ETHICS. SAMPLE SIZE CALCULATION

ETHICS

Primary ethical approval will be obtained from the Ethics Committee of the University of Tartu and thereafter each participating site will apply for local ethical approval. If, according to the local ethics approval, informed consent is needed for this observational study, we ask for approval of delayed informed consent that can be obtained from the patient or patient’s next of kin/proxy at the first possibility. In the event that the patient was in too severecondition to participate in this initial decision but the next of kin agreed with participation, then the patient will be asked secondarily. Patients will be excluded from the study and any data already collected will be deleted if the patient or the patient’s next of kin later declines participation in the study.

There are no interventions performed in this study. The study is purely observational, collecting medical data relating to the care provided in treatment of the patient. Data will be recorded in an electronic Case Report Form in a pseudonymized way. Each patient receives an identification number at the site (site number and patient number, e. g. 0101 for the first patient at site number 1); no personal data allowing identification of the patient are included in the database. Patients are identifiable only at the site via a coded patient log, accessible only to the primary investigator at each site.

The electronic Case Report Form will be created using theREDCap platform and stored on a secure server of the University of Tartu. Investigators will have accessto their own local data, to enter and editon the database, until all data collection is complete. Only the PI, the central study team in Estonia and the data quality control and analysis team will have access to the full database.

SAMPLE SIZE CALCULATION

An exact calculation of sample size is not applicable for this observational study with descriptive objectives. We considerthat at least 40 patients for each form of AMIare needed to describe incidence, outcome, diagnosis and management adequately. Based on preliminary results of a systematic review (CRD42021247148) we estimate that the proportion of NOMI (the least frequent form of AMI) is around 10% of all AMI cases. Accordingly, in total at least 400 patients will be needed. Based on our preliminary analysis of a systematic review (CRD42021247148) and a retrospective population-based study (NCT04867499) we estimate that 0. 06% (0. 05-0. 07) of all adult patients hospitalized in acute care hospitals have AMI. Accordingly, a total of about 666, 000 hospital admissions willneed to be screened to identifythese 400 patients. Therefore, 33 hospitals with a mean yearly case load of 40, 000 patients each recruiting patients for 6 months will be needed. Considering a possibly lower incidence in some countries/hospitalsand patients in whom informed consent is declined, we aim to recruit 40 hospitals to reach our final target. The concomitant number of cases with suspected but not confirmed AMI cannot be estimated and is expected to behighly dependent on local practices. In one prospective study, 34. 3% ofpatients with suspicion of AMI in the ED received a final diagnosis of AMI (10). In our more heterogeneous population including all hospitalized patients we estimate that thediagnosis of AMI will be confirmed in 1/5 of patients with suspectedAMI and therefore estimate that the total number of those with suspicion of AMI will be about2000.

Because of the defined study period common to all the sites with simultaneous but expectedly widely varying number of recruited patients, the maximal number of patients with AMI may reach 500 with up to 2500 patients overall.

Interim analysis will be performed at 4 months.

If the total number of patients with confirmed AMI is above 400 at this time point recruitment will be stopped. If the number of patients at this time point is below 250, the recruitment period will be prolonged to a maximum of 8 months.

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