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Ann Thorac Surg 2005;79:1584-1589
© 2005 The Society of Thoracic Surgeons

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Original articles: Cardiovascular

Patient-Reported Outcome After Randomization to On-Pump Versus Off-Pump Coronary Artery Surgery

^a Department of Thoracic and Cardiovascular Surgery, Rikshospitalet University Hospital, Oslo, Norway
^b Department of Surgery, Rikshospitalet University Hospital, Oslo, Norway
^c The Interventional Center, Rikshospitalet University Hospital, Oslo, Norway
^d Oslo University College of Nursing, Oslo, Norway
^e Institute of Public Health, Faculty of Social Sciences, University of Bergen, Bergen, Norway

Accepted for publication October 14, 2004.

^_* Address reprint requests to Mr Mathisen, Department of Thoracic and Cardiovascular Surgery, Rikshospitalet University Hospital, Oslo N-0027, Norway; (E-mail: lars.mathisen{at}rikshospitalet.no).

	Abstract

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
BACKGROUND: Clinical experience with off-pump coronary artery bypass surgery raises the question of a patient experienced benefit compared with on-pump surgery. This prospective and randomized study compared patient-reported outcome between surgical groups, as change scores at 3 months after surgery and longitudinally as time-averaged change from baseline through the first year after surgery.

METHODS: In all, 120 patients were randomly assigned to on- or off-pump coronary artery surgery. A questionnaire for patient self-report of angina (Canadian Cardiovascular Society scale), health status (Short Form 36, sleep and sexual difficulty), and overall quality of life (Quality of Life Scale) was administered at baseline and at 3, 6, and 12 months after surgery.

RESULTS: Patient groups were comparable with regard to age, symptoms, comorbidity, and surgical characteristics. Both groups experienced a median of two classes relief of angina at 3 months (p < 0.0005), maintained throughout follow-up. Paired t tests revealed significant improvement on all Short Form 36 subscales at 3 months after surgery, with the exception of physical role functioning in the on-pump group. No independent main effects of surgical group were observed in the between-groups covariance models. The longitudinal effect of sex was significant in four Short Form 36 subscales: physical functioning, bodily pain, and role limitation due to physical or emotional problems. Overall quality of life scores were stable in both groups.

CONCLUSIONS: Both on-pump and off-pump patients reported less angina and improved health status after surgery. There were no significant differences between surgical groups in health status or overall quality of life, neither cross-sectionally nor longitudinally.

	Introduction

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More than a decade of clinical experience and trials with off-pump coronary artery bypass [1, 2] has resulted in graft patency comparable with on-pump surgery in experienced hands [3–5]. Patient-reported outcomes allow for mapping of the impact of disease and for comparing perceived efficacy and impact of treatment [6]. Heart surgery with cardiopulmonary bypass and temporary cardiac arrest has been associated with neurologic impairment of varying duration and clinical and psychosocial significance [7]. Therefore, it is important to identify a possible impact from procedural redesign to off-pump coronary artery surgery on psychosocial as well as physical domains of patient experience [8]. In the present prospective and randomized study, the aim was to compare patient-reported health related quality of life between surgical groups at 3 months after on- or off-pump coronary artery bypass surgery. Furthermore, a longitudinal comparison was based on postoperative assessments at 3, 6, and 12 months. Health-related quality of life was conceptualized as the subjective assessment of the impact of disease and its treatment across biopsychosocial domains of functioning and well-being [9, 10].

	Patients and Methods

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Sample
One hundred and twenty patients from southeast Norway were included and randomized in blocks of 20 between March 1999 and March 2002. All patients had stable angina pectoris, were eligible for coronary artery bypass surgery, and had moderate or good left ventricular function. Based on prestudy feasibility analysis, a sex proportion of 22% female was expected. Exclusion criteria were ejection fraction less than 30% or serum creatinine greater than 200 mmol/L, or a lack of ability to read, write, or communicate verbally in Norwegian. Currently, half a standard deviation and 10-point changes on a 0 to 100 health status scale are regarded as clinically significant [11]. Sample size was calculated to detect differences between surgical groups of this magnitude, with 80% power and a two-sided alpha of 0.05.

Procedure
The study protocol was approved by the Regional Ethics Committee (May 23, 1998). After providing written and informed consent during work-up for coronary artery surgery, the patients completed a researcher administered questionnaire at admission before surgery, and were again seen at outpatient follow-up at 3 and 12 months after surgery. The procedure for all self-assessments was standardized and scheduled before diagnostic procedures or physician interview. At 6 months after surgery, a postal survey was conducted, with a telephone reminder to nonresponders. Randomization to the on- or off-pump procedure was performed after induction of anesthesia. The surgical procedures, and the clinical and neurologic outcomes after 3 months, have previously been reported [12, 13] and only a brief summary follows.

