Atlas of pathophysiology, 2 Edition

Part II - Disorders

Cardiovascular disorders

Coronary Artery Disease

Coronary artery disease (CAD) results from the narrowing of the coronary arteries over time because of atherosclerosis. The primary effect of CAD is a diminished supply of oxygen and nutrients to myocardial tissue because of decreased blood flow.

Age Alert

The lifetime risk of CAD after age 40 is 49% for men and 32% for women. As women age, their risk increases.

Causes

·   Atherosclerosis (most common)

·   Dissecting aneurysm

·   Infectious vasculitis

·   Syphilis

·   Congenital abnormalities

Pathophysiology

Fatty, fibrous plaques progressively occlude the coronary arteries, reducing the volume of blood that can flow through them and leading to myocardial ischemia.

As atherosclerosis progresses, luminal narrowing is accompanied by vascular changes that impair the ability of the diseased vessel to dilate. The consequent precarious balance between myocardial oxygen supply and demand threatens the myocardium distal to the lesion. When oxygen demand exceeds what the diseased vessel can supply, the result is localized myocardial ischemia.

Myocardial cells become ischemic within 10 seconds after coronary artery occlusion. Transient ischemia causes reversible changes at the cellular and tissue levels, depressing myocardial function. Within several minutes, oxygen deprivation forces the myocardium to shift from aerobic to anaerobic metabolism, leading to accumulation of lactic acid and reduction of cellular pH. Without intervention, this sequence of events can lead to tissue injury or necrosis.

The combination of hypoxia, reduced energy availability, and acidosis rapidly impairs left ventricular function. As the fibers become unable to shorten normally, the force of contractions and velocity of blood flow in the affected myocardial region become inadequate. Moreover, wall motion in the ischemic area becomes abnormal and each contraction ejects less blood from the heart. Restoring blood flow through the coronary arteries restores aerobic metabolism and contractility. Failure to do so results in myocardial infarction (MI).

Signs and symptoms

·   Angina (pain may be described as burning, squeezing, or tightness that radiates to the left arm, neck, jaw, or shoulder blade)

·   Nausea and vomiting

·   Cool extremities and pallor

·   Diaphoresis caused by sympathetic stimulation

·   Fatigue and dyspnea

·   Xanthelasma (fat deposits on the eyelids)

Age Alert

The older adult with CAD may be asymptomatic because the sympathetic response to ischemia is impaired. In an active older adult, dyspnea and fatigue are two key signals of ischemia.

Diagnostic test results

·   Electrocardiography shows ischemic changes during anginal episode.

·   Stress testing detects ST-segment changes during exercise or pharmacologic stress.

·   Coronary angiography reveals the location and degree of coronary artery stenosis or obstruction, collateral circulation, and the condition of the artery beyond the narrowing.

·   Myocardial perfusion imaging with thallium-201 may be performed during treadmill exercise to detect ischemic areas of the myocardium.

·   Stress echocardiography shows abnormal wall motion in ischemic areas.

·   Electron-beam computed tomography identifies calcium deposits in coronary arteries.

·   Cardiac catheterization reveals blockage in the coronary arteries.

·   Lipid profile shows elevated cholesterol levels.

Clinical Tip

The lipid profile consists of these components:

·   low-density lipoprotein (LDL)—“bad” lipoprotein, carries most of the cholesterol molecules

·   high-density lipoprotein (HDL)—“good” lipoprotein, removes lipids from cells

·   apolipoprotein B—major component of LDL

·   apolipoprotein A-1—major component of HDL

·   lipoprotein a—one of the most atherogenic lipoproteins.

Treatment

·   Drug therapy: angiotensin-converting enzyme inhibitors, thrombolytics, diuretics, glycoprotein IIb/IIIa inhibitors, nitrates, beta-adrenergic or calcium channel blockers; antiplatelet, antilipemic, antihypertensive drugs

·   Coronary artery bypass graft (CABG) surgery

·   “Keyhole” or minimally invasive surgery, an alternative to traditional CABG

·   Angioplasty

·   Atherectomy

·   Stent placement to maintain patency of reopened artery

·   Lifestyle modifications to limit progression of CAD: stopping smoking, exercising regularly, maintaining ideal body weight, and eating a low-fat, low-sodium diet

P.51

CORONARY ARTERIES

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CORONARY ARTERY AND ATHEROSCLEROSIS

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