全心电生理建模及体表电位标测图的仿真

虚拟心脏建模是连接心脏宏观和微观研究的有效手段之一。本研究利用微型计算机和可视人断层数据,通过图像增强、组织分割和三维重建,建立了分辨率为0.5 mm×0.5 mm×0.5 mm的心脏结构和胸前表面几何模型;以单细胞动作电位仿真为基础,使用改进的规则型算法,基于惠更斯原理的各向同性和各相异性波面型算法,分别完成了特殊传导系统、心房和心室电活动的仿真,时间精度可达1 ms;结合双域模型理论,使用偶极子等效心脏的电活动,同时结合躯体模型,完成了心脏电活动到体表心电的映射,进行正常和异常情况下体表电位标测图(BSPM)及12导联心电图的仿真。通过此模型得到的由窦房结起搏的体表12导联心电图,满足正常心电的诊断标准,证明了模型的真实性和可靠性,为进一步探讨传导和起搏异常的体表心电建立基础。     

超高静磁场引起心电图T波变化的电生理学初步仿真研究

目的初步仿真研究超高强度静磁场中的心电图T波幅度的改变机制。方法基于磁流体动力学模型,应用有限差分方法进行数值求解,通过改变磁场强度得到对应主动脉血流率;基于离子通道心室肌细胞模型,通过改变与ATP浓度相关的L型钙通道渗透率来仿真不同程度的心肌缺血情况。结果在超高静磁场中,人体主动脉的血流率减少可超过10%,可能会导致一定程度上的急性心肌缺血症;在不同心肌缺血情况下,心肌动作电位平台期受抑制,动作电位持续时间缩短,而透壁特异性增强,动态电生理力学心脏模型仿真得到心电图T波有较大改变。结论超高静磁场下主动脉血流率减少导致的心肌缺血会引起心电图T波幅度的明显增长,可能是超高静磁场对心电图T波影响的重要因素之一。     

电针穴位对家兔实验性缺血性心肌损伤的影响及其作用途径的初步探讨

为了探讨“心包经”某些穴位和心脏的联系途径,本文以心电图的Ⅱ和aVF导联的ST段、T波为指标,观察电针对家兔实验性缺血性心肌损伤恢复过程的影响及视前区——下丘脑前部在电针效应中的作用。     

心绞痛时ST-T伪性改善1例

1临床资料 患者男性,因间断性心前区疼痛2a,加重3d入院,即往有高血压病史.疼痛呈压榨性,范围手掌大小,持续5min左右,放射至左肩部,可自行缓解,发作频繁时3-4次/d.体检:血压180/90mmHg(1mmHg=0.133kPa),呼吸18次/min,双肺呼吸音清,心界向左下扩大,心率80次/min,心律齐,未闻及杂音.辅助检查:常规心电图示:窦性心律,TV1～V3直立,T V4～V5倒置,T V6低平,T V1 >T V6.X线示心肺无著变.超声心动图示:升主动脉扩张(D:46mm),心内形态结构未见异常.ECT示:左室下壁、后壁放射性稀疏,考虑为心肌缺血.酶学检查:GOT 27 IU/L,GPT 23 IU/L.血脂:5.01mmol/L.入院后行动态心电图检查发现无心绞痛发作时MV5导联ST段下0.03mV,T波倒置深度0.2mV,当心绞痛发作时原T波倒置的导联MV5变为直立,高度达0.5mV,ST段呈上斜型抬高0.2mV.疼痛缓解后直立的T波又变为倒置,ST段恢复到心绞痛发作前的水平,此类现象发生时间均与患者心绞痛发生的时间相对应,一日内发生3次.     

