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. Author manuscript; available in PMC: 2012 Apr 4.
Published in final edited form as: Am Heart J. 2010 Nov;160(5):943–950.e1-5. doi: 10.1016/j.ahj.2010.06.046

Who is missing from the measures? Trends in the proportion and treatment of patients potentially excluded from publicly-reported quality measures

Susannah M Bernheim *,, Yongfei Wang *,, Elizabeth H Bradley *, Frederick A Masoudi , Saif S Rathore *, Joseph S Ross §, Elizabeth Drye *,, Harlan M Krumholz †,
PMCID: PMC3319386  NIHMSID: NIHMS366521  PMID: 21095284

Abstract

Background

The Centers for Medicare and Medicaid Services (CMS) provides public reporting on the quality of hospital care for patients with acute myocardial infarction (AMI). CMS Core Measures allow discretion in excluding patients because of relative contraindications to aspirin, beta-blockers and angiotensin converting enzyme inhibitors. We describe trends in the proportion of AMI patients with contraindications that could lead to discretionary exclusion from public reporting.

Methods

We completed cross-sectional analyses of three nationally-representative data cohorts of AMI admissions among Medicare patients in 1994–5 (n=170,928), 1998–9 (n=27,432), and 2000–2001 (n=27,300) from the national Medicare quality improvement projects. Patients were categorized as ineligible (e.g. transfer patients), automatically excluded (specified absolute medical contraindications), discretionarily excluded (potentially excluded based on relative contraindications), or ‘ideal’ for treatment for each measure.

Results

For 4 of 5 measures the percentage of discretionarily excluded patients increased over the three time periods (admission aspirin 15.8% to 16.9% and admission beta-blocker 14.3% to 18.3%, discharge aspirin 10.3% to 12.3%, and ACE-I 2.8% to 3.9%, p<.001). Of patients potentially included in measures (those who were not ineligible or automatically excluded), the discretionarily excluded represented 25.5 % to 69.2% in 2000–01. Treatment rates among patients with discretionary exclusions also increased for 4 of 5 measures (all except ACE-I).

Conclusions

A sizeable and growing proportion of AMI patients have relative contraindications to treatments that may result in discretionary exclusion from publicly-reported quality measures. These patients represent a large population for which there is insufficient evidence as to whether measure exclusion or inclusion and treatment represents best care.

Background

The Centers for Medicare and Medicaid Services (CMS), in collaboration with the Hospital Quality Alliance, collects and disseminates quality measures for over 4000 US hospitals as a part of required reporting by hospitals for payment updates.13 Through use of the Hospital Compare Web site, which provides public access to CMS Core Measures data, one may judge an individual hospital’s performance on numerous quality metrics or directly compare institutions. Reported rates of compliance with the processes of care measured by CMS have improved over the past several years coinciding with public reporting of the measures.46 Furthermore, given the continued and growing interest of payers and policymakers in linking healthcare payment to measures of quality, performance on Core Measures will likely become ever more critical to hospitals.7

Many Core Measures do not, however, assess care for all patients. Measures of processes of care for acute myocardial infarction (AMI), including the use of aspirin and beta-blockers at admission and at discharge and angiotensin converting enzyme inhibitors (ACE-I) or angiotensin receptor blockers (ARBs) for patients with low left ventricular systolic function, allow physicians considerable discretion in excluding patients from reported metrics in order to account for potential contraindications to measured treatments.8 Prior work has shown that the overall prevalence of contraindications to AMI treatments is substantial and increasing over time.6, 9 However, the only patients uniformly excluded from process of care measures are those with specified absolute contraindications to AMI treatments (e.g. medication allergies). Most potential contraindications do not lead to automatic exclusion from a measure; instead process of care measures allow for individualized discretionary exclusions based on documentation of the medical team’s decision not to give the treatment, such as not giving a beta-blocker to an AMI patient with chronic obstructive pulmonary disease.8 Differential use of these discretionary exclusions across hospitals may undermine the utility of these metrics for comparing quality of care across institutions. Despite this concern, the prevalence and trends in the proportion of patients with relative contraindications resulting in discretionary exclusion has not been characterized, because prior studies have not differentiated between the absolute contraindications that automatically result in exclusion versus the relative contraindications that may result in discretionary exclusions.

In order to assess the extent to which rates of relative contraindications and their resultant discretionary exclusions may affect interpretation of quality metrics, we determined trends in the proportion of patients with AMI in several time periods between 1994–2001 with characteristics that would lead to their inclusion, or potential exclusion from current publicly-reported quality measures, as well as trends in the treatment of these patients. Using chart-review data from three national Medicare quality improvement projects, we sought to describe trends in the proportion of Medicare patients presenting with AMI with a) specific exclusions to a given drug therapy (“automatic exclusions” group) b) those with relative medical contraindications (“discretionary exclusions” group), and c) those with no contraindications (“ideal candidates”), and to describe trends in the rates of treatment for each of these groups.

Methods

Data Source and Study Sample

The data for this study were from three Centers for Medicaid and Medicaid Services (CMS) quality improvement projects. The first, the Cooperative Cardiovascular Project (CCP), collected chart-reviewed data on all fee-for-service Medicare patients admitted with a diagnosis of AMI (based on ICD-9 codes) between February 1994 and July 1995 (n=234796).10 The subsequent projects, the National Heart Care Project (NHC) and National Heart Care Remeasurement (NHC-R) collected data from April 1998 – March 1999 and October 2000 – June 2001 respectively. For the NHC and NHC-R, a systematic sample from each state based on age, race and hospital was used to obtain up to 850 representative discharges for AMI per state (n=35,713 for NHC and 35,407 for NHC-R). Details of these studies have been reported elsewhere.1015

Patient characteristics and performance measurement were obtained from medical records reviewed by trained data abstractors using standardized software, with data quality assessed via random record review. Variable definitions relevant to this analysis were consistent across the three studies. All charts had the same data fields abstracted regardless of treatment decisions. The abstractors had high level of agreement on abstracted data.11

Patients with AMI were identified based on principal discharge ICD-9 codes for AMI (410.X0 or 410.x1). In each of the AMI quality improvement projects, the diagnosis of myocardial infarction was confirmed using a combination of laboratory and electrocardiographic data. We excluded patients whose AMI was not confirmed (31186 (13.3%) for CCP, 4255 (11.9%) for NHC, 3647 (10.3%) for NHC-R), patients less than 65 years old (17593 (7.5%) for CCP, 3009 (8.4%) for NHC, 3038 (8.5%) for NHC-R), and later AMI admissions for the same patient within the time period of data collection (27498 (11.7%) for CCP, 2125 (6.0%) for NHC, 2068 (5.8%) for NHC-R), as well as those patients for whom vital status or correct state code was undetermined (4 for CCP, 21 for NHC, 423 (1.2%) for NHC-R). 50,229 patients met one or more of the above criteria, leaving a final cohort of 255,660 patients (170,928 from CCP, 27,432 from NHC, and 27,300 from NHC-R).

