Utility of treadmill testing and DCG in diagnosis of long QT syndrome

Background The hereditary long QT syndrome (LQTS) is a genetic channalopathy that is characterised by a prolonged QT interval, syncope, ventricular arrhythmias, and sudden death. The clinical diagnosis of LQTS remains challenging when ECG abnormalities are borderline or intermittent. And although genetic testing remains the diagnostic gold standard, it is not readily available. Evaluation of the rate adaptation of QT intervals may help in establishing the diagnosis of LQTS. Objective To investigate whether treadmill test and dynamic electrocardiogram (DCG) could help to identify LQTS patients and distinguish LQT1 from LQT2 genotypes. Methods Treadmill test group: a modified Bruce protocol treadmill exercise test was performed in 45 healthy subjects and 18 patients with LQTS (15 LQT2, 3 LQT1), with ECGs recorded at the end of every Bruce protocol level during exercise, at peak exercise, and at 2 min intervals during the recovery phase. The QT intervals, QTa intervals, T peak to T end intervals (Tp-Te intervals) and QT dispersion were measured at these ECGs. Rate adaptation of QT was studied as QT/heart rate slopes. Dynamic electrocardiogram group: DCGs were performed in 26 healthy subjects and 27 patients with LQTS (19 LQT2, 7 LQT1, 1LQT3). The QT intervals and Tp-Te intervals were measured at the maximal, minimal and mean heart rate. Result Treadmill test group: (A) LQTS patients had significantly longer QT intervals and corrected QT (QTc) than healthy subjects through exercise and recovery period (p Conclusion During exercise period, QT intervals shortened sufficiently in LQTS patients as with healthy subjects, which was consistent with LQT2 subtype. The QT/heart rate slopes were steeper in LQT2 patients than in LQT1 patients during exercise, which revealed the severe defect of repolarisation reverse in LQT1 patients, and the two group showed a distinct pattern of QT adaptation during recovery. QTa, Tp-Te intervals and QTd facilitated diagnosing and genotyping LQTS.