Special Article
Use of Medical Resources and Quality of Life after Acute Myocardial Infarction in Canada and the United States
N Engl J Med 1994; 331:1130-1135October 27, 1994
- Abstract
Background
Much attention has been directed to the use of medical resources and to patients' outcomes in Canada as compared with the United States. We compared U.S. and Canadian patients with respect to their use of medical resources and their quality of life during the year after acute myocardial infarction.
Methods
A total of 2600 U.S. and 400 Canadian patients were randomly selected from the Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries (GUSTO) trial. Base-line data from their initial hospitalizations were analyzed, and the patients were then interviewed by telephone 30 days, 6 months, and 1 year after myocardial infarction to determine their use of medical care and quality of life.
Results
The Canadian patients typically stayed in the hospital one day longer (P = 0.009) than the U.S. patients but had a much lower rate of cardiac catheterization (25 percent vs. 72 percent, P<0.001), coronary angioplasty (11 percent vs. 29 percent, P<0.001), and coronary bypass surgery (3 percent vs. 14 percent, P<0.001). At one year 24 percent of the Canadian and 53 percent of the U.S. patients had undergone angioplasty or bypass surgery at least once (P<0.001). The Canadians had more visits to physicians during the follow-up year (P<0.001), but fewer visits to specialists (P<0.001). At 30 days, functional status was equivalent in the patients from the two countries. However, after one year the U.S. patients had substantially more improvement than the Canadian patients (P<0.001). The prevalence of chest pain and dyspnea at one year was higher among the Canadian patients (34 percent vs. 21 percent and 45 percent vs. 29 percent, respectively; P<0.001).
Conclusions
The Canadian patients had more cardiac symptoms and worse functional status one year after acute myocardial infarction than the U.S. patients. The Canadian patients also underwent fewer invasive cardiac procedures and had fewer visits to specialist physicians. These results suggest, but do not prove, that the more aggressive pattern of care in the United States may have been responsible for the better quality of life.
Media in This Article
Figure 1
Outpatient Visits to Physicians during the Postinfarction Year, According to Country, along with Visits to Cardiologists, Internists, and Family or General Practitioners.Figure 2
Status of Cardiac Symptoms at One Year.Article Activity
- Article
Many studies have compared the structure and process of health care in the United States with those in Canada, but few have examined medical outcomes and almost none have compared quality of life1. Recently, Rouleau and colleagues compared U.S. and Canadian patients after acute myocardial infarction2. They found significantly more use of coronary angiography and coronary-revascularization procedures in the United States but equivalent mortality and rates of reinfarction. Although quality of life was not assessed, these investigators did find a significantly higher incidence of activity-limiting angina at one year in Canada.
From 1990 to 1993, the Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries (GUSTO) trial enrolled 41,021 patients with acute myocardial infarction in 15 countries in a randomized comparison of four strategies of thrombolytic treatment3. In the present study, a substudy of GUSTO, we examined patterns of medical practice and quality-of-life outcomes in a randomly selected subgroup of patients from Canada and the United States during the year after myocardial infarction.
Methods
Patients
The eligibility criteria for the GUSTO trial have been described previously3. Briefly, patients presenting to a participating hospital within six hours of the onset of symptoms consistent with a diagnosis of acute myocardial infarction and with electrocardiographic ST-segment elevation were eligible for enrollment unless they had had a previous stroke, were actively bleeding, or met other standard exclusion criteria for thrombolysis.
Overview of the Substudy
Patients from North America who were enrolled in the trial were randomly selected for additional participation in a substudy on economics and quality of life in GUSTO. The sampling fraction was approximately 1 in 8, yielding an enrollment in the substudy of 2600 U.S. patients (out of 23,105) and 400 Canadian patients (out of 2898). The substudy patients were contacted by telephone 30 days, 6 months, and 1 year after myocardial infarction. At 30 days and 1 year, they were asked to participate in a detailed 20- to 30-minute structured interview covering their medical care during the interval and their current health-related quality of life. At six months, they had a 10-minute structured interview covering medical care during the interval and selected quality-of-life measures. In the case of patients who died or were unable to be interviewed, a proxy interview concentrating on medical care during the interval was conducted with a member of the household or the nearest relative. No subjective assessments of quality of life were made on the basis of the proxy interviews. Interviews in the United States were conducted by the computer-assisted telephone interview unit of the Research Triangle Institute, whereas those in Canada were carried out by members of the Duke Coordinating Center staff and by a nurse in Quebec in the case of French-speaking participants. All the interviewers were trained at the beginning of the study by the senior coordinator of the substudy.
