Introduction

Ischemic heart disease and specifically acute myocardial infarction continue to be leading cause of cardiovascular admissions in the United States [1–4]. ST-segment elevation myocardial infarction (STEMI) constitutes about 30% of all acute myocardial infarction admissions in the United Sates. Despite the improvements in early coronary angiography and prompt percutaneous coronary intervention (PCI), STEMI continues to be associated with considerable mortality and morbidity. In addition, STEMI is associated with high resource utilization with estimated costs of hospitalization of United States Dollars 21,000–26,000 [5].

In the United States, prior studies in cardiac and non-cardiac patient populations have demonstrated that insurance status may have an association with clinical outcomes [6–9]. In patients with STEMI, large retrospective studies have previously demonstrated the lack of health insurance and Medicaid status to be associated with worse mortality and higher readmission rates compared to patients with private insurance [7, 10, 11]. While this may be partially be due to socioeconomic factors, other contributing factors include lifestyle issues, a lack of access to care in uninsured populations, and a higher burden of comorbidities and issues with medication adherence in Medicaid populations that preclude PCI [7, 10]. As of 2018, approximately 8.5% of people in the US are uninsured, and of those who have insurance, approximately 34% have a public plan such as Medicare and Medicaid [12]. As the population in the United States grows older and has higher comorbidity, cardiovascular emergencies continue to be a leading health care issue [13].

In the current era, it is unclear if insurance status continues to play a role in the management and outcomes of STEMI [10]. Using an 18-year national database, we sought to assess the management and outcomes of STEMI by primary payer status. In addition, we evaluated the temporal trends in admissions, use of cardiac procedures, and clinical outcomes of these populations.

Material and methods

Results

In the period from January 1, 2000 to December 31, 2017, there were 4,320,097 STEMI admissions, of which primary payer status could not be ascertained in 9,394 (0.2%). In the final cohort of 4,310,703 STEMI admissions, Medicare, Medicaid, Private, Uninsured and Others constituted 2,113,356 (49.0%), 269,507 (6.3%), 1,484,385 (34.4%), 311,773 (7.2%) and 131,682 (3.1%), respectively. The Medicare cohort was significantly older than other groups, with higher prevalence of females, white race, and higher comorbidity (all p<0.001) (Table 1). The Medicare cohort had lower rates of inferior STEMI (39.2%) as compared to the rest (43.5–49.5%) (p<0.001). The Medicare and Medicaid population had higher rates of cardiogenic shock, cardiac arrest, respiratory failure, acute kidney injury and complication rates compared to the other groups (Table 1).

Table 1

Characteristics of STEMI admissions stratified by primary payer status.

