Epidemiological Patterns, Management Strategies and Cost Analysis of Care for the Patient With Perioperative Myocardial Injury When BNP is Used as a Screening Tool for Non-Cardiac Surgery

Major cardiac complications are responsible for at least a third of perioperative deaths and are associated with significant morbidity, prolonged hospitalization and increased costs. This number is expected to rise as more surgeries are undertaken in older and frailer patients. The term myocardial injury after noncardiac surgery (MINS) is used to describe all myocardial injury due to ischemia occurring in the first 30 days after surgery. MINS includes:

1. myocardial infarction (cardiac troponin I ≥ 0.04 ug/L) with at least one of: symptoms of ischemia, new ST segment / T wave changes or new left bundle branch block, pathological Q waves, new loss of viable myocardium or regional wall motion abnormality on echocardiogram, intracoronary thrombus identified on angiogram.
2. myocardial injury without MI (elevated troponin without the additional criteria needed to diagnose MI).

The Canadian Cardiovascular Society (CCS) has developed a set of guidelines to help stratify which patients are at higher risk for cardiac mortality. In the latest revision of these guidelines, preoperative B-type natriuretic peptide (BNP) has been identified as a powerful independent predictor of perioperative cardiovascular complications. BNP is a protein released from ventricular cardiomyocytes. It is released in limited amounts during physiological conditions but this is increased significantly in ventricular failure, inflammation, fibrosis, ischemia and hypoxia. Rodseth et al. conducted a systematic review of the prognostic value of preoperative BNP and postoperative BNP in noncardiac surgery and showed that elevated preoperative BNP (i.e. ≥ 92 ng/l) carries a significant risk of 30-day mortality or nonfatal MI (21.8%). This is a significantly lower BNP value compared to what is typically seen in congestive cardiac failure patients. This study has been used to support the most recent CCS guidelines which add preoperative BNP as an important preoperative cardiac risk stratification tool. According to the CCS guidelines, patients with an elevated preoperative BNP should have daily troponins measured for 48 - 72 hours after surgery.

Troponins are components of the myocardial cell involved in contractility, specific subtypes I and T are expressed almost exclusively in the heart. An elevated troponin reflects necrosis of myocardial cells and is extremely useful in the diagnosis of a myocardial infarction. Even a slight elevation in postoperative troponins (TnTi ≥ 0.03ng/ml) without ischemic clinical symptoms can lead to a higher mortality, nonfatal cardiac arrest, nonfatal congestive heart failure, and nonfatal stroke.

While the value of screening for high risk patients through the use of preoperative BNP been demonstrated, the management of postoperative ischemia is less clear. At present, CCS guidelines recommend optimizing aspirin and statin therapy in patients with MINS, but no clear strategy has been elucidated. Evidence to support the use of aspirin and statins comes from the POISE trial. The MANAGE trial recommends starting patients who are not at risk of bleeding on the oral anticoagulant dabigatran for two years. Patients with ST-elevation MI carry a high mortality risk without reperfusion therapy (percutaneous coronary intervention or coronary artery bypass graft) and a high risk of bleeding with it. Patients with non ST-elevation MI may also require revascularization and subsequent dual antiplatelet therapy. It is evident from this brief overview that management of MINS varies from the non-invasive (aspirin and statin administration) to the invasive (PCI or CABG) depending on the extent of myocardial injury, hemodynamic stability and risk of bleeding secondary to the primary surgical procedure.