Coronary artery disease
Coronary artery disease: Excerpt from Professional Guide to Diseases (Eighth Edition)
Coronary artery disease (CAD) occurs when the arteries that supply blood to the heart muscle harden and narrow. The result is the loss of oxygen and nutrients to myocardial tissue because of diminished coronary blood flow. This reduction in blood flow can also lead to coronary syndrome (angina or myocardial infarction).
Causes and incidence
Atherosclerosis is the usual cause of CAD. In this form of arteriosclerosis, fatty, fibrous plaques, possibly including calcium deposits, narrow the lumen of the coronary arteries, reduce the volume of blood that can flow through them, and lead to myocardial ischemia. Plaque formation also predisposes to thrombosis, which can provoke myocardial infarction (MI).
Atherosclerosis usually develops in high-flow, high-pressure arteries, such as those in the heart, brain, kidneys, and in the aorta, especially at bifurcation points. It has been linked to many risk factors: family history, male gender, age (risk increased in those aged 65 or older), hypertension, obesity, smoking, diabetes mellitus, stress, sedentary lifestyle, high serum cholesterol (particularly high low-density lipoprotein cholesterol) or triglyceride levels, low high-density lipoprotein cholesterol levels, high blood homocysteine levels, menopause and, possibly, infections producing inflammatory responses in the artery walls.
Uncommon causes of reduced coronary artery blood flow include dissecting aneurysms, infectious vasculitis, syphilis, and congenital defects in the coronary vascular system. Coronary artery spasms may also impede blood flow. (See Coronary artery spasm.)
Coronary artery disease is the leading cause of death in the United States. According to the American Heart Association, someone in the United States suffers a coronary heart event approximately every 29 seconds, and someone dies from such an event approximately every 60 seconds.
Signs and symptoms
The classic symptom of CAD is angina, the direct result of inadequate oxygen flow to the myocardium. Anginal pain is usually described as a burning, squeezing, or tight feeling in the substernal or precordial chest that may radiate to the left arm, neck, jaw, or shoulder blade. Typically, the patient clenches his fist over his chest or rubs his left arm when describing the pain, which may be accompanied by nausea, vomiting, fainting, sweating, and cool extremities. Anginal episodes most often follow physical exertion but may also follow emotional excitement, exposure to cold, or a large meal.
Angina has four major forms: stable (pain is predictable in frequency and duration and can be relieved with nitrates and rest), unstable (pain increases in frequency and duration and is more easily induced), Prinzmetal’s or variant (from unpredictable coronary artery spasm), and microvascular (in which impairment of vasodilator reserve causes angina-like chest pain in a patient with normal coronary arteries). Severe and prolonged anginal pain generally suggests MI, with potentially fatal arrhythmias and mechanical failure.
Diagnosis
The patient history — including the frequency and duration of angina and the presence of associated risk factors — is crucial in evaluating CAD. Additional diagnostic measures include the following:
❑ Electrocardiogram (ECG) during angina may show ischemia and, possibly, arrhythmias such as premature ventricular contractions. ECG is apt to be normal when the patient is pain-free. Arrhythmias may occur without infarction, secondary to ischemia.
❑ Treadmill or exercise stress test may provoke chest pain and ECG signs of myocardial ischemia.
❑ Coronary angiography reveals coronary artery stenosis or obstruction, possible collateral circulation, and the arteries’condition beyond the narrowing.
❑ Myocardial perfusion imaging with thallium-201, Cardiolite, or Myoview during treadmill exercise detects ischemic areas of the myocardium, visualized as “cold spots.’’
❑ Stress echocardiography may show wall motion abnormalities.
❑ Electron-beam computed tomography identifies calcium within arterial plaque; the more calcium seen, the higher the likelihood of CAD.
