Signal averaging in Wolff-Parkinson-White syndrome: Evidence that fractionated activation is not necessary for body surface high frequency potentials

It is commonly assumed that the presence of high frequency components in bo dy surface potentials implies that fractionated activation fronts, caused b y heterogeneously viable tissue, are present in the heart. However, if is p ossible that non-fractionated activation fronts can also give rise to high frequency surface potentials and that the relative amount of high frequency power is related to the complexity of the activation sequence. In a test o f this idea, averaged body surface potentials were recorded during the enti re QRS complex of nine Wolff-Parkinson-White (WPW) patients in situations i n which fractionated activation fronts should not have been present, but wh ich represent increasing degrees of complexity of ventricular activation: ( 1) postoperative ectopic pacing from subepicardial wires placed during surg ery, when a single coherent activation front was present throughout most of the QRS; (2) Preoperative preexcited rhythm, when a single coherent activa tion front was present for one portion of the QRS (the delta wave); and (3) postoperative normal rhythm, when two or more activation fronts were prese nt in the ventricles throughout most of the QRS. For comparison, averaged b ody surface potentials were also analyzed during the last 40 ms of the QRS complex and the ST segment of 14 postinfarction patients with chronic ventr icular tachycardia. In the patients with WPW syndrome, relatively high freq uency content increased (attenuation -36.7 vs -27.2 vs -18.3 dB) and QRS wi dth decreased (160.7 vs 125.9 vs 94.1 ms) significantly from paced to preop erative to postoperative beats. Significant high frequency content was pres ent in all cases, showing that coherent activation fronts can give rise to high frequencies. interestingly, the postoperative QRS of WPW patients cont ained a larger proportion of high frequency power than did the late potenti als of the patients with ventricular tachycardia. Thus, while the presence of late fractionated body surface potentials may be a marker for ventricula r tachycardia, these potentials by themselves do not necessarily signify th at the underlying cardiac activation giving rise to these signals is fracti onated.