ELECTROPHARMACOLOGIC EFFECTS OF CLASS-I AND CLASS-III ANTIARRHYTHMIA DRUGS ON TYPICAL ATRIAL-FLUTTER - INSIGHTS INTO THE MECHANISM OF TERMINATION

Background-Acute effects of class I and class III antiarrhythmia drugs on the reentrant circuit of typical atrial flutter are not fully stud ied. Furthermore, the critical electrophysiologic determinants of flut ter termination by antiarrhythmia drugs are not clear. Methods and Res ults-The study population consisted of 36 patients (mean age, 53+/-17 years) with clinically documented typical atrial flutter, A 20-pole '' halo'' catheter was positioned around the tricuspid annulus. Increment al pacing was performed to measure the conduction velocity along the i sthmus and lateral wall, and extrastimulation was performed to evaluat e atrial refractory period in the baseline state and after intravenous infusion of ibutilide, propafenone, and amiodarone. Efficacy of these drugs in conversion of typical atrial flutter and patterns of termina tion were also determined, Ibutilide significantly increased the atria l refractory period and decreased conduction velocity in the isthmus a t short pacing cycle length. It terminated atrial flutter in 8 (67%) o f 12 patients after prolongation of flutter cycle length due to increa se (86+/-19%) of conduction time in the isthmus, Propafenone predomina ntly decreased conduction velocity with use dependency and significant ly increased atrial refractory period, but it only converted atrial fl utter in 4 (33%) of 12 patients. Amiodarone had fewer effects on atria l refractory period and conduction velocity than did ibutilide and pro pafenone, and it terminated atrial flutter in only 4 (33%) of 12 patie nts. Termination of typical atrial flutter was due to failure of wave front propagation through the isthmus, which occurred with cycle lengt h oscillation, abruptly without variability of cycle length, or after premature activation of the reentrant circuit. Conclusions-Ibutilide, with a unique increase in atrial refractoriness, was more effective in conversion of atrial flutter than were propafenone and amiodarone.