Incidence of CABG Restenosis
What is CABG?
Coronary artery bypass grafting (CABG) is a type of surgery that improves blood flow to the heart for those who suffer from severe coronary artery disease.Coronary artery disease is the buildup of fatty substance in your arteries. As these arteries become occluded, blood flow to your heart is decreased, thus causing chest pain.
If the plaque ruptures, a blood clot can form on its surface. A large blood clot can mostly or completely block blood flow through a coronary artery, causing a heart attack.
CABG is one treatment for CHD. During CABG, a healthy artery or vein from the body is connected, or grafted, to the blocked coronary artery. The grafted artery or vein bypasses (that is, goes around) the blocked portion of the coronary artery. This creates a new path for oxygen-rich blood to flow to the heart muscle.
Who needs it?
Class I indications for CABG from the American College of Cardiology (ACC) and the American Heart Association (AHA) are as follows:
- Left main coronary artery stenosis >50%
- Stenosis of proximal LAD and proximal circumflex >70%
- 3-vessel disease in asymptomatic patients or those with mild or stable angina
- 3-vessel disease with proximal LAD stenosis in patients with poor left ventricular (LV) function
- 1- or 2-vessel disease and a large area of viable myocardium in high-risk area in patients with stable angina
- >70% proximal LAD stenosis with either ejection fraction < 50% or demonstrable ischemia on noninvasive testing
Analysis from the Surgical Treatment for Ischemic Heart Failure (STICH) trial assessed exercise tolerance and mortality in patients with ischemic left ventricular dysfunction who underwent CABG and compared them to those who were treated with medical therapy. While its well known that poor exercise capacity is associated with increased mortality risk, the aim of this study was to assess how exercise capacity influences the risks and benefits of CABG compared to medical therapy. The study found that, compared to medical therapy, mortality was lower for patients who underwent CABG and were able to walk more than 300m. Those who were unable to walk 300m and underwent CABG, had higher mortality during the first 60 days of undergoing surgery. Compared to those with higher exercise tolerance,a patient with ischemic left ventricular dysfunction and poor exercise capacity faced increased early risk of mortality. Therefore, these patients would benefit from medical therapy. On the other hand, among those with increased exercise tolerance, CABG would be indicated.
One serious complication is graft stenosis, which can lead to chest pain, heart attack, or cardiac death. Other possible risks associated with coronary artery bypass graft surgery include:
- Bleeding during or after the surgery
- Blood clots that can cause heart attack, stroke, or lung problems
- Infection at the incision site
- Breathing problems
- Cardiac dysrhythmias/arrhythmias (abnormal heart rhythms)
A study compared the 10 year survival of patients who received an internal mammary artery to left anterior descending artery graft versus those who received saphenous venous grafts (SVG) alone. They found improved survival rates in arterial versus venous grafts as summarized below:
- One vessel disease – 93 versus 88 percent for SVGs
- Two vessel disease – 90 versus 80 percent
- Three vessel disease – 83 versus 71 percent
This graph illustrates the success of an arterial vs vein graft over 10 years. The Internal Mammary Artery had a significantly higher rate of success over the saphenous vein graft.
Two other studies found the benefits of survival in arterial versus venous grafts persisted after 15 and 20 years. The Coronary Artery Surgery Study followed patients 15 years after surgery. They found a 64% survival in patients with arterial grafts versus 53% in those with venous grafts. Not only did they have improved survival but they also had fewer rates of re-operations and lower recurrence of heart attack or chest pain.
The age of a saphenous vein graft plays a major role in the patency of the graft. About 65 to 80 percent of SVGs stay patent for five years after the operation. With 50 percent remaining patent for 15 years. Vein occlusions can happen between one month and one year surgery. There are many factors that can contribute to this process. They include platelet aggregation, growth factor secretion, and endothelial dysfunction. Occlusions that occur after the first year due to areas developing lipid deposits followed by atherosclerotic like plaque. After the first year SGVs will slowly obstruct at a rate of 2% per year.
Long term graft patency is much greater with arterial grafts than venous grafts. Arterial grafts have a 98 percent patency rate for 10 years. With such a high success rate, an attempt is usually made to place at least one arterial graft in every patient who undergoes coronary artery bypass surgery.
While restenosis is a possible complication, there are various therapies available to reduce this risk. Medical therapy as well as lifestyle modifications can significantly improve survival rates after this procedure.
Antiplatelet agents such as aspirin decrease the incidence of early and late graft stenosis. The 2012 American College of Chest Physicians (ACCP) recommends 75 to 162 mg/day within 48 hours of the procedure and continued indefinitely. Aggressive control of atherosclerotic cardiovascular disease with statin medications can also delay the progression of graft disease. Patients who reduced their LDL-cholesterol to <100 mg/dL had a 30% reduction in revascularization procedures and 24% reduction in cardiac death. Other important therapies include blood pressure control, smoking cessation, and control of serum glucose in diabetics.