Noninvasive three-dimensional cardiac activation imaging from body surface potential maps: a computational and experimental study on a rabbit model

Abstract

Three-dimensional (3-D) cardiac activation imaging (3-DCAI) is a recently developed technique that aims at imaging the activation sequence throughout the the ventricular myocardium. 3-DCAI entails the modeling and estimation of the cardiac equivalent current density (ECD) distribution from which the activation time at any myocardial site is determined as the time point with the peak amplitude of local ECD estimates. In this paper, we report, for the first time, an in vivo validation study assessing the feasibility of 3-DCAI in comparison with the 3-D intracardiac mapping, for a group of four healthy rabbits undergoing the ventricular pacing from various locations. During the experiments, the body surface potentials and the intramural bipolar electrical recordings were simultaneously measured in a closed-chest condition. The ventricular activation sequence noninvasively imaged from the body surface measurements by using 3-DCAI was generally in agreement with that obtained from the invasive intramural recordings. The quantitative comparison between them showed a root mean square (rms) error of 7.42 +/-0.61 ms, a relative error (RE) of 0.24 +/-0.03, and a localization error (LE) of 5.47 +/-1.57 mm. The experimental results were also consistent with our computer simulations conducted in well-controlled and realistic conditions. The present study suggest that 3-DCAI can noninvasively capture some important features of ventricular excitation (e.g., the activation origin and the activation sequence), and has the potential of becoming a useful imaging tool aiding cardiovascular research and clinical diagnosis of cardiac diseases.

Fig. 1

(A) An axial slice of the ventricles, in which the cardiac cells are undergoing depolarization. The red region behind the excitation wavefront represents the depolarized muscle cells, while the local equivalent current density field over each point along this wavefront, indicated by black arrow, represents propagation direction of the wavefront at these points. A transmural needle is inserted in the ventricular myocardium. (B) Left panel shows the time course of the TMPs ϕ₁ and ϕ₂ at electrode 1 and electrode 2. Right panel shows the time course to recorded bipolar electrogram |ϕ_b(r_k,t)| through electrode 1 and electrode 2 and the magnitude of local equivalent current density $\mid {\overrightarrow{\mathbf{j}}}_{eq}(r_k,t)\mid$. The activation time τ(r_k) at position r_k is indicated by red line at right panel.

Fig. 2

Schematic diagram of the experimental protocol. Simultaneous 3-dimentional (3-D) intra-cardiac mapping and body surface potential mapping were conducted and the measured activation sequence from 3-D intra-cardiac mapping is compared with the imaged activation sequence obtained by the 3-D cardiac activation imaging technique.

Fig. 3

(A) An example of electrocardiograms (ECGs) recorded from the anterior chest during ventricular pacing at left lateral wall of rabbit 4. The red block starting from the pacing stimuli represents a single beat that was applied in 3-DCAI. (B) Comparison between the time course of the estimated current density (top row) and the recorded bipolar electrograms in 3-D intra-cardiac mapping (bottom row) at two myocardial sites in ventricles of rabbit 2. Site 1 is located at left lateral wall. Site 2 is located at posterior wall. Red line marks the estimated activation time.

Fig. 4

Comparison between the 3-D activation sequence measured via 3-D intra-cardiac mapping (left column) and the 3-D activation sequence imaged by using 3-DCAI (right column). The activation sequence is color coded from blue to red, corresponding to earliest and latest activation. The pacing site and the estimated initial site of activation are marked by a red circle and a purple arrow. (A) Activation was paced at left posterior wall of ventricle in rabbit 1. A realistic geometry of ventricle for rabbit 1 is displayed (top left view). (B) Activation was induced by pacing at right lateral wall of ventricle in rabbit 2 (top anterior view). (C) Activation was induced by pacing at left lateral wall of ventricle in rabbit 3 (top anterior view). (D) Activation was induced by pacing at left lateral wall of ventricle in rabbit 4 (top left view).

Fig. 5

Comparison between the forward simulation activation sequence and imaged activation sequence (right column) during the computer simulation. A realistic geometry of ventricles is displayed, from a top anterior view. (A) Activation was paced at basal lateral wall of the LV. (B) Activation was paced at middle lateral wall of RV. (C) Activation was simultaneously paced at middle left wall (MLW) and middle anterior (MA) of ventricles.