Electrocardiographic Imaging for Cardiac Arrhythmias and Resynchronization Therapy

Helder Pereira; Steven Niederer; Christopher A. Rinaldi


Europace. 2020;22(10):1447-1462. 

In This Article

Cardiac Resynchronization Therapy Response

Electrocardiographic imaging may also play an important role in CRT. As an example, in patients with already-implanted CRTs, ECGi may aid in finding the pacing site with high accuracy, as demonstrated in a study of 29 patients by Revishvili et al.[41] Ploux et al.[39] aimed to evaluate the effectiveness of ECGi for predicting successful outcomes when applied to CRT compared to QRS duration. This was achieved by measuring ventricular activation time in patients with QRS of 120ms or more. They observed that the use of ECGi to establish ventricular electrical uncoupling (VEU), which is the difference between left ventricular activation time and RV activation time, provides a much more accurate picture of the CRT response than 12-lead ECG predictions of QRS duration. Jia et al.[54] also noted that ECGi can play a useful role by providing better insight into electrical synchrony and ventricular activation times, especially regarding the CRT response (Figure 8).

Figure 8.

ECGi activation maps of a clinical responder to cardiac resynchronization therapy. Epicardial ventricular surfaces are displayed in three views (from left to right): anteroposterior, left anterior oblique, and posterolateral. The right ventricular lateral breakthrough is followed by rapid activation of the RV. The wave front spreads to the LV, with a first base-to-apex line of slow conduction (crowding of isochrones). LV activation ends at the lateral base. Adapted from Eschalier et al.69 ECGi, electrocardiographic imaging; LV, left ventricle; RV, right ventricle.Author's permission granted and RightsLink License number 4851580660709.

It is still a challenge to understand why some patients are more likely to benefit from CRT than others. Innovative research is underway, focusing on intraventricular delay patterns, indexes of QRS prolongation and ventricular activation dyssynchrony, to provide some insight into this issue. In light of the capacity of ECGi to provide mechanistic insights for arrhythmias, it may be able to provide detailed information about the therapeutic response. Principally, ECGi can provide information that can be used to determine whether CRT would benefit specific patients.

The ability to predict whether a patient will benefit from CRT is a valuable asset. Silva et al.[53] demonstrated why accurate data are needed to predict CRT outcomes. In their study, the participants consisted of paediatric patients with heart failure who were in the process of obtaining some form of CRT. The mechanism studied was ventricular electrical dyssynchrony (ED), which is typically 20±4ms. When the subjects were divided into responders and non-responders to CRT, the study confirmed that the responder group had an ED index of 22ms, while non-responders had an ED index of 37ms. Thus, ECGi was able to provide data for determining which patients would benefit from CRT. These findings were further supported by another study where, in a group of 25 patients with non-ischaemic cardiomyopathy who had been previously implanted with a CRT device, ECGi, when performed during different programmed pacing, could accurately characterize CRT responders. During intrinsic rhythm, CRT responders showed very high dyssynchrony (ED = 35.5±3.9ms), which was significantly lowered (ED = 23.2±4.4ms) during optimal modes of CRT.[42] One final advantage of ECGi is its ability to guide lead placement during implantation. The mapping system can accurately pinpoint electrical activation sites and provide details on the location of the last excitation area.[53] This was shown in a study by Berger et al.[47] on patients with congestive heart failure undergoing CRT; ECGi can be helpful in identifying responders to CRT. By providing adequate visualization of both endocardial and epicardial ventricular activation, it may lead to patient-specific lead placement and improved device-programming.

Electrocardiographic imaging was used to assess the extent to which right ventricular pacing (RVP) in biventricular pacing leads to left ventricular activation during CRT. In 11 CRT patients with left LBBB, RVP was shown to have different effects on LBBB-induced conduction problems. This finding may change the perception of RVP having LBBB-like effects, which led to the avoidance of RVP during biventricular stimulation.[51]

Electrocardiographic imaging may be more specific, accurate and sensitive than 12-lead ECG in the assessment, diagnosis and management of cardiac arrhythmias.[36] The studies discussed above demonstrate that ECGi is a more insightful technology for the localization of arrhythmias, which once relied solely on 12-lead ECG. This is justified due to the higher validity and reliability shown by ECGi in a wide range of studies and in multiple patient groups. The mapping system has been used to assess various arrhythmias including AF and VF, PVCs, and WPW syndrome, all of which have been accurately defined and reported. Moreover, ECGi has been used to determine which patients will likely respond to CRT. Not only does the accuracy of ECGi inform its validation, but its reproducibility in many other studies also supports its reliability. These studies involved different numbers of patients and different methods, but their results were consistent. Finally, these studies reported that one of ECGi's features was that it could provide electrical activity and excitation times along the epicardium by measuring potentials, which, in effect, could render a 3D map of the heart.[70]