TACHYCARDIA-INDUCED CHANGE OF ATRIAL REFRACTORY PERIOD IN HUMANS - RATE DEPENDENCY AND EFFECTS OF ANTIARRHYTHMIC DRUGS

Background-Atrial fibrillation (AF) has been shown to shorten the atri al effective refractory period (ERP) and make the atrium more vulnerab le to AF. This study investigated the effect of atrial rats and antiar rhythmic drugs on ERP shortening induced by tachycardia. Methods and R esults-Seventy adult patients without structural heart disease were in cluded. For the first part of the study, right atrial ERP was measured with a drive cycle length of 500 ms before and after 10 minutes of ra pid atrial pacing using five pacing cycle lengths (450, 400, 350, 300, and 250 ms) in 10 patients. For the second part of the study, the rem aining 60 patients were included to study the effects of antiarrhythmi c drugs on changes in atrial ERP induced by AF. Atrial ERP was measure d with a drive cycle of 500 ms before and after an episode of pacing-i nduced AF. After the patients were randomized to receive one of six an tiarrhythmic drugs (procainamide, propafenone, propranolol, dl-sotalol , amiodarone, and verapamil), atrial ERP was measured before and after another episode of pacing-induced AF. In the first part of the study, atrial ERP shortened significantly after 10 minutes of rapid atrial p acing, and the degree of shortening was correlated with pacing cycle l ength. The second part of the study showed that atrial ERP shortened a fter conversion of AF (172+/-15 versus 202+/-14 ms, P<0.0001) and that ERP shortening was attenuated after verapamil infusion (-4.6+/-1.2% v ersus -15.1+/-3.4%, P<0.001) but was unchanged after infusion of the o ther antiarrhythmic drugs, Furthermore, all of these antiarrhythmic dr ugs could decrease the incidence and duration of secondary AF. Conclus ions-The atrial ERP shortening induced by tachycardia was a rate-depen dent response, Verapamil, but not other antiarrhythmic drugs, could ma rkedly attenuate this effect. However, verapamil and the other drugs c ould decrease the incidence and duration of secondary AF.