Predictors of Quality-of-Life Benefit After Percutaneous Coronary Intervention
Background— Improving patients’ quality of life is a primary indication for percutaneous coronary intervention (PCI), yet little is known about patient characteristics associated with greater quality-of-life improvement from the procedure. This study was conducted to identify patient characteristics associated with quality-of-life benefit after PCI.
Methods and Results— A consecutive series of 1518 patients undergoing PCI in nonacute myocardial infarction settings were prospectively enrolled into an observational study documenting their postprocedural health status. We examined univariate and multivariable associations between baseline patient characteristics and quality of life 1 year after the procedure using the disease-specific Seattle Angina Questionnaire (SAQ) to quantify the impact of patients’ coronary disease on their quality of life. Baseline angina frequency and physical function were the strongest predictors of quality-of-life improvement 1 year after PCI. In comparing patients without angina to those experiencing monthly, weekly, and daily angina, the quality-of-life improvements (mean±SEM) were 21.4±2.1, 30.7±2.2, and 34.6±2.6 points greater (P<0.001). Patients with mild, moderate, and severe physical limitation improved 13.8±1.9, 20.0±2.1, and 13.5±3.5 points more than those with minimal baseline physical limitation (P<0.001). These findings were maintained in multivariable models correcting for baseline differences in demographic, clinical, disease-severity, and health-status variables.
Conclusions— Preprocedural angina frequency is the most important prognostic indicator of quality-of-life improvement after PCI. Although substantial quality-of-life benefits are attained in most patients with preprocedural angina, more careful consideration of the potential benefits and risks of the procedure are needed in asymptomatic patients.
Received July 5, 2004; revision received September 17, 2004; accepted September 29, 2004.
The most common indication for percutaneous coronary intervention (PCI) is to improve patients’ quality of life.1 Although numerous studies describe the efficacy of PCI for angina relief and quality-of-life improvement,2–10 few investigators have sought to define the characteristics of patients who derive the greatest quality-of-life improvement from the procedure. Addressing this gap in the literature can help clinicians identify those patients who are likely to derive the greatest benefit from the procedure, as well as those in whom more careful individualization of treatment recommendations is needed to determine whether the benefits of PCI outweigh the risks of the procedure.
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To identify preprocedural patient characteristics associated with quality-of-life improvement after PCI, we consecutively enrolled patients undergoing the procedure into a prospective registry that collected baseline demographic, medical, disease-severity, and health-status variables as well as patients’ 1-year quality of life. This study was designed to identify patient characteristics that can be used prospectively to predict patients’ quality-of-life improvement after PCI.
The processes of patient recruitment, success, and possible selection biases have been described previously.11 Data were collected from a consecutive series of patients undergoing PCI from February 8, 1999, to August 8, 2000, at the Mid-America Heart Institute in Kansas City, Mo. Among all 2762 patients who underwent PCI during this period, 5 (0.2%) died during the procedure, 5 (0.2%) required urgent bypass surgery, 60 (2%) were non–English speaking, 936 (34%) refused to participate, and only 125 (4.5%) could not be identified and interviewed before discharge. The remaining 1631 patients were recruited into an observational study documenting their postprocedural health status. Detailed clinical, procedural, and outcomes data, including health-status measures, were collected on each consenting patient. Health-status questionnaires were administered at the time of the patients’ procedures and 1 year later. Patients undergoing PCI for acute myocardial infarction (MI) (n=105) were excluded from these analyses, because the principal indication for primary revascularization is to extend survival, and improvements in quality of life are a secondary goal. In addition, procedural data were unavailable for 8 patients. Therefore, our analyses focus on the 1518 patients undergoing PCI for a quality-of-life benefit. Approval from the Institutional Review Board of Saint Luke’s Hospital was received before the start of the study.
