Residency · Residency · Cardiothoracic Surgery

Conduit Selection for Coronary Bypass

Overview

The choice of conduit for CABG is one of the most consequential decisions in coronary surgery, directly influencing long-term graft patency, freedom from reintervention, and survival. This chapter reviews the biology, harvesting techniques, patency data, and evidence base for each conduit option, with emphasis on the growing case for total arterial revascularization.

Left Internal Mammary Artery (LIMA)

Anatomy and Biology

The LIMA arises from the first portion of the subclavian artery and runs along the inner chest wall, 1 to 2 cm lateral to the sternal edge. It possesses unique endothelial biology, producing high levels of nitric oxide and prostacyclin. Its intact internal elastic lamina and preserved endothelial function make it remarkably resistant to atherosclerosis. It is size-matched to the LAD in most patients (1.5-2.5 mm).

Patency Data

The LIMA achieves 90-95% patency at 10 years — the gold standard against which all conduits are measured. The LIMA-to-LAD graft is the cornerstone of every CABG operation (Class I recommendation). Loop et al. at the Cleveland Clinic demonstrated in 1986 that LIMA-to-LAD provides superior long-term survival compared to SVG-to-LAD.

Technical Considerations

The LIMA can be harvested as a pedicled graft (with accompanying veins, fascia, and pleural tissue) or skeletonized (isolated from surrounding tissue). Skeletonization increases length, preserves sternal blood supply, and reduces sternal wound infection in diabetics, but it is technically more demanding and carries a risk of IMA injury. Thermal injury during harvest must be avoided by using low cautery settings and clips for branch division.

Right Internal Mammary Artery (RIMA)

Anatomy and Biology

The RIMA is the mirror image of the LIMA with the same favorable endothelial biology. It can be used as an in-situ graft (crossed through the midline) or as a free graft from the LIMA in a Y or T composite configuration.

Patency Data

The RIMA achieves 85-90% patency at 10 years (slightly lower than LIMA in some series, likely due to technical factors). When used as a composite graft from the LIMA, patency is comparable to the LIMA itself.

Bilateral IMA (BIMA) Grafting

Multiple observational studies show improved long-term survival with BIMA versus single IMA plus SVG. The ART trial by Taggart et al. showed no significant difference at 10 years between BIMA and single IMA, but this result is tempered by a high crossover rate (14% of BIMA patients received only single IMA) and likely underpowering. Observational data from Cleveland Clinic (Lytle et al.) and the Melbourne group (Tatoulis et al.) consistently show 10-20% reduction in long-term mortality with BIMA.

The main concern with BIMA is sternal wound infection. Skeletonized technique reduces this risk. Risk factors for sternal complications include diabetes, obesity (BMI above 30), COPD, and chronic steroid use. In non-diabetic, non-obese patients, BIMA should be strongly considered. Some centers report acceptable infection rates even with skeletonized BIMA in diabetics.

<image>Diagram of the anterior chest showing the course of the left and right internal mammary arteries from their subclavian origins to their bifurcations. Labeled branches include the pericardiophrenic artery and intercostal perforators. Inset panels compare pedicled versus skeletonized harvest techniques, with cross-sectional views showing the included tissues (veins, fascia, pleura) in pedicled grafts versus the isolated artery in skeletonized grafts. A separate inset shows the sternal blood supply with collateral pathways from intercostal perforators.</image>

Radial Artery

Anatomy and Biology

The radial artery is a muscular artery with a thick medial layer that makes it prone to vasospasm. It is harvested from the non-dominant forearm after confirming adequate ulnar collateral flow with the Allen test or Doppler. Its endothelial function is intermediate between the IMA and SVG. Treatment with vasodilators (calcium channel blockers, papaverine, nitroglycerin) is essential.

Patency Data

The radial artery achieves 85-90% patency at 5 years and 80-85% at 10 years, superior to SVG but inferior to IMA. The RADIAL trial (Deb et al., 2012) demonstrated 89% radial artery patency versus 67% for SVG at 5 years. The RAPCO trial confirmed radial artery superiority over SVG at 10 years.

RADIAL Trial and Meta-Analysis (Gaudino et al., 2018)

An individual patient-level meta-analysis of 6 RCTs (1,036 patients) comparing radial artery to SVG showed the radial artery was associated with significantly lower adverse cardiac events and higher patency at 5 years. This evidence supports routine use of the radial artery as the second conduit of choice after LIMA.

Clinical Considerations

The radial artery should be used for targets with severe stenosis (above 70-90%) to avoid competitive flow and spasm-induced graft failure. Postoperative calcium channel blocker therapy (amlodipine or diltiazem) for 6 to 12 months is essential. Contraindications include a positive Allen test, Raynaud disease, dialysis dependence (preserve the arm for future AV fistula), and a calcified radial artery.

Saphenous Vein Graft (SVG)

Anatomy and Biology

The SVG is a superficial venous conduit from the lower extremity. It lacks the protective endothelial biology of arterial conduits and is susceptible to intimal hyperplasia (within 1-5 years) and accelerated atherosclerosis (5-10 years). Vein wall injury during harvest, especially from distension, accelerates graft disease.

Patency Data

SVG patency is approximately 80-90% at 1 year, 70-80% at 5 years, and 50-60% at 10 years, with an attrition rate of approximately 1-2% per year after the first year. This makes it the weakest link in the CABG operation.

