Obstruction in HCM
In the usual type of obstructive hypertrophic cardiomyopathy the patient's mitral valve is pushed by the force of flow into a wall of the heart, the interventricular septum. (The mitral valve is a normal cardiac structure that prevents blood from flowing backwards from the main pumping chamber, the left ventricle, into the left atrium.) The abnormal movement of the mitral valve can be easily detected on echocardiography. It is called systolic anterior motion (SAM) of the mitral valve. The obstruction caused by mitral-septal contact causes a pressure difference similar to the one that occurs when the nozzle of a hose is tightened. Obstruction makes HCM symptoms worse because the heart must work harder to pump blood to the body.
The diagram below shows what the heart looks like on echocardiography as the mitral valve is pushed into the septum. As the heart begins to eject blood (the two pictures on the left) the mitral valve is swept by the flow towards the heart wall itself. When the valve touches the septum, which is a wall of the heart (third picture) a pressure difference or gradient occurs. This pressure difference drives the mitral valve further into the septum, worsening the pressure difference. Obstruction begets further obstruction.
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|---|---|---|---|
| Coaptation | Just Before | Contact | After Contact |
Medical treatment of obstruction uses drugs called negative inotropes. These medicines slow the ejection of blood out of the heart, decrease the force on the mitral valve and may thereby eliminate mitral-septal contact.