Understanding the Utility of Endocardial Electrocardiographic Imaging in Epi-Endocardial Mapping of 3D Reentrant Circuits

Abstract

Background: Studies of VT mechanisms are largely based on a 2D portrait of reentrant circuits on one surface of the heart. This oversimplifies the 3D circuit that involves the depth of the myocardium. Simultaneous epicardial and endocardial (epi-endo) mapping was shown to facilitate a 3D delineation of VT circuits, which is however difficult via invasive mapping.

Objective: This study investigates the capability of noninvasive epicardial-endocardial electrocardiographic imaging (ECGI) to elucidate the 3D construct of VT circuits, emphasizing the differentiation of epicardial, endocardial, and intramural circuits and to determine the proximity of mid-wall exits to the epicardial or endocardial surfaces.

Methods: 120-lead ECGs of VT in combination with subject-specific heart-torso geometry are used to compute unipolar electrograms (CEGM) on ventricular epicardium and endocardia. Activation isochrones are constructed, and the percentage of activation within VT cycle length is calculated on each surface. This classifies VT circuits into 2D (surface only), uniform transmural, nonuniform transmural, and mid-myocardial (focal on surfaces). Furthermore, the endocardial breakthrough time was accurately measured using Laplacian eigenmaps, and by correlating the delay time of the epi-endo breakthroughs, the relative distance of a mid-wall exit to the epicardium or the endocardium surfaces was identified.

Results: We analyzed 23 simulated and in-vivo VT circuits on post-infarction porcine hearts. In simulated circuits, ECGI classified 21% as 2D and 78% as 3D: 82.6% of these were correctly classified. The relative timing between epicardial and endocardial breakthroughs was correctly captured across all cases. In in-vivo circuits, ECGI classified 25% as 2D and 75% as 3D: in all cases, circuit exits and entrances were consistent with potential critical isthmus delineated from combined LGE-MRI and catheter mapping data.

Conclusions: ECGI epi-endo mapping has the potential for fast delineation of 3D VT circuits, which may augment detailed catheter mapping for VT ablation.

Keywords: 3D Ventricular tachycardia; Electrocardiographic imaging; Endocardial Breakthrough.

Figure 1:

Illustration of a 3D reentrant circuit and its epicardial and endocardial observations. A: A mid-wall exit exhibits as a partial rotation at one surface and a focal activation at the other surface. B. Illustration of a simplified relation between the breakthrough times on both surfaces and the exit site.

Figure2:

ECGI workflow. Reconstruction of heart electrical potentials from body surface potentials by obtaining body surface recordings from 120 leads placed on the subject’s body and generating heart and torso meshes from MRI images.

Figure3:

Analyzing the ECGI solutions on epicardium and endocardium. A) Comparing ECGI pattern and amplitude on epicardium B) Comparing ECGI solution pattern and amplitude on endocardium C) example of identifying the endocardial breakthrough time from the Laplacian eigenmap of the ECGI solution.

Figure 4:

Timing (A) and Localization (B) error of Epicardial-breakthrough categorized by sub-epicardial and sub-endocardial groups.

Figure 5:

(A) Missing isthmus in ECGI (B) Artificially closing the loop (C) Epicardial breakthrough far from the circuit’s exit site.

Figure 6:

Illustration of the artificial macroscopic rotation pattern created on the endocardial surface by ECGI solutions.

Figure 7:

Inferring the 3D category of reentrant circuits using epi-endocardial activation patterns.

Figure 8:

Case-by-case comparison of ECGI recognition of 3D category of reentrant circuits versus simulated ground truth.

Figure 9:

using the delay between epicardial and endocardial breakthroughs to identify the closer surface to the exit site.

Figure 10:

MRI, EAM and ECGI analysis of animal data, case1 with a sub-endocardial anterior septal circuit.

Figure 11:

MRI, EAM and ECGI analysis of animal data, case2 with a sub-epicardial apical circuit.

Figure 12:

MRI, EAM and ECGI analysis of animal data, case3 with a mid-wall mid-basal anterior-septal circuit.

Figure 13:

MRI, EAM and ECGI analysis of animal data, case4 with a mid-wall circuit located at basal lateral-anterior region of the LV septum.