26 research outputs found

    Detecting Mechanical Alternans Utilizing Photoplethysmography

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    Mechanical alternans (MA) is a biomarker associated with mortality in heart failure patients. Its detection through continuous blood pressure (BP) monitoring is costly and impractical. In this work, we propose the use of photoplethysmography (PPG) as a non-invasive solution for MA detection. Continuous invasive BP and PPG were recorded and analyzed during ventricular pacing in 10 patients. The presence of MA was evaluated in BP and in features characterizing the PPG pulse morphology. Mechanical alternans was defined as an alternation in maximum dP/dt for a duration of 20 consecutive heart beats or more. Mechanical alternans was observed in BP in 5 patients (50%). The PPG-based MA surrogates showing the highest detection accuracy, were the maximum of the first derivative of the PPG pulse (V'M), and the pulse amplitude (A). Both features allow detection of MA positive patients with 100% sensitivity and 100% specificity. The magnitude of MA was correlated between BP and V'M PPG (R=0.92, p<0.001) and between BP and A PPG (R=0.89, p<0.001). In conclusion, MA can be accurately detected noninvasively through the PPG

    Non-Invasive Detection of Mechanical Alternans Utilizing Photoplethysmography

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    Background and Significance: Mechanical alternans (MA) is a biomarker associated with mortality and life-threatening arrhythmias in heart failure patients. Despite showing prognostic value, its use is limited by the requirement of measuring continuous blood pressure (BP), which is costly and impractical. Objective: To develop and test, for the first time, non-invasive MA surrogates based on photoplethysmography (PPG). Methods: Continuous BP and PPG were recorded during clinical procedures and tests in 35 patients. MA was induced either by ventricular pacing (Group A, N=19) or exercise (Group B, N=16). MA was categorized as sustained or intermittent if MA episodes were observed in at least 20 or between 12 to 20 consecutive beats, respectively. Eight features characterizing pulse morphology were derived from the PPG and MA surrogates were evaluated. Results: Sustained alternans was observed in 9 patients (47%) from Group A, whereas intermittent alternans was observed in 13 patients (68%) from Group A and in 10 patients (63%) from Group B. The PPG-based MA surrogate showing the highest accuracy, V'M, was based on the maximum of the first derivative of the PPG pulse. It detected both sustained and intermittent MA with 100% sensitivity and 100% specificity in Group A and intermittent MA with 100% sensitivity and 83% specificity in Group B. Furthermore, the magnitudes of MA and its PPG-based surrogate were linearly correlated (R 2 =0.83, p<0.001). Conclusion: MA can be accurately identified non-invasively through PPG analysis. This may have important clinical implications for risk stratification and remote monitoring

    Examination of myocardial electrophysiology using novel panoramic optical mapping techniques

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    Optical mapping of voltage signals has revolutionised the field and study of cardiac electrophysiology by providing the means to visualise changes in electrical activity at a high temporal and spatial resolution from the cellular to the whole heart level under both normal and disease conditions. The aim of this thesis was to develop a novel method of panoramic optical mapping using a single camera and to study myocardial electrophysiology in isolated Langendorff-perfused rabbit hearts. First, proper procedures for selection, filtering and analysis of the optical data recorded from the panoramic optical mapping system were established. This work was followed by extensive characterisation of the electrical activity across the epicardial surface of the preparation investigating time and heart dependent effects. In an initial study, features of epicardial electrophysiology were examined as the temperature of the heart was reduced below physiological values. This manoeuvre was chosen to mimic the temperatures experienced during various levels of hypothermia in vivo, a condition known to promote arrhythmias. The facility for panoramic optical mapping allowed the extent of changes in conduction timing and pattern of ventricular activation and repolarisation to be assessed. In the main experimental section, changes in epicardial electrical activity were assessed under various pacing conditions in both normal hearts and in a rabbit model of chronic MI. In these experiments, there was significant changes in the pattern of electrical activation corresponding with the changes in pacing regime. These experiments demonstrated a negative correlation between activation time and APD, which was not maintained during ventricular pacing. This suggests that activation pattern is not the sole determinant of action potential duration in intact hearts. Lastly, a realistic 3D computational model of the rabbit left ventricle was developed to simulate the passive and active mechanical properties of the heart. The aim of this model was to infer further information from the experimental optical mapping studies. In future, it would be feasible to gain insight into the electrical and mechanical performance of the heart by simulating experimental pacing conditions in the model

    Simplified Cardiodynamic Tissue Electrophysiology Characterization, Reduced Order Modeling with Therapeutic Perspective

