Antiarrhythmics - CVPR Flashcards
These antiarrhythmics are sodium channel blockers (direct action) with anticholinergic activity (indirect action). Slowing of the diastolic depolarization (Phase 4) leads to the reduced automaticity. Slowing of the rate of rise of the action potential (Phase 0) leads to the reduced excitability and reduced conduction velocity.
Class IA: Quinidine, Procainamide, and disopyramide
This Class IA antiarrhythmic is only used orally, as parenteral administration has marked hypotensive effects.
- The side effects include cinchonism, which is characterized by ringing in the ears, blurred vision, nausea, and vomiting.
- Thrombocytopenia can also be induced. iii. It also reduces the renal elimination of digoxin, which can lead to an increase in the toxicity from digoxin.
Quinidine
This Class IA antiarrhythmic can be used orally or intravenously.
- N-Acetylprocainamide is an active metabolite that behaves like a class III drug.
- A lupus-like syndrome can be induced, especially in patients who have a slow acetylator phenotype.
Procainamide
Therapeutic uses of Class IA drugs
Therapeutic uses: Quinidine is used in the treatment of a wide variety of arrhythmias, including atrial, AV junctional, and ventricular tachyarrhythmias. Procainamide is available in an intravenous formulation only and may be used to treat acute atrial and ventricular arrhythmias. However, electrical cardioversion or defibrillation and amiodarone have mostly replaced procainamide in clinical use. Disopyramide is used in the treatment of ventricular arrhythmias as an alternative to procainamide or quinidine and may also be used for maintenance of sinus rhythm in atrial fibrillation or flutter.
This is an oral antiarrhythmic that is also the most potent antimuscarinic.
Disopyramide
Adverse effects: Large doses of ? may induce the symptoms of cinchonism (for example, blurred vision, tinnitus, headache, disorientation, and psychosis). Drug interactions are common with ? since it is an inhibitor of both CYP2D6 and P-glycoprotein.
Quinidine
Intravenous administration of this Class IA may cause hypotension.
Procainamide
This Class IA has the most anticholinergic adverse effects of the class IA drugs (for example, dry mouth, urinary retention, blurred vision, and constipation). Both quinidine and ? should be used with caution with potent inhibitors of CYP3A4.
Disopyramide
Of the Class IA antiarrhythmics, which one is most commonly used and only available in IV?
Procainamide
Describe the mechanism of action of Class IA antiarrhythmic drugs.
Slow upstroke of action potential
PRolonged action potential duration
Increase refractory period
What effect do Class IA drugs have on the ERP and QT interval?
Decrease in slope of phase 0 and a delay of repolarization. This causes an increase in refractory period. Changing the slope in phase 0 causes a prolongation of QT interval.
What is a common adverse effect of procainamide?
Proarrhythmia in 2-8% of patients - Torsade de pointes , or “twisting of the point”
The underlying basis for rhythm disturbance is delay in phase 3 of the action potential.
Produces a lupus-like syndrome
Torsades de Pointes is more common in patients with what electrolyte imbalance?
Hypokalemic patients.
K+ occupancy of extracellular sites in K+ channels involved in repolarization increases currents mediated by these channels. In hypokalemia this facilitatory effect of K+ occupancy is reduced, leading to prolongation of the action potential.
CLASS IB antiarrhythmic drugs are sodium channel blockers without anticholinergic activity.
What is the mechanism of action?
Shorten phase 3 repolarization and decrease the duration of the action potential.
Drugs: Lidocaine, mexiletine, phenytoin
This Class IB antiarrhythmic causes central nervous system (CNS) effects including nystagmus (early indicator of toxicity), drowsiness, slurred speech, paresthesia, agitation, confusion, and convulsions, which often limit the duration of continuous infusions.
Lidocaine
