Coronary artery bypass grafting (CABG) remains one of the most commonly performed procedures in cardiac surgery. Despite the advancement in percutaneous revascularization, CABG continues to be an effective therapy with better long-term durability and good long term outcome for many patients (1-5). However, patients being referred for surgical revascularization now are more complex and have higher risks than in previous decades (1,2,6,7).
The choice of conduits for surgical revascularization plays a major role in long-term outcomes especially with the increasingly complex patient population. The use of left internal thoracic artery (LITA) to left anterior descending artery (LAD) has been well studied and has demonstrated reduced mortality and morbidity when compared to other conduits (8-13). But besides the LITA, the issue of which conduit is the next best choice for surgical revascularization has been studied and debated for a long time. The objective of this article is to review our choice on coronary conduits and grafting strategies used at our center.
Internal thoracic artery (ITA)
All patients requiring surgical revascularization should have the LITA to the LAD when possible. LITA as a bypass graft to the LAD has been proven to provide superior early and late survival after CABG (8-12). The unparalleled long-term patency and better clinical outcomes associated with the use of the LITA makes this the conduit of first choice for anastomosis to the LAD in almost all patients regardless of age or pathology. There are only a few exceptions where the ITA may not be used, including emergency or salvage operations, high-dose chest wall radiation exposure and subclavian artery or ITA occlusion.
Because of its unique characteristics, ITA demonstrates remarkable resistance to the development of atherosclerosis (14). It has a more resistant endothelium against harvest injury and the medial layer is thinner, with fewer smooth muscle cells and a lesser proliferative response to known mitogens and pulsatile mechanical stretch (14-17). The endothelium also has higher basal production of the vasodilators nitric oxide and prostacyclin, which has been shown to be beneficial (18). Furthermore, the ITA has a non-fenestrated internal elastic lamina that inhibits cellular migration and prevents intimal hyperplasia.
The patency rate of LITA is superior to other conduits in both short- and long-term follow-up. In the most recent studies, patency rates for LITA at 10 and 15 years average around 93% and 88%, respectively, whereas SVG patencies are approximately 71% and 32% at the same time intervals (19-21). Studies have also shown that there is no loss of ITA patency even for sequential anastomosis in parallel (22). This superior patency translates into improved 10-year survival (LITA-to-LAD artery 82.6% versus SVG-to-LAD artery 71%) with lower incidence of myocardial infarction (MI), hospitalization for cardiac events, and cardiac reoperations (9,12).
The use of bilateral internal thoracic artery (BITA) grafting rather than unilateral internal thoracic artery (ITA) grafting has been associated with increased survival and fewer cardiac events (23,24). Multiple studies have shown that maximizing the use of arterial conduits may yield improved clinical outcomes (23,25-27). Nasso et al. (28) concluded that myocardial revascularization with two arterial conduits in multi-vessel coronary disease offers improved event-free survival compared with a single arterial graft (LITA-LAD strategy), irrespective of which conduit is used as a second-choice arterial graft.
However, recent debates center on which arterial conduit is the next best choice after LITA for multiple revascularization. The right internal thoracic artery (RITA) and the radial artery (RA) have been considered to be the logical step forward to revascularize the non-LAD coronary arteries.
At our center, we use mostly RITA as our second arterial conduit of choice. The skeletonization technique for harvesting since a longer conduit is needed when both ITAs are being used and particularly in diabetic patients.
Right internal thoracic artery vs. radial artery
There is now mounting evidence supporting the superiority of the RITA over the RA. Navia et al. (25) studied a propensity score-matched patient population (n=1,447) and showed that patients with BITA grafts have higher survival rates (hazard ratio, 0.59; 95% confidence interval, 0.38-0.92; P<0.021) and lower incidence of reintervention and readmission when compared to those with a RA graft. In another propensity score analysis, Ruttman et al. (29) compared the survival and morbidity of two groups, BITA ± saphenous vein grafts (SVG) and LITA + RA ± SVG. Their results showed significantly lower perioperative major adverse cardiac and cerebrovascular events, significantly higher event-free survival, but no significant difference in sternal complications in the BITA ± SVG group compared to the LITA + RA ± SVG group. A retrospective angiographic study performed by Khot et al. (30) demonstrated a significantly lower patency rate for RA when compared with ITA or even SVG at a mean follow-up of 565 days. Tatoulis et al. (31) recently reported their outcomes (n=5,766) on RITA. In their experience, the late patency (10 years) of RITA is excellent, with similar outcomes to LITA for identical territories. Their results also showed that the RITA patency rate was always better than radial arteries (P<0.01) and SVGs (P<0.001). The long-term benefit of BITA grafting may be due to the composite structures of the ITA vessel walls and its higher capacity of nitric oxide release when compare to RA (32).
While there are concerns about using the RITA regarding its length, the ability to use it to revascularize the circumflex system, and the potential risk for increased sternal complication, recent improvements in surgical techniques have addressed many of these issues. Skeletonization of the IMA has been shown to have less sternal blood flow compromise and less sternal infections and complications, even in diabetic patients (33-35). Furthermore, the skeletonized graft has increased luminal diameter, free flow and conduit length compared to a pedicled graft (36).
To reduce the risk of chest wall ischemia and increase conduit length, we skeletonize our RITA. To further extend graft length, the RITA can be routed through the transverse sinus to reach circumflex targets as an in situ graft, or it can be used as a free T-graft or Y-graft off the LITA for grafting the left coronary system. The in situ patency of the right ITA is comparable to that of the left when directed to the same target vessels or when RITA is used as a Y-graft from the left ITA to the proximal targets (19,22,37). When both ITAs are used, the left ITA may be grafted to the circumflex system and the right in situ ITA to the LAD.
