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31.
目的 通过食道心房起搏负荷试验 ,使用彩色多普勒超声心动图对左心室室壁运动状态及左心室舒缩功能改变进行评价 ,以提高冠心病诊断的检出率 ;方法 使用心脏程序刺激仪经食道起搏导管调整心率达次极量 ;同时使用彩色多普勒超声心动仪进行左心室室壁运动记分并记录二尖瓣口及主动脉瓣环部血流频谱 ;结果 经食道心房起搏增加心脏负荷 ,应用左心室每搏量 (SV)、主动脉瓣环部流速积分 (VTIAO)、等容舒张时间 (IVRT)、二尖瓣口流速积分(VTIMV) )、快速充盈分数 (RFI)及室壁运动记分指数 (WMSI)作为指标在冠心病诊断中可提高检出率 ,以WMSI结合其它两项左心室舒缩功能阳性指标 ,其冠心病诊断的检出率为 95 % ,假阳性率为 3% ;结论 经食道心房起搏彩色多普勒负荷超声心动图 (TPDE)在冠心病诊断中有较高的应用价值 ,因其简便、实用和安全 ,宜在临床广泛推广使用  相似文献   
32.
Simultaneous electrical stimulation of tissue with the measurement of blood flow using an electromagnetic flowmeter system almost invariably results in large flow measurement inaccuracies. These inaccuracies are because the electrical energy from stimulating artefacts is amplified along with the flow signals. The paper describes the building and use of an inexpensive circuit to remove stimulation artefacts from electromagnetic flow measurements.  相似文献   
33.
To examine the effects of pulmonary vascular pressures and flow on pulmonary blood volume (PBV), experiments were performed at constant heart rate and zone 3 conditions (mean left atrial pressure (LAP) above airway pressure) in six anesthetized, open-chest dogs. PBV was calculated as the product of electromagnetic aortic flow and pulmonary mean transit time for ascorbate, obtained without blood withdrawal by polarographic recording of aortic ascorbate changes. In three series of experiments LAP was raised similarly in three steps, from 4.5 to 14.8 mmHg: by mitral constriction which reduced pulmonary blood flow, by blood volume expansion which more than doubled pulmonary blood flow, or by a combination of the two procedures which kept pulmonary blood flow constant. In all three series, LAP and mean pulmonary arterial pressure (PAP) rose in proportion, but PBV was better correlated to PAP (r=0.87±0.02) than to LAP (r=0.66±0.09). These experiments suggest that PAP is the most important factor in determining PBV under zone 3 conditions, whether PAP is raised by increasing pulmonary blood flow or by mitral constriction.  相似文献   
34.
Ablative techniques, using standard defibrillators and commonly available cardiac catheters, have been applied to the His bundle and bypass tracts for the management of arrhythmias. We have done in vitro studies of the physical effects of these high energy electrical impulses delivered via different pacing electrodes. Unipolar impulses of 10 to 400 joules were delivered via three U.S.C.I. bipolar electrodes and three Vitatron Helifix electrodes immersed in Ringer's solution. The effects were recorded on 35 mm still film, video tape, and high speed cine film. Pressure, voltage, and current were measured. The U.S.C.I. bipolar electrodes and the Vitatron Helifix electrodes safely withstood repeated delivery of 400-joule impulses which produced similar flash shapes. Each took the form of an incandescent, spherical "fire-ball" centered around the exposed electrode surface. The mean diameters of the "fire-ball" for 10 to 400 J using the U.S.C.I. electrodes were 5-24 mm and 3-20 mm for the Helifix catheter electrodes. Peak pressure excursions of over an atmosphere were observed 3 cm from the electrode tips. Higher pressures, lower voltages, and larger currents occurred using the U.S.C.I. pacing lead. The simple, 35 mm time exposure technique showed that at low energies the flashes appeared to emerge in a retrograde manner from the U.S.C.I. catheters and more distally from the Helifix electrode. This suggested that the latter might be more effective with lower energy impulses. It is concluded that lower energies should be used to take full advantage of the active fixation electrode.  相似文献   
35.
