Ann Thorac Surg 2006;82:615-619
© 2006 The Society of Thoracic Surgeons
Original article: Cardiovascular
Health-Related Quality of Life Outcome After On-Pump Versus Off-Pump Coronary Artery Bypass Graft Surgery: A Prospective Randomized Study
Reza Motallebzadeh, MRCSa,
J. Martin Bland, PhDd,
Hugh S. Markus, FRCPb,
Juan Carlos Kaski, MD, DScc,
Marjan Jahangiri, FRCSa,*
a Department of Cardiac Surgery, St. George's Hospital Medical School, London, United Kingdom
b Department of Clinical Neuroscience, St. George's Hospital Medical School, London, United Kingdom
c Department of Cardiological Sciences, St. George's Hospital Medical School, London, United Kingdom
d Department of Health Sciences, University of York, United Kingdom
Accepted for publication March 24, 2006.
* Address correspondence to Dr Jahangiri, Department of Cardiac Surgery, St. George's Hospital Medical School, London, SW17 0QT (Email: marjan.jahangiri{at}stgeorges.nhs.uk).
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Abstract
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BACKGROUND: The clinical benefit of off-pump coronary artery bypass graft surgery over on-pump surgery is a matter of controversy. The aim of this study was to assess quality of life in patients after on-pump and off-pump coronary artery bypass graft surgery, and compare the data with an age-matched and sex-matched standard population.
METHODS: Two hundred twelve patients admitted for elective coronary artery bypass graft surgery were randomized to on-pump (n = 104) and off-pump (n = 108) surgery. Quality-of-life assessments were made 6 and 18 months postoperatively using the standard form of the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36, version 2). The questionnaire yields eight subscores of functional health and well being. The eight SF-36 raw scores were standardized using means and standard deviations from a random sample of adults in Great Britain. Mean on-pump and off-pump SF-36 scores were compared using two-sample Student's t tests.
RESULTS: Questionnaires were completed for 72% (154 of 212) and 46% (98 of 212) of patients at the 6- and 18-month follow-up, respectively. There were no significant differences between on-pump and off-pump patients in any of the eight subscales at both stages. Fifty-six (72%) on-pump and 59 (75%) off-pump patients reported a better health status compared with the 6-month period before surgery (not significant).
CONCLUSIONS: Patients who have undergone off-pump coronary artery bypass graft surgery have a similar quality of life to on-pump patients at 6 and 18 months after surgery. For both groups, the majority of patients reported improved health after coronary artery bypass graft surgery compared with their preoperative status.
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Introduction
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The aim of coronary artery bypass graft surgery (CABG) is to reduce cardiac symptoms and mortality, and thus lead to an improvement in quality of life [1]. Major advances and refinements in surgical techniques, myocardial protection, and anesthetic management have contributed to reductions in postoperative morbidity and mortality after CABG. With the dramatic reduction in operative mortality throughout the ensuing decades, attention is now being focused on reducing operative morbidity and improving subtle outcome indicators such as neurocognitive function and quality of life [2–5]. However, the demographics of patients being referred for cardiac operations are changing, with a significant trend toward an older and sicker patient population [6, 7]. Myocardial revascularization in such patients remains associated with postoperative morbidity and mortality substantially higher than that observed in the younger patient population [8]. Hence, change in quality of life is an important outcome indicator in these patients.
For more than three decades surgical coronary revascularization has been achieved with the use of cardiopulmonary bypass (CPB). Traditionally, many of the adverse sequelae after CABG have been ascribed to the use of CPB. The potential benefits of avoiding CPB and cardioplegic arrest of the heart has led to off-pump surgery comprising 20% of all CABG procedures performed in North America and Western Europe [9]. The benefit of off-pump versus on-pump CABG is still a matter of much conjecture. Nonrandomized studies have shown that off-pump surgery leads to less morbidity, blood loss, and hospital stay [10, 11]. However, in a recent meta-analysis of nine randomized trials, there was no difference in the incidence of death or stroke at 30 days [12]. The aim of this study was to assess quality of life in patients after off-pump and on-pump CABG, and compare outcomes with an age-matched and sex-matched standard population.