Data on Consumption of Medical Resources
Data on the consumption of medical resources from the time of the base-line hospitalization were collected on the case-report form3. In each follow-up interview, patients were asked about medical care during the interval, including rehospitalization, cardiac catheterization, coronary angioplasty, coronary bypass surgery, myocardial infarction, nursing home placement, and outpatient visits to 11 different types of practitioners or care facilities. All cardiac procedures reported by the patients were documented from the source by checking both the occurrence and the date or dates of the procedure with the relevant facility providing medical care.
Quality-of-Life Assessment
We measured quality of life in five major domains with a battery of instruments4. Functional status was assessed with the Duke Activity Status Index,5 the Katz Activities of Daily Living Scale6 (at one year only), a single four-level question about the effects of the patient's health on overall functioning, and questions about bed days and reduced-activity days taken from the National Health Interview Survey7. Angina and dyspnea were assessed with the Rose questionnaires8. Perceptions of general health were assessed on a scale ranging from excellent to poor that was taken from the National Health Interview Survey7. Employment status was evaluated with a detailed set of questions adapted from the Bypass Angioplasty Revascularization Investigation9. General psychological well-being was evaluated with a 10-item scale created for this study from published instruments (available on request from Dr. Mark). In addition, the brief Carroll Depression Scale was used to assess depression10. In conjunction with these health-related quality-of-life assessments, we measured patients' preferences for their own states of health relative to excellent health at 30 days and 1 year11,12. At the one-year follow-up point, patients were also asked to rate their overall health on a scale ranging from 0 to 100, on which 100 represented excellent health.
Statistical Analysis
For the present study, all four thrombolytic treatment groups were combined and the U.S. and Canadian patients were compared. The descriptive statistics for this study are presented as medians and interquartile ranges (25th and 75th percentiles) in the case of continuous variables and as percentages in the case of discrete variables. Univariate testing was performed with standard contingency-table chi-square tests or Fisher's exact test for categorical variables and the Wilcoxon rank-sum test for continuous variables. Kaplan-Meier survival estimates (unadjusted) and the Cox proportional-hazards regression model (adjusted) were used to compare the complete U.S. and Canadian GUSTO cohorts with respect to survival to one year13,14. One-year mortality data for the entire North American cohort are 99 percent complete. For this substudy, interviews with patients (including proxies) were conducted with 96 percent of the scheduled follow-up contacts in both countries (there was a 1.6 percent refusal rate and a 2.1 percent loss to follow-up at one year). Multivariable linear-regression analysis was used to examine the relation of different degrees of revascularization during the first 30 days of the study to subsequent changes in functional status, as reflected in the Duke Activity Status Index. All reported P values are two-tailed.
