Accurate electrocardiographic assessment of the QT interval: teach the tangent

Heart Rhythm. 2008 Jul;5(7):1015-8. doi: 10.1016/j.hrthm.2008.03.037. Epub 2008 Apr 1.


Background: Long QT-Syndrome (LQTS) is a prevalent and possibly lethal disease. Unfortunately, it has recently been shown that the majority of physicians, including many cardiologists, do not recognize a long QT interval when they see one. Conversely, almost 40% of patients referred to specialized centers with a presumed diagnosis of LQTS have a normal QT.

Objective: The purpose of this study was to investigate whether we are able to teach inexperienced electrocardiogram (ECG) readers a method that will result in a higher accuracy of QT measurements.

Methods: Four previously published ECGs (two LQTS, two normal) were assessed by 151 medical students using the following QT measurement method: (1) the end of the T wave is the intersection of a tangent to the steepest slope of the last limb of the T wave and the baseline, in lead II or V5; (2) QTc = QT/ radicalRR; (3) QTc>450 ms is prolonged. Four months later, 71 students measured the ECGs again. Student results were compared with previously published results on the same ECGs of 25 LQTS experts, 106 arrhythmia experts, and 771 cardiologists and noncardiologists.

Results: Correct QT interval interpretations were achieved by 71% and 77% of students during the first and second test, respectively, as compared with 62% by the arrhythmia experts and <25% by the cardiologists and noncardiologists.

Conclusions: In this proof-of-principle study, inexperienced ECG readers were able to rather accurately and reproducibly diagnose prolonged and normal QT intervals on four ECGs, as opposed to 877 cardiologists and noncardiologists. If the presented method is used by physicians, a better stratification of their patients' risk for sudden death due to LQTS (drug induced or congenital) should be possible.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Death, Sudden, Cardiac / etiology*
  • Electrocardiography*
  • Female
  • Heart Conduction System / physiopathology
  • Humans
  • Long QT Syndrome / complications*
  • Long QT Syndrome / diagnosis*
  • Male
  • Reproducibility of Results
  • Risk Assessment