title: Ventricular repolarization and heart rate responses during cardiovascular autonomic function testing in LQT1 subtype of long QT syndrome.
abstract: BACKGROUND
  In the most prevalent LQT1 form of inherited long QT syndrome symptoms often occur during abrupt physical or emotional stress. Sympathetic stimulation aggravates repolarization abnormalities in experimental LQT1 models. We hypothesized that autonomic function tests might reveal the abnormal repolarization in asymptomatic LQT1 patients.
  
  
  METHODS
  We measured heart rates (HRs) and QT intervals in nine asymptomatic carriers of a C-terminal KCNQ1 mutation and 8 unaffected healthy subjects using an approach of global QT values derived from 28 simultaneous electrocardiographic leads on beat-to-beat base during Valsalva maneuver, mental stress, sustained handgrip, and light supine exercise.
  
  
  RESULTS
  LQT1 patients exhibited impaired shortening of both QTpeak and QTend intervals during autonomic interventions but exaggerated lengthening of the intervals--a QT overshoot--during the recovery phases. The number of tests with a QT overshoot was 2.4 +/- 1.7 in LQT1 patients and 0.8 +/- 0.7 in unaffected subjects (P = 0.02). Valsalva strain prolonged T wave peak to T wave end interval (TPE) in LQT1 but not in unaffected patients. LQT1 patients showed diminished HR acceleration in response to adrenergic challenge whereas HR responses to vagal stimuli were similar in both groups.
  
  
  CONCLUSIONS
  Standard cardiovascular autonomic provocations induce a QT interval overshoot during recovery in asymptomatic KCNQ1 mutation carriers. Valsalva maneuver causes an exaggerated fluctuation of QT and TPE intervals partly explaining the occurrence of cardiac events during abrupt bursts of autonomic activity in LQT1 patients.
authors.affiliation: Department of Cardiology, Helsinki University Hospital, Helsinki, Finland. petri.haapalahti@hus.fi
authors.forename: Petri
authors.initials: P
authors.lastname: Haapalahti
authors.forename: Matti
authors.initials: M
authors.lastname: Viitasalo
authors.forename: Merja
authors.initials: M
authors.lastname: Perhonen
authors.forename: Markku
authors.initials: M
authors.lastname: Mäkijärvi
authors.forename: Heikki
authors.initials: H
authors.lastname: Väänänen
authors.forename: Lasse
authors.initials: L
authors.lastname: Oikarinen
authors.forename: Anna-Mari
authors.initials: AM
authors.lastname: Hekkala
authors.forename: Yrjö
authors.initials: Y
authors.lastname: Salorinne
authors.forename: Heikki
authors.initials: H
authors.lastname: Swan
authors.forename: Lauri
authors.initials: L
authors.lastname: Toivonen
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology; D002319:Cardiovascular System / Q000503:physiopathology; D004594:Electrophysiology; D006339:Heart Rate; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D029597:Romano-Ward Syndrome / Q000503:physiopathology*