Coronary artery disease (CAD) is an important public health problem, resulting in significant morbidity, mortality, and loss of productivity. In Canada, people of South Asian origin comprise one of the largest non-white ethnic groups and include people originating from India, Pakistan, Sri Lanka, Nepal, or Bangladesh. South Asians experience among the highest rates of CAD in Canada and the world.1,2 Both traditional and novel risk factors have been associated with the development of CAD in South Asians.3,4 Studies also suggest that South Asians develop CAD at an earlier age and experience heart failure prematurely.5 Although conventional risk factors such as blood pressure, tobacco use, and lipids are predictive of myocardial infarction in South Asians,2 abdominal obesity and insulin resistance seem to explain much of the excess risk noted in South Asians compared with other populations.6,7 The Framingham risk score is widely used for coronary risk assessment across North America, although studies suggest that this risk score may underestimate the true coronary heart disease risk in South Asians.8 Recently, a new web-based calculator for assessing the risk of heart disease in ethnic minorities in the UK has been developed by modification of the Framingham risk score. This approach does suggest that South Asians have a higher coronary risk compared with many other ethnic groups.9
The accumulation of visceral adipocytes (abdominal obesity) leads to metabolic derangements, including insulin resistance, that heighten the risk of both diabetes and CAD.10 A therapeutic strategy likely to confer considerable benefit to abdominally obese populations should therefore include regular exercise and dietary modification. In fact, lifestyle interventions such as these have been shown to significantly reduce the development of diabetes in subjects with impaired glucose tolerance.11,12 Specifically, regular exercise and weight loss have been shown to prevent diabetes in insulin-resistant South Asians.13 These important lifestyle interventions are traditionally offered through cardiac rehabilitation (CR) programs. Randomized, controlled trials and large-scale meta-analyses demonstrate that CR offers clinical benefits and substantive reductions in cardiac mortality.14,15
South Asians with CAD stand to benefit considerably from CR, in addition to evidence-based pharmacotherapy. However, South Asians have been historically underrepresented in studies evaluating the effectiveness of CR. Our study aims to compare South Asians and whites in Canada participating in 6-month outpatient CR programs with respect to cardiovascular risk factors, program compliance, and exercise outcomes.
A retrospective analysis was conducted of all patients participating in 2 outpatient, hospital-based CR programs over a 3-year period. Rehabilitation records from 2 large community-based hospitals in the Greater Toronto Area were reviewed: the Peel Memorial campus of the William Osler Health Centre and the Centenary site of the Rouge Valley Health System. Both hospitals serve large populations of South Asians and have high volumes of patients with acute coronary syndromes. In addition, these 2 hospitals are comparable in size, patient volumes, subspecialty services, and clinical quality indicators.16 Cardiac rehabilitation services at both hospitals are similar in that they both provide a 6-month, multifactorial CR program that incorporates exercise training, risk factor modification, education, and psychosocial support, with no differences in access. Patients are referred by their general physicians or cardiologists, attend intake and completion visits, and have graded exercise testing performed at both visits. There is no direct charge to the patient for CR services. The ethics review committees of both hospitals approved the study.
South Asian ethnicity was classified by analysis of patient surnames and first names and by using self-reported ethnicity and country of birth, when available, a process that has been previously validated for the assignment of ethnicity.17 Of 1,303 consecutive CR patients, 220 (17%) were South Asian and 980 (75%) were white. The remaining 103 (8%) were of other ethnic backgrounds and were excluded from further analysis.
Cardiac rehabilitation charts were then reviewed for patient demographics, presence or absence of traditional cardiovascular risk factors, medications on entry, compliance with CR, and exercise outcomes at 6 months. Data abstraction and collection were performed by 2 trained medical students under the supervision of a supervising cardiologist at each site. A random audit of 10% of South Asian charts and 5% of white charts was performed to ensure consistency and accuracy of data collection.
