Postoperative myocardial infarction (POMI) is an important complication after noncardiac surgery, that is associated with increased risk of mortality. In order to improve prognosis, routine postoperative monitoring with cardiac biomarkers is recommended to identify patients at risk for POMI early after surgery. In this thesis, we have evaluated the effect of routine troponin monitoring, we explored determinants of myocardial injury (troponin elevation), and also determined patient selection criteria for monitoring.
Methods and results
First, the association between postoperative myocardial injury and mortality was studied in a cohort of 3,224 patients above 60 years of age after intermediate to high risk noncardiac surgery. Myocardial injury as measured by troponin elevation occurred in 22% of the patients. Patients with myocardial injury had a 1.4-2.2 times increased risk of mortality within one year after surgery as compared to patients without myocardial injury. Next, the causes of death and cardiac interventions in patients with myocardial injury were studied. Most patients with myocardial injury died of malignancies, and only 5% of patients were reported to have died of cardiac causes. A cardiac intervention including prescription of medication was carried out in only 16% of patients with myocardial injury.
Next, the prognostic value of troponin kinetics was determined. An absolute change in troponin of 200 ng/L was significantly associated with mortality, but such a rise-and-fall pattern had no additional prognostic value to predict mortality on top of the highest troponin value that was measured.
Furthermore, determinants of myocardial injury were explored. We found that hypotension, defined as an intraoperative decrease in mean arterial blood pressure of >40% as compared to the preoperative blood pressure with a duration of more than 30 minutes, may be associated with myocardial injury. Coronary artery disease was found to be more prevalent in patients with myocardial injury, as compared to patients without myocardial injury (50% versus 15%, Relative Risk 3.3). Incidentally, we found pulmonary emboli in 33% of the patients with myocardial injury, versus 20% of patients without myocardial injury, although this difference was not statically significant.
Finally, patient groups at highest risk of POMI were identified in order to define selection criteria for routine troponin monitoring. We found that emergency surgery patients, or elective surgery patients with a Revised Cardiac Risk Index >1 had the highest risk of POMI (>1%), hence these patients may be selected for routine troponin monitoring.
Routine troponin monitoring strongly identifies patients with an increased risk of POMI and death. However, it has yet little effect on interventions to prevent POMI and death, as in most patients the cause of the myocardial injury is not clear and treatment options are not well established. Therefore, future research should determine whether patients may benefit from routine troponin monitoring. As long as this is not elucidated, it should not be broadly implemented in clinical care.