Which electrocardiographic (ECG) findings suggest long QT syndrome (LQTS)?

Updated: Nov 29, 2017
  • Author: Ali A Sovari, MD, FACP, FACC; Chief Editor: Mikhael F El-Chami, MD  more...
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As the criteria for long QT syndrome (LQTS) by Schwartz et al suggest, the most helpful electrocardiographic (ECG) findings are prolongation of the QT interval, the presence of torsade de pointes, the presence of T-wave alternans, and the presence of certain morphology of the T waves (wide-based T wave, and notched T wave in three leads).

Correlation between the type of mutation and T-wave morphology has been suggested. Wide-based T waves are most frequently seen in LQT1, whereas notched T waves are most commonly seen in LQT2. In LQT3, T waves may appear normal, with a long, isoelectric ST segment.

T-wave analysis also appears to have the potential to differentiate acquired QT prolongation from congenital LQTS, [21]  as well as help identify on-therapy breakthrough arrhythmic risk in LQT1 and LQT2. [22]  Using an automated T-wave analysis program to retrospectively evaluate 12-lead ECGs of 38 patients with congenital LQTS and 114 patients with drug-induced and/or electrolyte-mediated QT prolongation, Sugrue et al noted the following differences in lead V5 of those with acquired QT prolongation could distinguish these individuals from patients with congenital LQTS in 77% of cases (90% sensitivity, 58% specificity) [21] :

  • Shallower T-wave right slope
  • Larger T-peak to T-end interval
  • Smaller T-wave center of gravity on the x axis

The same investigators used a T-wave analysis program to evaluate ECGs from 407 genetically confirmed patients with LQT1 (n = 246) and LQT2 (n = 161) over a mean follow-up of 6.4 ± 3.9 years and found two independent predictors of future LQTS-associated cardiac events were left slope of T waves in lead V6 and a T-wave center of gravity on the x axis in lead I, particularly in patients with LQTS2. [22]

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