Definition of candidacy for Performance Measures

We examined trends for 5 AMI quality measures: use of aspirin at admission, use of beta-blocker at admission, prescription of ACE-I at discharge for patients with left ventricular systolic dysfunction, prescription of aspirin at discharge, and prescription of beta-blocker at discharge. Drawing from the current CMS/Joint Commission (CMS/JC) quality measure definitions, patients were categorized as ineligible, automatic exclusions, discretionary exclusions, or ideal candidates for treatment (See Figure 1), although these measures were not publicly reported at the time of initial data collection. We defined ineligible patients (our terminology) as cases who would be ineligible and therefore excluded from current measures for non-medical reasons that either preclude assessment of quality of care or appropriate assignation of the responsible hospital, such being transferred out on the day of admission. Patients were categorized as automatic exclusions for a quality measure if they had a medical contraindication (i.e. medication allergy) for the therapy as defined by current CMS/JC measure specifications. Patients categorized as ineligible or automatically excluded are those who would uniformly be left out of the denominator in calculating rates of treatment for publicly reported data.

Figure 1.

Figure 1

Schematic of Sample and Patient Categories

We defined the discretionary exclusions group as those patients who may or may not be included in quality measures under current specifications, due to relative contraindications to treatment. To identify potential contraindications to categorize this group we compiled a list of the relative contraindications used by CMS prior to the current public reporting era.16 These are patients who could be excluded from a measure based on the CMS criteria allowing any patient to be excluded from a measure for "other reasons documented by a physician, nurse practitioner or physician assistant for not prescribing" the given treatment. (A complete list of comparing current CMS/JC measure specifications and the criteria used to categorize patients for this study can be found in Appendix Table 1). Finally, patients who did not fit into any of the above categories were considered ideal candidates for therapy (no contraindications).

Outcome variables

Treatment with measured processes of care was based on chart-reviewed data from each of the cohorts.

Statistical Analysis

We compared the clinical characteristics of patients from each of the three cohorts and then determined the distribution of patients classified as excluded, ineligible, discretionary, or ideal candidates for each of the five quality indicators. We also calculated the number of patients ideal for 0, 1, 2, 3, 4 or 5 of the drug therapies for each cohort.

We compared rates of use of medical therapies for patients in the excluded, discretionary, and ideal group. Patients classified as ineligible were not assessed because their exclusion from process of care measures is most often related to logistics of their admission and not medical reasons to withhold a particular therapy.

All comparisons between groups were done using survey data analysis methods with chi-squares test in cross table analyses for dichotomous variables and F-test in ANOVA model analyses for continuous variables. All analyses were done with SAS Version 9.1 (SAS institute, Inc. Cary, NC). Analysis of the CCP, NHC, and NHC-R databases was approved by the Yale University School of Medicine Human Investigation Committee. Dr. Bernheim was supported by a training grant from the National Institute on Aging (T32AG1934) when initially working on this study. Saif Rathore is supported by Agency for Healthcare Research and Quality dissertation grant (1R36HS018283-01). The authors are solely responsible for the design and conduct of this study, all study analyses and drafting and editing of the paper.

Results

Characteristics of study samples

The mean age of the 3 cohorts increased significantly over time, ranging from 76.3 years (1994–1995 cohort) to 78.0 years (2000–2001 cohort, p<0.001). Each cohort had high rates of comorbidities with significant increases over time, including hypertension, prior heart failure, and previous cardiac interventions. By contrast, measures of clinical severity at admission, such as rates of ST-segment elevation MI, cardiac arrest, shock, and pulmonary edema at admission, decreased over time (Table I).

Table I.

Patient Characteristics and Outcomes* by Time Period

Description 1994–1995 1998–1999 2000–2001 Overall
P
# % # % # %
All 170928 100.00 27432 100.00 27300 100.00
Demographics
Age: mean (SD) 76.30 7.34 77.40 16.83 77.99 18.25 <0.001
Female 82741 48.41 13446 50.31 13470 50.17 <0.001
Non-white 16529 9.67 4103 13.54 4591 14.84 <0.001
Medical history
Prior MI 49477 28.95 9436 35.04 9947 37.17 <0.001
Prior HF 35603 20.83 7125 27.55 7975 30.98 <0.001
Prior PTCA 11564 6.77 3204 11.48 3756 14.14 <0.001
Prior CABG 21254 12.43 4418 16.63 4691 17.66 <0.001
Prior CVA 23612 13.81 4625 17.32 5152 19.56 <0.001
COPD 34756 20.33 6097 22.85 6609 24.62 <0.001
Diabetes 52167 30.52 8704 32.58 9112 34.38 <0.001
Clinical Presentation
Shock 4364 2.55 513 1.81 313 1.15 <0.001
Hemorrhage 5251 3.07 1030 3.85 1051 4.11 <0.001
CHF/Pulmonary edema 48025 28.10 6136 23.71 5563 21.84 <0.001
Heart rate: mean (SD) 87.43 24.50 88.57 54.38 88.70 58.15 <0.001
Systolic blood pressure: mean (SD) 143.55 32.76 142.78 71.78 141.97 76.63 <0.001
Respiratory rate: mean (SD) 22.23 6.58 22.06 14.16 21.85 14.95 <0.001
Creatinine: mean (SD) 1.38 0.96 1.45 4.02 1.49 2.62 <0.001
ST-elevation 54608 31.95 8412 30.15 6905 24.47 <0.001
Assessment of LVEF
Without the measure 60845 35.60 9017 30.69 7989 27.69 <0.001
With the measure <0.001
Normal 46667 42.39 7914 41.37 8494 42.04
Mild/mild moderate/decreased 27517 25.00 4327 23.62 4476 23.73
Moderate/moderate severe/low 20438 18.57 3325 18.78 3372 17.79
Severe/very severe/very low/poor 15461 14.04 2849 16.24 2969 16.44
Outcomes
Length of stay: mean (SD.) 8.36 7.22 7.24 13.90 7.11 15.15 <0.001
30-Day mortality from discharge 8843 5.17 1733 6.46 1756 6.73 <0.001
One-year mortality from discharge 29782 17.42 5524 20.75 5688 22.19 <0.001
*

Results from survey analysis for % and P value are shown here.

