Antiarrhythmic treatment of atrioventricular tachycardias

Atrioventricular (AV) tachycardia includes both AV nodal reentrant tachycardia (AVNRT) and AV reentrant tachycardia (AVRT) using an accessory pathway. The treatment of the acute attack is different from the long-term treatment of both AVNRT and AVRT. Verapamil and adenosine, by prolonging the refractory period of the AV node, are highly effective in terminating acute attacks of AVNRT and orthodromic AVRT. Conversion to sinus rhythm is achieved in approximately 90% of the episodes of tachycardias with both agents given intravenously. The initial dose of verapamil is 0.075-0.1 mg/kg and a subsequent bolus of 5 mg can be given to a maximal dose of 15-20 mg. The initial dose of adenosine is 3 or 6 mg, but doses of 9 or 12 mg can be administered if smaller dosages have been unsuccessful. Other agents producing lengthening of the refractory period of the accessory pathway in AVRT or of the fast pathway in AVNRT often terminate reentry tachycardia. Such agents are class IC antiarrhythmic drugs such as flecainide or propafenone and class IA drugs such as procainamide. In patients with accessory pathways and antidromic tachycardia or atrial fibrillation conducting via an accessory pathway, treatment with verapamil or digoxin should be avoided because these agents may enhance the conduction properties of the accessory pathway, thereby leading to an increase of the ventricular rate or even to ventricular fibrillation. Prevention of AVNRT episodes can be obtained with various antiarrhythmic drugs. Digoxin alone or in combination with beta-blockers is effective in approximately 50% of the cases and especially when the combination proved to be successful during electrophysiological testing.(ABSTRACT TRUNCATED AT 250 WORDS)