Aberrant autonomic pattern during the post-exercise recovery phase in long QT syndrome patients

Objectives: It is well-established that the autonomic nervous system (ANS) plays a central role in arrhythmogenesis. During and after exercise the ANS is particularly active, and since long QT syndrome (LQTS) patients have an increased risk of lethal arrhythmias during physical activity, it is important to investigate the autonomic function in these patients. In this study we investigate the ANS response during and after exercise in LQTS patients and healthy age and sex matched controls. Methods: Forty-four genotype-verified adult LQTS patients and forty-four healthy age- and sex-matched controls performed a submaximal bicycle exercise stress test. Heart rate recovery (HRR) and heart rate variability (HRV) were analyzed from registered electrocardiogram (ECG) and vector electrocardiogram (VCG) recordings collected throughout rest, exercise and in the post-exercise phase. Results: LQTS patients had a slower HRR than controls at 1- and 4-min post-exercise (p < 0.001). During the postexercise phase, LQTS patients had a lower total power (p < 0.001), low frequency power (p < 0.001) and high frequency power (p < 0.001) than controls. In the same phase, LQTS patients off betablocker (BB) treatment showed a lower high frequency power (p = 0.01) and different low frequency/high frequency ratio (p = 0.003) when comparing with LQTS patients on BB treatment. Conclusions: The parasympathetic effect on both HRR and HRV after exercise appears depressed in this LQTS patient cohort compared to healthy controls. This indicates an aberrant ANS response during the post-exercise phase which might be compensated by BB treatment. Our findings emphasize the importance of performing further investigations to identify the role of the ANS in LQTS arrhythmogenesis.