Left Main Coronary Artery Disease: Revascularisation Strategy

Definition and Pathophysiology

Left main coronary artery disease (LMCAD) refers to atherosclerotic narrowing of the left main coronary artery, which supplies the left anterior descending and left circumflex coronary territories. Because these vessels perfuse a large proportion of the left ventricular myocardium, left main disease carries a substantial prognostic significance. The myocardial territory at risk has been described as approximately 75–100%, depending on coronary dominance.

Significant left main stenosis is generally defined as a diameter reduction of at least 50%. Severe proximal disease of both the proximal left anterior descending and proximal left circumflex arteries may constitute a functional equivalent of left main disease.

The clinical consequences depend on:

• The severity and location of stenosis

• Distal bifurcation involvement

• Coexisting multivessel disease

• The extent of jeopardized myocardium

• Left ventricular systolic function

• Diabetes and other comorbidities

• Anatomical complexity and completeness of possible revascularization

A proximal lesion jeopardizes more myocardium than a distal lesion. In observational data, a lesion proximal to the first septal perforator of the left anterior descending artery was associated with lower five-year survival than a more distal lesion.

Revascularisation improves myocardial blood flow and angina-related health status but does not reverse coronary atherosclerosis. Long-term benefit therefore depends on the integration of revascularisation with guideline-directed medical therapy and secondary prevention.

Clinical Presentation and Symptoms

The clinical presentation is variable. Patients may have:

• Stable angina or an anginal equivalent

• Exertional dyspnoea or reduced exercise tolerance

• Acute coronary syndrome

• Silent ischaemia

• Heart failure, particularly when left ventricular function is impaired

• Haemodynamic or electrical instability in advanced or acute presentations

Left main disease may be clinically silent, and revascularisation recommendations are not restricted to patients with symptoms. Current guidance supports revascularisation for significant left main stenosis irrespective of symptomatic status or the documented ischaemic burden.

In chronic coronary syndrome, revascularisation is particularly indicated when functionally significant disease produces persistent, lifestyle-limiting symptoms despite guideline-directed medical treatment. Neither CABG nor PCI should be performed when angina is present without anatomical or physiological criteria supporting revascularisation.

Evaluation and Physical Examination

Assessment should establish both clinical risk and the feasibility of complete revascularisation.

The clinical evaluation includes:

• Symptom burden and functional limitation

• Evidence of heart failure

• Haemodynamic stability

• Diabetes status

• Renal dysfunction and other important comorbidities

• Frailty

• Liver cirrhosis

• Cognitive function and life expectancy, especially in older adults

• Previous sternotomy or CABG

• Patient preferences and expectations

Frailty and liver cirrhosis are associated with increased postoperative mortality and should influence the choice between PCI and CABG.

Physical examination findings are not specific to left main disease. The examination should nevertheless assess the consequences of extensive myocardial ischaemia, including heart failure, haemodynamic compromise and rhythm disturbance. The source material does not provide a specific examination profile or diagnostic physical signs for LMCAD.

Diagnostic Assessment

Coronary angiography

Invasive coronary angiography defines:

• The presence and severity of left main stenosis

• Ostial, shaft or distal bifurcation involvement

• Disease in the left anterior descending and left circumflex arteries

• The number of additional diseased vessels

• Lesion morphology and technical feasibility of PCI

• The likely completeness of revascularisation with PCI or CABG

Left main disease is frequently associated with multivessel CAD. Disease classification should include both the left main lesion and the extent of additional coronary involvement.

Angiography alone may be insufficient when stenosis is intermediate. In such cases, intracoronary assessment is important:

• IVUS is reasonable for defining the severity of an intermediate left main stenosis.

• IVUS or OCT is recommended for planning and optimising PCI in anatomically complex disease, especially left main lesions, true bifurcations and long lesions.

Intracoronary imaging is particularly important for left main PCI optimisation, including assessment of stent expansion and prevention of side-branch compromise. Residual ischaemia after angiographically successful intervention has been described, especially in distal bifurcation disease.

Physiological assessment

FFR or iFR should be used to guide intervention when angiographic stenoses are intermediate and the clinical context includes angina or an anginal equivalent without documented ischaemia.

In stable patients:

• FFR >0.80 or iFR >0.89 argues against PCI for an intermediate stenosis.

• FFR, iFR or QFR is recommended to guide lesion selection in multivessel disease.

Physiological assessment is complementary to anatomical assessment. It is especially relevant when angiography does not clearly establish whether a lesion is functionally significant.

