more than vein conduits.

Dr Wessels said that most surgeons commonly implant the left internal mammary artery into the left anterior descending coronary artery, and this is the best method to use for about 90% of coronary bypass operations.

The internal mammary artery grafts are harvested by “skeletonization” with an ultrasound surgical aspirator. Currently, the internal mammary artery graft is frequently used in situations known to compromise long-term patency.

While more than 90% of coronary artery bypass surgeries are performed with single internal mammary arteries, about 10% use bilateral internal mammary arteries. The only difference between a single internal mammary artery and bilateral internal mammary artery graft is the number of internal mammary arteries used in the bypass surgery.

Dr Wessels explained: “Bilateral internal mammary arteries are not very commonly used in coronary artery bypass surgeries, and the decision to use them varies from patient to patient and from hospital to hospital.”

Dr Jassim pointed out that in the Middle East, bilateral internal mammary arteries are not used very much due to the high incidence of diabetes in the region, which would increase the risks.

Bilateral internal mammary artery

The preference for using bilateral internal mammary arteries over single internal mammary artery grafts for coronary artery bypass graft surgeries is on the rise, as is indicated by a study presented at the 2010 European Society of Cardiology (ESC) Congress in Stockholm. The report by Professor David Taggart from John Radcliff Hospital in Oxford, UK, emphasised the benefits of the use of bilateral internal mammary artery in coronary artery bypass graft surgeries and quelled safety concerns.

The study was based on evidence from the “The Arterial Revascularization Trial (ART)”, a randomised trial of bilateral internal mammary artery grafts versus single internal mammary artery grafts whose primary outcome was survival at 10 years.

According to Prof Taggart: “Observational data have also suggested that use of bilateral internal mammary arteries may provide superior revascularization with improved long-term survival and reduced need for repeat coronary artery bypass grafts.”

Dr Wessels emphasised that it is “important to know what to do with the other mammary arteries when using bilateral internal mammary arteries in bypass surgeries.” Some surgeons may place the right internal mammary artery onto the right coronary artery, while placing the left internal mammary artery onto the left anterior descending coronary artery. Other surgeons may place the right internal mammary artery onto the circumflex artery.

“An exception to the rule would be to place the right internal mammary artery onto the left anterior descending coronary artery, however this is rarely done.

“There are a few problems with the use of the right internal mammary artery,” Dr Wessels said. “First, there may be a problem with leaks with the right internal mammary artery. Second, for the grafting system, the artery may be too short. The anatomy must be ideal for the use of bilateral internal mammary arteries, and this is one of the distinctive factors between bilateral and single internal mammary artery use.”

With regards to equipment and skill, as long as a surgeon is able to perform a bypass surgery with the left internal mammary artery, the right internal mammary artery can be used just as easily and presents no extra challenge.

Evolution

Coronary artery bypass grafts have evolved significantly during the past the decade. Dr Jassim explains that in the Arab countries, as well as around the world, the standard procedure is the use of a single internal mammary artery along with supplemental vein grafts, usually two. This method yields excellent short and medium term outcomes, however the long term outcome of the standard procedure has remained under scrutiny. Although more than 70% of the patients are alive 12 years after surgery, the long-term results seem to be limited due to progressive vein graft failure1. Vein graft failure is highly unfavorable, as it leads to a high risk of recurrent angina as well as late myocardial infarction.

Prof Taggart explained: “There is a constant attrition of vein grafts such that by 10 years after the operation half of the vein grafts are occluded and half of the remainder are severely diseased; by contrast more than 90% of the internal mammary arteries are still patent.” Instigating further investigations, the risks in coronary artery bypass graft surgeries have led to new developments, such as the “off pump coronary artery bypass surgery” (OPCAB) and the use of other arterial conduits.

The great saphenous vein and radial artery from the forearm are also frequently used as conduits, explained Dr Jassim. He noted the favourability of the use of the radial artery for grafts, saying that the radial artery is easier to harvest and remains open for a longer time. Coronary arteries have an increased tendency to close.

