Absence of Frequency dependent Effects of Intravenous Propafenone at High Rates on Ventricular Action Potential and QRS Duration in Humans

Propafenone is an antiarrhythmic agent that blocks sodium channels in a frequency-dependent manner. In this study, frequency-dependent effects of intravenous propafenone on right ventricular action potential duration (APD90), QRS duration and ventricular effective refractory period (VERP)/APD90 ratio were investigated in 10 healthy subjects. Intravenous propafenone caused no significant difference in APD90 at 4 different pacing cycle lengths (600, 500, 400, 300 ms). On the other hand, a 22-24 % increase in QRS duration was seen after propafenone (p<0.05). Decreasing the pacing cycle length from 600 ms to 300 ms caused a 6.4% increase in QRS duration. Compared to baseline, this increase was not statistically significant (p>0.05). VERP/APD90 ratio increased by 4-13 % after propafenone but no frequency-dependent changes were evident in this ratio (p>0.05). In conclusion, intravenous propafenone caused no change in APD90 but led to an increase in QRS duration and VERP/APD90 ratio in 10 healthy subjects. Moreover, these changes were shown not to be frequency-dependent at the pacing cycle lengths used in this study.