Anatomical complexity scores

The SYNTAX score quantifies the anatomical complexity of left main and multivessel CAD. It considers the location and complexity of coronary lesions and assists Heart Team deliberation.

Its limitations include:

• Time-consuming lesion-by-lesion calculation

• Inter-observer variability

• Poor correlation between operator and core-laboratory scores

• Assessment of obstruction without quantification of plaque burden

• Failure to incorporate physiological or clinical variables

The SYNTAX II score combines anatomical and clinical characteristics and was developed to improve discrimination between PCI and CABG. SYNTAX score II 2020 provides estimates for five-year major adverse cardiovascular events and ten-year mortality, although prospective external validation remains limited.

The BCIS myocardial jeopardy score is an alternative anatomical tool that can predict mortality after PCI and assess completeness of revascularisation, but it is less commonly used.

Surgical and procedural risk assessment

The STS-PROM model is recommended for patients being considered for CABG. It provides estimates of operative mortality and complications and has demonstrated better calibration than EuroSCORE II for CABG patients.

The STS-PROM score can also contribute to assessment of revascularisation risk in multivessel disease, although its performance is not uniform across procedures or lesion subsets. In left main disease, STS models have predicted CABG outcomes more reliably than PCI outcomes for perioperative mortality and renal failure, whereas the STS stroke model performed better for PCI than for CABG.

Risk categories for CABG mortality described in the source material are:

No risk score should replace clinical judgement. Anatomical complexity, frailty, liver disease, ventricular function, renal function, life expectancy and patient preferences must be considered alongside numerical risk estimates.

Prognostic Significance of Left Main Disease

Left main disease is a high-risk anatomical subset because of the large myocardial territory supplied. Historical natural-history studies, conducted before contemporary revascularisation and secondary prevention, reported mortality of approximately 15–20% per year without revascularisation in severe left main disease. The modern risk is likely lower, although recent natural-history data were not provided.

Significant left main stenosis remains an indication for revascularisation. Prognosis is additionally influenced by:

• Left ventricular ejection fraction

• Number of diseased vessels

• Proximal left anterior descending involvement

• Distal bifurcation disease

• Diabetes

• Anatomical complexity

• Completeness of revascularisation

• Procedural risk

The interaction between multivessel disease and left ventricular dysfunction is particularly important. Reduced LVEF is associated with worse survival, and this adverse effect becomes more pronounced as the extent of CAD increases.

Choice Between CABG and PCI

General principles

CABG and PCI are both capable of producing excellent outcomes in appropriately selected patients. The decision should be based on:

• Clinical indication

• Coronary anatomy

• Anatomical complexity

• Left ventricular function

• Surgical and PCI risk

• Expected completeness of revascularisation

• Diabetes and comorbidities

• Operator and institutional expertise

• Patient preferences

• Long-term expectations regarding myocardial infarction and repeat intervention

A Heart Team comprising interventional cardiology, cardiac surgery and clinical cardiology is recommended when the optimal strategy is uncertain or the anatomy is complex. Treatment decisions should be patient-centred and include discussion of risks, benefits, alternatives, treatment consequences and the patient’s goals.

Comparative outcomes

Randomised comparisons of PCI and CABG in left main disease generally show:

• Similar long-term all-cause mortality in appropriately selected patients

• More spontaneous myocardial infarction after PCI

• More repeat revascularisation after PCI

• More early stroke after CABG

• Greater invasiveness, longer hospitalisation and longer recovery with CABG

• Lower repeat revascularisation with CABG

An individual-patient meta-analysis of four randomised trials reported five-year mortality of 11.2% with PCI and 10.2% with CABG, without a statistically significant difference. Spontaneous myocardial infarction occurred more often after PCI, whereas early stroke was less frequent with PCI than with CABG.

The clinical trial populations were highly selected. Enrolled patients were generally relatively young, had fewer comorbidities and had anatomy suitable for complete revascularisation by either method. Consequently, trial results should not be extrapolated uncritically to patients with extensive comorbidity, frailty or anatomy unsuitable for one of the procedures.

CABG

CABG is generally preferred when:

• Left main disease is accompanied by high-complexity or diffuse multivessel disease

• Complete revascularisation is more reliably achieved surgically

• The SYNTAX score is high

• Diabetes is present with multivessel disease involving the LAD

• The patient is an acceptable surgical candidate

• The long-term priority is reduction of spontaneous MI and repeat revascularisation

The 2021 ACC/AHA revascularisation guideline recommends CABG over PCI for significant left main disease with high-complexity CAD to improve survival. CABG is also reasonable over PCI in multivessel disease with complex or diffuse anatomy, such as a SYNTAX score >33.

