Which class of antiarrhythmic drug is the most commonly used for acute termination of supraventricular tachycardia in clinical practice?

Explanation

## Most Common Antiarrhythmic for SVT Termination ### Class IV Calcium Channel Blockers — First-Line Agent **Key Point:** Verapamil and diltiazem (non-dihydropyridine calcium channel blockers) are the most frequently used drugs for acute SVT termination because they: - Block AV nodal conduction (site of re-entry in most SVTs) - Work rapidly (within 1–3 minutes IV) - Have excellent safety profile - Are first-line per ACC/AHA guidelines ### Why Class IV is Superior for SVT | Feature | Class IV (Ca²⁺ blockers) | Class II (β-blockers) | Class I (Na⁺ blockers) | Class III (K⁺ blockers) | |---------|--------------------------|----------------------|------------------------|-------------------------| | **Speed of action** | Rapid (1–3 min IV) | Slower (5–10 min) | Variable | Slower | | **Site of action** | AV node (primary) | AV node + SA node | Atrial/ventricular tissue | Broad tissue | | **First-line for SVT?** | Yes | No (second-line) | No | No | | **IV formulation available** | Yes (verapamil, diltiazem) | Yes (metoprolol) | Limited | Yes (amiodarone) | **Clinical Pearl:** Adenosine is technically the fastest (blocks AV node within seconds) but is not a Vaughan-Williams class drug. Among the four classes, Class IV is most commonly used for acute SVT in routine practice. **High-Yield:** The mechanism is **AV nodal block** — most SVTs (AVNRT, AVRT) depend on AV nodal conduction for re-entry. Blocking this node terminates the arrhythmia. ### Why Other Classes Are Less Common for Acute SVT - **Class I:** Primarily affects atrial/ventricular tissue; slower onset; risk of proarrhythmia. - **Class II:** Slower onset than Class IV; less predictable AV nodal blockade. - **Class III:** Amiodarone is broad-spectrum but slower; reserved for refractory cases or hemodynamically unstable patients. [cite:Harrison 21e Ch 226]