OBJECTIVE: Unipolar intracardiac electrograms (uEGMs) measured inside the atria during electro-anatomic mapping contain diagnostic information about cardiac excitation and tissue properties. The ventricular far field (VFF) caused by ventricular depolarization compromises these signals. Current signal processing techniques require several seconds of local uEGMs to remove the VFF component and thus prolong the clinical mapping procedure. We developed an approach to remove the VFF component using data obtained during initial anatomy acquisition. METHODS: We developed two models which can approximate the spatio-temporal distribution of the VFF component based on acquired EGM data: Polynomial fit, and dipole fit. Both were benchmarked based on simulated cardiac excitation in two models of the human heart and applied to clinical data. RESULTS: VFF data acquired in one atrium were used to estimate model parameters. Under realistic noise conditions, a dipole model approximated the VFF with a median deviation of 0.029mV, yielding a median VFF attenuation of 142. In a different setup, only VFF data acquired at distances of more than 5mm to the atrial endocardium were used to estimate the model parameters. The VFF component was then extrapolated for a layer of 5mm thickness lining the endocardial tissue. A median deviation of 0.082mV (median VFF attenuation of 49x) was achieved under realistic noise conditions. CONCLUSION: It is feasible to model the VFF component in a personalized way and effectively remove it from uEGMs. SIGNIFICANCE: Application of our novel, simple and computationally inexpensive methods allows immediate diagnostic assessment of uEGM data without prolonging data acquisition.
Whole-chamber mapping using a 64-pole basket catheter (BC) has become a featured approach for the analysis of excitation patterns during atrial fibrillation. A flexible catheter design avoids perforation but may lead to spline bunching and influence coverage. We aim to quantify the catheter deformation and endocardial coverage in clinical situations and study the effect of catheter size and electrode arrangement using an in silico basket model. Atrial coverage and spline separation were evaluated quantitatively in an ensemble of clinical measurements. A computational model of the BC was implemented including an algorithm to adapt its shape to the atrial anatomy. Two clinically relevant mapping positions in each atrium were assessed in both clinical and simulated data. The simulation environment allowed varying both BC size and electrode arrangement. Results showed that interspline distances of more than 20 mm are common, leading to a coverage of less than 50% of the left atrial (LA) surface. In an ideal in silico scenario with variable catheter designs, a maximum coverage of 65% could be reached. As spline bunching and insufficient coverage can hardly be avoided, this has to be taken into account for interpretation of excitation patterns and development of new panoramic mapping techniques.
D. Frisch. Implementation and Assessment of Different Techniques for Removing the Ventricular Far Field in Unipolar Electrograms. Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT). Masterarbeit. 2017
A prevalent artifact in intra-atrial electrograms is the ventricular far field. Thats why most commonly, bipolar signals are used in clinical practice, even though the morphology and amplitude of the original unipolar electrograms is distorted in bipolar signals.In this thesis, methods are introduced that allow for a third class of signals: unipolar signals that exclusively exhibit signal components arising from local sources. Or put another way, a novel reference potential is computed that comprises of all the activity far from the current catheter position.There are two classes of methods. Map-based methods need a 4D map of the ventricular far field, recorded in advance, preferably in sinus rhythm. Simultaneous methods, on the other hand, are able to work entirely with the signals currently measured by the catheters electrodes.Map-based methods were quantitatively benchmarked with simulated data of two simulations, and they were also applied to clinical data. The simultaneous methods were applied to clinical data, and a first attempt has been made to develop a benchmark, using clinical data in sinus rhythm.The results confirmed that the ventricular far field can be successfully estimated by spatio- temporal modeling, and subsequently be removed from atrial electrograms.
D. Frisch. Patient-specific Modeling of Catheter Deformation to Extract Panoramic Intracardiac Electrograms during Simulated Atrial Fibrillation. Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT). Bachelorarbeit. 2014
In this work, a mathematical model of an elastically deformable basket catheter has been derived and implemented. It can be put into a patient-specic atrium dened by a triangular mesh. A graphical user interface has been developed that allows catheter positioning with immediate visual feedback. Catheter positions can be generated, saved and opened, and a quick view on the unipolar and full or pairwise bipolar electrogram is possible if the simulated extracellular potentials are available for that geometry.The catheter model has been parameterized to reject the geometry of a Constellation and FIRMap catheter, respectively. A representative set of clinically relevant catheter positions in a patient-specic left and right atrial geometry has been generated in close collaboration with an experienced cardiologist. Combined visualizations of the atrial geometry, the electrogram of selected electrodes and the transmembrane voltage distribution have been produced. It was noted that the electrode spacing must be smaller than half the wave length to be able to identify individual linear wavefronts and calculate the wave propagation velocity and direction. Statistics of atrial coverages, spline-spline distances and electrode-endocard distances have been created and compared between the Constellation and FIRMap basket catheter. The FIRMap catheter yields a better atrial coverage, but the Constellation catheter electrodes generally come to lie closer to the myocardium and therefore provide electrograms with a better signal-to-noise ratio. In addition, due tothe smaller distance between the Constellation electrodes, the activations can be localized more precisely in space and time.Furthermore, a new storage format for simulation data has been introduced. It allows to read signals at given locations in fractions of a second. Before, this process took about one hour.In future, catheter statistics like the atrial coverage and the spline-spline distance can be compared to catheter positions mapped in the clinic. But most notably, signal processing has to be done with the xtracted electrograms. It has to be evaluated whether interesting events like ectopic foci, rotors and flutter circuits can really be detected and localized with basket catheters, or if sequential high density mapping will remain the only approach providing sucient coverage and resolution.