What class of antiarrhythmics drug blocks potassium channels, prolonging phase 3 of the action potential and slowing the rate and conduction of the heart?
A) I
B) II
C) III
D) IV
C
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The class III antiarrhythmics block potassium, prolonging phase 3 of the action potential, which prolongs repolarization and slows the rate and conduction of the heart. Class I drugs block the sodium channels in the cell membrane during an action potential. Class II drugs are beta-adrenergic blockers that block beta-receptors, causing a depression of phase 4 of the action potential. Class IV drugs block calcium channels in the cell membrane leading to a depression of depolarization and a prolongation of phases I and II of repolarization, which slows automaticity.
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