Drug Induced Cardiac Arrhythmias Continued



Likely Mechanism


Clinical Features

Flecainide, Propafenone, Quinidine (rarer) Digoxin

Inappropriate use of IV verapamil

Frequent or difficult to terminate Conduction slowing in reentrant VT ("incessant" VT) circuits

Atrial tachycardia with AV block; ventricular bigeminy and others

Ventricular fibrillation

DAD-related triggered activity (±T vagal tone)

Severe hypotension and/or myocardial ischemia

Na+ bolus reportedly effective in some cases

Antidigoxin antibodies

Cardiac resuscitation (DC cardioversion)

Most often in patients with advanced myocardial scarring Coexistence of abnormal impulses with abnormal sinus or AV nodal function Misdiagnosis of VT as PSVT ^ inappropriate use of verapamil

*In each of these cases, recognition and withdrawal of the offending drug(s) are mandatory.

ABBREVIATIONS: AV, atrioventricular; DAD, delayed afterdepolarization; DC, direct current; EAD, early afterdepolarization; WPW, Wolff-Parkinson-White supraventricular tachycardia; IV, intra-8 venous; T, increase; decrease; ?, unclear. o

Sinus node

Sinus node

SA node

Action potentials

SA node

AV node ^Conducting system Purkinje fiber

AV node

AV node

Phase 4

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