Myocardial infarction – universal definition

Myocardial infarction – universal definition

Though ECG is the first test for a person with suspected myocardial infarction, the stress has shifted to cardiac markers with publication of Universal Definition of Myocardial Infarction. First universal definition was published in 2007 [1]and fourth definition has been published in 2018 by the Joint European Society of Cardiology (ESC)/American College of Cardiology (ACC)/American Heart Association (AHA)/World Heart Federation (WHF) Task Force [2]. There are types 1 to 5 with a sub classification of type 4 into a, b and c. Pathologically myocardial infarction is defined as myocardial cell death as a result of prolonged ischemia (lack of blood supply). Myocardial injury is defined as elevation of blood level of cardiac troponin above the 99^th percentile upper reference limit. Clinical evidence of acute ischemic myocardial injury makes it myocardial infarction.

Type 1 myocardial infarction: Type 1 myocardial infarction is due to atherothrombotic obstruction of a coronary artery, usually precipitated by a plaque rupture or erosion. A rise and/or fall of cardiac troponin values with at least one value above 99^th percentile upper reference limit (URL) along with one or more of the following is needed for diagnosis:

1. Symptoms of myocardial ischemia
2. New ischemic ECG changes
3. Development of pathological Q waves
4. Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality consistent with ischemic pattern.
5. Identification of a coronary thrombus by angiography including intracoronary imaging or by autopsy.

Type 2 myocardial infarction: Type 2 myocardial infarction is myocardial injury due to a supply-demand mismatch. Examples are a precipitous fall in hemoglobin due to acute gastrointestinal bleed or a sustained tachyarrhythmia with clinical manifestations of myocardial ischemia. Type 2 myocardial infarction is commoner in females and has a poorer prognosis than type 1 myocardial infarction due to the often associated comorbidities. There may be associated coronary atherosclerotic disease.

Type 3 myocardial infarction: In type 3 myocardial infarction, clinical and presumed ECG evidence of myocardial ischemia are present, but the person dies before biomarker evidence can be documented. In case a subsequent autopsy shows a fresh thrombotic occlusion of an infarct related artery, it should be reclassified as type 1 myocardial infarction.

Type 4a myocardial infarction: Type 4a myocardial infarction is associated with percutaneous coronary intervention. Myocardial injury in this setting is defined as cardiac troponin values above 99^th  percentile URL in patients with normal baseline or a rise of cardiac troponin values >20% of the baseline value when it is above the 99^th  percentile URL but it is stable or falling. Absolute value of cardiac troponin should be at least five times URL. The clinical and ECG criteria are the same as that of type 1 myocardial infarction. Angiographic criteria are a procedural flow limiting complication such as coronary dissection, occlusion of a major epicardial artery or a side branch occlusion/thrombus, disruption of collateral flow, or distal embolization.

Type 4b myocardial Infarction: Type 4b myocardial Infarction is one associated with coronary stent or scaffold (biodegradable) thrombosis, documented by angiography or autopsy. If it occurs within 24 hours it is acute. From 24 hours to 30 days, it is considered subacute; late if between 30 days and 1 year; very late if beyond 1 year of stent or scaffold implantation.

Type 4c myocardial Infarction: Type 4c Myocardial Infarction is due to restenosis after coronary stenting or balloon angioplasty with elevated troponin similar to that of type 1 myocardial infarction. But angiographic demonstration of restenosis as the cause is needed.

Type 5 myocardial Infarction: Type 5 myocardial Infarction is associated with coronary artery bypass grafting (CABG). Cardiac troponin value more than 10 times the 99^th percentile URL within 48 hours of CABG is taken as the cut off value for the definition. In addition at least one of the following must be present:

1. Development of new pathological Q waves
2. Angiographic evidence of graft occlusion or a new native coronary artery occlusion
3. Imaging evidence of new loss of viable myocardium or a new ischemic regional wall motion abnormality

References

1. Kristian Thygesen, Joseph S Alpert, Harvey D White, Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction. Universal definition of myocardial infarction. Eur Heart J 2007;28:2525-2538.
2. Kristian Thygesen, Joseph S Alpert, Allan S Jaffe, Bernard R Chaitman, Jeroen J Bax, David A Morrow, Harvey D White, Executive Group on behalf of the Joint European Society of Cardiology (ESC)/American College of Cardiology (ACC)/American Heart Association (AHA)/World Heart Federation (WHF) Task Force for the Universal Definition of Myocardial Infarction. Fourth Universal Definition of Myocardial Infarction (2018). J Am Coll Cardiol. 2018 Oct 30;72(18):2231-2264.