Dynamic Changes of Cardiac Repolarization Instability during Exercise Testing

Abstract

Introduction Physical exercise triggers efferent cardiac sympathetic activation. Here, we tracked the spatiotemporal properties of cardiac repolarization on a beat-to-beat basis throughout a standardized exercise test and hypothesized a detectable change at the point of the anaerobic threshold (AT). Methods The study included 20 healthy adults (age 35.3 ± 6.7 yr) undergoing a standardized incremental exercise test on a cycle ergometer. During exercise testing, high-resolution (2000 Hz) ECG monitoring in Frank lead configuration was performed. Three-dimensional beat-to-beat repolarization instability (dT°) was assessed by a novel vector-based method according to a previously published technology. In parallel, the lactate threshold (LT) was detected according to Dickhuth and Mader. Results We could identify a characteristic pattern of dT° signal during exercise testing. With increasing physical activity, dT° increased concordantly to heart rate. At an average of 164 ± 38 W, dT° and heart rate abruptly showed a discordant behavior, characterized by a transient drop of dT°. The maximal discordance between dT° and heart rate was defined as ATdT° and highly significantly correlated with LTDickhuth (r = 0.841, P < 0.001) and LTMader (r = 0.819, P < 0.001), which were at 156 ± 39 and 172 ± 46 W, respectively. The characteristic of dT° could not be provoked by fast atrial pacing in the absence of exercise. Conclusions Repolarization instability shows a characteristic pattern during standardized exercise in healthy individuals that allows for a noninvasive estimation of AT.

Large potassium shifts during dialysis enhance cardiac repolarization instability

“…In summary, we observed a link between potassium shifts during HD and PRD levels which indicates that removal of large amounts of potassium enhances the effect of efferent sympathetic activity on the ventricular myocardium. These changes were shown to be independent of changes in heart rates, a fact that has already been demonstrated in previous studies [8,10]. The independence of heart rate is important since fluid removal during HD per se might alter heart rate.…”

Estimation of the second ventilatory threshold through ventricular repolarization profile analysis

“…These results improve those of previous works in which, although the reported errors were likewise lower than 50 W, the translation from Watts to minutes resulted in larger errors due to the nature of the exercise test. 12 When evaluated in terms of V O 2 , the mean estimation error was of 1% and 3% for dT and LFdT, respectively, being these errors lower than the inter-evaluator agreement in the visual determination reported in, 25 which was comprised within 3%-16%.…”

“…In this way, we established a priori precision of the Bland-Altman plot (ie, limits of agreement) of ±50 W, which is approximately the value obtained in. 12 With respect, to the bias, it should be kept within the limits of inter-evaluator error in the visual estimation of the ventilatory threshold, which has been reported to lie within 3 to 16% of…”

“…11 Hence, HRV might not represent an appropriate approach for studying the role of the autonomic nervous system in the transition to anaerobic metabolism during high-intensity exercise. In a recent work, 12 a methodology for estimation of AnT LA was proposed based on the analysis of an index of ventricular repolarization instability, dT, and its characteristic temporal pattern in relation to HR. The use of blood lactate levels as a gold standard for detecting AnT in that work may, however, result in high uncertainty, considering that it can be only assessed on a discrete-time basis, usually with large sampling periods.…”

Effect of Hyperventilation on Periodic Repolarization Dynamics

“…In the present study, there was no correlation between heart rate changes and dT° as well as PRD changes. Previous studies showed that an increase of heart rate by means of fixed atrial pacing had no relevant effect on dT° and PRD levels (Rizas et al, 2014;Hamm et al, 2019). Furthermore, linear regression analysis excluded heart rate as a confounding factor for increased sympathetic activity associated repolarization instability.…”