Postoperative Myocardial Injury

Postoperative myocardial injury is a rise in cardiac troponin over the 99th percentile upper reference limit within 30 days of surgery, from any cause, ischaemic or not. It is usually silent and strongly predicts death and later cardiovascular events.

Epidemiology. With routine troponin measurement, about 8% to 20% of adults over 45 years having major noncardiac surgery are affected, and over 90% have no ischaemic symptoms. Thirty day mortality is about 10% in those with injury, compared with about 1% without.

Causes.

• Supply demand mismatch: tachycardia, hypotension, anaemia, hypoxaemia.
• Plaque rupture with thrombosis.
• Coronary spasm.
• Sepsis, pulmonary embolism, atrial fibrillation with rapid rate, heart failure, stress cardiomyopathy.
• Chronic kidney disease, myocarditis, stroke, cardioversion.

Risk factors. Age 65 or over, coronary, peripheral or cerebrovascular disease, diabetes, chronic kidney disease, anaemia, emergency and vascular surgery, intraoperative hypotension and tachycardia.

Pathophysiology.

Surgery raises catecholamines and oxygen demand, while anaesthesia, bleeding and hypotension reduce supply. In fixed coronary stenosis this produces ischaemic injury.

A minority arise from plaque rupture in a pro thrombotic, inflammatory postoperative state. Non-ischaemic injury arises from sepsis, strain on the right heart and direct myocardial stress.

Usually asymptomatic because of analgesia and sedation. When present: chest pain, dyspnoea, diaphoresis, palpitations, unexplained tachycardia, hypotension, new delirium or arrhythmia.

Red flags.

• ST-segment change or new Q waves.
• Haemodynamic instability.
• Ventricular arrhythmia.
• Acute heart failure.
• New wall motion abnormality.

Measure high sensitivity troponin 6 to 12 hours after surgery and daily on days 1 to 3 in patients aged 65 or over, or 45 to 64 with cardiovascular disease. Interpret using the assay specific 99th percentile, and look for a rise or fall (a relative change of 20% or more if the baseline is raised).

Obtain a 12-lead ECG and an echocardiogram. Work up non-ischaemic causes: infection, embolism, arrhythmia, anaemia, renal function. Consider coronary angiography or CT coronary angiography if infarction is suspected.

Differential diagnosis.

• Myocardial infarction (type 1 or type 2).
• Sepsis related injury.
• Pulmonary embolism.
• Atrial fibrillation with rapid rate.
• Stress cardiomyopathy.
• Myocarditis or pericarditis.
• Chronic kidney disease with baseline elevation.

Treat the cause. Correct hypotension (mean arterial pressure 65 mmHg or more), tachycardia (heart rate under 100/min), anaemia (transfuse at haemoglobin under 70 g/L, or under 80 g/L with cardiovascular disease, or under 80 to 100 g/L with active ischaemia), hypoxaemia, pain and sepsis.

Secondary prevention when bleeding risk allows.

• Aspirin: 75 to 100 mg orally once daily; long term; maximum 100 mg for this purpose; monitor haemoglobin and bleeding; stop or defer if surgical bleeding; avoid in active ulcer, and consider a proton pump inhibitor; avoid with creatinine clearance under 10 mL/min or severe hepatic impairment.
• Atorvastatin: 40 to 80 mg orally once daily; long term; maximum 80 mg; check liver enzymes at baseline and if symptomatic, and creatine kinase if myalgia; reduce dose with clarithromycin; avoid in active liver disease; no renal adjustment.
• Beta blocker only if tachycardia or hypertension persists without heart failure, bradycardia or hypotension; titrate cautiously.

Monitoring. Serial troponin to peak, ECG, blood pressure, haemoglobin, rhythm.

Referral and escalation. Cardiology review for any infarction features, arrhythmia, heart failure or large troponin rise. Urgent if ST change or instability.