Characteristics		Medicare	Medicaid	Private	Uninsured	Others	P
		(N = 2,113,356)	(N = 269,507)	(N = 1,484,385)	(N = 311,773)	(N = 131,682)
Age (years)		75.2 ± 10.4	54.0 ± 11.1	56.0 ± 10.2	52.5 ± 9.7	57.0 ± 11.5	<0.001
Female sex		46.2	36.1	23.4	23.9	20.4	<0.001
Weekend admission		25.8	27.2	27.6	27.4	26.6	<0.001
Race	White	66.0	47.9	63.0	55.0	55.9	<0.001
	Black	5.4	12.4	5.1	9.4	7.7
	Othersa	28.6	39.7	31.9	35.7	36.4
Quartile of median household income	0-25th percentile	22.9	34.9	16.5	31.1	26.4	<0.001
	26th-50th percentile	28.6	28.9	24.8	29.2	28.8
	51st-75th percentile	24.7	21.2	26.8	23.3	24.8
	75th-100th percentile	23.8	14.9	31.9	16.4	20.0
Charlson Comorbidity Index	0–3	23.5	75.4	79.6	85.6	75.0	<0.001
	4–6	58.4	21.1	17.9	13.1	21.3
	≥ 7	18.1	3.6	2.5	1.3	3.7
Hospital teaching status and location	Rural	16.0	9.6	7.8	10.1	12.2	<0.001
	Urban non-teaching	40.5	34.6	40.7	40.3	39.4
	Urban teaching	43.5	55.8	51.5	49.6	48.3
Hospital bed-size	Small	12.4	9.3	9.4	9.1	8.1	<0.001
	Medium	25.1	24.5	24.6	24.0	24.0
	Large	62.5	66.2	66.1	66.8	67.9
Hospital region	Northeast	18.6	21.4	18.6	11.6	9.0	<0.001
	Midwest	24.5	20.7	24.4	19.1	18.1
	South	39.2	33.4	37.7	55.2	46.9
	West	17.7	24.5	19.4	14.1	25.9
STEMI location	Anterior	31.1	34.6	33.3	34.5	33.2	<0.001
	Inferior	39.2	43.5	49.5	48.0	46.9	<0.001
	Other	29.3	21.4	17.1	17.4	19.1	<0.001
Cardiogenic shock		9.9	9.8	6.7	7.4	7.3	<0.001
Cardiac arrest		9.2	10.0	8.4	9.2	8.6	<0.001
Acute respiratory failure		11.2	11.0	6.5	7.6	7.7	<0.001
Acute kidney injury		11.9	9.2	5.1	5.6	6.6	<0.001
Systolic heart failure		5.4	6.2	3.1	3.9	4.0	<0.001
Vascular complications		1.0	0.9	0.9	0.7	0.9	<0.001
Hemorrhage		1.9	1.7	1.2	1.1	1.1	<0.001
Ischemic stroke		2.0	1.4	0.8	0.8	0.9	<0.001
Intracranial hemorrhage		0.4	0.3	0.2	0.2	0.2	<0.001
Intravascular ultrasound		1.2	2.3	2.0	2.0	1.7	<0.001
Coronary thrombectomy		0.9	2.0	1.3	1.3	1.4	<0.001
Pulmonary artery catheterization		1.5	1.5	1.2	1.1	1.2	<0.001
Invasive mechanical ventilation		10.1	10.6	6.2	7.5	7.2	<0.001
Hemodialysis		0.6	0.6	0.3	0.3	0.3	<0.001

Represented as percentage or mean ± standard deviation; ^aHispanic, Asian, Native American, Others

Abbreviations: STEMI: ST-segment-elevation myocardial infarction

Coronary angiography was used less frequently in the Medicare population (59.6%) compared to the other cohorts (77.4–82.2%) during this 18-year period. There was a steady increase in the use of coronary angiography across all insurance sub-groups; however the Medicare cohort had consistently lower use (Fig 1A). In adjusted analyses, compared to 2000, all primary payer cohorts showed a 5–6 fold increase in the use of coronary angiography in 2017 (Fig 1B). In a multivariable logistic regression analysis with Medicare population as referent category, coronary angiography was used less often in the Medicaid population (OR 0.93 [0.91–0.94]), and more often in all other populations–private insurance (OR 1.25 [95% CI 1.24–1.26]), uninsured (OR 1.09 [95% CI 1.07–1.10]) and other insurance (OR 1.14 [95% CI 1.12–1.16]); all p<0.001 (S2 Table). Early coronary angiography and PCI were performed less frequently in the Medicare population, and CABG was performed less frequently in the Medicare and uninsured admissions (Table 2). During this 18-year period, there was a steady increase in early coronary angiography and PCI use across all 5 cohorts; however the Medicare group had consistently lower utilization (Fig 2A and 2B). The Medicaid cohort had higher rates of mechanical circulatory support use compared to the other groups (Table 2). There was a steady decline in CABG use across all sub-groups and an initial peak till 2009 followed by a decline in mechanical circulatory support use across all cohorts (Fig 2C and 2D).

Fig 1

Temporal trends of coronary angiography use and in-hospital mortality in STEMI admissions stratified by insurance status.

A: 18-year unadjusted trends of in-hospital mortality in STEMI admissions; p<0.001 for trend over time; B: Adjusted multivariate logistic regression for temporal trends of in-hospital mortality in STEMI admissions (2000 as referent year)*; p<0.001 for trend over time; C: 18-year unadjusted trends of coronary angiography use in STEMI; all p<0.001 for trend over time; D: Adjusted multivariate logistic regression for temporal trends of coronary angiography use in STEMI admissions (2000 as referent year)**; p<0.001 for trend over time; *Adjusted for age, sex, race, socio-economic stratum, hospital characteristics, comorbidities, year of admission, STEMI location, cardiogenic shock, cardiac arrest, acute respiratory failure, acute kidney injury, systolic heart failure, prior CABG, complications, cardiac procedures, non-cardiac procedures, DNR status and palliative care referral; **Adjusted for age, sex, race, socio-economic stratum, hospital characteristics, comorbidities, year of admission, STEMI location, cardiogenic shock, cardiac arrest, do-not-resuscitate (DNR) status and palliative care referral; Abbreviations: STEMI: ST-segment elevation myocardial infarction.

