Disease-Specific Health Status After Stent-Assisted Percutaneous Coronary Intervention and Coronary Artery Bypass Surgery
One-Year Results From the Stent or Surgery Trial
Background— Functional status and quality of life are important outcomes in the evaluation of revascularization approaches for symptomatic coronary artery disease. Few data are available regarding the comparative improvement in disease-specific health status after CABG versus percutaneous coronary intervention (PCI) in the era of coronary stenting.
Methods and Results— Cardiac-specific health status was evaluated at baseline and at 6 and 12 months after intervention with the Seattle Angina Questionnaire (SAQ) in patients randomized to stent-assisted PCI (n=488) versus CABG (n=500) in the Stent or Surgery trial. Scores for physical limitation, angina frequency, and quality of life improved significantly for both treatment groups at 6 months (range of improvement from 13.6 to 34.7 points) and 12 months (14.3 to 38.2 points; all P<0.001). CABG patients had greater improvement than those assigned to PCI, although the magnitude of the difference decreased over time (difference at 6 months, 4.03 to 6.48 points; 12 months, 2.05 to 2.93 points). A component of this reduction is accounted for by PCI-arm patients who required repeat intervention. Differences between treatment groups were greatest for the 6-month angina frequency scores (difference=6.48 points; 95% CI 3.96 to 8.99). Overall, treatment satisfaction was high and did not differ significantly between groups.
Conclusions— Both CABG and stent-assisted PCI dramatically improved cardiac-related health status in patients with multivessel disease at 6- and 12-month follow-up. During the first postprocedure year, patients’ angina burden and physical limitations were alleviated to a greater extent with CABG.
Received December 30, 2002; de novo received May 9, 2003; revision received June 26, 2003; accepted June 26, 2003.
Functional status and quality of life are important outcomes of therapeutic interventions for patients with coronary artery disease (CAD).1–3 Percutaneous coronary intervention (PCI) and CABG, revascularization procedures performed for the relief of angina, were compared in the early 1990s in 6 major randomized trials and in a meta-analysis4; no significant differences in mortality and myocardial infarction were reported, although a more recent meta-analysis5 of 13 randomized trials showed an absolute survival advantage favoring CABG over PCI at 5 and 8 years in subgroup analyses for patients with multivessel CAD. Four of these 6 trials in the early 1990s included a comparison of patients’ generic health-related quality of life, which showed that CABG patients had greater improvement in quality of life scores.6–9 However, none of these trials used a disease-specific health status measure to compare effects of these procedures on patients’ complaints of angina and the effect of angina on functional status and disease-specific quality of life, perhaps the principal indication for the procedure from the patient’s perspective. Moreover, since the early 1990s, there have been various developments in both PCI and CABG, notably increased use of coronary stenting and improved myocardial protection with CABG, which emphasize the importance of reevaluating these procedures in the current era.
The Stent or Surgery (SoS) trial was a randomized trial comparing stent-assisted PCI with CABG in patients with multivessel CAD.10 The 1-year clinical and economic results from this trial showed that CABG offered lower mortality (0.8% versus 2.5%) but little increase in quality-adjusted life years, and at increased cost.11 The present evaluation, complementing prior studies, reports the comparative effects of PCI and CABG on disease-specific health status.
The design of the SoS trial has been described previously.10 In brief, this was a prospective, unblinded, randomized trial in 53 centers within 11 European countries and Canada. Symptomatic patients with multivessel CAD were eligible if they had typical angina pectoris and either revascularization procedure was clinically indicated. Exclusion criteria included previous CABG or thoracotomy.
The primary end point was the rate of repeat revascularization. Secondary end points included all-cause mortality, Q-wave myocardial infarction, costs, and functional status/quality of life. All patients were followed up for at least 1 year.
A total of 988 patients (488 PCI and 500 CABG) were enrolled between November 1996 and December 1999. Thirteen patients died within 6 months (PCI 10, CABG 3), and 3 more patients died between 6 months and 1 year after randomization (PCI 2, CABG 1). Therefore, 988 patients were included at baseline, 975 at 6 months, and 972 at 1 year.
