomized trials have failed to show a difference between on-pump and off-pump coronary artery bypass grafting [7–10], other reports have demonstrated favorable outcomes, including decreased release of myocardial enzymes [9, 22], transfusion [1, 3], and renal insufficiency [17, 29], and improved neurologic outcome [12–14]. Furthermore, decreased risk-adjusted mortality and morbidity have been a central finding in clinical series reviews and in large database analysis [17–19, 21–28]. Thus, the mix of positive and negative reports have led to ongoing interest regarding the optimal use and applicability of the off-pump coronary artery bypass grafting technique.

Accepted for publication June 28, 2005. Presented at the Fifty-first Annual Meeting of the Southern Thoracic Surgical Association, Cancun, Mexico, Nov 2– 4, 2004.

Patients and Methods

Address correspondence to Dr Brown, Division of Cardiac Surgery, University of Maryland Medical Center, N4W94, 22 S Greene St, Baltimore, MD 21201; e-mail: [email protected].

Between January 2000 and December 2003, a single surgeon prospectively assigned either an off-pump or an on-pump surgical plan for coronary artery bypass graft-

© 2006 by The Society of Thoracic Surgeons Published by Elsevier Inc

0003-4975/06/$32.00 doi:10.1016/j.athoracsur.2005.06.081

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Off-Pump Versus On-Pump Coronary Artery Bypass Grafting in Consecutive Patients: Decision-Making Algorithm and Outcomes

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BROWN ET AL OFF-PUMP CABG

CARDIOVASCULAR Fig 1. Decision-making algorithm used to decide between on-pump and off-pump approaches for coronary artery bypass grafting in this consecutive series of 592 patients. Primary consideration was first given to coronary artery anatomy and the complexity of the revascularization needed. Anticipated challenges with distal vessel size quality and location led to an on-pump approach. Given that an off-pump approach could be performed safely, the decision-making method was applied to the patient in terms of the comorbid conditions listed. In general, elderly patients with multiple comorbidities were approached with the off-pump technique. At all steps, surgeon judgment allowed deviation from the decision-making algorithm. For example, an 83-year-old patient with cerebrovascular disease, chronic obstructive pulmonary disease, a large heart, and small obtuse marginal targets would be returned to the off-pump strategy and the small obtuse marginal targets left ungrafted. (AV ⫽ atrioventricular; PDA ⫽ posterior descending artery; PLA ⫽ proximal left ascending artery; RCA ⫽ right coronary artery.)

Ann Thorac Surg 2006;81:555– 61

ing to 592 consecutive patients (Fig 1). The first criterion for assigning patients to each group was anatomy: angiographically small target vessel size (⬍1.25 mm), intramyocardial location, posterobasal location, multiple stenoses, or poor overall vessel quality were factors against an off-pump approach. Given the absence of the above, however, and that the anterior descending artery could be revascularized with an off-pump technique, the second criterion for placing the patient in the off-pump group included the presence of multiple comorbidities, in particular age older than 75 years in combination with pulmonary disease, chronic renal insufficiency, cerebral vascular disease, or peripheral vascular disease. Emergency situations and patients with hemodynamic instability received an on-pump operation. In practice, patients who had three or more major risk factors for adverse outcome were treated using an off-pump technique. For example, an elderly patient with multiple comorbid conditions would have undergo off-pump approach. However, small target vessels near the atrioventricular groove would be left ungrafted. A single surgeon with demonstrable good outcomes in more than 50 off-pump coronary artery bypass grafting operations before this report and who was therefore past the learning curve performed all operations. Operative technique included a sternotomy approach. Two patients in the off-pump group underwent thoracotomy and bypass to lateral wall vessels. Standard techniques of hypothermic cardiopulmonary bypass and cold oxygenated blood cardioplegic arrest were used for on-pump procedures. Off-pump operations used a suction footplate for epicardial stabilization, proximal control with siliconelastomer vascular tapes, and the placement of deep pericardial sutures for cardiac displacement or the use of an apical suction device. For patients who demonstrated a cardiac index less than 1.8, any instability, severe ventricular dysfunction, and high-grade left main stenosis, prophylactic intraoperative balloon pump placement was used in both groups [29, 30]. For patients who had severe aortic atherosclerosis determined by transesophageal echocardiographic evaluation or by intraoperative palpation by the surgeon, epiaortic ultrasound evaluation was performed. For severe atherosclerosis of the ascending aorta characterized by large or mobile atheroma, an off-pump, but no-touch, technique was used, with T grafts off the internal thoracic artery when necessary [31, 32]. For lesser degrees of atherosclerosis of the ascending aorta and arch, the approach was modified to include a single-clamp technique in the on-pump group and altered proximal placement in the off-pump group. Results were analyzed using Fisher’s exact test and The Society of Thoracic Surgeons database predicted risk. For continuous variables, a Student’s t test was used to assess between group differences. A p value of less than 0.05 was considered significant.

