The American Heart Association (AHA) released a scientific statement that aims to provide a formal and updated definition for Myocardial Infarction in the Absence of Obstructive Coronary Artery Disease (MINOCA). It also outlines a useful framework for the diagnostic approach and management of patients with potential MINOCA.
Myocardial infarction in the absence of obstructive coronary artery disease is found in 5-6% of all patients with acute infarction who are referred to angiography. Unlike other patients with an MI, patients with MINOCA are typically younger, female and do not necessarily have the typical coronary artery disease risk factors such as dyslipidemia, hypertension or diabetes mellitus. Additionally, patients with MINOCA are less likely to have electrocardiographic ST-segment deviation and usually have a smaller degree of troponin elevation. Despite the various reviews and statements surrounding MINOCA, some clinicians still exclude a myocardial infarction if no obstruction is identified on angiography.
The need to define MINOCA as an entity that differs from patients with an acute MI due to CAD is emphasized in this statement. Patients with MINOCA usually do better than patients with MI due to CAD. Also, there are multiple atherosclerotic and non-atherosclerotic causes of MINOCA that differ in their underlying pathophysiology from the typical patient with an acute MI. Finally, there are only limited studies that study MINOCA and therefore, there are difficulties in deciding on the optimal evidence-based therapy. According to the statement, the diagnosis of MINOCA can be made when the clinical presentation meets three different criteria: (1) The patient meets the definition of acute myocardial infarction as defined by a rise or fall in cardiac troponin with one value above the 99th percentile upper reference limit in addition to clinical evidence of infarction; (2) There are no obstructive coronary lesions on angiography; (3) There is no specific alternative diagnosis for the clinical presentation.
[perfectpullquote align=”full” bordertop=”false” cite=”” link=”” color=”” class=”” size=””]“It is likely that the newer high-sensitivity troponin assays will increase the number of patients appropriately and inappropriately diagnosed with MINOCA. Therefore, we wish to emphasize the importance of following the proposed algorithm so that only appropriate patients are identified as having MINOCA. Clinicians should consider a working diagnosis of MINOCA only in those patients who have a clinical presentation suggesting a true AMI as defined by the “Fourth Universal Definition of Myocardial Infarction” (2018) (ie, a clinical presentation consistent with myocardial ischemia and a rising or falling pattern of cardiac enzymes).” – Dr. Jacqueline E. Tamis-Holland, M.D.
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The algorithm provided in the statement highlights the need to consider alternative diagnoses, other than an acute myocardial infarction, that could explain the elevated troponin level. If an acute MI remains the diagnosis, authors suggest that all angiographic images be re-reviewed and to consider further imaging to exclude potentially overlooked obstructive CAD as well as other non-ischemic causes of myocardial injury. These would include myocarditis, Takotsubo syndrome and other cardiomyopathies. Cardiac magnetic resonance imaging (CMRI) is recommended as an investigation in the workup of MINOCA because it can exclude various conditions such as Takotsubo syndrome, myocarditis, and cardiomyopathy while simultaneously confirming the presence of myocardial necrosis. Although the authors do say that that this imaging modality is highly useful, they recognize that it is not widely available and is, therefore, not essential in the diagnosis of MINOCA. The statement then proceeds to explain the various atherosclerotic and non-atherosclerotic causes of MINOCA. These include plaque disruption, epicardial coronary vasospasm, coronary microvascular dysfunction, coronary embolism/thrombosis, spontaneous coronary artery dissection, and supply-demand mismatch. The authors also describe the diagnostic investigations that may be used to diagnose the underlying cause of MINOCA.
Unlike patients with an acute MI due to CAD, patients with MINOCA may have a lower atherosclerotic burden and may not benefit from the routine use of anti-ischemic therapies such as antiplatelet medication. While retrospective studies have demonstrated that the use of statins and ACE inhibitors/ARBs, there are no randomized controlled trials that have demonstrated the benefit of routine use of cardioprotective therapies in all MINOCA patients. Instead, the authors provide treatment recommendations based on the underlying cause of MINOCA. The authors end the statement by emphasizing the importance of following the proposed algorithm. With the increasing utilization of newer high-sensitivity troponin assays, it is likely that the number of patients who are diagnosed with MINOCA will increase. However, the diagnosis of MINOCA may be inappropriate in some of those patients. Additionally, the authors advocate the use of a MINOCA-specific term in the International Classification of Diseases–Tenth Revision. This would make identifying patients with MINOCA easier in the future. Finally, the authors emphasize the importance of researching the optimal treatment of MINOCA and recognize that this is a knowledge gap that needs to be assessed.