title: Positive head-up tilt table test in patients with the long QT syndrome.
abstract: OBJECTIVE
  Syncope in patients with the long QT syndrome is commonly attributed to a ventricular arrhythmia (torsades de pointes). The susceptibility of patients with the long QT syndrome (LQTS) to neurally mediated syncope is currently unknown.
  
  
  RESULTS
  Head-up tilt table testing (70 degrees) was performed in six patients with the long QT syndrome and a history of syncope. All patients had syncope with a mixed response. The RR interval was significantly decreased 2 min before the onset of syncope (980 +/- 125 ms vs 630 +/- 91 ms, P=0.003), and significantly increased during syncope (983.17 +/- 224.71; P=0.006). Non-significant changes in QT intervals were observed. Baseline QT was 513 +/- 86 ms and decreased to 450 +/- 59 ms 2 min before the onset of syncope (P=0.11). Although not statistically significant, QT intervals during syncope were longer than at 2 min before syncope (485 +/- 85 ms vs 450 +/- 59 ms; P=0.29).
  
  
  CONCLUSIONS
  Our results suggest that patients with the LQTS are susceptible to neurally mediated syncope. Whether this susceptibility differs from control populations remains unresolved. From a clinical standpoint, neurocardiogenic syncope should be considered a diagnostic alternative in patients with LQTS.
authors.affiliation: Department of Electrophysiology, Instituto Nacional de Cardiologia Ignacio Chávez, Mexico City, Mexico.
authors.forename: A G
authors.initials: AG
authors.lastname: Hermosillo
authors.forename: J C
authors.initials: JC
authors.lastname: Falcón
authors.forename: M F
authors.initials: MF
authors.lastname: Márquez
authors.forename: D
authors.initials: D
authors.lastname: Arteaga
authors.forename: M
authors.initials: M
authors.lastname: Cárdenas
mesh_terms: D000293:Adolescent; D002648:Child; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008133:Long QT Syndrome / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D019462:Syncope, Vasovagal / Q000150:complications / Q000503:physiopathology*; D018667:Tilt-Table Test