title: Pacing-induced increase in QT dispersion predicts sudden cardiac death following cardiac resynchronization therapy.
abstract: OBJECTIVE
  This study was designed to determine whether cardiac resynchronization therapy (CRT) by means of biventricular pacing (BiVP) alters the QT interval (QT(c)) and QT dispersion (QTD), and whether such changes relate to the risk of developing major arrhythmic events (MAE).
  
  
  BACKGROUND
  Prolonged QT(c) is associated with MAE. Left ventricular pacing and BiVP alter QT(c).
  
  
  METHODS
  A total of 75 patients with drug-resistant heart failure (New York Heart Association functional class III/IV) and QRS duration > or =120 ms underwent CRT. The QT(c) and QTD were measured before and 48 days after BiVP.
  
  
  RESULTS
  Over 807 days (range 93 to 1,543 days), 11 patients had a MAE. Compared to baseline, at 48 days after CRT, QTD increased in 47% of patients and QT(c) decreased in 53%. The QT(c) at follow-up was higher in MAE patients compared with no-MAE patients (35.9 +/- 14.2 ms vs. 0.52 +/- 6.0 ms; p = 0.0323). Similar differential responses for QTD were observed (46.4 +/- 13.5 ms in MAE vs. -5.1 +/- 4.1 ms in no MAE, p < 0.0001). The MAE occurred in 29% of patients exhibiting an increase in QTD and in 3% of those exhibiting a decrease (p = 0.0017). In multiple regression analyses, change in QTD from baseline (DeltaQTD) strongly predicted MAE, independent of DeltaQT(c), QRS duration, and left ventricular ejection fraction and end-diastolic volume (p < 0.001). Differences in survival curves were observed when patients were dichotomized according to whether QTD increased or decreased in relation to baseline values (p < 0.0001).
  
  
  CONCLUSIONS
  The MAE in patients with BiVP are related to pacing-induced increases in QTD. Measures of ventricular repolarization at the time of pacemaker implantation may guide selection of patients for combined CRT and defibrillator therapy.
authors.affiliation: Department of Cardiology, Good Hope Hospital, Sutton Coldfield, West Midlands, United Kingdom.
authors.forename: Shajil
authors.initials: S
authors.lastname: Chalil
authors.forename: Zaheer R
authors.initials: ZR
authors.lastname: Yousef
authors.forename: Sarkaw A
authors.initials: SA
authors.lastname: Muyhaldeen
authors.forename: Russell E A
authors.initials: RE
authors.lastname: Smith
authors.forename: Paul
authors.initials: P
authors.lastname: Jordan
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Gibbs
authors.forename: Francisco
authors.initials: F
authors.lastname: Leyva
mesh_terms: D000368:Aged; D001145:Arrhythmias, Cardiac / Q000150:complications* / Q000503:physiopathology / Q000628:therapy*; D002304:Cardiac Pacing, Artificial; D016757:Death, Sudden, Cardiac / Q000209:etiology*; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D011379:Prognosis; D012307:Risk Factors