Burst bicycle exercise facilitates diagnosis of latent long QT syndrome.
OBJECTIVE
The aim of this study was to develop a diagnostic technique to detect latent long QT syndrome.


BACKGROUND
Asymptomatic patients with genetically diagnosed long QT syndrome (LQTS) may have a normal resting QT interval, yet remain at risk for cardiac events. We hypothesized that the QT response during a novel burst exercise protocol simulating clinical events might distinguish patients with "latent LQTS" from healthy subjects.


METHODS
A burst bicycle protocol was performed on 31 healthy subjects and 31 patients with LQTS (13 LQT2, 3 LQT1, 15 unknown genotype). The bicycle exercise protocol involved sudden maximal exertion against a fixed workload (200 W) for 1 minute. Digitized 12-lead eletrocardiograms were acquired every 10 seconds at baseline for 1 minute, during 1 minute of burst exercise, and for 5 minutes during recovery. Patients with LQTS were segregated according to whether the baseline QTc was normal (< or = 440 milliseconds, n = 13) or abnormal (> 440 milliseconds, n = 18).


RESULTS
During exercise, the QTc increased to a greater extent in the group with latent LQTS (DeltaQTc 98 +/- 36 milliseconds) in comparison with controls (DeltaQTc 65 +/- 19 milliseconds, P < .01) and those with baseline QTc prolongation (DeltaQTc 17 +/- 70 milliseconds, P < .01). In patients with a normal baseline QTc, a DeltaQTc > 85 milliseconds had a sensitivity of 85% and a specificity of 86% for LQTS (P = .0004).


CONCLUSIONS
Marked QTc prolongation during burst bicycle ergometry provides potentially diagnostic information for patients with normal baseline QTc and suspected LQTS.
Walker
Bruce D
BD
Division of Cardiology, University of Western Ontario, London, Ontario, Canada.
Krahn
Andrew D
AD
Klein
George J
GJ
Skanes
Allan C
AC
Yee
Raymond
R
D000328:Adult; D005080:Exercise Test / Q000379:methods; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis*; D008297:Male