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  • Title: Utility of the recovery electrocardiogram after exercise: a novel indicator for the diagnosis and genotyping of long QT syndrome?
    Author: Chattha IS, Sy RW, Yee R, Gula LJ, Skanes AC, Klein GJ, Bennett MT, Krahn AD.
    Journal: Heart Rhythm; 2010 Jul; 7(7):906-11. PubMed ID: 20226272.
    Abstract:
    BACKGROUND: Exercise testing has shown modest utility in the ability to diagnose and genotype long QT syndrome (LQTS). Although numerous small studies have shown a genotype-specific repolarization response to exercise, the repolarization responses during recovery from exercise have received less focus. OBJECTIVE: The purpose of this study was to characterize genotype-specific QT responses during recovery from exercise and to determine its potential as a diagnostic and genotyping tool. METHODS: Seventy-five patients were age and sex matched into three groups (n = 25): LQT1, LQT2, and unaffected controls based on Schwartz score and genetic testing results. Each group underwent upright burst and gradual bicycle exercise testing while being monitored by 12-lead electrocardiogram. RESULTS: LQT1 patients had significantly longer corrected QT (QTc) than LQT2 intervals during early recovery (P <.01). Control subjects showed little variation in QTc throughout the recovery period, maintaining a QTc within normal limits. Each group showed a distinct pattern of QTc adaptation during recovery. LQT1 patients began the recovery period at a QTc of 492 +/- 11 ms, after which the QTc decreased by 33 +/- 11 ms during recovery. Conversely, the LQT2 patients began recovery at its lowest mean QTc of 420 +/- 10 ms, which increased by 40 +/- 16 ms. At the end of recovery, a QTc cut-off value of 445 ms distinguished 92% of LQTS patients from unaffected controls, while a start-of-recovery QTc cut-off of 460 ms correctly identified genotype in 80% of LQT1 and 92% of LQT2 patients. CONCLUSIONS: Genotype-specific differences exist in QT recovery after exercise. These differences can help to identify LQTS patients and distinguish LQT1 from LQT2 genotypes.
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