PROPAFENONE USE-DEPENDENCE - CLINICAL DEM ONSTRATION OF THE MODULATEDRECEPTOR HYPOTHESIS

The aim of this study was to assess use-dependence in patients with ve ntricular premature contractions (VPC's) treated with propafenone, by means of the increase in heart rate using transesophageal atrial pacin g. It was also analyzed whether this phenomenon was related to the ant iarrhythmic effect. Fifteen patients with more than 30 symptomatic VPC 's/sour were evaluated. Esophageal pacing was performed with cycles of 600 and 400 msec during periods of 1 min and with simultaneous record ing of 2 or 3 EKG leads with a paper speed of 100 mm/sec. Holter monit oring (HM) was carried out in all patients. Propafenone was administer ed in doses of 450 and 900 mg/day, during 5-7 days, at which moment an other HM and esophageal stimulation were repeated. The QRS duration (p re-treatment) was 82.6 +/- 13.5 msec (basal) and 82.4 +/- 13 msec duri ng pacing with 600 msec cycle length (p:NS). The QRS duration with P ( 900 mg/day) was 96.6 +/- 20 msec (basal) (p:NS vs. pre-treatment) but during atrial pacing with 600 msec cycle length it increased to 109.3 +/- 23 msec (p < 0,0004). This use-dependence was also observed with p acing at 600 msec in patients receiving doses of 450 mg/day: 95.3 +/- 13 msec (p < 0,0001 vs. baseline QRS) (Table 1). In conclusion: 1) the re was no significant increase in the QRS duration with P without paci ng; 2) propafenone showed use-dependence during atrial stimulation, ev en with cycle length of 600 msec and with the lower doses.