607 research outputs found
Quantification and classification of potassium and calcium disorders with the electrocardiogram: What do clinical studies, modeling, and reconstruction tell us?
Diseases caused by alterations of ionic concentrations are frequently observed challenges and play an important role in clinical practice. The clinically established method for the diagnosis of electrolyte concentration imbalance is blood tests. A rapid and non-invasive point-of-care method is yet needed. The electrocardiogram (ECG) could meet this need and becomes an established diagnostic tool allowing home monitoring of the electrolyte concentration also by wearable devices. In this review, we present the current state of potassium and calcium concentration monitoring using the ECG and summarize results from previous work. Selected clinical studies are presented, supporting or questioning the use of the ECG for the monitoring of electrolyte concentration imbalances. Differences in the findings from automatic monitoring studies are discussed, and current studies utilizing machine learning are presented demonstrating the potential of the deep learning approach. Furthermore, we demonstrate the potential of computational modeling approaches to gain insight into the mechanisms of relevant clinical findings and as a tool to obtain synthetic data for methodical improvements in monitoring approaches
Serum potassium concentration monitoring by ECG time warping analysis on the T wave
This doctoral thesis was developed within the joint Ph.D. program in biomedical engineering at Universitat Politècnica de Catalunya (Barcelona, Spain) and University of Zaragoza (Zaragoza, Spain) in the framework of Doctorats Industrials program co-financed by Laboratorios Rubió S.A. (Castellbisbal, Spain) and Agència de Gestió d’Ajuts Universitaris i de Recerca, Generalitat de Catalunya (Spain).
This thesis was performed in partnership with the Nephrology ward from Hospital ClÃnico Universitario Lozano Blesa (Zaragoza, Spain) and in collaboration with Dr J. RamÃrez from the William Harvey Research Institute, Queen Mary University of London (London, UK).End-stage renal disease (ESRD) patients demonstrate an increased incidence of sudden cardiac death (SCD) with declining kidney functioning as a consequence of blood potassium ([K+]) homeostasis impairment, which is restored by hemodialysis (HD) therapy. The clinically established method for the diagnosis of [K+] imbalance is blood tests, an invasive and costly procedure that limits continuous monitoring of ESRD patients. A non-invasive ambulatory index, able to quantify changes in [K+] level is an open issue. In this context, the electrocardiogram (ECG) and in particular, the T wave (TW) morphology, has been shown to be strongly correlated with [K+] imbalance. Therefore, the aim of this dissertation is to investigate and to propose TW-derived markers able to monitor changes in [K+] levels in ESRD patients undergoing HD. For that purpose, the time warping analysis, a technique that allows the comparison and quantification of differences between two different TW shapes, was investigated. The application of TW time warping based markers in monitoring [K+ ] variations (Δ [K+]) and the derivation of a heart-rate corrected marker is proposed and compared with respect to two well-established Δ [K+]-related TW-based indexes. All the markers are evaluated in a single lead approach and after having emphasised the TW energy content through spatial transformation by Principal Component Analysis (PCA). Results demonstrate that the proposed biomarkers outperform the already proposed indexes, also proving that the use of PCA transformed lead generates markers with a higher correlation with Δ [K+] than the single lead approach. The possibility to improve markers robustness in the case of low signal-to-noise ratio ECGs, by spatially transforming the signal maximising the beat-to-beat TW periodicity criteria through the so-called Periodic Component Analysis (pCA), is then explored. pCA-based markers show superior performance during and after the HD than those obtained by PCA suggesting improved stability for continuous Δ [K+] tracking. The thesis studies also the application of regressions models to quantify Δ [K+] from pCA-based time warping markers. The accuracy of the regression models is evaluated by correlation and estimation error between the actual and the corresponding model-estimated Δ [K+] values, and the smallest estimation error is found for quadratic regression models. Being the time warping derived markers sensitive to TW boundary delineation errors, which may endanger their prognostic power, the advantages of using a weighting stage is investigated for their robust computation. The performance of two weighting functions (WF)s is tested and compared with respect to the control no weighting case, in simulated scenarios and in real scenarios (i.e. for [K+] monitoring and SCD risk stratification). No improvements in [K+] monitoring are found, probably due to the considerable marked [K+]-induced TW morphological changes. On the contrary, both simulation tests and SCD risk