Twenty-four patients aged 10.1 +/- 4.5 (mean +/- SD) years with recurrent
paroxysmal supraventricular tachycardia underwent an electrophysiological study. Eleven patients had an overt and seven had a concealed accessory connection; six patients had no accessory connection. An orthodromic
reciprocating tachycardia was inducible in 17 of 18 patients with an accessory connection, and an
atrioventricular nodal reentrant tachycardia was inducible in four of six patients without accessory connection. After administration of
propafenone, the sinus cycle length decreased. Intra-arterial, intranodal, and His-ventricle intervals and QRS duration increased. The atrial and ventricular effective refractory periods and anterograde and retrograde effective refractory periods of the atrioventricular node increased. The cycle length at which nodal second-degree block occurred increased. Of 18 patients with accessory connection,
propafenone prolonged retrograde conduction in all, blocked anterograde conduction in five, and prolonged it in six. The
drug terminated the orthodromic
reciprocating tachycardia in all 17 patients and the
atrioventricular nodal reentrant tachycardia in three of four patients. In three of four patients with
atrioventricular nodal reentrant tachycardia and in 15 of 17 patients with orthodromic
reciprocating tachycardia, the
tachycardia was no longer inducible or nonsustained after
propafenone. A follow-up of 26 +/- 10 months revealed that the
drug when orally administered to all patients prevented recurrences of
tachycardia in 15 of 18 patients with and in four of six patients without accessory connection. The results of short-term
drug testing with
propafenone predict the response to long-term oral
therapy with this
drug.