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Heart rate and intermittent Wolff-Parkinson-White syndrome.

Five cases of intermittent Wolff-Parkinson-White (WPW) syndrome are described. Two cases showed a tendency to become normal during acceleration. In these cases, however, short PP intervals (in comparison to longer ones in their proximity) were followed by WPW complexes. In another case constant WPW syndrome appeared during acceleration. A fourth case presented with intermittent WPW complexes while the rate was constant. In a fifth case WPW was converted into normal during acceleration on one occasion, while on another occasion AV dissociation with WPW appeared. An explanation for these peculiarities is proposed. The accelerating factor may affect the idiofrequency of the three structures, i.e. sinus node, AV node, and the abnormal bundle, in the same direction but to a different degree. The pacing factor is the fastest of the three and conduction takes place through synchronization at a phase difference via the structure whose idiofrequency (as affected by the chronotropic factor) is closest to that of the pacemaker.