Trends in candidacy for drug-therapy

A large proportion of the patients in all three cohorts were ineligible for inclusion for each of the five quality of care measures (Table II). For admission use of aspirin and beta-blocker, 20–33% were ineligible, largely because they were transferred in or out, discharged on the day of admission, or died. Up to 85% of patients were ineligible for treatment with ACE-I because their left ventricular systolic function was not assessed or measured as greater than 40% ejection fraction. The proportion of ineligible candidates increased significantly over time for the admission measures (20% in 1994–5, 28% in 2000–1), while it decreased slightly for the discharge measures.

Table II.

Performance Measures by Time Period

Description 1994–1995 1998–1999 2000–2001 Overall
P
# % # % # %
All 170928 100.00 27432 100.00 27300 100.00
Medication on admission
Aspirin <0.001
 Ineligible 34441 20.15 7458 25.97 8190 27.75
 Excluded 18540 10.85 3327 12.55 3290 12.73
 Discretionary 26964 15.78 4402 16.49 4457 16.94
 Ideal 90983 53.23 12245 44.98 11363 42.58
BB <0.001
 Ineligible 34441 20.15 7458 25.97 8190 27.75
 Excluded 62620 36.64 9318 35.19 8584 33.03
 Discretionary 24518 14.34 4339 16.06 4764 18.31
 Ideal 49349 28.87 6317 22.78 5762 20.91
Medication at discharge
Aspirin <0.001
 Ineligible 56570 33.10 8645 31.51 8640 31.81
 Excluded 39558 23.14 6301 22.82 6486 23.72
 Discretionary 17669 10.34 3248 11.97 3306 12.25
 Ideal 57131 33.42 9238 33.71 8868 32.22
BB <0.001
 Ineligible 56570 33.10 8645 31.51 8640 31.81
 Excluded 46298 27.09 8906 31.87 9860 35.34
 Discretionary 43167 25.25 6710 25.06 6092 22.88
 Ideal 24893 14.56 3171 11.56 2708 9.97
ACEI <0.001
 Ineligible 146212 85.54 23098 82.97 22778 82.68
 Excluded 2535 1.48 456 1.95 473 1.71
 Discretionary 4824 2.82 883 3.44 1032 3.93
 Ideal 17357 10.15 2995 11.64 3017 11.68
*

Results from survey analysis for % and P value are shown here.

The proportion of patients with medical contraindications that would lead to automatic exclusion from the measures also increased slightly for most measures from 1994–5 to 2000–1, with the largest increase for the measure of beta-blocker at discharge (27% vs. 35%) and a slight decrease for beta-blocker at admission.

In the 2000–01 cohort, 41% of patients (admission aspirin) to 85% (ACE-I) would be uniformly excluded from any given measure denominator because they were either ineligible or had a medical contraindication leading to automatic exclusion. The proportion of patients that were either ineligible or had an automatic exclusion significantly increased for three of five measures over time, aspirin at admission (30.9% either ineligible or excluded for aspirin in 1994–95 vs. 40.5% in 2000–2001), beta-blocker at admission (56.7% 1994–1995 vs. 60.8% in 2000–2001) and beta-blocker at discharge (60.2% 1994–95 vs. 67.1% 2000–2001).

For all measures, except beta-blocker at discharge, the proportion of patients in the discretionary group, i.e., those with relative contraindications that are not automatic exclusions but which could lead to an individualized discretionary exclusion, increased significantly over time. The proportion of candidates in the discretionary group for aspirin on admission increased from 15.8% in 1994–1995 to 16.9% in 2000–2001. For beta-blocker on admission, the increase was greater (14.3% in 1994–1995, 18.3% in 2000–2001.) Moreover, when the proportion of patients that could be discretionarily excluded was calculated as a proportion of measure-eligible patients, i.e., patients who are not automatically excluded or ineligible, the patients with potential discretionary exclusions represented 25.5% of eligible patients for ACE-I, and 69.2% for discharge beta-blocker in 2000–2001. The percentage of discretionary exclusion patients among measure-eligible patients increased over time for all measures.

The combined increases in ineligible, automatically excluded and discretionary patients led to a decrease in the proportion of ideal candidates for each measure except ACE-I at discharge. In turn, the proportion of patients who are ideal for no measures (ineligible, excluded or discretionary for all groups) increased from 29.8% in 1994–5 to 37.1% in 2000–2001, and the proportion of patients who were ideal for all measures was less than 1% in all cohorts. (Table III)

Table III.

Number of Ideal Performance Measures by Time Period

Description 1994–1995 1998–1999 2000–2001 Overall
P
# % # % # %
N (%) 170928 100.00 27432 100.00 27300 100.00
Number of Ideal Performance Measures <0.001
0 50891 29.77 9772 35.35 10284 37.08
1 43242 25.30 6828 24.98 7112 26.42
2 45683 26.73 6663 23.99 6176 22.69
3 19934 11.66 2933 11.24 2701 9.87
4 10587 6.19 1167 4.20 984 3.77
5 591 0.35 69 0.23 43 0.17
*

Results from survey analysis for % and P value are shown here.

Trends in Drug Therapy

Use of all five drug therapies increased for automatically excluded, discretionary and ideal candidates, except for ACE-I use in automatically excluded and discretionary patients (Table IV) The use of aspirin and beta-blocker at admission and discharge was substantial and increased significantly for both automatically excluded and discretionary patients, that is to say, patients with potential medical contraindications to treatment. For example, admission use of aspirin went from 83% to 89% (p<0.001) among the discretionary patients and 60% to 73% use among excluded patients. Beta-blocker use at discharge among patients excluded from measures and among discretionary patients increased dramatically over this time period (excluded 40% in 1994–5 to 71% in 2000–2001, discretionary: 26% to 61%).

Table IV.