Results
Base-Line Characteristics and Medical Treatment
The clinical characteristics of the patients with acute myocardial infarction in Canada and the United States were generally similar at entry (Table 1Table 1
Characteristics of the Study Patients at Presentation.). More Canadians had a history of angina (P = 0.02), whereas more U.S. patients had a previous coronary angioplasty (P<0.001). Fewer Canadians had a history of hypertension, but the distribution of blood pressures at admission was significantly higher in Canada than in the United States. In-hospital use of intravenous nitroglycerin, intravenous beta-blockers, and lidocaine was more common in the United States (all P<0.001). At discharge, however, significantly more Canadian patients were sent home taking beta-blockers (P = 0.001) and angiotensin-converting-enzyme inhibitors (P = 0.02), whereas significantly more U.S. patients went home taking nitrates (P = 0.001), calcium blockers (P<0.001), or digitalis (P<0.001).Consumption of Medical Resources
Base-Line Hospitalization
The initial hospitalization lasted one day longer in Canada than in the United States (P = 0.009), whereas the length of stay in the intensive care unit was identical in the two countries (P = 0.81). More U.S. patients were hospitalized initially at a facility with the capability of performing cardiac catheterization (80 percent vs. 38 percent, P<0.001), angioplasty (56 percent vs. 34 percent, P<0.001), and bypass surgery (55 percent vs. 30 percent, P<0.001). Cardiac procedures were performed during the hospitalization for acute myocardial infarction significantly more often in U.S. patients: angiography in 72 percent, as compared with 25 percent of the Canadian patients (P<0.001); coronary angioplasty in 29 percent, as compared with 11 percent (P<0.001); and coronary bypass surgery in 14 percent, as compared with 3 percent (P<0.001). Similar trends were seen in the use of invasive procedures in the intensive care unit: among patients who did not undergo bypass surgery, U.S. patients received more pulmonary-artery catheters (11 percent vs. 3 percent, P<0.001), temporary transvenous pacemakers (7 percent vs. 4 percent, P = 0.03), intraaortic balloon pumps (4 percent vs. <1 percent, P<0.001), and mechanical ventilators (6 percent vs. 3 percent, P = 0.008).
Follow-up
The higher use of cardiac catheterization and revascularization in the United States persisted throughout the one-year follow-up. By the end of one year, 24 percent of the Canadian patients and 53 percent of the U.S. patients had undergone coronary angioplasty or bypass surgery at least once (P<0.001). Cardiac procedures were also performed sooner after infarction in the United States: for angiography, a median of 4 vs. 11 days (P<0.001), and for revascularization, 5 vs. 16 days (P<0.001).
Canadian patients were significantly more likely to visit a physician during the year after their myocardial infarction but were significantly less likely to visit a specialist (Figure 1Figure 1
Outpatient Visits to Physicians during the Postinfarction Year, According to Country, along with Visits to Cardiologists, Internists, and Family or General Practitioners.). Participation in cardiac-rehabilitation programs was significantly more common in the United States (38 percent, vs. 32 percent in Canada; P = 0.02).Medical and Quality-of-Life Outcomes
Survival, Reinfarction, and Stroke
The unadjusted survival rates for the entire U.S. cohort of 23,105 patients at 24 hours, 30 days, and 1 year were 97.3, 93.2, and 90.7 percent, respectively. The corresponding figures for the entire Canadian cohort of 2898 patients were 96.8, 92.4, and 90.3 percent, respectively (P = 0.33 for unadjusted comparisons). After adjustment for all available base-line prognostic factors with the Cox regression model, the U.S. cohort had a significantly higher survival than the Canadian cohort (P = 0.02). In-hospital reinfarction occurred in 3.7 percent of the U.S. and 4.5 percent of the Canadian patients in GUSTO (P = 0.06), whereas recurrent myocardial ischemia occurred in the hospital in 22 percent and 24 percent, respectively (P = 0.30). Rates of reinfarction after discharge were not assessed in this study. In-hospital stroke occurred in 1.6 percent of the U.S. and 1.5 percent of the Canadian patients (P = 0.69).
Quality of Life
One month after myocardial infarction, the Canadian and the U.S. participants reported generally comparable functional status as assessed by the Duke Activity Status Index, but by the end of one year of follow-up, the Canadian participants reported generally lower physical and emotional status (Table 2Table 2
Selected Quality-of-Life Measures at 30 Days and 1 Year.). The change in scores for individual patients from 30 days to 1 year, as well as the patients' own assessments of changes at 1 year relative to their status before myocardial infarction (Table 3Table 3
Changes in Quality of Life over the Course of One Year.) confirmed that significantly more Canadian than U.S. patients regarded their status as having worsened at 1 year. These results paralleled the findings with respect to symptoms, in which significantly more Canadians reported chest pain (34 percent vs. 21 percent) and dyspnea (45 percent vs. 29 percent) at one year (Figure 2Figure 2Status of Cardiac Symptoms at One Year.).General perceptions of health (rated from excellent to poor) were equivalent at both 30 days and 1 year, but general health at 1 year, rated on a scale from 0 to 100, was better in the U.S. cohort (Table 2). Employment status and number of hours worked per week were equivalent before myocardial infarction and at 1 year in the two groups (Table 2), but the time before a return to work after myocardial infarction was shorter in the United States: median, 58 days (25th to 75th percentile, 30 to 100 days), as compared with 81 days in Canada (25th to 75th percentile, 45 to 162 days; P<0.001). Among patients who were working at one year (either for pay or in the home), the amount and quality of work as compared with those before the myocardial infarction were considered the same in the two cohorts, but Canadians adjusted their work activities more often because of their health (Table 3).
