Session 1: Classification and Class I Antiarrhythmics Flashcards
Vaughan Williams Classification and Class I Antiarrhythmics
What is contractility in cardiac cells?
Ability of cardiac cells to shorten and return to their original length in response to an electrical impulse.
Define automaticity in cardiac cells.
Ability of cardiac pacemaker cells to depolarize spontaneously.
What is excitability in the context of cardiac cells?
Ability of resting, polarized cardiac cells to depolarize in response to an electrical impulse.
What does conductivity refer to in cardiac cells?
Ability of all cardiac cells to conduct electrical impulses to adjacent cardiac cells.
What is the effect of Class I sodium channel blockers on phase 0?
They inhibit fast sodium channels and reduce the maximal rate of rise of phase 0.
List the subclasses of Class I antiarrhythmic drugs.
- Class IA
- Class IB
- Class IC
What effect do Class IA antiarrhythmic drugs have on the action potential?
They moderately block sodium channels, raise threshold potential, widen action potential duration, decrease conduction velocity, prolong repolarization, and decrease automaticity.
What ECG changes are associated with Class IA antiarrhythmic drugs?
Increased QRS duration and increased QT interval.
What are the indications for Procainamide?
- Life-threatening ventricular tachycardia with normal LV function
- Atrial fibrillation with antegrade conduction over an accessory pathway.
What are some adverse effects of Procainamide?
- Mild negative inotrope
- Hypotension with IV dose
- Torsades de Pointes (rare).
What is a major indication for Disopyramide?
Life-threatening ventricular arrhythmias.
What are the adverse effects of Disopyramide?
- Marked negative inotropic effect
- Toxicity in renal insufficiency
- Ventricular arrhythmias; Torsades de Pointes.
What is Quinidine used for?
Effective against supraventricular and ventricular arrhythmias, particularly in re-entrant arrhythmias.
What ECG changes are associated with Quinidine?
Increased QT interval.
What are the indications for Lidocaine?
- Suppression of serious ventricular arrhythmias
- Acute management of VT.
- Ventricular arrhythmias caused by digoxin toxicity.
What are the common adverse effects of Lidocaine?
- CNS side effects (confusion, seizures)
- Dose-related side effects with increasing infusion rate.
What is Mexiletine’s primary indication?
Ventricular arrhythmias.
What are the common side effects of Mexiletine?
- New or worsened arrhythmias
- CNS side effects (dizziness, tremor).
- GI effects (indigestion, nausea).
What is Phenytoin primarily used for?
Treating epilepsy.
List some contraindications for IV Phenytoin.
- 2nd or 3rd degree heart block
- Sinus bradycardia.
What effects do Class IC sodium channel blockers have?
- Marked blockage of sodium channels
- Marked depression of the upstroke of action potential.
- Prolonged repolarization.
What are the indications for Flecainide?
- Paroxysmal supraventricular tachycardias
- WPW arrhythmias
- Paroxysmal atrial flutter or atrial fibrillation.
What are the contraindications for Flecainide?
- Structural heart disease
- 2nd or 3rd degree AV block.
What is Propafenone’s mechanism of action?
Marked blockage of sodium channels with potent membrane stabilizing activity.