We computed χ2 tests of significance for comparisons of categorical variables with a P value of <.05 used for inclusion. Independent t tests also were used to assess for significant differences for continuous variables using Microsoft Excel, version 2003.
A comparison of patients between the 2 hospital sites was performed, but no substantive heterogeneity in baseline demographics was noted. Therefore, the data from both sites were combined, consisting of 503 patients from William Osler Health Centre and 800 patients from Rouge Valley Health System. All subsequent analyses were performed on the total data set. Table 1 shows key patient characteristics and relevant medications at entry into CR. Significant differences were noted between South Asians and whites. South Asian participants were younger, more often male, had lower body mass index (BMI), had lower rates of hypertension, were less often smokers, and were more often diabetic. Use of β-blockers and angiotensin-converting enzyme inhibitors at baseline was similar, but South Asians were more likely to be treated with aspirin and statins despite similar frequency of self-reported hyperlipidemia. Both populations exhibited high levels of triglycerides, raised levels of low-density lipoproteins, and reduced levels of high-density lipoproteins. Frequency of prior myocardial infarction was similar, but South Asians were more likely to have had prior coronary artery bypass grafting.
Significant sex differences were noted in the demographic and clinical characteristics of the South Asian patients (Table 2). South Asian women were older than South Asian men and were less likely to be current or former smokers but were more often diabetic. Prevalence of prior myocardial infarction was higher among South Asian men. No significant differences were observed in the use of medications, apart from β-blockers, which were used more often reached at least 85% of their target heart rate.
Compliance and Exercise Outcomes
Compliance with the 6-month CR program was relatively poor in both groups, but South Asians were less likely to complete the CR program than were whites (Table 3). Compliance among South Asian women was significantly lower than among white women (Figure 1). Baseline maximum metabolic equivalents (METS) were similar at baseline stress testing between South Asians and whites, although the levels were lower for white and South Asian women compared with white and South Asian men (Table 4). At the baseline exercise tolerance test, South Asians had lower systolic blood pressure and similar diastolic blood pressure. After 6 months, maximum METS achieved during the exercise tolerance test improved in both groups; however, South Asian patients trended to a greater change and more often reached at least 85% of their target heart rate (Table 3). Furthermore, the higher change in exercise capacity was demonstrated in South Asian men and women compared with white men and women (Table 4).
Recognizing the large benefits of CR, major guidelines advocate the prescription of CR for all patients after a coronary event.18 Given that South Asians seem to be at particularly high coronary risk, their participation in CR is likely to yield incremental benefits. However, CR remains an underused and underresourced intervention in the care and management of patients with coronary disease.19
This study reveals that South Asians are less likely to fully adhere to a 6-month CR program despite equal access and no cost barrier. The limited number of studies that have assessed CR uptake in patients from ethnic minority groups in the United Kingdom have found that uptake and adherence are especially low in those ethnic populations who are most likely to benefit from CR.20-22 These studies suggest that lack of physician referral, having a medical condition, inability to speak English fluently, and inaccessible transportation represent culture-specific barriers that may limit the ability of ethnic groups to participate in a rehabilitation program.23-25
South Asian women had significantly lower participation rates in our study. In general, women have lower attendance and higher dropout rates from outpatient CR programs compared with men.26,27 Despite lower participation, women of all ages benefit from CR, with improvements in exercise capacity and cardiac risk factors that are comparable with or exceed those of men.28 Previous reviews of CR attendance behaviors suggest that there may be sex-specific barriers to attendance.29,30 In the present study, South Asian women were, on average, 5 years older than South Asian men, consistent with previous reports that women participating in CR tend to be significantly older than men.31 In addition, older women are less likely to remain in CR than older men are, even when they present with similar clinical profiles.30 Further factors that may prevent women's participation in and adherence to CR include family and domestic responsibilities, inadequate social support, and limited access to transportation.32,33 Although these findings may be relevant for South Asian women, further studies are required to determine optimal strategies to facilitate the inclusion of South Asian women in CR programs.
