Sodium Channel Blockers
Overview: Sodium channel blockers inhibit the movement of sodium into cells. In HCM, they have several different uses.
Sodium channel blockers were mainly developed as antiarrhythmics. Some were developed as local anesthetics. Two of these drugs play an important role in treating HCM patients.
Important Sodium Channel Blockers for HCM Patients
Disopyramide (Norpace) helps to reduce gradients in patients with obstruction. This is because of its ability to reduce the force of contraction of a heartbeat. Disopyramide is often used particularly in patients who have not benefited sufficiently from beta blockers. Taken with beta blockers, the result is a substantial reduction in symptoms of obstruction for many patients. Disopyramide is often used before proceeding to septal reduction by either myectomy or alcohol septal ablation.
Ranolazine (Ranexa) is used to treat chronic chest pain. It is especially valuable to HCM patients because nitrate-based angina drugs, like nitroglycerine, are contraindicated for those who are obstructed. Studies have found ranolazine to be safe for HCM patients.
Disopyramide's effect on the heart's force of contraction happens because the drug slows the action of the vagus nerve. Unfortunately, this can cause two important side effects. In men with enlarged prostate glands, it often leads to urinary problems. Disopyramide also tends to cause dry mouth in many patients. There are additional drug therapies that can help treat both of these problems.
Both drugs have other potential side effects. One effect of importance is that, like many other antiarrhythmic drugs, they tend to lengthen the QT interval in the cardiac cycle. If the QT interval becomes too long, a dangerous arrhythmia called torsades de pointes becomes possible.