Clinical Investigation
Acute Ischemic Heart Disease
The impact of the ESC/ACC redefinition of myocardial infarction and new sensitive troponin assays on the frequency of acute myocardial infarction

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Background

The prevalence of acute myocardial infarction (AMI) has increased due to the recent definitions, but the magnitude of this effect using contemporary highly sensitive troponin assays is unclear. The objective of this study is to compare the diagnosis of AMI using a contemporary troponin I (cTnI) biomarker and the 2003 American Heart Association (AHA) case definition with diagnoses made using the 1994 World Health Organization MONICA definition.

Methods

Contemporary troponin I measurements were performed with the Beckman Coulter AccuTnI assay (Chaska, MN) on plasma specimens originally assayed in 1996 for creatine kinase (CK)–MB mass from 486 emergency department patients presenting within 24 hours of onset of symptoms suggestive of cardiac ischemia.

Results

In a subgroup of 258 patients with 2 specimens drawn at least 6 hours apart (the AHA “adequate set of biomarkers”), AMI prevalence using CK-MB was 19.4% (95% CI 15.0-24.7) based on MONICA and 19.8% (15.4-25.1) based on the AHA case definition using the criterion for change of ≥20% between specimens. Using cTnI as the biomarker of choice, under the AHA definition, the prevalence increased to as high as 35.7% (30.1-41.7, a relative increase of 84%, P < .001) using the 99th percentile cutoff. In 121 patients with a lower index of suspicion and without the requisite 6-hour interval between measurements, positivity increased from 5% with CK-MB by MONICA up to 12% to 16% with cTnI by AHA.

Conclusions

A highly sensitive contemporary cTnI assay used with the AHA case definition results in a 62% to 84% increase in the frequency of AMI diagnosis compared with MONICA criteria.

Section snippets

Patient selection

In 1996, after institutional ethics approval, 458 patients representing 500 separate patient presentations to the emergency department (ED) were enrolled in a Cardiac Markers Study at the Oshawa General Hospital (now Lakeridge Health Corporation, Oshawa site). During recruitment, the only inclusion criterion was the assessment by the triage staff that the patient had symptoms suggestive of cardiac ischemia. There were no clinical exclusion criteria. Patients who presented to the ED on separate

Results

In the 486 patients with data and samples suitable for analysis, the median interval between the onset of symptoms and the collection of the presentation specimen was 3 hours (Table I). There were 32 ST-elevation myocardial infarctions (STEMIs) detected by ECG (prevalence 6.6%, 95% CI 4.7-9.2) and 29 non-STEMIs diagnosed using the results of the CK-MB tests performed on clinical and study specimens, according to the retrospective expert diagnosis. All but one patient with AMI had been diagnosed

Discussion

Our data demonstrate that, in a population originally classified by WHO MONICA criteria, a reclassification based on the ESC/ACC criteria, as operationalized with the AHA case definition and the use of a highly sensitive contemporary troponin assay, produces a substantial increase in the frequency of myocardial infarction.

The observed change in the frequency of AMI depends on the pre hoc criteria used for the diagnosis, the newly applied AMI criteria, and marker sensitivity. In Table II, our

Conclusions

These data have important implications for both physicians and patients. A large percentage of patients who in the past were admitted with chest pain will now likely be classified as having AMI. Because it is clear that these patients are at risk19 for both mortality and future cardiac events but respond well to more aggressive therapies such as low–molecular weight heparin,20 IIb/IIIa agents,21 and invasive strategies,22, 23 the ability to identify these patients will result in better care and

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      Class I Cardiac-specific troponin (troponin I or T when a contemporary assay is used) levels should be measured at presentation and 3 to 6 hours after symptom onset in all patients who present with symptoms consistent with ACS to identify a rising and/or falling pattern (21,64,67–71,152–156). ( Level of Evidence: A)

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    This work was partially supported by funds from Beckman Coulter Inc (Chaska, MN). The generous support of the Auxiliary of Lakeridge Health Oshawa, and the Oshawa General Hospital Foundation (Ontario, Canada) is gratefully acknowledged in enabling this study.

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