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Patients and Methods
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Study Population
Between August 2002 and March 2004, patients admitted for elective first-time isolated CABG were enrolled into a prospective randomized study of on-pump versus off-pump surgery. (This was a trial assessing intraoperative cerebral emboli and neurocognitive outcomes.) Approval for the study was obtained from the local research ethics committee, and all patients gave written informed consent. This trial was enlisted with a registry for randomized trials: Current Controlled Trials Limited (number: ISRCTN97967360). All patients who agreed to enter the study had preoperative carotid artery duplex ultrasound. Patients with the following criteria were excluded: (1) previous cerebrovascular accident (CVA) or transient ischemic attack, (2) right or left internal carotid artery stenosis of 50% or greater, (3) previous cardiac surgery, (4) concomitant surgery, eg, valve replacement, (5) previous psychiatric illness, eg, depression or schizophrenia, (6) dialysis-dependent renal failure, (7) Q-wave myocardial infarction in the past 6 weeks, (8) very poor left ventricular function (ejection fraction less than 0.20), and (9) illiteracy or nonfluency in English.
Patients were randomized according to a computer generated randomization list. Blocking was used to construct the allocation sequence. Assignments were on cards and enclosed in serially numbered, opaque, sealed envelopes, and each bearing on the outside the name and date of birth of the enrolled patient. Envelopes were opened sequentially and only on the day of surgery for that patient.
On-Pump Coronary Artery Bypass Grafting
On-pump CABG was performed with a Stöckert S3 roller pump (Stöckert, Munich, Germany), membrane oxygenators (Avant Sorin, Mirandola, Italy), and a 40-µm arterial blood filter (Dideco, Mirandola, Italy). Moderate hypothermia (32°C) and 
-stat management were used. Myocardial protection was achieved with cold antegrade blood-based cardioplegia. Perfusion pressure was kept at 60 mm Hg or greater, and a pump flow of 2 to 2.4 L · min–1
· m–2 was maintained throughout CPB. Blood from cardiotomy suckers was separated from the pump circuit and washed with a cell saving device (Dideco). After the distal anastomoses had been completed, the aortic cross-clamp was removed and the proximal anastomoses were carried out using a side-clamp on the aorta.
Off-Pump Coronary Artery Bypass Grafting
Off-pump CABG was conducted through a median sternotomy. A heparin dose of 150 IU/kg was given to maintain an activated clotting time of 400 seconds or longer. Occlusion and stabilization of the target coronary artery was achieved with the use of silastic snares and the CTS Retractor (Cardio Thoracic Systems Inc, Cupertino, CA). All distal anastomoses were performed first. The proximal anastomoses were subsequently fashioned onto the aorta with the use of a single side-clamp. Near normothermia (35°C) was maintained using warmed fluids and a heating mattress. Systolic blood pressure was kept at 70 mm Hg or greater.
Assessment of Health-Related Quality of Life
Quality-of-life assessments were made at 6 and 18 months postoperatively using the standard form of the second version of the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36, v2) [13, 14]. The SF-36 is a multipurpose health survey with 36 questions and is a widely used, reliable, and valid tool for assessing health-related quality of life. The questionnaire yields eight subscores of functional health and well being: physical functioning, role physical, bodily pain, general health, vitality, social functioning, role emotional, and mental health. Raw scores were adjusted using normative scales, with higher scores representing a better health state. (In norm-based scoring, the general population norm is built into the scoring algorithm). The eight SF-36 scales were standardized using means and standard deviations from a random sample of 2,056 adults living at home in Great Britain [15]. The respondents in this group were aged between 16 and 80 years old, of which 54% were older than 45 years old, 45% were male, and 55% female.
As described by Ware and colleagues [14], linear z score transformations were performed to transform scores to a mean of 50 and standard deviation of 10. Hence, in norm-based scoring, each scale is scored to have the same average (50 points) and the same standard deviation (10 points). All scores therefore above or below 50 can be interpreted as above or below the general population norm.
