Criteria
American College of Cardiology/American Heart Association[2][4]
The Fourth Universal Definition of Myocardial Infarction (2018) provides criteria for 5 distinct clinical presentations of myocardial infarction (MI), which are based on pathological, clinical, and prognostic factors.[4]
Evaluation begins with clinical history, obtaining an ECG(s), and assessing cardiac biomarkers. It is important to note that ECG abnormalities and elevated cardiac biomarkers do not alone establish the definition of NSTEMI. The ECG can be relatively normal but this does not exclude acute coronary syndrome (ACS). More commonly associated findings in NSTEMI include ST depression, transient ST elevation, and/or prominent T-wave inversions. While these findings are frequently present, they are not required for a diagnosis of NSTEMI.
If the diagnosis of ACS is indicated by history and ECG, the diagnosis of NSTEMI may be established if a biomarker of myocardial injury has been released (i.e., troponin elevation). If there is no evidence of biochemical marker release suggestive of myocardial necrosis in a patient with suspected ACS, they may be considered to have experienced unstable angina.[2]
Risk stratification scores[2]
ACS diagnosis and management requires continuous risk stratification for death or recurrent MI. Initial risk assessment includes the history, examination, ECG, and cardiac biomarkers, all of which can be compiled to estimate risk using the TIMI Risk Score, GRACE risk model, or the Killip Classification.
High-risk clinical features in patients with suspected ACS include ongoing chest pain, severe dyspnea, syncope/presyncope, or palpitations.
TIMI Risk Score[62]
All-cause mortality, rate of MI, and rate of revascularization at 14 days increase in proportion to the number of risk factors present on the TIMI score. One point is awarded for the presence of each of the following criteria (patients with a score of 0-2 are low risk, 3-4 are intermediate risk, and 5-7 are high risk):
Age >65 years
Presence of ≥3 coronary artery disease risk factors
Prior coronary stenosis >50%
ST-segment deviation on ECG
Elevated serum cardiac biomarkers
At least 2 anginal episodes in the past 24 hours
Use of aspirin in the past 7 days.
Global Registry of Acute Coronary Events (GRACE) risk model
The GRACE risk model is a web-based tool that can be used to predict in-hospital and post-discharge mortality or MI in patients following an initial ACS.
Killip Classification
The Killip classification risk stratifies patients with acute MI based on clinical evidence of left ventricular failure.
Class I: no evidence of congestive heart failure
Class II: presence of a third heart sound gallop, basilar rales, or elevated jugular venous pressure
Class III: presence of pulmonary edema
Class IV: cardiogenic shock.
Heart Score
Incorporates elements of the patient's history, ECG, age, risk factors, and troponin and is used for patients in the accident and emergency department setting to assess risk of acute MI, percutaneous intervention, coronary artery bypass graft, and death within 6 weeks of initial presentation.
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