Electrocardiographic Imaging for Cardiac Arrhythmias and Resynchronization Therapy

Helder Pereira; Steven Niederer; Christopher A. Rinaldi

Disclosures

Europace. 2020;22(10):1447-1462. 

In This Article

Emerging Technologies

A new, emerging concept seeks to develop a completely non-invasive technique for the ablation of ventricular arrhythmias. The basic idea is to combine ECGi with stereotactic body radiation therapy (SBRT), which is a method used to deliver high doses of radiation therapy to a precisely defined target, with minimal damage to the surrounding tissue.[81] It is adopted primarily for the treatment of tumours, however, experiments suggest that it could be used as an ablation technique for cardiac arrhythmias.[82] Cuculich et al.[57] reported a case series of five patients who underwent this non-invasive approach for the treatment of VT refractory to medication. First, ECGi was performed to identify the precise location of the VT activation focus. Next, based on the acquired ECGi image, ablative radiation using SBRT was administered to the target tissue. The results showed a 99.9% relative reduction in VT occurrence in a follow-up period of 12months.

To overcome the need for CT as part of the ECGi protocol, variants that use ultrasound and magnetic resonance imaging instead of CT are being developed.[4] The goal is to find an imaging modality that is as accurate and readily available as CT, but without the negative effect of radiation.

Further cooperation between engineers, basic scientists and physicians is essential for discovering an optimal combination of technical capabilities, insights into the pathological mechanism, and clinical benefits of ECGi.[25]

Recently, two studies tried to use a simplified ECGi method as part of a CRT assessment.[35,38] The system in these experiments consisted of a disposable ECG belt with only 53 electrodes that were arranged across the anterior and posterior thoracic walls. The protocol did not include any additional cardiac imaging. This simplified ECGi protocol was reported to have been useful for measuring ED before and after CRT implantation, thus helping in patient selection and optimization;[35] and for selecting an optimal site for left ventricular stimulation.[38]

Scar after myocardial infarction (MI) represents fibrotic tissue with an altered structural architecture and pathological cellular electrophysiology with a high possibility of becoming a source for arrhythmia.[83] In this regard, ECGi may be of particular interest in identifying and describing the electrophysiological substrate in post-MI cases. This was suggested in a study by Cuculich et al.,[44] where the authors successfully characterized the MI scars of 24 patients by low voltage and fractionation; thus, complementing MRI and SPECT imaging modalities provided electrophysiological information of the scar. Importantly, scar localization determined by ECGi corresponded to that observed with MRI and SPECT. Quantification of scar substrate, although in a small cohort was also reported accurately by Wang et al.[60]

Algorithms can be modified for specific patient groups. As an example, a study by Potyagaylo et al.[52] demonstrated the adaptation of a Fast Route algorithm with the additional application of dynamic time warping and its ability to correctly localize the origin of ectopic excitations in patients with CRT to account for local differences in conduction velocities.

In summary, current real-world clinical applications of ECGi can be seen in optimization of the CRT implantation site, identification of potential CRT responders, and more precise ablation therapies with reduced radiation exposure. Further potential uses include risk-stratification in various forms of arrhythmia. However, there is a need to validate such applications with large clinical trials. Such studies may provide robust clinical evidence that could change clinical practice in cardiology.

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