In chronic coronary syndrome, CABG is recommended over medical therapy alone for significant left main disease in patients at low surgical risk. It is also the preferred overall revascularisation modality over PCI because of the lower risks of spontaneous MI and repeat revascularisation.

PCI

PCI is an alternative when:

• Left main anatomical complexity is low or intermediate

• Complete revascularisation comparable to CABG can be achieved

• Surgical risk is high

• The patient prefers a less invasive approach

• Local expertise and procedural volume are appropriate

• The coronary anatomy is favourable, particularly in the absence of diffuse CAD

For significant left main disease with a SYNTAX score ≤22 and equivalent expected completeness of revascularisation, PCI is recommended as an alternative to CABG because it is less invasive and provides non-inferior survival. For intermediate complexity, defined in the source material as a SYNTAX score of 23–32, PCI should be considered when equivalent completeness of revascularisation is feasible.

PCI is not recommended for patients with more complex CAD when CABG is a suitable alternative. In patients with high surgical risk, PCI may be considered over medical therapy alone in selected cases.

Distal Bifurcation Left Main Disease

Distal bifurcation lesions are technically challenging and are associated with worse clinical outcomes than non-bifurcation left main lesions. True bifurcation disease may require two-stent techniques.

Although angiographic results can be excellent, residual ischaemia may persist after intervention and is associated with higher long-term cardiovascular mortality. Intracoronary imaging should be used to optimise stent expansion and reduce side-branch jailing.

The source material reports that, for distal left main lesions, a double-kiss crush two-stent strategy was superior to provisional stenting or culotte stenting, with reductions in major adverse cardiac events, repeat revascularisation and stent thrombosis. This evidence supports careful procedural planning and the use of experienced operators for complex distal left main PCI.

Operator experience is clinically important. Higher procedural volume has been associated with better outcomes in unprotected left main PCI, although high-volume operators may also treat patients with greater comorbidity and anatomical complexity.

Acute Coronary Syndromes and Cardiogenic Shock

ST-elevation myocardial infarction

For STEMI with ischaemic symptoms for less than 12 hours, primary PCI should be performed to improve survival.

PCI remains reasonable in stable patients presenting 12–24 hours after symptom onset. PCI is also indicated irrespective of time delay when STEMI is complicated by cardiogenic shock or haemodynamic instability. If PCI is not feasible, CABG may be used as the reperfusion modality.

Additional recommendations include:

• Rescue PCI should be performed after failed fibrinolytic reperfusion.

• Angiography within 3–24 hours after fibrinolysis, with the intention to perform PCI, is reasonable.

• In patients with ongoing ischaemia, acute severe heart failure or life-threatening arrhythmia, PCI may be beneficial regardless of delay.

• Emergency CABG should not be undertaken after failed primary PCI when there is no ongoing ischaemia or large myocardium at risk, or when a no-reflow state or poor distal targets makes surgery unsuitable.

• Routine aspiration thrombectomy before primary PCI is not useful.

In selected haemodynamically stable patients with STEMI and multivessel disease, staged PCI of a significant non-infarct artery after successful culprit-vessel PCI is recommended to reduce death or MI. Elective CABG may be reasonable for complex non-infarct multivessel disease. PCI of a non-infarct lesion at the time of primary PCI may be considered in selected stable patients with low-complexity disease, but should not routinely be performed in cardiogenic shock.

Cardiogenic shock

Rapid revascularisation of the infarct-related artery is the only evidence-based strategy described for mortality reduction in myocardial infarction–related cardiogenic shock. PCI with a drug-eluting stent is generally preferred.

Approximately 80% of patients with cardiogenic shock have multivessel disease. In this setting, culprit-only PCI with possible staged revascularisation is preferred to immediate multivessel PCI because it reduces 30-day mortality and the need for renal replacement therapy. Routine immediate PCI of non-culprit lesions should therefore be avoided.

Radial access is preferred over femoral access when feasible because of its greater safety. CABG is used infrequently, mainly when the coronary anatomy cannot be treated adequately with PCI.

Non-ST-elevation acute coronary syndrome

In NSTE-ACS:

• An invasive strategy with intent to revascularise is indicated in patients at elevated risk of recurrent ischaemic events who are suitable candidates.

