[Prograde conduction of the pathway in pre-excitation syndrome may shorten PJ interval]

To investigate whether the PJ interval in the patients with pre-excitation syndrome can be shortened by pathway conduction, and to explore the clinical implications of the prolonged PJ interval.

143 patients with single pathway, who experienced successful radiofrequency (RF) ablation, were divided into two groups: Group A (n = 132) with normal atrioventricular and ventricular conduction (sub-divided into 10 subsets further according to the location of the pathway) and Group B (n = 11) with first degree atrioventricular block or with bundle branch block. The ECG images with and without pathway conduction were analyzed.

(1) The PJ interval in the patients with right posterior pathway or with right septal pathway was shortened significantly after the RF [(226 +/- 18) ms vs (236 +/- 19) ms and (221 +/- 18) ms vs (238 +/- 31) ms respectively, both P < 0.05 ]; (2) The PJ interval in Group B was shortened to different extents. The PJ interval values in 4 patients with first degree atrioventricular block were shortened, but still beyond normal extent. The PJ interval values in 4 patients with bundle branch block were shortened to normal extent.

If the pre-excitation syndrome patients have normal atrioventricular conduction the PJ interval is normal or the PJ interval may be shortened. If the patients have prolonged atrioventricular conduction, the PJ interval may be shortened by the pathway prograde conduction. PJ interval prolongation indicates atrioventricular conduction delay or ventricular conduction block, but bundle branch block cannot be excluded when the PJ interval is normal.