Autonomic nervous system effects on ventricular repolarization and RR interval variability during head-up tilt

Changes in ventricular repolarization (VR) were analyzed using 32-lead high spatial resolution ECGs (HSRE). FFT-derived low (0.04-0.15 Hz) and high (0.15-0.4 Hz) frequency powers (LF & HF, respectively) of RR interval variability (RRIV) and their ratio were used to assess changes in the autonomic activity elicited by 70° tilt in 9 patients with structural heart disease (SHD) and 19 control (CON) subjects. Heart rate (HR) increased with tilt in CON and SHD. HF and LF/HF increased with tilt in CON, but not in SHD. Peak and mean T-wave amplitudes declined with tilt in CON but not in SHD. In contrast to CON subjects, RRIV and VR failed to change in SHD patients despite increased HR. This suggests preserved tonic but reduced rhythmic autonomic nervous system activity (ANSA) related modulation of HR, and reduced ANSA effects on VR