Porth's Essentials of Pathophysiology, 4e

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Disorders of Cardiac Function

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size, it cannot stretch sufficiently to accommodate rapid dilation of the heart or accumulation of pericardial fluid without increasing pericardial and intracardiac pressures. The pericardium is subject to many of the same pathologic processes (e.g., congenital disorders, infec- tions, trauma, and immune mechanisms) that affect other structures of the body. Pericardial disorders fre- quently are associated with other diseases in the heart or surrounding structures (Chart 19-1). The most common disorder of the pericardium is acute pericarditis. Acute Pericarditis Acute pericarditis, defined as signs and symptoms result- ing from pericardial inflammation of less than 2 weeks’ duration, may result from an infection or noninfectious disease. Viral infections (especially infections with cox- sackieviruses and echoviruses) are themost common cause of pericarditis and probably are responsible for many cases of idiopathic or pericarditis of unknown etiology. Other causes of acute pericarditis include bacterial or

SUMMARY CONCEPTS

Disorders of the Pericardium The pericardium is a double-layered fibroserous sac that encircles the heart. It isolates the heart from other thoracic structures, maintains its position in the tho- rax, prevents it from overfilling, and serves as a barrier to infection. The pericardium consists of two layers: a thin inner layer, called the visceral pericardium, adheres to the epicardium; and an outer fibrous layer, called the parietal pericardium, is attached to the great ves- sels that enter and leave the heart (see Chapter 17, Fig. 17-15). The two layers of the pericardium are sep- arated by a thin layer of serous fluid, which prevents frictional forces from developing as the heart contracts and relaxes. Although the fibrous tissue outer layer of the pericardium allows for moderate changes in cardiac ■■ Infective endocarditis involves the invasion of the endocardium by pathogens that produce vegetative lesions on the endocardial surface. The loose organization of these lesions permits the organisms and fragments of the lesions to be disseminated throughout the systemic circulation. Although several organisms can cause the condition, staphylococci have become the leading cause.Treatment of infective endocarditis focuses on identifying and eliminating the causative microorganism, minimizing the residual cardiac effects, and treating the pathologic effect of emboli. ■■ Rheumatic fever, an immune-mediated, multisystem inflammatory disease associated with group A ( β -hemolytic) streptococcal (GAS) pharyngitis, can result in serious and disabling impairment of the heart valves. Primary and secondary prevention strategies focus on appropriate antibiotic therapy. ■■ Dysfunction of the heart valves can result from a number of disorders, including congenital defects, rheumatic heart disease, trauma, ischemic heart disease, degenerative changes, and inflammation. Valvular heart disease causes disturbances of blood flow. A stenotic valvular defect is one that causes a decrease in blood flow through a valve, resulting in impaired emptying and increased work demands on the heart chamber that pushes blood across the diseased valve. A regurgitant valve permits blood flow to continue despite closure of the valve. Valvular heart disorders produce blood flow turbulence and often are detected through heart sound heard during cardiac auscultation.

CHART 19-1  Classification of Disorders of the Pericardium*

Idiopathic (no identifiable cause of disease) ■■ Infectious Viral (echovirus, coxsackievirus, and others) Bacterial (e.g., Staphylococcus, Streptococcus, Lyme disease, tuberculosis) Fungal (Hisplasmosis, candida)

■■ Autoimmune and collagen disorders Rheumatic fever Rheumatoid arthritis Systemic lupus erythematosus

■■ Metabolic disorders Uremia and dialysis Myxedema

■■ Ischemia and tissue injury Myocardial infarction Cardiac surgery Chest trauma (blunt and penetrating)

■■ Physical and drug-induced Radiation therapy Hydralazine, procainamide, and anticoagulants Neoplastic Disease ■■ Secondary (e.g., carcinoma of the lung or breast, lymphoma) Congenital Disorders ■■ Complete or partial absence of the pericardium ■■ Primary (mesothelioma, fibrosarcoma)

■■ Congenital pericardial cysts

*Chronic inflammatory pericarditis can be associated with some agents causing an acute inflammatory response.