stratification analysis show that the proposed WFs can enhance the robustness of TW time warping analysis against TW delineation errors. In conclusion, this Doctoral Thesis confirms the hypothesis that enhanced perforce in Δ [K+] tracking and quantification can be achieved by analysing the overall TW morphology by time warping analysis. The simplicity of the technology, together with its low cost and ease of acquisition, should provide a new opportunity for TW analysis to reach standard clinical practice. Moreover, the use of WFs to minimise the undesired effects of TW delineation errors on the computation of time warping markers revealed a noticeable improvement of the SCD risk stratification power of time warping derived indexes.Los pacientes con enfermedad renal en etapa terminal (ESRD) demuestran una mayor incidencia de muerte cardÃaca súbita (SCD) tras el deterioro del funcionamiento renal como consecuencia del desequilibrio del potasio ([K+]) en sangre. Este último se restablece mediante la terapia de hemodiálisis (HD). El desequilibrio de [K+] se diagnostica a través del análisis de sangre, un procedimiento invasivo y costoso que limita la monitorización de los pacientes con ESRD. Se necesita un Ãndice ambulatorio no invasivo, capaz de cuantificar los cambios en el nivel de [K+] (Δ [K+]). En este contexto, se ha demostrado que el electrocardiograma (ECG) y en particular la onda T (TW), están correlacionados con Δ [K+]. El objetivo de esta tesis es evaluar marcadores derivados de la TW capaces de monitorizar ¿[K+] en pacientes con ESRD sometidos a HD. Para ello, se aplicó el análisis time warping, una técnica que permite la comparación de dos formas diferentes de TW. En primer lugar, se evalúa la aplicación de marcadores basados en el time warping para el seguimiento de Δ [K+] asà como la derivación de un marcador corregido por la frecuencia cardÃaca, comparando los marcadores con respecto a dos Ãndices basados en TW bien establecidos y relacionados con Δ [K+]. Todos los marcadores se evalúan en las derivaciones independientes y después de haber enfatizado el contenido de energÃa de TW a través del Análisis de Componentes Principales (PCA). Los resultados demuestran mejores prestaciones de los marcadores time warping respecto a los ya propuestos y que el uso de PCA genera marcadores con una correlación más alta con Δ [K+] respecto a las derivaciones independientes. A continuación, se explora la posibilidad de mejorar la robustez de los marcadores en el caso de ECG con una relación señal/ruido baja, maximizando la periodicidad de TW latido a latido mediante el Análisisde Componentes Periódicos (pCA). Los marcadores basados en pCA muestran un rendimiento superior durante y después de la HD que los obtenidos por PCA, lo que sugiere una estabilidad mejorada para el seguimiento continuo de Δ [K+]. Luego, se evalúan modelos de regresión para cuantificar [K+] a partir de marcadores basados en pCA. La precisión de los modelos de regresión se evalúa mediante el error de estimación entre valores reales de Δ [K+] y los correspondientes estimados por el modelo. Con el error de estimación más pequeño, el modelo cuadrático es el más adecuado para la cuantificación de [K+].Siendo el análisis time warping sensible a los errores de delineación de los lÃmites de TW, lo que supone un riesgo para su poder pronóstico, se investigan las ventajas de usar una etapa de ponderación para el cálculo de marcadores time warping. El rendimiento de dos funciones de ponderación (WF) se prueba y se compara con respecto al caso de control sin ponderación, en escenarios simulados y en escenarios reales (para el seguimiento de [K+] y la estratificación del riesgo de SCD). No se encontraron mejoras en la monitorización de [K+] debido a los considerables cambios morfológicos de TW inducidos por Δ [K+]. Por otro lado, tanto las pruebas de simulación como el análisis de estratificación de riesgo de SCD muestran que los WF propuestos pueden mejorar la robustez del análisis time warping de TW contra los errores dedelineación de TW. En conclusión, esta tesis doctoral confirma la hipótesis de que se puede lograr un mejor seguimiento y cuantificación de Δ [K+] mediante el análisis de la morfologÃa de TW mediante el análisis time warping. La simplicidad de la tecnologÃa, junto con su bajo costo y facilidad de adquisición del ECG, deberÃa brindar una nueva oportunidad para que el análisis de TW en la práctica clÃnica rutinaria. Además, el uso de WF para minimizar los efectos no deseados de errores de delineación de TW en el cálculo de los marcadores time warping reveló una mejora del poder de estratificación del riesgoEnginyeria biomèdic
Serum potassium concentration monitoring by ECG time warping analysis on the T wave
This doctoral thesis was developed within the joint Ph.D. program in biomedical engineering at Universitat Politècnica de Catalunya (Barcelona, Spain) and University of Zaragoza (Zaragoza, Spain) in the framework of Doctorats Industrials program co-financed by Laboratorios Rubió S.A. (Castellbisbal, Spain) and Agència de Gestió d’Ajuts Universitaris i de Recerca, Generalitat de Catalunya (Spain).
