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Background: An altered adaptation of ventricular repolarisation to changes in heart rate may play an important role in arrhythmogenesis. Experiments in animals have indicated that right stellectomy might promote arrhythmias by uncoupling the QT from the RR interval response to exercise. Whether a similar phenomenon occurs in humans is not known. Methods and Results: Seven subjects (age 23-42 years), referred for thoracoscopic sympathicotomy for idiopathic hyperhydrosis, were studied before (C) and 6 weeks after right T1-2 sympathicotomy with T2 diathermy (postRS). High resolution ECG signal (Frank leads) was acquired during supine exercise at 70% V0 2max (Ex, 7min) and recovery (Rec, 15min), and a newly developed algorithm was employed to measure the RR and QT intervals on a beat-to-beat basis. RR and QT (ms) were increased postRS, both at rest (902±36 v 1078±58 and 373±7 v 398±9, mean±SEM, p<.05) and during steady-state Ex (433±19 v 479±21 and 267±5 v 287±6, p<.05). PostRS QT remained shortened during Rec despite the lengthening of RR, forming a wide hysteresis loop in the QT/RR relationship (typical raw data in Fig, C=shaded). The "width" of the hysteresis loop was taken as ΔQT=QT Ex -QT Rec (ms), and was measured at RR=(RR Rec -RR Ex )/2 (see Fig). PostRS ΔQT was markedly higher than ΔQT at C (71±6 v 39±4, p<.05). This was accompanied by an increase in the time lag (s) of QT adaptation to a steady-state RR during exercise (103±14 at C v 166±18 postRS) or during recovery (6±2 at C v 49±8 postRS, p<.05). In summary, we have found that right T1-2 sympathicotomy significantly alters the kinetics of the QT adaptation to changes in cycle length during exercise. These data provide new insight into the role of the sympathetic nervous system in the regulation of the QT/RR relationship in man. (Graph Presented).


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