Electrocardiographic Imaging for Cardiac Arrhythmias and Resynchronization Therapy

Helder Pereira; Steven Niederer; Christopher A. Rinaldi


Europace. 2020;22(10):1447-1462. 

In This Article

History of Electrocardiographic Imaging

The concept of ECGi, also referred to as electrocardiographic mapping, has been around for more than 40 years. Since the idea was first introduced in 1977,[24] it has undergone many modifications. It is now being recognized as an advantageous diagnostic tool.

Initial studies on the concept were based on either computational or eccentric sphere models or equivalent cardiac electric generators.[25] Most investigations that provided insight on the propagation of electrical activity were simulations in a membrane-based realistic-geometry computer models of the ventricles of the human heart.[26]

Extensive experiments on animal models investigated a wide range of physiological and pathological conditions. Most of these experiments were performed on large mammals, primarily dogs[27] and pigs,[28] to imitate the structure and relations of the heart inside the human body. One of the most important experimental setups was the torso tank (Figure 4).[18] It consisted of a tank shaped like a human torso filled with an electrolyte solution. A perfused dog heart was placed inside the torso tank in a position that resembles the human anatomy. The system included 384 torso-surface electrodes and the same number of rods with electrodes at their tips placed inside the tank around the heart touching the epicardium.

Figure 4.

Torso tank with part of the anterior surface removed to reveal the heart and rods. Rods project from the surface of the body radially inward toward the central axis of the heart. Adapted from Oster et al.18 Author's permission granted.

The potentials, measured with these two sets of electrodes, were than compared to correlate the results and the positions of 'invasive' vs. 'non-invasive' electrodes. Oster et al.[18] defined the basic principle for ECGi equipment and laid the groundwork for future investigations.

The technology evolved over the years, mainly through simulation and model studies. Bidomain models of the cardiac tissue were used to investigate the propagation of excitation wavefronts and associated potential distribution and electrograms.[29] Other studies used transmembrane voltages, epicardial potentials, and dipoles to validate ectopic origins through the inverse problem of electrocardiography.[30] Ultimately, after the method was validated in animal in vitro and in vivo models, it was applied in humans. Early human studies included comparisons of images obtained using non-invasive ECGi to direct intra-operative mapping in open-heart surgery patients (Figure 5).[31]

Figure 5.

Study design used by Ghanem et al.31 ECGi in comparison to intraoperative mapping.17 (A) Vest. (B) Cross-sectional CT slice showing the heart and body-surface electrodes. (C) Subject-specific heart-torso geometry digitized from CT (circles indicate electrode positions). (D) Non-invasive epicardial potentials obtained from CT and body-surface potential mapping data using electrocardiographic imaging. (E) Illustration of the intraoperative mapping procedure showing the anterior where the epicardial patch is going to be inserted. (F) Epicardial patches used for intraoperative mapping. CT, computed tomography; ECGi, electrocardiographic imaging. RightsLink License number 4851571240838

Besides sinus rhythm, ventricular pacing with an external pacemaker was also recorded, which provided crucial information regarding the location of ectopic foci involved in the pathophysiology of various arrhythmias.

The latest major obstacle for ECGi research has been the lack of standards and unbiased comparisons of approaches and techniques in different centres. Papers have not always described all the components in sufficient detail to allow verification and comparison of the results. To overcome this problem, the Consortium for Electrocardiographic Imaging (CEI) was created in 2014.[32] Its main goal is to provide researchers with unified and standardized frameworks for ECGi to facilitate collaboration and the validation of results.