Results Five hundred ninety-two consecutive patients undergoing coronary artery bypass grafting between January 2000



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Table 1. Preoperative Characteristics Off-Pump (N ⫽ 199)

Factor

No.

Percent

No.

Percent

p Value

Female Smoker Smoker current Family history CAD Diabetes Hypercholesterolemia Renal failure Hypertension CVA Chronic lung disease Peripheral vascular disease Cerebrovascular disease Previous CABG Myocardial infarction Myocardial infarction timing ⬍ or equal to 6 hours ⬎ 6 hours but ⬍ 24 hours 1 to 7 days 8 to 21 days ⬎ 21 days Congestive heart failure Cardiogenic shock Arrhythmia Classification NYHA IV Number of diseased vessels One Two Three Status nonelective Status Elective Urgent Emergent Emergent salvage

124 273 93 155 155 292 27 319 30 43 71 57 10 189

31.5 69.3 23.6 39.3 39.3 74.1 6.9 81.0 7.6 10.7 18.0 14.5 2.5 48.0

82 129 27 60 90 149 18 171 22 33 54 45 9 100

41.4 65.2 13.6 30.3 45.5 75.3 9.1 86.4 11.1 16.6 27.3 22.7 4.5 50.5

0.0183 0.3329 ⬍0.005 0.0328 0.1732 0.7697 0.3604 0.1013 0.1754 0.0404 0.0094 0.0131 0.2081 0.5820

6 5 96 16 66 55 17 56 209

1.5 1.3 24.4 4.1 16.8 14.0 4.3 14.2 53.0

2 2 36 15 45 49 7 51 104

1.0 1.0 18.2 7.6 22.7 24.7 3.5 25.8 52.0

0.6380 0.7953 0.9110 0.0747 0.0831 ⬍0.005 0.6763 ⬍0.005 0.9062

14 87 293 62

3.6 22.1 74.4 15.7

29 60 109 13

14.6 30.3 55.1 6.5

⬍0.005 0.0303 ⬍0.005 0.8490

331 44 17 2

84.0 11.2 4.3 0.5

185 11 2 0

93.4 5.6 1.0 0

⬍0.005 0.0271 0.0333 0.3406

Continuous Variables

Mean ⫾ Standard Deviation


p Value

Age (y) Ejection fraction STS predicted mortality (%)

63.4 ⫾ 10.1 0.451 ⫾ 0.132 3.6 ⫾ 5.7

69.8 ⫾ 10.6 0.433 ⫾ 0.136 5.2 ⫾ 6.5

⬍0.001 0.1077 0.0039

CABG ⫽ coronary artery bypass grafting; CAD ⫽ coronary artery disease; Association; STS ⫽ The Society of Thoracic Surgeons.

and December 2003 were prospectively assigned to undergo an on-pump or off-pump technique. The intent of the assignment protocol, which was to shift elderly patients with higher risk to the off-pump technique group, was realized as shown in Table 1. The off-pump group had a greater proportion of women and more chronic obstructive pulmonary disease, vascular disease, and cerebral vascular disease. The off-pump group also had a higher incidence of arrhythmias, predominantly atrial fibrillation. During the study period 2 of the 199 off-pump

CVA ⫽ cerebrovascular accident;

NYHA ⫽ New York Heart

patients were converted to an on-pump technique. The on-pump group, by contrast, had a higher proportion of urgent or emergent operations, more current smokers, and more patients with a family history of coronary artery disease. The off-pump group was more than 6 years older than the on-pump group. For the entire group of 592 patients, The Society of Thoracic Surgeons predicted mortality as 4.2%. Observed mortality was 1.3%. In spite of the greater proportion of urgent or emergent operations in the on-pump group, the mean predicted

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groups. The percent of each group receiving an internal mammary artery was the same. However, the off-pump group received fewer distal anastomoses per patient (3.3 versus 2.3; p ⬍ 0.05) . No other differences in short-term morbidities or length of stay were observed.

