Epidemiology

More than 85 million Americans (≈25% of the population) have some form of cardiovascular disease, with about 15.5 million having coronary heart disease. Cardiovascular disease begins early in life, and autopsy studies have shown that one in six American teenagers already has pathologic intimal thickening of the coronary arteries. The incidence and prevalence of ischemic heart disease increase with age, its symptoms and complications typically manifest later in midlife, and more than half of those affected are older than 59 years of age.

The annual mortality rate for cardiovascular diseases as a group has been declining since 1970. Despite this decline, cardiovascular diseases continue to be the leading cause of death in the United States, accounting for about 31% of all deaths. Coronary heart disease is the leading cause of death in the United States after age 65 years, and it is responsible for 735,000 new or recurrent heart attacks annually, of which more than 40% are fatal. Of the 735,000 Americans who have a heart attack each year, it is a first heart attack for 525,000 and a recurrent heart attack in the remaining 210,000. Men are at higher risk than women for having a heart attack or fatal coronary heart disease, and black men are at highest risk.

The average dental practice with 2000 patients is expected to include at least 100 patients with ischemic heart disease.

Etiology

The cause of coronary atherosclerosis is related to a variety of risk factors. These risk factors include male gender, older age, a family history of cardiovascular disease, hyperlipidemia, hypertension, cigarette smoking, physical inactivity, obesity, insulin resistance and diabetes mellitus, mental stress, and depression. In addition to these conventional risk factors, markers of inflammation such as C-reactive protein (CRP, an inflammatory marker), homocysteine, fibrinogen (procoagulant), plasminogen activator inhibitor (thrombolytic), and lipoprotein (a) are associated with atherosclerosis.

Before the age of 75 years, the risk of coronary atherosclerosis is greater for men than for women. MI and sudden death are rare in premenopausal women; however, after menopause, a rapid reduction occurs in this gender difference. The fact that men are more prone to the clinical manifestations of coronary atherosclerosis is accentuated in nonwhite populations (e.g., African Americans, Native Americans, Hispanics).

Genetics also play a role. Studies have confirmed that a paternal history, sibling history, or history in both parents of coronary atherosclerotic heart disease increases the risk for development of the disease at a younger age than that typical for those without such a history.

Elevation in serum lipid levels is a major risk factor for atherosclerosis. Increased levels of low-density lipoprotein (LDL) cholesterol pose the greatest risk for coronary atherosclerosis, whereas increased levels of high-density lipoprotein (HDL) cholesterol have been shown to reduce the risk. Persons with elevated triglyceride or β-lipoprotein levels have an increased risk for the disease. Obesity and a diet rich in total calories, saturated fats, cholesterol, sugars, and salts also enhance the risk of developing cardiovascular disease.

Increased blood pressure is one of the most significant risk factors for coronary atherosclerotic heart disease. In general, systolic blood pressure (SBP) is more strongly related to the incidence of cardiovascular disease than is diastolic blood pressure (DBP), especially in older adults. SBP rises throughout life, and DBP tends to level off or decrease after the age of 50 years. Most epidemiologic studies, however, recognize the importance of both DBP and SBP in the assessment of cardiovascular risk. It has been shown that morbidity and mortality increase linearly with blood pressures greater than 115/75 mm Hg. In the Framingham Study, even prehypertension (defined as SBP of 130 to 139 mm Hg and DBP of 85 to 89 mm Hg) was associated with a risk of cardiovascular disease double that for lower pressures.

Cigarette smoking is the single most important modifiable risk factor for coronary heart disease (see Chapter 8 ). Multiple prospective studies have clearly documented that, compared with nonsmokers, persons who smoke 20 or more cigarettes daily have a two- to fourfold increase in coronary heart disease. This increased risk appears to be proportionate to the number of cigarettes smoked per day, and quitting has well-documented benefits. In a study of 113,752 women and 88,496 men, smokers who quit by age 34 years gained 10 years of life, those quitting between 35 and 44 years gained 9 years, and those 45 to 54 years gained 6 years of life, on average, compared with those who continued to smoke. Pipe and cigar smoking apparently convey minor risk for development of heart disease.

