Approximately every five years, the American College of Cardiology, the American Heart Association, the European Society of Cardiology, and the World Heart Federation convene workgroups to try to standardize the definition of myocardial infarction (MI) for both documentation and research purposes.
The last iteration in 2012 produced five different classifications.
The classic MI due to plaque rupture in a coronary artery was designated as a Type 1 infarction. The 2012 article also notes that 5-20 percent of patients will have mild or no coronary artery disease (CAD) at angiography.
Myocardial necrosis due to oxygen supply/demand mismatch is Type 2 MI. This category includes vasospastic MI.
Sudden death with evidence of acute MI but no biomarkers is Type 3 MI. Cardiac necrosis associated with percutaneous coronary intervention (4a) and stent thrombosis (4b) is Type 4 MI. Cardiac necrosis associated with coronary artery bypass grafting (CABG) is Type 5 MI.
Subsequently, cardiologists identified two groups that did not fit neatly into any of the established classifications. One was patients with anginal-quality chest pain and abnormal stress testing, but mild or no epicardial coronary artery disease on angiogram. Heretofore many cardiologists (including myself!) tended to dismiss these patients as “false positives.” However, research has long shown that such patients do not have a benign prognosis, and thus the term “INOCA” (ischemia with no obstructed coronary arteries) was introduced to recognize the higher risk present in these patients.
The other problematic group is patients with elevated troponins and mild or no epicardial coronary artery blockage on angiogram. Cardiologists certainly respect elevated troponins, and most of these patients were not described as “false positives.” Nonetheless, it was not necessarily appreciated until recently that these patients are indeed at higher risk, even in the absence of significant coronary blockages. In recognition of the need to approach these patients more aggressively, the term “MINOCA” (myocardial infarction with no obstructed coronary arteries) was coined in 2013.
Generally speaking, INOCA is associated with conventional cardiac risk factors such as hypertension, hyperlipidemia, and obesity. It is much more common in women. Underlying mechanisms may involve decreased coronary flow reserve, endothelial dysfunction, and elevated platelet reactivity. Coronary intravascular ultrasound can reveal more extensive atherosclerosis than is appreciated on angiography, due to positive remodeling. This may indicate a diffuse inflammatory state in the vessels.
MINOCA encompasses a heterogeneous group, including the following:
- Plaque rupture without severe obstruction, but with resultant vasospasm, microscopic thromboembolism, or thrombosis with spontaneous thrombolysis. Technically a Type 1 MI.
- Vasospasm without plaque rupture
- Thromboembolism due to thrombophilic state
- Coronary dissection, if not visible on angiography
- Takotsubo (stress) cardiomyopathy
- Type 2 MI with other primary diagnosis (e.g. sepsis, hypertensive crisis, arrhythmia, severe valvular disease)
The challenge going forward will be to properly categorize all patients to create relatively homogeneous groups that will be meaningful for both clinical documentation and research purposes.
