Verapamil belongs to which class of the anti – arrhythmic drugs?
**Core Concept**
Verapamil is a calcium channel blocker that affects the heart's electrical activity. It is used to treat various heart rhythm disorders, including atrial fibrillation and supraventricular tachycardia. This medication works by slowing the electrical conduction through the atrioventricular (AV) node.
**Why the Correct Answer is Right**
Verapamil belongs to the class IV anti-arrhythmic drugs, which act by inhibiting the L-type calcium channels in the heart. This leads to a decrease in the heart's contractility and a prolongation of the action potential duration. As a result, the heart's electrical conduction is slowed down, which is beneficial in treating certain types of arrhythmias. The L-type calcium channels are responsible for the influx of calcium ions during the plateau phase of the action potential, and by blocking these channels, verapamil reduces the heart's excitability.
**Why Each Wrong Option is Incorrect**
**Option A:** Class I anti-arrhythmic drugs, such as lidocaine and mexiletine, act by blocking sodium channels, not calcium channels.
**Option B:** Class III anti-arrhythmic drugs, such as amiodarone and sotalol, act by prolonging the action potential duration and refractory period, but they do not specifically block calcium channels.
**Option C:** Class II anti-arrhythmic drugs, such as beta-blockers, act by reducing the sympathetic tone and heart rate, but they do not directly affect calcium channels.
**Clinical Pearl / High-Yield Fact**
Verapamil is often used in combination with other anti-arrhythmic drugs, such as digoxin, to treat atrial fibrillation. However, it should be used with caution in patients with heart failure, as it can worsen the condition.
**Correct Answer:** C. Class IV anti-arrhythmic drugs.