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    Atrial fibrillation (Afib) is the most common cardiac arrhythmia affecting millions of people around the world. Mapping and analysis of electrical activation patterns such as electric rotors during Afib is crucial in understanding arrhythmic mechanisms and assessment of diagnostic measures. To this end, there exists various mapping studies where textit{'quantitative'} features such as local activation time, dominant frequency, wave direction, and conduction velocity are extracted from recorded intracardiac electrograms (EGMs). However, obtaining quantitative features further adds to multiplicity of the data and henceforth does not help interpretation of measured signals as opposed to using a more compressed diagnostic terms such as linking the measurements to reentry mechanisms. Through some techniques it is possible to construct isopotential and phase mappings by the help of monophasic action potential recordings in higher spatial resolution. In those cases, however, both expensive mapping tools performing multi-site simultaneous recordings which are not available to most of electrophysiologists are required. On the other hand, the most commonly used catheters which provide high resolution but local measurements remain rather rudimentary in mapping a spatially more global arrhythmic behaviors in a simultaneous fashion. Spiral waves are tissue level phenomena observed in both clinical and experimental settings. They are the product of electrical rotors which are associated with reentry mechanisms during Afib. They can be reproduced using computer models of cardiac electrical activity. Current computer models vary in complexity, accuracy, and efficiency. One particular type is called biophysical models which are based on detailed ion channel interactions. Besides being computationally demanding, they are exceedingly complex and intractable preventing their use in a systems approach where multilevel events are generally considered together. Phenomenological models, on the other hand, include summarized details of ionic events yet preserve fundamental biophysical accuracy. A particular one of them, a minimal resistor model (MRM), was shown to reproduce relevant basic electrophysiological behaviors such as (action potential) AP and electrical restitution properties for human ventricular tissue. The objective in present thesis is to 'qualitatively' characterize fibrillatory wavefront propagation dynamics in cardiac tissue using simulated intracardiac EGMs obtained from most commonly used and lower cost catheter types providing high resolution but localized readings. Another purpose connected to the previous is to show adequacy of a phenomenological model, MRM, in reproducing biophysically related behaviors for human atria. In this respect, two category of problems are handled throughout the thesis: (1) parameter estimation of MRM and (2) discrimination of spiral wave behaviors through intracardiac EGMs simulated using MRM. In the first part, representativeness of MRM for human atrial electrophysiology is established through adaptation of it to a biophysically detailed model originated from experimental data. Specifically, a method is proposed for parameter estimation of the simple model, MRM, to match a targeted behavior such as AP and electrical restitutions first generated from a complex model, by using extended Kalman filter (EKF). In the second part, a method that receives intracardiac EGMs and returns corresponding wavefront propagation patterns classified in terms of electric rotor dynamics is introduced. The method incorporates an information theoretical distance which is called normalized compression distance (NCD) used for assessment of distance measure between simulated behaviors. Achieving outstanding performance together with robustness in discrimination through usage of simulated data enables a theoretical validation of the method. Proposed frameworks collectively yield (1) potential usability of a computationally efficient and easier in analysis model for tissue level cardiac events and (2) simplicity and practicality in clinics through a mapping from a multiple, complex EGM signals to electric rotor behaviors, symptoms more relevant to the diagnosis.Ph.D., Electrical Engineering -- Drexel University, 201

    The Effects of Gap Junction Modulation on Myocardial Structure and Function

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    The aim of the work in this thesis was to investigate the effects of gap junction modulation during acute myocardial infarction (MI) on ventricular arrhythmogenesis in the settings of acute reperfusion and chronic post-myocardial infarction. Ventricular arrhythmias can occur during reperfusion because of abrupt changes in electrophysiology, whilst arrhythmias occur post-MI because the healed infarct scar forms a substrate for re-entry, with increased inhomogeneity of scarring being associated with greater arrhythmia susceptibility. The effects gap junction modulation on reperfusion arrhythmogenesis were studied in an ex vivo rat model of acute ischaemia-reperfusion. Gap junction modulators were administered to hearts subjected to left anterior descending artery occlusion followed by reperfusion. The electrophysiological changes that accompany ischaemia-reperfusion were studied using optical mapping. Gap junction modulators, AAP10 and carbenoxolone, reduced the incidence of reperfusion arrhythmias. This was associated with the attenuation of the abrupt recovery of conduction during reperfusion, which may underlie their antiarrhythmic effects. A four-week rat chronic myocardial infarction model was developed to study the effects of acute gap junction modulation on late post-MI arrhythmias. Gap junction modulators, rotigaptide and carbenoxolone, were administered acutely for 7 days from the time of surgical MI, and rats were studied at 4 weeks post-MI with ECG-telemetry, programmed electrical stimulation, optical mapping, histomorphometry and connexin43 immunohistochemistry. Enhancing gap junction coupling with rotigaptide acutely during MI reduced heterogeneities in infarct border zone scarring and reduced susceptibility to ventricular arrhythmias on programmed electrical stimulation. Histomorphometric studies support a possible mechanism whereby homogenisation of the acute ischaemic insult and the cell death process may result in more homogeneous scarring and a less arrhythmic healed substrate. Gap junction modulation was anti-arrhythmic in the acute reperfusion setting, and the enhancement of coupling during acute MI may represent a novel therapeutic strategy to modify the morphology of the healed infarct and alter post-infarction arrhythmia susceptibility

