基于动态心脏模型的体表心电图仿真研究

以往的电生理心脏模型大多是静态的,而非动态模型.这样在用准静电场理论求解体表电位时,整个心动周期中等效心电偶极子（源点）与体表（场点）之间的距离假设为恒定不变,从而会引入较大的系统误差.因此,为了更准确仿真心电图,有必要采用动态或跳动的心脏模型.基于原来静态心脏模型,构造了一个动态心脏模型,并对体表12导联心电图进行仿真比较研究.在动态心脏模型中考虑了心肌电兴奋引起的心脏机械力学收缩,通过计算心动周期中心室壁的位移,从而将心脏与体表之间的相对距离变化考虑进体表电位计算过程.仿真结果表明,对于正常心电图,基于动态心脏模型的仿真结果比基于静态心脏模型的仿真结果更符合临床记录心电图,特别是V1-V6胸导联的ST段和T波.对于前壁轻微缺血情况,在动态心脏模型的仿真心电图中能明显看出ST段和T波的变化,而在静态心脏模型的仿真心电图中与正常心电图相比看不出什么变化.本研究的仿真研究证实了动态心脏模型的确能更准确地仿真体表心电图.     

Analysis of cardiac ventricular wall motion based on a three-dimensional electromechanical biventricular model

This paper describes a biventricular model, which couples the electrical and mechanical properties of the heart, and computer simulations of ventricular wall motion and deformation by means of a biventricular model. In the constructed electromechanical model, the mechanical analysis was based on composite material theory and the finite-element method; the propagation of electrical excitation was simulated using an electrical heart model, and the resulting active forces were used to calculate ventricular wall motion. Regional deformation and Lagrangian strain tensors were calculated during the systole phase. Displacements, minimum principal strains and torsion angle were used to describe the motion of the two ventricles. The simulations showed that during the period of systole, (1) the right ventricular free wall moves towards the septum, and at the same time, the base and middle of the free wall move towards the apex, which reduces the volume of the right ventricle; the minimum principle strain (E3) is largest at the apex, then at the middle of the free wall and its direction is in the approximate direction of the epicardial muscle fibres; (2) the base and middle of the left ventricular free wall move towards the apex and the apex remains almost static; the torsion angle is largest at the apex; the minimum principle strain E3 is largest at the apex and its direction on the surface of the middle wall of the left ventricle is roughly in the fibre orientation. These results are in good accordance with results obtained from MR tagging images reported in the literature. This study suggests that such an electromechanical biventricular model has the potential to be used to assess the mechanical function of the two ventricles, and also could improve the accuracy of ECG simulation when it is used in heart-torso model-based body surface potential simulation studies.     

Artificial neural network-based classification of body movements in ambulatory ECG signal

Abstract

Ambulatory ECG monitoring provides electrical activity of the heart when a person is involved in doing normal routine activities. Thus, the recorded ECG signal consists of cardiac signal along with motion artifacts introduced due to a person’s body movements during routine activities. Detection of motion artifacts due to different physical activities might help in further cardiac diagnosis. Ambulatory ECG signal analysis for detection of various motion artifacts using adaptive filtering approach is addressed in this paper. We have used BIOPAC MP 36 system for acquiring ECG signal. The ECG signals of five healthy subjects (aged between 22–30 years) were recorded while the person performed various body movements like up and down movement of the left hand, up and down movement of the right hand, waist twisting movement while standing and change from sitting down on a chair to standing up movement in lead I configuration. An adaptive filter-based approach has been used to extract the motion artifact component from the ambulatory ECG signal. The features of motion artifact signal, extracted using Gabor transform, have been used to train the artificial neural network (ANN) for classifying body movements.     

