QT Interval Variability and QT-HP Coupling Strength in Amyotrophic Lateral Sclerosis Patients

In the recent years we have witnessed an increasing interest in studying cardiac control in amyotrophic lateral sclerosis (ALS) patients. The variability of the overall duration of cardiac electrical activity comprising depolarization and repolarization periods, namely the QT interval, could provide information about the cardiac control of ALS patients complementary to that derived from the variability of heart period (HP). In this study we evaluate first the HP and QT variabilities in 10 ALS patients at rest in supine position (REST) and during 75° head-up tilt (TILT). The QT interval was approximated as RTapex and RTend intervals, representing the temporal distance between R-wave peak and T-wave apex and end, respectively. HP was taken as the time distance between two consecutive R-wave peaks. Time and frequency domain markers were computed over HP, RTa and RTe beat-to-beat series. The RTa-HP and RTe-HP squared coherence was calculated as well. We found that time and frequency domain indexes derived from QT variability changed during TILT in the direction expected for a healthy population. Frequency domain HP variability markers showed a blunted response to TILT. RTa-HP and RTe-HP squared coherence did not vary during TILT. QT variability and QT-HP coupling markers in ALS patients showed an apparently normal response to TILT not fully mirrored by HP variability indexes.