Noninvasive imaging of three-dimensional cardiac activation sequence during pacing and ventricular tachycardia

Abstract

Background: Imaging cardiac excitation within ventricular myocardium is important in the treatment of cardiac arrhythmias and might help improve our understanding of arrhythmia mechanisms.

Objective: This study sought to rigorously assess the imaging performance of a 3-dimensional (3D) cardiac electrical imaging (3DCEI) technique with the aid of 3D intracardiac mapping from up to 216 intramural sites during paced rhythm and norepinephrine (NE)-induced ventricular tachycardia (VT) in the rabbit heart.

Methods: Body surface potentials and intramural bipolar electrical recordings were simultaneously measured in a closed-chest condition in 13 healthy rabbits. Single-site pacing and dual-site pacing were performed from ventricular walls and septum. VTs and premature ventricular complexes (PVCs) were induced by intravenous NE. Computed tomography images were obtained to construct geometry models.

Results: The noninvasively imaged activation sequence correlated well with invasively measured counterpart, with a correlation coefficient of 0.72 ± 0.04, and a relative error of 0.30 ± 0.02 averaged over 520 paced beats as well as 73 NE-induced PVCs and VT beats. All PVCs and VT beats initiated in the subendocardium by a nonreentrant mechanism. The averaged distance from the imaged site of initial activation to the pacing site or site of arrhythmias determined from intracardiac mapping was ∼5 mm. For dual-site pacing, the double origins were identified when they were located at contralateral sides of ventricles or at the lateral wall and the apex.

Conclusion: 3DCEI can noninvasively delineate important features of focal or multifocal ventricular excitation. It offers the potential to aid in localizing the origins and imaging activation sequences of ventricular arrhythmias, and to provide noninvasive assessment of the underlying arrhythmia mechanisms.

Figure 1

Schematic diagram of the experimental protocol for validating the 3-D cardiac electrical imaging (3-DCEI) technique with simultaneous measurements from 3-D intra-cardiac mapping. A. Cross-sectional CT slices showing detailed heart chambers and location of body surface electrodes and plunge-needle electrodes. B. Realistic geometry heart-torso model (green spots showing body surface electrodes). C. Animal model. D. Butterfly plot of multiple-channel ECGs. E. Body surface potential maps (BSPMs). F. Multiple-channel intramural bipolar electrograms during 3-D intra-cardiac mapping (left) and reconstruction from CT images of an isolated rabbit heart with labeled pins (right). G. Activation sequence non-invasively imaged from 3-DCEI. H. Measured activation sequence from invasive 3-D intra-cardiac mapping.

Figure 2

Comparison between the 3-D activation sequence measured via 3-D intra-cardiac mapping and the 3-D activation sequence imaged by 3-DCEI when rabbit P6 was paced respectively at the endocardium (A) and epicardium (B) of LV basal anterior wall and when rabbit P3 was simultaneously paced at epicardium of LV apex and anterior basal left wall (C). The activation sequence is color coded from white to blue, corresponding to earliest and latest activation. In the left column, activation sequence is displayed on epicardial and endocardial surfaces, respectively. In the right column, four axial slices starting from ventricular base are displayed from left to right. The pacing site and the estimated initial site of activation are marked by a black asterisk in the left column and a black spot and a purple arrow in the right column. The scale bar is given for the axial slices. The epicardial and endocardial surfaces are displayed respectively in a left anterior view for rabbit P6 and in a left posterior view for rabbit P3.

Figure 3

Comparison between measured and imaged activation sequence when rabbit P9 was paced from the basal septum.

Figure 4

Comparison between measured and imaged activation sequence of PVCs in three activation patterns (A), (B), and (C) for rabbit V3 and a six-beat monomorphic VT (D) for rabbit V1. The epicardial and endocardial surfaces are displayed respectively in the anterior view for rabbit V3 and left posterior view for rabbit V1.