Class IV Antidysrhythmic Therapy (Calcium Channel Blockers)

Antidysrhythmic medications help correct irregular heart rhythms. Class IV antidysrhythmic medications, also known as calcium channel blockers, are a class of medications that help control dysrhythmias. Verapamil and diltiazem are the two calcium channel blockers used to treat dysrhythmias and are classified as nondihydropyridines.

Alright, so calcium is essential for electrical conduction through the heart, the contraction of heart muscle, and the normal function of vascular smooth muscle. Calcium channel blockers work by preventing calcium from entering cells and binding with receptors. This slows sinoatrial, or SA, node automaticity, and delays conduction through the atrioventricular, or AV, node. It also reduces myocardial contractility, promotes decreased peripheral resistance, blood pressure, and cardiac workload.

Now, even though antidysrhythmics are indicated to treat dysrhythmias, they tend to have prodysrhythmic properties, meaning they can make the dysrhythmia worse, or even cause new dysrhythmias.  Other side effects of calcium channel blockers are mostly related to vasodilation and can include headache, flushing, dizziness, peripheral edema, and hypotension.

Bradycardia is also a common side effect due to the decreased velocity of conduction through the heart.  Calcium channel blockers can cause constipation and heart block, as well as acute renal failure, and Stevens-Johnson syndrome.

As far as contraindications go, calcium channel blockers should not be used in patients with hypotension, acute myocardial infarction, second- or third-degree heart block, or sick sinus syndrome, unless the patient has a pacemaker. They should also be used with caution in patients with liver impairment.

Lastly, IV verapamil is considered a high alert medication, meaning there’s an increased risk of patient harm when the medication is used in error.

As far as interactions go, verapamil should not be given to patients who are also taking digoxin, since this can increase the risk of heart block. Verapamil also increases the serum level of digoxin, which increases the risk of digoxin toxicity. Both verapamil and diltiazem can interact with beta blockers, which can cause bradycardia and suppress cardiac contractility.