Perioperative Myocardial Infarction

Perioperative myocardial infarction is acute myocardial ischaemia with a rise and fall of troponin over the 99th percentile. It occurs during or within 30 days of surgery, most often in the first 48 hours.

Diagnosis also needs at least one of:

• Ischaemic symptoms
• New ischaemic ECG changes
• New pathological Q waves
• Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality
• Coronary thrombus on angiography

Epidemiology. About 0.5% to 1.5% of adults over 45 years having noncardiac surgery. Thirty day mortality is about 10% to 15%. Most cases are silent or atypical.

Types. Type 1 follows plaque rupture with thrombosis. Type 2 follows supply demand mismatch from hypotension, tachycardia, anaemia, hypoxaemia or arrhythmia, and is the commoner form.

Risk factors. Coronary disease, previous infarction, heart failure, diabetes, chronic kidney disease, age over 65, vascular surgery, emergency surgery and recent coronary stent.

Pathophysiology.

Perioperative sympathetic activation, hypercoagulability and inflammation promote plaque rupture and thrombosis.

Tachycardia and hypotension reduce coronary perfusion time while raising demand, which causes ischaemia in fixed stenosis.

Chest pain, dyspnoea, diaphoresis, nausea, palpitations, hypotension, new arrhythmia, acute heart failure, new delirium, or no symptoms.

Red flags.

• ST elevation or new left bundle branch block.
• Ongoing pain with dynamic ECG change.
• Cardiogenic shock.
• Ventricular tachycardia or fibrillation.
• Acute pulmonary oedema.
• Mechanical complication (new murmur).

• 12-lead ECG immediately and repeated at 15 to 30 minutes if non-diagnostic.
• Serial high sensitivity troponin.
• Echocardiography for wall motion, ejection fraction and mechanical complications.
• Coronary angiography for ST elevation, ongoing ischaemia or instability.
• Full blood count, electrolytes, renal function and blood gas to find triggers.

Differential diagnosis.

• Myocardial injury without infarction.
• Pulmonary embolism.
• Aortic dissection.
• Sepsis.
• Stress cardiomyopathy.
• Pericarditis.
• Atrial fibrillation with rapid rate.
• Pneumothorax.

Immediate. Oxygen if saturation is under 94%, continuous ECG, analgesia, and correction of triggers. Keep mean arterial pressure at 65 mmHg or more, heart rate under 100/min, and haemoglobin over 70 g/L (over 80 g/L with cardiovascular disease, 80 to 100 g/L with active ischaemia).

ST elevation. Primary angioplasty within 120 minutes of first contact. Fibrinolysis is usually avoided after major surgery in the previous 3 weeks.

Type 1 or high risk non-ST-elevation infarction, if bleeding risk is acceptable after discussion with the surgeon.

• Aspirin: 150 to 300 mg orally once as a loading dose, then 75 to 100 mg once daily long term; maximum 300 mg loading; monitor bleeding and haemoglobin; avoid in active bleeding or severe hepatic impairment.
• Enoxaparin: 1 mg/kg subcutaneously every 12 hours for 2 to 8 days or until revascularisation or discharge. Maximum 100 mg for each of the first two doses. Monitor haemoglobin, platelets and anti-Xa in obesity or renal impairment. Give 1 mg/kg once daily if creatinine clearance is under 30 mL/min.
• A second antiplatelet agent is added after angiography depending on stent need and surgical bleeding risk.
• Atorvastatin: 80 mg orally once daily; long term; maximum 80 mg; liver enzymes at baseline; reduce with clarithromycin.
• Bisoprolol: 1.25 to 2.5 mg orally once daily, titrated to heart rate 60 to 70/min. Maximum 10 mg daily in this setting. Monitor heart rate and blood pressure. Avoid in heart failure with shock, bradycardia or hypotension; reduce in severe renal or hepatic impairment.

Type 2 infarction. Correct the cause: control bleeding, give fluid or blood, treat arrhythmia, hypoxaemia and sepsis.

Monitoring. Telemetry for at least 48 to 72 hours, serial troponin to peak, daily ECG, haemoglobin, renal function and echocardiography.

Referral and escalation. Immediate cardiology contact for ST elevation, instability, high risk features or suspected stent thrombosis. Involve the surgical team to balance bleeding and thrombosis.