USEFULNESS OF PROPAFENONE FOR SUPRAVENTRICULAR ARRHYTHMIAS IN INFANTSAND CHILDREN

The relation between propafenone dose, serum level, electrocardiograph ic parameters, antiarrhythmic drug efficacy and adverse effects was st udied in 47 children with symptomatic supraventricular arrhythmias age d 1 day to 10.3 years (median 2.2 months) with a mean follow-up of 14. 3 months. Propafenone trough serum levels were measured using gas chro matography. Oral propafenone (mean dose 353 mg/m2/day) was effective i n 41 of the 47 patients (87.2%). Serum levels did not differ between p atients responding and not responding to propafenone (0.45 +/- 0.40 vs 0.36 +/- 0.41 mg/liter). PR interval and QRS complex duration increas ed more significantly with propafenone dose increments (p <0.001), tha n with propafenone serum levels (p <0.05). At successful treatment PR interval and QRS complex were prolonged by a mean of 19.2 and 20.5% co mpared with pretreatment status. Five patients exhibited unexpected ma rked QRS complex prolongation (50 to 200%) despite low propafenone dos age (<300 mg/m2/day) and level ranging from 0.05 to 1.33 mg/liter. Thr ee patients (6.1%) were suspected of being ''poor'' metabolizers of pr opafenone. Mild chronic elevation of serum liver enzymes was observed in 5 patients treated with a larger dose (mean 448 mg/m2/day, p <0.001 ). No proarrhythmia was noted on serial Hotter monitors. One patient w ith Wolff-Parkinson-White syndrome and a normal heart had cardiac arre st after aspiration. Serial monitoring of PR interval and QRS complex duration was more useful for proper dosage adjustment than propafenone serum levels. Serum liver enzymes should be closely monitored when us ing higher propafenone doses. Malignant proarrhythmia could not be exc luded in the 1 patient with cardiac arrest.