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The diagnostic utility of recovery phase QTc during treadmill exercise stress testing in the evaluation of long QT syndrome

  • Justin M. Horner
    Affiliations
    Department of Pediatric and Adolescent Medicine/Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota
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  • Melissa M. Horner
    Affiliations
    Department of Pediatric and Adolescent Medicine/Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota
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  • Michael J. Ackerman
    Correspondence
    Address reprint requests and correspondence: Michael J. Ackerman, M.D., Ph.D., Long QT Syndrome Clinic and Windland Smith Rice Sudden Death Genomics Laboratory, Guggenheim 501, Mayo Clinic, Rochester, Minnesota 55905
    Affiliations
    Department of Pediatric and Adolescent Medicine/Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota

    Department of Medicine/Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota

    Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, Minnesota
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      Background

      Nearly 40% of patients with long QT syndrome (LQTS) can have a nondiagnostic QTc at rest. Treadmill and cycle exercise stress testing are used in the diagnostic evaluation of LQTS.

      Objective

      The purpose of this study was to determine the diagnostic significance of peak exercise and recovery phase QTc values during treadmill stress testing in LQTS.

      Methods

      An Institutional Review Board–approved, retrospective analysis was performed on the treadmill stress tests in 243 patients including 82 LQT1, 55 LQT2, 18 LQT3, and 88 genotype-negative patients dismissed as normal. Blinded to genotype, QTc was calculated at rest, peak exercise, and 1, 2, 3, 4, and 5 minutes of recovery.

      Results

      Compared with those dismissed as normal, the average QTc was greater at all scored stages in LQT1 and LQT3 patients and at all stages in LQT2 patients except peak exercise and 1 minute of recovery (P <.01). Either an absolute QTc ≥460 ms during the recovery phase or a maladaptive, paradoxical increase in QTc, defined as QTc recovery − QTc baseline ≥ 30 ms (ΔQTc), distinguished patients with either manifest or concealed LQT1 from all other subsets (P <.0001). The presence of beta-blockers did not blunt these abnormal repolarization profiles.

      Conclusion

      Treadmill stress testing can unmask patients with concealed LQTS, particularly LQT1, with good diagnostic accuracy.

      Keywords

      Abbreviations:

      bpm (beats per minute), ECG (electrocardiogram), LQTS (long QT syndrome)
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