Treatment of Preclinical Hypertrophic Cardiomyopathy With Diltiazem

STUDY RATIONALE:

Hypertrophic cardiomyopathy (HCM) is a genetic disorder characterized by histopathologic findings of cardiac myocyte disarray and fibrosis, and clinical manifestations of unexplained left ventricular hypertrophy (LVH), diastolic dysfunction, and an increased risk for sudden death. It is a common disorder affecting approximately 1 in 1000 individuals in the general population. Dominantly-acting mutations in contractile proteins-genes encoding the elements of the sarcomere apparatus-- have been shown to be the genetic etiology of HCM. Contemporary management strategies for HCM focus on identification of individuals at high risk for sudden death and management of symptoms. There is no current therapy available which address disease prevention or phenotypic attenuation.

Dysregulation of intracellular calcium handling is a fundamental and early manifestation of sarcomere mutations. Animal models of HCM demonstrated abnormal Ca2+ cycling prior to the development of myocyte disarray or hypertrophy. Manipulation of intracellular Ca2+ handling in young, pre-hypertrophic mice with HCM via administration of the L-type Ca2+ channel blocker, diltiazem, attenuated the degree of hypertrophic remodeling and diminished the phenotypic manifestations of sarcomere mutations. Notably, if treatment was initiated later in life, after LVH was allowed to develop, there was no significant effect. Although this strategy has not yet been tested in humans, diltiazem is a commonly-used medication with a long track record of safety and tolerability.

Mutation carriers without discernible echocardiographic left ventricular hypertrophy (designated G+/LVH-) represent a unique population of individuals with early disease who are ideal candidates for preemptive strategies to attempt to attenuate phenotypic development. One clinical marker of early disease is a subtle abnormality of LV diastolic function, detectable by tissue Doppler echocardiography (TDI). Individuals with sarcomere mutations have evidence of abnormal diastolic function by TDI as demonstrated by a 13-19% reduction in early myocardial relaxation velocities (E'), as compared to healthy controls.

Since LVH develops in a age-dependent manner, genetic diagnosis provides a mechanism for early identification of individuals at risk for developing HCM, prior to the expression of diagnostic clinical manifestations. One goal for the next era of medicine is to evolve from contemporary symptom palliation of late stage disease to early preventive strategies which instead strive to alter the natural history of disease development.