Cardiovascular System



Cardiovascular System


Cardiovascular diseases are common and important causes of morbidity and mortality worldwide, particularly in industrialized countries. In spite of significant advances in primary prevention and therapy, cardiovascular disease, primarily the complications of atherosclerosis and hypertension (HTN), is still the leading cause of mortality in the United States.



Congenital Heart Disease


Congenital malformations of the heart and major blood vessels are produced during embryologic development of the cardiovascular system in the early fetus. They usually arise from randomly occurring defects in embryogenesis, but they sometimes develop as a result of intrauterine infections, such as rubella, or as components of genetic abnormalities such as trisomy 21 (Down syndrome) or cytogenetic disorders of sex chromosomes (Turner syndrome). The 3 major pathophysiologic categories of congenital heart disease are those causing a left-to-right shunt of blood across the circulation (e.g., ventricular septal defect [VSD], atrial septal defect [ASD], patent ductus arteriosus [PDA]), a right-to-left shunt (e.g., tetralogy of Fallot), and obstruction without a shunt (e.g., coarctation of the aorta).



Atherosclerotic Diseases


Atherosclerosis develops as an inflammatory response of the vessel wall to chronic, multifactorial injury produced by hyperlipidemia, HTN, products of cigarette smoke, diabetes mellitus, and other predisposing factors. The pathogenesis of intimal lesions involves endothelial dysfunction, influx of macrophages and T lymphocytes, vascular smooth muscle proliferation, accumulation of oxidized low-density lipoprotein, and deposition of collagen and elastic tissue. The resultant fibrous (atheromatous) plaques are raised intimal lesions with a fibrous cap and a core containing variable amounts of necrotic, lipid-rich debris, fibrous tissue, calcification, and vascularization from ingrowth of vessels from the vasa vasorum. The plaques involve the aorta and its major distributing branches, including the coronary, cerebral, and iliofemoral arteries, with a propensity for localization adjacent to branch points.


Progression of disease leads to luminal narrowing and the development of complicated lesions as a result of surface ulceration, intraplaque hemorrhage, and superimposed thrombosis. The frequently abrupt transition to a clinically overt state can present as coronary (ischemic) heart disease manifest as angina pectoris, myocardial infarction, or sudden cardiac death; cerebrovascular disease with transient ischemic attacks or cerebral infarcts (stroke); rupture-prone abdominal aortic aneurysm; or iliofemoral atherosclerosis, predisposing to gangrene of the lower extremities.



Coronary (Ischemic) Heart Disease


The underlying pathologic substrate for clinically apparent myocardial ischemia is coronary atherosclerosis in at least 90% of cases. Narrowing of one or more of the coronary arteries to less than 25% of the luminal area can be slowly progressive, giving rise to recurrent episodes of angina pectoris. Acute changes in plaques associated with platelet aggregation and vasospasm can precipitate myocardial ischemia, ventricular fibrillation, and sudden cardiac death. Sudden luminal occlusion due to thrombosis of an ulcerated plaque can give rise to an acute myocardial infarct, usually of the left ventricle (LV), in the distribution of the occluded coronary artery. Myocardial necrosis begins in the ischemic subendocardial myocardium and progresses in a wave-front fashion over a period of 3 or 4 hours to involve the subepicardial myocardium. Myocardial infarcts undergo organization into granulation tissue over approximately 2 to 3 weeks and complete healing as fibrous scars in 2 to 3 months. Larger healed infarcts can develop into ventricular aneurysms. During the first week to 10 days when healing is minimal, myocardial infarcts are susceptible to developing external rupture, giving rise to cardiac tamponade; rupture across the interventricular septum, producing a VSD; or rupture of a papillary muscle, giving rise to mitral regurgitation. However, such life-threatening complications occur in only approximately 5% of cases. A massive acute myocardial infarct involving 40% or more of the LV can give rise to fatal cardiogenic shock. As myocardium is lost from one or more acute myocardial infarcts, congestive heart failure (CHF) may ensue.



Hypertensive Disease


Hypertension results from excessive arteriolar constriction and peripheral vascular resistance in relation to the blood volume and, when sustained, leads to hypertensive cardiovascular disease as well as predisposing to atherosclerotic disease. Most patients have primary or essential HTN due to a complex of genetic and environmental influences. Approximately 10% of patients have secondary HTN due to renal, endocrine, or other disease processes. Slowly progressive (“benign”) hypertensive disease presents as mild to moderate blood pressure increase and leads to concentric hypertrophy of the LV and progressive damage to the microvasculature in the form of hyaline arteriolosclerosis. A leading complication is the development of hemorrhagic stroke. Rapidly progressive (“malignant”) HTN is characterized by marked increase of blood pressure; prominent microvascular damage in the form of hyperplastic arteriolosclerosis and fibrinoid necrosis; and rapid progression to renal failure, cardiac failure, cerebral edema, and hemorrhagic stroke.




