What's new in the “Fourth Universal Definition of Myocardial Infarction”
Salim Hayek, MD, FACC
The following are key points to remember from the 2018 Fourth Universal Definition of Myocardial Infarction Consensus Document:
1. Major changes include the
differentiation of myocardial infarction from injury, and delineation of
roles for cardiac magnetic resonance imaging (MRI) and computed
tomography (CT) angiography in the evaluation of acute coronary
syndromes.
2. Cardiac troponin levels should be drawn on initial assessment and 3-6
hours later, possibly earlier (1-3 hours) with high-sensitivity assays.
Defining a universal interval for serial sampling is challenging given
the impact of the variation in time of symptom onset on the rise and
fall of troponin measured by both conventional and high-sensitivity
assays. Incorporation of a sound clinical assessment is essential in
guiding sampling frequency and interpretation.
3. Myocardial injury is defined by only one criterion: the elevation of
cardiac troponin, with at least one value above the 99th percentile
upper reference limit, and thus represents an all-encompassing term for
elevated troponins of ischemic and nonischemic etiologies.
4. A myocardial infarction is a myocardial injury attributed specifically
to ischemia, i.e., with clinical evidence of a rise in troponin and at
least one of the following: ischemic symptoms or electrocardiographic
changes, development of pathologic Q waves, imaging evidence of new loss
of viable myocardial or regional wall motion abnormalities consistent
with ischemia, and last, identification of a coronary thrombus by
angiography or autopsy.
5. Type 1 acute myocardial infarctions refers to those secondary to acute
atherothrombosis. Type 2 is secondary to ischemia due to oxygen supply
and demand mismatch unrelated to acute thrombosis. Type 3 refers to
myocardial infarctions diagnosed post-mortem in patients who had
presented with signs and symptoms suggestive of myocardial ischemia and
passed before biomarkers were measured.
6. Type 4a and 5 events are post-percutaneous coronary intervention (PCI)
and post-coronary artery bypass grafting (CABG), respectively, occurring
<48 hours after the index procedure, and are defined by elevations in troponin beyond a prior stable baseline value and with electrocardiographic, angiographic, or imaging evidence of ischemia. Type 4b defines stent thrombosis (acute <24 hours, subacute 1-30 days, late 30 days-1 year, very late >1 year post-PCI), while type 4c
indicates restenosis following PCI in the infarct territory.
7. Myocardial injury can occur during nonrevascularization cardiac
procedures such as transcatheter aortic valve replacement by direct
trauma or coronary obstruction/embolization, and are not classified as
infarctions unless they meet biomarker and ischemia criteria for type 5
infarctions.
8. There are no specific categories for elevation in troponin in the
setting of acute heart failure, kidney disease, critical illness, or
noncardiac procedures. The diagnosis should be based on the presence or
absence of ischemia and acute thrombosis, given type I and type II
myocardial infarctions, or acute myocardial injury nonrelated to
ischemia can occur in all these clinical scenarios.
9. Elevation in troponin in the setting of atrial fibrillation with rapid ventricular rate and accompanying ST depression should not be classified as type 2 myocardial infarction unless signs of overt
ischemia are present. Otherwise, the rise in troponin should be
attributed to myocardial injury.
10. Myocardial infarction in nonobstructive coronary artery disease (MINOCA)
should be classified as either type 1 (thrombosis with recanalization)
or type 2 (coronary spasm, coronary dissection) depending on the
clinical presentation and angiogram findings.