Hypertrophic cardiomyopathy arrhythmogenesis

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

Overview
Patients with hypertrophic cardiomyopathy are at risk of arrhythmias and sudden death. Abnormal filling of the left atrium may result in the left atrial dilation which may predispose the patient to atrial fibrillation. The presence of myocardial disarray and myocardial ischemia (due to microvascular dysfunction and episodes of reduced cardiac output) may predispose the patient to ventricular tachycardia, ventricular fibrillation, and sudden cardiac death.

Atrial Arrhythmias
Impaired filling of the left ventricle can lead to left atrial stretch and left atrial dilation. This in turn can predispose the patient to the development of atrial fibrillation. The onset of atrial fibrillation can be quite dangerous in these patients as the loss of left atrial kick and the more rapid heart rate can both diminish left ventricular filling which can lead to severe hemodynamic compromise. This hemodynamic compromise can in turn be associated with sudden cardiac death.

Ventricular Arrhythmias
Ventricular arrhythmias and degeneration into sudden cardiac death may be due to the following:


 * Primary arrhythmias
 * The presence of myocardial disarray
 * The presence of scar or fibrosis
 * Hemodynamic instability with diminished stroke volume
 * the presence of ischemia

It must be emphasized that atrial arrhythmias (which are commonly detected on ambulatory monitoring) can lead to ischemia and hemodynamic compromise which may in turn lead to sudden cardiac death in these patients as well.

Autonomic Imbalance
Assessment of autonomic function in patients with HCM often reveals abnormal responses of heart rate and blood pressure to exercise in two-thirds, which was associated with a more malignant clinical course, suggesting that autonomic imbalance may also be important in the genesis of sudden cardiac death in these patients.