Augmented preexcitation assessed by scintigraphic phase analysis during atrial pacing

To assess the ability of phase analysis to demonstrate changes in the degrees of preexcitation(P), blood pool scintigraphy was performed at rest and with atrial pacing(AP) in 9 patients(PTS) with WPW and normal ventricular function. There were 6 PTS with left lateral and 3 with right lateral bypass pathways(BP) confirmed on electrophysiologic study(EPS). In 6 PTS with minimal P at rest, ventricular phase patterns were symmetrical and earliest phase single(PA) occurred simultaneously in the septum and at the site of the BP. The site of earliest PA in the remaining PTS occurred at the BP with a difference in mean ventricular PA of 5.2/sup 0/. Additionally, PA moved the site of latest PA the site of ''fusion,'' away from the BP again consistent with augmented P, and widened the QRS complex from a mean of .10 to .12 secs. Phase analysis can demonstrate dynamic changes in the level of P and may complement EPS in the evaluation of these disorders.