Left Main Coronary Artery Disease

Left main coronary artery disease is atherosclerotic narrowing of the left main trunk. Significant disease is a diameter stenosis of 50% or more on angiography, a minimal lumen area under 6 mm2 on intravascular ultrasound, or a fractional flow reserve of 0.80 or less in a patient with a doubtful angiographic severity.

It is found in about 4 to 6% of patients having angiography. The distal bifurcation is involved in most cases, and most patients have additional vessel disease. The left main supplies about 75% of left ventricular myocardium in right dominant systems, so occlusion often causes shock or sudden death.

Left main equivalent disease is a severe stenosis of both the proximal left anterior descending and proximal circumflex arteries.

Untreated significant disease carries high mortality. Revascularisation, by bypass surgery or in selected patients percutaneous intervention, improves outcome.

Pathophysiology.

Plaque forms at the carina of the distal bifurcation, where shear stress is low. Ostial lesions arise from aortic root disease, and shaft lesions are less frequent.

Occlusion or high grade narrowing impairs perfusion of both the anterior and lateral walls, producing diffuse ST depression with ST elevation in aVR, and large territory ischaemia.

The anatomical complexity of the left main and downstream disease is graded by a scoring system (low 22 or less, intermediate 23 to 32, high 33 or more), which helps choose between surgery and stenting.

Angina (often severe or crescendo), dyspnoea, syncope, acute coronary syndrome, acute pulmonary oedema, ventricular arrhythmia and cardiogenic shock. Many patients are asymptomatic or have atypical symptoms until a major event. Examination is often normal.

• ECG: ST depression in several leads with ST elevation of 1 mm or more in aVR (supports left main or proximal multivessel disease); with complete occlusion, anterior and lateral ST elevation and bundle branch block.
• Troponin (high sensitivity assay), echocardiography (regional wall motion, ejection fraction).
• Coronary angiography is the key test. Left main stenosis can be underestimated in short trunks and ostial disease, so confirm with intravascular ultrasound (minimal lumen area under 6.0 mm2; under 4.5 mm2 in some Asian populations) or a pressure wire in the downstream vessels.
• CT coronary angiography can exclude significant disease and plan treatment in stable patients.
• Surgical risk score and frailty assessment, anatomical complexity score, kidney function and bleeding risk, to direct the heart team decision.

Differential diagnosis.

• Spontaneous coronary artery dissection of the left main.
• Left main spasm, ostial stenosis from aortitis, and embolism.
• Takotsubo syndrome and myocarditis with ST-elevation in aVR.
• Aortic dissection involving the left main ostium.

Acute presentation with shock or occlusion (emergency).

• Immediate catheter laboratory activation. Aspirin 150 to 300 mg loading dose; unfractionated heparin 70 to 100 units/kg intravenously. P2Y12 inhibitor loading with ticagrelor 180 mg (or clopidogrel 600 mg when surgery is likely).
• Haemodynamic support: noradrenaline 0.05 to 0.5 microgram/kg/min for mean arterial pressure over 65 mmHg, intra-aortic balloon pump, percutaneous left ventricular assist device or veno arterial extracorporeal membrane oxygenation, with early angiography and revascularisation.
• Emergency percutaneous intervention restores flow in most patients with ST elevation. Emergency bypass surgery is chosen for unsuitable anatomy or failed stenting.

Stable and non-ST-elevation presentations.

• Medical therapy: aspirin 75 to 100 mg daily; atorvastatin 40 to 80 mg daily; metoprolol succinate 25 to 200 mg daily; ramipril 2.5 to 10 mg daily (ejection fraction 40% or under, diabetes, hypertension or kidney disease); glyceryl trinitrate 400 to 800 microgram sublingually for pain. Anticoagulation with enoxaparin 1 mg/kg subcutaneously every 12 hours (once daily when creatinine clearance is under 30 mL/min) until revascularisation.
• Revascularisation is indicated in all suitable patients, in the same admission when the presentation is acute.

Choice of revascularisation (heart team).

• Bypass surgery is preferred for high anatomical complexity (score 33 or more), diabetes with multivessel disease, reduced ejection fraction, and when additional vessels need grafting. Left internal mammary artery to the left anterior descending artery plus further grafts (radial artery or saphenous vein).
• Percutaneous intervention is a reasonable alternative for low to intermediate complexity (score 32 or less), isolated ostial or shaft lesions, high surgical risk and patient preference. Use intravascular ultrasound or optical coherence tomography for planning and optimisation. For distal bifurcation disease, a single stent strategy with provisional side branch treatment is preferred, and a two stent technique (double kissing crush) is used for large, diseased side branches. Final kissing balloon and high pressure optimisation.

Antithrombotic therapy after revascularisation.

• After stenting: aspirin 75 to 100 mg daily and ticagrelor 90 mg twice daily (or clopidogrel 75 mg daily; prasugrel 10 mg daily, 5 mg when weight is under 60 kg or age is 75 or over) for 12 months after an acute coronary syndrome and 6 months in chronic coronary syndromes, shortened to 1 to 3 months when bleeding risk is high. Pantoprazole 40 mg daily.
• After surgery: aspirin 75 to 100 mg daily lifelong, started within 6 hours of surgery. After an acute coronary syndrome, add ticagrelor 90 mg twice daily for 12 months when bleeding risk allows.
• Before elective surgery: stop ticagrelor 3 to 5 days before, clopidogrel 5 days and prasugrel 7 days, and continue aspirin.

Secondary prevention. LDL cholesterol under 1.4 mmol/L with ezetimibe 10 mg daily and a PCSK9 monoclonal antibody when needed; blood pressure under 130/80 mmHg; smoking cessation; SGLT2 inhibitor for heart failure or diabetes (dapagliflozin 10 mg or empagliflozin 10 mg daily); cardiac rehabilitation.

Monitoring. Symptoms and ECG at 4 weeks; echocardiography at 1 to 3 months; functional testing or CT angiography for recurrent symptoms; lipids at 4 to 12 weeks; surveillance imaging of the left main stent at 6 to 12 months in high risk anatomy.

Referral and escalation. All left main disease needs a heart team decision, ideally within the same admission. Refer immediately for shock, ventricular arrhythmia or ongoing ischaemia.

Special groups.

• Women and older adults: higher bleeding risk, so adjust antithrombotic duration and doses.
• Diabetes and chronic kidney disease: surgery is favoured when anatomy is complex; limit contrast.
• Pregnancy: spontaneous coronary artery dissection is the usual cause; avoid routine stenting in stable patients.