Polarisation impendance of pacemaker electrodes:in vitro studies simulating practical operation

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.     

依那普利对原发性高血压患者血清胶原及透明质酸浓度的影响

目的　观察原发性高血压（ＥＨ）患者使用依那普利前后血清Ⅲ、Ⅳ型前胶原、透明质酸的浓度变化;探讨依那普利干预血清前胶原生成以及抑制左室肥厚（ＬＶＨ）形成的作用。方法应用放免技术测定３７例ＥＨ患者及２１例体检正常者血清Ⅲ、Ⅳ型前胶原神经末端肽（ＰⅢＰ、ＰⅣＰ）及透明质酸（ＨＡ）浓度。ＥＨ患者口服依那普利治疗１２周后复测上述指标。结果治疗前ＥＨ组血清ＰⅢＰ、ＰⅣＰ、ＨＡ浓度显著高于对照组（Ｐ＜０．０１）;依那普利治疗后ＥＨ组相应指标较治疗前明显降低（Ｐ＜０．０１）。结论血清ＰⅢＰ、ＰⅣＰ、ＨＡ水平与血压升高密切相关;依那普利在降压的同时,降低血清ＰⅢＰ、ＰⅣＰ、ＨＡ的生成,具有抑制ＬＶＨ的作用。     

低心室容量负荷未能影响兔离体心肌的氧耗反应时间

为了解心肌容量负荷是否影响心肌的氧化磷酸化过程,采用兔离体灌流心肌线粒体氧耗反应时间测定方法,对一下正常心室容量负荷和低心室容量负荷时的心肌线粒体氧耗反应时间进行比较,结果提示心肌作功负荷变化未能影响心肌线粒体的能量代谢动态调节过程。     

QT Dispersion Level and Its Clinical Significance.in Dilated Cardiomyopathy

［1］Richardson CP, Mckenna RM, Bristow CM, et al.Report of the 1995 Word Health Organization/International Society and Federation of Cardiology Task Force on the definition and classification of cardiomyopathies. Circulation, 1996,93: 841 ［2］Barr CS, Naas A, Freeman M, et al. QT dispersion and sudden unexpected death in chronic heart failure. Lancet, 1994,343:327 ［3］Martin AB, Garson A, Perry JC, et al. Prolonged QT interval in hypertropic and dilated cardiomyopathy in children. Am Heart J, 1994,127(1):64 ［4］Pye M, Quinn AC, Cobble SM. QT dispersion: a non-invasive marker of susceptibility to arrhythmia in patients with sustained ventricular arrhythmias?Br Heart J, 1994,71(5):51 ［5］Berger RD, Kasper EK, Baughman KL, et al. Beat to beat QT interval variability: novel evidence for repolarization lability in ischemic and non ischemic dilated cardiomyopathy. Circulation, 1997, 96 (5):1557 ［6］Wolfram G, Ulrike S, Volker M, et al. QT dispersion and arrhythmic events in idiopathic dilated cardiomyopathy. Am J Cardiol, 1997,78: 458 ［7］Fei L, Goldman JH, Prasal K, et al. QT dispersion and RR variations on 12-lead ECGs in patients with congestive heart failure secondary to idiopathic dilated cardiomyopathy. Eur Heart J, 1996,17: 258 ［8］Pan YZ, Guo NS, Xing ZF, et al. The relation between QT dispersion and ventricular arrhythmia of dilated cardiomyopathy. Chin J Inter Medi, 1996,35(11):73 ［9］Galinier M, Vialette JC, Fourcade J, et al. QT interval dispersion as a predictor of arrhythmic events in congestive heart failure. Importance of aetiology. Eur Heart J, 1998,19(7) :1054     

Determination of left ventricular volume by two-dimensional echocardiography: comparison with magnetic resonance imaging

Left ventricular volume was determined in 12 healthy volunteersusing a newly developed two-dimensional echocardio-graphic delineationmethod. The results were compared with those of magnetic resonanceimaging, which served as the method of reference. Left ventricularend-diastolic volume was 123 ± 12 ml, echocardiographicallydefined, and 121 ± 12 ml calculated with magnetic resonanceimaging. End-systolic volume was 41 ± 7 ml on echocardiographyand 37±6 ml on magnetic resonance imaging. Left ventricularejection fraction was 67 ± 4%, echocardiographicallydefined, and 70 ± 5%, calculated with magnetic resonanceimaging. There was no statistical difference for any of themeasured parameters. Interstudy and inter-observer variabilitywas minimal. In conclusion, in healthy volunteers left ventricularvolume was accurately defined, using this newly developed two-dimensionalechocardiographic delineation method. During endocardial delineationa dynamic display is continuously available on a second window,allowing precise visual edge-detection. Moreover, correctionscan be made easily and quickly. These two advantages enhancethe accuracy of the method, even in cases of poor echogenicity.     

