title: Electromechanical coupling in patients with the short QT syndrome: further insights into the mechanoelectrical hypothesis of the U wave.
abstract: BACKGROUND
  Patients with a short QT syndrome (SQTS) are at risk of sudden cardiac death (SCD). It is not known whether abbreviation of cardiac repolarization alters mechanical function in SQTS. Controversies persist regarding whether the U wave is a purely electrical or mechanoelectrical phenomenon.
  
  
  OBJECTIVE
  The present study uses echocardiographic measurements to discriminate between the hypotheses for the origin of the U wave.
  
  
  METHODS
  Diagnostic work-up including echocardiography and electrocardiogram was performed in 5 SQTS patients (39 +/- 19 years old) from 2 unrelated families with a history of SCD and 5 age-matched and gender-matched control subjects.
  
  
  RESULTS
  QT intervals were 268 +/- 18 ms (QTc 285 +/- 28 ms) in SQTS versus 386 +/- 20 ms (QTc 420 +/- 22 ms) in control subjects (P < .005). In SQTS patients, the end of the T wave preceded aortic valve closure by 111 +/- 30 ms versus -12 +/- 11 ms in control subjects (P < .005). The interval from aortic valve closure to the beginning of the U wave was 8 +/- 4 ms in patients and 15 +/- 11 ms in control subjects (P = .25). Thus, the inscription of the U wave in SQTS patients coincided with aortic valve closure and isovolumic relaxation, supporting the hypothesis that the U wave is related to mechanical stretch.
  
  
  CONCLUSIONS
  Our data show for the first time a significant dissociation between the ventricular repolarization and the end of mechanical systole in SQTS patients. Coincidence of the U wave with termination of mechanical systole provides support for the mechanoelectrical hypothesis for the origin of the U wave.
authors.affiliation: 1st Department of Medicine-Cardiology, University Hospital Mannheim, Mannheim, Germany. rainer.schimpf@med.ma.uni-heidelberg.de
authors.forename: Rainer
authors.initials: R
authors.lastname: Schimpf
authors.forename: Charles
authors.initials: C
authors.lastname: Antzelevitch
authors.forename: Dariush
authors.initials: D
authors.lastname: Haghi
authors.forename: Carla
authors.initials: C
authors.lastname: Giustetto
authors.forename: Alfredo
authors.initials: A
authors.lastname: Pizzuti
authors.forename: Fiorenzo
authors.initials: F
authors.lastname: Gaita
authors.forename: Christian
authors.initials: C
authors.lastname: Veltmann
authors.forename: Christian
authors.initials: C
authors.lastname: Wolpert
authors.forename: Martin
authors.initials: M
authors.lastname: Borggrefe
mesh_terms: D000328:Adult; D001145:Arrhythmias, Cardiac / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016022:Case-Control Studies; D016757:Death, Sudden, Cardiac / Q000517:prevention & control*; D004452:Echocardiography; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D008297:Male; D012307:Risk Factors; D013318:Stroke Volume; D013997:Time Factors