Use of Medications Among the Corresponding Performance Measures by Time Period

Description 1994–1995 1998–1999 2000–2001 Overall
P
# % # % # %
Medication on admission or during hospital
Aspirin 140774 82.36 24338 88.09 24429 88.81 <0.001
 Excluded 11169 60.24 2385 70.97 2434 72.79 <0.001
 Discretionary 22252 82.52 3992 90.23 4033 89.21 <0.001
 Ideal 80961 88.98 11593 94.20 10793 94.66 <0.001
BB 84353 49.35 18337 66.81 20993 77.41 <0.001
 Excluded 25331 40.45 5582 59.74 6397 74.77 <0.001
 Discretionary 11127 45.38 2844 65.57 3581 75.70 <0.001
 Ideal 32535 65.93 5212 82.97 5067 88.24 <0.001
Medication at discharge
Aspirin 87200 51.02 16569 58.86 17316 61.16 <0.001
 Excluded 20931 52.91 3870 58.48 4267 63.10 <0.001
 Discretionary 11946 67.61 2509 74.49 2612 76.78 <0.001
 Ideal 43627 76.36 7748 83.13 7625 84.42 <0.001
BB 49345 28.87 12638 45.93 15383 55.75 <0.001
 Excluded 18555 40.08 5390 60.73 7014 71.19 <0.001
 Discretionary 11382 26.37 3061 45.66 3702 60.62 <0.001
 Ideal 12503 50.23 2267 71.18 2157 78.87 <0.001
ACEI 43298 25.33 9617 34.93 10815 38.97 <0.001
 Excluded 1279 50.45 238 51.00 227 47.77 0.695
 Discretionary 1886 39.10 371 39.49 387 35.87 0.260
 Ideal 10761 62.00 2092 70.07 2213 71.48 <0.001
*

Results from survey analysis for % and P value are shown here.

Discussion

Our results demonstrate that an increasing proportion of older patients with AMI have medical conditions that could lead to their exclusion from publicly-reported process of care measures. Indeed, of the patients that could be included in a given quality measure (that is, of those that are not uniformly excluded) up to 69% were in the discretionary category based on chart-abstracted data in 2000–01; they did not have a specified contraindication that would automatically lead to their exclusion from the measure, nor were they ideal for the given treatment. We found, additionally, that rates of treatment with medications for which these patients had potential contraindications also increased. These results highlight the uncertainties surrounding the best care for older patients with relative contraindications to treatment: it is unclear whether inclusion and treatment or discretionary exclusion represents the better care.

Our results build upon prior work that described the growing proportion of older AMI patients with coexisting conditions and potential contraindications to treatment for AMI.6, 9 A study by Masoudi et. al. indicated, for example, that the proportion of patients ideal for aspirin at admission dropped from 67% to 47% over 10 years, with similar drops found for other measured drug therapies. In our study, less than 1% of Medicare patients were ideal candidates for all 5 process of care measures in 2001, which is to say that for nearly every Medicare beneficiary presenting with an AMI, a complex decision has to be made about whether to provide at least one standard medical treatment.

These findings echo concerns about the evidence-base for current quality measures for older patient groups.17, 18 Although the CMS process measures for AMI are based upon substantial clinical evidence, older and sicker patients are rarely included in clinical trials that established standards of care. A number of observational studies have supported the use of aspirin, beta-blocker and ACE-I in older patient populations,1921 but these generally have also excluded patients with potential contraindications to care. Without the inclusion of such patients in treatment studies it is difficult to judge what treatment decisions are in the patients’ best interest, thus leaving clinicians with challenging medical decisions.

Our findings also raise questions about how best to account for patients with relative contraindications when measuring quality of care. An earlier approach delineated a comprehensive list of potential contraindications for each therapy and excluded all such patients, whether or not they received treatment.9 In more recent efforts, CMS and the Joint Commission, recognizing the potential overriding benefit of treatment for many patients with relative contraindications, now specify a much narrower set of absolute exclusion criteria. This approach supports more individualized decision-making about care, but the allowance for discretionary exclusions complicates interpretation of publicly reported data. First, the use of discretionary exclusions are invisible to the health care consumer, so the public can not discern to what extent the quality measures are representative of the full population of patients seen at the hospital. Second, use of discretionary exclusions may vary greatly between hospitals and thus limit the comparability of measures. Furthermore, the combined factors of 1) discretion about whether to include patients with contraindications and 2) the lack of evidence about what is best for such patients create a situation that may give hospitals an incentive to treat patients despite relative contraindications, and thus hospitals could seemingly receive credit for care whether or not it is in the patient’s best interest. Indeed, we found rates of treatment for patients with potential contraindications have increased over time.

Finally, the exclusion of large numbers of patients from quality indicators raises broader questions about quality measurement. If a substantial proportion of patients are not represented in quality measures, because they are excluded or ineligible, we cannot provide any definitive assurances regarding the care they receive. This is particularly disconcerting because exclusion and ineligibility for process of care measures cluster in older, sicker patients who are more medically vulnerable and are being missed by quality of care measurement. This also has implications for our ability to ascertain quality at institutions when a notable proportion of patients, typically a sicker cohort, are not included in their overall assessment of quality.

There are a number of potential implications of our work. The first, as described, is the need for more evidence upon which to base treatment decisions for older patient groups with multiple coexisting conditions. Second, quality reporting for older patients may be improved by reporting outcomes or quality of life, as opposed to processes of care. Clinical outcomes could include all patients after risk-adjustment for clinical differences between populations and may be more meaningful to patients. Finally, more detailed information on the portion and characteristics of included patients should be reported for currently reported process measures.

A number of factors must be taken into consideration when interpreting of our work. First, we examined older data and cannot determine what course the observed trends in treatment have taken in more recent years. However, these data permitted detailed analysis of coexisting illnesses and treatment. We know of no other nationally representative source of chart-review data on AMI care. Second, we cannot be sure that all of the increases in discretionary exclusions are due to changes in the AMI population; it is possible that some of these changes represent changes in documentation. However, data collection was done prior to the era of public reporting and we know of no national effort to better document relative contraindications to care at that time. Third, our study is based on applying current measure criteria to patient populations prior to the era of public reporting. Thus, although we illuminate important changes in the populations of AMI patients that could be excluded from the measures, we do not know how this would translate into actual practice. The goal of this work was to highlight the growing population of AMI patients that could be excluded and the lack of transparency around these exclusions. Finally, our categorizations of patients were based on variables selected for prior quality improvement projects and do not precisely match current CMS/Joint Commission criteria. However, it is unlikely that this would dramatically change the trends described.

