[Should the Isuprel test be performed systematically in Wolff-Parkinson-White syndrome?]

The isoprenaline (Is) test was designed by Wellens et al. in 1982 to evaluate the effect of catecholamines on the effective refractory period (ERP) of Kent's bundle (K). The purpose of our study was to assess the value of this test in the prognosis of Wolff-Parkinson-White syndrome (WPW), to define its criteria of severity and to determine the usefulness of the test. Out of 33 patients with WPW syndrome, 10 (group I) had a clinical history of severe arrhythmia and 23 (group II) were asymptomatic or had paroxysmal nodal tachycardia. The prognosis of WPW syndrome was evaluated by measuring Kent's bundle ERP under coupled atrial stimulation (S1 S2) and the shortest cycle conducted by K during induced atrial fibrillation (AF) and atrial pacing (AP) both in the basal state (B) and under a 20-30 micrograms Is infusion. (table; see text). Analysis of the results showed constant shortening of ERP in group I and reproduction of the clinical tachycardia in 6 cases. In group II patients isoprenaline unmasked the WPW syndrome in 3 cases and reproduced the clinical tachycardia in 5 cases. The ERP of Kent's bundle evaluated by S1 S2 became smaller or equal to 220 ms in 70 p. 100 of the cases, and this shortening was not specific. The shortest cycle in AF or AP became inferior of equal to 220 ms in only 6 cases, the history being concordant with clinical findings in 4 of them. Altogether, the most reliable and simplest way of evaluating the severity of WPW syndrome is the highest frequency conducted by Kent's bundle in atrial pacing during the Is test which should be performed in all patients in view of its specificity, simplicity and safety.