Hypertrophic cardiomyopathy overview

Editors-In-Chief: C. Michael Gibson, M.S., M.D. [mailto:mgibson@perfuse.org]

Overview
Hypertrophic cardiomyopathy, or HCM, is a disease of the myocardium (the muscle of the heart) in which a portion of the myocardium is hypertrophied (thickened) without any alternate cause such as hypertension, amyloid or aortic stenosis. Although HCM has gained notoriety as a leading cause of sudden cardiac death in young athletes, it should be noted that HCM is a cause of sudden cardiac death in any age group and may be associated with cardiac morbidity and disabling cardiac symptoms as well.

Variants
There are two variants of hypertrophic cardiomyopathy: an obstructive variant, and a non-obstructive variant. A non-obstructive variant of HCM is known as apical hypertrophic cardiomyopathy ,which is also known as nonobstructive hypertrophic cardiomyopathy and Japanese variant hypertrophic cardiomyopathy or the Yamaguchi variant (since the first cases described were all in individuals of Japanese descent).

Pathophysiology
In hypertrophic cardiomyopathy (HCM), the sarcomeres (contractile elements) in the heart replicate causing heart muscle cells to increase in size, which results in the thickening of the heart muscle. In addition, the normal alignment of muscle cells is disrupted, a phenomenon known as myocardial disarray. Myosin heavy chain mutations are associated with development of familial hypertrophic cardiomyopathy. HCM also causes disruptions of the electrical functions of the heart.

Genetics
Hypertrophic cardiomyopathy is most commonly due to a mutation in one of 14 sarcomeric genes that results in a mutated protein in the sarcomere, the primary component of the myocyte (the muscle cell of the heart).

Epidemiology and Demographcs
While most literature so far focuses on European, American, and Japanese populations, HCM appears in all racial groups. The prevalence of HCM is about 0.2% to 0.5% of the general population.

Screening
HCM is frequently asymptomatic until sudden cardiac death, and for this reason some suggest routinely screening certain populations for this disease.

Symptoms
The symptoms associated with hypertrophic cardiomyopathy are quite variable and range from no symptoms, to the development of heart failure, to the occurrence of sudden cardiac death. The symptoms may vary tremendously from individual even within a family. The timing of symptom onset is quite variable as well and may range from infancy to adulthood. Symptoms may include:


 * Chest pain,
 * Dizziness,
 * Fainting, especially during exercise
 * Heart failure (in some patients)
 * High blood pressure (hypertension)
 * Light-headedness, especially with or after activity or exercise, or when standing up suddenly
 * Sensation of feeling the heart beat (palpitations)
 * Shortness of breath
 * Fatigue
 * Reduced activity tolerance
 * Shortness of breath when lying down (orthopnea)

Medical Therapy
The medical management of the patient with hypertrophic cardiomyopathy involves minimizing diastolic dysfunction, reducing left ventricular outflow tract obstruction, optimizing heart failure management, maintaining normal sinus rhythm, rate control and anticoagulation in the presence of atrial fibrillation, and implantation of an automatic implantable cardiac defibrillator in those patients who survive sudden cardiac death.

Management During Pregnancy
Women with hypertrophic cardiomyopathy should be managed by a skilled cardiovascular specialist and a high-risk obstetrician during pregnancy. Among HCM patients who chronically have mild symptoms, pregnancy is generally well tolerated. Although pregnancy causes vasodilation which should exacerbate the outflow gradient, pregnancy also causes fluid retention and an increase in plasma volume which increases preload and offsets the reduction in afterload. In a series of 100 HCM patients, only one of 28 asymptomatic patients developed NYHA Class III or IV heart failure.

Epidural Anesthesia Should Be Avoided due to the potential for venous pooling. Bleeding should be minimized. Blood should be crossed and typed in case a transfusion is needed for bleeding, which can exacerbate outflow obstruction. Although both beta blockers and verapamil may improve symptoms in the mother, the dosing should be limited to minimize the risk of fetal bradycardia, growth retardation and hypoglycemia. There is more experience with the use beta blockers during pregnancy. Home delivery without IV access is not preferred. Vaginal delivery is usually successful.