Coronary artery bypass graft surgery (CABG) remains an important option for significant blockage of the heart or coronary arteries. Despite the use of CABG for decades, most have little understanding but many questions.
Who will benefit from coronary artery bypass graft surgery?
The greatest benefit for those who undergo CABG are those who have a significant blockage of the heart artery which provides the main blood supply to the muscle of the main pumping chamber of the heart; namely the left main artery (LM) or left anterior descending artery (LAD). There are two other major arteries in the heart, one to the left of the LAD called the left circumflex artery (LCX) and the other to the right of the LAD called the right coronary artery (RCA).
Generally, survival benefit from CABG, as compared to medical therapy, is seen in those with a narrowing of more than 50 per cent of the LM and/or more than 70 per cent stenosis of the initial segment of the LAD. In addition, if there is a demonstrable large area of heart muscle with insufficient blood supply or if there is poor heart pump function in the presence of at least two major heart arteries with more than 70 per cent narrowing, there is also evidence of improving survival when CABG is performed.
However, if you have a significant more than 70 per cent blockage of either the LCX or RCA without significant LM or LAD disease, the latest practice guidelines from the American College of Cardiology Foundation and American Heart Association categorises CABG in this situation as being harmful without additional survival benefit as compared to medical therapy.
An exception is made when the patient has an unacceptable degree of chest pain despite optimal medical therapy. The benefit is mainly symptom relief and has to be balanced against the risks of CABG.
Is there a difference in the choice of bypass grafts?
CABG is not always a permanent solution as bypass grafts degenerate over time. The best graft is obtained from the internal mammary arteries (IMA), which arise from the arm arteries and course downwards toward the breast bone. Using the left IMA to graft the LAD to bypass the blockage has been shown to improve survival. Ten years after CABG, up to 85 to 90 per cent remain patent. Where practical, the right IMA should also be used to graft across the LCX or RCA where there is critical stenosis. For those with diabetes or obesity, use of IMA grafts can sometimes be associated with an increase in infection of the breastbone wound.
Saphenous vein grafts (SVGs) harvested through an incision on the leg are the commonest grafts used. The major disadvantage with a SVG is that it degenerates faster than IMA with only 50 to 60 per cent of the grafts remaining patent after 10 years. While high volume centres with experienced surgeons report up to 25 per cent occlusion of SVG after one year of CABG, real world figures may vary substantially. In the relatively recent PREVENT IV trial by Mehta published in the Circulation journal in 2011, one year after CABG, about 40 to 50 per cent of grafts were significantly occluded (more than 75 per cent occlusion).
Another artery that is often used in CABG is the forearm or radial artery. A randomised controlled trial by Goldman of the Southern Arizona VA Health Care System published in the Journal of the American Medical Association in 2011 showed that there was no difference in the one-year patency between radial artery graft and SVG. Hence, the data is not completely clear as to its advantage over SVG.
The greatest concern of CABG is the risk of stroke which varies from about 1 per cent to 5 per cent. One of the contributory causes of stroke after CABG is the development of abnormal heart rhythms immediately after CABG, particularly atrial fibrillation (AF) - an abnormal rapid irregular rhythm arising from the upper heart chambers. AF can occur in up to 50 per cent of patients and is associated with an increased risk of stroke and death. A prospective study by Mariscalco published in Circulation journal in 2008 showed that hospital mortality was six-fold higher in AF patients than those without AF (3.3 per cent versus 0.5 per cent). Other common complications include acute kidney damage (2 to 3 per cent), re-operation as a result of bleeding, wound infection and fluid accumulation in the chest wall (pleural effusion). There is conflicting data on the impact of CABG on cognitive decline. A 2008 study by Knipp published in the Annals of Thoracic Surgery reported that new ischaemic brain lesions were seen on magnetic resonance imaging in 51 per cent of patients. However, the presence of new brain lesions did not correlate with the degree of cognitive decline. These brain lesions may potentially be reduced by ultrasound of the aorta during surgery to find a "clean" site for insertion of the graft, thereby preventing cholesterol debris from dislodging and travelling to the brain.
Tips on preparing for the best outcome
For those who have to undergo CABG, careful preparation can help reduce complications and improve outcomes. Improve graft patency by use of aspirin before and within six hours after CABG, using newer endoscopic or robotic techniques of harvesting grafts to reduce the likelihood of graft damage and using the IMA graft. Reduce stroke risk by checking your neck arteries with ultrasound, doing an ultrasound of the aorta to find a "clean" potential graft site during surgery, controlling your "bad" or LDL cholesterol to less than 100 mg/dl by taking cholesterol lowering medication (statins) and preventing AF by commencement of beat-blocker medication at least 24 hours before CABG and continuing it after CABG. Prevent infection by continuous insulin infusion to keep the blood glucose below 180 mg/dl for diabetics and administering pre-operative antibiotics. Finally, knowing what to expect will prepare you not just physically but mentally for CABG.
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