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Sympathoexcitation Increases the QT/RR Slope in Healthy Men: Differential Effects of Hypoxia, Dobutamine, and Phenylephrine
Author(s) -
XHAËT OLIVIER,
ARGACHA JEANFRANCOIS,
PATHAK ATUL,
GUJIC MARKO,
HOUSSIERE ANNE,
NAJEM BOUTAÏNA,
DEGAUTE JEANPAUL,
VAN DE BORNE PHILIPPE
Publication year - 2008
Publication title -
journal of cardiovascular electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.193
H-Index - 138
eISSN - 1540-8167
pISSN - 1045-3873
DOI - 10.1111/j.1540-8167.2007.01039.x
Subject(s) - dobutamine , medicine , phenylephrine , hypoxia (environmental) , cardiology , repolarization , anesthesia , heart rate , qt interval , long qt syndrome , reflex , blood pressure , hemodynamics , electrophysiology , chemistry , organic chemistry , oxygen
Dynamic ventricular repolarization assessed by QT/RR slopes studies the effects of modifications in cardiac repolarization independently of variations in RR interval (RR). The effects of changes in sympathetic and vagal activity on the QT/RR slope are controversial. We tested the hypothesis that sympathoexcitation is an important determinant of the QT/RR slope. Methods and Results: We compared the effects of a reflex sympathetic activation in response to hypoxia, to the direct effects of the infusion of the beta‐adrenergic agent dobutamine, on the QTa (apex) and QTe (end)/RR slopes. Dobutamine was titrated to obtain similar increases in cardiac output than with hypoxia. Cardiac vagal activity was estimated by rMSSD and pNN50. In a second group of healthy subjects, we assessed the effect of a reflex cardiac vagal activation in response to phenylephrine infusion on the same variables. We observed a similar increase in QTa and QTe slopes during hypoxia and dobutamine (both P < 0.017 vs. normoxia), despite divergent changes in cardiac vagal activity, as rMSSD and pNN50 decreased with hypoxia compared to normoxia (P < 0.001) but increased during dobutamine infusion compared to hypoxia (P < 0.017). In contrast, these slopes did not change during the rises in rMSSD and pNN50 elicited by phenylephrine (P > 0.7). Conclusion: Beta‐adrenergic stimulation induces comparable increases in the QT/RR slopes than hypoxia, but in the presence of a larger cardiac vagal activity. Vagal cardiac activation by phenylephrine does not change the QT slopes. This reveals that the sympathetic system is an important determinant of QT/RR dynamicity in healthy men.