Patients with diabetes mellitus have a greater incidence of coronary atherosclerotic heart disease and more extensive lesions. They develop the condition at an earlier age than that typical for persons who do not have diabetes. Almost 81 million Americans have some degree of abnormal glucose tolerance (prediabetes)—a condition along with obesity that markedly increases the risk for type 2 diabetes and premature atherosclerosis. Patients with diabetes have two- to eightfold higher rates of future cardiovascular events compared with age-matched and ethnically matched nondiabetic patients. Three fourths of all deaths among patients with diabetes result from coronary heart disease. Compared with unaffected persons, patients with diabetes have a greater degree of atherosclerosis in the major arteries and in the microvascular circulation. Although hyperglycemia is associated with microvascular disease, insulin resistance itself promotes atherosclerosis even before it produces frank diabetes, and available data corroborate the role of insulin resistance as an independent risk factor for atherothrombosis. Metabolic syndrome is the term used to describe a cluster of pathologic findings consisting of obesity, insulin resistance, low HDL cholesterol, elevated triglycerides, and hypertension, all of which are risk factors for atherosclerosis. The recognized importance of this clinical syndrome as a setting for the development of atherosclerosis reflects a synergistic effect of the multiple risk factors. The prevalence of metabolic syndrome among adults in the United States is estimated to be about 34%, which increases with age.

Numerous studies have reported an association between periodontal disease and cardiovascular disease, raising the question of whether periodontal disease is a risk factor for cardiovascular disease. Although the mechanism to explain this relationship is unclear, evidence is accumulating that the chronic inflammatory burden of periodontal disease may lead to impaired functioning of the vascular endothelium. At present, despite studies showing that tooth scaling is associated with decreased risk of cardiovascular disease outcomes and improved endothelial function, a direct relationship (i.e., causation) between periodontal disease and cardiovascular disease has not been established. Additional studies are required to further elucidate this relationship.

No single risk factor is responsible for the development of coronary atherosclerosis, but many factors act synergistically. Evidence suggests that modification of risk factors that can be controlled, such as cigarette smoking, hypertension, obesity, physical activity, hyperlipidemia, and diabetes, can reduce or modify the clinical effects of the disease.

Etiology

The cause of coronary atherosclerosis is related to a variety of risk factors. These risk factors include male gender, older age, a family history of cardiovascular disease, hyperlipidemia, hypertension, cigarette smoking, physical inactivity, obesity, insulin resistance and diabetes mellitus, mental stress, and depression. In addition to these conventional risk factors, markers of inflammation such as C-reactive protein (CRP, an inflammatory marker), homocysteine, fibrinogen (procoagulant), plasminogen activator inhibitor (thrombolytic), and lipoprotein (a) are associated with atherosclerosis.

Before the age of 75 years, the risk of coronary atherosclerosis is greater for men than for women. MI and sudden death are rare in premenopausal women; however, after menopause, a rapid reduction occurs in this gender difference. The fact that men are more prone to the clinical manifestations of coronary atherosclerosis is accentuated in nonwhite populations (e.g., African Americans, Native Americans, Hispanics).

Genetics also play a role. Studies have confirmed that a paternal history, sibling history, or history in both parents of coronary atherosclerotic heart disease increases the risk for development of the disease at a younger age than that typical for those without such a history.

Elevation in serum lipid levels is a major risk factor for atherosclerosis. Increased levels of low-density lipoprotein (LDL) cholesterol pose the greatest risk for coronary atherosclerosis, whereas increased levels of high-density lipoprotein (HDL) cholesterol have been shown to reduce the risk. Persons with elevated triglyceride or β-lipoprotein levels have an increased risk for the disease. Obesity and a diet rich in total calories, saturated fats, cholesterol, sugars, and salts also enhance the risk of developing cardiovascular disease.