Harvest Techniques

Open harvest provides longitudinal incision and direct visualization. Endoscopic vein harvest (EVH) is standard at most centers and reduces wound complications and pain, though some studies have raised concerns about lower patency with EVH due to endothelial handling (newer evidence with improved technique suggests equivalence). The "no-touch" technique — harvesting the vein with surrounding perivascular tissue intact — preserves the vasa vasorum and reduces spasm. Souza et al. demonstrated improved 16-year patency rivaling arterial conduits, though this technique requires open harvest.

Optimizing SVG Patency

Gentle handling and avoidance of overdistension (below 300 mmHg) are paramount. Storage should be in heparinized blood or balanced salt solution (not saline alone). Dual antiplatelet therapy postoperatively may benefit selected patients. External stenting devices (such as VEST) are under investigation to reduce vein graft disease.

Right Gastroepiploic Artery (RGEA)

The RGEA is an in-situ arterial conduit from the greater curvature of the stomach that can reach the inferior cardiac surface (PDA and distal RCA). Its 5-year patency is 80-85%, lower than IMA and radial artery. It is rarely used in current practice due to the need for abdominal entry and its marginal patency, though it may have a role when other conduits are unavailable.

Inferior Epigastric Artery

This free graft, harvested from the rectus sheath, has limited length (8-12 cm) and small caliber. Patency data are sparse, and it has been largely abandoned in favor of the radial artery. It holds primarily historical interest.

Total Arterial Revascularization

Rationale

Total arterial revascularization eliminates SVGs, which have the worst long-term patency. This theoretically improves long-term survival, freedom from MI, and freedom from reintervention. A growing body of observational evidence supports improved outcomes.

Configuration Options

Several configurations are available: BIMA in-situ (LIMA to LAD, RIMA crossed to LAD system or in-situ to RCA); LIMA plus free RIMA Y-graft (RIMA anastomosed end-to-side to LIMA with sequential grafting to non-LAD targets); LIMA plus radial artery Y-graft (radial artery anastomosed to LIMA with sequential grafts to circumflex/RCA territory); and the aortic no-touch approach combined with total arterial revascularization for maximum stroke risk reduction.

Evidence

The ROMA trial is the first large RCT comparing total arterial versus single arterial plus SVG revascularization. Multiple propensity-matched observational studies support improved 10-to-20-year survival with total arterial grafting. The 2021 ACC/AHA guidelines give a Class IIa recommendation for use of a second arterial conduit (radial or RIMA) beyond the LIMA.

<image>Composite illustration showing four different CABG conduit configurations on an anterior view of the heart. Panel A: Single arterial (LIMA-to-LAD) with SVGs to obtuse marginal and PDA. Panel B: Bilateral IMA with in-situ LIMA to LAD and in-situ RIMA crossing to obtain marginal. Panel C: Y-composite graft with LIMA-to-LAD and free RIMA from LIMA as a Y-graft to circumflex branches. Panel D: Total arterial revascularization with LIMA-to-LAD and radial artery T-graft from LIMA to two sequential circumflex targets. Each configuration is labeled with expected 10-year patency rates for each graft.</image>

Conduit Comparison Summary

Clinical Pearls

LIMA-to-LAD is non-negotiable — it is the single most evidence-backed technical detail in all of cardiac surgery. The radial artery should be considered the second conduit of choice after LIMA based on individual patient meta-analysis data showing superiority over SVG. Bilateral IMA grafting improves long-term outcomes in observational studies; the ART trial's negative result is likely due to high crossover and underpowering and should not be used to dismiss BIMA. SVGs are the weakest link in CABG, with 40-50% occluding by 10 years; minimizing SVG use through total arterial revascularization is an important quality goal. Skeletonized IMA harvest should be the default in diabetics and obese patients to reduce sternal wound infection risk while preserving the benefits of arterial grafting. The radial artery must be used for targets with severe stenoses (above 70%) — using it for moderate stenoses risks spasm-induced graft failure from competitive flow. The "no-touch" SVG harvest technique is the most promising strategy for improving SVG patency and should be adopted when open harvest is performed. Postoperative calcium channel blocker therapy is essential when radial artery conduits are used.

References

• Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internal-mammary-artery graft on 10-year survival and other cardiac events. N Engl J Med. 1986;314(1):1-6.
• Taggart DP, Benedetto U, Gerry S, et al. ART Trial: Bilateral versus single internal-thoracic-artery grafts at 10 years. N Engl J Med. 2019;380(5):437-446.
• Gaudino M, Benedetto U, Bakaeen F, et al. Radial artery or saphenous vein as the second graft: a patient-level pooled analysis of 6 RCTs. J Am Coll Cardiol. 2018;72(22):2733-2743.
• Souza DSR, Johansson B, Bojo L, et al. Harvesting the saphenous vein with surrounding tissue for CABG provides long-term graft patency comparable to the left internal thoracic artery. J Thorac Cardiovasc Surg. 2006;132(2):373-378.
• Gaudino M, Bakaeen FG, Benedetto U, et al. Arterial Grafts for Coronary Bypass: A Critical Review After the Publication of ART and RADIAL. Circulation. 2019;140(15):1273-1284.
• Aldea GS, Bakaeen FG, Pal J, et al. STS Clinical Practice Guidelines on Arterial Conduits. Ann Thorac Surg. 2016;101(2):801-809.

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