Total arterial revascularisation CABG is a sophisticated surgical procedure in which only arteries are used as conduits to bypass blocked Coronary Arteries. Common arterial tubes (conduits) used for total arterial revascularisation CABG include the left and right sided Internal Mammary Arteries (taken from inside the chest), and the Radial Artery (taken from the forearm). Why are arteries preferred as conduits over veins? Read on…..!
Arteries and Veins, what are the differences
Arteries are blood vessels (endothelium lined tubes) that usually carry oxygenated blood away from the heart to all parts of the body. Veins are blood vessels that usually carry deoxygenated blood back towards the heart. The intraluminal pressure in the arteries is much higher than in the veins.
The walls of arteries are thicker than those of veins. There are also other structural differences in the walls of arteries and veins primarily because arteries have to withstand much higher intraluminal pressures than veins.
If veins are subjected to arterial pressures, initially, there are no changes but if they are subjected to arterial pressures for a long period of time, they develop structural degenerative changes and may result in an intraluminal obstruction and a reduction in blood flow through them. This is why veins fail as grafts more often than arteries when used as conduits in “non” total arterial revascularisation CABG operations.
Data supporting Total Arterial Revascularisation CABG.
There is a lot of scientific data to suggest to show that total arterial revascularization CABG improves both short and long term graft patency and mortality in coronary artery bypass grafting (CABG) patients when compared with the traditional single internal mammary artery (IMA) and vein grafts. Furthermore, this benefit is noticeable in both younger and older (>70 years) patients.
The commonly used total arterial revascularization CABG techniques involve the use of both the right and left (bilateral) Internal Mammary Arteries and Radial Artery. These conduits may be used in many combinations.
The bilateral Internal Mammary Artery graft approach, uses the left Internal Mammary Artery as a pedicled graft and the right Internal Mammary Artery as either a pedicled or free graft. The Radial Artery is always used as a free graft.
There is plenty of evidence to suggest that bilateral Internal Mammary Artery Grafts offer additional prognostic advantages over a single Internal Mammary Artery and Radial Artery grafting strategy. Some concerns about deep sternal wound infection, the well known complication of bilateral Internal Mammary Artery harvest, have limited its widespread use.
Complications of using both IMAs.
Recent studies have conclusively demonstrated that the risk of sternal wound infection can be significantly reduced with the use of skeletonized Internal Mammary Arteries. Traditionally the use of both Internal Mammary Arteries is contraindicated in diabetics (especially if their blood sugars are poorly controlled), obesity, immunocompromised patients, and patients with severe chronic obstructive airways disease of the lungs.
Contraindications to the use of the Radial Artery
The Radial artery is available in most patients and its use causes minimal morbidity. The Radial Artery can also be harvested concurrently with the Internal Mammary Arteries, saving operative time. There are however, some patients in whom contraindications to RA harvest exist;
- a positive Allen’s test indicating an incomplete arterial palmar arch,
- heavily calcified radial arteries typically seen in insulin dependent diabetics and in patients with end stage renal failure
- patients who have experienced a Raynauds phenomenon,
- manual laborers in cold environments (hand claudication has been described after RA harvest).
There is evidence that cannulation and wiring of the Radial Artery can sometimes cause damage to its inner lining (intima), or induce a hyper reactivity and spasm. This can rarely cause an in situ thrombosis of the Radial Artery. In the vast majority of patients however, the Radial Artery is an excellent conduit to augment the Internal Mammary Arteries in a total arterial revascularisation CABG.
It is long and can reach any coronary vessel on the heart. The Radial Artery is extremely versatile as a conduit and can be used as an aorto coronary graft or as a Y graft that comes off an in situ IMA. Since the Radial Artery does not kink easily, it can also be used as a sequential graft.
One of the disadvantages of the Radial Artery is an increased “failure rate” when used to bypass coronary arteries with less than critical stenoses. Competitive flow in the native vessel leads to an increased incidence of graft failure. This is commonly observed in coronary arteries which have a less than 70% stenosis.
Advantages of the Radial Artery.
The ease and convenience of harvesting the Radial Artery, as well as its length and usability make it a more attractive option in many ways compared to the free right Internal Mammary Artery graft. Harvesting of the Radial Artery is associated with negligible morbidity.
Power and function of the forearm and hand are usually un affected and blood flow in the hand is preserved with compensatory increase in blood flow through the ulnar artery. The Radial Artery harvest site also heals well with much lower incidences of infection and wound dehiscence, even in poorly controlled diabetics
Other Arterial Conduits.
Other arterial conduits such as the right Gastroepiploic Artery and the Inferior Epigastric Artery have been used, in total arterial revascularisation CABGs, but have not gained popularity due to their propensity to spasm and short useable lengths.
Unfortunately, total arterial revascularisation CABG generally remains an underused grafting technique in many parts of the world. total arterial revascularisation CABG in the US based Society of Thoracic Surgeons’ database remains under 10%. The overwhelming evidence in favor of arterial grafts in both young and elderly patients mandates a shift in practices worldwide.
The unfortunate bottom line.
Surgeons across many parts of the world however, have been reluctant to move to a total arterial revascularisation CABG technique with use of both Internal Mammary Arteries for several reasons.
Harvesting both Internal Mammary Arteries takes a longer time in the operating room, the risk of sternal wound infection is higher, and the increasing prevalence of obese diabetes means that harvest of both Internal Mammary Arteries is (relatively) contraindicated in up to 35% of patients. Skeletonizing the Internal Mammary Arteries does reduce this risk, but does not eliminate it completely.