ECG Ventricular Repolarization Dynamics during Exercise: Temporal Profile, Relation to Heart Rate Variability and Effects of Age and Physical Health.

Adrián Hernández-Vicente,Raquel Bailón,Germán Vicente-Rodríguez,David Hernando,Esther Pueyo,Nuria Garatachea

doi:10.3390/ijerph18189497

Abstract

Periodic repolarization dynamics (PRD) is a novel electrocardiographic marker of cardiac repolarization instability with powerful risk stratification capacity for total mortality and sudden cardiac death. Here, we use a time-frequency analysis approach to continuously quantify PRD at rest and during exercise, assess its dependence on heart rate variability (HRV) and characterize the effects of age (young adults/middle-aged adults/older adults), body mass index (non-overweight/overweight) and cardiorespiratory fitness level (fit/unfit). Sixty-six male volunteers performed an exercise test. RR and dT variabilities (RRV, dTV), as well as the fraction of dT variability unrelated to RR variability, were computed based on time-frequency representations. The instantaneous LF power of dT (PdTV), representing the same concept as PRD, and of its RRV-unrelated component (PdTVuRRV) were quantified. dT angle was found to mostly oscillate in the LF band. Overall, 50–70% of PdTV was linearly unrelated to RRV. The onset of exercise caused a sudden increase in PdTV and PdTVuRRV, which returned to pre-exercise levels during recovery. Clustering analysis identified a group of overweight and unfit individuals with significantly higher PdTV and PdTVuRRV values at rest than the rest of the population. Our findings shed new light on the temporal profile of PRD during exercise, its relationship to HRV and the differences in PRD between subjects according to phenotypic characteristics.

Highlights

In line with previous findings, we observed a significant exercise‐induced increase in the instantaneous LF power of dT variability (dTV), PdTV, with respect to rest and recovery, which we proved to be accompanied by gradual increases in its RRV‐unrelated component, PdTVuRRV, but not in its RRV‐related one, PdTVrRRV, in response to incremental exercise
Oscillations in dT mostly occur in the low-frequency band and as much as 50–70% of them are unrelated to heart rate variability
The instantaneous LF power of dT, PdTV, increases by two orders of magnitude during an incremental exercise protocol as compared to values at rest and during recovery from exercise, high inter-individual variability is observed in the temporal profiles of PdTV

Summary

Introduction

Sudden cardiac death is responsible for 15–20% of all deaths in Western societies [1]. It is strongly associated with, and can be caused by, ventricular arrhythmias. Rare, when an athlete’s life is claimed by sudden cardiac death, the impact on society is very high. The absolute number of cases in athletes is not higher than in the general population, but intense exercise appears to increase the risk of sudden cardiac death in individuals harboring certain cardiac conditions [2].

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