Augmented preexcitation assessed by scintigraphic phase analysis during atrial pacing

Abstract We sought to characterize the effect of augmented preexcitation on the phase image pattern associated with scintigraphic acquisition during conduction via accessory arteriovenous connections. For this reason we assessed phase image scintigraphy, acquired in sinus rhythm and during rapid atrial pacing in 12 patients with documented right (five patients) or left (seven patients) lateral accessory pathways. Augmented preexcitation during atrial pacing was documented at electrophysiologic study in all patients during atrial pacing at similar rates. Phase analysis was abnormal in only 8 patients during sinus rhythm but in all 12 patients during atrial pacing. Atrial pacing brought a significant delay in both mean left and right ventricular phase angles, LVφ and RVφ, respectively. With atrial pacing, the site of earliest phase angle, interpreted to indicate the site of earliest excitation, shifted to the site of the accessory pathway. There was increased relative “prematurity” of the mean phase angle of the ipsilateral ventricle and an absolute increase in the difference between mean and earliest left and right ventricular phase angles, Δφ (LV-RV) and Δ φ 0 (LV-RV), respectively. In patients with right-sided pathways, Δφ (LV-RV) increased from 9.5 ± 12.6 degrees to 47.9 ± 22.8 degrees, whereas Δ φ 0 (LV-RV) increased from 28.1 ± 18.0 degrees to 67.6 ± 25.0 degrees (both p φ 0 (LV-RV) decreased from 3.4 ± 14.2 degrees to −27.4 ± 17.9 degrees (both p