Aneurysms


An aneurysm is an external bulging of a vascular structure. Severe atherosclerosis is the cause of the relatively common abdominal aortic aneurysm as well as aneurysms of the descending thoracic aorta and iliofemoral arteries. Medial degenerative disease, also known as cystic medial necrosis, gives rise to dissecting hematoma (aneurysm) with origin in the ascending thoracic aorta (type A) or the transverse or descending thoracic aorta (type B), as well as nondissecting aneurysms of the ascending thoracic aorta. Medial degeneration develops as a result of a genetic defect, as in Marfan syndrome and Ehlers-Danlos syndrome, or as a result of hemodynamic stress accelerated by HTN. Both dissecting and nondissecting aneurysms are prone to external rupture leading to exsanguination. Infections of a major artery can give rise to mycotic (mushroomlike) aneurysms. Cardiovascular syphilis is a form of tertiary syphilis with ascending aortic aneurysm.



Valvular Heart Disease


Acute rheumatic fever (RF) is an acute multisystem disorder involving the skin, joints, brain, and heart that is triggered by an autoimmune reaction after streptococcal pharyngitis. Most of the inflammation resolves without consequence except for the distortion and subsequent wear and tear on the cardiac valves, particularly the mitral and aortic valves, giving rise months to years later to chronic rheumatic heart disease (RHD).


Infective endocarditis (IE) of the valvular or mural endocardium results from infection with microorganisms (bacteria, fungi, or rickettsia) that gain access to the bloodstream through the gastrointestinal tract, skin, surgical instrumentation, or other means. Key clinical features of IE are fever and cardiac murmur, and positive blood cultures are confirmatory of the diagnosis. Acute IE is produced by highly virulent organisms, such as Staphylococcus aureus, involving a previously normal valve, whereas subacute IE is characterized by a more indolent clinical course with infection produced by a less virulent organism, such as Streptococcus viridans, often involving a previously diseased valve. In both acute and subacute IE, the infected vegetations produce destruction and incompetence of valves, CHF, and emboli to other organs.


A large variety of entities can produce valvular dysfunction, but the following figure prominently into the differential diagnosis. Mitral valve stenosis is virtually always due to RHD. Mitral valve incompetence (regurgitation) results from RHD, IE, or mitral valve prolapse due to myxomatous degeneration. Aortic valvular stenosis results from chronic RHD involving a tricuspid valve, age-related (senile) sclerosis and calcification of a tricuspid valve, or fibrosis and calcification of a congenitally bicuspid valve. Aortic valvular incompetence can develop from valvular lesions, such as IE, or aortic aneurysms producing distortion of the aortic annulus. Pulmonary and tricuspid valvular disease is produced by congenital defects and, less commonly, acquired causes.



Myocardial and Pericardial Diseases


Myocarditis and pericarditis may be induced by infection with microorganisms (viruses, rickettsiae, bacteria, fungi, and protozoa) or noninfectious, immune-mediated processes. Bacterial infections produce neutrophil-rich suppurative inflammation. Viral infections are associated with lymphohistiocytic infiltrates. Granulomatous inflammation may represent sarcoidosis or tuberculous infection. Myocarditis can produce heart failure or sudden death from arrhythmia. Pericardial involvement is often manifest as fibrinous pericarditis with a pericardial effusion.


Cardiomyopathies are diseases of the heart muscle. Etiologically, primary cardiomyopathies are intrinsic diseases of the heart muscle, and secondary cardiomyopathies develop as a component of a defined disease process usually originating extrinsic to the myocardium. Pathophysiologically, cardiomyopathies are classified as dilated (congestive), hypertrophic, or restrictive. Dilated (congestive) cardiomyopathy is characterized by progressive eccentric hypertrophy, cardiomegaly, and CHF. The condition may have a genetic basis or occur because of an acquired condition, such as viral myocarditis or long-term alcoholism. Hypertrophic cardiomyopathy is due to mutations in contractile protein genes and includes the classic idiopathic hypertrophic subaortic stenosis (IHSS) as well as other variants. Restrictive cardiomyopathy typically has a relatively normal-sized heart coupled with evidence of cardiac failure due to infiltration of the myocardium by amyloid material or severe fibrosis.


Primary tumors of the heart occur at least 10 times less frequently than metastatic tumors of the heart, and most are benign. The most common primary tumor of the heart in adults is the myxoma, which usually occurs in the left atrium and presents with symptoms mimicking mitral stenosis. The most common primary tumor of the heart in infants and children is the rhabdomyoma, which can produce a mass effect in the myocardium as well as ventricular cavity obstruction.



TABLE 2-1


CONGENITAL MALFORMATIONS OF THE HEART AND MAJOR VESSELS


















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Figure 2-1 Ventricular Septal Defect: Membranous Type
Congenital heart disease results from malformations of the heart and major vessels that develop during embryogenesis and are present at birth. A general classification of congenital malformations of the heart and major vessels is presented in Table 2-1. The ventricular septal defect (VSD) is the most common malformation presenting in infancy and childhood. Most VSDs result from defective closure of the membranous interventricular septum, although some are located in the muscular interventricular septum. As a result of the left-to-right shunt, patients present with systolic murmur, CHF, and progressive pulmonary HTN. If not surgically corrected, pulmonary arterial pressure reaches the systemic level, and the shunt becomes predominantly right to left, leading to late onset of cyanosis (Eisenmenger syndrome).









Jun 28, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Cardiovascular System
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