This thesis was performed in partnership with the Nephrology ward from Hospital ClÃnico Universitario Lozano Blesa (Zaragoza, Spain) and in collaboration with Dr J. RamÃrez from the William Harvey Research Institute, Queen Mary University of London (London, UK).End-stage renal disease (ESRD) patients demonstrate an increased incidence of sudden cardiac death (SCD) with declining kidney functioning as a consequence of blood potassium ([K+]) homeostasis impairment, which is restored by hemodialysis (HD) therapy. The clinically established method for the diagnosis of [K+] imbalance is blood tests, an invasive and costly procedure that limits continuous monitoring of ESRD patients. A non-invasive ambulatory index, able to quantify changes in [K+] level is an open issue. In this context, the electrocardiogram (ECG) and in particular, the T wave (TW) morphology, has been shown to be strongly correlated with [K+] imbalance. Therefore, the aim of this dissertation is to investigate and to propose TW-derived markers able to monitor changes in [K+] levels in ESRD patients undergoing HD. For that purpose, the time warping analysis, a technique that allows the comparison and quantification of differences between two different TW shapes, was investigated. The application of TW time warping based markers in monitoring [K+ ] variations (Δ [K+]) and the derivation of a heart-rate corrected marker is proposed and compared with respect to two well-established Δ [K+]-related TW-based indexes. All the markers are evaluated in a single lead approach and after having emphasised the TW energy content through spatial transformation by Principal Component Analysis (PCA). Results demonstrate that the proposed biomarkers outperform the already proposed indexes, also proving that the use of PCA transformed lead generates markers with a higher correlation with Δ [K+] than the single lead approach. The possibility to improve markers robustness in the case of low signal-to-noise ratio ECGs, by spatially transforming the signal maximising the beat-to-beat TW periodicity criteria through the so-called Periodic Component Analysis (pCA), is then explored. pCA-based markers show superior performance during and after the HD than those obtained by PCA suggesting improved stability for continuous Δ [K+] tracking. The thesis studies also the application of regressions models to quantify Δ [K+] from pCA-based time warping markers. The accuracy of the regression models is evaluated by correlation and estimation error between the actual and the corresponding model-estimated Δ [K+] values, and the smallest estimation error is found for quadratic regression models. Being the time warping derived markers sensitive to TW boundary delineation errors, which may endanger their prognostic power, the advantages of using a weighting stage is investigated for their robust computation. The performance of two weighting functions (WF)s is tested and compared with respect to the control no weighting case, in simulated scenarios and in real scenarios (i.e. for [K+] monitoring and SCD risk stratification). No improvements in [K+] monitoring are found, probably due to the considerable marked [K+]-induced TW morphological changes. On the contrary, both simulation tests and SCD risk stratification analysis show that the proposed WFs can enhance the robustness of TW time warping analysis against TW delineation errors. In conclusion, this Doctoral Thesis confirms the hypothesis that enhanced perforce in Δ [K+] tracking and quantification can be achieved by analysing the overall TW morphology by time warping analysis. The simplicity of the technology, together with its low cost and ease of acquisition, should provide a new opportunity for TW analysis to reach standard clinical practice. Moreover, the use of WFs to minimise the undesired effects of TW delineation errors on the computation of time warping markers revealed a noticeable improvement of the SCD risk stratification power of time warping derived indexes.Los pacientes con enfermedad renal en etapa terminal (ESRD) demuestran una mayor incidencia de muerte cardÃaca súbita (SCD) tras el deterioro del funcionamiento renal como consecuencia del desequilibrio del potasio ([K+]) en sangre. Este último se restablece mediante la terapia de hemodiálisis (HD). El desequilibrio de [K+] se diagnostica a través del análisis de sangre, un procedimiento invasivo y costoso que limita la monitorización de los pacientes con ESRD. Se necesita un Ãndice ambulatorio no invasivo, capaz de cuantificar los cambios en el nivel de [K+] (Δ [K+]). En este contexto, se ha demostrado que el electrocardiograma (ECG) y en particular la onda T (TW), están correlacionados con Δ [K+]. El objetivo de esta tesis es evaluar marcadores derivados de la TW capaces de monitorizar ¿[K+] en pacientes con ESRD sometidos a HD. Para ello, se aplicó el análisis time warping, una técnica que permite la comparación de dos formas diferentes de TW. En primer lugar, se