Antiarrhythmics Flashcards
Class IA mechanism
Moderate Na block along with K block
Slows ERP and ADP
Prolongs QT and QRS
Class IB mechanism
Mild Na block, no effect on K
Shortens APD by increasing repolarization
No effect of ERM
Effective refractory period
The time it takes for sufficient sodium channels to return to resting state, and a new action potential can occur.
Action potential duration
The time it takes to return membrane potential to the diastolic resting membrane potential
Increased APD
by sustaining a depolarized Em and slowing Na channel recovery will INCREASE the ERP and impair conduction
Class I Mechanism of action
Block Na channels
- phase 0 of fast response
- phase 4 of slow
Slow or block conduction and abolish pacemakers
Sometimes effects K channels too
Class IA MOA, Ex.
Moderate Na+ AND K+ block
Slows ERP and ADP
prolongs QRS and QT interval
Ex: procainamide, quinidine
Class IB MOA, Ex.
Mild Na+ block, NO K+ block
Shortens APD by increaseing repolarization. No effect on ERP
effective for ventricular arrhythmias assoc. w/ depol
Ex: phenytoin (Dilantin), Lidocaine
Class IC MOA, Ex.
Marked Na+ block, no K+ blockade
small effects on ERP and ADP
Marked QRS prolongation
Ex: flecainide, propafenone. can be very pro-arhythmic
Class III MOA
blocks potassium channels, effects phase 2-3 repolarization in fast response cell Increases APD and ERP, phase 4 is not effected like in class I
Class III Ex., EKG
amiodarone
delays phase 2-3 repol. prolongs QT interval, no effect on QRS
Adenosine MOA
suppresses nodal action potentials via hyperpolarization
increases K+ current, decreases CA++ current
decreases slope of phase 4
inhibits AV nodal conduction and increases refractory period
Class II MOA
Beta-1-adrenergic receptor blockers
slows phase 4 depolarization and phase 0 nodal conduction. suppresses AV nodal reentrant arrhythmias and ABN pacemakers
Reduces Na+ and Ca++ current during diastole (slow response)
Class II Drugs
Metoprolol
esmolol (IV ONLY)
Propranolol
Digoxin
parasympathomimetic - vagal activation which gives ACh- like effects
used in tx of rapid atrial or AV nodal arrhythmias
Magnesium
helpful in digoxin induced arrhythmias and cases of torsades de pointe
Class IV MOA
Calcium channel blockers, Greater effect in tissue that fires frequently, is more depolarized at rest and are more dependant on Ca++ current for activation
AV/SA nodes are greatly effected - slows phase 0 to prolong AV conduction and ERP
Class IV drugs
Verapamil, Diltiazem