Disease-Specific Health Status
Cardiac-related health status was assessed at baseline (before the procedure) and at 6 and 12 months after intervention with the Seattle Angina Questionnaire (SAQ), a 19-item self-administered questionnaire that measures 5 domains of CAD-related health status: physical limitation, angina stability, angina frequency, treatment satisfaction, and disease perception/quality of life.12,13 Scores range from 0 to 100 for each domain, with higher scores indicating better functioning. The physical limitation subscale measures how daily activities are limited by symptoms of CAD. The angina stability subscale assesses change over the prior 4 weeks in the frequency of angina at the patient’s most strenuous level of activity, whereas the angina frequency subscale quantifies the frequency of angina over the preceding 4 weeks. The treatment satisfaction subscale evaluates the patient’s level of satisfaction with their current angina treatment, and the quality-of-life subscale characterizes the patient’s perception of the impact of CAD on their quality of life. All SAQ domains have been demonstrated to be valid, reliable, responsive, and prognostic of death and acute coronary syndromes.12–14 Each domain measures a unique dimension of CAD, and no summary score is available. A clinically important change is between 5 and 8 points.13
Baseline clinical and demographic characteristics were compared between treatment groups by χ2 or Fisher exact test for categorical variables and t test or Wilcoxon 2-sample test for continuous variables. The percent of missing SAQ scores for 5 subscales and 3 time points were compared by χ2 test, and the average time between baseline and follow-up SAQ evaluations was compared by Wilcoxon 2-sample test.
Multiple imputation (Monte Carlo Markov chain approach)15 was used to impute missing SAQ scores for surviving patients for the 5 domains and 3 time points. Covariates used in each of the multiple imputation models included all SAQ scores at the 3 time points, treatment assignment, demographic factors (age, as a continuous variable, and gender), and clinical characteristics (prior myocardial infarction, Canadian Cardiovascular Society classification, New York Heart Association functional status, acute coronary syndrome, hypertension, diabetes, hyperlipidemia, current or ex-smoker of cigarettes, cerebral vascular accident, peripheral vascular disease, transient ischemic attacks, and the number of diseased coronary artery vessels). An additional variable used in the imputation models was an indicator of whether the patient underwent repeat revascularization between baseline and 6 months (for the 6-month analysis) and between 6 months and 1 year (for the 1-year analysis).
Unadjusted SAQ scores at each of the 3 time points were compared by independent t tests. The primary analysis, however, compared changes in SAQ scores from baseline at 6 and 12 months between treatment groups with ANCOVA, with adjustment for baseline SAQ scores, age ≥65 years, gender, and all other baseline clinical characteristics included in the imputation models. Only covariates with a significant effect (P<0.05) were included in the final models. Additional changes from baseline in SAQ scores at 6 and 12 months related to CABG versus PCI were evaluated with the coefficient for the treatment effect and its associated probability value. Comparisons of 6- and 12-month SAQ scores among CABG patients and PCI patients with and without repeat revascularization were performed with ANCOVA, with adjustment for baseline scores and other significant baseline covariates. Results for the angina stability domain are compared only for baseline because it is a cross-sectional measurement of short-term changes over the prior 4 weeks and is not appropriate for longitudinal analyses.
Comparisons between treatment groups were analyzed according to the intention-to-treat principle. All tests of statistical significance were 2-tailed, and a probability value <0.05 was considered significant. Statistical analyses were performed with Statistical Analysis System, version 8.2 (SAS Institute).
Baseline demographic and clinical characteristics at entry were similar in both groups. The mean age was 61.4 years, and 79.0% of patients were male, 14.4% had diabetes, 24.4% had acute coronary syndromes, and 45.2% had hypertension.
Average, unimputed SAQ scores at each of the 3 time points and percent missing data are presented in Table 1. The initial scores were depressed, all below 60, except treatment satisfaction. Although CABG patients were more likely to have missing baseline SAQ data than PCI patients (P<0.03 for all scales), there were no significant differences in the percent missing at 6 months and 1 year. CABG patients had the baseline evaluation 1 week earlier relative to the intervention than did the PCI group (9.4 days for PCI versus 16.0 days for CABG, P<0.001), most likely because of the greater logistical complexity in scheduling CABG. There were no differences between treatment groups in the length of time between intervention and the 6-month or 1-year SAQ completion dates (6 months, 193.1 days for PCI versus 196.0 days for CABG, P=0.12; 1 year, 383.4 days versus 389.4 days, P=0.50). In both treatment groups, there was a tendency for patients with missing SAQ data to have a greater degree of comorbidity than patients with complete data. At baseline, there were insignificant trends toward lower SAQ scores for all scales except treatment satisfaction with CABG. At 6 months, there were better scores for all scales except treatment satisfaction with CABG. At 1 year, there was a better score for angina frequency in the CABG group.