evalúa la aplicación de marcadores basados en el time warping para el seguimiento de Δ [K+] asà como la derivación de un marcador corregido por la frecuencia cardÃaca, comparando los marcadores con respecto a dos Ãndices basados en TW bien establecidos y relacionados con Δ [K+]. Todos los marcadores se evalúan en las derivaciones independientes y después de haber enfatizado el contenido de energÃa de TW a través del Análisis de Componentes Principales (PCA). Los resultados demuestran mejores prestaciones de los marcadores time warping respecto a los ya propuestos y que el uso de PCA genera marcadores con una correlación más alta con Δ [K+] respecto a las derivaciones independientes. A continuación, se explora la posibilidad de mejorar la robustez de los marcadores en el caso de ECG con una relación señal/ruido baja, maximizando la periodicidad de TW latido a latido mediante el Análisisde Componentes Periódicos (pCA). Los marcadores basados en pCA muestran un rendimiento superior durante y después de la HD que los obtenidos por PCA, lo que sugiere una estabilidad mejorada para el seguimiento continuo de Δ [K+]. Luego, se evalúan modelos de regresión para cuantificar [K+] a partir de marcadores basados en pCA. La precisión de los modelos de regresión se evalúa mediante el error de estimación entre valores reales de Δ [K+] y los correspondientes estimados por el modelo. Con el error de estimación más pequeño, el modelo cuadrático es el más adecuado para la cuantificación de [K+].Siendo el análisis time warping sensible a los errores de delineación de los lÃmites de TW, lo que supone un riesgo para su poder pronóstico, se investigan las ventajas de usar una etapa de ponderación para el cálculo de marcadores time warping. El rendimiento de dos funciones de ponderación (WF) se prueba y se compara con respecto al caso de control sin ponderación, en escenarios simulados y en escenarios reales (para el seguimiento de [K+] y la estratificación del riesgo de SCD). No se encontraron mejoras en la monitorización de [K+] debido a los considerables cambios morfológicos de TW inducidos por Δ [K+]. Por otro lado, tanto las pruebas de simulación como el análisis de estratificación de riesgo de SCD muestran que los WF propuestos pueden mejorar la robustez del análisis time warping de TW contra los errores dedelineación de TW. En conclusión, esta tesis doctoral confirma la hipótesis de que se puede lograr un mejor seguimiento y cuantificación de Δ [K+] mediante el análisis de la morfologÃa de TW mediante el análisis time warping. La simplicidad de la tecnologÃa, junto con su bajo costo y facilidad de adquisición del ECG, deberÃa brindar una nueva oportunidad para que el análisis de TW en la práctica clÃnica rutinaria. Además, el uso de WF para minimizar los efectos no deseados de errores de delineación de TW en el cálculo de los marcadores time warping reveló una mejora del poder de estratificación del riesgoPostprint (published version
Estimation of potassium levels in hemodialysis patients by T wave nonlinear dynamics and morphology markers
Noninvasive screening of hypo- and hyperkalemia can prevent fatal arrhythmia in end-stage renal disease (ESRD) patients, but current methods for monitoring of serum potassium (K+) have important limitations. We investigated changes in nonlinear dynamics and morphology of the T wave in the electrocardiogram (ECG) of ESRD patients during hemodialysis (HD), assessing their relationship with K+ and designing a K+ estimator. Methods: ECG recordings from twenty-nine ESRD patients undergoing HD were processed. T waves in 2-min windows were extracted at each hour during an HD session as well as at 48 h after HD start. T wave nonlinear dynamics were characterized by two indices related to the maximum Lyapunov exponent (¿t, ¿wt) and a divergence-related index (¿). Morphological variability in the T wave was evaluated by three time warping-based indices (dw, reflecting morphological variability in the time domain, and da and daNL, in the amplitude domain). K+was measured from blood samples extracted during and after HD. Stage-specific and patient-specific K+ estimators were built based on the quantified indices and leave-one-out cross-validation was performed separately for each of the estimators. Results: The analyzed indices showed high inter-individual variability in their relationship with K+. Nevertheless, all of them had higher values at the HD start and 48 h after it, corresponding to the highest K+. The indices ¿ and dw were the most strongly correlated with K+ (median Pearson correlation coefficient of 0.78 and 0.83, respectively) and were used in univariable and multivariable linear K+ estimators. Agreement between actual and estimated K+ was confirmed, with averaged errors over patients and time points being 0.000 ± 0.875 mM and 0.046 ± 0.690 mM for stage-specific and patient-specific multivariable K+ estimators, respectively.ariability allow noninvasive
monitoring of [K+] in ESRD patients.
