Coronary Artery Disease
CORONARY ARTERY DISEASE–HEART ATTACKS AND ANGINA
Overview
Coronary artery disease refers to those syndromes caused by blockage to the flow of blood in those arteries supplying the heart muscle itself, i.e., the coronary arteries. Like any other organ, the heart requires a steady flow of oxygen and nutrients to provide energy for movement, and to maintain the delicate balance of chemicals which allow for the careful electrical rhythm control of the heart beat. Unlike some other organs, the heart can survive only a matter of minutes without these nutrients, and the rest of the body can survive only minutes without the heart–thus the critical nature of these syndromes.
Causes of blockage range from congenital tissue strands within or over the arteries to spasms of the muscular coat of the arteries themselves. By far the most common cause, however, is the deposition of plaques of cholesterol, platelets and other substances within the arterial walls. Sometimes the buildup is very gradual, but in other cases the buildup is suddenly increased as a chunk of matter breaks off and suddenly blocks the already narrowed opening.
Risk Factors
Certain factors seem to favor the buildup of these plaques. A strong family history of heart attacks is a definite risk factor, reflecting some metabolic derangement in either cholesterol handling or some other factor. Being male, for reasons probably related to the protective effects of some female hormones, is also a relative risk. Cigarette smoking and high blood pressure Rare definite risks, both reversible in most cases. Risk also increases with age. Elevated blood cholesterol levels (both total and low density types) are risks, whereas the high density cholesterol level is a risk only if it is reduced; the latter adds very little to predictive value over the total cholesterol level. Possible, but less well- defined factors include certain intense and hostile or time- pressured personality types (so- called type A), inactive lifestyle, and high cholesterol diets.
The Mechanism of Symptoms
As plaques begin to clog the coronary arteries, several things may occur. In some, no symptoms are noted until a fatal heart attack or sudden death occur as the first (and last) event. In others, no symptoms are noted at rest, but with exercise or other stress, a dull aching pain is noted in the chest, neck, jaw, upper abdomen, arm, or back. Typically, this subsides with rest.
Called “angina,” this crushing type of pain represents the area of the heart which is trying to function with inadequate supply from its coronary artery, much as an overutilized muscle in the leg might hurt under similar circumstances.
If the stress is relieved, the previous level of circulation to that area of heart is again adequate, and recovery takes place with no permanent loss of muscle in the heart. However, if the stress continues, or if the blockage is so critical that even at rest the blockage is too great, the patient experiences further symptoms–progressive pain, profuse sweating, shortness of breath, palpitations, and finally collapse. A severe sense of dread or impending doom is, understandably, reported by many patients. As the jeoporadized area of heart muscle finally dies, a heart attack or myocardial infarction is said to occur.
Effects of a Heart Attack
The outcome of a heart attack depends on the location and size of the area of heart involved. Even a “small” one, if located in a critical area of the heart, or if it sets off an unstable rhythm (see cardiac arrhythmia section) can be fatal. Large heart attacks kill so much muscle that the pumping action is inadequate, resulting in severe low blood pressure and circulation to the body (shock) or congestive heart failure. Many heart attacks are intermediate, and various degrees of complications are noted. In these cases total or nearly total recovery is very common.
In the pre-hospital minutes of a heart attack, there is a nearly 50% incidence of cardiac arrest due to ventricular fibrillation or total stoppage of the heart (see arrhythmias). This is where cardiopulmonary resuscitation, or CPR, saves lives. This technique is discussed further elsewhere in HealthNet.
Prevention
The primary risk factors have been discussed, and prevention is a matter of eliminating these when possible. Of confirmed value are smoking cessation, blood pressure control, and treatment of some severe metabolic problems such as
diabetes and marked cholesterol elevation. Please refer to the appropriate sections for further information.
Diagnosis
Two thirds of patients with heart attacks have warning symptoms of chest pain, marked fatigue, or other problems in the month before the event. Sometimes the symptoms are typical as described, but often they are atypical or subtle. If there is doubt, a physician evaluation is critical. If unexplained chest, neck, abdominal, back, jaw, or arm pain occur, the safest course is immediate medical attention. Fleeting sharp pains, lasting only seconds, are much less often related to the heart.
The medical evaluation includes a thorough history and physical exam. In addition, an electrocardiogram (EKG) is often done, although even if normal both angina and heart attack in the early stages cannot be ruled out. Blood tests may reveal chemical changes of a heart attack, but sometimes only intense observation in the cardiac unit with repeated blood tests and EKG’s is adequate.
