Digoxin

Digoxin is a potent pro-arrhythmic drug. At therapeutic plasma level, it causes nonspecific ST segment depression that has a scooping appearance (A) or looks like a reversed “?” (B).

(See Case 067: Abnormal ECG at http://www.medicine-on-line.com.) At toxic levels, digoxin can cause virtually all kinds of arrhythmia but particularly sinus bradycardia, SA and AV blocks, atrial and junctional tachycardias, and VPB and ventricular tachycardia.

Anti-arrhythmic Drugs

Quinidine, procainamide, and disopyramide (Class IA agents) prolong the QRS duration and the QT interval with or without the appearance of U wave and have the propensity to cause polymorphic ventricular tachycardia (torsade de pointes).

Sotalol and amiodarone (Class III agents) can increase PR, QRS, and QT intervals, leading to similar risks of torsade de pointes. They also have significant beta-blocking properties, causing bradyarrhythmias.