Significance: ECG markers have the potential to be used for hypo- and hyperkalemia screening in ESRD patient
Redefinition of uraemic cardiomyopathy with cardiac magnetic resonance imaging
Patients with end stage renal disease (ESRD) have a 20-100 fold risk of premature cardiovascular death compared to age matched controls from the general population. These patients have many ‘conventional’ cardiovascular risk factors such as diabetes, ischaemic heart disease, hypertension, cigarette smoking and hyperlipidaemia. However, the relationship between the presence of these risk factors and cardiovascular outcomes is less clear in ESRD than in the general population. In the cases of hyperlipidaemia and hypertension a paradoxical relationship has been demonstrated where lower cholesterol or blood pressure is associated with an increased risk of cardiovascular events. One factor previously demonstrated to be associated with poor prognosis is the presence of uraemic cardiomyopathy, found in approximately 70% of ESRD patients at initiation of dialysis therapy, usually defined echocardiographically as the presence of left ventricular (LV) abnormalities, including left ventricular hypertrophy (LVH), LV dilatation and LV systolic dysfunction. However, echocardiography makes assumptions regarding LV geometry, which is frequently distorted in patients with ESRD. Furthermore any errors in measurements are amplified by the changes in hydration status which occur during the dialysis cycle, leading to changes in LV chamber dimensions. For these reasons, cardiac magnetic resonance imaging (CMR), by providing high fidelity measurements, potentially offers a ‘volume independent’ method of quantifying LV dimensions. Furthermore, by using gadolinium based contrast agents, tissue abnormalities particularly myocardial fibrosis, indicated by late gadolinium enhancement (LGE) may by identified.
The work contained in this thesis examines the relationship between cardiac dimensions, as defined by CMR and cardiovascular risk factors (both conventional and specific to uraemia). In a study of 145 patients with ESRD using CMR with gadolinium, two specific pathological processes were demonstrated. First, the presence of subendocardial LGE indicating previous myocardial infarction was associated with the presence of conventional cardiovascular risk factors such as previous ischaemic heart disease and diabetes. Patients with subendocardial LGE frequently had LV systolic dysfunction. Second, diffuse LGE, representing fibrosis throughout the LV wall was identified in patients with LVH. This was an unexpected finding and appears specific to uraemia. Using CMR, isolated LV dilatation was rare. These findings suggest that in uraemia two forms of cardiomyopathy exist- LV systolic dysfunction due to underling myocardial ischaemia and LVH which is a true ‘uraemic cardiomyopathy’ associated with diffuse myocardial fibrosis. Attempts were made to reassess the relationship between CMR and echocardiographic measures of cardiac dimensions. In keeping with a previous study, it was demonstrated that M-mode echocardiography overestimates LV mass compared to CMR in this population. Thus, CMR may be used to optimise echocardiographic formulae to calculate LV mass. Furthermore, it appeared that either by echocardiography or by CMR the chief determinant of LVH in this population was blood pressure, in particular systolic blood pressure. This has implications for treatment as recent studies aimed at correcting anaemia, previously associated with LVH, either to reduce LV mass or to improve survival, have generally demonstrated increased cardiovascular events with higher haemoglobin. Therefore, if LV mass is a goal of treatment, attempts should be made to reduce blood pressure further in this population.
The patients studied in these investigations were candidates for renal transplantation, the definitive treatment for chronic renal failure. Cardiovascular disease is the leading cause of death both in patients on the renal transplant list, as well as post successful transplantation. There is a great deal of interest in identifying patients at high cardiovascular risk, to allow strategies to be adopted to minimise this risk, frequently by undertaking invasive investigation such as coronary angiography. In a survival study of 300 potential renal transplant recipients, factors associated with increased risk of mortality were increased age, ischaemic heart disease whilst receipt of a renal transplant was protective. Although the presence of LGE was associated with poorer outcome, this finding was not independent of other variables. One interesting finding was that patients with greater exercise tolerance, measured objectively using the full Bruce exercise test had better outcomes. This observation represents a simple pragmatic method to risk-stratify such patients. A study using the biomarker brain natriuretic peptide (BNP) a peptide released from the LV in response to stretch and hypertrophy, in 114 patients, demonstrated that whilst BNP has potential as a diagnostic tool for the presence of uraemic cardiomyopathy, in particular LVH, this peptide added little prognostic value.
