Dynamic Changes of Cardiac Repolarization Instability during Exercise Testing

Introduction Physical exercise triggers efferent cardiac sympathetic activation. Here, we tracked the spatio-temporal 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 years) undergoing a standardized incremental exercise test on a cycle ergometer. During exercise testing high-resolution (2000 Hz) ECG-monitoring in frank leads 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 anaerobic threshold (ATdT°) and highly significantly correlated with LTDickhuth (r=0.841; p

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