Unadjusted, imputed average scores for each SAQ domain at each time point by treatment group are shown in Figure 1. No significant differences between treatment groups in baseline scores were found for any domain, either before or after adjustment for baseline covariates. The population was moderately limited in physical functioning because of angina, had stable angina several times per week, and perceived their quality of life to be quite limited by angina. Treatment satisfaction was high for both treatment groups at baseline, as well as at both 6- and 12-month follow-ups.
At both 6 months and 1 year, physical limitation, angina frequency, and quality of life improved from baseline within each treatment group both before and after adjustment for significant covariates. At 6 months, the mean improvement ranged from 16.5 to 35.1 points in unadjusted analyses and from 13.6 to 34.7 points in adjusted analyses. At 12 months, the mean improvement ranged from 17.7 to 34.9 points in unadjusted analyses and from 14.3 to 38.2 points in adjusted analyses (all P<0.001). CABG patients had significantly greater improvement from baseline at 6 months than PCI patients for each of these 3 domains (differences between treatment groups: 5.13 to 7.77 points in unadjusted analyses, 4.03 to 6.48 points in adjusted analyses). Although the magnitude of the relative effect of CABG versus PCI decreased between 6 months and 1 year (differences at 12 months: 3.62 to 4.60 points in unadjusted analyses, 2.05 to 2.93 points in adjusted analyses), it remained statistically significant for all 3 domains in the unadjusted analyses and for the angina frequency and physical limitation domains in the adjusted analyses (Figure 2). The greatest overall changes from baseline, as well as the greatest influence of CABG versus PCI, were seen for the angina frequency domain. At 6 months, adjusted changes from baseline in angina frequency were on average 6.48 points (95% CI 3.96 to 8.99) greater for CABG than for stent-assisted PCI (Figure 2).
To better explain differences in health status between treatment groups, an additional analysis was performed to investigate the effect of repeat revascularization on the relative benefit of CABG versus PCI. Little difference in follow-up SAQ scores was observed between PCI patients who did not require repeat intervention and CABG patients (Table 2). However, among those PCI patients who required a repeat revascularization, average SAQ scores at 6-month follow-up were particularly low (P<0.05 for all scores compared with CABG). The health status of these patients improved substantially between 6 months and 1 year but remained lower than the average scores for CABG patients (P<0.05 for all scores) or PCI patients not undergoing repeat revascularization.
We performed additional analyses that examined the influence of missing data on the overall results. Data were missing because the SAQ was not administered or filled out completely (reflected by varying degrees of missing data across domains) or because of death that occurred before the follow-up visit. Our primary analysis, the results of which are described above, excluded patients who died before follow-up and was based on the data set for which missing scores for surviving subjects were estimated by multiple imputation. Three additional sets of analyses were performed for each of 3 SAQ domains to examine the separate and combined effects of imputation versus no imputation and exclusion of patients who died versus setting SAQ scores for patients who died equal to zero (the worst score) on the estimated effect of CABG versus PCI. Table 3 summarizes results from these analyses; the coefficient for the estimated effect of CABG versus PCI is presented (with corresponding probability value), as well as the significant predictors for models corresponding to each follow-up time point. Note that for each of the domains, the second row of results corresponds to the primary overall analysis, described previously. Although changes from baseline within each domain are consistently estimated to be greater for CABG than for PCI, the magnitude and statistical significance of the effect of CABG versus PCI is larger for models based on unimputed (versus imputed) data and for models that set scores for patients who died equal to zero versus excluding them from the analysis. Results from the primary analysis performed on the imputed data set for all surviving patients yielded the lowest, or most conservative, estimate of the CABG effect. These results suggest that CABG patients with missing SAQ data were estimated to have poorer health status than CABG patients with nonmissing data. The greater estimated effect of CABG on SAQ scores from the analyses that set scores equal to zero for patients who died is due to the significantly greater death rate in the PCI group.
Both CABG and stent-assisted PCI resulted in significant improvement in angina-related health status at 6 months and 1 year after intervention. In the SoS trial, the survival advantage of CABG was an unanticipated finding. Although CABG is initially much more expensive, this cost advantage of PCI may be lost, largely because of frequent additional procedures over time. Therefore, justification for CABG versus PCI might reasonably be based on the comparison of patients’ functional status/quality of life in the postintervention period.