• Emergency revascularisation is recommended in cardiogenic shock.

• Immediate invasive management is indicated for refractory angina or haemodynamic or electrical instability.

• An early invasive strategy, within 24 hours, is reasonable in stabilised patients at high clinical risk.

• Invasive management before discharge is reasonable in stabilised patients at intermediate or low risk.

• Emergency CABG is reasonable after failed PCI when ongoing ischaemia, haemodynamic compromise or threatened occlusion places substantial myocardium at risk.

• Routine same-setting multivessel PCI of non-culprit lesions should not be performed in cardiogenic shock.

Revascularisation in Left Ventricular Dysfunction

Left ventricular dysfunction substantially modifies prognosis and treatment selection.

CABG is recommended in suitable patients with chronic coronary syndrome, multivessel CAD and LVEF ≤35% to improve long-term survival. In patients with heart failure with reduced ejection fraction who are suitable for surgery, CABG should generally be considered the first-choice revascularisation strategy, particularly when diabetes or multivessel disease is present.

Revascularisation should also be considered to relieve persistent angina or an anginal equivalent despite optimal medical therapy. Improvement in prognosis requires individual assessment of:

• Coronary anatomy

• Proximal disease severity

• Left main or proximal LAD involvement

• Comorbidities

• Life expectancy

• Procedural risk

• Patient perspectives

PCI may be considered as an alternative to CABG after Heart Team evaluation when anatomy, comorbidities or surgical risk support that approach.

Patients with chronic coronary syndrome and heart failure should be enrolled in a multidisciplinary heart-failure management programme. Recommended heart-failure therapies described in the source material include:

• An ACE inhibitor, mineralocorticoid receptor antagonist and SGLT2 inhibitor for HFrEF

• A beta-blocker in stable patients with HFrEF

• An ARB when an ACE inhibitor or ARNI cannot be tolerated

• Sacubitril/valsartan as a replacement for an ACE inhibitor or ARB in HFrEF

• Diuretics for congestion

• SGLT2 inhibitors in HFmrEF or HFpEF

An ICD is recommended in selected patients with symptomatic ischaemic heart failure, LVEF ≤35% despite at least three months of optimised therapy and expected survival substantially longer than one year with good functional status. CRT is recommended for symptomatic patients in sinus rhythm with LVEF ≤35%, QRS duration ≥150 ms and LBBB morphology despite guideline-directed therapy.

Diabetes and Multivessel Disease

Diabetes strengthens the case for CABG when left main or multivessel disease is present, particularly when the LAD is involved.

In patients with diabetes and multivessel CAD involving the LAD who are appropriate surgical candidates, CABG using a LIMA-to-LAD graft is recommended over PCI to reduce mortality and repeat revascularisation.

In the FREEDOM trial population, which included diabetes and multivessel disease without left main disease, PCI was associated with higher long-term mortality than CABG during the reported follow-up. The survival advantage of CABG was particularly evident among younger patients in extended analyses, although the extended follow-up was incomplete.

PCI remains an option for diabetic patients who require revascularisation but are poor surgical candidates. In diabetic patients with left main disease and low- or intermediate-complexity disease elsewhere, PCI may be considered as an alternative to CABG.

Technical and Procedural Considerations

Stent selection

Drug-eluting stents are preferred over bare-metal stents during PCI because they reduce restenosis, MI and acute stent thrombosis.

Lesion preparation

In fibrotic or heavily calcified lesions:

• Rotational atherectomy may improve procedural success.

• Orbital atherectomy, balloon atherectomy, laser angioplasty or intracoronary lithotripsy may be considered.

Intracoronary imaging

IVUS or OCT is recommended for anatomically complex PCI, particularly left main, true bifurcation and long lesions. Imaging is used to define lesion characteristics, guide stent placement and optimise expansion.

Haemodynamic support

In selected high-risk patients undergoing complex PCI, elective insertion of an appropriate haemodynamic support device may be reasonable to prevent procedural haemodynamic compromise.

Prior CABG and saphenous vein graft disease

When PCI is required after previous CABG:

• If technically feasible, embolic protection during SVG PCI is reasonable to reduce distal embolisation.

• PCI of a feasible native coronary artery is preferred over PCI of a severely diseased SVG.

• PCI of a chronically occluded SVG should not be performed.

