IntroductionIntermittent pre-excitation (I-PX) in patients with Wolff Parkinson White syndrome (WPW) is thought to indicate low risk of a life-threatening event (LTE), which is reflected by recent guidelines. We sought to determine if I-PX is associated with a lower incidence of a high-risk accessory pathway (AP).MethodsUsing an international, multicenter database of young WPW subjects (<25yrs) with and without LTE (sudden death SD, aborted SD, or pre-excited atrial fibrillation PAF), we analyzed clinical and electrophysiology study (EPS) data. Subjects were classified as having I-PX or persistent pre-excitation (P-PX). I-PX was defined as loss of pre-excitation on ECG, Holter, or exercise stress testing. A high-risk AP was defined as having any one high-risk EPS characteristicAP effective refractory period (APERP), shortest pre-excited R-R interval (SPERRI), or shortest paced pre-excited cycle length (SPPCL) ≤ 250ms.ResultsOf the 776 WPW subjects evaluated, 151 had I-PX and 625 had P-PX. There were no differences in mean age at EPS (13.7 vs 13.4 yrs, p=0.399) or sex (57% vs 59% male, p=0.640). There was no difference in incidence of LTE in the I-PX and P-PX groups (8% vs 5%, p=0.242). LTE occurred in 12 subjects with I-PX1 with aborted SD, 5 with PAF and SPERRI <240ms, and 6 with PAF and SPERRI ≥240ms or unknown SPERRI. AP characteristics were assessed at EPS in 138 (91%) and 583 (93%) patients with I-PX and P-PX, respectively. Patients with I-PX had longer mean APERP (316±55 vs 305±53ms, p=0.034) and SPPCL (338±85 vs 308±72ms, p=0.001), with no difference in SPERRI (289±65 vs 314±77ms, p=0.138) compared to P-PX. The incidence of high-risk APs in I-PX and P-PX groups was similar (20% vs 27%, p=0.120) at baseline. AP characteristics were assessed on isoproterenol in 44/138 (32%) of I-PX and in 131/583 (22%) of P-PX patients and there were no differences in APERP (271±38 vs 263±45 ms, p=0.381), SPERRI (276±41 vs 294±47ms, p=0.382), or SPPCL (276±62 vs 256±51ms, p=0.082) between groups. On isoproterenol, there was a lower incidence of high-risk APs for patients with I-PX compared to P-PX (41 vs 64%, p=0.007).ConclusionsYoung patients with WPW and I-PX are at risk of LTE. I-PX does not indicate a lower frequency of high-risk APs as compared to P-PX.