基于小波包变换的心电图ST段提取

目的:ST段是心电图的重要组成部分,其起始于心电图QRS波群的结束点并结束于T波的开始点。ST段的压低、分上斜形和下垂形压低、水平压低和以及鱼钩样改变都可以反映各种心脏疾病,所以,精确提取心电图ST段具有重要意义。因此,本文提出了基于小波包变换的心电图ST段精确提取算法。方法:首先对心电图信号进行去噪处理,滤去工频干扰信号以及基线漂移信号;然后,提取单周期的心电图信号;最后,引入小波包变换算法提取QRS波群、T波的主频带,重构QRS波群、T波的波形并确定ST段的始末位置。结果:本文算法在时域心电图上实现了ST的精确定位,提取了心电图的ST段。通过在经典数据库中的验证,本文算法具有非常好的表现。结论:实验结果表明,相较传统的对心电图加时间窗的方式提取ST段,本文算法可以精确提取心电图ST段,这为心电图ST段的自动精确识别,以及用于自动医疗检测与便携式医疗设备提供了依据。     

动态心电图ST段分析要注意的几个问题

目前对无症状心肌缺血的诊断,判断冠心病的预后及临床疗效评价,都依赖于对动态心电图ST移位的精确定量分析进行诊断。因此在对HolteryST段分析时,对下列影响ST段记录及分析精确度的一些因素应予特别重视。一、影响ST段记录精确度的因素导联的选择三通道动态心电图记录仪CMv5导联对左室前壁引起的ST段下移较敏感,主要用于检测前壁心肌缺血;CSavf对下壁心肌缺血敏感性高,用于观察下壁心肌缺血。Holter检测对左室下壁的缺血性ST段改变敏感性较低。     

心室电活动对胸表心电场的影响及其心电图表现

通过基于二维全心脏电生理模型的仿真，揭示了心室电活动对同侧及对侧胸表心电场的影响及其心电图表现，这种影响可因心室兴奋时序的变化以及室壁心肌组织主动与被动电学性质的变化而发生改变，由此产生多种心电图波形的变异。通过对这种曩进行分析，不同导联间心电图波形的关联性能够得到识别，其临床意义得到充分揭示。作为例子，我们对某些右胸导联心电图波形进行了解释。     

无创心电指标与恶性心律失常及猝死关系的研究进展

临床上很多原发性心电疾病患者的首发症状就是不可立逆的恶性心律失常和猝死。自1991年西班牙学者Brugada P和Brugada J两兄弟首次从体表心电图上发现右束支传导阻滞伴右胸导联ST段抬高和T波倒置与恶性室性心律失常及猝死有明确的相关性以来[1]。各国临床医学家都在不遗余力的寻找和探索发现恶性室性心律失常及猝死的高危因素和心电图标志。目前已被临床熟知的包括Brugada波、特发性J波、Epsilon波、Lambda波、长QT综合征、短QT综合症、QT离散度、心率变异性、T波电交替及窦性心率震荡现象等。随着心室复极异常的心电图表现、电生理…     

基于Ⅰ导联ECG的心肌梗死特征提取EI北大核心CSCD

提出了基于ECG导联Ⅰ的单周期信号的心肌梗死特征提取算法,避免了利用多导联ECG检测心肌梗死带来的不便。首先对导联Ⅰ的ECG信号进行去噪处理;然后,引入小波包算法提取QRS波群、T波的主频带,重构QRS波群、T波的波形并确定ST段的始末位置;最后,运用小波的多分辨分析对ST段进行分解并提取导联Ⅰ信号的心肌梗死的特征波形。实验结果表明,本文算法具有较高识别率,这为ECG导联Ⅰ信号用于心肌梗死的检测与诊断提供了依据。     

V1导联联合aVL及aVR导联在阵发性室上速中诊断价值分析

目的探讨V1导联联合aVL及aVR导联在阵发性室上速中诊断价值。方法对因阵发性室上性心动过速(PSVT)行心脏射频消融术(RFCA)患者135例,均行食道电生理检查,确定心动过速类型。并成功诱发出室上性心动过速,对比诱发前与室上速发作时体表心电图。结果 aVL切迹、aVR导联伪r'波与V1导联伪r'波发生在AVNRT的比例均大于AVRT(P均0. 001)。aVR导联ST段抬高发生在AVNRT的比例小于AVRT(P=0. 000 1)。并且在AVRT患者中72. 4%为左侧旁道。aVL导联aVR导联鉴别AVNRT敏感性高于V1导联。结论 V1导联联合aVL及aVR导联能够进一步保证典型阵发性室上速的诊断效果,提高诊断率。     

