QT INTERVAL AND DISPERSION IN PRIMARY AUTONOMIC FAILURE

Objective-To investigate the role of the autonomic nervous system in d etermining QT interval and dispersion. Patients and methods-32 patient s with chronic primary (idiopathic) autonomic failure (19 men, mean ag e 60 years) and 21 normal controls (11 men, mean age 59) without sympt oms of ischaemic heart disease were studied retrospectively. Autonomic failure was diagnosed by a combination of symptomatic postural hypote nsion, subnormal plasma noradrenaline response to head-up tilt, and ab normal cardiovascular responses to standing, Valsalva manoeuvre, menta l stress, cutaneous cold, isometric exercise, and deep breathing. QT i ntervals were measured from surface electrocardiograms and QT dispersi on was defined as maximum QT - minimum QT occurring in any of the 12 l eads. Results-Mean heart rate (RR intervals) was similar in patients w ith autonomic failure and controls (S2 lead: 865 (132) v 857 (108) ms, P = NS; V2 lead: 865 (130) v 868 (113) ms, P = NS). QT intervals meas ured from electrocardiogram leads S2 and V2 were significantly longer in patients than in controls (401 (40) v 376 (16) ms, P < 0.01; and 40 3 (41) v 381 (20) ms, P < 0.05 respectively). The mean maximum QT inte rval in any lead, which is the best estimate of the maximum duration o f electrical systole, was significantly longer in the patients than in controls (417 (48) v 388 (23) ms, P < 0.005). Linear regression analy sis of QT and RR intervals for both groups showed a significant differ ence between the slopes of the two regression lines (F = 8.4, P < 0.00 1). However, QT dispersions were similar between patients and controls . Conclusions-Patients with primary autonomic failure have prolongatio n of QT intervals, indicating that the autonomic nervous system is an important determinant of QT interval. However, QT dispersion does not seem to be affected by chronic primary autonomic denervation.