To define predictors of improved quality of life after PCI, we used the disease-specific Seattle Angina Questionnaire (SAQ) to measure patients’ health status (their symptoms, function, and quality of life). The SAQ is a 19-item instrument that quantifies 5 clinically relevant domains of coronary disease, including physical limitation, change in anginal symptoms, angina frequency, satisfaction with treatment, and quality of life.12 It has well-established validity and reliability and is more sensitive to clinical change than generic health status measures.13 In addition, it has been shown to be predictive of 1-year mortality.14 The Angina Frequency, Physical Function, and Quality-of-Life scales were used to assess patients’ health status. Scores in these domains range from 0 to 100, where higher scores indicate better function, fewer symptoms, and better quality of life.
Quality of life is a multidimensional concept that is inversely related to the discrepancy between how patients are living and their desired symptoms and function.15,16 Thus, whereas 2 patients may have similar amounts of angina and physical limitation because of that angina, their quality of life may differ substantially because of differing expectations and needs. The greater the current manifestations of their disease deviate from their desired state, the worse their quality of life. The SAQ Quality-of-Life scale directly assesses patients’ perceptions of their quality of life by measuring patients’ enjoyment of life, their satisfaction with their current health state, and their fear of dying or having a heart attack. The SAQ Quality-of-Life domain at 1 year was the primary outcome of interest in this study.
Clinical and Procedural Assessments of Disease Severity
The Mid-America Heart Institute has maintained a procedural database for patients undergoing coronary interventions since 1982. Using data definitions compatible with the American College of Cardiology’s National Cardiovascular Data Registry,17 this database provides a detailed description of the patients’ coronary anatomy, the technique of revascularization, procedural results, and postprocedural complications.
Patients were contacted 1 year after their procedure for reassessment of their quality of life. Before patients were called, queries of the Social Security Administration Death Master File and local hospital records were conducted to minimize the likelihood of contacting the families of deceased patients. Patients were then contacted by telephone for an interview that included a report of their health status, interval events, and cardiac procedures outside of the Mid-America Heart Institute. A minimum of 8 and in some cases more than 20 attempts were made to contact each patient.
Because PCI is performed to improve patients’ quality of life, analyses were conducted to identify baseline patient characteristics associated with changes in quality of life. These included the demographic, clinical, and disease severity variables listed in Table 1. Baseline health status variables were also incorporated, including the SAQ Angina Frequency and Physical Limitation scores. To facilitate interpretation of patients’ health status, baseline Angina Frequency and Physical Limitation scores were each grouped into 4 ranges: Angina Frequency scores were grouped into daily angina (SAQ scores=0 to 30), weekly angina, (31–60), monthly angina (61–99), or no angina (100). Physical Limitation scores were grouped as severe limitation (0–25), moderate limitation (26–50), mild limitation (51–75), or slight to no limitation (>75).
Baseline characteristics associated with 1-year change in quality of life were evaluated using both univariate and multivariable models. Univariate associations were estimated using linear regression or 1-way ANOVA. To provide a patient-level assessment of quality-of-life benefit, an additional analysis was conducted to describe the proportion of patients who experienced a clinically significant (≥10-point) change in the SAQ Quality-of-Life scale by baseline frequency of angina and category of physical limitation.
Independent effects were then estimated by the construction of 3 general linear models. The first model included only the patients’ demographic (age, race, and sex) and clinical (previous revascularization, previous MI, hypertension, diabetes, hyperlipidemia, chronic obstructive pulmonary disease, renal insufficiency, and heart failure) characteristics. The second model added disease severity characteristics (number of diseased vessels and ejection fraction) to the first model. The final model included demographic, clinical, and disease severity characteristics along with the patients’ baseline health status (SAQ Physical Function and Angina Frequency scores). This order of model development provides a description of the incremental contribution from adding disease severity variables to the patient characteristics (model 2) and health status to patient and disease severity characteristics (model 3). To describe the strength of association between model variables and outcome, a coefficient of multiple determination (R2) was used.
