1 - Improvement in interventional cardiology
Advances in percutaneous coronary intervention (PCI) have given this therapeutic option -exclusive internal mammary artery CABG - a key and irrevocable role in the management of CAD. There has been a considerable and steady increase in the number of PCI procedures, furthermore, the indications have spread to include triple vessel disease and left main stem lesions which were classically considered exclusive surgical territory.
Surgeons are thus confronted to performing more complex, multiple vessel coronary revascularisation after failure of PCI approach. Target arteries are often multistented or multistenosed with small calibre and poor run-off. Patients are also referred later to surgery with worsening symptoms and greater co-morbidities. Thus the challenge is to achieve complete revascularisation in an unfavourable setting with a greater risk of graft occlusion.
The bypass conduit is a dominant factor in the long-term follow-up of CABG. While the saphenous vein has been considered a predominant graft, venous graft atherosclerosis continues to be the major cause of late failure of CABG (1).
2 - The use of the internal thoracic artery
Parallel to improvement in interventional cardiology and progress from bare metal to drug eluting and biodegradable stents, surgical revascularisation of the myocardium has undergone major advances. Selection of the bypass graft with adequate flow and the greatest longevity is thus of vital importance and consequently the use of the internal thoracic artery (ITA) instead of saphenous vein grafts is preferred whenever possible. The ITA has demonstrated superior long-term clinical results after CABG compared to saphenous vein grafts with 85% to 95% freedom from significant stenosis at 7 to 10 years (2-5). Moreover, the ITA outperforms other arterial grafts, namely the radial and gastroepiploic arteries, and is now undeniably the conduit of choice for surgical revascularisation.
The structure of the ITA is adapted to arterial pressures and high flow rates and produces greater amounts of relaxing factors namely nitric oxide providing a superior reactivity to flow requirements in the coronary arteries (6). Bypass of the left anterior descending (LAD) artery by the left ITA has been widely accepted as a major positive prognostic factor in patients undergoing CABG and has been standard for more than two decades (7-9).
The use of both ITA has demonstrated additional advantages over the use of single ITA in combination with vein grafts. Bilateral ITA grafting is an independent predictor of improved long-term survival and freedom from recurrence of angina, late myocardial infarction, reoperation, angioplasty and other cardiac-related events (5,10-13). This remains true when ITA is used as in-situ, sequential, or free graft (14,15). Purely ITA grafting for triple-vessel-diseased patients by connecting the free right ITA end-to-side to the in-situ left ITA as a Y graft has been reported with encouraging long term results (16,17).
3 - Description of the technique
The technique consists of complete extra-pleural skeletonised harvesting of both ITA. The fascia is peeled off the ITA while the internal thoracic veins are left in-situ to preserve a certain degree of vascularisation of the sternum. The right ITA is divided at its origin and connected end-to-side to the in-situ left ITA in a Y fashion (ITA-Y anastomosis, figure 1).
The left ITA is generally used to bypass the anterior coronary arteries (LAD, diagonal and ramus intermedius) and the right ITA to the lateral and inferior coronary arteries of the heart (ramus intermedius, obtuse marginal, posterior descending and right posterolateral) in a sequential fashion (figure 2).
Clinical results of the ITA-Y and sequential side-to-side ITA-coronary anastomoses have been inferred from clinical signs and cardiac functional assessments (scintigraphy, exercise ECG, …etc) but their patency has also been evaluated by direct graft visualisation (coronary angiography and CT angioscan) (18). Furthermore, similar patency rates of LITA and RITA connected to the same coronary arteries regardless of the targeted coronary artery or whether they are used in-situ or as free grafts have been reported (19-21).
Figure 1 : End-to-side anastomosis of the right ITA on the in-situ left ITA in a Y fashion
Figure 2 : In the schematic representation, the left ITA is used to bypass the anterior coronary (LAD and diagonal) arteries and the right ITA to the lateral and inferior coronary (obtuse marginal and posterior descending) arteries of the heart in a sequential fashion
Exclusive internal thoracic artery bypass is reproducible and safe to perform routinely. Although more demanding technically, this procedure allows arterial reconstruction of the coronary tree without increasing the postoperative morbidity and mortality, providing complete myocardial revascularisation in triple-vessel-diseased patients with an excellent quality of anastomoses and outcome.