All operations were performed with a balanced opiate, barbiturate, and inhalation anesthesia. The internal mammary artery was used for revascularization of the left anterior descending coronary artery, and saphenous vein grafts for all other vessels. The distal anastomoses were performed first and the proximal anastomoses successively thereafter, using a partial aortic clamp. Graft blood flow was measured with transit time Doppler flow measurement (MediStim, Oslo, Norway) and the graft revised if indicated. At the end of the operation, graft angiography was performed on the table, followed by graft revision if questionable quality of the anastomosis or the graft was revealed. Angiography was performed again after 3 and 12 months in all patients regardless of symptoms.

In the on-pump group, the entire blood-contact surface of the bypass circuit was coated with the Duraflo II heparin surface (Bentley/Baxter, Uden, Netherlands), and activated coagulation time (ACT) was maintained above 480 seconds. All operations were performed under moderate general hypothermia (28°C to 32°C) with topical slushed ice cooling, and cold St. Thomas antegrade cardioplegic solution. Bypass management included membrane oxygenators, arterial line filters, use of a roller pump and cardiotomy suction, nonpulsatile flow of 2.4 L · min^–1 · m^–2, and a mean arterial pressure greater than 50 mm Hg.

In the beating heart patients, heparin (1 mg/kg) was administered during take-down of the internal mammary artery, and ACT was maintained above 250 seconds. The distal anastomoses were performed with the use of snares (GoreTex 3-0; W. L. Gore & Associates, Flagstaff, Arizona) and Octopus stabilizers (Medtronics, Minneapolis, Minneapolis), combined with a deep pericardial retraction suture and, as needed, an apical suction device (Starfish; Medtronics). A CO₂ blower (Ethicon Cardiovations, Summerville, New Jersey) was used to obtain a bloodless field.

Questionnaire
Background variables included age, sex, years of education, comorbidity, county of residence, sources of income, whether or not the patient lived alone, depression on the Hospital Anxiety and Depression Scale [14], and illness-related social support [15]. Occurrence of significant life events was reported at follow-up. The following instruments were included at all four time points:

ANGINA
The four-step Canadian Cardiovascular Society scale [16] was translated from English (by L.M., M.A.), slightly modified to facilitate self-report, and anchored to a 4-week time-frame aligning with the Short Form 36.

SHORT FORM 36
The 36-item Medical Outcomes Study Short Form (SF-36) reflects health status during the past 4 weeks on eight subscales: physical functioning, limitations of physical role functioning, bodily pain, general health, vitality, social functioning, limitations of emotional role functioning, and mental health. Raw scores are transformed per manual to a 0 to 100 scale; higher scores indicate better health status [17].

SLEEP
Four items regarding the quality of sleep demonstrated internal consistency (Cronbach's alpha >0.80) and were summarized as a single index ranging from 4 (lowest quality of sleep) to 23 (uneventful sleep).

SEXUAL DIFFICULTY
A single item was included in the questionnaire to probe for sexual difficulty perceived to be related to the heart disease itself or to its treatment, ranging from 1 (no difficulty experienced) to 7 (greatest difficulty).

OVERALL QUALITY OF LIFE
The 16-item Quality of Life Scale-Norwegian (QOLS-N) yields a single sum score, range 16 to 112, with higher scores indicating better quality of life. The instrument covers relationships and material well-being, health and functioning, and personal, social, and community commitment [18].

Statistical Analysis
Analysis was by intention to treat. Angina pectoris was modeled as a causal indicator influencing health status and overall quality of life [19]. No difference was expected between off-pump and on-pump surgery regarding the effect of surgery on self-reported angina, and significant improvement of health status was expected for both groups. The design was intended to detect clinically significant differences between surgical groups in health status or overall quality of life.

As only 5 patients were lost to follow-up, between-groups tests were based on available cases. Missing items in multi-item scales were replaced with patient-specific mean values for the scale, as long as at least 50% of the scale items were scored by the patient at that assessment. Data management and analysis were handled with SPSS version 12.0 (SPSS, Chicago Illinois). Angina class was treated as ordered categories. For the remaining dependent variables, the cross-sectional comparison of surgical groups used change scores from baseline to 3 months after surgery. Longitudinal comparison was accomplished using time-averaged area under the curve change scores from baseline to 3, 6, and 12 months after surgery, assuming a linear development between assessments. Sex influences the experience of heart disease and cardiac surgery [20], and a two-way analysis of variance model was chosen using baseline scores as covariates. Considering multiple end points and intercorrelations, we set a p value of less than 0.05 as statistically significant for angina and the SF-36 subscales, and p less than 0.01 for sleep, sexual difficulty, and overall quality of life.