Potential bias introduced by missing data was evaluated using propensity methods. Propensity scores were generated using logistic regression to estimate the probability of missing SAQ Quality-of-Life scores (n=498), incorporating all baseline demographic and clinical data as predictors. Models 1 to 3, predicting change in quality of life on the complete data, were then replicated after stratifying the population by quintile of propensity score. This allows a comparison of the models across subgroups of patients who were increasingly likely to have had missing data. All effect sizes for patient characteristics, disease severity, and baseline health status were comparable across propensity strata, and interaction terms by propensity were all nonsignificant (P>0.1). Furthermore, no consistent trend by likelihood of missing data was observed, suggesting that any observable selection biases in the results presented are likely to be minimal.
Descriptive summaries are presented as mean±SD for continuous variables and frequency and percent for categorical variables. Estimated effect sizes from regression models are presented as mean±SEM. Statistical significance was assumed when the 2-sided probability value was ≤0.05. Analyses were performed with SAS version 8.2 (SAS Institute, Inc) and R version 184.108.40.206a
Of 1518 eligible patients, 41 (2.7%) died before their 1-year follow-up. Of the surviving patients, 1020 (69%) completed the SAQ Quality-of-Life scale both at baseline and at 1-year follow-up; baseline characteristics are summarized in Table 1. The 498 patients who did not complete questionnaires were slightly younger (mean age, 64±12 versus 66±11 years, P=0.005) and more likely to be male (74% versus 69%, P=0.024). They also had slightly less frequent angina (mean SAQ Angina Frequency score, 71±27 versus 68±26, P=0.024) and had a slightly lower ejection fraction (48±12 versus 50±12, P=0.021). In addition, heart failure (13% versus 7%, P=0.001), renal insufficiency (10% versus 7%, P=0.04), and chronic obstructive pulmonary disease (13% versus 9%, P=0.006) were more prevalent in the group without complete follow-up. There were no other significant differences in the Table 1 variables between those with and without complete follow-up, and propensity models suggested no significant bias in observed results.
Improvement in Disease-Specific Quality of Life
Overall, PCI conferred substantial benefit to the population of patients who underwent the procedure. The mean (±SD) SAQ Physical Limitation, Angina Frequency, and Quality-of-Life scores increased by 18±25, 24±28, and 30±26 points, respectively (P<0.0001 for all). The large SD of change highlights the substantial variability of benefit observed for individual patients. Table 2 describes the estimated effects of different patient characteristics on the 1-year change in patients’ disease-specific quality of life after PCI. The first column presents the univariate results, whereas columns 2 to 4 provide adjusted estimates after controlling for demographic/clinical, disease severity, and health status characteristics, respectively.
Univariate models suggest that only age, baseline physical limitations because of angina, and preprocedural angina frequency were significantly related to improvements in quality of life. We observed a mean (±SE) improvement of 1.5±0.7 points on the SAQ Quality-of-Life scale for each 10-year increase in patient age (P<0.05). Compared with patients with little or no physical limitation (46% of the population), those with mild physical limitation (27%) experienced a 13.8±1.9-point greater quality-of-life improvement 1 year after PCI. Those who were moderately limited (21%) and those who were severely limited (6%) at baseline experienced 20±2.1- and 13.5±3.5-point greater quality-of-life improvements than those with minimal limitations at the time of their procedures (P<0.001). The most important predictor of quality-of-life benefit from PCI was preprocedural angina frequency. Compared with those without angina at baseline (23% of the population), patients with monthly (40%), weekly (21%), and daily (10%) angina had 21.4±2.1-, 30.7±2.2-, and 34.6±2.6-point greater disease-specific quality-of-life improvements (P<0.001).
These univariate relationships were largely maintained in the multivariable models. In the first model, which included only patient demographic and clinical characteristics, important predictors were age and previous revascularization, although neither was statistically significant. This model explained only 0.7% of the observed variance in quality-of-life benefit from PCI. Model 2, in which disease severity characteristics were added to model 1, explained only 1.2% of the variance in patients’ quality-of-life benefit after PCI.
