Differential diagnosis between LQT1 and LQT2 by QT/RR relationships using 24‐hour Holter monitoring: A multicenter cross‐sectional study

Abstract

Abstract Background The clinical course and therapeutic strategies in the congenital long QT syndrome (LQTS) are genotype‐specific. However, accurate estimation of LQTS genotype is often difficult from the standard 12‐lead ECG. Objectives This study aims to evaluate the utility of QT/RR slope analysis by the 24‐hour Holter monitoring for differential diagnosis of LQTS genotype between LQT1 and LQT2. Methods This cross‐sectional study enrolled 54 genetically identified LQTS patients (29 LQT1 and 25 LQT2) recruited from three medical institutions. The QT‐apex (QTa) interval and the QT‐end (QTe) interval at each 15‐second were plotted against the RR intervals, and the linear regression (QTa/RR and QTe/RR slopes, respectively) was calculated from the entire 24‐hour and separately during the day or night‐time periods of the Holter recordings. Results The QTe/RR and QTa/RR slopes at the entire 24‐hour were significantly steeper in LQT2 compared to those in LQT1 patients (0.262 ± 0.063 vs. 0.204 ± 0.055, p = .0007; 0.233 ± 0.052 vs. 0.181 ± 0.040, p = .0002, respectively). The QTe interval was significantly longer, and QTe/RR and QTa/RR slopes at daytime were significantly steeper in LQT2 than in LQT1 patients. The receiver operating curve analysis revealed that the QTa/RR slope of 0.211 at the entire 24‐hour Holter was the best cutoff value for differential diagnosis between LQT1 and LQT2 (sensitivity: 80.0%, specificity: 75.0%, and area under curve: 0.804 [95%CI = 0.68–0.93]). Conclusion The continuous 24‐hour QT/RR analysis using the Holter monitoring may be useful to predict the genotype of congenital LQTS, particularly for LQT1 and LQT2.

Keywords

• ECG
• Holter monitoring
• long QT syndrome
• QQ/RR relationships