- Systolic ejection murmur with characteristic changes during
- 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
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 ...