title: The electrophysiological characteristics of accessory pathways in pediatric patients with intermittent preexcitation.
abstract: BACKGROUND
  Accessory pathways (APs) with intermittent preexcitation (IPX) are thought to be of lower risk, but there are reports of IPX patients presenting with rapidly conducted atrial fibrillation.
  
  
  METHODS
  Retrospective study performed on patients with preexcitation who underwent an electro-physiological study (EPS). IPX was defined as loss of the delta wave on electrocardiogram prior to EPS. Patients with IPX were compared with those with persistent preexcitation (PPX) or suppression of the delta wave on exercise test (IPX-ET). Congenital heart disease and prior ablations were excluded.
  
  
  RESULTS
  Of 328 patients with preexcitation, 41 (12.5%) had IPX. Patients with IPX or PPX were similar in age (12.9 years vs 13.0 years, P = 0.8) and AP location (left-sided 54% vs 50%, P = 0.7; septal 32% vs 35%, P = 0.4). Testing on isoproterenol was performed in 17 (41%) IPX and 41 (14%) PPX patients. Although IPX patients had a longer median refractory period compared to PPX patients (340 ms vs 310 ms, P = 0.001), the incidence of APs with refractory periods ≤250 ms was similar (10% vs 12%, P = 1.0). Exercise tests were performed on 208 patients and 24 (12%) had IPX-ET. Compared with IPX patients, IPX-ET had similar median AP refractory periods (320 ms, P = 0.4) and incidence of APs with refractory periods ≤250 ms (13%, P = 1.0).
  
  
  CONCLUSIONS
  Patients with IPX had longer AP refractory periods than those with PPX, but the incidence of pathways with refractory periods ≤250 ms was not significantly different. The finding of IPX on a baseline electrocardiogram does not rule out potentially high-risk pathways.
authors.affiliation: Department of Cardiology, Boston Children's Hospital, Boston, Massachusetts; the Department of Pediatrics, Harvard Medical School, Boston, Massachusetts.
authors.forename: Douglas Y
authors.initials: DY
authors.lastname: Mah
authors.forename: Elizabeth D
authors.initials: ED
authors.lastname: Sherwin
authors.forename: Mark E
authors.initials: ME
authors.lastname: Alexander
authors.forename: Frank
authors.initials: F
authors.lastname: Cecchin
authors.forename: Dominic J
authors.initials: DJ
authors.lastname: Abrams
authors.forename: Edward P
authors.initials: EP
authors.lastname: Walsh
authors.forename: John K
authors.initials: JK
authors.lastname: Triedman
mesh_terms: D058606:Accessory Atrioventricular Bundle / Q000175:diagnosis* / Q000401:mortality* / Q000601:surgery; D000293:Adolescent; D001900:Boston / Q000453:epidemiology; D002648:Child; D015897:Comorbidity; D004562:Electrocardiography / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D015203:Reproducibility of Results; D012307:Risk Factors; D012680:Sensitivity and Specificity; D015996:Survival Rate; D014927:Wolff-Parkinson-White Syndrome / Q000175:diagnosis* / Q000401:mortality* / Q000601:surgery
keywords: Wolff-Parkinson-White; high-risk pathway; intermittent preexcitation