**6. Calcium channel blocker agents**

There are two types of CCBs:

*New Insight into Cerebrovascular Diseases - An Updated Comprehensive Review*

of dihydropyridines may be unmasked, though, in the presence of β blockers and

Also, they can have a significant impact on coronary artery dilation; for this reason, CCB can prevent or relieve coronary vasospasm and improve myocardial blood flow. On the other hand, CCBs have negative chronotropic effect. Verapamil and diltiazem (but not the dihydropyridines) slow the rate of firing of the sinoatrial node and slow the conduction of the electrical impulse through the atrioventricular node. Reflex tachycardia does not occur with these drugs, and they also slow the rate of rising in heart rate during exercise. CCBs play an essential role in reducing cardiac contractility as most calcium channel blockers (particularly verapamil) have some negative inotropic effects. Amlodipine does not impair myocardial

**222**

contractility.

**Figure 5.**

**Figure 4.**

*Effects of calcium channel blocker agents.*

patients with heart failure.

*Calcium channel blocker sites of action.*

**A.** Dihydropyridines: amlodipine, clevidipine, felodipine, isradipine, lercanidipine, nicardipine, nifedipine, nimodipine, and nisoldipine

Dihydropyridines exhibit much higher arterial vasodilation than nondihydropyridines while having relatively little impact on cardiac tissue (i.e., there is less depression on myocardial contractility, less impairment on SA node automaticity, and less slowing on AV node conduction velocity) (**Table 1**, **Figure 4**).

**B.** Non-dihydropyridines:


Non-dihydropyridines are more effective in tissue with frequent channel openings (i.e., SA node, AV node, and cardiac myocytes), and channel inhibition increases in proportion to heart rate. The negative chronotropic and inotropic effects on non-dihydropyridine agents appear greater for verapamil than diltiazem. The phenylalkylamine verapamil and the benzothiazepine diltiazem have both cardiac and vascular actions (**Table 1**, **Figure 4**). These drugs have antiarrhythmic, antianginal, and antihypertensive activity.
