What are the types of myocardial infarction? Cardiology Basics

What are the types of myocardial infarction? Cardiology Basics

World Heart Federation along with major European and North American Heart Societies have brought forth the universal definition of myocardial infarction. It has been revised the fourth time in 2018. In the latest revision myocardial infarction has been classified into 5 types, of which type 4 has three subtypes as well.

Type 1 is the type of myocardial infarction which all of us are familiar with. It occurs due to sudden occlusion of a coronary artery. This leads to chest pain and ECG changes. Myocardial damage can be noted on echocardiography as well as other imaging modalities like cardiac magnetic resonance imaging (CMR). A thrombus is observed within the coronary artery on coronary angiography.

Type 2 occurs when there is supply-demand mismatch. Sudden drop in hemoglobin due to any bleeding can reduce the supply of oxygen to the myocardium and consequent damage. Type 2 is more common in women and has poorer outcome due the often associated comorbidities.

In type 3, death occurs before troponin estimation which is essential for the diagnosis of myocardial infarction as per the definition can become positive. The person would have chest pain and early ECG changes, though the troponin evidence is lacking.

Type 4a is myocardial infarction associated with percutaneous coronary interventions. They will have symptoms and ECG changes as in type 1. Coronary angiogram will show a fresh obstruction which is related to a procedural complication.

In type 4b a coronary stent implanted during a percutaneous intervention gets obstructed later due to thrombosis formation inside it. This is known as stent thrombosis.

Type 4c is caused by in-stent restenosis due overgrowth of tissue into the stent. This is documented by coronary angiogram.

Type 5 is associated with coronary artery bypass grafting (CABG). It is also documented by ECG and coronary angiogram. Echocardiography or other imaging studies will show the new damage to myocardium.

Documentation of myocardial infarction in all these types needs cardiac troponin elevation in addition to other evidences, except in type 3. Troponin levels rise in a delayed pattern after a myocardial infarction, reaching a peak at 24 hours. Usually diagnostic levels are reached at about 6 hours after the coronary occlusion. So, in type 3, the levels do not reach diagnostic levels due to early death.