Master Class IV Antiarrhythmics (Ca2+ Channel Blockers) with Picmonic for Medicine

Class IV antiarrhythmics are indicated to treat supraventricular tachycardia (SVT), particularly those due to AV nodal reentry. These drugs can also be used for atrial flutter and fibrillation.

Nimodipine is a calcium channel blocking drug which is indicated during subarachnoid hemorrhage. This drug has higher effects on vascular smooth muscle than on cardiac conduction and contractility.

Ca²⁺ channels are especially concentrated in the sinoatrial and atrio-ventricular nodes, and these agents block Ca²⁺ channels, thus they can be used to decrease impulse conduction and velocity through the AV node.

It should be noted that Ca²⁺ channels are located in smooth muscle as well, and use of Ca²⁺ channels helps treat hypertension and vasospasm.

These drugs work to decrease conduction through the heart's AV node. This slowed cardiac conduction leads to an increase in PR and ERP.

Verapamil is a cardioselective Ca²⁺ channel blocker, and has higher activity on slowing AV conduction than it does on vasodilation. It is indicated for use in arrhythmia prevention, hypertension, angina and cluster headaches (cerebral vasospasm).

Diltiazem is a cardioselective Ca²⁺ channel blocker which has actions similar to verapamil. It is used for SVT, angina, atrial flutter and fibrillation, as well as hypertension.

Nimodipine is a vasoselective Ca²⁺ channel blocker, and is used to treat subarachnoid hemorrhage.

There are numerous cardiovascular side effects implicated with Ca²⁺ channel blocker use. These include CHF, AV block, and sinus node depression.

Constipation is seen in this class of drugs, especially verapamil, as Ca²⁺ is a 2nd messenger for Gastrin, which is important for gastric motility. As Ca²⁺ is blocked, GI motility becomes impaired.