Clinical application of magnetocardiography

Magnetocardiography is a noninvasive contactless method to measure the magnetic field generated by the same ionic currents that create the electrocardiogram. The time course of magnetocardiographic and electrocardiographic signals are similar. However, compared with surface potential recordings, multichannel magnetocardiographic mapping (MMCG) is a faster and contactless method for 3D imaging and localization of cardiac electrophysiologic phenomena with higher spatial and temporal resolution. For more than a decade, MMCG has been mostly confined to magnetically shielded rooms and considered to be at most an interesting matter for research activity. Nevertheless, an increasing number of papers have documented that magnetocardiography can also be useful to improve diagnostic accuracy. Most recently, the development of standardized instrumentations for unshielded MMCG, and its ease of use and reliability even in emergency rooms has triggered a new interest from clinicians for magnetocardiography, leading to several new installations of unshielded systems worldwide. In this review, clinical applications of magnetocardiography are summarized, focusing on major milestones, recent results of multicenter clinical trials and indicators of future developments.     

Analysis of fetal heart rate variability obtained by magnetocardiography

OBJECTIVE: To obtain fetal magnetocardiogram (fMCG) recordings in preterm fetuses in both shielded and unshielded clinical settings. METHODS: Seventeen fMCG recordings were obtained from 6 low-risk fetuses of 26-35 weeks' postmenstrual age. The superconducting quantum interference device biomagnetometer was positioned over the gravid abdomen, and the signals, associated with the bioelectrical activity of the fetal heart, were digitized at a sampling rate of 1 kHz. The fMCG signal was recorded for 5 minutes along with the reference maternal electrocardiogram in both the shielded and unshielded environment. A nonsyntactic QRS detection algorithm based on Pan-Tompkins scheme was employed for extracting fetal RR time series. RESULTS: The growth rate of 1.97 decibels (dB) exhibited by the low-frequency (LF) band is almost 2 1/2 times that of the high-frequency (HF) band. HF/LF power ratio was calculated to have a negative growth rate of -0.17 dB/wk (P = .004). Total power increased at approximately 1.35 dB/wk (P = .031). CONCLUSIONS: Consistent with the literature, the total power, or the variance, as well as the LF and HF powers independently, indicates an increasing trend with increasing postmenstrual age.     

HIV infection and abnormal regional ventricular function

To examine the effect of HIV infection on regional left ventricular dysfunction in cardiovascularly asymptomatic individuals. Nineteen HIV-negative and 27 HIV-positive cardiovascularly asymptomatic study participants in Baltimore, Maryland were selected and underwent tagged cardiac magnetic resonance imaging. Regional left ventricular myocardial mid-wall peak systolic circumferential strain (Ecc) and early diastolic strain rate (SRE) of the left ventricle were assessed with the use of the harmonic phase analysis. The average Ecc and SRE measurements were compared between HIV-negative and HIV-positive individuals. Compared with the HIV-negatives, the HIV-positives had lower average Ecc and SRE measurements in 90% of the 16 standard left ventricular segments. Of the 14 segments with decreased Ecc strain, 3 were statistically significant and of 14 with decreased strain rate (SRE), 6 were statistically significant. HIV infection may be associated with subclinical regional left ventricular systolic and diastolic dysfunction in individuals free of overt cardiovascular disease.     

正常人群心磁图特征的探讨

目的:采用无屏蔽式心磁图仪MCG-7,探讨我国正常人群的心磁图(MCG)特征,并比较不同年龄组间心磁图各指标是否存在差异。方法:采用德国Magscan公司生产的无屏蔽式MCG-7记录仪,选择平均分级(averageclassification of total maps,ACTM)、异常磁图比率(ratio of abnormal maps,RAM)、复合心室激动指数(complexventricular excitation index,CVEI)、R波与T波顶点的最大磁场值比值(R-max/T-max比值)、T波起始处电流密度最大电轴方向(Tbegin)、T波顶点处电流密度的最大电轴方向(T-max)来描述100例正常人心磁图结果。结果:正常人MCG在ST-T整个复极过程中存在双极对称结构,仅有一个主要电流方向,指向左下0°～90°,Tbegin在10°～25°之间,T-max在25°～35°之间。RAM为18%左右(9.10%～25.75%),ACTM平均值为2.36(2.10～2.50),CVEI平均值为18.68(-12.75～64.00),R-max/T-max比值为4.04(2.53～4.65)。各年龄组心磁图各项指标差异无统计学意义(P>0.05)。结论:心磁图是诊断心肌缺血的有用工具,正常人群不同年龄组间心磁图参数差异无统计学意义。     

