Anti-Arrhythmics Flashcards
What are the three requirements of reentry circuit?
Partial depolarization of the pathway. Unidirectional Block. Circuit takes longer than effective refractory period.
What are Class Ia drugs according to the Vaughan-Williams Classification? What is the prototype? What are the main effects?
Class Ia are sodium channel blockers with intermediate dissociation kinetics. Procainamide is the prototype. They decrease conduction velocity and automaticity while increasing refractoriness.
What are Class Ib drugs according to the Vaughan-Williams Classification? What is the prototype? What are its main effects?
Class Ib are sodium channel blockers with rapid dissociation kinetics. Lidocaine is the prototype. They have NO EFFECT on conduciton velocity, but may decrease refractoriness.
What are Class Ic drugs according to the Vaughan-Williams Classification? What is the prototype? What are its main effects?
Class Ic are sodium channel blockers with slow dissociation kinetics. The prototype is flecainide. They have NO EFFECT on refractoriness, but decrease conduction velocity.
What is procainamide? What are its effects on electrical conduction?
Procainamide is a Class Ia anti-arrhythmic. It slows action potential upstroke prolonging action potential. Also, prolongs conduction velocity and QRS.
What are the therapeutic uses and extra-cardiac effects of procainamide?
Used in atrial and ventricular arrhythmias. Also acts as a ganglion-blocker causing decreased PVR.
What is a key metabolite of procainamide? What are its toxic effects (4)?
N-acetylprocainamide is a metobalite produced by the liver. It acts as a class III anti-arrhythmic and can cause torsades des pointes. Toxic effects include prolongation of action potential, prolongation of QT interval, hypotension, and lupus-like syndrome.
What can class Ib drugs not be used to treat?
atrial arrhythmias
What is the effect of lidocaine on electrical conduction? What are its therapeutic uses?
Causes shortened action potential by increasing the rate of phase 3.
Used to treat ventricular tachycardia and ventricular fibrillation after cardioversion.
Describe the metabolism of lidocaine and its route of administration. In what situation would an increased dose and decreased dose be required? What are the toxic effects of lidocaine?
Lidocaine is heavily metabolized by the liver and must be given by IV.
In MI or acute illness, an increase dose may be required due to the presence of alpha1 acid glycoprotein.
In congestive heart failure a decreased dose may be needed due to low volume of distribution and low clearance.
Toxicity will result in hypertension, tremors, and parasthesias.
What is a major contraindication for class Ic drugs?
These drugs cannot be used in structural heart disease due to high incidence of drug-induced arrhythmias.
What are the effects on electrical conduction, therapeutic uses, and toxic effects of flecainide?
Slows conduciton velocity by decreasing the rate of phase 0. Used to treat supraventricular arrhythmias. Exacerbation of arrhythmias.
What are the effects on electrical conduction and therapeutic uses of beta-blockers?
Beta-blockers decrease heart rate, conductivity, oxygen demand, and automaticity. The therapeutic uses are tachyarrhythmias, atrial fibrillations, atrial flutter, and hypertension.
What are the prototype potassium channel blockers and its effects on electrical conduction?
Amiodarone and sotalol are the prototypes. It prolongs phase 3, increasing the duration of action potentials and effective refractory periods.
What are the effects of amiodarone on other channels/receptors and its therapeutic uses?
Strongly blocks sodium channels, and weakly blocks calcium channels and adrenergic receptors. Therapeutic uses include atrial fibrillation, ventricular tachycardia, and adjunct to implantable cardioverter defibrillator.
