Browsing by Author "Ravikumar, Vasanth"
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Item Cardiac Voltage Analysis Software for Interpretation of Transmembrane Voltage Movies Obtained via the Langendorff Perfusion Setup(2021) Callaway, Trenton; Talkachova, Alena; Ravikumar, VasanthUsing the Langendorff perfusion setup to study and compare healthy and arrhythmic heart conditions is an increasingly common practice. This technique requires the ex-vivo perfusion of the heart, wherein cardiac tissue is injected with a voltage sensitive fluorescent dye, allowing for video analysis of electrical activity in the heart under normal and arrhythmic conditions. When conducted in this study, this technique resulted in recorded movies of cardiac tissue interpretable as 3D matrices whereby the spatial dimensions are defined by the movie resolution of 80 by 80 pixels, and the temporal dimension is based on the length of the movie in frames. The goal of this project was to further develop and investigate the efficiency of a data analysis application, CVAS (Cardiac Voltage Analysis Software), which is capable of analyzing these matrices in a user-friendly, intuitive way. This MATLAB based software is designed to be capable of creating highly modular plots, calculations, and optical maps for analysis on both paced and arrhythmic data. This task is one that would heavily benefit contemporary electrophysiological cardiology, and provide easy assessment of electrophysiological properties of the heart during normal and abnormal cardiac rhythms. By collecting new data for this software to analyze, CVAS was critiqued and improved to optimize its ease of use and interaction with researchers. Additionally, its ability to generate high quality and immediately presentable optical maps, plots, and calculations for both paced and arrhythmic data was strengthened. CVAS’s current capabilities include loading in and masking optical movie data sets, visualizing the electrical activity of the heart with fluorescence movies and action potential traces, and allowing for visualization and analysis of both paced and arrhythmic data sets through the use of action potential duration, activation time, conduction velocity, dominant frequency, and multiscale frequency maps.Item Signal processing approaches for the spatiotemporal analysis of cardiac arrhythmias using intracardiac electrograms(2022-02) Ravikumar, VasanthEach heartbeat is controlled by an electrical wave of excitation that propagates throughthe heart and initiates cardiac contraction. The normal heartbeat is initiated by pacemaker cells in the sinus node located in the right atrium, propagate throughout the atria, and then enters the ventricles via the atrioventricular junction and finally ends in the Purkinje fibers. The rate and regularity of these cardiac rhythms are determined by the intrinsic firing rate (automaticity) of the pacemaker cells and the influence of extrinsic factors, including various ionic mechanisms and drugs. Abnormal regimes of wave initiation and propagation result in cardiac arrhythmias. Various mechanisms, including local ectopic activity, focal triggers, wave breaks, and functional reentry, drive the arrhythmic activity in the heart. The spatiotemporal complexity of each of these underlying mechanisms is different, with more complexity seen in tachyarrhythmias and less complexity for bradyarrhythmias. Understanding the spatiotemporal complexity of the different arrhythmias is of great interest to electrophysiologists. In recent years, catheter ablation therapy (non-pharmacological approach) has had anincreasingly important role in curing many arrhythmias. The underlying spatiotemporal complexity of each arrhythmia plays an important role in deciding the target sites for ablation in this therapy. Currently, existing signal analysis techniques are not robust for all types of arrhythmias. Therefore it is essential to develop new approaches that can fully capture the intrinsic dynamics and the spatiotemporal complexity of both atrial and ventricular arrhythmias using intracardiac electrogram signals. Some novel approaches, namely multiscale frequency, multiscale entropy, kurtosis, and Shannon entropy was developed using the ex-vivo optical mapping of rabbit hearts. But, the nature of signals obtained during optical mapping is very different from the intracardiac electrograms obtained during the catheter ablation procedure. Also, the clinical recordings suffer from limitations such as sparse spatial data availability and sequential mapping. Therefore it is essential to enhance the above techniques to work on the intracardiac electrograms and also identify the spatial sites in the heart that maintain these arrhythmic activities. For my study, the intracardiac analysis was performed under two different types ofcardiac arrhythmic rhythms, namely Atrial Fibrillation (AF) and Ventricular Fibrillation (VF). Atrial Fibrillation (AF) is an arrhythmia in the upper two chambers (atria) of the heart. AF is responsible for significant impairment in quality of life and contributes to substantial morbidity and health care expenditure. AF is the most common arrhythmia in humans and, as such, is heterogeneous in its mechanism, presentation, and clinical course and therefore requires individualized treatment. Ventricular fibrillation (VF) is a type of lethal heart rhythm. During ventricular fibrillation, disorganized heart signals cause the lower heart chambers (ventricles) to quiver, and the heart does not pump blood to the rest of the body. Ventricular fibrillation is an emergency that requires immediate medical attention. It's the most frequent cause of sudden cardiac death. Although both these rhythms originate at different locations of the heart and havedifferent types of rhythms and morphology, the underlying spatiotemporal organizations and intracardiac electrogram analysis approaches are similar. Therefore, my thesis consists of the following three objectives: 1. Clinical implementation and validation of novel approaches using intracardiac electrograms to characterize the spatiotemporal dynamics of the AF arrhythmic activities. 2. Development of a similarity score using a combination of various iEGMs analysis techniques to more accurately identify the spatial location of active sites in AF patients. 3. Development of an analytical approach to characterize the organization (organized or disorganized) of VF electrical activities using clinical intracardiac electrograms.Item Software Design to Aid in Analysis of Cardiac Voltage Matrices Obtained Via the Langendorff Perfusion Technique(2020) Callaway, Trenton; Talkachova, Alena; Ravikumar, VasanthThere does not currently exist any open source software usable by researchers to create and analyze optical mappings of the heart. When analyzing the heart and especially its action potentials, ex-vivo perfusion of the heart is performed using the Langendorff perfusion setup. Next, voltage sensitive fluorescent dye is injected into the ex-vivo heart, illuminating the target area with a 532 nm wavelength green laser tuned to the dye’s activation range. The illuminated area of the heart can then be recorded at high frames per second (fps) to create a movie which collects light intensity data correlating to the transmembrane voltage of the heart at that pixel. This creates a voltage matrix for every frame, where each pixel is a numerical value. The goal of this project is to find out if the process of analyzing this three dimensional voltage matrix can be made intuitive, available, and open source. The creation of the software is being done on MATLAB (Natick, MA) and incorporates a user friendly graphics user interface (GUI) , that allows the user to quickly and easily analyse this three dimensional matrix of fluorescence values in a multitude of ways. The software aims to allow the user to input the file name of their fluorescence data, along with the fps used in the experiment, and from that perform several calculations. The software is intended to automatically locate the start and end frames of every action potential (AP) in the data. With this, the user is able to plot the AP across the frame numbers, calculate and map the dominant frequency (DF) and multiscale frequency (MSF) of the action potentials, determine the mean conduction velocity of the transmembrane voltage, create colour maps for both activation time (AT) and action potential duration (APD), and lastly display an animation of the voltage as is flows across the tissue. The benefits of creating a robust software go beyond the provision of effective and intuitive analysis. This software would also allow for quick and easy modifications that would otherwise require rewriting sections of code to perform. As an example, this software is able to account for various frame rates, desired voltage thresholds for identifying action potential initiation, alterations to color mapping domains, and more. The ease of life provided will allow more institutions to conduct similar studies to those currently being done in the Talkachova Lab at the University of Minnesota Twin Cities, helping to further the understanding of cardiac signals, arrhythmia, and healthy heart activity.