Coronary Revascularization and Quality-of-Life Outcomes at One Year
For patients who did not have coronary angioplasty or bypass surgery within the first 30 days after enroll ment, the distribution of Duke Activity Status Index scores at 30 days was very similar in the two countries (Figure 3Figure 3
Comparison of 30-Day and 1-Year Values on the Duke Activity Status Index, According to Revascularization Status at 30 Days.). By one year, however, although both cohorts improved significantly, the scores for the U.S. cohort had shifted up in relation to those of the Canadian cohort (P<0.001). Patients from the two countries who underwent revascularization in the first 30 days had equivalent Duke Activity Status Index scores at 30 days (P = 0.47) and higher scores in the United States at 1 year (P = 0.03).In a multiple linear-regression model with the change in Duke Activity Status Index between 30 days and 1 year used as the dependent variable and with adjustment for the 30-day score and other predictors of change in this measure (including sex, education, prior myocardial infarction, and prior angina), undergoing revascularization in the first 30 days predicted a 2.3-point increase in the Duke Activity Status Index (P<0.001), whereas being a U.S. rather than a Canadian patient independently predicted a 3.6-point increment at 1 year (P<0.001).
Discussion
In this prospective comparison of 2600 U.S. and 400 Canadian patients, the U.S. participants had a substantially better quality of life one year after acute myocardial infarction. Previous studies have reported more activity-limiting angina2 and lower scores on the Duke Activity Status Index15 after myocardial infarction in Canadian than in U.S. patients. The present study extends these observations with a broader quality-of-life assessment. Our results challenge the contention that the greater use of cardiac procedures in the United States as compared with Canada2,15,16 has no effect on health outcomes.
One possible explanation for our findings is that the U.S. and Canadian subjects had important sociocultural differences in their perceptions of quality of life. Another is that the interviews were conducted differently. The similarity in the responses of the U.S. and Canadian patients at 30 days with regard to general health, functional status, and psychological status, with the subsequent emergence of increasing differences over the ensuing 11 months, argues against such explanations.
Another possible explanation for our findings is that the Canadians were more impaired than their U.S. counterparts at the time of enrollment in the study or had more severe myocardial infarctions. The absolute difference in rates of angina at entry (6 percent) seems unlikely to explain the observed differences in functional status at one year. Adjustment for levels of education and income, both of which were lower among the Canadian patients, did not affect the differences in one-year functional status. Furthermore, the severity of myocardial infarction was not greater in Canada, as evidenced by an equivalent prevalence of previous myocardial infarction and similar distributions of Killip class, infarct location, and initial heart rate.
The third possible explanation for our findings is that the differences in quality of life observed at follow-up were due to the different patterns of medical care in Canada and the United States. However, establishing a direct causal link between the different levels of use of invasive cardiac procedures or other aspects of care and subsequent quality-of-life outcomes is quite difficult. Revascularization procedures do affect health directly, but this effect is complex and is determined to an important degree by the level of impairment present before treatment. For example, if revascularization was applied in Canada primarily to patients with severe coronary disease who were too sick to recover completely, whereas in the United States a more aggressive approach was taken, with most of the moderately and severely impaired patients undergoing revascularization, such differences in the pattern of care could affect both the average difference between countries in one-year functional status and the functional status of subgroups defined by the presence or absence of a revascularization procedure during the preceding year. The difficulty of assigning a causal relation to these observations stems in part from our inability to obtain a true base-line assessment of quality of life. Such assessments were not feasible in the present study.
