Lower income, higher risk: disparities in treatments and outcomes of patients with acute myocardial infarction

Comment on the article ‘Differences in Treatment Patterns and Outcomes of Acute Myocardial Infarction for Low- and High-Income Patients in 6 Countries’, recently published in JAMA, https://doi.org/jama.2023.1699. This is a cross-sectional cohort study based on population-representative administrative data from an International Health System Research Collaborative (IHSRC) involving six countries [United States (USA), Canada (only two provinces), England, the Netherlands, Taiwan, and Israel)] aiming to determine whether treatment patterns and outcomes for elderly patients presenting with acute myocardial infarction (AMI) differ for low- vs. high-income individuals.1 The authors’ hypothesis was that there would be larger income-based disparities in the USA than in other countries. From 2013 to 2018, a total of 1 132 422 patients aged 66 years or older were hospitalized for at least 1 day (or died on the day of admission) with a primary diagnosis of ST-elevation MI (STEMI; n = 289 376) or non-STEMI (NSTEMI; n = 843 046) in any of the six IHSRC countries. Diagnoses were defined according to relevant International Classification of Diseases, Ninth Revision (ICD-9) and ICD-10 codes. High-income patients were defined as those living in areas (e.g. postal code) in the top 20% of the income distribution and low-income as those living in areas in the bottom 20% of the income distribution. The primary outcomes were 30-day and 1-year mortality, adjusted for age, sex, and comorbidities. Secondary outcomes included rates of cardiac catheterization, percutaneous coronary intervention (PCI), and coronary artery bypass graft (CABG) surgery, hospital length of stay (LOS) and readmission within 30 days of discharge. The incidence of STEMI and NSTEMI was higher for low-income patients than for high-income patients in all countries (e.g. STEMI incidence in the USA was 1.24 vs. 1.08 per 1000 among low- vs. high-income patients). Adjusted 30-day mortality was 1% to 3% lower (absolute difference) in high-income than in low-income patients for both STEMI and NSTEMI, with consistent results in all countries (except Taiwan). The largest differences were observed in Canada for STEMI [14.9% vs. 17.8%; difference, −2.9% (95% confidence interval, CI, −4.7% to −1.2%)] and Israel for NSTEMI [8.8% vs. 11.5%; difference, −2.8% (95% CI, −6.4% to 0.9%)]. Differences in adjusted 1-year mortality were even larger [e.g. −9.1% (95% CI, −16.7% to −1.6%) for STEMI and −6.7% (95% CI, −12.4% to −0.9%) for NSTEMI in Israel]. Cardiac catheterization and PCI rates were higher among high- vs. low-income patients in all countries, with the largest absolute differences recorded in England [i.e. 6.1% (95% CI, 1.2% to 11.0%) for PCI in STEMI and 6.5% (95% CI, 4.4% to 8.5%) for PCI in NSTEMI]. Rates of CABG surgery were comparable among low- vs. high-income patients presenting with STEMI, whereas they were 1% to 2% higher among high-income patients presenting with NSTEMI. Hospital LOS tended to be shorter (difference, 0.2–0.5 days) for high-income patients for both STEMI and NSTEMI. Rates of hospital readmission within 30 days were consistently lower for higher-income patients for both STEMI and NSTEMI, with absolute differences ranging from 1% to 3%. A great deal of data indicate that poverty is associated with reduced life expectancy, largely related to an increased mortality due to cardiovascular disease (CVD).2 A number of factors seem to contribute to this finding, including a greater burden of CV risk factors, limited opportunities to engage in healthier lifestyle behaviours, and difficulties in accessing health care facilities for lower-income populations.3 Over the past two decades, the identification of these issues has prompted considerable efforts in promoting CVD prevention, access to care, and quality of care, resulting in a significant decline of both AMI hospitalizations and mortality across all income groups.4 Yet, despite declining over time, AMI hospitalization rates remain higher in lower-income subgroups.4 Differences in the organization and financing of health systems might have an impact on income-based disparities in CV health care; however, only a small number of previous studies assessed between-country differences in health care for racial minorities or lower income populations, and these comparisons usually lacked detailed information on disease-specific processes of care and outcomes.5 This analysis of population-representative, administrative data of more than 1 million individuals has the major strength of focusing on AMI-specific treatment patterns and outcomes, and being representative of different countries with developed health care systems, albeit with significant heterogeneity in financing, organization, and performance in international rankings. Thirty-day and 1-year mortality rates were generally higher for low-income patients with AMI, whereas rates of cardiac catheterization and PCI were lower. These findings suggest that poverty and inequalities are present in all countries irrespective of culture, health care system, and social safety net. Of note, absolute differences in 30-day mortality between low- and high-income populations were of 2–3 percentage points (corresponding to a 10%–20% relative difference) for STEMI in almost all countries, which is comparable to the mortality benefit obtained with primary PCI itself.6 It is important to acknowledge that only patients older than 65 years were included in the analysis, which might have reduced income-based disparities, as older patients are eligible for Medicare coverage in the USA. Previous studies showed larger income-based disparities in health outcomes for adults aged 55 through 64 years as compared with older patients in the USA.7 A less aggressive management with lower rates of both cardiac catheterization and PCI might have contributed to the worse outcomes of low-income populations. Although the causes are likely multifactorial, the heterogeneous availability of hospitals that perform PCI and/or CABG surgery or the quality of health care within an area compared with another might explain, at least in part, these observations. Yet, both the incidence of MI and 30-day hospital readmission rates were consistently higher for low-income patients, suggesting that we may need to move the focus outside the health care delivery system to find additional areas for intervention, such as social determinants of health, and clinical prevention efforts in the outpatient setting (both primary and secondary prevention). It is a matter of fact that clinical practice is significantly more variable in the outpatient setting than in hospital care for AMI patients.8 For example, use of guideline-recommended medical therapies is both lower and more variable in the outpatient setting for primary and secondary AMI prevention compared with the in-hospital setting.8 Unfortunately, it is known from previous prevention initiatives that involvement of low-income subgroups and minorities can be challenging,9 suggesting that these programs need to be strategically widened to vulnerable populations to reduce disparities. This study has several limitations. First, the population included, by definition, had to be hospitalized due to AMI. Previous studies have shown that CV deaths prior to hospitalization are not infrequent, and disproportionately occur in low-income neighbourhoods, so that ascertainment bias cannot be excluded.10 Second, the income distributions used to define high- and low-income populations were based on regions within countries (except for Israel and England, where they were national). Regions and countries are large and heterogeneous, and more granular data on the quality of CV care received by AMI patients could not be obtained. Moreover, low-income regions usually have fewer residents than high-income ones, and are significantly more rural. Of note, rurality has been associated with adverse CV outcomes and shorter life expectancy.11 Finally, this analysis relied on administrative claims data, lacking detailed information about race and ethnicity, CV risk factors (e.g. smoking rates), AMI severity, or treatments, which represent potentially important confounders. Despite the improvements in admission rates and mortality for AMI achieved over the past two decades,4 significant income-based disparities persist even in countries with universal health insurance and robust social safety net systems. A better understanding of the underlying causes of disparities in AMI treatment patterns and outcomes at multiple levels (hospitals, cities, regions, and countries) should be the basis for future policies, programs, and nationwide campaigns in low-income populations, focusing improvement efforts not only on in-hospital care but also on social determinants of CV health and prevention. No new data were generated or analysed in support of this research. All authors declare no funding for this contribution.

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