This is a retrospective observational, single-center cohort trial with prospectively collected data. Ethical approval was obtained from the Regional Ethical Committee in Stockholm (registration number: Dnr 2017/1178-31).
Study population
Between 2020 and 2022 patients undergoing vascular surgery were recruited for a prospective trial registered at ClinicalTrials.gov (NCT03317561). Patients recruited for that study were assessed for eligibility for inclusion in the present trial. The inclusion criteria were adults (>18 years of age) undergoing elective arterial vascular surgery including open or endovascular aortic repair (EVAR), peripheral vascular surgery and carotid endarterectomy. The exclusion criteria were arterio-venous fistulas or surgery on veins, cognitive difficulties, communication difficulties and patient inclusion in other ongoing interventional trials.
Perioperative care
All patients received perioperative care, surgery, and anesthetic management according to the local routine practice. The anesthetic technique was determined by the attending anesthesiologist. Generally, local anesthesia was used for patients undergoing less complex EVAR and carotid surgery, regional anesthesia for peripheral surgery and general anesthesia for complex EVAR and open aortic surgery. All patients received postoperative care according to local routines and were monitored at a high-dependency post-anesthesia care unit, for at least four hours, before being discharged to the surgical ward. Biomarkers including High-sensitivity cardiac troponin T (hs-cTnT) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) were measured preoperatively and repeated after 4 to 6, 24 and 48 hours postoperatively. These biomarkers were measured using Cobas Immunoanalyser, Roche Diagnostics, Rotkreutz, Switzerland. Furthermore, preoperative 12-lead ECG was collected in all patients according to routine within seven days before index surgery. In some cases, postoperative ECG was collected within 48 hours after the surgery, at the discretion of the attending vascular surgeon or anesthesiologist.
Outcome
Two different definitions of PMI were used. Both distinguish between chronic hs-cTnT elevation and acute perioperative hs-cTnT elevation.
PMI1was defined according to the European Society of Cardiology’s guidelines as an absolute increase in hs-cTnT ≥14 ng/L from preoperative baseline within 48 hours of surgery (9).
PMI2 was defined as an increase of hs-cTnT from a preoperative value ≤14 ng/L to a postoperative value > 14 ng/L or an increase of hs-cTnT with ≥14 ng/L from a preoperative value >14 ng/L. This combines the definition above with the universal definition of myocardial injury (8,9).
ECG
The primary exposure of preoperative ECG signs of ischemia was defined as one or more of ST-elevation, ST-depression, T-wave inversion or pathological Q-wave. Each of these ECG changes was defined according to the most recent guidelines, for a more exact specification of the criteria used see Appendix A.
Statistics
The explorative nature of this observational study precluded the possibility of doing a pre-hoc power calculation. Perioperative characteristics are presented in Table 1 and preoperative ECG characteristics are presented in Table 2. Continuous data is presented as medians and interquartile ranges (IQR). Categorical data is presented with absolute count (n) and percentages (%). Univariate analysis was used to calculate P-values in Table 1 and 2, using Chi-squared test for categorical data, and Mann-Whitney U test for continuous data, as appropriate.
A logistic regression model was used to assess the unadjusted association between preoperative ECG signs of ischemia and both PMI1 and PMI2. The adjusted association between preoperative ECG signs of ischemia and both PMI1 and PMI2 was analyzed using multiple regression while adjusting for the following relevant confounders (based on domain knowledge): age, ASA score (American Society of Anesthesiologists), preoperative hs-cTnT value.
To explore the validity of our results among patients without major perioperative hemorrhage we chose to perform a sensitivity analysis where we repeated the multiple regression analysis described previously, to assess the association between preoperative ECG signs of Ischemia and PMI1 and PMI2, respectively, among patients with perioperative hemorrhage <1000 ml.
For all tests, P values <0.05 were considered statistically significant. All statistical analysis was performed using the statistical software R version 4.3.2 (R Core Team (2020). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria).