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Chapter 30 Coordinating Care for Patients With Cardiac Disorders
CORONARY ARTERY DISEASE Epidemiology
Table 30.1 Risk Factors for the Development of Coronary Artery Disease
Lifestyle
Person Related Disease Related
Coronary artery disease (CAD) affects an estimated 20.1 million people over the age of 20 and occurs when the blood vessels that deliver oxygen-rich blood to the heart muscle become obstructed or dysfunctional. It is also known as coronary heart disease or ischemic heart disease. There are racial and gender differences in prevalence. According to the American Heart Association (AHA), the prevalence of CAD is higher in non-Hispanic White males than in Black males, Hispanic males, and Asian males (8.7%, 6.7%, 6.8%, and 5.0%, respectively). Black females had the highest prevalence rate of 7.2%, followed by His- panic females at 6.4%, White females at 6.0%, and Asian females at 3.2%. The prevalence in American Indian and Native Alaskan populations is estimated to be highest of all groups at 8.6%. Another form of CAD nonobstructive coronary artery disease is becoming better understood and more fre- quently identified in patients. Although obstructive and nonobstructive diseases can occur in both sexes, males tend to have more obstructive disease, and females have nearly double the incidence of nonobstructive disease. Nonob- structive coronary artery disease accounts for 5% to 8% of patients presenting with acute coronary syndromes. Risk factors for coronary artery disease continue to be identified and include those that are lifestyle, genetic, and environment related. Specific risk factors include sex, race, genetics, and age. In general, males have a higher risk of heart disease than females. Risk increases with a family history of CAD and aging. Other risk factors include increased total cholesterol, hypertension, diabetes, obesity, smoking, and physical inactivity. Stress and excessive alcohol consumption can also contribute to CAD risk. New risk factors such as air pollution and the social determinants of health are emerg- ing. Lower socioeconomic status, which includes income, housing, education, and occupation, is associated with higher incidence of myocardial infarction and cardiovascular death. The risk factors for CAD are summarized in Table 30.1. Pathophysiology Traditionally, coronary artery disease is characterized by the obstruction of blood flow within the coronary arter- ies. Atherosclerosis , or plaque within the lumen of the vessels, is the principal cause of obstruction to blood flow. The arterial wall is made up of three layers: the tunica intima, tunica media, and tunica adventitia (Fig. 30.1). The tunica intima is composed of endothelium and base- ment membrane. It has been suggested that atherosclerosis begins with an injury to the endothelium that causes an inflammatory response. That inflammatory response ini- tiates a series of specific cellular and molecular reactions that lead to the accumulation of atherosclerotic plaque. Low-density lipoprotein (LDL) enters the tunica intima layer of the arterial wall and becomes trapped. Inside the
z Tobacco use z High total choles-
z Sex z Race z Aging z Family history
z Hypertension z Diabetes
terol, high LDL level, low HDL levels, and high triglycerides
z Obesity and overweight z Sedentary lifestyle/ physical inactivity z Stress z Excessive alcohol consumption z Lack of sleep
HDL, High-density lipoprotein; LDL, low-density lipoprotein.
tunica intima, the trapped LDL is modified through the process of oxidation. Once modified, the LDL attracts macrophages, which absorb the LDL to become foam cells. Fatty streaks within the tunica intima are an accumu- lation of foam cells. As the process continues, various com- ponents in the blood, such as macrophages, calcium, and cholesterol, adhere to the injured part of the vessel, form- ing plaque. The plaque deposits increase in size over time, causing narrowing of the coronary arteries, which impedes oxygen-rich blood flow to the heart (Fig. 30.2). When the heart muscle does not get enough oxygen and nutrients to meet its demands, myocardial ischemia results. This pathology is known as obstructive coronary artery disease. The next and most dangerous step in the development of atherosclerosis is potential plaque rupture. When that occurs, platelets aggregate on the ruptured plaque sur- face. The coagulation cascade is initiated, and thrombus formation is stimulated. This clotting further decreases or obstructs blood flow altogether, leading to unstable angina, myocardial infarction (MI), or sudden cardiac death. In nonobstructive coronary artery disease, patients have symptoms similar to obstructive coronary artery disease, but they do not have significant plaque that occludes the coronary arteries. Rather, ischemic symptoms are caused by reduced blood flow through the coronary microvascular system due to endothelial dysfunction. In such cases, the microvascular system is not able to dilate in response to the myocardial demand for oxygen or there may be stenosis present. Clinical Manifestations The clinical manifestations of CAD are virtually silent until the artery is approximately 40% blocked by plaque in obstructive disease. Ischemia develops when there is
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