Porth's Essentials of Pathophysiology, 4e

458

Circulatory Function

U N I T 5

treatment and consequently having a profound effect on outcome. 29 This may result from the prior admin- istration of antibiotics, because the infection is grow- ing slowly, or because it is challenging to culture in a laboratory (i.e., the organism requires a special culture medium). Transthoracic and transesophageal echocar- diography are the primary techniques for detection of vegetation and cardiac complications resulting from IE and are important tools in the diagnosis and manage- ment of the disease. 27 Treatment of IE focuses on identifying and eliminat- ing the causative microorganism, minimizing the resid- ual cardiac effects, and treating the pathologic effect of emboli. The choice of antimicrobial therapy depends on the organism cultured and whether the infection involves a native or prosthetic valve. The widespread emergence of multidrug-resistant organisms, including S. aureus, poses a serious challenge in the treatment of IE. In addition to antibiotic therapy, surgery may be needed for unresolved infection, severe heart failure, and significant emboli. Prevention of IE through the use of prophylactic antibiotics is controversial. The current recommenda- tions conclude that only a very small number of IE cases might be prevented by antibiotic prophylaxis for den- tal procedures. Therefore, prophylaxis is recommended only for patients with predisposing congenital or val- vular disorders undergoing select dental and surgical procedures. 31,32 Rheumatic Heart Disease Rheumatic fever (RF) is an immune-mediated, multi- system inflammatory disease (involving heart, skin, and connective tissue) that occurs a few weeks after a group A ( β -hemolytic) streptococcal (GAS) pharyngitis (sore throat) in children and young adults. It rarely occurs with streptococcal infections at other sites (e.g., skin). 6 Acute rheumatic heart disease (RHD) is the cardiac manifesta- tion of RF and is associated with inflammation of all three layers of the heart (myocardium, pericardium, and endocardium including the heart valves). Chronic defor- mity and impairment of one or more of the heart valves is the most important consequence of RHD. Although RF and RHD are rare in developed countries, the disor- ders continue to be major health problems in underde- veloped countries, where inadequate health care, poor nutrition, and crowded living conditions still prevail. 33 Data from recent studies that used echocardiography to screen for RHD indicate that the prevalence of RHD is increasing in these regions. As a result, there has been an increased awareness and interest in RF and RHD. 34 Pathogenesis. The pathology of RF does not involve direct bacterial infection of the heart. Rather, the time frame for development of symptoms relative to the onset of pharyngitis and the presence of antibodies to the GAS organismstrongly suggests an immunologic response. 33–35 It is thought that antibodies directed against the M pro- tein of certain strains of streptococci cross-react with glycoprotein antigens in the heart, joints, and other

As the lesions grow, they cause valve destruction and dysfunction such as regurgitation, ring abscesses with heart block, and perforation. The loose organiza- tion of these lesions permits the organisms and frag- ments of the lesions to form emboli and travel in the bloodstream, causing cerebral, systemic, or pulmonary emboli. The fragments may lodge in small blood ves- sels, causing small hemorrhages, abscesses, and infarc- tion of tissue. The bacteremia also can initiate immune responses thought to be responsible for skin manifes- tations, polyarthritis, glomerulonephritis, and other immune disorders. 6,27 Manifestations. Signs and symptoms of IE can include fever and signs of systemic infection, development of a new heart murmur, change in the character of an exist- ing heart murmur, and evidence of embolic distribu- tion of the vegetative lesions. 27 In the acute form, the person is likely to develop a high fever accompanied by chills. In the subacute form, the fever usually is low grade, of gradual onset, and frequently accom- panied by other systemic signs of inflammation, such as anorexia, malaise, and lethargy. Small petechial hemorrhages frequently result when emboli lodge in the small vessels of the skin, nail beds, and mucous membranes. Splinter hemorrhages (i.e., dark red lines) under the nails of the fingers and toes are common. 27 Cough, dyspnea, arthralgia or arthritis, diarrhea, and abdominal or flank pain may occur as the result of systemic emboli. Diagnosis and Treatment. Infective endocarditis con- tinues to pose major challenges in terms of diagnosis and treatment. 27–31 The blood culture remains the most definitive diagnostic procedure and is essential for guid- ing the treatment. However, the indiscriminate use of antibiotics has made identifying the causative organism much more difficult. Negative blood cultures can occur in up to 30% of cases of IE, delaying diagnosis and FIGURE 19-12. Gross pathology of subacute bacterial endocarditis involving the mitral valve. Left ventricle of the heart has been opened to show mitral valve fibrin vegetations due to infection with Haemophilus parainfluenza. Autopsy. (From the Centers for Disease Control and Prevention Public Health Images Library No. 851. Courtesy of Edwin P. Ewing Jr.)