Hypertrophic cardiomyopathy (HCM) is a primary disorder of the heart muscle characterized by inappropriate myocardial hypertrophy of a nondilated left ventricle (LV) and not secondary to a cardiovascular or systemic disease (i.e., hypertension or aortic stenosis). It most often involves the interventricular septum (asymmetric septal hypertrophy) and may be associated with dynamic LV outflow tract obstruction (hypertrophic obstructive cardiomyopathy). Another term that has been used to describe HCM is idiopathic subaortic stenosis.
Is HCM genetic or acquired?
In more than half of the patients, the disease appears to be genetically transmitted as a single-gene autosomal-dominant trait with variable expression and penetrance. In the remaining patients, HCM occurs sporadically.
What are the most common variants of HCM?
The pattern and extent of LV hypertrophy in patients with HCM vary greatly, and different patterns may occur in the same family pedigree. Asymmetric septal hypertrophy, the most common variant, accounts for 90% of patients. The septal hypertrophy may affect the basal one-third of the septum (subaortic area) only, the basal two-thirds (down to papillary muscles), or the entire septum from base to apex. The other two common variants are apical (involving the apical one-third of the ventricle) and midventricle hypertrophy (maximal thickening at the level of the papillary muscles).
Is the histology of HCM unique?
The histologic picture of HCM is characterized by myocardial hypertrophy and myocardial fiber disarray. There is disorganization of the muscle bundles, abnormalities in the cell-to-cell arrangements, and disorganization of the myofibrillar architecture, but these findings also may occur in other acquired and congenital cardiac conditions. The disarray of HCM is unique only in its ubiquity and frequency, with virtually all patients with HCM having some degree of disarray and most having at least 5% of the myocardium affected, whereas in non-HCM patients it usually involves only about 1% of the myocardium.
What are the most frequent symptoms in patients with HCM?
Most patients with HCM are asymptomatic and are identified during screening of relatives with known disease. In patients who are symptomatic, the most common symptoms are:
‚ Present in up to 90% of symptomatic patients
‚ Secondary to LV diastolic dysfunction, impaired ventricular filling, and elevation of left atrial and pulmonary venous pressures
‚ Occurs in up to 75% of symptomatic patients
‚ Secondary to imbalance between oxygen supply and demand with greatly increased myocardial mass, impaired vasodilatory coronary reserve (due to thickened and narrowed small intramural coronary arteries), and subendocardial ischemia (due to increased oxygen demand in the presence of an outflow gradient and increased filling pressure)
Syncope and presyncope
‚ Due to inadequate cardiac output with exertion or to cardiac arrhythmias
‚ Identify patients at increased risk for sudden death (especially in children and young adults, the first clinical presentation may be sudden death)
Describe the classic murmur of obstructive HCM and bedside maneuvers that help distinguish it from other common etiologies.
The classic murmur of obstructive HCM is a crescendo-decrescendo systolic murmur, typically harsh, that usually begins well after the first heart sound (since ejection is not impeded early in systole). Bedside maneuvers that help differentiate this murmur from others are listed in the accompanying table.