Key result
Sudden intense burst exercise produced a two-fold greater QT-rate slope than graded exercise in LQTS patients on beta-blockers (-82 vs -36 x10^-5, P=0.0016), off beta-blockers, and controls.
Why the study?
Does burst exercise compared to graded exercise increase QT-rate adaptation and T wave complexity in patients with long QT syndrome and normal subjects?
Does burst exercise compared to graded exercise increase QT-rate adaptation and T wave complexity in patients with long QT syndrome and normal subjects?
p-value: p=0.0016
Sudden intense exercise provokes greater QT-rate adaptation and T wave complexity variability than gradual exercise in both LQTS patients and healthy controls, highlighting the physiological impact of exercise intensity on repolarization.
May warrant caution during sudden intense activity in LQTS; hypothesis-generating for intensity-specific repolarization risk.
Sudden intense physical activity is a trigger for ventricular arrhythmias in long QT syndrome (LQTS), and beta-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 beta-blockers) and normal subjects, with similar findings among the three groups of patients.
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Chauhan et al. (2004) studied Long QT syndrome (n=46). Burst exercise (sudden intensity) vs. Graded exercise (symptom-limited bicycle ergometry, 30 W, increment 20 W/min) was evaluated on QT-rate adaptation (slope of the QT cycle length relationship) (p=0.0016). Sudden intense burst exercise produced a two-fold greater QT-rate slope than graded exercise in LQTS patients on beta-blockers (-82 vs -36 x10^-5, P=0.0016), off beta-blockers, and controls.