High-frequency QRS (HFQRS) analysis of surface ECG is a reliable marker of cardiac ischemia (CI). This study aimed to assess the response of HFQRS signals from standard intracardiac electrodes (iHFQRS) to CI in swine and compare them with conventional ST-segment deviations. Devices with three intracardiac leads were implanted in three swine in a controlled environment. CI was induced by inflating a balloon in epicardial coronary arteries. A designated signal-processing algorithm was applied to quantify the iHFQRS content before, during, and after each occlusion. iHFQRS time responses were compared to conventional ST-segment deviations. Thirty-three over thirty-nine (85%) of the occlusions presented significant reduction in the iHFQRS signal, preceding ST-segment change, being the only indicator of CI in brief occlusions. iHFQRS was found to be an early indicator for the onset of CI and demonstrated superior sensitivity to conventional ST-segment deviations during brief ischemic episodes.

Purpose: Diagnosing and monitoring pleural effusion ( PE ) is challenging due unsuitability of existing modalities. In the present study, a novel parametric electrical impedance tomography (pEIT) technique, tailored to a clinically feasible system to diagnose PE is presented. Methods: An electrical impedance tomography (EIT) numeric solver was applied to a 3D realistic normal model and five PE models to simulate sets of surface measurements. Simulations were triggered by a series of eight independent projections using five electrodes positioned around the thorax. The relative changes in the potential between the PE models and the normal model were assessed and the error in the estimated PE volume was examined at varying signal to noise ratio (SNR) levels. For experimental feasibility, measurements were performed in four healthy subjects and were correlated with the potentials that were calculated from the normal model. Results: Relative potential changes were notable (reached until similar to 55%) and increased with the increasing PE volumes. Maximal error of +/- 20 [mL] was obtained for SNR levels > 50 [ dB ]. The feasibility real measurements in healthy subjects showed a strong linear correlation (R-2 > 0.85) and a successful diagnosis for all subjects. Conclusion: The proposed technique can estimate PE volumes from a redundant set of measurements in a realistic 3D human model and may be utilized for monitoring PE patients. (C) 2021 IPEM. Published by Elsevier Ltd. All rights reserved.

Monitoring methods of bone mineral density (BMD), the standard measure for osteoporosis diagnosis, are both costly and complex. Since changes in bone permittivity and conductivity values occur due to changes in BMD, they can be used as a simple and inexpensive tool for monitoring BMD. In this work the parametric electrical impedance tomography (pEIT) method for monitoring BMD in the spine using 3D human model is theoretically evaluated. Numerical solver on the forward problem in 3D is used for computing electric potential measured on body surface. Varied spinal BMD are simulated by varying bone relative permittivity and conductivity values which represent different disease stages. The inverse problem is solved by creating a lookup-table of different BMD values.

Objectives: High frequency QRS (HFQRS) analysis has been shown to be an accurate marker for myocardial ischemia. Our objective was to test the use of HFQRS in diagnosing ACS in the emergency department.Methods: 324 patients presenting to the ED with chest pain were enrolled. Resting ECG was recorded and later analyzed by an HFQRS algorithm. Results were compared to the conventional ECG diagnosis by 3 independent interpretations: treating physician, expert cardiologist and an automated computer program.Results: The HFQRS analysis demonstrated improved sensitivity (67.5%) for the NSTE-ACS group compared to the human interpreters (59.7% and 53.2% for the treating physician and cardiologist respectively) with similar specificity. The automatic program had significantly lower sensitivity (31%) with a higher specificity (77%).Conclusions: HFQRS which has shown great promise in diagnosing stable CAD may also be helpful in the ED for diagnosing ACS. (C) 2017 Elsevier Inc. All rights reserved.

