Coronary Artery Disease and Coronary Bypass Grafting

Coronary artery disease (CAD) is the leading cause of death for both men and women in the United States. The process of atherosclerosis is the hardening of an artery due to a lipid build up, resulting in functional loss. Fatty deposits, or plaques, may accumulate inside the arterial wall and cause stenosis, or an abnormal narrowing the artery wall. This causes the flow of blood to be reduced or completely stop and the vessel wall to lose its flexibility and ability to handle pulsatile flow. There are several forms of treatment available for CAD depending on the severity of the disease, including lifestyle changes, medicines, angioplasty, and coronary artery bypass grafting (CABG).

CABG is the preferred treatment for patients with multiple areas of coronary artery narrowing or blockage and also for patients with higher percentages of stenosis, this relation can be seen in figure 1 above. Patients typically have 1 to 5 bypasses within one surgical procedure. This form of treatment is the most common type of surgery in the United States, with about 500,000 surgeries per year. Typically, the patient’s saphenous vein from the leg, internal mammary artery (IMA), or the radial artery from the arm is used. Figure 2 shows the location of the saphenous vein and IMA. These vessels are removed and grafted onto the hardened artery to revascularize the affected area.

Figure 2

Advantages and Disadvantages of the Current Gold Standard

The current gold standard for the CABG procedure is the use of autologous (from self) saphenous vein and IMA because of their resemblance to the native coronary artery and their relatively high patency rates. It was not until recently that the radial artery has been widely studied as another source for this procedure. The five and ten year artery patency rates for these have all shown to be greater than 70% and 50%, respectively. These rates vary depending on the blood vessel used for the procedure.

Even with the success this procedure has had, there are several disadvantages that may lead to complications. Removing an autologous vein for the procedure may cause donor site morbidity, which can lead to problems such as groin infection near the site of the saphenous vein removal. In addition, there is only a limited supply of donor vessels for this procedure. Up to 30% of patients undergoing lower limb bypass do not have a suitable vein. This can be problematic for patients who need multiple CABGs or have had previous procedures. There is also a greater risk with the use of multiple vessels. For example, there are more incidents of deep sternal wound infection when both IMAs are used for this procedure, especially for patients with obesity and diabetes.

Existing Vascular Grafts and Improvements

Although living autologous vessels seem to be the ideal conduits for CABG, there are several factors, as discussed above, which have prompted efforts to develop a more suitable donor vessel. The ideal blood vessel substitute should mimic the characteristics of a native blood vessel, including its composition, structure, function, and mechanical properties. It should be durable enough to endure the mechanical stresses, as well as the threat of biodegradation and infection within the body after implantation. The vessel should be made up of materials that promote cell-specific interactions and needs to be able to have similar viscoelastic properties as a normal artery to avoid a compliance mismatch. It should be flexible in order to maintain its contour, yet rigid enough to prevent kinking. The materials used, especially on its luminal surface, must be nonthrombogenic to prevent blood clotting in the vascular graft. It is favorable that the vessel is easily and quickly manufactured, and should be readily available in multiple lengths and sizes.

However, no existing conduit possesses all the properties and qualities of the ideal arterial vascular graft listed above. Current alternatives to autologous vascular grafts are prosthetic conduits based on expanded polytetrafluoroethylene (ePTFE) and polyethylene terephthalate (Dacron ®). Their patency at 5 years is 40% to 50%, which is acceptable but relatively low. Tissue engineering has proven to be successful in wound management, burns, and cartilage repair; therefore their has been a growing interest in designing biological blood vessels as an alternative to autologous vascular grafts and current prosthetic conduits. However, previously proposed and designed tissue engineered vascular grafts were not durable, were prone to early thrombosis, and had poor patency rates. This means that a new vascular graft with all the above mentioned qualities is yet to be manufactured, but is a hopeful potential cure for the future.

This entry was posted on Friday, July 6th, 2007 at 1:23 am and is filed under Health. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.