Comment

Fig 2. (A) Bar graph showing distribution of The Society of Thoracic Surgeons’ (STS) predicted risk in the on-pump group (light bars) and the off-pump coronary artery bypass grafting (OP CAB) group (dark bars). Values on the vertical axis are expressed as the percent of patients within the particular group. The horizontal axis is the predicted risk groupings. The decision-making algorithm resulted in the shifting of the off-pump group to the right or more toward moderate STS predicted risk. (B) Pie chart depicting percent of patients from both the on-pump and off-pump coronary artery bypass grafting (OP CAB) groups that fell into a moderate risk level (between 2.5 and 10 STS predicted risk). More patients (p ⬍ 0.01) in the offpump group were at moderate risk compared with the on-pump group.

mortality in the off-pump group was higher than the on-pump group. This was explained by a shift of the patient population toward the moderately high-risk range of between 2.5% and 10% (Fig 2). The short-term outcome measures are shown in Table 2. Thirty-day mortality was decreased in the off-pump group compared with The Society of Thoracic Surgeons predicted mortality. Incrementally, there was a greater percentage point reduction in unadjusted mortality in the off-pump group (3.7% decrease versus 2.4%). However, observed to expected ratios were the same in both

Previous work investigating the outcomes, safety, and cost-effectiveness of off-pump coronary artery bypass grafting have included prospective randomized trials [1–16], analysis of large database outcomes [17–19], and clinical series [20 –28]. Several randomized trials have been unable to demonstrate clear differences in morbidity and mortality comparing on-pump and off-pump techniques [7–10]. However, none of these studies were of large scale, and although prospectively randomized in some cases generated cohorts of patients, which would favor a negative report. For example the application of the off-pump technique by surgeons still relatively early in their learning curve or the randomizing of low-risk patient groups could with a relatively small number of patients in each group easily explain the lack of a positive result. Furthermore, the study by Kahn and associates [9] demonstrated lower follow-up graft patency for off-pump patients, which might have been part of a learning curve phenomenon, given clear results demonstrating equal patency [2]. By contrast, studies of off-pump coronary artery bypass grafting have demonstrated to a varying degree decreased blood loss and need for transfusion, decreased length of stay, less myocardial enzyme leak, less inflammation, and less renal and neurologic impairment in addition to decreased cost [1–16]. Cleveland and colleagues [17], in a study of greater than 100,000 patients in The Society of Thoracic Surgeons database, demonstrated a reduction in risk-adjusted mortality and commensurate decrease in overall morbidity. Similar findings were confirmed by analysis of the Veterans Affairs database [18] and the National Heart and Lung database in the United Kingdom [19]. The finding that the offpump technique decreased risk-adjusted mortality and morbidity in these large database studies suggested that on-pump or off-pump technique assignment by surgeons could modify outcome by matching patient needs with a technique. The disparate outcomes of prospective randomized trials suggest that trials of matched and unselected patient populations might make demonstrating differences in operative mortality and other outcome measures more rather than less difficult. In spite of the multiple favorable results reported for off-pump surgery, the variety of results in the above trials, ranging from no difference to dramatic difference, and the relatively small number of patients prospectively randomized in limiting circumstances have led to confusion and opinionated encampment by health-care providers and even patients. The question remains: which technique for which patient when? In this study, we prospectively assigned patients to a treatment strategy (Fig 1) using off-pump coronary artery



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Table 2. Postoperative Characteristics

Factor Observed mortality obs: exp ratio Reop for bleeding Infection sternum deep Neurologic stroke perm Pulmonary ventilator prolong Renal dialysis Other atrial fibrillation Blood products

No.

Off-Pump

Percent

No.