Treatment
The goal of treatment in patients with angina is to either reduce myocardial oxygen demand or increase oxygen supply. Therapy consists primarily of nitrates such as nitroglycerin (given sublingually, orally, transdermally, or topically in ointment form) to dilate coronary arteries and improve blood supply to the heart. Glycoprotein IIb-IIIa inhibitors and antithrombin drugs may be used to reduce the risk of blood clots. Beta-adrenergic blockers may be used to decrease heart rate and lower the heart’s oxygen use. Calcium channel blockers may be used to relax the coronary arteries and all systemic arteries, reducing the heart’s workload. Angiotensin-converting enzyme inhibitors, diuretics, or other medications may be used to lower blood pressure.
Percutaneous transluminal coronary angioplasty (PTCA) may be performed during cardiac catheterization to compress fatty deposits and relieve occlusion in patients with no calcification and partial occlusion. PTCA carries a certain risk but its morbidity is lower than that for surgery. (See Relieving occlusions with angioplasty, pages 1098 and 1099.)Laser angioplasty corrects occlusion by vaporizing fatty deposits. In addition, a stent may be placed in the artery to act as a scaffold to hold the artery open. Another procedure is rotational atherectomy, which removes arterial plaque with a high-speed burr. Obstructive lesions may necessitate coronary artery bypass graft (CABG) surgery and the use of vein grafts.
A surgical technique available as an alternative to traditional CABG surgery is minimally invasive coronary artery bypass surgery, also known as “keyhole” surgery. This procedure requires a shorter recovery period and has fewer postoperative complications. Instead of sawing open the patient’s sternum and spreading the ribs apart, several small cuts are made in the torso through which small surgical instruments and fiber-optic cameras are inserted. This procedure was initially designed to correct blockages in just one or two easily reached arteries; it may not be suitable for more complicated cases.
Coronary brachytherapy, which involves delivering beta or gamma radiation into the coronary arteries, may be used in patients who’ve undergone stent implantation in a coronary artery but then developed such problems as diffuse in-stent restenosis. Brachytherapy is a promising technique, but its use is restricted to the treatment of stent-related problems because of complications and the unknown long-term effects of the radiation. However, in some facilities, brachytherapy is being studied as a first-line treatment of coronary disease.
Because CAD is so widespread, prevention is of incalculable importance. Dietary restrictions aimed at reducing intake of calories (in obesity) and salt, saturated fats, and cholesterol serve to minimize the risk, especially when supplemented with regular exercise. Abstention from smoking and stress reduction are also beneficial. Other preventive actions include control of hypertension, control of elevated serum cholesterol or triglyceride levels (with antilipemics), and measures to minimize platelet aggregation and the danger of blood clots (with aspirin or other antiplatelet agents).
Special considerations
❑ During anginal episodes, monitor blood pressure and heart rate. Take an ECG during anginal episodes and before administering nitroglycerin or other nitrates. Record duration of pain, amount of medication required to relieve it, and accompanying symptoms.
❑ Keep nitroglycerin available for immediate use. Instruct the patient to call immediately whenever he feels chest, arm, or neck pain.
❑ Before cardiac catheterization, explain the procedure to the patient. Make sure he knows why it’s necessary, understands the risks, and realizes that it may indicate a need for surgery.
❑ After catheterization, review the expected course of treatment with the patient and his family. Monitor the catheter site for bleeding. Also, check for distal pulses. To counter the dye’s diuretic effect, make sure the patient drinks plenty of fluids. Assess potassium levels.
❑ If the patient is scheduled for surgery, explain the procedure to him and his family. Give them a tour of the intensive care unit and introduce them to the staff.
❑ After surgery, monitor blood pressure, intake and output, breath sounds, chest tube drainage, and ECG, watching for signs of ischemia and arrhythmias. Also, observe for and treat chest pain and possible dye reactions. Give vigorous chest physiotherapy and guide the patient in removal of secretions through deep-breathing, coughing, and expectoration of mucus.
❑ Before discharge, stress the need to follow the prescribed drug regimen (antihypertensives, nitrates, and antilipemics, for example), exercise program, and diet. Encourage regular, moderate exercise. Refer the patient to a self-help program to stop smoking.
Pictures
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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