基于电生理-力学复合心脏模型的右心室三维运动分析

在原有电生理心脏模型基础上,我们采用有限元方法和复合材料理论建立了一个电生理-力学复合双心室模型,并基于该模型对右心室心壁在收缩期的三维运动进行仿真分析。模型建立过程中,考虑了心肌的纤维旋向、心电兴奋产生的心肌收缩力。心室壁位移、最小主应变(E 3)等用来表征心室的运动。仿真结果与加标记磁共振成像的实验结果基本一致。另外,仿真结果还表明,虽然心基部位移最大,但最大收缩力却发生在心尖部,这个结果用一般的动物实验或人体实验是难以得到的。因此,电生理-力学复合双心室模型对于今后进一步评价心脏功能具有重要意义。     

MagnetoHemoDynamics in the aorta and electrocardiograms

This paper addresses a complex multi-physical phenomenon involving cardiac electrophysiology and hemodynamics. The purpose is to model and simulate a phenomenon that has been observed in magnetic resonance imaging machines: in the presence of a strong magnetic field, the T-wave of the electrocardiogram (ECG) gets bigger, which may perturb ECG-gated imaging. This is due to a magnetohydrodynamic (MHD) effect occurring in the aorta. We reproduce this experimental observation through computer simulations on a realistic anatomy, and with a three-compartment model: inductionless MHD equations in the aorta, bi-domain equations in the heart and electrical diffusion in the rest of the body. These compartments are strongly coupled and solved using finite elements. Several benchmark tests are proposed to assess the numerical solutions and the validity of some modeling assumptions. Then, ECGs are simulated for a wide range of magnetic field intensities (from 0 to 20 T).     

Assessment of the principal components of the equivalent cardiac generator on recorded electrocardiographic potentials

The relative contribution of the various multipolar components to the total surface potential was determined in experiments on the isolated heart located in a spherical volume conductor. These contributions were calculated for distances from the electrodes to the center of the cardiac ventricles that corresponded to the placement of standard and thoracic ECG recording electrodes in different age groups. On the basis of these results the optimal model of an equivalent cardiac generator can be chosen for a given electrocardiographic recording system.     

T waves are independently generated in both right and left ventricles: the clinically recorded T is a summation of two separate repolarizations, and is thus always biventricular

The T-wave of the electrocardiogram (ECG) is generated both from the left and the right ventricles of the heart. Each ventricle may produce a normal, an "ischemic", or a "secondary" T-wave, depending on segmental perfusion, intraventricular pressure, or QRS complex duration. The direction of the T-wave is determined by the particular inward rectifier potassium channels recruited by various layers and segments in the two ventricles. The observed T-wave in the clinical ECG is the summation of the left and right ventricular T waves, and is thus biventricular. Clinical observations in right bundle branch block (RBBB) and in right ventricular hypertensive states such as pulmonary embolism suggest that many ECG's interpreted as inferior or anterior left ventricular ischemia are in fact examples of abnormal potassium channel recruitment in the right ventricle. Consideration of the right ventricular component of the T-wave in every electrocardiographic interpretation improves diagnostic understanding and accuracy, as the possible right ventricular origin of observed anterior or superior T waves will not be overlooked.     

Three-dimensional simulation of epicardial potentials using a microcomputer-based heart-torso model

Previous cardiac simulation studies have focused on simulating the activation isochrones and subsequently the body surface potentials. Epicardial potentials, which are important for clinical applications as well as for electrocardiography inverse problem studies, however, have usually been neglected. This paper presents a procedure of simulating epicardial potentials using a microcomputer-based heart-torso model with real geometry. The heart model developed earlier which was composed of more than 60,000 cell units was used in this study. To simulate the epicardial potentials, an epicardial surface model which enclosed the whole heart was constructed. The heart model, together with the epicardial surface model, are mounted in an inhomogeneous human torso model. Electric dipoles, which are proportional to the spatial gradient of the action potential, are generated in all cell units. These dipoles give rise to a potential distribution on the epicardial surface, which is calculated by means of the boundary element method. The simulated epicardial potential maps during a normal heart beat and in patients with left bundle branch block (LBBB) are in close agreement with those reported in the literature.     