Influence of left ventricular filling proffle during preceding control beats on pulse pressure during ventricular premature contractions

We investigated whether the left ventricular filling profile,defined as the early to late diastolic left ventricular fillingvolume ratio, during the preceding control beats actually affectsthe pulse pressure during a ventricular premature contraction(PVC). Twenty patients underwent invasive electrophysiologicalstudy for sinus bradycardia. VPCs with various coupling intervalswere induced by right ventricular electrical stimulation, andthe mitral filling flow velocity pulsed Doppler echocardiography,the femoral arterial pressure curve and the electrocardiogramwere simultaneously recorded The early to late diastolic velocity-rimeintegral ratio (E₁/A₁ ratio) of the mitral filling flow velocityduring the control beats which preceded the VPC was measuredas an index characterizing left ventricular filling profile.The coupling interval of each VPC and the extrasystolic beatpulse pressure were measured The ratio of the extrasystolicbeat pulse pressure to the control beat pulse pressure was expressedin % (% extrasystolic beat pulse pressure). The correlationbetween the coupling interval and the % extrasystolic beat pulsepressure was investigated. Coupling intervals of 0·80,0·70, 0·60, 0·50, and 0·45 s wereused At a coupling interval of 0·80 or 0·45 s,the % extrasystolic beat pulse pressure showed no significantcorrelation with the E₁/A₁ ratio. In contrast, the % extrasystolicbeat pulse pressure with coupling intervals of 0·70,0·60, and 0·50 s showed a significant positivecorrelation with the E₁/A₁ ratio (r=0·67, 0·74,and 0·66 P<0·01, respectively). In additionto the prematurity and the site of origin of the VPCs, the leftventricular filling profile during the preceding control beatsmay significantly affect the height of the pulse pressure duringextrasystoles with medium length coupling intervals.     

Observations of the relationship between left ventricular aneurysm and ST segment elevation in patients with a first acute anterior Q wave myocardial infarction

Seventy-eight consecutive survivors of a first acute anteriorQ wave myocardial infarction (AMI) underwent two-dimensionalechocardiography (2D echo), colour Doppler echo and radionuclideangiography (RNA) for the diagnosis of left ventricular (LV)anteroapical aneurysm, in order to study the relationship ofthis complication to precordial ST segment elevation in thesepatients. The ST elevation (mm) in lead V₂, the maximum ST elevationin V₁-V₆ and the sum of ST elevation in V₁ to V₆ were calculated.LV aneurysm was present in 19 patients by 2D echo, of whom 12had a paradoxical systolic flow pattern (red and outward towardsthe transducer) at the apex. There was no difference between the mean ST elevation in V₂or the maximum ST elevation in V₁-V₆ in patients with and withoutan aneurysm, although the sum of ST elevations in V₁ to V₆ washigher in the former group (P<0.01). ST elevation of patientswith and without paradoxical systolic flow also did not differsignificantly. Wall motion abnormality (akinesis and dyskinesis)by 2D echo in the anterior wall was seen in 74% of patientswith and 36% of patients without an aneurysm (P<0.005), andin the septal region in 63% and 47% of respective patients (P-NS).There was no difference between the magnitude of ST elevationin subgroups of patients with ejection fraction (EF) 30% to40%, but the mean EF of patients with (23 ± 2.1%) andwithout a LV aneurysm (34 ± 1.3%) differed (P<0.001). It is concluded that precordial ST segment elevation does notclearly and in the diagnosis of an anteroapical LV aneurysm.It is related to akinesis and dyskinesis in anterior and septalregions inherent in patients with AMI and does not indicateimpaired LV function.     

Pulmonary venous flow as assessed by Doppler echocardiography: potential clinical applications

During the past few years Doppler assessment of pulmonary venous flow has gained increasing interest. The growing experience with the use of transesophageal echocardiography, the approach that nearly always yields registrations adequate for quantitative analysis, has markedly contributed in this respect. The Doppler-derived pulmonary venous flow pattern can be regarded as a measure of left atrial inflow and it augments the clinical significance of Doppler transmitral flow in the evaluation of diastolic left ventricular function. This article summarizes physiological background, possible applications, and limitations of Doppler echocardiography of pulmonary venous flow in clinical cardiology.     

Left Ventricular Mass Estimation by Echocardiography

Echocardiographic determination of left ventricular mass provides prognostic information that is independent of blood pressure. This prognostic information has a graded and continuous relationship with outcome, and is independent of traditional risk factors. This article addresses the prognostic and clinical utility of echocardiography for detection of left ventricular mass. Recommendations will be offered regarding the use of echocardiography for screening in select individuals.     

左室重量与左心功能不全相关性的研究

目的：研究可否用左室重量表达并判定左心功能不全的可能性。方法：将左心功能不全按NYHA标准分成4个级别,每级1组,并设正常对照组,用超声心动图测量同一个病人的左室射血分数（LVEF）和左室重量。用SAS统计软件做方差分析。结果：LVEF与左心功能不全高度负相关（R＝－0．77270）,左室重量与左心功能不全高度正相关（R＝0．73421）。LVEF、左室重量各级指标间差别显著（n＝153,F＝64．85,P＜0．01;n＝153,F＝53．39,P＜0．0001）。各级与对照组比统,LVEF指标从Ⅱ级开始方有显著差别（P＜0．05）;而左室重量指标从Ⅰ级开始就有显著差别（P＜0．05）。结论：LVEF与左室重量指标均与左心功能不全高度相关,但心功能Ⅰ级的病人,左室重量指标更为敏感。