Porth's Essentials of Pathophysiology, 4e

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Circulatory Function

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and arrhythmogenic right ventricular dysplasia. The mixed cardiomyopathies, which include dilated and restrictive cardiomyopathy, are of both genetic and non- genetic origin. Acquired cardiomyopathies include those that have their origin in the inflammatory process (e.g., myocarditis), pregnancy (peripartum cardiomyopathy), and stress (takotsubo cardiomyopathy). In many cases the cause is unknown, and in these cases it is referred to as an idiopathic cardiomyopathy. Hypertrophic Cardiomyopathy Hypertrophic cardiomyopathy (HCM) is character- ized by unexplained left ventricular hypertrophy with disproportionate thickening of the ventricular septum, abnormal diastolic filling, cardiac arrhythmias, and, in some cases, intermittent left ventricular outflow obstruc- tion (Fig. 19-18). It is one of the most common types of cardiomyopathy, occurring in approximately 1 out of 500 persons in the general population. 46 Hypertrophic cardiomyopathy is the most common cause of sudden cardiac death in young athletes. 47 Hypertrophic cardiomyopathy is an autosomal dom- inant disorder caused by mutations in genes encoding proteins of the cardiac sarcomere (i.e., muscle fibers). Histologically, HCM specimens have myocyte hypertro- phy with myofibril disarray and increased cardiac fibro- sis. More than 400 mutations have been identified in 11 sarcomeric genes. 46–48 Although HCM is inherited, it may present at any time from early childhood to late adulthood with a broad category of manifestations and a variable clinical course. Clinically, HCM is characterized by a massively hypertrophied left ventricle with a reduced chamber size and a paradoxical decrease in stroke volume that results from impaired diastolic filling; in about 25% of cases, dynamic obstruction of left ventricular outflow occurs due to disproportionate thickening of the interventricu- lar septum. 6 Hypertrophic cardiomyopathy is frequently associated with the development of left ventricular

SUMMARY CONCEPTS (continued)

Cardiomyopathies Cardiomyopathies are disorders of the heart muscle. They are usually associated with disorders of myocar- dial performance, which may be mechanical (e.g., heart failure) or electrical (e.g., life-threatening arrhythmias). The definition and classification of the cardiomyopathies have evolved tremendously with the advance of molecu- lar genetics. The American Heart Association’s classifica- tion system divides the cardiomyopathies into two major groups: primary cardiomyopathies, which are confined to the myocardium, and secondary cardiomyopathies, which are associated with other disease conditions. 45 Primary Cardiomyopathies The primary cardiomyopathies are classified as genetic, mixed, or acquired, based on their etiology. 45 The genetic cardiomyopathies include hypertrophic cardiomyopathy or exudate, how quickly it accumulates, and the elasticity of the pericardium determine the effect the effusion has on cardiac function. ■■ Cardiac tamponade represents a life-threatening compression of the heart resulting from excess fluid in the pericardial sac. It may be caused by bleeding into the pericardial sac due to conditions such as chest trauma or rupture of the heart following myocardial infarction. ■■ In constrictive pericarditis, scar tissue develops between the visceral and parietal layers of the serous pericardium. In time, the scar tissue contracts and interferes with cardiac filling.

FIGURE 19-18. Normal heart (A) and hypertrophic cardiomyopathy (B) in which disproportionate thickening of the intraventicular septum causes intermittent left ventricular outflow obstruction.

A

B