Dr Wessels pointed out that stenosis is reduced with use of the radial artery.

Benefits

Artery grafts are preferable to vein grafts in terms of patency rates. The patency rate of a graft using the left internal mammary artery to the left anterior descending artery after ten years is about 95-98% and is a “fantastic graft”, according to Dr Wessels. “The graft still functions well many years down the road. With vein grafts, only about 60-70% are still patent in 10 years, while about 40% close down.”

Dr Wessels explained that when the use of bilateral internal mammary arteries is anatomically suitable, this type of graft provides superior long-term benefit. A bilateral internal mammary artery graft has a higher rate of long-term patency. With regards to long-term outcome, vein graft failure does not become commonplace until seven years after coronary artery bypass graft surgeries, however it is crucial to consider that the benefits of bilateral internal mammary artery grafts are likely to increase with longer duration of follow up. When the long-term patency rate is high, the long-term survival rate for the patient is also increased.

The patient’s quality of life may also be significantly improved after 10 years, more than with single internal mammary artery grafts. Bilateral internal mammary artery grafts also reduce the need for repeat graft surgeries. The incidence of adverse outcomes is also reduced, but not significantly, according to Dr Wessels. “The reduction is only
about 3-5%.”

This was confirmed by Prof Taggart who reported to the ESC that the combined incidence of death and myocardial infarction was lower with bilateral internal mammary artery grafts compared to single internal mammary artery grafts.

Favourable outcomes

Despite the many advantages, the question must be posed: Can the favourable outcomes of bilateral internal mammary arteries be attributed largely to the type of patients who receive bilateral internal mammary artery grafts?

A typical candidate for a bilateral internal mammary artery graft, according to Dr Jassim, can be described as a younger, lower risk patient, with favourable patient characteristics, and who does not have diabetes.

Concerns

While bilateral internal mammary artery grafts are used in leading cardiac centres around the world, they are used with caution due to the risks associated with the procedure. Prof Taggart alluded to these in his presentation to the ESC last year saying that studies indicate that they are associated with increased early mortality and major morbidity, and the procedure may be technically more challenging.

Dr Jassim agreed that the procedure is technically more challenging and noted that it involved harvesting two arteries as opposed to one. He also pointed out that the surgeon must know how to close the sternum properly and ensure that there is no bleeding.

A concern shared by surgeons familiar with the bilateral internal mammary artery grafts procedure said the risk of a sternal wound infection is a particular danger.

Dr Wessels said that the development of a sternal wound infection is a critical risk with bilateral internal mammary artery grafts.

“This is a very serious problem, particularly in patients with diabetes,” he said.

Dr Jassim mentioned that the incidence of diabetes is very high in Arab countries, thus bilateral internal mammary artery grafts present a major risk for the region. Specifically, the graft would be unfavourable for an elderly, overweight, diabetic patient.

Dr Wessels explained that “skeletonization" of the arteries has been shown to help reduce the risk of sternal wound infection from the bilateral internal mammary artery graft procedure. Skeletonisation of the two mammary arteries is usually done with an ultrasonic scalpel, whereby excess tissue surrounding the artery is removed and side branches are controlled.

Future

The risks involved with bilateral internal mammary artery grafts have decreased significantly through research and investigation of the procedure.

With regards to the future, Dr Wessels concludes: “If the indications are favourable, bilateral internal mammary arteries are pretty safe for use in coronary artery bypass surgeries, and the use of bilateral internal mammary arteries should be expanded.”

● References 1. Taggart, DP. Bilateral internal mammary artery grafting: are BIMA better? Heart 2002; 88:7-9. 2. Endo, M, Kasanuki, H, et al. Benefit of bilateral over single internal mammary artery grafts for multiple coronary artery bypass grafting. Circulation 2001; 104:2164. 


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ate of upload: 17th Feb 2011

 

                                  
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