	Results

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Demographic and Background Variables
Baseline data were obtained at median 2 days before surgery. The two groups were similar regarding demographic variables at baseline except for sex (Table 1). Sex was significantly related to number of comorbidities, ejection fraction, education, sleep index, and to all SF-36 subscales except mental health, but not to sexual difficulty or overall quality of life (data not shown). However, no statistical difference was found between surgical groups overall (Fig 1) or by sex regarding angina class at baseline (between-groups Fisher's exact test: female p = 0.452, male p = 0.132).

View larger version (15K): [in this window] [in a new window]   Fig 1. Self-reported angina at (top) baseline and (bottom) 3 months after off-pump surgery (open bars) versus on-pump surgery (solid bars). Canadian Cardiovascular Society (CSS) scale [16]: I = angina with strenous or prolonged exertion; II = slight limitation of ordinary activity; III = marked limitation of ordinary physical activity; IV = inability to carry on any physical activity without discomfort, may experience angina at rest. Bars indicate counts of patients by CCS class. The p values refer to between-groups Fisher's exact tests. Account of missing data: at baseline, 3 invalid responses in the off-pump group and 2 invalid responses in the on-pump group; at 3 months, 1 death and 2 withdrawn in the off-pump group and 1 death and 1 invalid response in the on-pump group.

Angina
Angina was significantly relieved in both surgical groups at 3 months after bypass surgery (Wilcoxon signed ranks, within-groups analysis, p < 0.0005) with a median improvement of 2 angina scale steps. There were no significant differences in distribution of scores between surgical groups at 3 months (Fig 1), 6 months (Fisher's exact test, p = 0.617), or 12 months (p = 0.809), supporting our first hypothesis. Broken down by preoperative angina class, change scores confirmed an equal distribution of results between groups.

Health Status
Baseline and change scores of health status and overall quality of life are detailed in Tables 2 and 3. Both groups improved significantly on all SF-36 subscales from baseline to 3 months after surgery (paired t tests of total scores, data not shown), with the exception of limitations in physical role functioning in the on-pump group. Controlling for baseline scores, there was a main effect of procedure in the social functioning domain at 3 months. However, this effect was not independent but appeared in interaction with sex. The interaction effect size was small, and the covariance model explained 36.5% of domain variance.

Comparison of time-averaged change scores at 12 months revealed no significant differences between surgical groups. Among the SF-36 subscales, sex was identified as a significant independent variable in four of eight domains: physical functioning, bodily pain, and role limitation due to physical or emotional problems. All effect sizes were small with eta² less than 0.1. No interaction effect was detected between sex and procedure.

Overall Quality of Life
No significant differences between surgical groups were demonstrated in the cross-sectional or longitudinal covariance model. The stability of overall quality of life was evident in total scores on the Quality of Life Scale at all three follow-up assessments, with an exception from baseline to 12 months for the off-pump group as a whole (paired t tests, mean improvement 3.0 points [SD 8.29], p = 0.010).

	Comment

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We used a simple angina classification for self-report by patients, evaluated separately from clinical assessments and testing. A few patients did acknowledge uncertainty in differentiating nonanginal chest discomfort from angina at follow-up. As residual nonanginal chest pain may be prevalent after bypass surgery [21], patient counseling remains important to assist interpretation of chest discomfort. At 1 year after surgery, 26.8% of patients (15 of 56) in the off-pump group and 24.1% (14 of 58) in the on-pump group reported some degree of angina. By that time, 9 patients had undergone percutaneous coronary artery procedures, 5 in the off-pump group (6 procedures) and 3 in the on-pump group where an additional patient had coronary intervention pending. Assuming comparable self-report methodology, these percentages are similar to a cohort study of 577 patients with advanced coronary artery disease where 27% reported chest pain at 1 year after bypass surgery [22]. In contrast, the Bristol group pooled follow-up of 401 patients at 1 and 2 years reported 14% with recurrent angina in the on-pump group compared with 12% in the off-pump group [3]. For available cases, we determined improvement of angina versus no change or worsening at follow-up. We then analyzed the influence of surgical group and sex on improvement in a logistic regression model, finding no significant influence at 3 months (n = 110), 6 months (n = 107), or 12 months (n = 109). As reported earlier from this sample, postoperative characteristics were statistically comparable between surgical groups, except for greater mean postoperative bleeding in the off-pump group. In the on-pump group, the number of major complications did not statistically separate the surgical groups but did include 1 case of mediastinitis and 2 incidents of stroke, 1 fatal and 1 patient recovering completely [13].

