In a patient with 60% stenosis in the Left Main Coronary Artery (LMCA) and no significant stenosis in the Left Anterior Descending artery (LAD), how do the patency rates compare between a Left Internal Mammary Artery (LIMA) graft and a Saphenous Vein Graft (SVG) to the LAD?

LIMA vs SVG Patency in LAD with Upstream LMCA Stenosis

In a patient with 60% LMCA stenosis and no significant LAD stenosis, a saphenous vein graft (SVG) to the LAD is strongly preferred over LIMA because the non-critical LAD stenosis will create competitive flow that leads to arterial graft failure through vasospasm and atrophy.

Understanding Competitive Flow and Arterial Graft Failure

The critical issue in this scenario is competitive flow, not the inherent superiority of LIMA grafts:

• Arterial grafts like LIMA are muscular conduits that respond to low-flow states with vasospasm and eventual atrophy when competitive flow exists 1
• The 60% LMCA stenosis is hemodynamically non-significant (guidelines define significant left main stenosis as >50% for intervention consideration, but this refers to flow-limiting disease) 2
• Since the LAD itself has no significant stenosis, antegrade flow through the native LAD will compete directly with the LIMA graft, promoting graft closure 1, 3

Evidence-Based Conduit Selection Algorithm

Step 1: Assess Target Vessel Stenosis Severity

• For left-sided vessels including LAD, arterial grafts require ≥70% stenosis to avoid competitive flow-related failure 1, 4
• In this case, the LAD has no significant stenosis, making it unsuitable for arterial grafting 1

Step 2: Apply Guideline-Based Contraindications

• Using arterial grafts to bypass vessels without adequate stenosis severity is classified as Class III: HARM 1
• The American College of Cardiology explicitly recommends that arterial grafts should not be used to bypass vessels with less than critical stenosis specifically because of competitive flow-related failure 1

Step 3: Select Appropriate Conduit

• SVG is the appropriate choice when target vessel stenosis is <70%, where arterial grafts would develop competitive flow complications 1, 4
• SVG grafts are less susceptible to competitive flow effects compared to arterial conduits 1

Clinical Evidence Supporting This Approach

A case report demonstrates the real-world consequence of this phenomenon:

• A patient with LMCA stenosis and functioning LIMA graft developed complete LIMA atresia after PCI of the LMCA normalized antegrade LAD flow 3
• This confirms that restoring native vessel flow (whether through PCI or having minimal native stenosis) creates competitive flow that causes arterial graft failure 3

Expected Patency Outcomes

While LIMA generally demonstrates superior long-term patency compared to SVG in appropriate circumstances:

• LIMA to LAD shows >90% patency at 10-15 years when grafting significantly stenosed vessels 4, 5
• SVG patency is 50-60% at 10 years with appropriate target vessel stenosis 4
• However, these patency rates only apply when target vessels have adequate stenosis severity 1, 4

In your specific scenario with non-stenotic LAD:

• LIMA would have markedly reduced patency due to competitive flow, potentially approaching zero as demonstrated in case reports 3
• SVG would maintain reasonable patency as it is less affected by competitive flow dynamics 1

Critical Surgical Decision Point

Before proceeding with CABG in this patient, reassess whether LAD grafting is even indicated:

• The 60% LMCA stenosis alone may not meet criteria for surgical revascularization 2
• CABG should not be performed with the primary intent to improve survival in patients with coronary stenoses that are not anatomically or functionally significant (<70% diameter non-left main stenosis) 2
• If other vessels require grafting and LAD grafting is planned prophylactically, SVG remains the appropriate conduit choice 1