Verapamil antiarrhythmic properties

Bepridil does not seem to have much structural relationship to verapamil. In addition to slow Ca2+ channels, it also inhibits fast Na+ channels and exerts useful antiarrhythmic properties as well as antianginal effects. 

Verapamil. Verapamil hydrochloride (see Table 1) is a synthetic papaverine [58-74-2] C2qH2 N04, derivative that was originally studied as a smooth muscle relaxant. It was later found to have properties of a new class of dmgs that inhibited transmembrane calcium movements. It is a (+),(—) racemic mixture. The (+)-isomer has local anesthetic properties and may exert effects on the fast sodium channel and slow phase 0 depolarization of the action potential. The (—)-isomer affects the slow calcium channel. Verapamil is an effective antiarrhythmic agent for supraventricular AV nodal reentrant arrhythmias (V1-2) and for controlling the ventricular response to atrial fibrillation (1,2,71—73). 

Therapeutic uses. Because of their narrow therapeutic margin, antiarrhythmics are only employed when rhythm disturbances are of such severity as to impair the pumping action of the heart, or when there is a threat of other complications. Combinations of different antiarrhythmics are not recommended (e.g., quinidine plus verapamil). Some agents, such as amiodarone, are reserved for special cases. This iodine-containing substance has unusual properties its elimination half-life is 50-70 days depending on its electrical charge, it is bound to apolar and polar lipids, stored in tissues (corneal opacification, pulmonary fibrosis) and it interferes with thyroid function. 

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