Porth's Essentials of Pathophysiology, 4e

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Circulatory Function

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DCM who do not undergo cardiac transplantation is poor with the average 5-year survival rate being less than 50%. Removing or avoiding causative agents (if identified); avoiding myocardial depressants, including alcohol; and spacing rest with asymptomatic levels of exercise or activity are also important. Primary Restrictive Cardiomyopathy Restrictive cardiomyopathy is a rare form of heart muscle disease in which ventricular filling is restricted because of excessive rigidity (but not necessarily thick- ening) of the ventricular walls, although the contractile properties or systolic function of the heart remain rela- tively normal. 6 Restrictive cardiomyopathy can be idio- pathic or associated with other conditions that affect the myocardium, principally radiation fibrosis, amyloidosis, sarcoidosis, or metastatic tumors. Genetics may also play a role because familial forms of restrictive cardio- myopathy have been reported. 46 Symptoms of restrictive cardiomyopathy include dyspnea, PND, orthopnea, peripheral edema, ascites, fatigue, and weakness. The manifestations of restrictive cardiomyopathy resemble those of constrictive pericar- ditis. In the advanced form of the disease, all the signs of heart failure are present except cardiomegaly. Myocarditis Myocarditis, or inflammatory cardiomyopathy, can be defined as an inflammation of the heart. 6,51,52 The clinical spectrum of the disease is broad: at one end, the disease is asymptomatic with full recovery, and at the other end it has a precipitous onset of heart failure or arrhythmias, occasionally with sudden cardiac death. An acquired cardiomyopathy, myocarditis is associ- ated with a number of etiologies; however, it is usually caused by a viral infection, most commonly an entero- virus (coxsackievirus group B). 6,52–54 In young children adenovirus and parvovirus are the most likely causative agents. Other etiologies include bacterial or fungal infections, hypersensitivity to certain drugs, and auto- immune diseases, such as systemic lupus erythematosus. Myocarditis is a frequent pathologic cardiac finding in persons with acquired immunodeficiency syndrome (AIDS), although it is unclear whether it is due to the human immunodeficiency virus infection itself or to sec- ondary infections. The pathogenesis of myocarditis is one of cardiac injury, followed by an immunologic response.Myocardial injury due to infectious agents is thought to result from necrosis caused by direct invasion of the offending organ- ism, toxic effects of exotoxins or endotoxins produced by a systemic pathogen, or destruction of cardiac tissue by immunologic mechanisms initiated by the infectious agent. The immunologic response may be directed at for- eign antigens of the infectious agent that share molecular characteristics with those of the host cardiac myocytes (i.e., molecular mimicry; see Chapter 16), providing a continuous stimulus for the immune response even after the infectious agent has been cleared from the body.

The heart is enlarged (two to three times its normal weight) and flabby with dilation of all four chambers (Fig. 19-19). Because of wall thinning that accompa- nies dilation, the ventricular thickness may be less than, equal to, or greater than normal. The histologic abnor- malities in DCM are nonspecific. Microscopically, most myocytes are hypertrophied with enlarged nuclei, but many are thinned, stretched, and irregular or atrophied. Clinical Manifestations. The most common clinical manifestations of DCM are those related to heart fail- ure, such as dyspnea, orthopnea, and reduced exercise capacity. In the end stages, persons with DCM often have ejection fractions of less than 25% (normal ejec- tion fraction 50% to 65%). 6 As the disease progresses, stasis of blood in the walls of the heart chambers can lead to thrombus formation and systemic emboli. Secondary mitral valve regurgitation and abnormal car- diac rhythms are common. Death is usually due to heart failure or arrhythmias and can occur suddenly. Treatment. The treatment of DCM is directed toward relieving the symptoms of heart failure, reducing the work of the heart, and preventing atrial and ventricular dysrhythmias. Pharmacologic agents include diuretics to reduce preload, beta blockers to reduce heart rate and myocardial oxygen demand, afterload-reducing agents to decrease left ventricular filling pressures, and angio- tensin converting enzyme (ACE) inhibitors to prevent vasoconstriction. Anticoagulant and antiarrhythmic drugs (e.g., amiodarone for atrial fibrillation) may be used. Other treatments may include a biventricular pacemaker, an implantable cardioverter–defibrillator for chronic symptomatic DCM with reduced systolic function, and in cases that are refractory to treatment, cardiac transplantation. The prognosis for patients with FIGURE 19-19. Idiopathic dilated cardiomyopathy. A transverse section of the enlarged heart reveals conspicuous dilation of both ventricles. Although the ventricular wall appears thinned, the increased mass of the heart indicates considerable hypertrophy. (From Saffitz JE.The heart. In: Rubin E, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of Medicine., 6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2012:525.)