Myocardial infarction in the absence of obstructive coronary artery disease - can the underlying causes be identified by cardiac magnetic resonance?
Authors: Martins De Carvalho M , Pinto RA , Proenca T , Grilo P , Resende CX , Amador AF , Costa CM , Calvao J , Torres S , Cabrita A , Marques C , Vasconcelos M , Macedo F 
Published: July 2021

Abstract

Funding Acknowledgements
Type of funding sources: None.

Background
Myocardial Infarction in the Absence of Obstructive Coronary Artery Disease (MINOCA) is a clinical entity that occurs in up to 15% of all acute coronary syndromes (ACS). It is a "working diagnosis", as it is constituted by several etiologies.

Purpose
To identify the utility of CMR in determining the etiological diagnosis of MINOCA events, with potential impact in the therapeutic management of these patients.

Methods
Patients with MINOCA who were admitted to the Cardiology department at a tertiary center, between 2015 and 2020, were included. MINOCA was defined as an ACS with non-obstructive (&lt;50%) coronary artery disease and no other clinically specific cause, in accordance with definition adopted in the 2020 ESC Guidelines for the management of ACS in patients presenting without persistent ST-segment elevation. Patients who did not had a coronary exam (either CT or invasive angiogram) or a CMR were excluded. All CMR exams were performed in a 3 Tesla equipment using a comprehensive protocol (cine, T2-weighted, and late gadolinium sequences). Clinical, electrocardiographic, echocardiographic and CMR data were collected.

Results
In a population of 29 patients, the mean age was 55 ± 17 years-old at the time of the cardiac event, 51.7% were male. Concerning to cardiovascular risk factors, 58.6% of patients had dyslipidaemia, 51.7% had hypertension, 13.7% were diabetic, 41.4% were smokers or previous smokers and 31.0% had obesity. Atrial fibrillation was present in 3.4% of patients. As for the EKG patterns, 41.4% of the patients had ventricular repolarization changes, 13.8% had a transitory ST elevation pattern, 6.9% had a complete left bundle branch block and 37.9% had a normal EKG; most of the ischemic EKG alterations were on the anterior wall (66.7%). The median high sensitivity I troponin levels were 1877.5 (IQR 225.3 – 5985.8) ng/L. The majority of patients (58.6%) had echocardiographic wall motion abnormalities; of those, the most common (41.1%) were on the left anterior descendent artery territory. CMR (performed at a median of 5 days from presentation) was able to identify the cause for the troponin rise in 58.6% of the cases; late gadolinium enhancement and oedema were present in 41.4% and 62.1% of patients, respectively. The mean left ventricle ejection fraction (EF) was 57.7 ± 8.5% and the mean right ventricle EF was 61.5 ± 6.1%. An ischemic pattern was present in 29.4% of the total population. In 17.6% of the patients findings were consistent with Takotsubo syndrome and in 29.4% with myocarditis.

Conclusion
CMR established the etiological cause in 58.6% of the cases, with potential implications in medical therapy. These findings highlight the importance of CMR in MINOCA diagnosis and the potential improvement in patient care with multi-modality imaging.