Localization of the site of origin of reentrant arrhythmia from body surface potential maps: a model study

We have developed a model-based imaging approach to estimate the site of origin of reentrant arrhythmia from body surface potential maps (BSPMs), with the aid of a cardiac arrhythmia model. The reentry was successfully simulated and maintained in the cardiac model, and the simulated ECG waveforms over the body surface corresponding to a maintained reentry have evident characteristics of ventricular tachycardia. The performance of the inverse imaging approach was evaluated by computer simulations. The present simulation results show that an averaged localization error of about 1.5 mm, when 5% Gaussian white noise was added to the BSPMs, was detected. The effects of the heart-torso geometry uncertainty on the localization were also initially assessed and the simulation results suggest that no significant influence was observed when 10% torso geometry uncertainty or 10 mm heart position shifting was considered. The present simulation study suggests the feasibility of localizing the site of origin of reentrant arrhythmia from non-invasive BSPMs, with the aid of a cardiac arrhythmia model.     

Noninvasive three-dimensional activation time imaging of ventricular excitation by means of a heart-excitation model

We propose a new method for imaging activation time within three-dimensional (3D) myocardium by means of a heart-excitation model. The activation time is estimated from body surface electrocardiograms by minimizing multiple objective functions of the measured body surface potential maps (BSPMs) and the heart-model-generated BSPMs. Computer simulation studies have been conducted to evaluate the proposed 3D myocardial activation time imaging approach. Single-site pacing at 24 sites throughout the ventricles, as well as dual-site pacing at 12 pairs of sites in the vicinity of atrioventricular ring, was performed. The present simulation results show that the average correlation coefficient (CC) and relative error (RE) for single-site pacing were 0.9992+/-0.0008/0.9989+/-0.0008 and 0.05+/-0.02/0.07+/-0.03, respectively, when 5 microV/10 microV Gaussian white noise (GWN) was added to the body surface potentials. The average CC and RE for dual-site pacing were 0.9975+/-0.0037 and 0.08+/-0.04, respectively, when 10 microV GWN was added to the body surface potentials. The present simulation results suggest the feasibility of noninvasive estimation of activation time throughout the ventricles from body surface potential measurement, and suggest that the proposed method may become an important alternative in imaging cardiac electrical activity noninvasively.     

Electrocardiogram signal generation using electrical model of cardiac cell: application in cardiac ischemia

Abstract

One of the most common causes of heart failure is ischaemia. In this disease, the heart muscles die due to the lack or insufficiency of the blood in the cardiac veins. As a result of such a phenomenon, the action potential in that part of the heart would fade. In this article, using the electric model of the cardiac cell and the mechanism of producing an ECG signal in the heart, the process of producing cardiac electrical potential has been modelled. In this regard, the basic constituent signals of the ECG are generated. Afterward, by accumulating these signals, the final ECG is reproduced. In addition, by variation of the presented model parameters, the cardiac ischaemic signal is simulated in a way that the influence of ventricle ischaemia on the ventricular tissues is considered. The results of such a simulation demonstrate a sufficient match between the model output and the reported changes of the cardiac arrhythmia including ischaemic failures. Here, we report the 91% match between the simulated signal and the considered clinical data.     

Evaluation of T-wave alternans in high-resolution ECG maps recorded during the stress test in patients after myocardial infarction

Introduction

Recent studies point to analysis of T-wave alternans as a promising indicator of an increased risk of life-threatening ventricular arrhythmias. In this study the occurrence of T-wave alternans in the high-resolution ECGs recorded during the exercise stress test and scintigraphic tests (SPECT) in patients with ischemic heart disease was examined.

Material and methods

The study group consisted of 33 patients after myocardial infarction. In the group of patients after myocardial infarction and with low left ventricular ejection fraction correlations of 70% between the test results of T-wave alternans and SPECT and 60% between the test results of T-wave alternans and stress test were found.