In contrast to the minimal association of traditional patient factors with improvements in quality of life, the third multivariable model reveals that patients’ baseline health status contributes substantially to the quality-of-life benefits conferred by PCI. This model, including demographic, clinical, disease severity, and health status variables, explained 25.3% of the observed variance (R2) in quality-of-life improvements. The best predictor of quality-of-life improvement was patients’ frequency of angina before PCI. Patients with monthly, weekly, and daily angina improved 20.0±2.4, 28.3±2.5, and 32.0±3.2 points more than patients without angina at baseline (P<0.001). Patients’ physical limitations also remained a significant predictor of quality-of-life benefit. Compared with patients with little preprocedural physical limitation, those with mild, moderate, and severe limitation had SAQ Quality-of-Life improvements of 7.8±2.0, 12.8±2.2, and 4.7±3.6 points, respectively (P<0.001). Finally, age was also an independent predictor of quality-of-life benefit from PCI (2.0±0.7-point improvement per 10-year-greater age, P<0.01). Figure 1 illustrates the strength of association between baseline demographic, medical history, disease severity, and health status data. The gray bars represent the unadjusted results from those factors listed in each category (ie, demographic/medical history, disease severity, and health status), and the black bars reveal the strength to association in the fully adjusted model (ie, model 3 in Table 1).
Proportion of Patients Deriving a Meaningful Quality-of-Life Benefit From PCI
To provide a more interpretable description of the quality-of-life benefits associated with the presence of angina, we categorized change in SAQ Quality-of-Life scores into large deterioration (change <−20), moderate deterioration (−10 to −20), minimal change (−10 to +10), moderate improvement (+10 to +20) and large improvement (>+20). Figure 2 displays the distribution of change in patients with and without angina. Thirteen percent of patients without baseline angina had worse quality of life 1 year later, and 51% experienced no significant change, compared with 3% and 12% of those who had symptomatic angina at the time of PCI. Furthermore, only 17% and 19% of patients without angina experienced moderate and large improvements in their quality of life, compared with 13% and 72% of those with angina. These results underscore the critical role of angina at the time of PCI as a predictor of procedural benefit, from the patients’ perspectives.
To identify preprocedural patient characteristics associated with quality-of-life improvement from PCI, we prospectively enrolled a large, consecutive cohort of patients undergoing the procedure. We found that the only baseline characteristics independently associated with quality-of-life benefits 1 year after PCI were age, physical function, and angina frequency. The strongest predictor of benefit was preprocedural angina. Those with monthly, weekly, and daily angina experienced 21-, 31-, and 35-point greater improvements on the SAQ Quality-of-Life scale compared with those without angina. In fact, fewer than 36% of patients without angina had a clinically significant improvement in their quality of life, compared with more than 85% of those with at least some angina.
These insights provide an important complement to existing knowledge of patient outcomes after PCI. Although many investigators have described the impact of PCI on patient health status,2–10 only a few studies have examined which patient characteristics are most strongly associated with the quality-of-life benefits from PCI. In contrast, most studies have focused on cross-sectional associations that included patients’ symptoms at the time of follow-up and their influence on quality of life. For example, a 106-patient study by Permanyer-Miralda and colleagues18 demonstrated that residual angina after PCI was the most important determinant of lower 3-year quality of life. Similarly, Pocock and colleagues2,19 demonstrated important associations between angina, breathlessness, and physical function with 1-year quality of life. However, none of these studies focused primarily on changes in quality of life or patients’ preprocedural characteristics associated with greater quality-of-life benefits from the procedure.
One study examined preprocedural predictors of quality-of-life benefit. Nash and colleagues20 identified baseline Short Form-36 Physical and Mental Component Summary scores as the most important independent predictors of these domains at follow-up. By examining predictors of 6-month general health status scores, as opposed to change scores, these investigators modeled patients’ follow-up health status rather than the benefit they received from the procedure. We believe that the present analysis is more clinically relevant and extends the previous study by incorporating a more robust characterization of patients’ cardiac symptoms and function at the time of their PCI.
