Pathophysiology
Individuals with HCM have some degree of left ventricular hypertrophy. Usually this is an asymmetric hypertrophy, involving the inter-ventricular septum, and is known as asymmetric septal hypertrophy. This is in contrast to the concentric hypertrophy seen in aortic stenosis or hypertension. About two-thirds of individuals with HCM have asymmetric septal hypertrophy.
About 25% of individuals with HCM demonstrate an obstruction to the outflow of blood from the left ventricle during rest. In as much as 70% of patients however obstruction can be provoked under certain conditions. This is known as dynamic outflow obstruction, because the degree of obstruction is variable and is dependent on the loading conditions (ventricular filling and arterial blood pressure) and the contactility state of the left venticle.
Myocardial hypertrophy and extracellular fibrosis predispose to increased left venticular stiffness which in concert with compromised cellular energetics and abnormal calcium handling lead to diastolic dysfunction manifested as dyspnea and exercise intolerance.
The altered structure of the coronary vessels and increased diastolic pressure (reduced blood supply) together with the hypertrophy and the outflow tract obstruction (increased demand) cause myocardial ischemia that is manifested as angina and may be responsible for the triggering of venticular arrhythmias.
In about 30% of patients there are abnormal vascular responses and inability to increase systolic blood pressure during exercise. This is attributed to exaggerated cardiac inhibitory reflexes initiated by increased myocardial wall stress and to elevated levels of vasodilating substances (natriuretic peptides).
Read more about this topic: Hypertrophic Cardiomyopathy