Cardiomyopathy III: Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy results from mutations in genes encoding sarcomeric proteins. The most common mutations occur in MYH7 (beta-myosin heavy chain), MYBPC3 (myosin-binding protein C), and cardiac troponin T genes. Over 1400 mutations across at least 11 different genes have been identified. These mutations cause cardiac muscle cells to hypertrophy, become disorganized, and orient obliquely or perpendicularly to each other.

In hypertrophic cardiomyopathy, disorganized cardiac muscle cells cause thickening of ventricular walls, especially the interventricular septum. The thickened septum obstructs blood flow out of the left ventricle during systole. Additionally, thickened walls decrease ventricular compliance, impairing ventricular filling during diastole and causing diastolic dysfunction. This combination of obstruction and reduced filling significantly compromises cardiac output.

Patients with HCM may be asymptomatic or experience fatigue from decreased cardiac output, exertional dyspnea from elevated left ventricular diastolic pressure, angina from increased left ventricular mass, and syncope from aortic outflow obstruction during activity. Arrhythmias such as atrial fibrillation, ventricular tachycardia, and ventricular fibrillation can also cause syncope and sudden cardiac events.

Echocardiography is the cornerstone diagnostic test, assessing heart muscle thickness and outflow tract obstruction. Chest palpation may reveal an exaggerated, left-displaced apical impulse. Auscultation detects an S4 heart sound and systolic murmur. ECG typically shows ventricular hypertrophy, ST-T wave abnormalities, and arrhythmias. Heart catheterization and nuclear stress testing assist in diagnosis and treatment planning.

Calcium channel blockers like verapamil and beta-blockers like metoprolol improve heart filling by slowing heart rate and reducing contractility. Amiodarone or sotalol treats arrhythmias. For severe symptoms unresponsive to medication, surgical myectomy removes part of the thickened septal muscle. Percutaneous transluminal septal myocardial ablation uses alcohol injection to reduce left ventricular outflow obstruction.

Implantable cardioverter-defibrillators are the most effective intervention for preventing sudden cardiac death in high-risk HCM patients with prior cardiac arrest, sustained ventricular arrhythmias, or strong family history of sudden cardiac death. ICDs monitor heart rhythm and deliver therapy when dangerous arrhythmias occur, significantly improving survival outcomes in vulnerable populations.

Patients should avoid dehydration and activities that increase systemic vascular resistance. Rest and leg elevation improve venous return and help manage chest pain. Counseling addresses emotional impacts of genetic heart conditions and discusses family screening and genetic testing options. Psychological support helps patients cope with anxiety related to activity restrictions and sudden cardiac event risks. Learn more about post operative nursing management for surgical interventions.