Cardiac-Related Health Status
The focus of cardiovascular patient care is not curative but rather management of chronic illness, including alleviation of symptoms, improvement of functional capability, and retardation of disease progression.2 In other words, the focus is to restore the patient to as normal a life as possible. As a result, evidence of a meaningful benefit from the patient perspective is an important consideration in the comparison of treatment strategies for patients with CAD.1 Researchers have used either generic measures, such as the 36-item Short Form (SF-36),16 or disease-specific health status measures, such as the SAQ,12,13 to monitor a patient’s health status after intervention. Generic measures provide a broad assessment of health status and allow comparisons of health-related quality of life between groups of patients with different conditions. Disease-specific instruments are designed to measure health-related quality of life by assessing those areas of life that may be most affected by the specific disease or condition.17,18 The SAQ is more sensitive and responsive to detecting changes in angina-related health status than the SF-36, and it provides more clinically relevant information with respect to the disease of interest.18 The SAQ has been used in other clinical trials (not comparing CABG to PCI) either as an end point19–21 or as a predictor of outcomes14 for patients with CAD.
Comparison With Previous Studies
Previous studies in the early and late 1990s that compared health status and quality of life in patients treated with CABG versus PCI used generic measures such as the Duke Activity Status Index6 or the Nottingham Health Profile.8,9 Those studies reported that CABG was associated with greater improvement in quality of life after intervention.6–9,22 Previous randomized trial comparisons of PCI and CABG have not used a disease-specific instrument to examine angina burden and its associated effect on functional status and quality of life. One previous nonrandomized comparison of health status comparing PCI to CABG used the SAQ and showed results similar to those of the present study.23
The present study has shown improved health status after either PCI or CABG and, consistent with previous trials, greater improvement with CABG. Although the present study also found improved survival with CABG, this is not consistent with results from other studies, except for patients with treated diabetes in the Bypass Angioplasty Revascularization Investigation (BARI) trial.24 Although these results might suggest that CABG should be the first choice for revascularization for this patient population, there is greater variation in outcome within the revascularization arms than between the arms. Furthermore, many patients may not be willing to undergo the greater initial suffering of CABG compared with PCI to achieve the margin of improved health status after recovery. Thus, these results from SoS should be used to help inform decision making rather than as a definitive prescription for CABG in all cases.
Limitations of the Study
Although this study provides important information about comparative improvement in disease-specific health status, there are some limitations. One-year follow-up may not reflect the true long-term effect of CABG versus stent-assisted PCI on cardiac-related health status. Treatment group assignment was not blinded, and the patients’ knowledge of the procedure they received may have influenced responses to the SAQ questionnaire. However, the import of patients’ perspectives of their illness is unquestioned and congruent with the recent suggestion by the Institute of Medicine to make the healthcare system more patient centered.25 Also, SAQ data were not collected during the early recovery period, and there may be relevant differences between procedures in the early recovery process.
Finally, PCI patients who require repeat revascularization were the ones who accounted for much of the difference in health status between PCI and CABG. The advent of drug-eluting stents may decrease restenosis and the need for subsequent revascularization and thereby attenuate the difference in health status between PCI and CABG.
In summary, this is the first randomized study to compare improvement in cardiac-related health status, using a disease-specific instrument to evaluate the burden of angina, in patients undergoing stent-assisted PCI versus CABG. The results show that CABG is more effective than PCI in relieving angina, increasing physical functioning, and improving quality of life during the first year after revascularization. Patient-centered functional status outcomes, such as cardiac-related health status as measured by the SAQ, when incorporated into the clinical trials, can provide critical data from which to inform patient management.
This study was supported by Bard (now Medtronic), Tolochennaz, Switzerland; Guidant, Santa Clara, Calif; and Schneider (now Boston Scientific), Ratingen, Germany. The authors thank the SoS investigators, who are listed in the SoS main clinical paper.
Dr Stables has received grants from Bard (now Medtronic; Tolochennaz, Switzerland), Guidant (Santa Clara, Calif), and Schneider (now Boston Scientific; Ratingen, Germany). The SoS Trial was supported by funding from a consortium of stent manufacturers, as follows: Bard, Guidant ACS, and Schneider. Funding was given to the Royal Brompton Clinical Trials and Evaluation Unit, who are employees of Drs Booth and Nugara. The study design, data management and analysis, and reporting were independent of funding organizations. Dr Spertus owns the copyright to the Seattle Angina Questionnaire.
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