Fig 2

Temporal trends in cardiac procedures use in STEMI admissions stratified by insurance status.

Eighteen-year trends of early coronary angiography (A), percutaneous coronary intervention (B), coronary artery bypass grafting (C), and mechanical circulatory support (D) in STEMI admissions stratified by insurance status; all p<0.001 for trend.

Table 2

Clinical outcomes of STEMI admissions stratified by primary payer status.

Outcomes		Medicare	Medicaid	Private	Uninsured	Others	P
		(N = 2,113,356)	(N = 269,507)	(N = 1,484,385)	(N = 311,773)	(N = 131,682)
In-hospital mortality		14.2	6.7	4.1	5.4	5.9	<0.001
Coronary angiography		59.6	77.4	82.2	82.2	79.3	<0.001
Early coronary angiography (day 0)		35.6	52.4	51.4	54.7	50.4	<0.001
Percutaneous coronary intervention		45.3	62.9	68.9	69.7	66.2	<0.001
Coronary artery bypass grafting		7.7	8.4	8.8	7.7	8.9	<0.001
Mechanical circulatory support	Total	7.9	9.7	8.4	8.2	8.2	<0.001
	IABP	7.6	9.2	8.1	7.9	7.9	<0.001
	pLVAD	0.3	0.5	0.3	0.3	0.3	<0.001
	ECMO	0.1	0.2	0.1	0.1	0.1	<0.001
Palliative care referral		1.9	1.0	0.6	0.6	1.7	<0.001
Do-not-resuscitate status		2.7	1.1	0.5	0.7	1.1	<0.001
Length of stay (days)		5.5 ± 6.3	5.5 ± 9.7	4.2 ± 5.0	4.2 ± 5.2	4.4 ± 5.3	<0.001
Hospitalization costs (x1000 USD)		59 ± 79	79 ± 111	63 ± 77	65 ± 69	66 ± 83	<0.001
Disposition	Home	55.6	74.7	79.5	83.2	78.8	<0.001
	Transfer	13.5	10.4	12.0	10.0	11.7
	Skilled nursing facility	18.5	5.6	3.3	1.8	4.4
	Home with HHC	11.8	6.8	4.7	2.8	3.9
	Against medical advice	0.6	2.5	0.4	2.3	1.2

Represented as percentage or mean ± standard deviation

Abbreviations: ECMO: extracorporeal membrane oxygenation; HHC: home health care; IABP: intra-aortic balloon pump; pLVAD: percutaneous left ventricular assist device; STEMI: ST-segment-elevation myocardial infarction; USD: United States Dollars

The unadjusted all-cause in-hospital mortality was the highest in the Medicare cohort (14.2%) compared to the other groups (4.1–6.7%) (Table 2). The Medicare population had consistently higher in-hospital mortality during the 18-year study period, despite a comparable decline in 2017 compared to 2000 across all cohorts (Fig 1C and 1D). In a multivariable logistic regression analysis with Medicare as the referent population, in-hospital mortality was higher in the uninsured (OR 1.14 [95% CI 1.11–1.16]), and lower in all other populations–Medicaid (OR 0.96 [95% CI 0.94–0.99]; p = 0.002), privately insured (OR 0.73 [95% CI 0.72–0.75]) and other insurance (OR 0.91 [95% CI 0.88–0.94]); all p<0.001 (S3 Table).

Multiple sensitivity analyses were performed to confirm the results of the primary findings. The primary results were consistent in all sub-groups except those aged >75 years and with use of palliative care referral and DNR status use (Table 3). The Medicare and Medicaid populations had longer lengths of hospital stay, and the Medicare population had the least hospitalization costs and fewer discharges to home (Table 2). Palliative care and DNR status use were low (<3%) with the highest rates in the Medicare population (Table 2).

Table 3

In-hospital mortality in STEMI admissions stratified by patient characteristics.

