Dynamics of the uncorrected QT interval during vagal-induced lengthening at RR intervals

Analysis of 21 episodes of vagal-induced atrioventricular block showed that the uncorrected QT intervals at the end of the corresponding RR pauses wer e not prolonged, in reference to the pre-block QT intervals, with pauses sh orter than 1,280 ms. Subsequently, they gradually lengthened as the RR paus es progressively increased to 13,710 ms. This dynamic behavior of the QT in terval in subjects without structural heart disease could have resulted fro m a complex interaction between the cumulative effects of previous cycle le ngths (memory effect?) and the autonomic nervous system.