APPARENT BRADYCARDIA-DEPENDENT BLOCK IN THE ACCESSORY PATHWAY IN INTERMITTENT WOLFF-PARKINSON-WHITE-SYNDROME

A case of intermittent Wolff-Parkinson-White syndrome is reported, whi ch is the first report of an apparent bradycardia-dependent block in t he accessory pathway. When the P-P interval gradually lengthened to a critical value of 0.89 second or more, preexcitation Failed to occur, but thereafter, when the P-P interval gradually shortened to 0.89 seco nd or less, preexcitation again occurred. These findings seem to sugge st that bradycardia-dependent block occurred in the accessory pathway. In the electrocardiogram taken on another day, however, when a ventri cular extrasystole was followed by a compensatory pause, the ensuing Q RS complex showed preexcitation, although the pause was markedly longe r than the critical period of 0.89 second. This indicates that this ca se is not one of true bradycardia-dependent block in the accessory pat hway. Rather, the effect occurred because increased vagal tone depress ed conductivity in the accessary pathway to a greater degree than auto maticity in the sinus node.