In the last years, signs and symptoms of autonomic nervous system and cardiac control impairment have been described in amyotrophic lateral sclerosis (ALS) patients. The analysis of the variability of the overall duration of cardiac electrical activity comprising depolarization and repolarization periods, namely the QT interval, could provide additional and more precise information about the cardiac control of ALS patients. The aim of this study was to evaluate the QT variability and the strength of the relation between QT and heart period (HP) in 10 ALS patients (2 males, age: 62.5±7.55 years) at rest in supine condition (REST) and during 75° head-up tilt (TILT). HP was measured as the temporal distance between two consecutive R-wave peaks. The QT interval was approximated as the time distance between R-wave peak and T-wave apex (RTa) and end (RTe). Time domain and spectral indexes in low frequency (LF, 0.04-0.15 Hz) and in high frequency (HF, 0.15-0.5 Hz) bands were computed over HP, RTa and RTe beat-to-beat series. The squared coherence between HP and RTa, or RTe, was calculated as well. Similarly to the well-known findings in healthy population, the RTa and RTe variances (19.08±21.51 vs. 59.38±73.75 and 84.66±73.64 vs 165.81±159.23 ms2, respectively) and the LF power (4.18±5.32 vs. 14.93±17.18 and 20.59±16.67 vs 54.65±69.05 ms2, respectively) increased during TILT. At difference with the healthy population, HP variance, power in the HF band, and squared coherence between HP and RTa, or RTe, variability remained stable during TILT. We conclude that only QT variability spectral markers suggest an apparently physiological response to TILT in ALS patients and QT variability analysis provides complementary information compared to HP variability analysis to typify cardiac control of ALS patients.
The study was partially supported by AriSLA, Fondazione Italiana di Ricerca per la Sclerosi Laterale Amiotrofica.