Recent studies about the development of endocardial radiofrequency (RF) ablation lesions (ALs) tried to identify reliable electrogram (EGM) markers for assessment of lesion transmurality. Additional clinically relevant information for physicians can be provided by examining endocardial EGM parameters like signal morphology, amplitude or time points in the signal. We investigated EGM features of the pulmonary vein ostia before and after RF ablation for three point-shaped lesions. Using high-density (HD) mapping, local activation time (LAT) and voltage maps were created, which provided information about the RF ALs regarding the lesion size and showed activation time delay as well as low-voltage areas with bipolar peak-to-peak voltages smaller than 2mV. The time delay of the depolarization front comparing the activation times anterior and posterior to the RF AL was up to 51.5 ms. In a circular area with 5mm radius around an RF AL the mean peak-to-peak voltage decreased by 62-94% to about 0.12-0.44mV and the mean maximal absolute EGM derivative was reduced by 65-96 %. Comparing the results of this study with EGMs of similar clinical settings confirmed our expectations regarding the low-voltage areas caused by the ablation procedure. An improved understanding of the electrophysiological changes is of fundamental importance to provide more information for enhanced RF ablation assessment.
Student Theses (2)
M. Stritt. Local Impedance Mapping of the Atria - What can we Lean about the Atrial Substrate?. Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT). Masterarbeit. 2019
The acquisition of electroanatomical mapping data with clinically relevant information on the atrial substrate still poses a challenging problem in the field of medical and med- ical engineering research. In recent times, studies about the use of a former ablation catheter for the purpose of local impedance (LI) measurements provided promising findings. For the extraction of substrate characteristics, however, influencing factors without relevant information have to be removed from clinical LI signals. The primary aim of this work is to identify influencing factors contributing to the measured LI signals. To perform substrate mapping, it is important to know which of the influencing factors contain relevant information for substrate mapping and which factors only flaw the measurement. Lastly, this work investigates whether the identified influencing factors can be detected, quantified, and removed, and to which degree they affect the LI compared to each other. This thesis aims at identifying all influencing factors of LI measurements using signal processing of clinical data, by the analysis of in vitro measurements, and with the help of catheter simulations. The impact of factors like the catheter movement, the distance to the endocardial surface and overall orientation were shown in both signal processing and simulation. Recurring phenomena like the artifacts caused by steerable sheath segments and the distortions caused by the cardiac rhythm were analyzed. The influence of sodium chloride solution irrigation and the influence of the concentration of the solution commonly used in clinical practice were determined. Approaches to quantify the behavior of initial fast impedance decreases in both in vitro and clinical measurements were implemented in catheter simulations using spherical irrigation volumes. Regarding the influence of cardiac geometry, simulations showed significant LI differences depending on the surrounding tissue settings. The analysis of patho- logical influences showed exemplary substrate LI values of fibrotic and fatty regions which could be distinguished by LI mapping in future applications. Challenges in the current clinical system with special regard to recommendations for future hardware optimization were discussed. In conclusion, it was shown that the identification of influences on the LI signal is possible and that currently the lack of information on real time anatomic data leads to flawed mapping results. Therefore, pathological substrate is not yet distinguishable from healthy tissue with LI mapping.
M. Stritt. High-density Mapping of Ablation Lesions for the Assessment of Myocardial Scar. Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT). Bachelorarbeit. 2017
In the recent past, various studies tried to assess and utilize high-density mapping in clinical practice. Studying the additional value of high-density mapping is of fundamental impor- tance regarding modern cardiac arrhythmia treatment. Enhancing the treatment of cardiac arrhythmias like atrial fibrillation or atrial flutter can be achieved by improving different parts in the treatment chain, like the mapping itself, the signal processing or the measurement method. Progress with regard to hardware and software development is part of the research in biomedical engineering with the goal to provide improved clinical tools for physicians and the overall clinical personnel. The goal of this thesis is the visualization of ablation lesions using the data of a modern high-density mapping system and the assessment of the later developed myocardial scar. Technically solving the task of lesion assessment can be done by identifying reliable markers in the intracardiac electrograms (EGMs) and comparing these markers with similar previous clinical or in-silico studies. Furthermore, the development of a mapping tool for research purposes is tested through the example of a so called path-driven EGM analysis. The investigated high-density mapping data of this research are data sets of a clinical setup where point-shaped radiofrequency (RF) ablation lesions were created on a line of an ipsilateral circumferential antral pulmonary vein isolation. Analyzing these data sets with the developed algorithms and methods leads to the conclusion that in low-voltage areas close to ablation lesions, high-density mapping ensures a higher availability of evaluable intracardiac EGMs. Additional data improves the basis of ablation lesion assessment and the possibility to search for EGM markers regarding lesion size or geometry. This is a main reason why further clinical or in-silico studies using high-density mapping data could play a crucial role in the search of reversible or irreversible electrophysiological effects of RF ablation. To ensure the correctness of the developed 3D maps I statistically compared uni- and bipolar parameters and analyzed the relation of the excitation propagation with the theoretically expected outcome. We further examined an activation time delay of the depolarization front (51.5 ms) by comparing the activation times measured in regions anterior and posterior to the RF ablation lesions. EGM markers like the decrease of the bipolar peak- to-peak voltage (62-94 %) and the decline of the mean maximal absolute EGM derivative (65-96 %) mostly matched with the results of previous studies.Even though there are still not enough EGM markers to provide convincing clinically relevant information, the potential of this branch of research for possible future projects on lesion formation, gap detection or even transmurality seems promising. Fast acquisition of high resolved electroanatomical data together with a combination of visual map investigation and EGM analysis is going to lead to improvements in future research and treatment.