1.0

3

4 0.28 8 1 2 56 0 70 158

Percent

p Value

1.5

0.6224 ⬍0.0001a 0.2831 0.0816 ⬎0.995 0.2811 N/A 0.4822 0.7068

0.29 2.0 0.3 0.5 14.2 0 17.8 40.1

7 3 1 35 0 40 76

1.5 0.5 17.7 0 20.2 38.4

Continuous Variables



p Value

LOS mean LOS median Distal anastomoses arterial conduit Distal anastomoses vein grafts Distal anastomoses—total Initial hours ventilated

6.3 ⫾ 5.2 5.0 0.94 ⫾ 0.5 2.4 ⫾ 0.9 3.3 ⫾ 0.6 20.5 ⫾ 30.7

8.0 ⫾ 10.7 5.0 0.91 ⫾ 0.5 1.4 ⫾ 0.9 2.3 ⫾ 0.6 20.8 ⫾ 41.4

0.03 N/A 0.45 ⬍0.0001 ⬍0.0001 0.9536

a

p is observed mortality to STS predicted.

LOS ⫽ length of stay; N/A ⫽ not applicable; Society of Thoracic Surgeons.

obs:exp ⫽ observed to expected;

bypass grafting simply as an alternative rather than a competing technique. In general, patients who were elderly with two or more comorbidities were preferentially approached by an off-pump technique, given that anatomy allowed this approach to be effective and safe. Internal mammary artery grafting to the anterior descending artery remained a priority for all patients and was the same between the two groups. However, by intent, fewer other grafts were placed in the off-pump group, and this was determined by target vessel size, degree of proximal stenosis, regional myocardial viability, and factors outlined in Figure 1. Whether occasional intentional or unintentional incomplete revascularization was a detriment for long-term outcome is unclear from this study, because we do not have long-term follow-up data. However, the off-pump group, with advanced age and comorbidities, likely exists on a steeper down-slope survival curve, driven down by both cardiac but also noncardiac illness. An overaggressive grafting strategy has never been shown to be a benefit and, in some situations, is detrimental [33]. Furthermore, the off-pump group received the same rate of revascularization of the left anterior descending artery with the internal mammary artery as the on-pump group. This population’s tendency for higher comorbidities is reflected in the off-pump group’s Society of Thoracic Surgeons predicted mortality risk of 5.2%. The observed to expected mortality ratios for the group as a whole and for the off-pump and on-pump groups were both identical and favorable. We found no other differences between the groups with regard to postoperative outcomes and hospital length of

Perm ⫽ permanent;

Reop ⫽ reoperation;

STS ⫽ The

stay. This is in conflict with other positive studies, which have demonstrated less transfusion requirement and shorter length of stay. The neurologic morbidity was already low in both groups and therefore the same. It is likely that the same preoperative factors that contributed to higher predicted mortality in the off-pump group also tended to equalize such postoperative measures as ventilator time, transfusion practice or requirement, and length of stay. Therefore, in contrast to prospective randomized trials of nonselected patients, this series intentionally selected patients on the basis of anatomy and patient comorbid conditions for the off-pump group. It was our intent to match patient characteristics to a therapeutic intervention strategy, aimed at maximal incremental risk reduction for all patients and the greatest therapeutic margin, that is the difference between benefit and risk, for the patients deemed to be part of the moderately high-risk group. This prospective strategy was successful at shifting higher-risk, although less-emergent and more hemodynamically stable, patients to an off-pump strategy. This strategy was successful at achieving a significant reduction in observed mortality compared with The Society of Thoracic Surgeons predicted mortality and the identical observed to expected mortality between the two groups. Limitations of this study include a lack of prospective randomized design, a lack of demonstration of graft patency, lack of intermediate and long-term follow-up, and the lack of information regarding long-term outcome health-related quality of life [34]. Furthermore, the assignment to the two treatment groups was not rigid, but