Once an acute heart attack or unstable angina are ruled out, the question is often whether a chest pain is from heart problems or some less serious disorder. Useful tests include exercise tests, where the EKG, blood pressure and other factors are monitored during treadmill or bicycle exercise. Used alone, the sensitivity and accuracy of this is limited, since a sizeable percent of normal people may have some abnormality on standard exercise testing, and many people with definite coronary disease have a normal study. The test may be improved by adding an injection of a slightly radioactive substance the course of which is traced through the heart. This is called a Thallium stress test, or a radionuclide angiography, depending on technique. Though not perfect, these improved tests are very helpful in many cases.
If there remains significant doubt about the cause of the pain, and if making this diagnosis would significantly alter medical management, the ultimate test is called coronary angiography, or cardiac catheterization. Most patients never require this, but controversy rages over when to do it. This involves passing a small tube into the coronary arteries, injecting an x-ray dye, and visualizing the arteries on film. The test is discussed further elsewhere in HealthNet. It is most useful when coronary bypass surgery is being considered, as noted below.
Treatment
Treatment of symptoms is divided into medical and surgical types. The choices are complicated, and depend largely on individual factors, as well as regional resources and preferences. General comments on the major options are included in this section, although exceptions are common.
MEDICAL THERAPY–Each of these drugs is discussed in greater detail in the drug section of HealthNet, and the reader is referred to the appropriate section for more detail.
Medications are increasingly effective for symptom control, as well as prevention of complications. The oldest and most common agents are the nitrates, derivatives of nitroglycerine. They include nitroglycerine, isosorbide, and similar agents. Newer forms include long acting oral agents, plus skin patches which release a small amount through the skin into the bloodstream over a full day. They act by reducing the burden of blood returning to the heart from the veins and also by dilating the coronary arteries themselves. Nitrates are highly effective for relief and prevention of angina, and sometimes for limiting the size of a heart attack. Used both for treatment of symptoms as well as prevention of anticipated symptoms, nitrates are considered by many to be the mainstay of medical therapy for angina.
The second group of drugs are called “beta blockers” for their ability to block the activity of the beta receptors of the nervous system. These receptors cause actions such as blood pressure elevation, rapid heart rate, and forceful heart contractions. When these actions are reduced, the heart needs less blood, and thus angina and even the extent of a heart attack may be reduced. Because the electrical irritability of damaged areas of heart is reduced, these drugs can reduce the incidence of sudden death due to ventricular fibrillation in some patients at risk.
The newest group of drugs for coronary disease is called the calcium channel blockers. Calcium channels refer to the areas of the membranes of heart and other cells where calcium flows in and out, reacting with other chemicals to modulate the force and rate of contractions. In the heart, they can reduce the force and rate of contractions and electrical excitability, thereby having a calming effect on the heart. Although their final place in heart disease remains to be seen, they promise to play an increasingly important role.
SURGERY
Coronary bypass surgery has become commonplace. The procedure consists of transplanting veins from the leg (or vessels from elsewhere in the chest) to the blocked area, bypassing or “jumping over” the obstructions. As many as four or five vessels may be bypassed, thus restoring flow to the area previously blocked off. During the operation, the heart is temporarily replaced by the “heart-lung” machine. Mortality in better centers is less than one percent.
There is major controversy surrounding the benefits and selection of patients for surgery. A few facts are accepted: 1. Patients with severe blockage of the main trunk of the coronary arteries live longer if operated upon–“left main disease.” 2. Patients with severe pain unresponsive to intense medical therapy, or intolerant of it, often feel better after surgery; whether they live longer is unclear. 3. Patients with hearts that are not pumping well, i.e. with a degree of congestive heart failure, have a higher mortality from surgery than others.
Beyond that, there is more emotion than fact. It is clear that unless surgery is contemplated or the diagnosis is in question, most patients do not require catheterization or surgery. Furthermore, surgery as a life-prolonging measure is questionable for most patients, and no study has been done comparing surgery with medical management using the newer drugs. Until these points are clarified, the choice is a difficult one best left to individualized considerations.
One newer means of therapy is termed angioplasty. This involves passing a catheter through an artery to the point of blockage in the coronary, then inflating a tiny balloon at the tip of the artery. This squeezes and flattens the blocked area, thereby opening a larger passage for the blood, and imporving the blockage. Not all types or locations of blockage are amenable to this treatment, and it is not without its risks. Furthermore, some blockages recur after treatment. Currently angioplasty is available in selected major medical centers only, but when appropriately applied, it can avoid the need for surgery in selected patients.
The Good News
One final optimistic note– since the late 60’s, the incidence and mortality of coronary disease has been steadily declining, and rather markedly at that. The reasons are not clear, but may be related to changes in diet, blood pressure control, and activity levels. As this trend continues, and newer treatments are perfected, this once dread disease may well be conquered by modern medicine, if not completely, at least to a large extent.