The radial artery has its own limitations, including susceptibility to vasospasm and intimal hyperplasia, potential calcification, poor quality conduit in patients with peripheral vascular disease and diabetes and the need for a proximal anastomosis. Furthermore, RA patency is significantly influenced by competitive coronary flow, with at least 80% coronary stenosis being a widely accepted cutoff and evidence showing enhanced RA graft patency with 90% stenosis (37,38).
Radial artery vs. saphenous vein
Surprisingly, despite support from previous data and reports, the use of multiple arterial conduits for coronary revascularization remains uncommon (<15%) in the US and Europe (4,39,40). It has been documented that multiple arterial conduits results in better long-term graft patency and improved patient outcomes for surgical revascularization (23,25-27). While the evidence on RITA could be convincing, reports comparing RA and SVG demonstrated conflicting results. Recent data seems to show RA has no significant benefit in outcome over SVG.
A meta-analysis by Benedetto et al. demonstrated no advantage of using the RA when compared to SVG, and that their results were not influenced by any follow-up period (41). Athanasious et al. conducted a systematic review (42) and reported no significant difference in early and late graft failure when comparing RA to SVG. In a prospective randomized trial (n=735), Goldman et al. (20) reported that the use of RA did not improve graft patency or outcomes when compared to SVG. Fukui et al. (43) further demonstrated only a 69.5% patency at one year for the RA, which is significantly worse than that of the RITA graft and SVG. Hayward and colleagues (44) have recently published the results of their prospective randomized trial comparing RA with SVG. Angiography performed at 5 years demonstrated no significant difference in patency between RA and SVG.
Desai and colleagues (12) have studied target-vessel characteristics to assist in clinical decisions on when and where to use the RA versus SVG conduit. In a large group of patients (n=440), they documented that diabetes mellitus and small target-vessel diameter were associated with an increased risk of graft occlusion for both RA and SVG. However, a history of peripheral vascular disease was associated with an increased risk of RA occlusion that was not seen with SVG. In a retrospective review, Khot et al. (30) demonstrated a significantly lower patency rate for RA compared with SVG in women and in patients with peripheral vascular disease.
A “no-touch” technique for saphenous vein harvest has been proposed. In a randomized trial, Dreifaldt et al. showed the patency rate is higher for “no-touch” SVG then RA graft (95% vs. 84%) at a mean follow-up of 36 months (45).
At our center, we use SVG and RITA more often than RA as our preferred conduit after the LITA. For the vein graft, we use both one vein per target and sequential grafting especially for smaller coronary vessels (1.5 mm or smaller) using a side-to-side anastomosis. Vein sequential grafting has been shown to have greater patency rates (46,47) as well as hemodynamic advantages including improved distal runoff and consequently increased total graft (48).
If the RA is used, the proximal anastomosis is placed directly on the aorta or via a vein hood and almost always will reach any target as a single graft. Y-grafting to one distal anastomosis or T-grafting to both the circumflex and right coronary artery to achieve all arterial revascularization can be performed (49).
Right gastroepiploic artery and inferior epigastric artery
The right gastroepiploic artery (RGEA) or inferior epigastric artery (IEA) is rarely used unless the above described conduits are unavailable or inadequate. The RGEA has a thick smooth muscle media that is prone to spasm. Furthermore, harvest of the arteries requires intra-abdominal entry or an extra abdominal incision which increases operative time and may be associated with additional complications. Both artery sizes can also vary significantly from patient to patient.
There is less supporting evidence for using the RGEA and IEA compared to the previously described conduits. While multiple reports revealed patency of RGEA is no better than that of the SVG, some studies have shown a patency rate of >82% for the RGEA (50,51) and 85.7% for the IEA (52) at a 5-year follow-up. Both the RGEA and IEA can be used for total arterial revascularization or when there is a lack of other available conduits.
Allografts and artificial grafts
We rarely, if ever, use artificial conduits unless as part of a clinical trial. The choice of either arterial or venous conduits is almost always available. There has been limited success with cryopreserved SVG, bovine chemically treated ITA and expanded polytetrafluoroethylene (ePTFE) grafts, with reported patency rates less than 30% at one year follow-up (53-56).
Long-term outcome for surgical revascularization depends on multiple variables, including the choice of conduit. It has been well demonstrated that using the LITA to the LAD has significant early and late benefits. The use of two ITAs has been shown to have more favorable outcomes compared to using a single arterial conduit. Multiple arterial revascularization may further improve long-term survival and reduce adverse events in patients requiring surgical revascularization. While there is now mounting evidence that the use of RITA has a patency and survival advantage over RA, the choice between RA and SVG can be controversial and less clear. However, we usually prefer a SVG to RA if the SVG is of adequate quality.
Patency rate is also related to technical factors (quality of coronary anastomosis, endothelial integrity of the conduit during harvesting and intraoperative handling), preservation of the conduit before usage, pharmacological treatment to prevent spasm or thrombosis and other postoperative patient complications that can compromise conduit functionality, such as low cardiac output and vasopressor requirement.
The choice of conduit for coronary revascularization should be individualized for each patient. When selecting a conduit, the surgeon will have to balance anatomical criteria, patient characteristics, conduit availability and surgical expertise on specific conduit harvesting. Ongoing clinical trial data will help determine which subsets of patients would benefit the most from multiple arterial revascularization and those patients with associated co-morbidities that would be better suited for a hybrid approach or a single ITA and SVG.
Disclosure: The authors declare no conflict of interest.
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