Professor of Medicine and Chief, Division of Cardiology Wayne State University
IN MOST CASES, HEART ATTACKS are caused by atherosclerosis, which slowly narrows the coronary arteries, and a blood clot that suddenly forms and blocks off the coronary artery completely, thus limiting blood flow to the heart. When a patient comes into a hospital emergency room early in the course of a heart attack, physicians may administer a clot-dissolving drug.
The most common clot-dissolving drug is tPA (tissue plasminogen activator). During the first ninety minutes, this drug will dissolve the clot that is blocking the coronary in about 75 percent of patients, restoring blood flow to the heart and limiting the amount of heart damage.
Because this is a very potent drug that dissolves clots anywhere in the body, bleeding is one possible side effect of tPA. Therefore, patients must be carefully selected to have minimal risk for bleeding. It cannot be used in patients who have had a recent stroke, in patients with severe high blood pressure, or in patients with bleeding stomach ulcers. However, when it is given to carefully selected patients in the first six to twelve hours after the onset of a heart attack, it can definitely improve their outcome.
If you develop angina pectoris or what's thought to be an angina equivalent, your physician probably will start with an electrocardiogram. If it's abnormal or in certain cases even if it's normal, your physician may decide to do some form of stress testing. Depending on the results, and sometimes even without testing, your physician may decide to do a type of cardiac catheterization called coronary arteriography, in which catheters are used to inject the coronary arteries with radiopaque dye. This helps doctors see if blockages are present, where they are located, and how severely the artery is blocked.
In most angina cases, the treatment is medication, dietary changes, and exercise. Several medications are popularly prescribed to treat angina:
y Nitrates dilate coronary arteries. They do not necessarily dilate the area with the blockage, but they can dilate beyond the blockage and lower the overall resistance to blood flow. y Beta blockers work directly on the heart muscle. Beta blockers cause the heart to contract more slowly and with less vigor, reducing the amount of oxygen demanded by the heart muscle. y Ace inhibitors dilate arteries throughout the body, which lowers the resistance to blood flow. The heart does not have to work as hard to deliver the same amount of blood to the body, allowing the heart itself to get by with less oxygenated blood. y Calcium channel blockers are particularly helpful in patients who have some degree of coronary artery spasm. They prevent the arteries from going into spasm or at least decrease the incidence and severity of the spasm.
If a severe blockage is present, more aggressive measures may be needed to get oxygenated blood to the heart. One option is interventional therapy, or the use of catheter-based therapies.
When a coronary artery has a severe degree of blockage — more than 70 percent but usually less than 100 percent — cardiologists may be able to dilate the artery with a balloon catheter (Fig. 8.5). Sometimes even arteries that are totally blocked can be reopened with catheters.
In this procedure, a catheter, which looks like a long piece of spaghetti, is threaded through the arterial system, usually through an artery in the groin or arm. The catheter is tipped with a tiny sausage-shaped balloon that is deflated and guided into the coronary artery and positioned directly opposite the narrowed area. The balloon is inflated, crushing the plaque material against the arterial wall and opening up the artery. It may have to be Inflated several times.
A disadvantage to using a balloon is restenosis. Doctors have found that In about 40 percent of patients who undergo this procedure, within a year or less the artery begins to close again, or restenose, which can occur for various reasons. This means another catheter procedure is necessary, or perhaps open heart surgery.
Recently, a device called a stent has been developed to combat restenosis. It is used with the balloon. Stents look like wire or mesh tubes, and they are usually flexible. In this procedure, the stent is placed over the balloon, and both are guided to the obstruction. When the balloon is inflated, the stent expands and is lodged in the artery (Fig. 8.6A). The stent remains in place after the balloon and catheter are withdrawn (Fig. 8.6B). Its major advantage lies in its ability to lessen the chance that the artery will become obstructed again, although it does require placing a foreign object into the coronary artery.
Balloon catheters are not the only interventional option. Another is a tiny drill called a rotablator. This device literally shaves atherosclerotic material off the arterial wall. Under certain conditions, a laser can be used to carve out, or vaporize, some of the atherosclerotic material. These devices are usually not used in a coronary artery that is totally blocked, particularly if that blockage has been present for a long time.
The feasibility of using catheters depends on the severity of the blockage. In some cases, when catheters are forced beyond total blockages, they may perforate the wall of the coronary artery and cause
Coronary arteries that are blocked with atherosclerotic material can be opened with a balloon-tipped catheter in a procedure called percutaneous transluminal coronary angioplasty.