Effect of cardiac motion on body surface electrocardiographic potentials: an MRI-based simulation study

This paper describes an electrical model of cardiac ventricles incorporating real geometry and motion. The heart anatomy and its motion through the cardiac cycle are obtained from segmentations of multiple-slice MRI time sequences; the special conduction system is constructed using an automated mapping procedure from an existing static heart model. The heart model is mounted in an anatomically realistic voxel model of the human body. The cardiac electrical source and surface potentials are determined numerically using both a finite-difference scheme and a boundary-element method with the incorporation of the motion of the heart. The electrocardiograms (ECG) and body surface potential maps are calculated and compared to the static simulation in the resting heart. The simulations demonstrate that introducing motion into the cardiac model modifies the ECG signals, with the most obvious change occurring during the T-wave at peak contraction of the ventricles. Body surface potential maps differ in some local positions during the T-wave, which may be of importance to a number of cardiac models, including those incorporating inverse methods.     

Analysis and processing of laser Doppler perfusion monitoring signals recorded from the beating heart

Laser Doppler perfusion monitoring (LDPM) can be used for monitoring myocardial perfusion in the non-beating heart. However, the movement of the beating heart generates large artifacts. Therefore the aim of the study was to develop an LDPM system capable of correlating the laser Doppler signals to the cardiac cycle and to process the signals to reduce the movement artifacts. Measurements were performed on three calves, both on the normal beating heart and during occlusion of the left anterior descending coronary artery (LAD). The recorded LDPM signals were digitally processed and correlated to the sampled ECG. Large variations in the output (perfusion) and DC signals during the cardiac cycle were found, with average coefficients of variation of 0.36 and 0.14 (n-14), respectively. However, sections with a relatively low, stable output signal were found in late diastole, where the movement of the heart is at a minimum. Occlusion of the LAD showed the importance of recording the laser Doppler signals at an appropriate point in the cardiac cycle, in this case late systole, to minimise movement artifacts. It is possible to further reduce movement artifacts by increasing the lower cutoff frequency when calculating the output signal.     

New approaches to the analysis of ECG data

Recently, techniques for analyzing computerized ECG data have been developed in time domain, frequency domain and micro level analysis of signals. In body surface ECG mapping, reverse problem analysis from body surface to cardiac surface was investigated, but findings were not sufficient to be clinically useful. Heart rate variability analysis from Holter ECG tapes showed the utility for determination of autonomic nervous function by time and frequency domain analysis. Late ventricular potentials recorded by Signal Averaged ECG have been beneficial for predicting malignant ventricular tachyarrhythmias, as well as delayed potentials in atrial activity. QT dispersion from 12-lead ECG has been studied as one of the indicators of ventricular instability and there was some difficulty in detecting the end points of QT intervals such as that in patients with flat T waves. The recently developed automatic analysis of the Least square fit method for detecting terminal points of T wave might be optimal compared with the other methods. Micro volt T wave alternans by spectrum frequency analysis of T wave in consecutive heart beats is a unique technique for predicting cardiac sudden death, however the mechanism remains obscure.     

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.     

Interactions between cardiac activity and conscious somatosensory perception

Fluctuations in the heart's activity can modulate the access of external stimuli to consciousness. The link between perceptual awareness and cardiac signals has been investigated mainly in the visual and auditory domain. Here, we investigated whether the phase of the cardiac cycle and the prestimulus heart rate influence conscious somatosensory perception. We also tested how conscious detection of somatosensory stimuli affects the heart rate. Electrocardiograms (ECG) of 33 healthy volunteers were recorded while applying near‐threshold electrical pulses at a fixed intensity to the left index finger. Conscious detection was not uniformly distributed across the cardiac cycle but significantly higher in diastole than in systole. We found no evidence that the heart rate before a stimulus influenced its detection, but hits (correctly detected somatosensory stimuli) led to a more pronounced cardiac deceleration than misses. Our findings demonstrate interactions between cardiac activity and conscious somatosensory perception, which highlights the importance of internal bodily states for sensory processing beyond the auditory and visual domain.     

