Myocardial infarction with non-obstructive coronary arteries (MINOCA) (i.e.<50% stenoses) on coronary angiography) is an underappreciated clinical entity concerning 5-6% of patients with acute myocardial infarction. Approximately 50% of these patients remain without appropriate diagnosis and treatment.

The MINOCA study aims at systematically assessing the frequency of underlying pathologies of MINOCA and outcomes with a multidisciplinary etiologic work-up and follow-up of 5 years including, for the first time, an implantable cardiac monitor (ICM) to assess the frequency of atrial fibrillation as underlying cause for MINOCA.

Approximately 5-6% of patients with acute myocardial infarction (AMI) have myocardial infarction with non-obstructive coronary arteries (MINOCA) (i.e.<50% stenoses) on coronary angiography and up to 50% of these patients remain without appropriate diagnosis and treatment. A multidisciplinary etiologic work-up of MINOCA has recently been proposed by international consensus documents. The present study aims for a structured scientific data collection from a full guideline-based work-up after MINOCA and follow-up of 5 years to assess clinical outcomes.

Untreated atrial fibrillation is a potentially neglected underlying cause of MINOCA. As implantable cardiac monitors (ICM) can detect atrial fibrillation with high accuracy, the aim of this study is, for the first time, to assess the occurrence of first diagnosed atrial fibrillation with the use of ICM in patients with MINOCA.

To allow for an all-comers data collection, patients with contraindication(s) to ICM implantation will be enrolled into the non-ICM group to assess the frequency of underlying causes of MINOCA and clinical outcomes throughout 5 years.

Inclusion Criteria ICM group

1. ≥18 years of age
2. Written informed consent
3. Acute myocardial infarction (AMI) type 1 in accordance with the 4th universal definition of myocardial infarction
4. Non-obstructive coronary arteries on angiography defined as the absence of coronary artery stenoses ≥50% in any potential infarct-related artery
5. No clinically overt specific cause for the acute presentation
6. Subendocardial or transmural late gadolinum enhancement (LGE) consistent with an ischemic etiology on cardiac magnetic resonance imaging (CMR)
7. No clear underlying cause of MINOCA and therefore increased probability of atrial fibrillation

Exclusion Criteria ICM group:

1. Known atrial fibrillation or atrial flutter
2. History of atrial fibrillation or atrial flutter ablation
3. Known coronary artery disease
4. Previous MI
5. Previous percutaneous coronary intervention (PCI)
6. Previous coronary artery bypass grafting (CABG)
7. Contraindications to CMR (i.e. non-MR-compatible implantable cardiac device, glomerular filtration rate (GFR) <30 ml/min)
8. Contraindications to ICM implantation
9. Clear underlying cause of MINOCA before ICM implantation

Inclusion Criteria non-ICM group:

1. ≥18 years of age
2. Written informed consent
3. AMI type 1 in accordance with the 4th universal definition of myocardial infarction
4. Non-obstructive coronary arteries on angiography defined as the absence of coronary artery stenoses ≥50% in any potential infarct-related artery
5. No clinically overt specific cause for the acute presentation
6. Subendocardial or transmural LGE consistent with an ischemic etiology on CMR

Exclusion Criteria non-ICM group:

1. Known coronary artery disease
2. Previous MI
3. Previous PCI
4. Previous CABG
5. Contraindications to CMR (i.e. non-MR-compatible implantable cardiac device, GFR <30 ml/min)

Consecutive patients with cardiac magnetic resonance imaging (CMR) confirmed MINOCA at 2 large tertiary care centers in Switzerland