Important progress has been made in the last decade toward making care provided by hospitals to AMI patients more transparent. Most indications suggest that there has been simultaneous improvement in the quality of care provided to AMI patients. Our work identifies ongoing challenges with performance measurement in this population by revealing potential limitations of process measurements that incorporate discretionary exclusion of patients. Despite allowing for patient-specific decision-making, discretionary exclusion may lead to variability in patient populations included in measures across hospitals. Public quality reports, by failing to indicate who is excluded from measures, do not reflect the care provided to a large group of older patients whose inclusion or discretionary exclusion is invisible to the healthcare consumer.

Figure 2.

Figure 2

Percentage of patients with discretionary exclusions among measure eligible patients

Appendix

Appendix Table 1.

Comparison of CMS measure specification with study cohort specifications for patients identified as ineligible, excluded or discretionary

CMS MEASURE SPECIFICATIONS STUDY COHORT SPECIFICATIONS
ADMISSION MEASURES
Excluded for all admission measures Ineligible for all Admission Measures
<18 years of age [Cohort includes >65 y.o only]
Patient transferred to another acute care hospital or federal hospital on day of or day after arrival Transferred out on the day or the day after admission
Patient discharged on day of arrival Discharged on the day or the day after admission
Patient expired on day of or day after arrival Expired on the day or the day after admission
Patients who left AMA on day of or day after arrival Left AMA on day of or day after admission
Patients with comfort measures only documented by a physician, APRN or PA Patients with terminal illness
Patients received in transfer from another hospital or ER Patient received in transfer or admission source unknown
ASPIRIN ON ADMISSION
Additional exclusions for ASA on admit Absolute Contraindications
Aspirin allergy Aspirin allergy
Active bleeding on arrival or within 24 hours after arrival Bleeding on arrival or within 48 hours prior to arrival
Coumadin as pre-arrival medication Coumadin prior to admission
Any other reason documented by PA/MD for not giving ASA on admission Relative Contraindications
Bleeding risk
History of internal bleeding
History of bleeding disorder
Chronic liver disease
First platelet count drawn within 24 hours of arrival < 100×109/L
Anemia
History of peptic ulcer disease
Renal insufficiency on admission
BETA-BLOCKER ON ADMISSION
Additional exclusions for Beta-blocker on admission Absolute Contraindications
Beta-blocker allergy Beta blocker allergy
Bradycardia (HR < 60) on arrival or within 24 hours after arrival while not on a beta-blocker Bradycardia on admission without taking a beta blocker
Heart failure on arrival or within 24 hours after arrival Heart failure at admission
CHF/pulmonary edema on admission
Pulmonary edema on chest x-ray within 24 hours of arrival
CHF on chest x-ray within 24 hours of arrival
Shock on arrival or within 24 hours after arrival Shock on admission
2nd or 3rd degree heart block on ECG on arrival or within 24 hours after arrival and does not have a pacemaker Heart block
2nd or 3rd degree heart block
first degree PR interval > 240 milliseconds on arrival EKG
Right bundle block and left fascicular block on arrival EKG
ICD-9-CM heart block codes
Any other reason documented by PA/MD for not giving Beta-blocker on admission Relative Contraindications
Heart failure at admission
History of HF
Previous LVEF < 50 and LVEF not equal to missing
COPD
History of COPD
ICD-9-CM COPD codes
Asthma
Peripheral vascular disease
Hypotension
Renal insufficiency
DISCHARGE MEASURES
CMS Exclusions for all discharge measures Ineligible for all discharge measures
< 18 years of age* [Cohort includes >65 y.o only]
Patients who left AMA * Patients who left AMA
Patients discharged to hospice* Terminal Illness
Patients with comfort measures only documented by a physician, APRN or PA* Terminal Illness
Patients transferred to another acute care hospital or federal hospital Patient transferred out of the hospital
Patients who expired Patient dead at discharge or discharge status unknown
ASPIRIN ON DISCHARGE
Additional exclusions for ASA at discharge Absolute Contraindications
Aspirin allergy History of allergy to ASA or reaction to ASA during hospitalization
Active bleeding on arrival Bleeding on admission
Active bleeding during hospital stay Bleeding during hospitalization
Coumadin prescribed at discharge Warfarin prescribed at discharge
Any other reason documented by PA/MD for not giving ASA on discharge Relative Contraindications
Bleeding risk
History of internal bleeding
History of bleeding disorder
Chronic liver disease
Low platelet count
Anemia
History of peptic ulcer disease
Acute UGI disorder during index admission
Renal insufficiency
BETA-BLOCKER AT DISCHARGE
Additional exclusions for BB at discharge Absolute Contraindications
Beta-blocker allergy History of allergy to beta blockers or reaction to beta blockers during hospitalization
Second or third degree heart block on ECG on arrival or during hospital stay and does not have a pacemaker Heart block
2nd or 3rd degree heart block
first degree PR interval > 240 milliseconds on arrival EKG
Right bundle block and left fascicular block on arrival EKG
Heart block second or third degree on any EKG during hospital stay
Right bundle block and left fascicular block during hospital
ICD-9-CM heart block codes
Bradycardia (<60bpm) on day of discharge or day prior to discharge while not on beta blocker Bradycardia
Bradycardia during hospital stay
Last pulse documented < 60 and did not take beta blocker on discharge
Any other reason documented by PA/MD for not giving beta-blocker on discharge Relative Contraindications
Heart failure and (LVEF<50 or unknown)
Heart failure on admission
CHF on chest x-ray within 24 hours of arrival
Heart failure during stay
ICD-9-CM heart failure codes
LVEF unknown or less than 50
LVEF less than 30
Shock
Shock on arrival
Shock during stay
ICD-9-CM shock codes
Hypotension
Hypotension during stay
Last systolic BP < 100mm Hg and did not take beta blocker on discharge
COPD
History of COPD
ICD-9-CM COPD codes
Asthma
Peripheral vascular disease
ACE-I USE AT DISCHARGE
Additional Exclusions for ACE-I at Discharge Ineligible
Chart documentation of an LVEF < 40% or a narrative description of LVS function consistent with moderate or severe systolic dysfunction LVEF not between 0 and 40
Absolute Contraindications
ACE-I allergy History of allergy to ACE or reaction to ACE during hospitalization
Moderate or severe aortic stenosis Aortic stenosis
Aortic stenosis
Cardiac cath aortic stenosis
ICD-9-CM aortic stenosis codes
Any other reason documented by PA/MD for not giving ACE-I on discharge Relative Contraindications
Creatinine > 2 on admission or during hospitalization
Hypotension at discharge and did not have ACE at discharge

Appendix Table 2.

