anti-arrhythmics Flashcards
3 ways to counter arrhythmias
decrease automaticity, increase refractoriness, decrease conduction velocity
5 ways to decrease automaticity
increase threshold, decrease phase 4 slope, increase AP duration, slow SA/AV depolarization, increase maximum diastolic potential (more negative)
3 Class IA
quinidine, procainamide, disopyramide
2 class IB
Lidocaine, mexilitine
2 class IC
flecainide, propafenone
5 class II (beta blockers)
esmolol, metoprolol, propranolol, atenolol, timolol
5 class III
amiodarone, dronedarone, dofetilide, sotalol, ibutilide
2 class IV
verapamil, diltiazem
Class IA target/mech
Na channels (slow action potential, flatter phase 0 slope), also affect potassium (prolong AP duration/repolarization)
Class IB target/mech
weak Na block, shortened repolarization
Class IC target/mech
strong Na block (affect on phase 0) and minimal repolarization effect
overall mech for class I
slow the resetting of fast Na+ channels after AP- makes them selective for rapidly depolarizing tissue
IA toxicities
prolonged QT and torsade
IC toxicities
proarrhythmic, avoid w/ pts who have structural abnormalities
class II mech for decreasing automaticity
decrease phase 4 slope by competing w/ adrenergic stimulation and slowing HCN channel opening
class III mech for decreasing automaticity
block K+ channels and prolong repolarization
class III toxicities
prolonged QT and torsade
EXCEPT amiodarone
class IV mech to lower automaticity
slow depolarization in nodal cells by blocking Ca++ channels (responsible for phase 0 upstroke in pacemakers)
adenosine mech for lowering automaticity
increase (more negative) maximum diastolic potential, bind to specific adenosine receptors, promotes K+efflux and inhibits adenylate cyclase (and cAMP) and thus the Ca++ channels as well
PK of adenosine
short half life less than 30 seconds, must be administered by rapid IV bolus
ways to inhibit reentrant arrhythmias
increase refractory period, slow conduction
how to increase refractory period?
class IA and III- block K+ channels and repolarization, prolonging AP
Class IA-C and adenosine- inhibit recovery of Na+ (Ca++ for adenosine) channels prior to next AP, does not prolong current AP
why want to slow conduction velocity?
blocking/slowing impulse along AV node can protect ventricles from atrial arrhythmias
how to slow AV conduction?
Class II beta blockers (slow HCN Na+ influx) or class IV Ca++ blockers (slow Ca++ phase 0) or adenosine (hyperpolarization at maximum diastolic potential)
