Evaluation of noninvasive tests for identifying patients with preexcitation syndrome at risk of rapid ventricular response.

Intermittent preexcitation, block in the accessory pathway after intravenous injection of ajmaline or procainamide, and block in the accessory pathway during exercise usually exclude a short antegrade refractory period of an accessory pathway in patients with the Wolff-Parkinson-White syndrome. This report describes three patients with these findings suggestive of a relatively long antegrade effective refractory period of the accessory pathway in whom life-threatening ventricular response occurred during atrial fibrillation. In the first patient with a pattern of intermittent preexcitation, rapid ventricular response with wide QRS was present during atrial fibrillation. In the second patient in whom preexcitation disappeared after intravenous injection of ajmaline or procainamide as well as during exercise testing, atrial pacing showed 1:1 conduction over the accessory pathway at a cycle length of 220 msec and the shortest R-R interval during induced atrial fibrillation was 190 msec. The third patient, with no evidence of preexcitation during sinus rhythm, presented antidromic reciprocating tachycardia and atrial fibrillation with life-threatening ventricular response, the minimal R-R interval being 220 msec. Noninvasive tests in the preexcitation syndrome lack sufficient prognostic sensitivity. The evaluation of ventricular response during induced atrial fibrillation represents the most reliable means of identifying such patients at risk.