Verapamil (Benzenacetonitrile) is a calcium ion influx inhibitor (calcium entry blocker or calcium ion antagonist). The mechanism of the antianginal and antiarrhythmic effects of verapamil is believed to be related to its specific cellular action of selectively inhibiting transmembrane influx of calcium in cardiac muscle, coronary and systemic arteries and in cells of the intracardiac conduction system.
Verapamil blocks the transmembrane influx of calcium through the slow channel (calcium ion antagonism) without affecting, to any significant degree the transmembrane influx of sodium through the fast channel. This results in a reduction of free calcium ions available within cells of the above tissues. Verapamil is used to treat irregular heartbeats (arrhythmias) and high blood pressure. It relaxes your blood vessels so your heart does not have to pump as hard. It also increases the supply of blood and oxygen to the heart to control chest pain (angina). If taken regularly, verapamil controls chest pain, but it does not stop chest pain once it starts. Your doctor may give you a different medication to take when you have chest pain.
Verapamil belongs to a class of medications called calcium channel blockers. These medications block the transport of calcium into the smooth muscle cells lining the coronary arteries and other arteries of the body. Since calcium is important in muscle contraction, blocking calcium transport relaxes artery muscles and dilates coronary arteries and other arteries of the body. By relaxing coronary arteries, verapamil is useful in treating and preventing chest pain (angina) resulting from coronary artery spasm. Relaxing the muscles lining the arteries of the rest of the body lowers blood pressure, which reduces the burden on the heart as it pumps blood to the body. Reducing heart burden lessens the heart muscle's demand for oxygen, and further helps to prevent angina in patients with coronary artery disease. For more detailed information related to coronary artery disease, please read the Chest Pain, Cholesterol, and Heart Attack articles. Verapamil can decrease electrical conduction in the heart and slow heart rate.
Chest pain (angina) occurs because insufficient oxygen is delivered to the heart muscles. Insufficient oxygen may be a result of a coronary artery blockage or spasm, or because of physical exertion which increases heart oxygen demand in a patient with coronary artery narrowing. Verapamil is used for the treatment and prevention of angina resulting from coronary artery spasm as well as from exertion. Verapamil is also used in the treatment of high blood pressure. Verapamil slows electrical conduction in the heart. It has been used in treating abnormally fast heart rhythms such as atrial fibrillation, and in the prevention of recurrent episodes of rapid heart rhythm originating from the atria.
Verapamil's antiarrhythmic effects are believed to be brought about largely by its action on the sinoatrial (SA) and atrioventricular (AV) nodes. Verapamil depresses AV nodal conduction and prolongs functional refractory periods. Verapamil does not alter the normal atrial action potential or intraventricular conduction time, but depresses amplitude, velocity of depolarization and conduction in depressed atrial fibers. Through this action, it interrupts re-entrant pathways and slows the ventricular rate.
Verapamil is a potent smooth muscle relaxant with vasodilatory properties, as well as a depressant of myocardial contractility, and these effects are largely independent of autonomic influences. Its antianginal action in exertional angina seems to result from a decrease in resistance in the systemic vasculature, as well as from a direct effect on myocardial contraction. The net pharmacologic effect is a decrease in myocardial oxygen consumption. Verapamil's effectiveness in vasospastic angina is due to a decrease in coronary vascular tone.