Patruno N, Critelli G, Pulignano G, Urbani P, Villanti P, Reale A. Cardiologia 1989 Sep;34(9):777-81. Noninvasive assessment of the conducting capability of the accessory pathway (AP) in asymptomatic patients with a preexcitation ECG pattern is desirable, since life-threatening arrhythmias and sudden death may be the first manifestation of the Wolff-Parkinson-White (WPW) syndrome. To investigate whether in patients with preexcitation ECG pattern the absence of clinical arrhythmias excludes the potential for rapid ventricular responses, transesophageal atrial pacing (TAP) was performed in 11 subjects (9 male, 2 female), aged 5 to 43 years. The extrastimulus technique was used in order to define the refractory periods and in the attempt to induce reciprocating tachycardia. Incremental TAP up to the occurrence of block in the AP was instituted, and attempts to induce atrial fibrillation (AF) with rapid burst pacing were made. One to one atrioventricular conduction over the AP at progressively increased cycle lengths (CLs), and the shortest R-R interval between pre-excited beats during induced AF were evaluated. The following findings were considered predictors of potential life-threatening arrhythmias: 1) anterograde refractory period of the AP equal to or shorter than 250 ms; 2) one to one AP conduction at CLs shorter than 300 ms; 3) shortest R-R interval, during induced AF, less than 250 ms. Sustained reciprocating tachycardia could not be induced in all patients in spite of the use of the use of an aggressive stimulation protocol. The anterograde refractory period of the AP could not be defined in 9 patients. In the remaining 2 this parameter was longer than 250 ms. In 8 patients (72%), the shortest CL maintaining 1:1 AP conduction ranged from 220 to 280 ms (mean 253 +/- 19).