As familiarity with CMR techniques developed, it became clear that vascular function could be investigated with this imaging modality. Previous studies using alternative measures of vascular function have suggested that arterial stiffness is an important predictor of long term outcome in patients with ESRD. A study of 147 uraemic patients using aortic distensibilty and aortic volumetric arterial strain as CMR measures of aortic stiffness demonstrated that both these parameters were associated with an increased risk of cardiovascular events and mortality. To date there do not appear to be any similar outcome studies using these measures, although a number of authors have noted an association between aortic distensibilty and cardiovascular risk factors. These factors may represent potential targets for therapy aimed at reduction of cardiovascular risk in patients with ESRD.
One unfortunate development during the period during which these studies were undertaken, was the emergence of a link between exposure to gadolinium based contrast agents and nephrogenic systemic fibrosis (NSF), a potentially life threatening skin disorder in patients with advanced renal failure. This finding lead to the cessation of contrast CMR studies. A retrospective investigation of factors present in patients in North Glasgow affected by NSF, confirmed that patients with NSF were more likely to have undergone contrast based imaging than unaffected patients, frequently undergoing multiple scans, with high doses of gadodiamide used. Until this issue is clarified, future scans using these agents in this population should be undertaken with caution.
These studies have characterised for the first time the relationship between both uraemic cardiomyopathy and uraemic arterial stiffness and both cardiovascular risk factors and long term outcome. CMR measures of cardiac dimensions and vascular function represent future targets for interventions aimed at reducing cardiovascular risk in patients with advanced renal failure
Monitoring of serum potassium and calcium levels in end-stage renal disease patients by ecg depolarization morphology analysis
Objective: Non-invasive estimation of serum potassium, [K+], and calcium, [Ca2+], can help to prevent life-threatening ventricular arrhythmias in patients with advanced renal disease, but current methods for estimation of electrolyte levels have limitations. We aimed to develop new markers based on the morphology of the QRS complex of the electrocardiogram (ECG). Methods: ECG recordings from 29 patients undergoing hemodialysis (HD) were processed. Mean warped QRS complexes were computed in two-minute windows at the start of an HD session, at the end of each HD hour and 48 h after it. We quantified QRS width, amplitude and the proposed QRS morphology-based markers that were computed by warping techniques. Reference [K+] and [Ca2+] were determined from blood samples acquired at the time points where the markers were estimated. Linear regression models were used to estimate electrolyte levels from the QRS markers individually and in combination with T wave morphology markers. Leave-one-out cross-validation was used to assess the performance of the estimators. Results: All markers, except for QRS width, strongly correlated with [K+] (median Pearson correlation coefficients, r, ranging from 0.81 to 0.87) and with [Ca2+] (r ranging from 0.61 to 0.76). QRS morphology markers showed very low sensitivity to heart rate (HR). Actual and estimated serum electrolyte levels differed, on average, by less than 0.035 mM (relative error of 0.018) for [K+] and 0.010 mM (relative error of 0.004) for [Ca2+] when patient-specific multivariable estimators combining QRS and T wave markers were used. Conclusion: QRS morphological markers allow non-invasive estimation of [K+] and [Ca2+] with low sensitivity to HR. The estimation performance is improved when multivariable models, including T wave markers, are considered. Significance: Markers based on the QRS complex of the ECG could contribute to non-invasive monitoring of serum electrolyte levels and arrhythmia risk prediction in patients with renal diseas
Monitoring blood potassium concentration in hemodialysis patients by quantifying T-wave morphology dynamics.
