Background Many patients with myocardial infarction with non-obstructive coronary arteries (MINOCA) are discharged without a known aetiology for their clinical presentation. This study sought to assess the effect of this ‘indeterminate MINOCA’ diagnosis on the prevalence of recurrent cardiovascular events and presentations to the Cardiac Emergency Department (CED). Methods We retrospectively analysed all patients meeting the diagnostic MINOCA criteria presenting at a large secondary hospital between January 2017 and April 2019. Participants Patients were divided into the (1) ‘indeterminate MINOCA’, or (2) ‘MINOCA with diagnosis’ group. The primary outcome was the occurrence of major adverse cardiac events (MACE) defined as the composite of all-cause mortality, non-fatal myocardial infarction, stroke and any revascularisation procedure. Secondary outcomes were all recurrent visits at the CED, and MACE including unplanned cardiac hospitalisation. Results In 62/198 (31.3%) MINOCA patients, a conclusive diagnosis was found (myocardial infarction, (peri)myocarditis, cardiomyopathy, or miscellaneous). MINOCA patients with a confirmed diagnosis were younger compared to those with an indeterminate diagnosis (56.7 vs. 62.3 years, p = 0.007), had higher maximum troponin-T [238 ng/L vs. 69 ng/L, p < 0.001] and creatine kinase (CK) levels [212U/L vs. 152U/L, p = 0.007], and presented more frequently with electrocardiographic signs of ischaemia (71.0% vs. 47.1%, p = 0.002). Indeterminate MINOCA patients more often showed recurrent CED presentations (36.8% vs. 22.6%, p = 0.048), however the occurrence of cardiovascular events was equal (8.8 vs. 8.1%, p = 0.86). Multivariable analysis showed that elevated levels of troponin-T and CK, ST-segment deviation on electrocardiography, reduced left ventricular ejection fraction, regional wall motion abnormalities, and performance of additional examination methods were independent predictors for finding the underlying MINOCA cause. Conclusions Only in one-third of MINOCA patients a conclusive diagnosis for the acute presentation was identified. Recurrent CED visits were more often observed in the indeterminate MINOCA group, while the occurrence of cardiovascular events was similar across groups. Trial registration Retrospectively registered

Funding Acknowledgements Type of funding sources: None. Background and purpose Although cardiac rehabilitation (CR) after myocardial infarction (MI) has been proven to be beneficial, only a minority of patients participate. This study was performed to gain more knowledge about referral and participation rates for CR in patients with myocardial infarction with Nonobstructive Coronary Arteries(MINOCA). Methods All patients meeting the diagnostic MINOCA criteria and admitted between January 2017 and April 2019 were retrospectively analysed. They were divided into the 1) ‘Conclusive MINOCA’ (confirmed MI, (peri)myocarditis, cardiomyopathy, or miscellaneous) and 2) ‘Indeterminate MINOCA’ group. Patients who died in hospital were excluded. Referral and participation in CR was verified. Results Of the 196 included MINOCA patients, 110 (56%) were female and the mean age was 60±13.7 years. 62 Patients(31.6%) had conclusive MINOCA and 134 patients (68.4%) had indeterminate MINOCA. In Figure 1 the distribution of CR referral and participation is shown. Figure 2 shows the referral and participation rates for conclusive and indeterminate MINOCA patients. Conclusive MINOCA patients were more likely to be referred(79.0% vs. 61.9%, p=0.018) and participated more often in CR (45.2% vs. 26.1%, p=0.008). This relation was even stronger when confirmed MI was the final diagnosis as compared to the other MINOCA patients (referral91.3% vs. 64.2%, p=0.009; participation 69.6% vs. 27.2%, p&lt;0.001). Conclusion Only one-third of MINOCA patients participate in CR. Referral and participation rates were significantly higher in MINOCA with confirmed underlying diagnosis (especially confirmed MI) as compared to MINOCA with indeterminate diagnosis. MINOCA patients should be more often referred to CR with a focus on MINOCA with indeterminate underlying diagnosis.