Global sequence and dispersion of ventricular repolarization: In vivo validation of non-invasive parameters using monophasic action potential mapping technique
The purposes are to validate the noninvasive parameters, QT interval, QT dispersion, Tpeak-Tend interval, and the activation recovery time (ART) for estimation of global dispersion of ventricular repolarization (DVR), and to investigate the changes of repolarization sequence and DVR by altered ventricular pacing sites. The material consisted of 12 patients (Study I) and two series healthy pigs with 10 in each (Studies II and III; Studies IV and V). In Study I, endocardial MAPs and unipolar electrograms were recorded using the CARTO system in 12 patients. End of repolarization (EOR) times from the MAPs and ARTs from the unipolar electrograms were acquired and 3-dimensional maps of global EOR and ART were reconstructed. The ART sequence was consistent with that of EOR and no significant diffence was found between EOR times and ART. A significant, positive correlation between the ART and the EOR time was also found in all maps. These findings suggest the usefulness of the ART in evaluation of global sequence and dispersion of ventricular repolarization. In Studies II and III, MAP mapping was performed over both the ventricular endo- and the epicardium using the CARTO system in 10 open-chest pigs, from which the EOR times over the epi- (EORepi), endocardium (EORendo) and over both (EORtotal) were obtained- 12-lead ECG were recorded simultaneously. The QTpeak intervals were significantly smaller than the maximal EORepi. No significant difference was found between the maximal QTend interval and the maximal EORendo, between the maximal QTend interval and the maximal EORtotal nor between the minimal QTpeak interval and the minimal EORtotal, which suggests that not only the transmural gradients, but also the apico-basal repolarization gradients contribute to the genesis of the T wave. In addition, the maximal Tpeak-Tend intervals were consistent with the dispersion of EOR-total, and significantly correlated with the dispersion of EOR-total. However, the mean Tpeak-Tend intervals, and Tpeak-Tend intervals from lead II and V5 were all significantly smaller than and poorly correlated with the dispersion of EOR-total, as were the QTpeak and QTend dispersions. These findings suggest that the maximal Tpeak-Tend interval may be used as a noninvasive estimate of the global DVR, but not the QTpeak and QTend dispersions, nor the mean Tpeak-Tend interval and that from a single lead. In Studies IV and V, global MAPs were recorded from the ventricular endocardium during right atrial (RA), RV apex endocardial (RVEndo) and LV laterobasal epicardial (LVEpi) pacing in 10 pigs, with ECG simultaneously recorded. During RA pacing, the EOR sequence followed the AT sequence in both ventricles. Strikingly, the EOR sequence was also consistent with the AT sequence in both ventricles during RVEndo and LVEpi pacing, even though the mapping was performed after an abrupt change of the pacing site. In all maps, there was a negative correlation between the MAP duration and the AT and a positive correlation between the EOR time and the AT under each pacing protocol. These findings suggest the importance of activation sequence in governing repolarization patterns. Significant changes in repolarization from an altered activation sequence may happen within a few hours in vivo, implying that electrical remodeling of the ventricles may be rapidly induced by altered activation sequence. In addition, the global dispersion of EOR times during LVEpi pacing was significantly greater than those during RA and RVEndo pacing, whereas no significant difference was found between those during RA and RVEndo pacing. In addition, the QT intervals, QT dispersion and Tpeak-Tend intervals during LVEpi pacing were all significantly greater than those during RA and RVEndo pacing These findings provide in vivo evidence supporting the involvement of increased DVR in the incidence of malignant ventricular arrhythmias in a subgroup of patients with biventricular pacing.
Source Type:Doctoral Dissertation
Keywords:MEDICINE; Cardiovascular system; Kardiovaskulära systemet; dispersion; electroanatomical mapping; T wave; epicardial pacing; Ventricular repolarization; monophasic action potential
Date of Publication:01/01/2007