Myocardial Injury in Noncardiac Surgery in Sweden (MINSS) Study: Multi-centre, Observational Cohort Study of Patients Undergoing Elective, Major Abdominal Surgery.

Inclusion Adults at least 50 years old undergoing elective, major or major/complex abdominal surgery defined according to the Surgical Outcome Risk Tool (www.sortsurgery.com), requiring general anaesthesia and at least one overnight stay. Exclusion Patients with acute coronary syndromes, new or decompensated heart failure at presentation, documented severeaortic stenosis, severely reduced ejection fraction (<40%) and inability to follow the procedures of the study or lack of capacity to give informed consent. Transplantation, trauma, endocrine, vascular and endovascular surgical procedures will also be excluded due to their distinct risk profiles compared with the intended population. Outcome The composite endpoint is all-cause mortality at 30 days and MACCE, the latter defined as nonfatal cardiac arrest, acute MI, congestive heart failure, new cardiac arrhythmia, angina and stroke. Secondary endpoints are 365-day all-cause mortality and MACCE. Data collection Relevant clinical and peri-operative data for example comorbidities, RCRI, ASA-PS score, type and length of surgery, blood loss and intra-operative lowest blood pressure will be collected.

Plasma levels of hsTnT, NTproBNP, Copeptin, MR-proADM and CT-proET1 will be measured at five sampling points: pre-operatively, immediately postoperatively, and on Days 1 to 3 postoperatively or until discharge. Data on MACCE will be obtained from patient records and structured telephone interviews at 30 and 365 days by assessors blinded to the results of the biomarker analyses.

Statistics Based on an assumed incidence of MINS of 10%(1) and 365-day mortality in the non-MINS group of 11% (estimate based on current data from the Swedish Perioperative Registry), the required sample size to detect an effect size of 10% is 1142. To account for drop-outs and missing data, we will recruit up to 1600 patients.

Receiver operating curve analysis will be used to determine the optimal threshold of each biomarker in predicting mortality/MACCE. The net reclassification index will be used to assess if biomarkers confer added value to the RCRI for the classification of MACCE.

A multivariable Cox proportional hazard models will be used to test the independent prognostic value of biomarkers. The sample size allows for adjustment of the following prespecified variables, selected on the basis of clinical plausibility and prior evidence: age, sex, ASA-PS class, RCRI, Charlson Comorbidity Index, length and type of surgery, presence of intra-operative hypotension, pre-operative creatinine and haemoglobin, biomarkers (alone and in combination). An independent statistical analysis will be conducted after recruitment of 600 patients to assess the frequency of outcomes and missing data, after which the sample size may be adjusted.