We believe that our data suggest an important opportunity to initiate a process for quantifying the appropriateness of PCI procedures. Since its introduction in the late 1970s, the frequency of PCI has grown substantially, with more than 1 200 000 procedures currently being performed annually in the United States alone.21 Furthermore, a 6-fold variation in its use has been documented among Medicare beneficiaries.22 Given the prevalence, expense, and variability of PCI, much work is needed to create tools that quantify the indications or “appropriateness” of PCI so that systematic efforts at quality assessment and improvement can be pursued. Although traditional “disease severity” variables such as ejection fraction, severity of coronary disease, etc, have been used previously to examine the appropriateness of PCI,23,24 they predict little of the quality-of-life benefits obtained by patients after PCI. Thus, although they may be applicable to mortality outcomes, they do not reflect the patients’ perspectives of the quality-of-life benefits from PCI. These study results suggest that angina symptoms should be one of the criteria for classifying an appropriate intervention and that greater scrutiny of the appropriateness of PCI in the 23% of asymptomatic patients should be considered.
Several potential limitations of this study should be considered. First, this was a single-center study, and it is possible that unique characteristics of the patients, the physicians, or the institution may limit the generalizability of these results. Further research should examine predictors of quality-of-life improvement in larger, multicenter studies. An additional concern is that only 69% of the patients involved in baseline analyses completed 1-year follow-up. However, lower follow-up is not uncommon in consecutive registries and may be offset by the benefit of a cohort that is more representative of the general patient population undergoing PCI than a secondary analysis of patients enrolled in a clinical trial. Although conducting these analyses in the context of clinical trials may allow higher rates of follow-up, the selection bias of who gets enrolled into the clinical trials may significantly offset this benefit.25 Furthermore, a propensity analysis based on the likelihood of missing data suggested that no significant biases were introduced into our documented association between worse preprocedural health status and greater quality-of-life benefits from the procedure. An additional limitation is that some patients undergoing PCI were not included in the registry. Although approached to participate, 34% refused. Although these patients may have introduced a bias in our results, current ethics of informed consent mandate obtaining patient approval, and there is no a priori reason to expect that the relationships defined by these analyses would be unique to only those who agreed to participate in our study.
Although considered good for models of health status outcomes, our best models still explained only 25.3% of the variation in patients’ quality-of-life benefits from PCI. Thus, some patients with no baseline angina may derive a substantial quality-of-life benefit from PCI, and conversely, some with daily angina may receive little benefit. Clinical judgment should dominate decisions on the application of PCI, although much greater benefit should be anticipated among those with greater symptomatic burden. Further research to define additional demographic, clinical, physiological, and genetic factors associated with patients’ quality-of-life benefits after PCI is warranted. Finally, it is possible that patients who received little quality-of-life benefit from the procedure may have done worse with medical therapy or that PCI could have prevented future worsening of their health status. Our findings should not be interpreted as a suggestion that PCI is inappropriate for patients with little baseline angina or good physical function. Rather, more careful consideration of the potential benefits versus risks of the procedure is necessary for minimally symptomatic patients.
This study provides an important step toward understanding the predictors of quality-of-life improvement after PCI. It is hoped that this information will allow clinicians to prospectively understand the degree of postprocedural benefit patients are likely to experience, thereby supporting medical decision-making and augmenting physicians’ ability to convey anticipated benefits to patients. This is an especially important contribution in light of evidence that patients often overestimate the likely benefits of PCI.26 Although further research should replicate this work, it appears that substantially less benefit, from the patients’ perspectives, should be anticipated when PCI is performed in asymptomatic individuals.
This project was supported in part by an unrestricted grant from Searle Pharmaceuticals and in part by grant R-01-HS-11282-01 from the Agency for Healthcare Research and Quality of Life.
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