Increased blood pressure is one of the most significant risk factors for coronary atherosclerotic heart disease. In general, systolic blood pressure (SBP) is more strongly related to the incidence of cardiovascular disease than is diastolic blood pressure (DBP), especially in older adults. SBP rises throughout life, and DBP tends to level off or decrease after the age of 50 years. Most epidemiologic studies, however, recognize the importance of both DBP and SBP in the assessment of cardiovascular risk. It has been shown that morbidity and mortality increase linearly with blood pressures greater than 115/75 mm Hg. In the Framingham Study, even prehypertension (defined as SBP of 130 to 139 mm Hg and DBP of 85 to 89 mm Hg) was associated with a risk of cardiovascular disease double that for lower pressures.

Cigarette smoking is the single most important modifiable risk factor for coronary heart disease (see Chapter 8 ). Multiple prospective studies have clearly documented that, compared with nonsmokers, persons who smoke 20 or more cigarettes daily have a two- to fourfold increase in coronary heart disease. This increased risk appears to be proportionate to the number of cigarettes smoked per day, and quitting has well-documented benefits. In a study of 113,752 women and 88,496 men, smokers who quit by age 34 years gained 10 years of life, those quitting between 35 and 44 years gained 9 years, and those 45 to 54 years gained 6 years of life, on average, compared with those who continued to smoke. Pipe and cigar smoking apparently convey minor risk for development of heart disease.

Patients with diabetes mellitus have a greater incidence of coronary atherosclerotic heart disease and more extensive lesions. They develop the condition at an earlier age than that typical for persons who do not have diabetes. Almost 81 million Americans have some degree of abnormal glucose tolerance (prediabetes)—a condition along with obesity that markedly increases the risk for type 2 diabetes and premature atherosclerosis. Patients with diabetes have two- to eightfold higher rates of future cardiovascular events compared with age-matched and ethnically matched nondiabetic patients. Three fourths of all deaths among patients with diabetes result from coronary heart disease. Compared with unaffected persons, patients with diabetes have a greater degree of atherosclerosis in the major arteries and in the microvascular circulation. Although hyperglycemia is associated with microvascular disease, insulin resistance itself promotes atherosclerosis even before it produces frank diabetes, and available data corroborate the role of insulin resistance as an independent risk factor for atherothrombosis. Metabolic syndrome is the term used to describe a cluster of pathologic findings consisting of obesity, insulin resistance, low HDL cholesterol, elevated triglycerides, and hypertension, all of which are risk factors for atherosclerosis. The recognized importance of this clinical syndrome as a setting for the development of atherosclerosis reflects a synergistic effect of the multiple risk factors. The prevalence of metabolic syndrome among adults in the United States is estimated to be about 34%, which increases with age.

Numerous studies have reported an association between periodontal disease and cardiovascular disease, raising the question of whether periodontal disease is a risk factor for cardiovascular disease. Although the mechanism to explain this relationship is unclear, evidence is accumulating that the chronic inflammatory burden of periodontal disease may lead to impaired functioning of the vascular endothelium. At present, despite studies showing that tooth scaling is associated with decreased risk of cardiovascular disease outcomes and improved endothelial function, a direct relationship (i.e., causation) between periodontal disease and cardiovascular disease has not been established. Additional studies are required to further elucidate this relationship.

No single risk factor is responsible for the development of coronary atherosclerosis, but many factors act synergistically. Evidence suggests that modification of risk factors that can be controlled, such as cigarette smoking, hypertension, obesity, physical activity, hyperlipidemia, and diabetes, can reduce or modify the clinical effects of the disease.

Pathophysiology and Complications

Atherosclerosis is an inflammatory disorder of the cellular lining of the arteries, with inflammation playing a fundamental role at all stages of the disease. The formation of atheromatous plaques involves several steps. The first step involves an inflammatory repair response of the injured arterial intima. Chronic minimal injury to the arterial endothelium is common and results from both physiologic and pathologic processes. Physiologic injury often occurs as the result of disturbed blood flow at bending points or bifurcations (branch points) in the artery. Endothelial injury or dysfunction also may be caused by hypercholesterolemia, oxidative stress, glycation end products in diabetes, irritants in tobacco smoke, circulating vasoactive amines, immune complexes, and infection.

