Coronary Angioplasty (cont.)
How is CAD treated?
Angina medications reduce the heart muscle's demand for oxygen in order to compensate for the reduced blood supply, and also may partially dilate the coronary arteries to enhance blood flow. Three commonly used classes of drugs are the nitrates, beta blockers, and calcium blockers. Examples of nitrates include isosorbide (Isordil), isosorbide mononitrate (Imdur), and transdermal nitrate patches. Examples of beta blockers include propranolol (Inderal), atenolol (Tenormin), and metoprolol (Lopressor). Examples of calcium blockers include nifedipine (Procardia, Adalat), verapamil, (Calan, Verelan, Verelan PM, Isoptin, Isoptin SR, Covera-HS), diltiazem (Cardizem, Dilacor, Tiazac), and amlodipine (Norvasc). Many patients benefit from these angina medications and experience reduction of angina during exertion. When significant ischemia still occurs, either with ongoing symptoms or with exercise testing, coronary arteriography is usually performed, often followed by either PCI or CABG.
Patients with unstable angina have severe coronary artery narrowing and often are at imminent risk of heart attack. In addition to angina medications, they are given aspirin and the intravenous blood thinner, heparin. A form of heparin, enoxaparin (Lovenox), may be administered subcutaneously, and has been demonstrated to be as effective as intravenous heparin in patients with unstable angina. Aspirin prevents clumping of blood clotting elements called platelets, while heparin prevents blood from clotting on the surface of plaques. Newer potent IV anti platelet agents ("super aspirins") are also available to help initially stabilize such patients. While patients with unstable angina may have their symptoms temporarily controlled with these potent medications, they are often at risk for the development of heart attacks. For this reason, many patients with unstable angina are referred for coronary angiography, and possible PCI or CABG.
PCI can produce excellent results in carefully selected patients who may have one or more severely narrowed artery segments which are suitable for balloon dilatation, stenting, or atherectomy. During PCI, a local anesthetic is injected into the skin over the artery in the groin or arm. The artery is punctured with a needle and a plastic sheath is placed into the artery. Under x-ray guidance (fluoroscopy), a long, thin plastic tube, called a guiding catheter, is advanced through the sheath to the origin of the coronary artery from the aorta. A contrast dye containing iodine is injected through the guiding catheter so that x-ray images of the coronary arteries can be obtained. A small diameter guide wire (0.014 inches) is threaded through the coronary artery narrowing or blockage. A balloon catheter is then advanced over the guide wire to the site of the obstruction. This balloon is then inflated for about one minute, compressing the plaque and enlarging the opening of the coronary artery. Balloon inflation pressures may vary from as little as one or two atmospheres of pressure, to as much as 20 atmospheres. Finally, the balloon is deflated and removed from the body.
Intracoronary stents are deployed in either a self-expanding fashion, or most commonly they are delivered over a conventional angioplasty balloon. When the balloon is inflated, the stent is expanded and deployed, and the balloon is removed. The stent remains in place in the artery. Atherectomy devices are inserted into the coronary artery over a standard angioplasty guide wire, and then activated in varying fashion, depending on the device chosen.
CABG surgery is performed to relieve angina in patients whose illness has not responded to medications and are not good candidates for balloon angioplasty. CABG is best performed in patients with multiple blockages in multiple locations, or when blockages are located in certain arterial segments which are not well-suited for PCI. CABG is often also used in patients who have failed to attain long-term success following one or more PCI procedures. CABG surgery has been shown to improve long- term survival in patients with significant narrowing of the left main coronary artery, and in patients with significant narrowing in multiple arteries, especially in those with decreased heart muscle pump function.
Next: What are the complications of PCI? »
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