Chapter 14

• Dyspnea.
• Systolic ejection murmur with characteristic changes during bedside maneuvers.
• Marked asymmetric left ventricular hypertrophy on echocardiogram.
• Normal or hyperkinetic left ventricular systolic function.

The term “hypertrophic cardiomyopathy (HCM)” can best be defined as a condition characterized by idiopathic or unexplained myocardial hypertrophy that is associated with small or normal ventricular cavity size, hyperdynamic ventricular function, and diastolic dysfunction. The qualifier unexplained is used to suggest that this condition may coexist with hypertension or aortic valve disease, although the extent and distribution of hypertrophy are disproportionate to these associated disorders. Therefore, mild-to-moderate hypertension and mild or moderate aortic valve disease cannot be implicated in massive asymmetric hypertrophy with hyperdynamic ventricular function. (The definition also requires hyperdynamic systolic function, a feature that is rarely absent even in the late stages of HCM.)

Although the condition has also been called idiopathic hypertrophic subaortic stenosis, which connotes a condition characterized by myocardial hypertrophy without underlying cause, HCM is a more accurate term because it describes the major feature of idiopathic hypertrophy, especially in patients with no evidence of subaortic stenosis or intraventricular obstruction.

HCM can be classified as nonobstructive or obstructive, based on the presence and the location (midventricle or outflow tract) of intraventricular obstruction. Other classifications may relate to the distribution of the hypertrophy: asymmetric septal hypertrophy, disproportionate upper septal thickening, apical asymmetric hypertrophy, and the like. Such approaches are generally not fruitful except when apical hypertrophy is localized.

The underlying cause and pathogenesis of this disease are largely unknown. The asymmetric type of HCM is commonly transmitted genetically, but sporadic cases are also recognized. An abnormal response of the myocardium to normal catecholamines has been postulated as a pathogenetic mechanism. The clinical association between HCM and pheochromocytoma, neurofibromatosis, and lentiginosis suggests a genetic disorder of neural crest tissue. More recent studies have linked familial HCM to the cardiac myosin heavy-chain genes on chromosome 14 in some—but not all—families, indicating genetic heterogeneity. The presence of different disease genes or mutations within a given gene may account for differences in the clinical expression of familial HCM.

The pathologic findings at autopsy are remarkably uniform and include massive and generally asymmetric hypertrophy. Both the atria and the ventricles are affected, with the left ventricle most commonly involved. The interventricular septum is generally far more massively hypertrophied than the free wall, a peculiar asymmetric septal hypertrophy that may provide the necessary hemodynamic conditions to cause a dynamic outflow obstruction. In this situation, the condition is referred to as hypertrophic obstructive cardiomyopathy (HOCM). Localization of such hypertrophy in the midlateral wall may result in midventricular obstruction and distribution of the hypertrophy in the right ventricular infundibulum in subpulmonic stenosis. Asymmetric localization of hypertrophy can involve virtually any segment of the left ventricle, except for the posterobasal region.

In some patients, the hypertrophy involves primarily the apical portion of the left ventricle (asymmetric apical hypertrophy) rather ...

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