Statistical Methods
The SF-36 scores are presented as mean ± standard deviation. Comparisons were made between the on-pump and off-pump SF-36 scores using two-sample Student's t tests. Results for categorical variables are expressed as number (percent). Continuous variables that were normally distributed were compared with unpaired Student's t tests, and nonnormally distributed variables were compared with Mann-Whitney tests. The 
2 test was used to compare categorical variables. A probability value less than 0.05 was considered significant. Statistical analyses were performed on Stata 8.2 software (Stata Corp, College Station, TX).
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Results
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Two hundred twelve patients were randomized: 104 to on-pump and 108 to off-pump surgery. There was no treatment crossover. At 6 months, questionnaires were completed for 76 of 104 (73%) on-pump and 78 of 108 (72%) off-pump patients. Baseline characteristics are shown in Table 1. Both sets of patients had a similar length of schooling and intelligence quotient scores.
In-hospital mortality was 1% (1 of 104) in the on-pump and 1.9% (2 of 108) in the off-pump group (p = 1.0). In the on-pump group, 1 patient died on the ninth postoperative day as a result of a cerebellar and brainstem stroke. (Strokes were defined as patients who suffered a focal neurologic deficit lasting more than 24 hours. In patients who had clinical evidence of a stroke, the defect was located by computed tomography scanning.) There were 2 in-hospital deaths after off-pump surgery: 1 on the second postoperative day owing to rupture of a chronic aortic dissection, and 1 on the 13th postoperative day as a result of respiratory failure. By 6 months, 3 on-pump and 1 off-pump patients had died, resulting in an overall mortality rate of 4% (4 of 104) and 3% (3 of 108), respectively (p = 0.72). There were three nonfatal strokes within 30 days of surgery in the on-pump group: 1 patient had an infarct in the lentiform nucleus on the second postoperative day, 1 patient experienced sudden unilateral ischemic optic neuropathy as a result of an infarct of the corona radiata (and anterior limb of the internal capsule) on the sixth postoperative day, and 1 patient had a left temporal cortex infarct on the 11th postoperative day. One patient suffered a nonfatal embolic parietal area cerebral infarct 83 days after surgery as a result of a left ventricular thrombus. Only 1 patient experienced a nonfatal stroke in the off-pump group (14 days after surgery). The overall 6-month incidence of stroke for on-pump and off-pump CABG was 5% (5 of 104) and 1% (1 of 108), respectively (p = 0.11). Patients who suffered a stroke were not excluded from quality-of-life assessments.
At the 6-month stage, there were no significant differences between the on-pump and off-pump patients in any of the eight scales of the SF-36 questionnaire (Fig 1). In comparison with an age-matched and sex-matched population, the entire cohort of patients was significantly impaired in all of the scales of the SF-36 questionnaire (physical functioning, p < 0.001; role physical, p < 0.001; bodily pain, p < 0.001; general health, p = 0.001; vitality, p = 0.002; social functioning, p < 0.001; and role emotional, p < 0.001), except for mental health (p = 0.11). There were no significant differences in the reported health transition between the two groups (Table 2).
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Fig 1. Short Form (SF-36) Health Survey Questionnaire (version 2) scores at 6 months after on-pump (gray bars) and off-pump (white bars) coronary artery bypass graft surgery, age-matched and sex- matched comparison with a standard British population (British Omnibus Survey, 1992). (BP = bodily pain; GH = general health; MH = mental health; PF = physical function; RE = role emotional; RP = role physical; SF = social function; VT = vitality.)
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Follow-up was completed for 50 of 104 (48%) on-pump and 48 of 108 (44%) off-pump patients at the 18-month follow-up. Similar to the 6-month assessment, there were no significant differences between the two groups in any of the scales (Fig 2). In comparison with an age-matched and sex-matched population, the entire cohort of patients was significantly impaired in the following modalities: physical functioning, p < 0.001; role physical, p < 0.001; general health, p = 0.002; and role emotional, p = 0.003. However, there were no significant differences for bodily pain (p = 0.16), vitality (p = 0.09), social functioning (p = 0.20), and mental health (p = 0.59).