This study demonstrates that South Asians derive benefit from CR, as this high-risk population had a greater increase in maximal achieved METS at exercise testing after completion of the program and were more likely to reach 85% of their target heart at the end of 6 months. This is evident among South Asian men and women. Considering that South Asians have lower physical activity patterns compared with the general population,34,35 it is worthy to note that they have the ability to improve functional capacity and thus potentially modulate their cardiac condition.
The clinical characteristics of the South Asian patients in our study were different from those of the white participants, confirming previous observations and validating that our patient population is typical of other South Asian cardiovascular cohorts. Individuals of South Asian origin had significantly higher rates of diabetes despite having lower BMI and also had lower smoking rates, findings consistent with those in other studies.3,4,36-40 In addition, South Asian women were more likely to enter CR with a diagnosis of diabetes, a general observation also reported in earlier studies.41,42 The overall higher prevalence of diabetes in the South Asian population could have contributed to the lower compliance, as diabetic patients withdraw more often from CR programs because of an exacerbation of the medical problem.43
South Asian adults with diabetes show a markedly increased predisposition to CAD compared with whites, particularly at younger ages.44 We have previously shown that South Asians are younger at the time of cardiac catheterization, have larger myocardial infarctions, and develop heart failure at a younger age.4,5 Therefore, it is not surprising that South Asians participating in CR are also younger than whites. Although employment data were not available, it is possible that younger patients, pressured to return to work compared with older and retired patients, may have difficulty complying with a CR program. The data here show a greater improvement in fitness in South Asians that may be related to their younger age, signifying that CR may offer greater improvements in quality of life and productivity to younger patient populations.45
There have been few reports on the efficacy of medications to treat CAD specifically among South Asians. Baseline use of evidence-based therapy was low in both groups. This may partly reflect practice patterns during the years that these data were collected. Patients received education regarding the importance of drug therapy (and medication adherence) as part of the rehabilitation program, but medication adherence data were not available to us. Statins were prescribed more often to South Asians despite similar rates of hyperlipidemia in both populations. In addition, our study reflects insulin resistance being commonly noted in South Asians experiencing dyslipidemia, particularly in having raised levels of triglycerides and low-density lipoprotein cholesterol and reduced high-density lipoprotein cholesterol.3-5 Because South Asians were more likely to be diabetic or to have had prior bypass surgery, statin use may have been higher because of a perceived higher risk attributed to South Asians.
This study has some limitations. It was based upon retrospective review of charts from 2 hospital sites, and thus, the results are not necessarily generalizable to the entire South Asian population. However, the communities served by these 2 hospitals are richly populated with South Asians and are likely representative of other, similar communities across Canada. Furthermore, determination of ethnicity was made retrospectively and may involve cross contamination of case participants based on surnames and given names of ambiguous ethnic origin. However, this method of ethnicity determination has been previously validated.17 The rehabilitation chart data were occasionally incomplete, although rates of incomplete data were similar among South Asian and white patients. The observation that South Asians were more likely to achieve 85% of their target heart rate may not have reflected a direct benefit from CR, as it is possible that rates of β-blocker use and dosing at the end of CR may have differed between South Asians and whites. Furthermore, the improved functional capacity seen in South Asians may be caused by a greater selection bias (because of the higher dropout rate) of those patients continuing for the full 6-month program. Finally, medication, lipid profiles, and BMI were reported only at baseline and were not documented at discharge from CR. Thus, we are unable to determine if adherence to medications or changes in surrogate outcomes such as BMI and lipid levels differed between ethnic groups. Long-term outcomes were also not available.
This seems to be the first study to examine (empirically) compliance and exercise-related outcomes among South Asians participating in a CR program. The low rates of participation in CR programs among South Asians in our study lead to fundamental questions about the accessibility and practicality of CR programs for various ethnic groups. Further research is required to better understand the barriers faced by South Asians for successfully participating in and completing CR programs. In addition, CR services need to be readily accessible and culturally appropriate for this high-risk ethnic population.
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