Long-Term Microgravity Exposure Increases ECG Repolarization Instability Manifested by Low-Frequency Oscillations of T-Wave Vector.

Saúl Palacios,Esther Pueyo,Enrico G Caiani,Federica Landreani,Juan Pablo Martínez

doi:10.3389/fphys.2019.01510

Abstract

Ventricular arrhythmias and sudden cardiac death during long-term space missions are a major concern for space agencies. Long-duration spaceflight and its ground-based analog head-down bed rest (HDBR) have been reported to markedly alter autonomic and cardiac functioning, particularly affecting ventricular repolarization of the electrocardiogram (ECG). In this study, novel methods are developed, departing from previously published methodologies, to quantify the index of Periodic Repolarization Dynamics (PRD), an arrhythmic risk marker that characterizes sympathetically-mediated low-frequency oscillations in the T-wave vector. PRD is evaluated in ECGs from 42 volunteers at rest and during an orthostatic tilt table test recorded before and after 60-day –6° HDBR. Our results indicate that tilt test, on top of enhancing sympathetic regulation of heart rate, notably increases PRD, both before and after HDBR, thus supporting previous evidence on PRD being an indicator of sympathetic modulation of ventricular repolarization. Importantly, long-term microgravity exposure is shown to lead to significant increases in PRD, both when evaluated at rest and, even more notably, in response to tilt test. The extent of microgravity-induced changes in PRD has been associated with arrhythmic risk in prior studies. An exercise-based, but not a nutrition-based, countermeasure is able to partially reverse microgravity-induced effects on PRD. In conclusion, long-term exposure to microgravity conditions leads to elevated low-frequency oscillations of ventricular repolarization, which are potentiated following sympathetic stimulation and are related to increased risk for repolarization instabilities and arrhythmias. Tested countermeasures are only partially effective in counteracting microgravity effects.

Highlights

After almost 60 years of human spaceflight, there is good evidence on detrimental effects on the human body associated with long-term space missions (Williams et al, 2009; GarrettBakelman et al, 2019)
Comparison of Periodic Repolarization Dynamics (PRD) Computed by Continuous Wavelet Transform (CWT)- and Phase-Rectified Signal Averaging (PRSA)-Based Methods
Note that the case shown in blue presents low-frequency oscillations in dT◦ of small magnitude, which translates into low values of PRDCWT and PRDPRSA

Summary

Introduction

After almost 60 years of human spaceflight, there is good evidence on detrimental effects on the human body associated with long-term space missions (Williams et al, 2009; GarrettBakelman et al, 2019). Reported bradycardia (Meck et al, 2001), changes in electrolyte composition of blood plasma (Smith and Zwart, 2008), psychological stress (Kanas et al, 2001) and, very relevantly, adaptation of cardiac autonomic modulation (Fritsch-Yelle et al, 1996) may all concur to adversely affect ventricular electrophysiology. Reported alterations in the sympathetic nervous system might contribute to the documented increase in spatio-temporal inhomogeneity of ventricular repolarization, potentially providing an electrophysiological substrate for arrhythmias (Caiani et al, 2016). Further evidence on elevated arrhythmic risk during long-term space missions and its underlying mechanisms is yet to be established

Objectives

Methods

Results

Discussion

Conclusion