RT-41
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Analysis of the non-linear
relationship between cycle length and QT interval in healthy subjects
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Gabriella Malfatto, Antonio
Zaza*, Gastone Leonetti, Mario Facchini.
Divisione di Cardiologia, Istituto Scientifico Ospedale San Luca, Istituto
Auxologico Italiano IRCCS, *Dipartimento di Fisiologia e Biochimica Generali, Universitą
di Milano, Milano, Italy
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Abstract
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To characterize the modulation of ventricular
repolarization by heart rate, we applied an experimentally validated hyperbolic fitting to
describe the relationship between RR intervals and QT duration in 14 normal subjects (37
± 13 years). During a bicycle stress test, the RR at steady state at each load and the QT
in V5 (50 mm/s, 20 mV/cm) were fitted (R > 0.95) by the equation QT=QTmax*RR/(RR*RR50).
In this equation, QTmax (i.e., QT extrapolated at infinite RR) is a
rate-independent measure of QT (and of action potential duration). In this healthy
population, QTmax was 426 ± 43 ms. Women had longer QTmax than men.
Thus, a non-linear relationship may be demonstrated between ventricular repolarization and
cycle length in normal subjects, by simply measuring RR and QT intervals during a routine
stress test when heart rate is within physiological range. The parameter QTmax
can help the understanding of repolarization characteristics in healthy subjects, and the
study of their abnormalities during drug therapy, or during diseases.
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Key Words
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QT interval
healthy subjects, RR intervals, OA
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