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Sudden Intense Exercise Increases QT Heart Rate Slope and T Wave Complexity in Long QT Syndrome and Normal Subjects
Author(s) -
CHAUHAN VIJAY S.,
KRAHN ANDREW D.,
MITOFF PETER,
KLEIN GEORGE J.,
SKANES ALLAN C.,
YEE RAYMOND
Publication year - 2004
Publication title -
pacing and clinical electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.686
H-Index - 101
eISSN - 1540-8159
pISSN - 0147-8389
DOI - 10.1111/j.1540-8159.2004.00647.x
Subject(s) - medicine , cardiology , long qt syndrome , qt interval , heart rate , intensity (physics) , heart rate variability , electrocardiography , blood pressure , physics , quantum mechanics
Sudden intense physical activity is a trigger for ventricular arrhythmias in long QT syndrome (LQTS), and β‐blockers (B) reduce the risk of ventricular arrhythmias in LQTS. We compared the effect of graded (gradual intensity) versus burst (sudden intensity) exercise on QT‐rate adaptation and T wave complexity in LQTS + B (n = 21), LQTS − B (n = 5), and normal controls (n = 20). Graded exercise consisted of symptom‐limited bicycle ergometry (30 W, increment 20 W/min). Burst exercise involved a fixed 200 W load for 1.0 minute. ECGs were digitally recorded every 10 seconds during exercise and a 10 minute recovery period. QT‐rate adaptation was quantified using the slope of the QT cycle length relationship fit to a quadratic function. Principle component analysis (PCA) was used to quantify T wave complexity. The QT‐rate slope was two‐fold greater with burst exercise than graded exercise for LQTS + B (−82E ± 40E vs −36E ± 40E, P = 0.0016), LQTS − B (−85E ± 60E vs −30E ± 50E, P = 0.011) and controls (−100E ± 60E vs −48E ± 100E, P = 0.0011) (E = x10 −5 ). For each exercise protocol, there was no difference in QT‐rate slope between the three groups. In contrast, the QT‐rate slope during the 10 minute recovery period was similar between the burst and graded protocol for LQTS + B (25E ± 40E vs 30E ± 50E), LQTS − B (81E ± 80E vs 85E ± 70E) and controls (90E ± 80E vs 82E ± 80E). The coefficient of variability of PCA (T wave complexity variability) during burst exercise was greater than that during graded exercise for LQTS + B (41 ± 15 vs 30 ± 10, P = 0.017), LQTS − B (47 ± 25 vs 26 ± 4, P = 0.016), and control (46 ± 14 vs 33 ± 19, P = 0.012). For each exercise protocol, no difference in T wave complexity variability was seen between the three groups. In conclusion, QT heart rate slope and T wave complexity variability are greater during sudden intense exercise than graded exercise in LQTS patients (on and off β‐blockers) and normal subjects, with similar findings among the three groups of patients.