Adaptation of ventricular repolarization time following abrupt changes in heart rate: comparisons and reproducibility of repeated atrial and ventricular pacing

Abstract

Adequate adaptation of ventricular repolarization (VR) duration to changes in heart rate (HR) is important for cardiac electromechanical function and electrical stability. We studied the QT and QTpeak adaptation in response to abrupt start and stop of atrial and ventricular pacing on two occasions with at least one month's interval in 25 study subjects with permanent pacemakers. Frank vectorcardiography was used for data collection. Atrial or ventricular pacing was performed for 8 minutes aiming at a cycle length (CL) of 500 ms. We measured the immediate response (IR), the time constant (τ) of the exponential phase, and T90 End, the time to reach 90% change of QT and QTpeak from baseline to steady-state during and after pacing. During atrial pacing the CL decreased on average 45% from mean (SD) 944 (120) to 518 (46) ms and QT on average 18% from 388 (20) to 318 (17) ms. For QT, T90 End was 103 (24) and 126 (15) s after start versus stop of atrial pacing, a difference of 24 (27) s (p=0.006). The response pattern was similar for τ but IR did not differ significantly between pacing start and stop. The response pattern was similar for QTpeak and also for QT and QTpeak following ventricular pacing start and stop. The coefficients of variation for repeated measures were 7-21% for T90 End and τ. In conclusion, the adaptation of VR duration was significantly more rapid following increasing than decreasing HR and intra-individually a relatively reproducible process.

Sex and Rate Change Differences in QT/RR Hysteresis in Healthy Subjects

“…Our observation of, on average, slower hysteresis speed during heart rate acceleration contradicts a recent report by Axelsson et al (2021) who observed the opposite. Nevertheless, they investigated the phenomenon in patients with permanent pacemakers and, thus, abnormalities in cardiac electrophysiology in whom QT/RR hysteresis might be different to that in the healthy subjects who were investigated in this study.…”

Accelerated QT adaptation following atropine‐induced heart rate increase in LQT1 patients versus healthy controls: A sign of disturbed hysteresis

“…The hysteresis of QT adaptation to HR change has been studied in several reports by investigating the QT/RR relationship during exercise testing or from Holter recordings, applying different measures of hysteresis with conflicting results as reviewed recently (Gravel et al, 2018 ). Differences between studies may at least in part be due to the well‐known difference in hysteresis when increasing versus decreasing the HR, faster in the former as shown also in humans (Seethala et al, 2011 ; Axelsson et al, 2021 ). This essential feature of QT hysteresis was pointed out (together with other limitations) in one previous very thorough QT/RR study (Malik et al, 2008 ).…”

“…Although atrial and ventricular pacing result in similar dynamics in QT hysteresis, ventricular pacing induces potentially confounding repolarization changes related to ventricular activation‐induced short‐term cardiac memory, at least when ventricular pacing lasts 8 minutes or more (Axelsson et al, 2021 ; Rosen & Bergfeldt, 2015 ). Incremental atrial pacing is presumably most physiological and was applied in one of our previous studies on patients with supraventricular tachycardia but otherwise healthy undergoing heart catheterization for ablation therapy (Axelsson et al, 2020 ).…”

“…Difficulties with keeping 1:1 atrio‐ventricular conduction at a fixed atrio‐ventricular conduction interval and HR turned out to be a problem in that study. Sudden start/stop of atrial pacing was used by Seethala et al 2011 and in one of our previous studies (Axelsson, Gransberg, Lundahl, Vahedi, & Bergfeldt, 2021 ). Provided the maximum HR is not too high (in those studies 120 beats per minute), neither keeping 1:1 conduction nor tolerability was a problem.…”

Discussion on Repolarization Reserve between Patients with Coronary Heart Disease and Normal Controls

“…When the heart rate is fast, the ventricular repolarization period is shortened while significantly prolonged when the heart rate is slow [3,4]. This kind of frequency adaptability of ventricular repolarization which is called ventricular repolarization reserve, also known as ventricular repolarization adaptability, is of great significance to the automatic regulation and effectiveness of ventricular contraction and relaxation under physiological conditions [5,6]. In recent years, evidences have shown that the inward late sodium current in the plateau phase of cell membrane plays a key role in the frequency adaptation of ventricular repolarization [7][8][9].…”