Porth's Essentials of Pathophysiology, 4e

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Disorders of Cardiac Function

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vegetations and destruction of underlying cardiac tis- sues. 6 Although other microorganisms, such as fungi, can cause endocarditis, the vast majority of cases are caused by bacteria. Infective endocarditis is commonly classified into acute or subacute–chronic forms, depending on the onset, etiology, and severity of the disease. 27 The onset of acute IE is usually rapid and occurs in patients with pre- viously normal cardiac valves who are healthy and per- haps have a history of intravenous drug abuse, whereas subacute-chronic IE evolves over months, usually in per- sons who have underlying heart valve abnormalities. 28 Etiology and Pathogenesis. Two factors contribute to the development of IE: a portal of entry by which the organism gains access to the circulatory system and a damaged endocardial surface. The portal of entry into the bloodstream may be an obvious infection, a dental or surgical procedure that causes transient bacteremia, intravenous injection of a contaminated substance directly into the blood, or an occult source such as the oral cavity, gut, or a subcutaneous injury. 6 Although infective endocarditis can develop in individuals with normal heart valves, persons with structural abnor- malities of the values, such as mitral valve prolapse or congenital heart disease, are at significantly higher risk. Host factors such as neutropenia, immunodefi- ciency, malignancy, therapeutic immunosuppression, diabetes, and alcohol or intravenous drug use are pre- disposing factors. 6 Infections may also be associated with cardiovascular prostheses and devices, such as pacemakers, defibrillators, and left ventricular assist devices. Staphylococcal infections are the leading cause of IE, with streptococci and enterococci as the other two most common infectious agents. Other bacterial agents include the so-called HACEK group ( Haemophilus species, Actinobacillus actinomycetemcomitans, Cardio­ bacterium hominis, Eikenella corrodens, and Kingella kingae ), all commensals in the oral cavity. 6,27 Less com- monly, gram-negative bacteria and fungi are involved. The causative agents differ somewhat in high-risk groups. For example, Staphylococcus aureus is the major offender in intravenous drug users, whereas prosthetic heart valve infective endocarditis tends to be caused by coagulase-negative staphylococci (e.g., Staphylococcus epidermidis). 6 In both acute and subacute–chronic forms of IE, fria- ble, bulky, and potentially destructive vegetative lesions form on the heart valves (Fig. 19-12). The aortic and mitral valves are the most common sites of infection, although the right heart may also be involved, par- ticularly in intravenous drug abusers. The vegetative lesions consist of a collection of infectious organisms and cellular debris enmeshed in the fibrin strands of clotted blood. The lesions may be singular or multiple, may grow as large as several centimeters, and usually are found loosely attached to the free edges of the valve surface. 6 The infectious loci continuously release bac- teria into the bloodstream and are a source of persis- tent bacteremia, sometimes contributing to pericarditis.

Endocardial and Valvular Disorders The endocardium, which lines the heart and covers the heart valves, is continuous with the tunica intima of the blood vessels entering and leaving the heart. It is com- posed of an inner endothelium, consisting of endothe- lial cells and subendothelial connective tissue; a middle layer of connective tissue and smooth muscle cells; and a deeper layer of loose connective tissue, called the sub- endocardial layer, which is continuous with the con- nective tissue of the myocardium. The subendocardium contains small blood vessels, nerves, and Purkinje fibers from the cardiac conduction system. Disorders of the Endocardium Among the disorders that affect the endocardium are infective endocarditis, rheumatic fever, and valvular heart disorders. Infective Endocarditis Infective endocarditis (IE) is a serious and potentially life-threatening infection of the inner surface of the heart including the cardiac valves. Although rare in most con- temporary population surveys (annual incidence 3 to 7 per 100,000 persons), 24,25 IE is associated with sig- nificant mortality. 26 Infective endocarditis is character- ized by colonization or invasion of the valves and the mural endocardium by a microbial agent, leading to Serum biomarkers, which are useful tools for predicting the extent and progress of MI, represent intracellular contents of necrotic cells that have diffused into the blood. ■■ Unstable angina/NSTEMI is an accelerated form of angina that is caused by subtotal or intermittent coronary occlusion. ■■ Acute STEMI, also known as heart attack, refers to the ischemic death of myocardial tissue associated with obstructed blood flow in the coronary arteries, potentially fatal arrhythmias, and other adverse cardiac events. ■■ The chronic ischemic heart diseases include chronic stable angina, variant (vasospastic) angina, and silent myocardial ischemia. Chronic stable angina is associated with a fixed atherosclerotic obstruction and pain that is precipitated by increased work demands on the heart and relieved by rest. Variant angina results from spasms of the coronary arteries or other dysfunctions. Silent myocardial ischemia occurs without symptoms.