Class IA antiarrhythmic agents have little effect on:
A. AV node
B. SA node
C. Purkinje fibers
D. Bundle of His
Correct Answer: B. SA node
Class IA antiarrhythmics have little effect on the SA node. It causes moderate degree blockage of fast sodium channels. Drugs include quinidine, procainamide, and disopyramide. These are the most pro-arrhythmic of the sodium channel blockers due to prolonged QTc interval; use is limited due to proarrhythmic potential.
Option A: Quinidine is used in selected patients with Brugada syndrome as an alternative to the implantable cardioverter-defibrillator placement (ICD). Treatment with quinidine can be useful in patients with short QT syndrome and recurrent ventricular arrhythmias (VA). In patients with short QT syndrome who undergo ICD placement, therapy with quinidine may reduce the number of shocks.
Option C: Procainamide is a recommended agent to restore sinus rhythm in patients with Wolff-Parkinson-White (WPW) in whom atrial fibrillation (AF) occurs without hemodynamic instability in association with a wide QRS complex or with a rapid pre excited ventricular response. It also can be useful in an attempt to terminate ventricular tachycardia and arrhythmia.
Option D: Disopyramide is still used occasionally with hypertrophic obstructive cardiomyopathy (HOCM). Particularly, as a combination with beta-blocker or verapamil in the treatment of symptoms such as angina or dyspnea in patients with HOCM who do not respond to beta-blockers or verapamil alone.