Myocardial Injury After Noncardiac Surgery

Myocardial injury after noncardiac surgery (MINS) is prognostically relevant myocardial injury due to presumed ischaemia, occurring during or within 30 days after noncardiac surgery, without a clearly non-ischaemic cause. It is defined by troponin thresholds and does not need symptoms or ECG change.

Diagnostic thresholds. For high sensitivity troponin T, a value of 20 to under 65 ng/L with an absolute rise of 5 ng/L or more from baseline, or a value of 65 ng/L or more. For troponin I, use assay specific thresholds tied to the local 99th percentile and a rise.

Epidemiology. It affects about 8% to 20% of adults over 45 years having major surgery. More than 85% are asymptomatic. Thirty day mortality rises with peak troponin, from about 3% to about 10%.

Risk factors. Age 65 or over, coronary, peripheral or cerebrovascular disease, diabetes, chronic kidney disease, anaemia, emergency or vascular surgery, intraoperative mean arterial pressure under 65 mmHg for 10 to 15 minutes or more, tachycardia and bleeding.

Pathophysiology.

Most cases are type 2 supply demand ischaemia in patients with fixed coronary stenosis, driven by hypotension, tachycardia, anaemia and hypoxaemia against raised catecholamine demand.

A minority follow plaque rupture in a hypercoagulable, inflammatory state.

Mostly silent, with analgesia and sedation masking symptoms. Possible chest pain, dyspnoea, tachycardia, hypotension, arrhythmia or delirium.

Red flags.

• Ischaemic ECG change.
• Haemodynamic instability.
• Ventricular arrhythmia.
• New heart failure.
• Troponin over 65 ng/L and rising.

Surveillance with high sensitivity troponin 6 to 12 hours after surgery and on days 1 to 3 is needed to detect MINS in high risk patients (aged 65 or over, or 45 to 64 with cardiovascular disease). Confirm with a 12-lead ECG and echocardiogram. Exclude overt non-ischaemic causes before assigning MINS: sepsis, pulmonary embolism, rapid atrial fibrillation, stress cardiomyopathy.

Differential diagnosis.

• Perioperative myocardial infarction.
• Sepsis related injury.
• Pulmonary embolism.
• Rapid atrial fibrillation.
• Stress cardiomyopathy.
• Chronic troponin elevation from kidney disease.

Correct triggers. Keep mean arterial pressure at 65 mmHg or more, heart rate under 100/min, haemoglobin over 70 g/L (over 80 g/L with cardiovascular disease, 80 to 100 g/L with active ischaemia), and oxygen saturation 94% to 98%. Treat pain, sepsis and bleeding.

Prevention. Continue chronic statin and beta blocker; avoid starting high dose beta blocker on the day of surgery. Avoid intraoperative hypotension.

Pharmacotherapy when bleeding risk is acceptable.

• Aspirin: 75 to 100 mg orally once daily; long term; maximum 100 mg; monitor bleeding and haemoglobin; defer with surgical bleeding; avoid in active ulcer or severe hepatic impairment.
• Atorvastatin: 40 to 80 mg orally once daily; long term; maximum 80 mg; liver enzymes at baseline and creatine kinase if myalgia; reduce with clarithromycin; avoid in active liver disease.
• Dabigatran (limited evidence from a single study): 110 mg orally twice daily, started within 35 days of injury and continued up to 2 years in that study; maximum 220 mg daily; monitor creatinine clearance, haemoglobin and bleeding; avoid if creatinine clearance is under 30 mL/min, with a mechanical valve, active bleeding or strong P-glycoprotein inhibitors.

Monitoring. Serial troponin to peak, ECG, haemodynamics and bleeding.

Referral and escalation. Cardiology for troponin over 65 ng/L, ECG change, symptoms, arrhythmia or heart failure. Arrange outpatient review and cardiovascular risk management after discharge.