Recently, a device called a stent has come into use. This device is placed on the balloon (A) and remains in the artery after the dilatation (B).
These coronary an-giography films were taken before and after a stenting procedure. The blocked artery, left, is contrasted with the open artery, right, after a stent was put in place with a balloon-tipped catheter. Introduced in the early 1990s, coronary stents are designed to hold open a blocked coronary artery after a balloon widening.
severe complications. In the most important coronary artery, the left main coronary, cardiologists are usually reluctant to dilate blockages or attempt other catheter procedures to open the artery because some of the material could suddenly break off, possibly blocking the blood flow to the left ventricle and causing a fatal heart attack. There are centers, however, where research is being done on using balloons and related techniques in the left main coronary under special conditions.
If interventional catheter techniques aren't viable, doctors usually turn to the coronary bypass graft. There are cases, however, when the coronary artery disease is so severe and so widespread, or diffuse, that there's really nowhere to place the bypass graft.
For these patients, a relatively new procedure called transmyocardial laser revascularization may be considered. In this operation, a laser, used either through a catheter or directly through a surgical incision, is used to burn tiny holes in the heart muscle itself. It is hoped these channels will, over time, connect with some of the smaller blood vessels and form new circulation.
In a September 1999 issue of The New England Journal of Medicine, Dr. O. Howard Frazier from the Texas Heart Institute reported on a multicenter study in which ninety-one patients were randomly assigned to undergo transmyocar-dial laser revascularization and another one hundred one patients were randomly assigned to continued medical treatment.
After twelve months, the study group found that the patients who underwent transmyocardial laser treatment had much better control of their angina than their medicine-treated counterparts. Seventy-two percent were improved compared with only 13 percent of the patients who were receiving continued medical treatment. The group also found that the quality of life was significantly improved in the laser-treated group.
In the group that underwent laser treatment, 3 percent died in the hospital after the surgery. At twelve-month follow-up, 85 percent of the patients who had undergone laser treatment were alive as compared with 79 percent in the medically treated group.
Frazier's report, therefore, Indicates that at least up to the first twelve months after the laser procedure, the patients who had the procedure are improved over a similar group treated only with medicines.
In patients with substantial left main coronary artery disease, physicians typically choose coronary bypass graft surgery instead of catheter techniques or leaving the disease untreated.
Studies have shown that people who undergo the surgery will, on average, live longer than a similar group who forgo the operation. Patients with triple-vessel coronary disease, in which all three of their major coronary arteries have severe blockages, and particularly those who also have left ventricular dysfunction (perhaps related to a previous heart attack), also benefit from coronary artery bypass grafting and on the average live longer than those who do not have the surgery. Patients with severe double- or single-vessel coronary disease can also be candidates for coronary bypass grafting, depending on the circumstances.
A doctor would often consider recommending bypass surgery if the patient had a substantial blockage of the left anterior descending coronary artery, particularly if the blockage were where it is attached to the left main coronary. Doctors are frequently reluctant to dilate the artery there or put a stent there because it could interfere with the left main coronary.
If the left anterior descending coronary artery is totally blocked upstream but is a good vessel beyond that, as determined by the number of collateral blood vessels feeding it, and the heart muscle is alive beyond this blockage, bypass surgery is often a good choice if angina is bothersome.
Complications of Heart Attacks Requiring Heart Surgery
If a heart attack has occurred, there are possible complications. These include left ventricular aneurysm, which may require surgery, and post-myocardial infarction ventricular septal defect and papillary muscle rupture, both of which almost always require surgical repair.
When a coronary artery such as the left anterior descending is blocked, a portion of the heart muscle may die and turn into scar tissue. Sometimes, however, as it's turning into scar tissue, the dying or dead tissue stretches and forms a sac (Fig. 8.9A). Later, as the living portions of the heart muscle contracts, some blood may be pushed back into the sac so it actually absorbs part of the heart's pumping energy, thus contributing to heart failure.
These sacs or aneurysms can also be the source of certain types of serious irregular heart rhythms. In addition, blood clots can form in them that can occa
The papillary muscles, which connect the valve leaflets to the interior wall of the heart, can sometimes rupture during a heart attack. This condition usually results in valve replacement.
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