High frequency QRS (HFQRS) analysis was shown to be more accurate than ST changes in detecting stress induced ischemia in designed clinical studies.Since it utilizes energy extracted from the frequency band of 150-250 Hz, HFQRS analysis is performed with high end electrocardiographs which are equipped with adequate hardware.In this study, we aim to examine whether it is possible to perform the HFQRS analysis using ECG data acquired by a 500 Hz commercial electrocardiograph and also to assess the clinical performance of such analysis.One hundred and thirty two ECG records of bicycle exercise tests were obtained from the FINCAVAS database.Fifteen records with a wide QRS duration and 28 patients who have not reached their target heart rate were excluded.HFQRS and computerized ST-segment analyses were performed for the remaining 89 records in a blinded fashion.Three records were excluded due to excessive high frequency noise.Accordingly, the group of records with a definite HFQRS interpretation included 57 patients without stenosis and 29 patients who had >75% stenosis.Angiography, was used as gold standard.The clinical performance of both methods were assessed.The HFQRS has statistically significant higher sensitivity of 86% comparing to the 41% of the ST (p<0.005) with a statistically insignificant difference in specificity of 68% vs. 67% for the HFQRS and the ST respectively (p=0.84).This analysis demonstrated that HFQRS analysis may be applied for ECG data acquired by standard 500 Hz electrocardiographs and demonstrates its potential in diagnosing stress induced ischemia.

In recent years High Frequency QRS analysis (HFQRS) which uses information from the depolarization phase of the cardiac cycle has shown superior accuracy in the detection of stress induced ischemia compared to changes in the repolarization phase.HFQRS analysis typically uses the frequency band of 150-250 Hz and therefore the default requirement was for the ECG to be sampled at 1 kHz.In the present study we examined how HFQRS measurements are affected by a lower sampling rate and evaluated the clinical performance of such analysis.A group of 174 stress ECG records, which were originally sampled at 1 kHz, were analyzed twice using the same HFQRS application: once with the original files and once following decimation to simulate records sampled at 500 Hz.17% of the patients had significant ischemia and the gold standard was determined according to myocardial perfusion imaging (SPECT).Identical sensitivity of 70% was achieved for both analyses and statistically insignificant difference in specificity was found (81% vs 76%, p=0.39 for the 500 Hz compared to the original records, respectively).The results imply that much of the HFQRS essential information for detecting ischemia exists in the limited frequency band and that the diagnostic performance of the HFQRS are not significantly affected as a result of using a sampling frequency of 500 Hz.

Atrial arrhythmia resulting from irregularly rapid focal activity in the atria may be revealed in an altered P-wave morphology (PWM) in the ECG. A 3D computerised model of the heart was used for simulating the electrical activity of the atria measured in the 12 ECG leads during normal rhythm and during focal atrial tachycardia. This simulation was conducted for determining the focal origin of the atrial tachycardia by analysing the P-wave morphology in the simulated 12 ECG leads and compare these results to previously published clinical results.

Osteoporosis is defined as bone microstructure deterioration resulting a decrease of bone's strength. Measured bone mineral density (BMD) constitutes the main tool for Osteoporosis diagnosis, management, and defines patient's fracture risk. In the present study, parametric electrical impedance tomography (pEIT) method was examined for monitoring BMD, using a computerized simulation model and preliminary real measurements. A numerical solver was developed to simulate surface potentials measured over a 3D computerized pelvis model. Varying cortical and cancellous BMD were simulated by changing bone conductivity and permittivity. Up to 35% and 16% change was found in the real and imaginary modules of the calculated potential, respectively, while BMD changes from 100% (normal) to 60% (Osteoporosis). Negligible BMD relative error was obtained with SNR>60 [dB]. Position changes errors indicate that for long term monitoring, measurement should be taken at the same geometrical configuration with great accuracy. The numerical simulations were compared to actual measurements that were acquired from a healthy male subject using a five electrodes belt bioimpedance device. The results suggest that pEIT may provide an inexpensive easy to use tool for frequent monitoring BMD in small clinics during pharmacological treatment, as a complementary method to DEXA test.

Goal. The purpose of this computer modeling study is to validate the feasibility of a home monitoring system for wrist bone mineral density (BMD) measurement which is based on the parametric electrical impedance tomography (pEIT) method. Methods. A solution to the forward problem of the developing potential around the wrist due to current injection was developed using a Matlab numerical simulation of an adult computer human phantom. The backward problem is solved by building a lookup table of different bone densities which represent different disease stages. Results. The real part of the complex potential exhibits an average change of 30.7%-12% (between the most sensitive and the least sensitive electrodes) perBMDdecrease of 23%. A 2 times higher sensitivity to a deterioration of the cortical bone than of the trabecular bone alone was found. Asignal to noise ratio (SNR) level above 30 dB is required for a maximal performance of the system. The robustness to a deposition of the electrodes array in different directions is limited. Conclusion. It was found that the corticalBMDchanges govern the model. The required SNR level is within the specs of similar systems. In a real device, the issue of sensors repositioning should be addressed. The proposed pEIT system makes self-monitoring of wristBMDpossible. It brings an added-value by enabling the monitoring of BMDbetween treatments and between traditional DEXA screenings.