The SF-36 has demonstrated postoperative responsiveness in previous studies of heart surgery, both to improvement [23] and decline [24], with preoperative scores as a major determinant of predicted change [25]. The social functioning subscale reflects interference with social activities from physical or emotional problems. In this domain, we found a significant interaction effect of surgical procedure and sex, limited to the comparison at 3 months and not mirrored in other psychosocial domains including sleep and sexual difficulties. The overall mean female score at baseline was 11.7 points lower than the by sex and age group comparable normal Norwegian population [26], implying a potential for improvement. At 3 months, the female scores hetereogeneously diverged by surgical group while male scores improved in both groups. We were unable to explain this finding by loss of graft patency, or by adding social support, depression, marital status, and life events to a regression model. The initial finding was augmented by a trend among male respondents toward limitation by maximum possible subscale score (ceiling effect), increasing the pull of lower scores. Furthermore, the smaller female off-pump subgroup included 1 person to be withdrawn for noncardiac disease. Repeat analysis excluding this individual removed the statistical significance of procedure without changing results on other outcomes.

Among the previously published randomized and prospective studies including patient-reported outcomes, one reported angina but not health status [3]. However, data were obtained from 328 of 401 randomized patients in this cohort at median 3 years' follow-up in a posttest only design, finding no significant differences between surgical groups regarding disease specific or general health status [27]. A Dutch multicenter study prospectively included health status outcome but not self-reported angina, finding no significant differences between the on-pump and off-pump group at 3 and 12 months after surgery [28]. A single-center trial reported similar cardiac and patient-reported outcomes at 1 year after surgery [5]. Summing up, there is currently no evidence from randomized trials to support a claim of different self-reported health status at 3 months or 1 year after surgery. It does not appear that the possible benefit of avoiding cardiopulmonary bypass is of sufficient size in itself, or relative to the risk inherent in the more challenging off-pump procedure, to show up in a broad range of patient-reported outcomes including physical as well as psychosocial domains. Our findings align with the objective, neuropsychological tests earlier reported [28], although one would not have been surprised to observe self-report reflecting psychosocial aspects that cognitive tests might not reveal. As in the other randomized studies, this study was not powered to detect small effect sizes of possible clinical significance and in the range of 2 to 5 points, which are relevant in epidemiologic studies but require too large a number for the smaller randomized trials. Also, the variance in health status scores may not only reflect interindividual variation, but suggests consideration of the whole mosaic of surgical treatment, where use of cardiopulmonary bypass is but one element of the pathway from admission to completed outpatient rehabilitation.

Some limitations of our study should be acknowledged. First, while both procedures were effective more than 12 months without statistically significant differences, this study of low-risk patients was not designed to prove equivalence or map outcomes beyond the first year after surgery. Sex stratification could have improved our study design. We studied development beyond the early postoperative recovery period, obscuring possible short-term group differences after hospital discharge. However, our questionnaire requested patients' perceptions during the last 4 weeks, suggesting that the experience of postoperative week 8 to 12 would be represented in our material. While blinding until induction of anesthesia was accomplished, the medical chart could not be blinded after surgery, limiting full control over untoward disclosure of procedure. Available knowledge at the start of inclusion suggested a broad design with multiple indicators, as surgical innovations may have unknown and unforeseen effects that are latent in nonrandomized designs but do show up in a randomized trial. Thus, additional risk of type I error was accepted. Although the overall amount of missing data were considered minimal, a possibility of informative censoring could not be excluded. We repeated the analysis with an augmented data set, constructed according to the assumed nature of missingness. All results concurred with those of the initial analysis.

Our sample was smaller than the multicenter study reported by van Dijk and coworkers [28]. However, a prospective single-center trial offers greater control of standardization and reduces interviewer and institution bias. We were able to enrol all patients approached, and to randomize all patients recruited, thus reducing selection bias within our low-risk patient group. By deferring randomization until after induction of anesthesia, no instances of cross-over from the on-pump to the off-pump group occurred, which is unique compared with the other clinical trials prospectively reporting on health status outcomes [5, 28].

In conclusion, this randomized trial of patient-reported outcomes after on-pump versus off-pump coronary artery bypass surgery was powered to detect moderate size effect differences. Questioning patients on symptoms, health status, and overall quality of life at 3, 6, and 12 months after surgery revealed significant improvement in symptoms and health status within both surgical groups. There were no significant differences in health status or overall quality of life between groups, cross-sectionally or longitudinally, explained by independent main effects of surgical procedure.

	Acknowledgments

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	References

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Runar Lundblad Erik Fosse Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Mathisen, L. Articles by Fosse, E. Search for Related Content PubMed PubMed Citation Articles by Mathisen, L. Articles by Fosse, E. Related Collections Minimally invasive surgery