Effect of atropine and isoproterenol on tachycardia induction in asymptomatic patients with Wolff-Parkinson-White electrocardiographic pattern.

OBJECTIVE

To determine if pharmacological interventions aimed at altering autonomic tone would allow induction of orthodromic atrioventricular reentrant tachycardia in asymptomatic patients with the Wolff-Parkinson-White electrocardiographic pattern.

DESIGN

Prospective interventional protocol in consecutive eligible patients.

SETTINGS

University hospital.

PATIENTS

Eighteen asymptomatic patients (13 male and five female) with the Wolff-Parkinson-White electrocardiographic pattern without inducible tachycardia in the drug-free state.

INTERVENTION

Electrophysiological assessment was performed at baseline, after intravenous administration of atropine (0.03 mg/kg) and during isoproterenol infusion (0.5 to 2 micrograms/min).

RESULTS

Orthodromic reciprocating tachycardia was not inducible at baseline because of absent retrograde accessory pathway conduction in seven patients. In five patients, orthodromic atrial echo beats could be induced (which blocked retrogradely in the accessory pathway in three patients and anterogradely in the atrioventricular node in two). In the remaining six patients, neither orthodromic echo beats nor reciprocating tachycardia could be induced despite intact retrograde accessory pathway conduction. Following atropine administration (mean dose 1.9 +/- 0.3 mg), anterograde and retrograde accessory pathway effective refractory periods decreased from 360 +/- 172 to 284 +/- 62 ms and from 340 +/- 38 to 296 +/- 32 ms, respectively (both P < 0.05 versus control). Orthodromic reciprocating tachycardia was induced in two patients (nonsustained in one). During isoproterenol infusion (mean dose 1.0 +/- 0.3 micrograms/min), anterograde and retrograde accessory pathway effective refractory periods decreased further to 243 +/- 23 and 248 +/- 22 ms, respectively (both P < 0.05 versus after atropine); two further patients had inducible orthodromic reciprocating tachycardia (nonsustained in one). No patient with absent retrograde accessory pathway conduction developed retrograde accessory pathway conduction or reciprocating tachycardia with isoproterenol and/or atropine.

CONCLUSIONS

Isoproterenol and/or atropine allowed tachycardia induction in four of 18 asymptomatic patients with the Wolff-Parkinson-White electrocardiographic pattern. In the majority of these patients, tachycardia is not inducible because of deficient retrograde accessory pathway conduction which does not improve with autonomic facilitation.