We investigated the ability of time-warping-based ECG-derived markers of T-wave morphology changes in time ([Formula: see text]) and amplitude ([Formula: see text]), as well as their non-linear components ([Formula: see text] and [Formula: see text]), and the heart rate corrected counterpart ([Formula: see text]), to monitor potassium concentration ([Formula: see text]) changes ([Formula: see text]) in end-stage renal disease (ESRD) patients undergoing hemodialysis (HD). We compared the performance of the proposed time-warping markers, together with other previously proposed [Formula: see text] markers, such as T-wave width ([Formula: see text]) and T-wave slope-to-amplitude ratio ([Formula: see text]), when computed from standard ECG leads as well as from principal component analysis (PCA)-based leads. 48-hour ECG recordings and a set of hourly-collected blood samples from 29 ESRD-HD patients were acquired. Values of [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] were calculated by comparing the morphology of the mean warped T-waves (MWTWs) derived at each hour along the HD with that from a reference MWTW, measured at the end of the HD. From the same MWTWs [Formula: see text] and [Formula: see text] were also extracted. Similarly, [Formula: see text] was calculated as the difference between the [Formula: see text] values at each hour and the [Formula: see text] reference level at the end of the HD session. We found that [Formula: see text] and [Formula: see text] showed higher correlation coefficients with [Formula: see text] than [Formula: see text]-Spearman's ([Formula: see text]) and Pearson's (r)-and [Formula: see text]-Spearman's ([Formula: see text])-in both SL and PCA approaches being the intra-patient median [Formula: see text] and [Formula: see text] in SL and [Formula: see text] and [Formula: see text] in PCA respectively. Our findings would point at [Formula: see text] and [Formula: see text] as the most suitable surrogate of [Formula: see text], suggesting that they could be potentially useful for non-invasive monitoring of ESRD-HD patients in hospital, as well as in ambulatory settings. Therefore, the tracking of T-wave morphology variations by means of time-warping analysis could improve continuous and remote [Formula: see text] monitoring of ESRD-HD patients and flagging risk of [Formula: see text]-related cardiovascular events
Ultrasonography Evaluation of Patency of Implanted Infra-Renal Vascular Grafts in the Rat Model.
Introduction: Intensive research over the last six decades has resulted in minimal improvement in vascular graft development. Small animal models are the first line of species exposed to vascular graft implantation and invasive monitoring of experimental graft patency may contribute to pain, suffering, higher cost and earlier sacrifice. Non-invasive ultrasonographic evaluation of vascular implants during the conduction of animal studies allows for chronic follow-up with multiple assessments. This study aims to apply and endorse the utilization of ultrasound as a less invasive diagnostic method in determining patency of vascular grafts in units where imaging modalities like Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) are not readily available. Methods: Pre-operative control ultrasound evaluation of the ejection fraction, aortic diameter and aortic velocity were conducted on Wistar rats (250-350g). Infra-renal aortic vascular graft implantation was then performed, with 8 rats receiving straight (1.8mm ID, 18mm length) expanded polytetrafluoroethylene (ePTFE) grafts, while 12 rats received a long (1.8mm ID, 100mm length) looped ePTFE conduit with a sealed mid-graft (10mm length) section. Ultrasonography was conducted on days 1, 3, 7 and weeks 4, 8 and 12 post operatively. Grafts were explanted if there was any ultrasonographic evidence of occlusion or at twelveweek termination of the study. Explant was preceded by angiography and followed by histological assessment of the grafts for patency. Results: Three of the looped and all 8 of the straight grafts were patent at the 12 week explant time point, as correctly assessed by ultrasound and confirmed by angiography and histology. Three of the nine occluded looped grafts were explanted at eight weeks due to early ultrasonographic detection of occlusion; the remaining 6 were explanted at twelve weeks. There were two false positive results, which were incorrectly assessed as patent at twelve weeks of implantation on ultrasonographic evaluation, but confirmed to be occluded on angiography at explant. The results of ultrasonography evaluation of implanted infra-renal vascular grafts had a high specificity of 100% with a sensitivity of 78%. The outcome of the results between ultrasound and angiography corresponded in 18 out of 20 vascular grafts, with a calculated positive predictive value (PPV) of 100% and a negative predictive value (NPV) of 85%. 4 Conclusion: Ultrasound is easily available and a non-invasive diagnostic modality allowing for safe and reliable results, which may be repeated at different time frames following vascular implants in small animal models. Ultrasonographic limitations exist, emphasizing the need for an experienced operator with adequate knowledge and training. Its use may be complicated by tortuous geometries of vessels, which is technically more challenging to evaluate with ultrasound than with imaging techniques like CT and MRI. It does, however, add information without additional loss of life or increased use of animal numbers. Ultrasound is an essential additive diagnostic tool for chronic follow-up and evaluation of vascular graft implants
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