title: Delayed paced ventricular activation in the long QT syndrome is associated with ventricular fibrillation.
abstract: BACKGROUND
  LQTS may cause sudden cardiac death (SCD), but the mechanisms linking gene mutations to ventricular fibrillation (VF) are unclear.
  
  
  OBJECTIVE
  To determine whether ventricular activation delays in congenital long QT syndrome (LQTS) are associated with VF and to describe these delays clinically by measuring activation through ventricular myocardium after a premature extrastimulus.
  
  
  METHODS
  Forty-six patients with LQTS, including 16 with VF (LQTS VF) were investigated, and the results were compared with those from 24 patients with hypertrophic cardiomyopathy and VF (HCM VF). Electrograms in response to premature stimuli were analyzed for increases in electrogram duration (DeltaED) and the S1S2 coupling intervals at which electrogram latency starts to increase (S1S2(delay)). Two piecewise continuous straight line segments were fitted to the last electrogram deflection as a function of S1S2 interval in the LQTS and HCM VF populations, and the difference in their gradient (alpha) was taken as an index of the abruptness of the onset of this delay.
  
  
  RESULTS
  Thirteen LQTS VF and six LQTS non-VF patients had values of DeltaED and S1S2(delay) comparable to those in HCM VF patients, while the remainder (three LQTS VF and 24 LQTS non-VF) had lower values (P<.001). There was only a weak correlation between delay and the corrected QT interval. The HCM and LQTS VF patients could be separated by the value of alpha (P<.01), with the LQTS patients having a more abrupt onset of delay.
  
  
  CONCLUSIONS
  Large delays in ventricular activation after an extrastimulus occur in patients with the LQTS, especially those with VF. The change in delay is abrupt in the LQTS, indicating sudden block to activation creating a dynamic substrate for arrhythmogenesis.
authors.affiliation: Department of Cardiology, Papworth Hospital, Cambridge, United Kingdom. ag@mole.bio.cam.ac.uk
authors.forename: Richard C
authors.initials: RC
authors.lastname: Saumarez
authors.forename: Mariusz
authors.initials: M
authors.lastname: Pytkowski
authors.forename: Maciej
authors.initials: M
authors.lastname: Sterlinski
authors.forename: Richard N W
authors.initials: RN
authors.lastname: Hauer
authors.forename: Richard
authors.initials: R
authors.lastname: Derksen
authors.forename: Martin D
authors.initials: MD
authors.lastname: Lowe
authors.forename: Hannah
authors.initials: H
authors.lastname: Szwed
authors.forename: Christopher L-H
authors.initials: CL
authors.lastname: Huang
authors.forename: David E
authors.initials: DE
authors.lastname: Ward
authors.forename: A John
authors.initials: AJ
authors.lastname: Camm
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Grace
mesh_terms: D000293:Adolescent; D000328:Adult; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects*; D002648:Child; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008133:Long QT Syndrome / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D014693:Ventricular Fibrillation / Q000209:etiology* / Q000503:physiopathology