Ultra-high frequency electrocardiogram mapping in cardiac resynchronisation therapy

Walton, Jamie Thomas (2025) Ultra-high frequency electrocardiogram mapping in cardiac resynchronisation therapy. Doctoral thesis (DClinSci), Manchester Metropolitan University.

Preview

Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (4MB) | Preview

Abstract

Cardiac resynchronisation therapy (CRT) has become an established treatment for patients with heart failure and prolonged QRS duration (QRSd), improving quality of life, reducing heart failure hospitalisation, and mortality. As a treatment for electrical dyssynchrony, current indications for CRT are a QRS duration ≥130ms and/or a left bundle branch block (LBBB). Despite improvements in selection criteria and technology, only 70-80% of patients benefit from CRT. Traditional surface electrocardiogram (ECG) parameters, QRSd and QRS morphology, are limited in their ability to detect electrical dyssynchrony. The assessment of dyssynchrony has been considered extensively, as well as the relationship of electrical conduction with mechanical activity. Furthermore, echocardiographic measures of “mechanical” dyssynchrony have not consistently improved CRT outcomes, suggesting that electrical dyssynchrony may be a critical factor of response. Recent and renewed innovations such as: vectorcardiography, ECG imaging, body surface potential mapping (BSPM) and ultra-high frequency ECG (UHFECG) have been developed to improve CRT response by providing enhanced electrical dyssynchrony metrics. UHFECG, specifically has evolved through the study of high frequency potentials within the surface ECG, outside the standard frequency range. These potentials not only have value in detecting ischaemia and arrhythmic risk, but also in the evaluation of patients with significant conduction issues in the context of heart failure. Computation of these “ultra-high” frequency signals provide temporo-spatial information on the transmural ventricular activation. This technique enables precise assessment of a novel dyssynchrony metric, e-DYS, which has shown potential in predicting CRT response and optimising patient selection. Current evidence on the use of ultra-high-frequency ECG (UHFECG) to detect dyssynchrony across different QRS morphologies is limited. I present our observations of UHFECG maps in these QRS morphologies, demonstrating substantial differences in e-DYS, between patients with underlying LBBB and other ECG morphologies. This suggests that e-DYS is sensitive to dyssynchrony, particularly relevant for CRT candidacy. While QRSd is a binary measure of interventricular conduction delay, e-DYS and UHFECG provide nuanced insights into the directionality and patterns of dyssynchrony. Notably, dyssynchrony detected by UHFECG in non-LBBB morphologies, highlights that QRSd and QRS morphology alone may not sufficiently define electrical dyssynchrony, underscoring the need for an individualised approach to patient selection. In patients undergoing CRT, we observed significant reductions in e-DYS, QRS area, and QRSd post-implantation, though this reduction in e-DYS did not associate with LVRR (left ventricular reverse remodelling) or improvement in LVEF (left ventricular ejection fraction), limiting its application. However, UHFECG detected subtle changes in dyssynchrony with varied CRT programming, particularly with adjustments in interventricular (VV) pacing delay. These findings demonstrate UHFECG's potential to aid CRT device optimisation. Further research with larger cohorts is necessary to confirm its impact on clinical CRT outcomes.