Patient characteristicsa			Odds ratio	95% confidence interval		P
				Lower Limit	Upper Limit
Age group	≤75 years	Medicare	Reference category
		Medicaid	0.69	0.67	0.71	<0.001
		Private	0.54	0.54	0.55	<0.001
		Uninsured	0.84	0.82	0.86	<0.001
		Others	0.64	0.62	0.67	<0.001
	>75 years	Medicare	Reference category
		Medicaid	0.91	0.86	0.97	0.002
		Private	1.03	1.00	1.05	0.048
		Uninsured	1.14	1.05	1.23	0.001
		Others	1.26	1.19	1.34	0.000
Sex	Male	Medicare	Reference category
		Medicaid	0.75	0.72	0.77	<0.001
		Private	0.60	0.59	0.61	<0.001
		Uninsured	0.91	0.89	0.94	<0.001
		Others	0.75	0.72	0.78	<0.001
	Female	Medicare	Reference category
		Medicaid	0.77	0.75	0.80	<0.001
		Private	0.67	0.66	0.69	<0.001
		Uninsured	0.87	0.84	0.91	<0.001
		Others	0.88	0.84	0.94	<0.001
Race	White	Medicare	Reference category
		Medicaid	0.75	0.72	0.77	<0.001
		Private	0.61	0.60	0.62	<0.001
		Uninsured	0.86	0.83	0.89	<0.001
		Others	0.77	0.74	0.80	<0.001
	Non-whiteb	Medicare	Reference category
		Medicaid	0.77	0.74	0.79	<0.001
		Private	0.64	0.63	0.66	<0.001
		Uninsured	0.93	0.90	0.96	<0.001
		Others	0.81	0.77	0.85	<0.001
Tertiles of study period	2000–2005	Medicare	Reference category
		Medicaid	0.84	0.81	0.86	<0.001
		Private	0.65	0.64	0.67	<0.001
		Uninsured	0.90	0.87	0.94	<0.001
		Others	0.78	0.74	0.81	<0.001
	2006–2011	Medicare	Reference category
		Medicaid	0.80	0.77	0.83	<0.001
		Private	0.67	0.66	0.69	<0.001
		Uninsured	0.96	0.92	1.00	0.06
		Others	0.81	0.77	0.86	<0.001
	2012–2017	Medicare	Reference category
		Medicaid	0.67	0.64	0.69	<0.001
		Private	0.57	0.56	0.59	<0.001
		Uninsured	0.89	0.85	0.93	<0.001
		Others	0.80	0.75	0.85	<0.001
Percutaneous coronary intervention	Yes	Medicare	Reference category
		Medicaid	0.73	0.71	0.76	<0.001
		Private	0.54	0.53	0.55	<0.001
		Uninsured	0.87	0.84	0.90	<0.001
		Others	0.65	0.62	0.69	<0.001
	No	Medicare	Reference category
		Medicaid	0.77	0.75	0.79	<0.001
		Private	0.70	0.68	0.71	<0.001
		Uninsured	0.90	0.88	0.93	<0.001
		Others	0.89	0.85	0.92	<0.001
Palliative care or do-not-resuscitate status	Yes	Medicare	Reference category
		Medicaid	0.94	0.86	1.02	0.11
		Private	1.38	1.31	1.45	<0.001
		Uninsured	1.47	1.32	1.63	<0.001
		Others	1.59	1.45	1.74	<0.001
	No	Medicare	Reference category
		Medicaid	0.75	0.74	0.77	<0.001
		Private	0.60	0.59	0.61	<0.001
		Uninsured	0.88	0.86	0.90	<0.001
		Others	0.74	0.72	0.77	<0.001

^aEach sub-group was adjusted for age, sex, race, socio-economic stratum, hospital characteristics, comorbidities, year of admission, STEMI location, cardiogenic shock, cardiac arrest, acute respiratory failure, acute kidney injury, systolic heart failure, prior CABG, complications, cardiac procedures, non-cardiac procedures, DNR status and palliative care referral

^bBlack, Hispanic, Asian, Native American, Others

Discussion

In the largest study looking at the influence of primary payer status on the outcomes of STEMI, we noted that the Medicare beneficiaries differed significantly in age, socio-demographic characteristics, and their clinical course. The Medicare beneficiaries consistently received less frequent guideline-directed procedures, had higher rates of in-hospital complications and worse in-hospital outcomes. Though age may partly explain these differences, there remain significant differences between the various insurance categories.

