22 Questions
What is the mechanism of action of class IA antiarrhythmics?
block fast Na+ channels decrease rate of phase 0 depolarization decrease contractility
Which drugs are class IA antiarrhythmics?
procainamide quinidine disopyramide moricizine
What is the mechanism of action of class IB drugs?
minimally block fast sodium (Na+) channels shorten repolarization in late phase 2 shorten the duration of action potential and refractory period
Which drugs are class IB antiarrhythmics?
lidocaine mexilitine tocainide phenytoin
Class IB drugs are used for ___________ arrhythmias?
Is class IC first line treatment?
No - it is reserved for use in refractory ventricular arrhythmias.
What is the mechanism of action of class IC antiarrhythmic drugs?
block fast sodium channels depress phase 0 depolarization markedly inhibit the His-Purkinje conduction system
Which drugs are class IC antiarrhythmics?
flecainide propafenone
The class II drugs are ________________.
beta blockers
What is the MOA of class II antiarrhythmics?
decrease the rate of spontaneous phase 4 depolarization decrease SNS activity decrease HR, conduction, contractility prolong PR interval
Which drugs are class II antiarrhythmics?
esmolol propranolol acebutolol
Which drugs are class III antiarrhythmics?
amiodarone sotalol ibutilide dofetilide bretylium
What is the MOA of class III drugs?
block potassium in phase 3 increase duration of action potential and refractory period decrease the time spent in "excitation"
What are characteristics of amiodarone, and which receptors & channels does it block?
exhibits class I, II, & IV properties. class I: blocks Na+ channels class II: blocks beta receptors class IV: blocks calcium channels amiodarone blocks: Na, K, Ca, alpha and beta
Which drugs are class IV?
nondihydropyridine calcium channel blockers--verapamil and diltiazem
What is the MOA of class IV antiarrhythmics?
block slow calcium channels slow conduction in SA and AV nodes decrease contractility
What phase of the nodal action potential does digitalis work to slow HR?
phase 4 - digitalis works to slow the HR by slowing phase 4 depolarization in cells in the SA and AV nodes
Which phase of the nodal action potential do calcium channel blockers work to slow the HR?
phase 4 - CCBs (verapamil, diltiazem) slow HR by slowing down phase 4 depolarization of SA node and AV node cells.
What phase dose lidocaine and phenytoin work on to control ventricular arrhythmias?
lidocaine and phenytoin suppress spontaneous phase 4 depolarization in ventricular cells
What phase of the ventricular action potential do CCBs work?
CCBs work on phase 2 of the ventricular action potential.
What happens to phase 2 (plateau) when there is hypocalcemia?
With hypocalcemia, Ca2+ diffuses into the cell more slowly. This prolongs the plateau phase of the action potential.
What happens to phase 2 (plateau) when there is hypercalcemia?
Hypercalcemia causes calcium to diffuse into the cell much faster, which shortens the duration of the plateau phase.
Test your knowledge on the mechanism of action and drugs belonging to class IA and IB antiarrhythmics. Learn which type of arrhythmias class IB drugs are used for and if class IC drugs are considered first line treatment.
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