Number and proportion of patients with given contraindications

Characteristics Total 1994–1995 1998–1999 2000–2001 Overall P
# % # % # % # %
ASA at Admission
Ineligible
Discharged/left AMA/transferred out/died on admission day or day after 23849 11.05 16975 9.93 3279 11.27 3595 12.13 <0.001
Terminal illness 726 0.24 624 0.37 64 0.22 38 0.13 <0.001
Transferred in 27316 14.05 18005 10.53 4411 15.51 4900 16.73 <0.001
Excluded (medical contraindication)
Aspirin allergy 9827 6.96 7398 4.33 1199 10.79 1230 10.43 <0.001
Active bleeding on arrival or within 48 hours 7332 3.64 5251 3.07 1030 3.85 1051 4.11 <0.001
Coumadin/Warfarin as pre-arrival medication 16226 8.42 11411 6.68 2344 9.26 2471 9.82 <0.001
Discretionary (Relative contraindication)
Bleeding risk 24035 12.12 16673 9.75 3505 12.89 3857 14.11 <0.001
History of internal bleeding 20327 10.17 14147 8.28 2870 10.39 3310 12.13 <0.001
History of bleeding disorder 1423 0.77 905 0.53 263 0.99 255 0.84 <0.001
Chronic liver disease 791 0.31 649 0.38 69 0.26 73 0.28 0.0031
First platelet count drawn within 24 hours of arrival < 100×109/L 2585 1.44 1701 1.00 468 1.87 416 1.55 <0.001
Anemia 13704 7.51 9388 5.49 1952 7.79 2364 9.55 <0.001
History of peptic ulcer disease 29976 12.93 22961 13.43 3557 12.77 3458 12.49 <0.001
Renal insufficiency on admission 8388 4.37 5843 3.42 1187 4.56 1358 5.28 <0.001
Beta-blocker on admission
Ineligible
Discharged/left against AMA/transferred out/died on the admission day or the day after 23849 11.05 16975 9.93 3279 11.27 3595 12.13 <0.001
Terminal illness 726 0.24 624 0.37 64 0.22 38 0.13 <0.001
Transferred in 27316 14.05 18005 10.53 4411 15.51 4900 16.73 <0.001
Excluded (medical contraindication)
Beta-blocker allergy 1332 1.10 846 0.49 193 1.57 293 2.26 <0.001
Bradycardia (heart rate less than 60 bpm) on arrival or within 24 hours after arrival while not on beta-blocker 15020 6.03 11717 6.85 1732 5.86 1571 5.25 <0.001
Heart failure on arrival or within 24 hours after arrival 79745 35.44 61221 35.82 9536 36.11 8988 34.43 0.0018
CHF/pulmonary edema on admission 59724 24.73 48025 28.10 6136 23.71 5563 21.84 <0.001
Pulmonary edema on chest x-ray within 24 hours of arrival 25841 13.29 19654 12.75 3424 15.30 2763 12.15 <0.001
CHF on chest x-ray within 24 hours of arrival 51710 26.48 39457 25.60 6213 27.34 6040 26.76 <0.001
Second or third degree heart block on ECG on arrival or within 24 hours after arrival and does not have a pacemaker 16050 7.52 11576 6.77 2222 7.91 2252 8.01 <0.001
2nd or 3rd degree heart block 2845 1.18 2295 1.44 282 1.05 268 0.99 <0.001
first degree PR interval > 240 milliseconds on arrival EKG 1670 3.14 782 2.95 888 3.31
Right bundle block and left fascicular block on arrival EKG 5055 2.38 3753 2.20 637 2.53 665 2.47 0.0052
ICD-9-CM heart block codes 8509 3.15 6961 4.07 850 2.83 698 2.39 <0.001
Shock on arrival or within 24 hours after arrival 5190 1.87 4364 2.55 513 1.81 313 1.15 <0.001
Discretionary (Relative contraindication)
Heart failure at admission 56411 29.34 39350 23.02 8067 31.14 8994 34.87 <0.001
History of HF 50703 26.17 35603 20.83 7125 27.55 7975 30.98 <0.001
Previous LVEF < 50 and LVEF not equal to missing 14473 8.83 8820 5.16 2525 9.75 3128 12.15 <0.001
COPD 53789 25.53 39408 23.06 6973 26.18 7408 27.76 <0.001
History of COPD 47462 22.49 34756 20.33 6097 22.85 6609 24.62 <0.001
ICD-9-CM COPD codes 35613 16.86 26341 15.41 4535 17.24 4737 18.16 <0.001
Asthma 4158 2.06 2868 1.68 619 2.15 671 2.40 <0.001
Peripheral vascular disease 160 0.09 111 0.06 22 0.08 27 0.14 0.0613
Hypotension 16847 7.67 12520 7.32 2097 7.51 2230 8.20 <0.001
Aspirin on discharge
Ineligible
Patients transferred to another acute care hospital or federal hospital 41191 17.90 31265 18.29 5049 17.96 4877 17.41 0.0795
Patients who died 31239 13.27 24596 14.39 3322 12.53 3321 12.65 <0.001
Patients who left AMA 314 0.23 181 0.11 67 0.31 66 0.29 <0.001
Patients with unknown discharge status 676 0.67 148 0.09 173 0.61 355 1.38 <0.001
Terminal illness 726 0.24 624 0.37 64 0.22 38 0.13 <0.001
Excluded (medical contraindication)
History of allergy to ASA or reaction to ASA during hospitalization 10019 4.58 7537 4.41 1217 4.65 1265 4.72 0.0955
Active bleeding on arrival or during hospital stay
Bleeding on admission 7332 3.64 5251 3.07 1030 3.85 1051 4.11 <0.001
Bleeding during hospitalization 39807 18.79 29215 17.09 4914 18.34 5678 21.12 <0.001
Coumadin/Warfarin prescribed at discharge 24609 11.41 19169 11.21 2826 12.13 2614 11.05 0.0045
Discretionary (Relative contraindication)
Bleeding risk 24035 12.12 16673 9.75 3505 12.89 3857 14.11 <0.001
History of internal bleeding 20327 10.17 14147 8.28 2870 10.39 3310 12.13 <0.001
History of bleeding disorder 1423 0.77 905 0.53 263 0.99 255 0.84 <0.001