The data from this study are consistent with prior work from the HCUP-NIS database as well as other databases that have evaluated insurance-based disparities in STEMI care. A 2019 study by Patel et al used the HCUP-NIS database from 2012–2015 to compare STEMI outcomes in Medicaid and private insurance patients in a propensity-matched analysis, finding that there were higher rates of revascularization, lower in-hospital mortality, and a lower cost of hospitalization in patients with private insurance [7]. The authors provide several potential explanations for these findings including residual confounders despite propensity matching and provider reluctance to initiate dual antiplatelet therapy due to concerns for medication adherence. A 2018 study by Niedzwiecki et al that used AMI data from the California Office of State Health Planning and Development from 2001–2014, found that Medicaid populations, which had a disproportionately higher mix of black and Hispanic populations and higher prevalence of peripheral vascular disease, pulmonary disease, diabetes mellitus, and renal failure, had lower rates of PCI than privately insured and uninsured populations, with a significantly higher mortality at 30 days, 90 days, and 1 year [6]. In addition, these insurance categories further reinforce racial disparities in health care access and delivery. Notably, these outcomes held true even when the study was limited to STEMI populations, despite patients having a high likelihood of being admitted to PCI-capable hospitals. The authors hypothesized that financial factors may play a role as Medicaid reimbursement may be lower than that from uninsured population, as Medicaid rates in California are among the lowest in the United States. Similarly, a 2017 study by Pancholy et al, the authors use HCUP-NIS 2003–2014 database to study the effect of insurance status on the adult STEMI population [10]. In that study, the Medicare population had lower rates of coronary intervention than the other insurance categories, with higher rates of numerous in-hospital outcomes such as cardiogenic shock, pneumonia, gastrointestinal hemorrhage, acute stroke, and increased length of stay. Furthermore, vulnerable populations, such as older adults and racial minorities have poor awareness of symptoms and experience delays in seeking health care which may contribute to poorer outcomes in these populations [42, 43]. The lack of insurance was an independent risk factor for higher in-hospital mortality despite lower incidence of comorbidities, for which the authors suggest that the uninsured group likely has unrecognized disease associated with poor lifestyle choices and lack of preventative medicine [42, 43].

As noted in this study, the Medicare population appears to have consistently higher rates of in-hospital mortality than the other insurance groups, though this difference is declining over time. A large part of this is due to the intrinsic differences between the populations bearing Medicare versus other insurance types–the Medicare population is older, with higher comorbidity, and greater severity of illness [10]. However, importantly, the Medicare population consistently received lower rates of coronary angiography and PCI despite robust clinical guidelines [44]. The insurance-based disparities were prominent in those aged ≤75 years but not in older adults. Despite prior data showing the value of PCI in older adults, this study continues to note a lower use of PCI in this population [13, 45]. Despite being adjusted for comorbidities and acuity, the Medicare population continued to have worse in-hospital outcomes. This study that shows that Medicare and Medicaid populations had higher rates of invasive mechanical ventilation and hemodialysis compared to the other insurance populations, suggesting that the choice to reduce PCI usage in Medicare populations may have been a risk-avoidance strategy or the refusal of advanced care in older patients. While Medicaid populations seem to have relatively similar rates of these complications, the overall mortality is much lower than in Medicare populations, which is likely a function of being younger with lower comorbidity. This is consistent with the literature, as cardiovascular, pulmonary, and renal comorbidities have been associated with worse outcomes after STEMI [22, 23, 25, 26, 30]. Notably, in the current study, the Medicare population has lower hospitalization costs, possibly related to the lower coronary angiography rates, more frequent use of palliative care referral, higher rates of do-not-resuscitate status, and higher in-hospital mortality compared to patients with private insurance. It has been previously shown that older patients were more likely to have elected for DNR status, even when controlling for severity of illness, compared to younger populations [46]. Moreover, prior studies have demonstrated that DNR status was associated with higher mortality rates in patients with AMI, which is consistent with the results seen in this analysis [47]. Therefore, in this study and others, it appears that insurance status is closely related to social, economic, and environmental factors that need to be considered in future qualitative studies.

Conclusions

Compared to other types of primary payers, STEMI admissions with Medicare coverage have lower use of guideline-directed procedures, have higher rates of complications, and worse in-hospital outcomes. Further data are needed to understand the complex socio-demographic underpinnings associated with insurance coverage which may determine quality of care and outcomes in this acutely ill population.