Disturbance in the blood supply to the brain causes a stroke or cerebrovascular accident. This can be due to ischemia caused by blockage (thrombosis, arterial embolism) or a hemorrhage. In this study, the feasibility of basic electrical impedance technique for monitoring such damage was analyzed using a computerized model. Simulations were conducted on a realistic 3D numerical model of the head. Tissues were assumed to act as linear isotropic volume conductors, and the quasi-static approximation was applied. Electrical potentials were calculated by solving Poisson's equation, using the finite volume method and the successive over relaxation method. Left-right asymmetry was calculated for several conductivities and volumes of the damaged region. The results were compared with the left-right asymmetry in a head model with normal brain. A negative asymmetry was revealed for blockage (i.e. the potential amplitude over the ischemic hemisphere was greater than that over the intact hemisphere). In case of hemorrhage, a positive asymmetry was found. Furthermore, correlation was found between the location of the damaged region and the electrodes with significant asymmetry. The 3D numerical simulations revealed that the electrical conductivity and the size of the damaged tissue have an effect on the left-right asymmetry of the surface potential.

In congestive heart failure (CHF) patients an increased interstitial fluid leads to collection of large amounts of fluids in the lungs which are major cause of mortality. Classifying and monitoring pulmonary congestions is a significant clinical challenge, due to lack of direct access to the pleural cavity. In this study, we investigate the feasibility of the Parametric Electrical Impedance Tomography (pEIT) technique in classifying and monitoring pleural effusion. The investigation is based on pEIT with a reduced number of electrodes applied in a computerized 3D model of the human thorax. The Forward Problem for Poisson's equation was implemented using Finite Volume Method (FVM) to estimate the potentials developed on the body surface. Significant linear regression (r-square>0.81) was found in 7 and 6 out of 8 independent projections for the right and the left lung, respectively, indicating an increase in surface potential while increasing lungs fluids. Moreover, the study results show that the projection's sensitivity is higher for cross sectional projections during pleural effusion. Hence, monitoring and classifying pleural effusion can be achieved with the pEIT technique making it feasible in monitoring lung fluid status in patients with pleural effusion.

Over four decades of high frequency electrocardiography research have provided a body of knowledge about QRS changes during myocardial ischemia, and the techniques to measure and quantify them. High-frequency QRS (HFQRS) components, being closely related to the pattern of ventricular depolarization, carry valuable clinical information. Changes in HFQRS amplitude and morphology have been shown to be sensitive diagnostic markers of myocardial ischemia, often superior to measures of ST-T segment changes. Clinical studies in patients undergoing exercise testing have consistently demonstrated the incremental diagnostic value of HFQRS analysis in detection of demand ischemia. In 6 studies that evaluated the HyperQ™ technology, the average sensitivity and specificity of HFQRS analysis were 75%±6% and 80%±6%, respectively, compared to average sensitivity 48%±16% and average specificity 70%±15% of ST segment analysis. In patients with acute supply ischemia, recent studies characterized and quantified the ischemic HFQRS patterns. HFQRS morphology index was found to be higher in patients with acute coronary syndrome (ACS), compared to non-ischemic, with good sensitivity in patients without ST elevation. These research findings may be translated into commercially-available ECG systems and be used in clinical practice for improved diagnosis and monitoring of myocardial ischemia.

Detection of pulmonary edema is possible with the bio-impedance technique. In the present study two approaches, the whole-thoracic impedance and the Electrical Impedance Tomography, for monitoring pulmonary congestion level were compared. A good correlation ratio of R=0.75 (p-value<;0.01) was found between the two data sets. The results suggest that the EIT method with 8 electrodes has the potential to be used for monitoring patients with congestive heart failure.

