Evaluation of QT interval response to marked RR interval changes selected automatically in ambulatory recordings

A new approach was developed to evaluate the QT interval response to RR interval changes in 24-hour ambulatory recordings, regarding different settings of the recording. First, a method was proposed to automatically identify beat positions in the following two situations: a) preceded by stable heart rate, b) after a sharp change in rate. Also, the evaluation across the complete recording was considered. For each recording, QT adaptation to RR changes was independently assessed in the three described settings by using a global optimization technique that led to a characterization of the influence of a history of past RR intervals on each QT measurement. Results showed that in stable heart rate situations, QT is mainly influenced by its immediately preceding RR interval; however, in periods containing abrupt rate changes, a marked hysteresis effect was observed; this hysteresis was also noticeable in the 24-hour evaluation, although less manifest. Moreover, the time course of QT adaptation in response to sharp RR changes derived in this study showed that there is a very rapid reaction during the first 50 seconds followed by a slower adjustment that takes nearly 2 minutes to complete.