Class IV antiarrhythmic agents

Inhibits L-type Ca" channels in cardiac and vascular smooth muscle cells more selective for the myocardium with minimal vasodilatory effects compared with dihydropyridines class IV antiarrhythmic agents Inhibits L-type Ca " " channels in cardiac and vascular smooth muscle cells by modulating ion channel gating mechanisms decreases systemic blood pressure and heart contractility Binds with high affinity to the alpha2-delta subunit of voltagegated Ca " " channels in CNS anticonvulsant drug Inhibits neuronal fast Nay channels, and thus blocks the action potential inhibits also cardiac Nay channels... 

Verapamil (Class IV antiarrhythmic drug) is an effective agent for atrial or supraventricular tachycardia. A Ca++ channel blocker, it is most potent in tissues where the action potentials depend on calcium currents, including slow-response tissues such as the SA node and the AV node. The effects of verapamil include a decrease in heart rate and in conduction velocity of the electrical impulse through the AV node. The resulting increase in duration of the AV nodal delay, which is illustrated by a lengthening of the PR segment in the ECG, reduces the number of impulses permitted to penetrate to the ventricles to cause contraction. 

Fig. 6. Influences of different types of antiarrhythmic agents (Vaughan-William s classification) on the shape of cardiac action potentials. First row Class I-agents action potentials of ventricular myocardial cells. Second row (from left to right) Action potential of SA-node cells influence of a )0-hlocker (class II). Action potential of ventricular myocardial cells influence of a class Ill-antiarrhythmic. Action potential of AV nodal cells influence of a class IV-antiarrhythmic (verapamil, diltiazem).

Class III antiarrhythmic agent with additional classes I, II, III, and IV actions. Prolongs action potential duration and effective refractory period in all cardiac tissues,... 

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