    Cardiac Arrhythmias

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    Cardiac arrhythmias are common triggers of emergency admission to cardiology or high-dependency departments. Most cases are easy to diagnose and treat, while others may present a challenge to healthcare professionals. A translational approach to arrhythmias links molecular and cellular scientific research with clinical diagnostics and therapeutic methods, which may include both pharmacological and non-pharmacologic treatments. This book presents a comprehensive overview of specific cardiac arrhythmias and discusses translational approaches to their diagnosis and treatment

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    The ECG in the evaluation of pacemaker function and diagnosis of malfunction

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    The contact electrogram and its architectural determinants in atrial fibrillation

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    The electrogram is the sine qua non of excitable tissues, yet classification in atrial fibrillation (AF) remains poorly related to substrate factors. The objective of this thesis was to establish the relationship between electrograms and two commonly implicated substrate factors, connexin 43 and fibrosis in AF. The substrates and methods chosen to achieve this ranged from human acutely induced AF using open chest surgical mapping (Chapter 6), ex vivo whole heart Langendorff (Chapter 7) with in vivo telemetry confirming spontaneous AF in a new species of rat, the Brown Norway and finally isolated atrial preparations from an older cohort of rats using orthogonal pacing and novel co-localisation methods at sub-millimetre resolution and in some atria, optical mapping (Chapter 8). In rodents, electrode size and spacing was varied (Chapters 5, 10) to study its effects on structure function correlations (Chapter 9). Novel indices of AF organisation and automated electrogram morphology were used to quantify function (Chapter 4). Key results include the discoveries that humans without any history of prior AF have sinus rhythm electrograms with high spectral frequency content, that wavefront propagation velocities correlated with fibrosis and connexin phosphorylation ratios, that AF heterogeneity of conduction correlates to fibrosis and that orthogonal pacing in heavily fibrosed atria causes anisotropy in electrogram-fibrosis correlations. Furthermore, fibrosis and connexin 43 have differing and distinct spatial resolutions in their relationship with AF organisational indices. In conclusion a new model of AF has been found, and structure function correlations shown on an unprecedented scale, but with caveats of electrode size and direction dependence. These findings impact structure function methods and prove the effect of substrate on AF organisation.Open Acces

    Photoplethysmography in noninvasive cardiovascular assessment

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    The electro-optic technique of measuring the cardiovascular pulse wave known as photoplethysmography (PPG) is clinically utilised for noninvasive characterisation of physiological components by dynamic monitoring of tissue optical absorption. There has been a resurgence of interest in this technique in recent years, driven by the demand for a low cost, compact, simple and portable technology for primary care and community-based clinical settings, and the advancement of computer-based pulse wave analysis techniques. PPG signal provides a means of determining cardiovascular properties during the cardiac cycle and changes with ageing and disease. This thesis focuses on the photoplethysmographic signal for cardiovascular assessment. The contour of the PPG pulse wave is influenced by vascular ageing. Contour analysis of the PPG pulse wave provides a rapid means of assessing vascular tone and arterial stiffness. In this thesis, the parameters extracted from the PPG pulse wave are examined in young adults. The results indicate that the contour parameters of the PPG pulse wave could provide a simple and noninvasive means to study the characteristic change relating to arterial stiffness. The pulsatile component of the PPG signal is due to the pumping action of the heart, and thus could reveal the circulation changes of a specific vascular bed. Heart rate variability (HRV) represents one of the most promising quantitative markers of cardiovascular control. Calculation of HRV from the peripheral pulse wave using PPG, called pulse rate variability (PRV), is investigated. The current work has confirmed that the PPG signal could provide basic information about heart rate (HR) and its variability, and highly suggests a good alternative to understanding dynamics pertaining to the autonomic nervous system (ANS) without the use of an electrocardiogram (ECG) device. Hence, PPG measurement has the potential to be readily accepted in ambulatory cardiac monitoring due to its simplicity and comfort. Noncontact PPG (NPPG) is introduced to overcome the current limitations of contact PPG. As a contactless device, NPPG is especially attractive for physiological monitoring in ambulatory units, NICUs, or trauma centres, where attaching electrodes is either inconvenient or unfeasible. In this research, a prototype for noncontact reflection PPG (NRPPG) with a vertical cavity surface emitting laser (VCSEL) as a light source and a high-speed PiN photodiode as a photodetector is developed. The results from physiological experiments suggest that NRPPG is reliable to extract clinically useful information about cardiac condition and function. In summary, recent evidence demonstrates that PPG as a simple noninvasive measurement offers a fruitful avenue for noninvasive cardiovascular monitoring. Key words: Photoplethysmography (PPG), Cardiovascular assessment, Pulse wave contour analysis, Arterial stiffness, Heart rate (HR), Heart rate variability (HRV), Pulse rate variability (PRV), Autonomic nervous system (ANS), Electrocardiogram (ECG).EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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