Results

In the group of patients after myocardial infarction but with high left ventricular ejection fraction correlations were respectively 39% and 48%. The analysis of the electrocardiographic maps showed a strong dependence of this correlation on the T-wave alternans amplitude and location of the ECG measuring electrode on the chest. The results might suggest that in patients after myocardial infarction and at increased risk for sudden cardiac death T-wave alternans may also provide information about cardiac electrical instability associated with ischemia.

Conclusions

It can also be assumed that the position of the electrode where the highest level of the T-wave alternans was detected can indicate the location of the ischemic region of the heart.     

Sensitivity analysis of ventricular activation and electrocardiogram in tailored models of heart-failure patients

Cardiac resynchronization therapy is not effective in a variable proportion of heart failure patients. An accurate knowledge of each patient’s electroanatomical features could be helpful to determine the most appropriate treatment. The goal of this study was to analyze and quantify the sensitivity of left ventricular (LV) activation and the electrocardiogram (ECG) to changes in 39 parameters used to tune realistic anatomical-electrophysiological models of the heart. Electrical activity in the ventricles was simulated using a reaction-diffusion equation. To simulate cellular electrophysiology, the Ten Tusscher-Panfilov 2006 model was used. Intracardiac electrograms and 12-lead ECGs were computed by solving the bidomain equation. Parameters showing the highest sensitivity values were similar in the six patients studied. QRS complex and LV activation times were modulated by the sodium current, the cell surface-to-volume ratio in the LV, and tissue conductivities. The T-wave was modulated by the calcium and rectifier-potassium currents, and the cell surface-to-volume ratio in both ventricles. We conclude that homogeneous changes in ionic currents entail similar effects in all ECG leads, whereas the effects of changes in tissue properties show larger inter-lead variability. The effects of parameter variations are highly consistent between patients and most of the model tuning could be performed with only ~10 parameters.     

Diurnal Variations of ECG Parameters During 23-Hour Monitoring in Cardiac Patients With Ventricular Arrhythmias or Ischemic Episodes

ECG and physical activity (recorded with motion detectors) were continuously monitored during 23 hours in 31 male cardiac patients (81% with myocardial infarction). According to the occurrence of ventricular arrhythmias (VA) or ischemic episodes (IE), each patient was grouped in one of three diagnostic categories: neither VA nor IE, VA with or without IE, and IE only. Analysis of the ECG parameters was done beat-by-beat and averaged on a 1-min basis. Results were derived from the 2-hour means between 2 p.m. and 12 p.m. MANOVA revealed significant group differences for heart rate variability (greater for the group with VA), R-wave amplitude (higher for the group with IE), and P-wave amplitude (higher for the group with VA). Significant time effects were observed for all variables except QRS- and P-wave durations. As may be expected, physical activity and heart rate were lower at night. Heart rate variability, PQ-interval, PR-segment, QT-interval, ST-segment, and T-wave duration increased during the night. R-wave amplitude also increased but the relative P- and T-wave amplitudes decreased. The corrected QT-interval, QTc, was shorter at night and the ST-segment, J + 60-point, S-wave, and J-point amplitudes were less negative. Group X Time interactions were observed for T-wave amplitude. For this amplitude, the decrease during the night was prominent only for the VA group. The results of this study suggest that the three diagnostic groups can be differentiated by diverse ECG parameters.     

Improved relationship between left and right ventricular electrical activation after cardiac resynchronization therapy in heart failure patients can be quantified by body surface potential mapping

OBJECTIVES:

Few studies have evaluated cardiac electrical activation dynamics after cardiac resynchronization therapy. Although this procedure reduces morbidity and mortality in heart failure patients, many approaches attempting to identify the responders have shown that 30% of patients do not attain clinical or functional improvement. This study sought to quantify and characterize the effect of resynchronization therapy on the ventricular electrical activation of patients using body surface potential mapping, a noninvasive tool.

