What is the best second conduit to use after the Left Internal Mammary Artery (LIMA) in Coronary Artery Bypass Grafting (CABG) for an adult patient with significant coronary artery disease?

Best Second Conduit After LIMA in CABG

The radial artery is the preferred second conduit after LIMA in coronary artery bypass grafting, offering superior long-term patency compared to saphenous vein grafts and similar outcomes to the right internal mammary artery (RIMA) with fewer perioperative complications. 1

Conduit Hierarchy and Evidence

First Choice: Radial Artery

• The radial artery demonstrates superior graft patency compared to saphenous vein grafts, with 5-year functional occlusion rates of 12.0% versus 19.7% (P=0.03) and complete occlusion rates of 8.9% versus 18.6% (P=0.002) 1
• The radial artery achieves 89% patency at 4-5 years compared to 65-80% for saphenous vein grafts 2
• Multiple observational studies confirm superior long-term survival rates with radial artery grafting, even after propensity matching 1
• Radial artery grafting reduces the risk of late mortality (HR 0.79; 95% CI 0.64-0.98) compared to saphenous vein grafts 3

Second Choice: Right Internal Mammary Artery (RIMA)

• RIMA provides excellent long-term patency (>90% at 10 years) similar to LIMA 1
• RIMA and radial artery demonstrate equivalent long-term survival (68.2% vs 66.7% at 16 years, P=0.127) with both significantly superior to saphenous vein grafts 4
• RIMA as a second conduit improves overall survival compared to radial artery in some studies (HR 1.9 for RA mortality; 95% CI 1.2-3.1; P=0.008) 5
• However, one recent analysis found increased mortality risk with RIMA compared to saphenous vein (weighted HR 1.37; 95% CI 1.13-1.68), though this study had limited RIMA numbers 3

Last Resort: Saphenous Vein Graft

• Saphenous vein grafts have declining patency: 10-25% occlude within 1 year, additional 1-2% per year during years 1-5, and 4-5% per year during years 6-10 1
• Only 50-60% of saphenous vein grafts remain patent at 10 years, with half showing atherosclerotic changes 1
• Saphenous vein patency drops to 25-50% at 10-15 years 6

Clinical Decision Algorithm

Choose Radial Artery When:

• Patient has significant stenosis (>70% for left-sided vessels, >90% for right coronary artery) - radial artery performs best with severe stenoses 1, 2
• Patient is diabetic or obese (radial artery shows particular advantage in these populations) 5, 7
• Patient has chronic obstructive pulmonary disease (COPD) or is elderly (radial artery reduces major adverse events: OR 0.05 for COPD, OR 0.40 for older patients) 7
• Patient does not have chronic kidney disease requiring future dialysis access 2
• Allen test confirms adequate ulnar collateral circulation 2
• No recent transradial catheterization 2

Choose RIMA When:

• Patient is younger with multivessel disease (bilateral IMA provides survival benefit) 6
• Surgeon has extensive experience with RIMA harvesting and concerns about radial artery spasm 1
• Patient has diabetes and obesity (RIMA shows stronger advantage: HR 3.3 for diabetics, HR 2.1 for obese) 5
• Target vessel is severely stenotic (>90%) to prevent graft atrophy 1

Use Saphenous Vein When:

• Patient requires preservation of radial arteries for future dialysis access 2
• Insufficient arterial conduits available 1
• Target vessel has moderate stenosis (<70%) where arterial grafts may develop string sign 1

Critical Technical Considerations

For Radial Artery Use:

• Objectively assess palmar arch completeness with Allen test before harvesting 2
• Avoid radial artery after transradial catheterization 2
• Prescribe oral calcium channel blockers for the first postoperative year to prevent vasospasm 2
• Use radial artery preferentially for left-sided coronary arteries with ≥70% stenosis 1
• The radial artery is a muscular artery susceptible to spasm and atrophy when grafting moderately stenotic vessels 1

For RIMA Use:

• RIMA does not increase deep sternal wound infection risk (P=0.8) despite common perception 5
• RIMA can be used as free graft (68%) or in situ graft (32%) 4
• Consider skeletonized harvesting technique to reduce sternal complications 1

For Saphenous Vein Use:

• Use no-touch harvest technique in low-risk patients for better long-term patency 2
• Use endoscopic harvest only in patients at high risk for wound complications (reduces leg wound infection from 20-26% to 4-7%) 2
• Endoscopic harvesting associated with reduced long-term graft patency 6, 2
• Administer perioperative aspirin and dipyridamole to improve early and 1-year patency 1

Common Pitfalls to Avoid

• Do not use radial artery for moderately stenotic vessels - the string sign occurs more frequently (3.4% vs 0%, P=0.01) 1
• Do not harvest radial artery without confirming adequate ulnar compensation 2
• Avoid bilateral IMA in patients at high risk for sternal wound complications (though evidence shows RIMA doesn't increase this risk) 5
• Do not use endoscopic vein harvesting routinely - it compromises long-term patency despite better wound outcomes 6, 2
• Recognize that only 9% of CABG procedures in the US use radial artery despite superior outcomes 1