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Fig 2. Short Form (SF-36) Health Survey Questionnaire scores at 18 months after on-pump (gray bars) and off-pump (white bars) coronary artery bypass graft surgery. (BP = bodily pain; GH = general health; MH = mental health; PF = physical function; RE = role emotional; RP = role physical; SF = social function; VT = vitality.)
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Comment
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We have shown that there are no differences in quality-of-life measures between patients undergoing on-pump and off-pump CABG at both 6 and 18 months after surgery. Similarly, the randomized studies of on-pump versus off-pump surgery by Puskas and associates [16] and by van Dijk's group [17] showed no significant differences in postoperative health-related quality-of-life outcomes at 1 year. In a study of 504 patients undergoing CABG, Immer and colleagues [18] showed that patients who had undergone off-pump surgery had significantly better physical and emotional role function SF-36 scores at 10 months' follow-up, compared with on-pump patients. It should be emphasized that this was a nonrandomized study, with only one eighth of the total number of patients in the off-pump group. There were significantly more patients in the off-pump group with single-vessel coronary artery disease, and hence it is possible that the off-pump group had a lower severity of angina (Canadian Cardiovascular Score) and fewer patients in New York Heart Association grade III or IV heart failure. As a result, patients who have undergone off-pump CABG would be expected to have better postoperative physical role scores. In support of this, it has recently been shown that preoperative heart failure is predictive of worse quality of life at 1 year after CABG [19]. Furthermore, there might have been imbalances in other demographic factors such as years of education and employment status. These have been shown to be significant factors correlating with long-term quality-of-life outcomes [2].
The whole set of patients had significantly worse SF-36 scores at the 6-month follow-up compared with an age-matched and sex-matched population, and the scores in our investigation are lower than that seen in van Dijk's study [17]. However, by 18 months the scores for bodily pain and vitality were not significantly different from the control group. It is possible that at 6 months patients still have noncardiac problems such as wound or leg pain, which would limit physical functioning [20].
Quality-of-life data are useful as outcome measures of the impact of disease and the benefit of medical or surgical therapy. Rumsfeld and colleagues [4] showed that both physical and mental health status improved at 6 months after CABG, and that patients with low scores were the most likely to show an improvement in quality of life. Moreover, patients with higher preoperative scores showed a marked decline in quality of life. These findings can, however, be explained by regression to the mean. Regression to the mean is the statistical phenomenon whereby extreme baseline scores tend to become less extreme after repeated examinations, even though true change has not occurred [21, 22]. The effect of regression to the mean is present whenever there is an intrasubject variation on a repeated test and is thus an inevitable feature of quality-of-life testing. Regression to the mean suggests that high-scoring individuals will do worse on repeat testing, and that lower scoring people will do better. Rumsfeld and colleagues [4] analyzed their data using change in mean scores. A better method would be analysis of covariance. Analysis of covariance takes regression to the mean into account and is a powerful method of analyzing test–retest data [23]. This is similar to analyzing the difference before to after, but better. It allows for the possibility that people with higher baseline scores may be more likely to experience greater declines, for example.
One limitation of this study is the absence of baseline testing, and therefore there may have been preoperative imbalance in SF36 scores between the two groups. Hence, we cannot comment on change in preoperative to postoperative quality of life. Nevertheless, it should be noted that 72% of on-pump and 76% of off-pump patients reported better health status compared with 1 year before assessment, ie, in comparison with before surgery. Another limitation is the loss to follow-up, particularly for the 18-month assessment, and therefore patients with low SF36 scores might have been excluded from analysis. However, as the follow-up rate was similar for on-pump and off-pump CABG at both times, the possibility of not including patients with very low (or high) SF36 scores should be the same for both groups.
In summary, patients who have undergone off-pump CABG have a similar quality of life to on-pump patients at both 6 and 18 months after surgery. For both groups, the majority of patients reported improved health after CABG compared with their preoperative status.
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Acknowledgments
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This study was supported by a research grant form the Royal College of Surgeons of England.
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Abstract
Introduction