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incorporated in a general protocol framework, allowing for an individual surgeon’s judgment. As such, it models a practice situation of cardiothoracic surgeons. Given the remaining questions on the part of referring physicians and patients as to which patients are the best candidates for an off-pump technique, the demonstrated favorable outcomes lend support to a clinical approach as demonstrated in this report. This paper adds to the growing body of evidence that in select patient subpopulations, an incremental reduction in mortality and therapeutic advantage can be gained by an off-pump technique. Furthermore, as far as revascularization strategies of limited number of coronary perfusion distributions, especially the anterior descending, the off-pump technique can be compared with percutaneous techniques vis-à-vis outcome [35, 36]. Recently, the subject has been reviewed, and comments similar to this paper were made [37]. The observation from published papers that off-pump coronary artery bypass grafting reduces mortality or at least morbidity has been difficult to prove for reasons discussed above. However, the conclusion of the paper by Sellke and coworkers [37] was that a large-scale prospective randomized trial was necessary comparing on-pump and off-pump techniques. This is true. However, simply designing the trial would by definition alter the hypothesis and the answer. This report proposes a clinical approach to consecutive patients that is sensible and broadly applicable by practicing surgeons. In summary, this consecutive analysis of a series of nearly 600 patients referred for coronary artery bypass grafting demonstrates that good outcomes can be achieved using a protocol-driven decision-making algorithm to choose between on-pump and off-pump approaches. We recommend a strategy that uses the offpump technique simply as a tool in the cardiovascular surgeon’s armamentarium, rather than as a competing technique. When applied in this manner, it can be associated with favorable outcomes.

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26. Lund C, Hol PK, Lundblad R, et al. Comparison of cerebral embolization during off-pump and on-pump coronary artery bypass surgery. Ann Thorac Surg 2003;76:765–70. 27. Schmitz C, Weinreich S, Schneider R, et al. Off-Pump versus on-pump coronary artery bypass: can OPCAB reduce neurologic injury? Heart Surg Forum 2003;6:127–30. 28. Keizer AM, Hijman R, van Dijk D, Kalkman CJ, Kahn RS. Cognitive self-assessment one year after on-pump and offpump coronary artery bypass grafting. Ann Thorac Surg 2003;75:835–9. 29. Suzuki T, Okabe M, Handa M, Yasuda F, Miyake Y. Usefulness of preoperative intra aortic balloon pump therapy during off-pump coronary artery bypass grafting in high-risk patients. Ann Thorac Surg 2004;77:2056 – 60. 30. Craver JM, Murrah CP. Elective intraaortic balloon counterpulsation for high-risk off-pump coronary artery bypass operations. Ann Thorac Surg 2001;71:1220 –3. 31. Kim K, Kang CH, Chang W, et al. Off-pump coronary artery bypass with complete avoidance of aortic manipulation. Ann Thorac Surg 2002;74(Suppl)S1377– 82. 32. Dewey TM, Crumrine K, Herbert MA, et al. First-year outcomes of beating heart coronary artery bypass grafting using proximal mechanical connectors. Ann Thorac Surg 2004;77:1542–9.


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DISCUSSION DR JOHN H. CALHOON (San Antonio, TX): Having looked at your data, and enjoying your presentation, I am not sure I understand from your presentation how you tend to choose somebody for off-pump versus on-pump. Are there certain things you see in the vessels or the angiogram or a combination of things that allows you to decide you want to pursue off-pump as your strategy of choice versus on-pump?

interested in epiaortic scanning, and for my own interests and perhaps for the interests of the audience, you said you liberally applied it. Can you give us a rough estimate of what percentage of patients that you applied it to which gave you the opportunity to change the operative technique and perhaps benefit the patient?

DR BROWN: Thank you. First priority was anatomy. We do off-pump surgery to all regions. Assuming that it could be accomplished safely and effectively, it came down to a simple bedside formula of three strikes and those comorbidities that I listed. So, for example, if the patient was 82 and they had a creatinine of 2 and peripheral vascular disease, then we would put them in the off-pump group. I call it a bit of a three-strike rule, leading to off-pump.

DR BROWN: I think in both groups that number lies between 5% and 10%. We have a protocol that we paste on our operating room wall. We start with transesophageal echo evaluation and then, of course, the surgeon’s palpation. If any of those things are positive, we perform an epiaortic scan. If there are atheromas in the way of cannulating or cross-clamping, we change the cannulation point or use a single-clamp technique. In the elderly group, we tended to find more severe atheroma. In that case, we would change plans and try not to touch that aorta. At one point we used the proximal connector, but we are not doing that anymore.

DR JOHN W. HAMMON (Winston-Salem, NC): Doctor Brown, I congratulate you on your excellent results. We also are very

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