Class I antiarrhythmics vs Classes II, III, and IV antiarrhythmics
How to tell Class I antiarrhythmics and Classes II, III, and IV antiarrhythmics apart when a board question makes them look alike.
Class I block sodium channels; class II are beta blockers, class III block potassium channels, class IV block AV-node calcium channels.
Side by side
Class I drugs block fast sodium channels and are subdivided into IA, IB, and IC by action-potential effects.
Class II are beta blockers, class III prolong potassium-mediated repolarization, and class IV are non-dihydropyridine calcium channel blockers.
Sodium channel blockade changes phase 0 depolarization in fast-response cardiac tissue.
The other core classes target sympathetic tone, phase 3 repolarization, or AV nodal calcium entry.
Lidocaine, flecainide, procainamide, or quinidine language should trigger class I sodium-channel sorting.
Metoprolol points class II; amiodarone or sotalol points class III; verapamil or diltiazem points class IV.
The trap
Many antiarrhythmics affect more than one channel, but the exam often tests the first-pass class map.
The repair move
Before memorizing drug names, recite the channel map: I sodium, II beta, III potassium, IV calcium.
Try a free question
CoreA patient with ventricular arrhythmia receives lidocaine. The drug works primarily through fast sodium channel blockade in cardiac myocytes. Which antiarrhythmic class is this?
Show answer and explanation
Answer: A. Class I. Class I antiarrhythmics are sodium channel blockers; lidocaine is a class IB example.
Why the other choices are tempting
- B. Class II drugs are beta blockers.
- C. Class III drugs mainly prolong repolarization through potassium-channel effects.
- D. Class IV drugs are non-dihydropyridine calcium channel blockers.
- E. Adenosine-like agents act through transient AV nodal suppression rather than sodium-channel blockade.
Flashcards
Tap a card to flip it.
What is the fastest separator for Class I antiarrhythmics vs Classes II, III, and IV antiarrhythmics?
Class I block sodium channels; class II are beta blockers, class III block potassium channels, class IV block AV-node calcium channels.
What clue should make you choose Class I antiarrhythmics?
Class I drugs block fast sodium channels and are subdivided into IA, IB, and IC by action-potential effects.
Quick answers
What is the fastest way to tell Class I antiarrhythmics from Classes II, III, and IV antiarrhythmics?
Class I block sodium channels; class II are beta blockers, class III block potassium channels, class IV block AV-node calcium channels.
What is the key clue for Class I antiarrhythmics?
Class I drugs block fast sodium channels and are subdivided into IA, IB, and IC by action-potential effects.
What is the key clue for Classes II, III, and IV antiarrhythmics?
Class II are beta blockers, class III prolong potassium-mediated repolarization, and class IV are non-dihydropyridine calcium channel blockers.
What is the common trap with Class I antiarrhythmics vs Classes II, III, and IV antiarrhythmics?
Many antiarrhythmics affect more than one channel, but the exam often tests the first-pass class map.