Factors Contributing to Increased Left Ventricle Size in Patients With Abnormally Enlarged Hearts

Overview

The human heart is divided into four chambers. One of the four chambers, the left ventricle, is the chamber mainly responsible for pumping blood out of the heart into the circulation. There is an inherited condition affecting the heart, passed on through genetics, hypertrophic cardiomyopathy (HCM). HCM causes the left ventricle to become abnormally enlarged (left ventricular hypertrophy LVH). Some patients with the abnormal genes that may cause HCM do not have the characteristic LVH. Approximately 20 - 40% of patients with the genetic abnormality (missense mutation of genes encoding for sarcomeric protein) actually have an enlarged left ventricle. Because of this, researchers believe there may be other factors, along with the genetic abnormality that contribute to the development of HCM. Researchers are interested in learning more about several factors they suspect may play a role in the development of HCM. Specifically, researchers plan to study levels of a hormone and the protein it attaches to, which may contribute to the development of an abnormally enlarged heart. Insulin-like growth factor (IGF-1) and insulin-like growth factor binding protein (IGFBP) work together with growth hormone (GH) in the development and maturation of many organ systems. Previous studies have suggested that these hormones affect the development and function of the heart. Patients participating in this study will undergo a variety of tests including collection of blood samples, echocardiogram of the heart, treadmill exercise test, and continuous electrical monitoring of heart activity (Holter monitor).

Hypertrophic cardiomyopathy (HCM) is a genetic disease with an autosomal dominant pattern of inheritance which is characterized by left ventricular hypertrophy (LVH). HCM is often caused by missense mutations of genes that encode for sarcomeric proteins. The LVH varies markedly in patients with identical sarcomeric gene mutations, and notably, 20 to 40% of subjects with disease mutation do not have LVH as assessed by echocardiography. These findings suggest that other factors affect LV wall thickness in HCM. We wish (1) to investigate the potential role of IGF-I and its binding protein, IGFBP3, in determining increased LV mass in HCM caused by sarcomeric mutations; and (2) to assess myocardial ultrasound backscatter, exercise tolerance, and propensity to arrhythmias, in subjects who have inherited sarcomeric mutations but who do not have LVH.