Correlating changes in the thoracic conductivity distribution with the volume changes of the heart can help providing a non-invasive Stroke Volume (SV) quantification method. Electrical Impedance Tomography is a non-invasive non-ionizing imaging technique in which tissues can be diferentiated based on their electrical properties. The method uses measured surface potentials in order to reconstruct information of the spatial conductivity distribution within the thorax. In the current study, parametric ElT (PElT) scheme was applied in a high-resolution 4D model of the human thorax to determine the left ventricular volume (LVV) at different cardiac cycle phases. The effect of breathing is examined by allowing both heart and respiratory motions. The results emphasize the fact that the estimation of the LVV using pElT is affected by breathing. About J 0% change in the lungs' volume causes 8% change in the estimated Sv. The contribution of both motions to the change of potential distributions can be separated. The separated potential distributions are used to estimate the LVV while neutralizing the effect of breathing. The preliminary results show a decrease in the SV estimation error; 3% compared to 12% without using the correction algorithm. The results suggest that the LVV can be estimated using pElT method while neutralizing the effect of respiratory motion and that the method has the potential to be used for monitoring purposes.

The present theoretical study examines the ability to estimate cardiac stroke volume (CSV) in patients with implanted cardiac pacemaker using parametric electrical impedance tomography (pEIT) in a 2D computerized model of the thorax. CSV is a direct indicator of the cardiac pumping efficiency. The commonly used methods for measuring CSV require the invasive procedure of right heart catheterization or use expensive imaging techniques (i.e., MRI). Hence, experience with these techniques for diagnosis and monitoring has been limited to hospitalized patients. In the present study, pEIT scheme was applied in a computerized 2D model of the human thorax with implanted cardiac device to determine the left ventricular (LV) volume at different cardiac cycle phases. The LV was simulated as a prolate ellipse with its axes' lengths as the reconstruction parameters while all other geometries and conductivity values remained constant. An optimization was carried out in order to ensure that the ellipse is the appropriate model for the LV at each cardiac cycle phase. LV volumes calculated by both the pEIT algorithm and the ellipsoid model are consistent. A high correlation (ρ = 0.99) between the true and reconstructed volumes was found. The SV calculation error was ∼1%. The results suggest that the LV volume can be estimated using the pEIT method in a 2D computerized model, and that the method has the potential to be used for monitoring patients with implanted cardiac pacemaker.

Detection of pulmonary edema using an implantable cardiac resynchronisation device is possible with the bio-impedance technique. In this study, the ability of the parametric electrical impedance tomography (pEIT) scheme and the intra-thoracic impedance technique to monitor lung fluid status in patients with implantable pacemaker was compared using simulation in a theoretical model of the thorax. Applying pEIT scheme and the intra-thoracic impedance technique in a computerised two dimensional model of the thorax demonstrates that the pEIT converges to the exact values of lung conductivity with sensitivity of 1,400% change/S/m. The intra-thoracic impedance has lower sensitivity of 550% change/S/m for edema in both lungs and in case of unilateral left lung edema, and very low sensitivity of 26% change/S/m when unilateral right lung edema is present. When additive white Gaussian noise is added, the pEIT method requires an SNR greater than 70 dB. The simulation results suggest that the pEIT may be applicable f...

Background The 12-lead electrocardiogram (ECG) is a primary tool in the evaluation and risk stratification of patients with suspected acute myocardial infarction (AMI), even though the initial ECG of these patients is often normal or nondiagnostic. Myocardial ischemia induces depolarization changes that can be quantified by analysis of high-frequency QRS (HFQRS) components. We aimed to demonstrate the potential usefulness of HFQRS analysis in diagnosing myocardial ischemia by characterizing the morphological patterns of the HFQRS signals in patients with AMI before and following reperfusion. Methods Five-minute high-resolution ECG was acquired from 30 patients with AMI (age 55 +/- 11 years, 26 men) upon their admission to the intensive coronary care unit (ICCU). Serial ECGs were acquired following coronary revascularization and after additional 24 hours (24h). High-frequency morphology index (HFMI), quantifying the extent of ischemic patterns was computed by a custom software, and its values were compared between the serial ECG measurements. Results HFMI values were significantly higher on the admission ECG as compared to the post intervention ECG (4.6 +/- 2.9% vs 3.4 +/- 2.3%, P < 0.05) and to the 24h ECG (4.6 +/- 2.9% vs 2.8 +/- 2.1%, P < 0.01). In 79% of the patients who were successfully revascularized HFMI value decreased from admission ECG to 24h ECG. Conclusions Analysis of HFQRS morphology in patients with AMI provides information about the existence and severity of myocardial ischemia. HFQRS analysis may aid in risk stratification of patients with suspected myocardial ischemia, complementarily to conventional ECG.