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.     

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.     

辅以体外反搏的胸部充气背心辅助循环装置

本文介绍一种用于心衰治疗的新型无创辅助循环装置。它以奔腾PC机和16住80C196KC单片机组成的上下位机为控制主机，以心电R波为触发产生控制脉冲去控制胸部充气背心(VEST)和下半身序贯加压(增强型体外反搏，EECP)，实施辅以体外反搏的胸部充气背心辅助循环术(VCAC)，即收缩期VEST辅助心脏射血，舒张期EECP改善心肌血供。此外，还有实施EECP，实时监测心电、脉搏血氧等基本生理信号和采集8道其他模拟信号和数据存盘分析等功能。犬心衰模型动物实验初步表明，VEAC具有VEST和EECP的优点且互补，同时增强心脏射血和改善心肌血供，达到了辅助循环的目的。     

Myocardial perfusion monitoring during coronary artery bypass using an electrocardiogram-triggered laser Doppler technique

Electrocardiogram (ECG)—triggered laser Doppler perfusion monitoring (LDPM) was used to assess myocardial perfusion, with minimum myocardial tissue motion influence, during coronary artery bypass grafting (CABG). Thirteen subjects were investigated at six phases: pre- and post-CABG; post aorta cross-clamping; pre and post left internal mammary artery (LIMA) graft declamping; and post aorta declamping. The perfusion signal was calculated in late systole and late diastole, with expected minimum tissue motion, and compared with arrested heart measurements. Patient conditions or artifacts caused by surgical activity made it impossible to perform and analyse data in all six phases for some patients. No significant (n=5) difference between perfusion signals pre- and post-CABG was found. Diastolic perfusion signal levels were significantly (p<0.02) lower compared with systolic levels. After aorta cross-clamping, the signal level was almost zero. A distinct perfusion signal increase after LIMA and aorta declamping, compared with pre-LIMA declamping, was found in ten cases out of 13. A significantly (p<0.04) lower perfusion signal in the arrested heart compared with in the beating heart was registered. Influence from mechanical ventilation was observed in 14 measurements out of 17. In conclusion, ECG-triggered LDPM can be used to assess myocardial perfusion during CABG. Perfusion signals were lower in the arrested heart compared with in the beating heart and in late diastole compared with late systole. No significant difference between pre- and post-CABG was found.     

Myocardial tissue motion influence on laser Doppler perfusion monitoring using tissue Doppler imaging

Tissue motion of the beating heart generates large movement artifacts in the laser Doppler perfusion monitoring (LDPM) signal. The aim of the study was to use tissue Doppler imaging (TDI) to localise intervals during the cardiac cycle where the influence of movement artifacts on the LDPM signal is minimum. TDI velocities and LDPM signals were investigated on three calves, for normal heartbeat and during occlusion of the left anterior descending coronary artery. Intervals of low tissue velocity (TDI_int<1 cm s⁻¹) during the cardiac cycle were identified. During occlusion, these intervals were compared with low LDPM signal intervals (LDPM_int<50% compared with baseline). Low-velocity intervals were found in late systole (normal and occlusion) and late diastole (normal). Systolic intervals were longer and less sensitive to heart rate variation compared with diastolic ones. The overlap between LDPM_int and TDI_int in relation to TDI_int length was 84±27% (n=14). The LDPM signal was significantly (p<0.001, n=14) lower during occlusion if calculated during minimum tissue motion inside TDI_int), compared with averaging over the entire cardiac cycle without taking tissue motion into consideration. In conclusion, movement artifacts are reduced if the LDPM signal is correlated to the ECG and investigated during minimum wall motion. The optimum interval depends on the application; late systole and late diastole can be used.