Chronic liver disease 791 0.31 649 0.38 69 0.26 73 0.28 0.0031
Low platelet count 2585 1.44 1701 1.00 468 1.87 416 1.55 <0.001
Anemia 13704 7.51 9388 5.49 1952 7.79 2364 9.55 <0.001
History of peptic ulcer disease 29976 12.93 22961 13.43 3557 12.77 3458 12.49 <0.001
Acute UGI disorder during index admission 910 0.47 668 0.39 108 0.49 134 0.54 0.0214
Renal insufficiency 16476 8.25 11791 6.90 2226 8.52 2459 9.56 <0.001
Beta-blocker on discharge
Ineligible
Patients transferred to another acute care hospital or federal hospital 41191 17.90 31265 18.29 5049 17.96 4877 17.41 0.0795
Patients who died 31239 13.27 24596 14.39 3322 12.53 3321 12.65 <0.001
Patients who left AMA 314 0.23 181 0.11 67 0.31 66 0.29 <0.001
Patients with unknown discharge status 676 0.67 148 0.09 173 0.61 355 1.38 <0.001
Terminal illness 726 0.24 624 0.37 64 0.22 38 0.13 <0.001
Excluded (medical contraindication)
Beta-blocker allergy 2267 1.11 1505 0.88 307 0.98 455 1.48 <0.001
Bradycardia (heart rate less than 60 on day of discharge or day prior to discharge while not on a beta-blocker) 93199 44.84 66604 38.97 12431 45.11 14164 51.24 <0.001
Bradycardia during hospital stay 88839 43.60 62574 36.61 12216 44.37 14049 50.82 <0.001
Last pulse documented < 60 and did not take beta blocker on discharge 14818 4.87 12930 7.56 1028 3.55 860 2.98 <0.001
Second or third degree heart block on ECG on arrival or during hospital stay and does not have a pacemaker 24809 11.21 18547 10.85 3064 11.13 3198 11.68 0.0050
2nd or 3rd degree heart block 2845 1.18 2295 1.44 282 1.05 268 0.99 <0.001
first degree PR interval > 240 milliseconds on arrival EKG 1670 3.14 782 2.95 888 3.31
Right bundle block and left fascicular block on arrival EKG 5055 2.38 3753 2.20 637 2.53 665 2.47 0.0052
Heart block second or third degree on any EKG during hospital stay 8950 3.38 7372 4.31 769 2.78 809 2.84 <0.001
Right bundle block and left fascicular block during hospital 11317 5.12 8638 5.05 1287 5.06 1392 5.24 0.6213
ICD-9-CM heart block codes 8509 3.15 6961 4.07 850 2.83 698 2.39 0.0000
Discretionary (Relative contraindication)
Heart failure and (LVEF<50 or unknown) 93241 42.19 70710 41.37 11265 42.40 11266 42.95 <0.001
Heart failure on admission 59724 24.73 48025 28.10 6136 23.71 5563 21.84 <0.001
CHF on chest x-ray within 24 hours of arrival 63042 28.37 48026 28.10 7705 29.28 7311 27.87 0.0056
Heart failure during stay 96159 43.91 72744 42.56 11434 43.49 11981 45.80 <0.001
ICD-9-CM heart failure codes 89659 40.72 68159 39.88 10771 41.02 10729 41.40 0.0003
LVEF unknown or less than 50 162509 71.25 124160 72.64 19528 71.30 18821 69.63 <0.001
LVEF less than 30 21299 10.63 15499 9.07 2842 11.23 2958 11.85 <0.001
Shock 18424 7.87 14387 8.42 2084 7.73 1953 7.37 <0.001
Shock on arrival 5190 1.87 4364 2.55 513 1.81 313 1.15 <0.001
Shock during stay 16370 12.71 12683 7.42 1857 24.88 1830 22.36 <0.001
ICD-9-CM shock codes 11538 4.98 8988 5.26 1280 4.75 1270 4.86 0.0040
Hypotension 66620 30.15 49529 28.98 8264 29.44 8827 32.11 <0.001
Hypotension during stay 57708 27.48 41424 24.23 7803 27.84 8481 30.82 <0.001
Last systolic BP < 100mm Hg and did not take beta blocker on discharge 21714 6.30 19936 11.66 955 3.26 823 2.93 <0.001
COPD 53789 25.53 39408 23.06 6973 26.18 7408 27.76 <0.001
History of COPD 47462 22.49 34756 20.33 6097 22.85 6609 24.62 <0.001
ICD-9-CM COPD codes 35613 16.86 26341 15.41 4535 17.24 4737 18.16 <0.001
Asthma 4158 2.06 2868 1.68 619 2.15 671 2.40 <0.001
Peripheral vascular disease 160 0.09 111 0.06 22 0.08 27 0.14 0.0613
ACE-I at discharge
Ineligible
Patients transferred to another acute care hospital or federal hospital 41191 17.90 31265 18.29 5049 17.96 4877 17.41 0.0795
Patients who died 31239 13.27 24596 14.39 3322 12.53 3321 12.65 <0.001
Patients who left AMA 314 0.23 181 0.11 67 0.31 66 0.29 <0.001
Terminal illness 676 0.67 148 0.09 173 0.61 355 1.38 <0.001
Patients with unknown discharge status 726 0.24 624 0.37 64 0.22 38 0.13 <0.001
LVEF not between 0 and 40 177111 76.74 134930 78.94 21245 75.71 20936 75.17 <0.001
Excluded (medical contraindication)
History of allergy to ACE or reaction to ACE during hospitalization 2344 1.20 1474 0.86 365 1.26 505 1.52 <0.001
Aortic stenosis 15049 6.91 11339 6.63 1871 7.27 1839 6.92 0.0225
Aortic stenosis 5845 5.10 4246 4.44 794 5.63 805 5.38 <0.001
Cardiac cath aortic stenosis 2522 2.29 2198 3.88 169 1.71 155 1.33 <0.001
ICD-9-CM aortic stenosis codes 10454 5.09 7550 4.42 1449 5.49 1455 5.51 <0.001
Discretionary (Relative Contraindications)
Creatinine > 2 on admission or during hospitalization 38490 18.82 27878 16.31 4968 18.94 5644 21.54 <0.001
Hypotension at discharge and did not have ACE at discharge 22156 6.62 20095 11.76 1036 3.50 1025 3.57 <0.001

