Equivalent moving dipole localization of cardiac ectopic activity in a swine model during pacing

Abstract

Localization of the initial site of cardiac ectopic activity has direct clinical benefits for treating focal cardiac arrhythmias. The aim of the present study is to experimentally evaluate the performance of the equivalent moving dipole technique on noninvasively localizing the origin of the cardiac ectopic activity from the recorded body surface potential mapping (BSPM) data in a well-controlled experimental setting. The cardiac ectopic activities were induced in four well-controlled intact pigs by either single-site pacing or dual-site pacing within the ventricles. In each pacing study, the initiation sites of cardiac ectopic activity were localized by estimating the locations of a single moving dipole (SMD) or two moving dipoles (TMDs) from the measured BSPM data and compared with the precise pacing sites (PSs). For the single-site pacing, the averaged SMD localization error was 18.6 ± 3.8 mm over 16 sites, while the averaged distance between the TMD locations and the two corresponding PSs was slightly larger (24.9 ± 6.2 mm over five pairs of sites), both occurring at the onset of the QRS complex (10-25 ms following the pacing spike). The obtained SMD trajectories originated near the stimulus site and then traversed across the heart during the ventricular depolarization. The present experimental results show that the initial location of the moving dipole can provide the approximate site of origin of a cardiac ectopic activity in vivo, and that the migration of the dipole can portray the passage of an ectopic beat across the heart.

Figure 1

Schematic diagram of electrocardiogram inverse solution and evaluation procedure (Note that the rigid co-registration approach used here for the LV pacing sites and the RV pacing sites was the same as that used in our previous study [23]). IS represents the estimated ‘initiation site’ of the ectopic activity, PS represents the ‘pacing site’ recorded by the intracavitary noncontact mapping (NCM) system, and AS represents the estimated ‘activation sequence’ of the ectopic activity using a dipole trajectory.

Figure 2

Results in an animal for pacing at the site of LVL. A. Torso model with illustration of body surface electrode positions, and selected ECG waveforms within the area marked by the white dotted line on the anterior chest. B. Results during ventricular depolarization following pacing (from 17 ms after pacing spike). In subfigures B: (i) Body surface isopotential contour maps and (ii) Estimated dipole trajectory of the cardiac activation. Each isopotential map is depicted at a different time instant by the increment of 0.05 mV. In the dipole trajectory, dark blue represents the earliest activated dipole marked by ‘IS’ and red represents the latest activated one. The green ball represents the position of pacing stimulus marked by ‘PS’. The axis of X, Y, and Z is consistent with that of torso model, which are in terms of the right-left, the posterior-anterior, and the inferior-superior, respectively.

Figure 2

Results in an animal for pacing at the site of LVL. A. Torso model with illustration of body surface electrode positions, and selected ECG waveforms within the area marked by the white dotted line on the anterior chest. B. Results during ventricular depolarization following pacing (from 17 ms after pacing spike). In subfigures B: (i) Body surface isopotential contour maps and (ii) Estimated dipole trajectory of the cardiac activation. Each isopotential map is depicted at a different time instant by the increment of 0.05 mV. In the dipole trajectory, dark blue represents the earliest activated dipole marked by ‘IS’ and red represents the latest activated one. The green ball represents the position of pacing stimulus marked by ‘PS’. The axis of X, Y, and Z is consistent with that of torso model, which are in terms of the right-left, the posterior-anterior, and the inferior-superior, respectively.

Figure 3

Results in another animal for pacing at the site of RVA. See figure caption of Fig. 2.

Figure 4

Estimated dipole locations during simultaneous dual-site pacing on an animal. A. The RVA-RVS sites are within a single-chamber of the RV, and B. the RVS-LVA sites are within the dual-chamber pair of the RV and LV. The blue dipole and red dipole represent the estimated dipole locations of initial sites after simultaneous pacing from the RVS and RVA or LVA sites marked by ‘IS_RVS’ and ‘IS_RVA’ or ‘IS_LVA, respectively. The green ball correspondingly represents the positions of these pacing sites marked by ‘PS_RVS’ and ‘PS_RVA’ or ‘PS_LVA.

Figure 4

Estimated dipole locations during simultaneous dual-site pacing on an animal. A. The RVA-RVS sites are within a single-chamber of the RV, and B. the RVS-LVA sites are within the dual-chamber pair of the RV and LV. The blue dipole and red dipole represent the estimated dipole locations of initial sites after simultaneous pacing from the RVS and RVA or LVA sites marked by ‘IS_RVS’ and ‘IS_RVA’ or ‘IS_LVA, respectively. The green ball correspondingly represents the positions of these pacing sites marked by ‘PS_RVS’ and ‘PS_RVA’ or ‘PS_LVA.