Atrial pacing (AAI) in sick sinus syndrome (SSS) has been questionedbecause of the risk of distal conduction disturbances (DCD)and atrial tachyarrhythmias. The authors studied the incidenceof clinically relevant DCD and arrhythmias in 52 SSS patientswith AAI. The observation time was 25–67 (mean 48) months. Invasive electrophysiologic investigation was performed preoperativelyin 29 cases and preoperative atrial pacing to Wenckebach blockor to 150 ppm in 23. The preoperative investigation showed prolongedHV-time in three cases and Wenckebach block at 110ppm in onecase, while six patients had LAH-block, five RBB-block and twofirst degree A V-block. No further DCD developed in any of thesepatients. Second-degree type IA V-block developed in two patientsafter 2 and 19 months, respectively. One had been treated withdigitalis and verapamil and was asymptomatic. The other patient,who had a low ventricular rate, experienced near-syncope. Thesetwo blocks could not be predicted from the preoperative andperoperative investigations. In five patients (10%) permanent atrial fibrillation developedduring the follow-up period. The incidence of concomitant supraventriculartachyarrhythmias in the patients with the bradycardia-tachycardiasyndrome appeared to be unaffected by the pacemaker treatment.  相似文献   
36.
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38.
A microcomputer-based pacemaker system for the evaluation of pacemaker treatment of tachycardia is described. The system may be used to study tachycardia initiation, tachycardia termination or a combination of the two. The software incorporates a visual display unit screen handling package which provides the user-system interface. System-patient interfacing is performed by a separate pacing and sensing unit which communicates with the computer via standard digital input/output lines. Several pacing options are available, selectable from a screen-displayed menu. Each selection also has an associated set of programmable parameters which may be adjusted, within allowed limits, to suit particular studies. Examples of the use of the system for tachycardia termination are given. The main programming language for the controlling software was Fortran IV. Some routines were necessarily written in assembly language. The system is useful for evaluation purposes and forms the basis of a cardiac pacemaker development tool.  相似文献   
39.
The electrical properties of pacemaker electrodes were studiedin vitro under conditions prevailing in practical pacemaker operation. Emphasis was laid on a clear distinction between the changing modes of the pacemaker action. During sensing, the electrode can be represented by an a.c. series polarisation resistance and capacitance, generally accepted for biological electrodes obeying linearity rules. During stimulation, the electrode operates in the non-linear region. A nearly constant-voltage, short, rectangular pulse applied directly to the electrode-heart system, causes the electrode voltage and current to respond as a transient exponential, characterised approximately by a single time constant. This response allows modelling of the d.c. equivalent circuit of the electrode, in the form of a polarisation capacitance with a small resistance in series, shunted by a parallel resistance. Formulae were derived for calculation of these elements. The response of the electrode-heart system to a single stimulus was tested as a function of the amplitude and duration of the applied pulse. Also, the effect of repetitive stimulations was checked at a normal pacing rate. A nearly constant-voltage pacing source, as compared with a constant-current one, appears to be advantageous for preservation of the longevity of the electrode.  相似文献   
40.
Dual chamber pacing (DDD) maintains atrioventricular (AV) sequence; AV delay programmability modifies the relationship between atrial and ventricular contraction. To evaluate the hemodynamic effects of such a modification, ten patients with a DDD unit for complete AV block were studied by time-motion (M-mode) and Doppler echocardiography during inhibited ventricular pacing (VVI), atrial-triggered ventricular pacing (VDD) and atrioventricular sequential pacing (DVI) at different AV delay (90, 140, 190, 240 msec). A significant improvement in stroke volume (SV) (15%-20%, P less than 0.05) was seen during DDD versus VVI pacing; no changes, however, were observed in the same patient with different AV delay or during DVI versus VDD pacing. These data suggest that programming of AV delay does not affect systolic performance at rest; longer diastolic filling times recorded during DDD pacing with "short" AV delay (90-140 msec) do not seem to be a hemodynamically relevant epi-phenomenon of PM programming.  相似文献   
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