Hybrid Coronary Revascularisation

Hybrid coronary revascularisation combines an internal mammary artery graft to the LAD with PCI of non-LAD vessels. The surgical component is usually performed through a minimally invasive left anterior mini-thoracotomy or by robotic-assisted LIMA-to-LAD grafting.

The rationale is to combine the prognostic value of a LIMA graft to the LAD with contemporary PCI for vessels that might otherwise receive vein grafts, which are prone to occlusion.

Randomised evidence is limited, and decisions should be made by the Heart Team. Clinical features that may support a hybrid strategy include:

• Multivessel disease with an LAD suitable for bypass and non-LAD lesions suitable for PCI

• Ascending aortic atheroma

• Unprotected left main disease unsuitable for PCI

• Complex LAD disease

• Advanced age

• LVEF ≤30%

• Frailty

• Diabetes

• Renal failure

• Prior sternotomy

• Lack of suitable bypass conduits

Guideline-Based Treatment Framework

Chronic coronary syndrome

The principal recommendations are summarised below.

The 2021 ACC/AHA recommendations additionally state that:

• STS risk assessment should be performed before CABG.

• A Heart Team should be used when the optimal strategy is unclear.

• FFR or iFR should guide PCI decisions for angiographically intermediate stenoses.

• PCI should not be performed in stable patients with FFR >0.80 or iFR >0.89.

• CABG is recommended for significant left main disease.

• PCI is reasonable when it can provide equivalent revascularisation in selected left main disease.

• CABG is preferred over PCI for high-complexity left main disease.

• CABG is preferred in diabetes with multivessel CAD involving the LAD.

• Drug-eluting stents should be used in preference to bare-metal stents.

Revascularisation before non-cardiac surgery

Routine prophylactic coronary revascularisation before non-cardiac surgery is not recommended solely to reduce perioperative cardiovascular events in patients with non-left-main, non-complex CAD.

This does not exclude revascularisation when there is a conventional indication, such as significant left main disease, a large amount of jeopardized myocardium or refractory symptoms. The decision should be based on individual risk-benefit assessment, and surgery should allow sufficient time for safe management of dual antiplatelet therapy when PCI has been performed.

Medical Therapy and Secondary Prevention

Revascularisation does not treat the underlying atherosclerotic process. Guideline-directed medical therapy remains essential before and after PCI or CABG.

The source material emphasises:

• Maximisation of guideline-directed medical therapy in chronic coronary disease

• Treatment of angina and prevention of non-fatal events

• Secondary prevention after revascularisation

• Management of heart failure when LV dysfunction is present

• Individualisation according to comorbidities, life expectancy and patient preference

Specific anti-anginal drug doses are not provided in the source material. Similarly, detailed antiplatelet, lipid-lowering, antihypertensive and glycaemic treatment regimens are not specified and therefore cannot be detailed here.

Prognosis and Follow-up

Prognosis

Prognosis is determined by the interaction of anatomy, ventricular function, clinical risk and the chosen revascularisation strategy.

CABG and PCI provide broadly similar long-term mortality in selected patients with left main disease, but their risk profiles differ:

• PCI: higher spontaneous MI and repeat revascularisation

• CABG: greater invasiveness and more early stroke

• PCI: less procedural morbidity and shorter recovery

• CABG: more durable freedom from repeat intervention

In complex multivessel disease, diabetes and high SYNTAX scores, the balance generally favours CABG. In low-complexity left main disease with equivalent completeness of revascularisation, PCI offers a less invasive alternative with non-inferior survival.

Follow-up priorities

Follow-up should include:

• Assessment of recurrent angina or anginal equivalents

• Functional status and exercise tolerance

• Heart-failure symptoms and volume status

• Adherence to guideline-directed medical therapy

• Management of diabetes and other comorbidities

• Assessment of recurrent ischaemic events

• Recognition of the higher likelihood of repeat revascularisation after PCI

• Monitoring of left ventricular function when impaired

• Ongoing shared decision-making regarding symptoms, quality of life and future interventions

Patients with complex left main PCI require particular attention to recurrent symptoms and procedural durability. Intracoronary imaging and physiological assessment are important during the index intervention when appropriate, but the source material does not define a routine surveillance imaging schedule for asymptomatic patients.

Overall, the optimal strategy is not determined by angiographic severity alone. It requires integrated assessment of myocardial jeopardy, lesion complexity, surgical and PCI risk, ventricular function, comorbidities, procedural expertise, expected completeness of revascularisation and patient values.