Atheroma formation is initiated by adherence of monocytes to an area of injured or altered endothelium. Usually, monocytes do not adhere to intact endothelium; however, triggers of atherosclerosis such as a high saturated fat diet, smoking, hypertension, hyperglycemia, obesity, and insulin resistance initiate the expression of adhesion molecules by the endothelial cells, thus promoting attachment. The attached monocytes then migrate into the intima of the vessel and become macrophages. Lipids derived from plasma LDLs also enter through the injured or dysfunctional endothelium, forming extracellular deposits or small pools. Macrophages then engulf lipid molecules to become foam cells, which are characteristic features of the fatty streak. Foam cells are joined by T lymphocytes, and together they produce a variety of inflammatory cytokines, which promote the migration and proliferation of smooth muscle cells and collagen to surround the foam cells, thereby forming a fibrous covering or cap. The arrival of the smooth muscle cells triggers a coalescence of the foam cells and small extracellular pools of lipid into a larger pool or lipid core. The T lymphocytes secrete cytokines that inhibit the further production of collagen, possibly leading to weakening and thinning of the fibrous cap and rendering it susceptible to rupture. With rupture or disruption of the plaque surface, tissue factor comes into contact with blood, and a thrombus is subsequently formed ( Fig. 4.1 ).

Evolution of arterial wall changes in the response to injury hypothesis. ECM, Extracellular matrix.

(From Schoen FJ: Blood vessels. In Kumar V, et al, editors: Robbins and Cotran pathologic basis of disease, ed 8, Philadelphia, 2010, Saunders.)

Plaques may grow and proliferate outwardly, away from the lumen of the artery, or inwardly, into the lumen. With inward proliferation, the size of the lumen is progressively reduced (stenosis). Thus, blood flow may be chronically decreased, and when the demand for oxygen exceeds supply, the outcome is ischemic pain. Ischemic symptoms may be produced when occlusion reaches 75% of the cross-sectional area of the artery ( Fig. 4.2 ). Of interest, however, in most instances of an acute coronary event, the vessels typically are less than 50% occluded by plaque growth.

Photomicrograph of a cross-section of a coronary artery with severe stenosis and narrowing.

(Courtesy of W. O’Conner, MD, Lexington, KY.)

Most acute coronary syndromes (ACSs, e.g., unstable angina [UA], MI) are caused by physical disruption or fracture of the vulnerable atheromatous plaque, most commonly of a plaque that did not cause extreme stenosis. In plaque rupture, the fibrous cap tears, allowing arterial blood to enter the lipid core, where contact with tissue factor and collagen induces platelet adhesion and aggregation and activation of the coagulation cascade. This series of events results in clot or thrombus formation and sudden expansion of the lesion. Blood flow through the affected artery may become compromised or completely blocked.

Atherosclerosis usually is a focal disease that commonly occurs in certain areas or regions of arteries while sparing others. Those affected include the brain, heart, aorta, and peripheral arteries ( Fig. 4.3 ). For example, the proximal left anterior descending coronary artery is a common area of atherosclerotic involvement; however, the internal mammary artery is rarely affected. The lumen of an affected artery may be circumferentially narrowed evenly or eccentrically, depending on the location and extent of the plaque.

The segment of aorta on the left demonstrates advanced atheromatous plaques, and the specimen on the right side is unaffected.

(Courtesy of W. O’Conner, MD, Lexington, KY.)

The outcome of the atherosclerotic process is extremely variable. Some lesions never progress past the fatty streak phase; however, in most Western societies, the presence of frank plaques is the norm. Even so, most atheromatous plaques are not associated with clinical signs and symptoms and may never produce clinical manifestations. Several factors may be responsible, including arterial remodeling, in which the plaque grows outward away from the lumen with a compensatory increase in the diameter of the vessel. In addition, collateral circulation may develop to compensate for diminished blood flow. For lesions that do produce symptoms, flow-limiting intact plaques typically precipitate symptoms such as chest pain (angina) when oxygen need exceeds demand, as during exercise. However, plaque rupture produces an acute or unstable clinical picture with signs and symptoms such as angina at rest, MI, or sudden death. Not all plaques have the same propensity to rupture, and risk depends on the physical and biochemical characteristics of the plaque.

