Which option correctly describes Vaughan Williams Class 4 effects?

Which option correctly describes Vaughan Williams Class 4 effects?

• A. Blocks calcium channels
• B. Increases depolarization threshold; Lengthens phase 0
• C. Slows nodal action potential
• D. Prolongs repolarization

Answer: (B)

Class IV antiarrhythmics are calcium channel blockers, notably affecting the SA and AV nodes. In nodal tissue, the phase 0 upstroke is driven by calcium influx, so blocking these L-type calcium channels slows the rise of phase 0, effectively raising the threshold for depolarization. This results in slower AV conduction and a longer time before the next action potential can fire. While they block calcium channels, they do not primarily prolong repolarization (that’s more the domain of Class III). Thus describing the effect as increasing the depolarization threshold and lengthening phase 0 captures the essential nodal-specific action of Vaughan Williams Class 4 drugs. Examples include verapamil and diltiazem.

Class IV antiarrhythmics are calcium channel blockers, notably affecting the SA and AV nodes. In nodal tissue, the phase 0 upstroke is driven by calcium influx, so blocking these L-type calcium channels slows the rise of phase 0, effectively raising the threshold for depolarization. This results in slower AV conduction and a longer time before the next action potential can fire. While they block calcium channels, they do not primarily prolong repolarization (that’s more the domain of Class III). Thus describing the effect as increasing the depolarization threshold and lengthening phase 0 captures the essential nodal-specific action of Vaughan Williams Class 4 drugs. Examples include verapamil and diltiazem.