QT Dynamics During Exercise in Asymptomatic Children with Long QT Syndrome Type 3

Abstract

Sympathetic provocative testing is commonly used to detect the abnormal QT dynamics in long QT syndrome (LQTS) patients, particularly LQTS type 1 and type 2. However, little is known about LQTS type 3 (LQT3). We investigated QT dynamics during exercise testing in LQTS patients, particularly LQT3. This study included 37 subjects, comprising 16 genotyped LQTS patients and 21 unrelated healthy subjects without QT prolongation. LQTS patients were divided into LQT3 and non-LQT3 groups. During exercise tests using a modified Bruce protocol, 12-lead electrocardiogram monitoring was performed using a novel multifunctional electrocardiograph. QT intervals were automatically measured. The QT/heart rate (HR) relationship was visualized by plotting the beat-to-beat confluence of the recorded data. A linear regression analysis was performed to determine the QT/HR slope and intercept. Estimated QT intervals at HR 60 bpm (QT60) were calculated by the regression line formula. QT/HR slopes were steeper for each LQTS group than for the control group (P < 0.001). QT60 values demonstrated a moderate correlation with QT intervals at rest (P < 0.0001) for both groups. The corrected QT intervals (QTc) at 4 min of recovery after exercise were significantly longer in the non-LQT3 group than in the control group but were not different between the LQT3 and the control groups. Abnormal QT dynamics during exercise testing were observed in both LQT3 patients and other LQTS subtypes. This method may be useful for directing genetic testing in subjects with borderline prolonged QT intervals.

Utility of Provocative Testing in the Diagnosis and Genotyping of Congenital Long QT Syndrome: A Systematic Review and Meta‐Analysis

“…Studies were included in this meta‐analysis if (1) patients with LQTS and control (healthy population or low probability of LQTS 5 , 13 , 16 , 24 ) were both included in the study; (2) LQTS was diagnosed by clinical features and/or cardiac channel gene screening; (3) provocative testing was performed in both patients with LQTS and control; and (4) provocative testing included abrupt stand testing, treadmill test, bicycle test, or epinephrine infusion testing. Studies were excluded if (1) <10 patients with LQTS enrolled; (2) studies included either patients with LQTS or control; (3) the most appropriate studies were included, 7 , 9 , 13 , 16 , 19 , 24 , 25 , 26 then duplicate groups were excluded 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ; (4) studies in which QTc interval or ΔQTc could not be extracted, and conference abstracts were excluded; and (5) provocative testing including adenosine exposure, 38 mental stress, 18 , 39 Valsalva maneuver, 40 , 41 and cold pressor test 7 , 41 , 42 were excluded because fewer studies were insufficient for analysis.…”

Prolonged QT Interval in Athletes: Distinguishing between Pathology and Physiology

“…Abnormal QT prolongation during recovery of exercise testing has been found to characterize individuals with LQTS type 1 and 2, whereas QT changes during recovery appear not to differ between LQTS type 3 and controls [49, 50, 53]. Individuals with LQTS type 1 display a sustained QTc prolongation throughout the whole recovery with decreasing magnitude of QTc prolongation from early to late recovery, while for LQTS type 2 the magnitude of QTc prolongation increases from early to late recovery [52, 54].…”

The congenital long QT syndrome Type 3: An update

“…Exercise stress testing: Takahashi et al. [20] investigated QT dynamics during exercise testing in LQT3. The study included 37 subjects, comprising 16 genotyped LQTS patients and 21 unrelated healthy subjects without QT prolongation.…”