METHODS:

This retrospective study included 91 resynchronization patients with a mean age of 61 years, left ventricle ejection fraction of 28%, mean QRS duration of 182 ms, and functional class III/IV (78%/22%); the patients underwent 87-lead body surface mapping with the resynchronization device on and off. Thirty-six patients were excluded. Body surface isochronal maps produced 87 maximal/mean global ventricular activation times with three regions identified. The regional activation times for right and left ventricles and their inter-regional right-to-left ventricle gradients were calculated from these results and analyzed. The Mann-Whitney U-test and Kruskall-Wallis test were used for comparisons, with the level of significance set at p≤0.05.

RESULTS:

During intrinsic rhythms, regional ventricular activation times were significantly different (54.5 ms vs. 95.9 ms in the right and left ventricle regions, respectively). Regarding cardiac resynchronization, the maximal global value was significantly reduced (138 ms to 131 ms), and a downward variation of 19.4% in regional-left and an upward variation of 44.8% in regional-right ventricular activation times resulted in a significantly reduced inter-regional gradient (43.8 ms to 17 ms).

CONCLUSIONS:

Body surface potential mapping in resynchronization patients yielded electrical ventricular activation times for two cardiac regions with significantly decreased global and regional-left values but significantly increased regional-right values, thus showing an attenuated inter-regional gradient after the cardiac resynchronization therapy.     

心外膜电位仿真研究

以往的心电理论研究，一方面强调从体表电位分布到心外膜电位分布的求逆；另一方面利用计算机心脏仿真模型只侧重于体表电位的仿真，而忽视了对心外膜电位的仿真，不利于心电逆问题研究的发展。本文阐明了心外膜电位对临床诊断和心电逆问题研究的重要性，并在ＬＦＸ计算机心脏仿真模型［１～３］的基础上建立了心外膜电位仿真的数学描述和心外膜模型。文中对正常心脏和左束支传导阻滞的心外膜电位进行了仿真研究，获得了一些有价值的结论     

Laplacian心电图的研究进展

Laplacian心电图技术是利用表面Laplacian值的概念,通过对体表电位进行微分,得以更准确、全面地反映心脏电活动的情况。本文详细介绍了Laplacian心电图研究的发展和现状,主要包括理论背景、实际测量、数据处理方法以及临床应用等方面,并指出了Laplacian心电图的研究困难及发展前景。     

Origin of the Electrocardiographic U Wave: Effects of M Cells and Dynamic Gap Junction Coupling

The electrophysiological basis underlying the genesis of the U wave remains uncertain. Previous U wave modeling studies have generally been restricted to 1-D or 2-D geometries, and it is not clear whether the U waves generated by these models would match clinically observed U wave body surface potential distributions (BSPDs). We investigated the role of M cells and transmural dispersion of repolarization (TDR) in a 2-D, fully ionic heart tissue slice model and a realistic 3-D heart/torso model. In the 2-D model, while a U wave was present in the ECG with dynamic gap junction conductivity, the ECG with static gap junctions did not exhibit a U wave. In the 3-D model, TDR was necessary to account for the clinically observed potential minimum in the right shoulder area during the U wave peak. Peak T wave simulations were also run. Consistent with at least some clinical findings, the U wave body surface maximum was shifted to the right compared to the T wave maximum. We conclude that TDR can account for the clinically observed U wave BSPD, and that dynamic gap junction conductivity can result in realistic U waves generated by M cells.     

体表心电图中T波交替现象的检测

T波交替（T-wave alternans,TWA）的检测对于预测室性心律失常有重要意义.本文首先利用基于经验模态分解（empirical mode decomposition,EMD）的降噪方法进行心电信号的降噪,然后采用小波变换进行心电信号特征点的识别,最后给出以T波峰值点为参考点提取T波窗口的方法.通过对连续的128个T波窗口进行功率谱分析证实,上述方法实现了微伏级TWA的检测,可用于TWA的临床诊断.