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).

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Figure 2-2 Patent Ductus Arteriosus
The ductus arteriosus is an arterial connection between the origin of the left pulmonary artery and the aorta that normally closes within hours after birth. Failure of this connection to close results in PDA. PDA is another type of high-pressure left-to-right shunt producing symptomatic disease in infants and children. Other anomalies of the aortic arch system, such as an aberrant right subclavian artery, give rise to anatomic variations of the normal pattern of origin of the great arteries. Some of these anomalies produce vascular rings that can compress the trachea and esophagus.

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Figure 2-3 Atrial Septal Defects
Ostium secundum defect, the most common atrial septal defect (ASD), is located in the middle portion of the interatrial septum in the region of the foramen ovale. This ASD occurs as a result of defective formation of septum primum and septum secundum tissue, which leads to failure of the ostium secundum to close. Sinus venosus defect, located high in the interatrial septum, is the result of defective incorporation of the sinus venosus into the RV. This ASD is associated with anomalous drainage of the right upper lobe pulmonary veins into the right atrium. Failure of formation of the septum primum and septum secundum results in a common atrium. Because left-to-right shunting occurs at low pressure, patients with ASDs tend to have pulmonary HTN and become symptomatic later in childhood or as adults in contrast to the usual course of patients with VSDs and PDAs.

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Figure 2-4 Atrioventricular Septal Defects
Atrioventricular septal defects (AVSDs) result from significantly defective formation of endocardial cushion tissue. The ASD component is low in the interatrial septum because of failure of closure of the ostium primum. The VSD component is in the region of the membranous interventricular septum. The partial endocardial-cushion defect is composed of an ostium primum type of ASD, a defective mitral valve with a cleft in the anterior leaflet, and subtle anomalies in the LV, but it is associated with a closed membranous interventricular septum. The complete endocardial-cushion defect, also called a persistent common atrioventricular canal, consists of a large ostium primum ASD, a membranous VSD, and an abnormal common atrioventricular valve straddling the AVSD.

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Figure 2-5 Tetralogy of Fallot
The tetralogy of Fallot is the most common form of cyanotic congenital heart disease, a state characterized by a right-to-left shunt with cyanosis at the time of presentation (i.e., cyanotic congenital heart disease). Depending on the severity of the defects, the presentation may occur in infancy (blue baby syndrome) but is not usually apparent until at least early childhood. The 4 components of the tetralogy of Fallot are (1) VSD; (2) obstruction of the right ventricular outflow tract, usually as a result of subpulmonic, infundibular stenosis; (3) an aorta that overrides the VSD; and (4) right ventricular hypertrophy. Complete surgical correction of the tetralogy of Fallot includes closure of the VSD and expansion of the right ventricular outflow tract.

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Figure 2-6 Transposition of the Great Vessels
Transposition of the great vessels, or more specifically, congenitally complete transposition of the great vessels, is a condition in which the aorta takes origin anteriorly from the RV and the pulmonic trunk arises posteriorly from the LV. Transposition of the great vessels is compatible with postnatal life only when the anomaly occurs in association with one or more other defects, usually VSD, ASD, or PDA. The lower diagram shows the embryological development of transposition. Normally, two pairs of truncal swellings develop. In transposition, the wrong pair of truncal swellings becomes involved in partitioning the truncus, resulting in the abnormal position of the great vessels.

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Figure 2-7 Tricuspid Atresia
Tricuspid atresia, a severe complex anomaly of the right side of the heart with underdevelopment (hypoplasia) of the RV and a right-to-left shunt through an ASD, a VSD, or a PDA, results in severe cyanotic heart disease in infants. Next to transposition of the great vessels, it is the most common cause of severe cyanosis in the neonatal period, and the degree of cyanosis is usually more marked than in cases of transposition.

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Figure 2-8 Coarctation of the Aorta
Coarctation of the aorta is a common obstructive congenital anomaly. There are 2 major types: (1) an infantile form, with tubular hypoplasia of the aortic arch proximal to a PDA, typically resulting in clinical problems in early childhood; and (2) an adult postductal form, in which there is a discrete ridgelike infolding of the aorta, just opposite the closed ductus arteriosus (the ligamentum arteriosum). The postductal type of coarctation leads to the development of an extensive collateral circulation (top image) to bypass the obstruction. The patient presents with HTN in the upper extremities and normal pressures in the lower extremities. Rib notching (produced by the enlarged collateral arteries) is seen on chest radiograph.

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Figure 2-9 Aortic Atresia and Aortic Valvular Stenosis
Left ventricular outflow tract (LVOT) obstruction can result from aortic stenosis or atresia. In severe congential aortic malformation, LVOT obstruction leads to underdevelopment (hypoplasia) of the LV and ascending aorta. There is a dense, porcelainlike endocardial fibroelastosis of the diminutive LV. The ductus arteriosus is open. This constellation of anomalies constitutes the hypoplastic left heart syndrome, a condition that is fatal in the first several days of postnatal life when the ductus closes, unless high-risk surgery is performed. Less severe congenital aortic stenoses are compatible with longer survival. The congenital bicuspid aortic valve occurs in approximately 1% to 2% of the population and can give rise to aortic stenosis in adulthood because of hemodynamic turbulence that leads to fibrosis and calcification.

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Figure 2-10 Atherosclerosis
Atherosclerosis, the most prevalent and important form of arteriosclerosis, is a disease that typically affects the aorta and its major muscular distributing branches. The lesion of established atherosclerosis is the atherosclerotic (fibrous or atheromatous) plaque (gross photo, upper right). The fatty streak is the most obvious precursor lesion (gross photo, upper left). The photomicrographs show the features of atherosclerotic plaques, including fibrous capsule and lipid-rich core containing foam cells and cholesterol crystals.

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

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