Intraarterial complications of coronary atherosclerosis consist of luminal narrowing, intramural hemorrhage, thrombosis, embolism, and aneurysm. Intramural hemorrhage, which results from weakening of the intimal tissues, may lead to thrombosis. The localized blood also may serve as an irritant to precipitate a reflex reaction, resulting in spasm of the collateral vessels. Once formed, a thrombus may become encapsulated and may undergo fibrous organization and recanalization.

If the degree of ischemia that results from coronary atherosclerosis is significant and the oxygen deficit is prolonged, the area of myocardium supplied by that vessel may undergo necrosis. Reduced blood flow may result from thrombosis of the affected artery, a hypotensive episode, an increased demand for blood, or emotional stress. The infarct, or area of necrosis, may be subendocardial or transmural, the latter involving the entire thickness of the myocardium ( Fig. 4.4 ). The extent of involvement is reflected in the electrocardiogram (ECG), in which the ST segment is not elevated in cases with only partial obstruction to blood flow and limited myocardial necrosis, but elevation of the ST segment is seen in cases with more complete obstruction, profound ischemia, and a larger area of necrosis. Complications of MI include weakened heart muscle, resulting in acute congestive heart failure, postinfarction angina, infarct extension, cardiogenic shock, pericarditis, and arrhythmias. Causes of death in patients who have had an acute MI include ventricular fibrillation, cardiac standstill, congestive heart failure, embolism, and rupture of the heart wall or septum.

Progression of myocardial necrosis after coronary artery occlusion.

(From Schoen FJ, Mitchell, RN: The heart. In Kumar V, et al, editors: Robbins and Cotran pathologic basis of disease, ed 8, Philadelphia, 2010, Saunders.)

Clinical Presentation

Laboratory and Diagnostic Findings

Blood tests are used in the evaluation of patients with symptoms of angina pectoris to screen for abnormalities that may contribute to or worsen coronary heart disease. These tests include a complete blood count to rule out anemia, thyroid function tests to exclude hyperthyroidism, renal function tests to exclude renal insufficiency, lipid screening for hypercholesterolemia, glucose screening for diabetes, homocysteine level determination, and CRP assay. Other diagnostic modalities that are specific for coronary heart disease include resting ECG, chest x-ray studies, exercise stress testing, ambulatory (Holter) electrocardiography, stress thallium-201 perfusion scintigraphy, exercise echocardiography, ambulatory ventricular function monitoring, and cardiac catheterization and coronary angiography.

To establish the diagnosis of acute MI and to determine the extent of the infarction, serum enzyme determinations are necessary along with the physical examination and diagnostic testing (ECG and echocardiogram) findings. Cardiac serum biomarkers of acute MI include troponin I, troponin T, creatine kinase isoenzyme (CK-MB), and myoglobin. The troponins and CK-MB are enzymes released only when cell death (infarction) or injury occurs. Troponins are proteins derived from the breakdown of myocardial sarcomeres. Troponin assays are the most sensitive and specific in differentiating cardiac muscle damage from trauma to skeletal muscle or other organs and are virtually absent in the plasma of normal persons and are found only after cardiac injury. Troponins are first detectable 2 to 4 hours after the onset of an acute MI; they are maximally sensitive at 8 to 12 hours, peak at 10 to 24 hours, and persist for 5 to 14 days.

CK-MB is another enzymatic marker of cardiac cell injury with characteristics similar to those of the troponins; however, CK-MB is also found after injury to skeletal muscle and other tissues. Despite this relative lack of specificity, elevated levels of CK-MB usually are considered to be the result of an MI. CK-MB is detectable within 3 to 4 hours after infarction; it reaches peak values at 12 to 24 hours and persists for 2 to 4 days. In many cardiac centers, troponin assay has replaced CK-MB determination as the diagnostic test of choice for MI because of its sensitivity and specificity and as a result of cost issues. In any case, definitive diagnosis of MI requires serial testing (every 6 to 8 hours) over several days, rather than reliance on single test results. Testing for levels of B-natriuretic peptide, which is produced largely by the left ventricle, also aids in determining the extent of ventricular damage and the prognosis of heart failure.

Medical Management