Verapamil is a drug which can be used to treat high blood pressure, angina and fast abnormal heart rhythms, particularly those coming from the upper chambers of the heart. In cardiomyopathy it is commonly used in the treatment of left ventricular outflow tract obstruction, due to hypertrophic cardiomyopathy. It is part of a group of drugs known as a ‘calcium channel blockers’.

Calcium is an electrolyte which is required for the contraction of all muscles. Muscle cells have channels, like gates, in their walls and when the muscle is stimulated these channels open to allow calcium to flow in through the cell membrane into the cell. In the heart muscle cells this enables a strong contraction to pump the blood out of the ventricles.

Left ventricular outflow tract obstruction is a complication of hypertrophic cardiomyopathy, where the thickening of the muscle occurs higher up on the wall which divides the right and left ventricle, the septum. This can affect the mitral valve, which sits between the left atrium and left ventricle, causing one of the valve leaflets to partly obstruct the flow of blood out of the left ventricle. This can cause symptoms of breathlessness, fatigue and chest pain, which can debilitating in some people.

The initial recommended treatment for obstruction is with beta blockers. Where this is ineffective, or the person can’t tolerate beta blockers, or they can’t be used due to another medical condition, calcium channel blockers are used. There are different types of calcium channel blockers and verapamil is part of the group known as non dihydropiridines. Its action is more focussed on the heart, rather than the wider circulatory system.

As a calcium channel blocker verapamil does what its title suggests, it blocks the channels in the cell wall to inhibit the flow of calcium into the heart muscle cells. This has the effect of reducing the force of the contraction of the heart and also slowing the heart rate. This relaxing of the heart can result in a reduction of the level of obstruction and, in turn, improve symptoms.

Grapefruit juice should be avoided as it can increase the effect of verapamil. Common side effects of verapamil are constipation and headache.

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