cardiovascular disorders
Hypertrophic Cardiomyopathy Arrhythmias
Introduction
Any hypertrophic cardiomyopathy can produce cardiac and systemic factors that predispose to arrhythmias, including bradyarrhythmias, atrial and ventricular tachyarrhythmias, and sudden death, and eventually end-stage dilated cardiomyopathy. Arrhythmias may cause palpitations, syncope, and/or cardiac arrest. Diagnosis includes ECG, cardiac imaging, and genetic testing. Treatment is usually an implantable cardioverter-defibrillator (ICD), antiarrhythmic drug therapy, and standard measures for heart failure. (See also Overview of Arrhythmogenic Cardiomyopathies and Hypertrophic Cardiomyopathy in general is reviewed elsewhere in THE MANUAL. This topic focuses on its arrhythmogenic features. Hypertrophic cardiomyopathy is a congenital or acquired disorder characterized by marked ventricular hypertrophy with diastolic dysfunction in the absence of increased afterload (eg, due to Aortic Stenosis , Inherited hypertrophic cardiomyopathy is a common (1/500) cardiac disorder, usually autosomal dominant with variable penetrance. The underlying etiology is one of more than 1500 reported mutations in genes encoding myofilament proteins of the sarcomere, but genetic testing is negative in approximately 2/3 of patients with hypertrophic cardiomyopathy. The phenotype is very diverse but typically is characterized by left ventricular hypertrophy (LVH) often accompanied by left ventricular outflow tract obstruction, atrial tachyarrhythmias, ventricular tachyarrhythmias, sudden death, and end-stage dilated cardiomyopathy. The LVH is typically asymmetrical, in which the anterior septum and anterior free wall are hypertrophied much more than is the posterior wall. Nevertheless, subtypes with concentric left ventricular hypertrophy or isolated left ventricular apical hypertrophy are recognized. Cardiac function is compromised because hypertrophy results in a stiff, noncompliant left ventricle that resists diastolic filling, elevating end-diastolic pressure and thus increasing pulmonary venous pressure. As resistance to filling increases, cardiac output decreases, an effect worsened by any outflow tract gradient present. Because tachycardia allows less time for filling, symptoms tend to appear (or worsen) mainly during exercise or tachyarrhythmias. (See also Heart failure with preserved ejection fraction (HFpEF) .) In regards to arrhythmias, the hypertrophy is associated with myofibril disarray, microvasculopathy, microvascular insufficiency, ischemia, and myocardial scarring, all of which predispose to ventricular tachyarrhythmias and sudden death. Atrial Fibrillation is also very frequent and may be particularly poorly tolerated secondary to aggravation of ventricular diastolic dysfunction by rapid ventricular rates. Symptoms and signs often are exertional and include dyspnea, chest pain (usually resembling typical angina), palpitations, and syncope. The syncope may be caused by arrhythmia or outflow tract obstruction. 