Dynamic QT response to cold‐water face immersion in long‐QT syndrome type 3

BACKGROUND: Abnormal dynamics of QT intervals in response to sympathetic nervous system stimulation are used to diagnose long‐QT syndrome (LQTS). We hypothesized that parasympathetic stimulation with cold‐water face immersion following exercise would influence QT dynamics in patients with LQTS type 3 (LQT3). METHODS: Study participants (n = 42; mean age = 11.2 years) comprised 20 genotyped LQTS children and 22 healthy children. The LQTS group was divided into LQT3 (n = 12) and non‐LQT3 (n = 8) subgroups. Provocative testing for assessing QT dynamics comprised a treadmill exercise followed by cold‐water face immersion. The QT intervals were automatically measured at rest and during exercise, recovery, and cold‐water face immersion. The QT/heart rate (HR) relationship was visualized by plotting beat‐to‐beat confluence of the data. RESULTS: The QT/HR slopes, determined by linear regression analysis, were steeper in the LQTS group than in the control group during exercise and immersion tests: −2.16 ± 0.63 versus −1.21 ± 0.28, P < 0.0001, and −2.02 ± 0.76 vs −0.75 ± 0.24, P < 0.0001, respectively. The LQT3 patients had steeper slopes in the immersion test than did non‐LQT3 and control individuals: −2.42 ± 0.52 vs −1.40 ± 0.65, P < 0.0001, and vs −0.75 ± 0.24, P < 0.0001. CONCLUSIONS: The QT dynamics of LQT3 patients differ from those of other LQTS subtypes during the post‐exercise cold‐water face immersion test in this study. Abnormal QT dynamics during the parasympathetic provocative test are concordant with the fact that cardiac events occur when HRs are lower or during sleep in LQT3 patients.