REFERENCES

  • 1.Jha AK, Li Z, Orav EJ, Epstein AM. Care in U.S. hospitals--the Hospital Quality Alliance program. N Engl J Med. 2005 Jul 21;353(3):265–274. doi: 10.1056/NEJMsa051249. [DOI] [PubMed] [Google Scholar]
  • 2.Hospital Quality Alliance. [Accessed July 23, 2009]; http://www.hospitalqualityalliance.org/. [Google Scholar]
  • 3.Department of Health and Human Services. Hospital Compare homepage. [Accessed June, 23, 2009]; http://www.hospitalcompare.hhs.gov/Hospital/Home2.asp?version=alternate&browser=IE%7C6%7CWinXP&language=English&defaultstatus=0&pagelist=Home.
  • 4.Williams SC, Schmaltz SP, Morton DJ, Koss RG, Loeb JM. Quality of care in U.S. hospitals as reflected by standardized measures, 2002–2004. N Engl J Med. 2005 Jul 21;353(3):255–264. doi: 10.1056/NEJMsa043778. [DOI] [PubMed] [Google Scholar]
  • 5.Lindenauer PK, Remus D, Roman S, et al. Public reporting and pay for performance in hospital quality improvement. N Engl J Med. 2007 Feb 1;356(5):486–496. doi: 10.1056/NEJMsa064964. [DOI] [PubMed] [Google Scholar]
  • 6.Masoudi FA, Foody JM, Havranek EP, et al. Trends in acute myocardial infarction in 4 US states between 1992 and 2001: clinical characteristics, quality of care, and outcomes. Circulation. 2006 Dec 19;114(25):2806–2814. doi: 10.1161/CIRCULATIONAHA.106.611707. [DOI] [PubMed] [Google Scholar]
  • 7.White House. [Accessed July 24, 2009]; http://www.whitehouse.gov/MedicareFactSheetFinal/.
  • 8.Quality Net. [Accessed March 29, 2009];Specifics manual 2.5. http://qualitynet.org/dcs/ContentServer?c=Page&pagename=QnetPublic%2FPage%2FQnetTier4&cid=1203781887871. [Google Scholar]
  • 9.Rathore SS, Wang Y, Radford MJ, Ordin DL, Krumholz HM. Quality of care of Medicare beneficiaries with acute myocardial infarction: who is included in quality improvement measurement? J Am Geriatr Soc. 2003 Apr;51(4):466–475. doi: 10.1046/j.1532-5415.2003.51154.x. [DOI] [PubMed] [Google Scholar]
  • 10.Marciniak TA, Ellerbeck EF, Radford MJ, et al. Improving the quality of care for Medicare patients with acute myocardial infarction: results from the Cooperative Cardiovascular Project. JAMA. 1998 May 6;279(17):1351–1357. doi: 10.1001/jama.279.17.1351. [DOI] [PubMed] [Google Scholar]
  • 11.Burwen DR, Galusha DH, Lewis JM, et al. National and state trends in quality of care for acute myocardial infarction between 1994–1995 and 1998–1999: the medicare health care quality improvement program. Arch Intern Med. 2003 Jun 23;163(12):1430–1439. doi: 10.1001/archinte.163.12.1430. [DOI] [PubMed] [Google Scholar]
  • 12.Jencks SF, Cuerdon T, Burwen DR, et al. Quality of medical care delivered to Medicare beneficiaries: A profile at state and national levels. JAMA. 2000 Oct 4;284(13):1670–1676. doi: 10.1001/jama.284.13.1670. [DOI] [PubMed] [Google Scholar]
  • 13.Jencks SF, Huff ED, Cuerdon T. Change in the quality of care delivered to Medicare beneficiaries, 1998–1999 to 2000–2001. JAMA. 2003 Jan 15;289(3):305–312. doi: 10.1001/jama.289.3.305. [DOI] [PubMed] [Google Scholar]
  • 14.Ellerbeck EF, Jencks SF, Radford MJ, et al. Quality of care for Medicare patients with acute myocardial infarction. A four-state pilot study from the Cooperative Cardiovascular Project. JAMA. 1995 May 17;273(19):1509–1514. [PubMed] [Google Scholar]
  • 15.Jencks SF, Wilensky GR. The health care quality improvement initiative. A new approach to quality assurance in Medicare. JAMA. 1992 Aug 19;268(7):900–903. [PubMed] [Google Scholar]
  • 16.Rathore SS, Mehta RH, Wang Y, Radford MJ, Krumholz HM. Effects of age on the quality of care provided to older patients with acute myocardial infarction. Am J Med. 2003 Mar;114(4):307–315. doi: 10.1016/s0002-9343(02)01531-0. [DOI] [PubMed] [Google Scholar]
  • 17.Tinetti ME, Bogardus ST, Jr, Agostini JV. Potential pitfalls of disease-specific guidelines for patients with multiple conditions. N Engl J Med. 2004 Dec 30;351(27):2870–2874. doi: 10.1056/NEJMsb042458. [DOI] [PubMed] [Google Scholar]
  • 18.Boyd CM, Darer J, Boult C, Fried LP, Boult L, Wu AW. Clinical practice guidelines and quality of care for older patients with multiple comorbid diseases: implications for pay for performance. JAMA. 2005 Aug 10;294(6):716–724. doi: 10.1001/jama.294.6.716. [DOI] [PubMed] [Google Scholar]
  • 19.Gottlieb SS, McCarter RJ, Vogel RA. Effect of beta-blockade on mortality among high-risk and low-risk patients after myocardial infarction. N Engl J Med. 1998 Aug 20;339(8):489–497. doi: 10.1056/NEJM199808203390801. [DOI] [PubMed] [Google Scholar]
  • 20.Krumholz HM, Radford MJ, Ellerbeck EF, et al. Aspirin in the treatment of acute myocardial infarction in elderly Medicare beneficiaries. Patterns of use and outcomes. Circulation. 1995 Nov 15;92(10):2841–2847. doi: 10.1161/01.cir.92.10.2841. [DOI] [PubMed] [Google Scholar]
  • 21.Krumholz HM, Chen YT, Wang Y, Radford MJ. Aspirin and angiotensin-converting enzyme inhibitors among elderly survivors of hospitalization for an acute myocardial infarction. Arch Intern Med. 2001 Feb 26;161(4):538–544. doi: 10.1001/archinte.161.4.538. [DOI] [PubMed] [Google Scholar]

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