It is likely that other aspects of care besides revascularization account for some of the differences we observed in quality of life. A comparison of medication use shows a higher rate of early use of intravenous beta-blockers and nitrates in the United States. However, the in-hospital use of prophylactic lidocaine and calcium blockers (lower in Canada for both) and the use of beta-blockers and angiotensin-converting-enzyme inhibitors after discharge (both higher in Canada) conformed to a pattern of care in Canada more consistent with the results of recent randomized trials and meta-analyses. The greater use of specialty care in the United States during follow-up, including both more visits to specialist physicians and more use of cardiac-rehabilitation services, is another potential explanation for the observed differences. Furthermore, our regression analysis of changes in functional-status scores indicates a significant residual country-related effect that may well represent unmeasured differences in the process of care or in sociocultural factors.
There are several important limitations to our study. First, the participants at both the provider and the patient level were volunteers. The rates of invasive cardiac procedures for Canada in this study were substantially higher than is typical of the country overall. Physicians participating in the trial in these countries were probably more aggressive and perhaps more technologically oriented than the overall population of physicians caring for patients with acute myocardial infarction. On balance, it seems likely that the use of volunteer sites and patients would act to reduce variation and increase similarity between countries.
Second, since quality of life is a subjective phenomenon, proof that the assessment instruments used in a particular study measured what they were intended to measure (and nothing else) is always indirect and incomplete4. To minimize this problem, we used a battery of standard instruments instead of relying on a single instrument; the consistency of our results with multiple types of measures argues against problems of validity involving any particular scale.
Although most measures of quality of life in this study showed consistently more favorable outcomes for U.S. patients, two important measures did not. The patients' perceptions of general health, rated from excellent to poor on an ordinal scale, were similar at both 30 days and 1 year. In contrast were the patients' ratings of their current health (at one year) on a scale from 0 to 100 and their own comparisons with their status before myocardial infarction, both of which indicated more favorable outcomes in the U.S. patients. Employment rates were also similar in the two cohorts, both before myocardial infarction and at one year.
In conclusion, our results suggest that U.S. patients with acute myocardial infarction are likely to have better functional status and fewer cardiac symptoms during the first year after myocardial infarction than Canadian patients. The evidence from this study supports, but cannot definitively prove, the hypothesis that these superior outcomes are due to differences in the process of care -- specifically, the greater use of revascularization procedures and specialist services in the United States. Although these findings cannot be generalized to support arguments about the overall performance of one system as compared with the other, they should stimulate more careful and detailed assessment of the relation between structural aspects of different health care systems and associated health outcomes.
Supported in part by research grants (HS-05635 and HS-06503) from the Agency for Health Care Policy and Research; by a grant from Genentech, South San Francisco, Calif.; by research grants (HL-36587 and HL-17670) from the National Heart, Lung, and Blood Institute; and by a grant from the Robert Wood Johnson Foundation.
We are indebted to the North American GUSTO clinicians and study coordinators for their contributions to this project; to the GUSTO Steering Committee for reviewing the manuscript and substantially improving it with their suggestions; to Celia Hybels, M.S.P.H., Julia Burchett, M.A., and Marie-Claude Caron, R.N., for their extensive data-collection activities; and to Lori Baysden, Serena Smith, and Maria Lee for their assistance in the preparation of the manuscript.
Source Information
From the Economic and Quality of Life Research Group (D.B.M., J.D.K., C.L.N., N.E.C.-C.) and the Clinical Trials Coordinating Center (R.M.C., C.B.G., K.L.L.), the Division of Cardiology (D.B.M., R.M.C., C.B.G.), the Department of Medicine and the Division of Biometry, Department of Community and Family Medicine (K.L.L.), Duke University Medical Center, Durham, N.C.; the Department of Medicine, University of Toronto (C.D.N., W.S.), and the Institute for Clinical Evaluative Sciences (C.D.N.), Toronto; the Department of Medicine, University of Alberta, Edmonton (P.W.A.); the Division of Health Services Research, Department of Health Research and Policy, Stanford University Medical Center, Stanford, Calif. (M.A.H.); and the Department of Cardiology, Cleveland Clinic, Cleveland (E.J.T., L.P.).
Address reprint requests to Dr. Mark at P.O. Box 3485, Duke University Medical Center, Durham, NC 27708-3485.
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