Influence of abnormal breathing conditions on right ventricular function

Conclusion Clinical data collected in our intensive care unit during respiratory therapy of patients with acute respiratory faillure of various causes, confirm and illustrate some previously well-known concepts concerning the influence of breathing conditions on right ventricular performance. Venous return was found to be highly sensitive to the level of pleural pressure. On the other hand, right ventricular output impedance appears to largely depend on the degree of lung distension. Moreover, in the light of our data, a somewhat new concept might be individualized according to which the antagonistic actions of the thoracic and right ventricular pumps could severely compete in that original clinical setting represented by acute asthma.This work was supported by a Grant of the U.E.R. Paris-Ouest     

美托洛尔与乙吗噻嗪对心室晚电位阳性的室性心律失常影响的研究

８８例心室晚电位（ＶＬＰ）阳性的室性心律失常（ＶＡ）患者随机分为Ａ、Ｂ两组，分别服用美托洛尔及乙吗噻嗪，４周后复查２４小时动态心电图（ＤＣＧ）及ＶＬＰ。结果：乙吗噻嗪虽能有效控制ＶＡ，但不能使ＶＬＰ转阴，且有致心律失常作用（３／４２）；而美托洛尔不但能较好控制ＶＡ（３８／４６），且可使ＶＬＰ逆转（３９／４６），又无致心律失常及其它明显副作用，疗效与５０～１００ｍｇ／ｄ剂量之间无明显关系。作者认为：对ＶＬＰ阳性的ＶＡ患者的药物治疗，只要无β受体阻滞剂应用的禁忌证，应首选美托洛尔     

Cardioplegia and ventricular late potentials in cardiac surgical patients

Background and objective  

Ventricular late potentials (LP) recording with signal-averaged electrocar- diogram allow identifying patients at risk of sudden death and ventricular tachycardia. Cardiac surgery with cardiopulmonary bypass (CPB) could predispose to the development of myocardial ischemia related to imperfect cardioplegia. To the best of our knowledge, no study investigated the protection of cardioplegia and CPB regarding the occurrence of LP in patients without previous myocardial infarction and undergoing cardiac surgery.     

Characterization of fetal arrhythmias by means of fetal magnetocardiography in three cases of difficult ultrasonographic imaging

Characterization of ultrasound detected fetal arrhythmias is generally performed by means of M-mode and pulsed Doppler echocardiography (fECHO), sonographic techniques that allow only indirect and approximate reconstruction of the true electrophysiological events that occur in the fetal heart. Several studies demonstrated the ability of fetal magnetocardiography (fMCG) to identify fetal arrhythmias. We report on three women, studied after the 32nd gestational week, who were referred for fMCG because of unsatisfying fetal cardiac visualization with fECHO due to maternal obesity, fetus in constant dorsal position hiding the fetal heart, intrauterine growth retardation, and oligohydramnios. Minor pericardial effusion was present in the third patient and digoxin therapy was given. FMCG were recorded with a 77-channel MCG system working in a shielded room. Independent Component Analysis (FastICA algorithm) was used to reconstruct fetal signals. The good quality of the retrieved fetal signals allowed real-time detection of arrhythmias and their classification as supraventricular extrasystoles (SVE), with/without aberrant ventricular conduction and/or atrioventricular block. The time course of the fetal cardiac rhythm was reconstructed for the entire recording duration; hence, fetal heart rate variability could be studied in time and frequency. Since isolated extrasystoles may progress to more hazardous supraventricular tachycardias, the noninvasive antenatal characterization of, even transient, fetal arrhythmias and their monitoring during pregnancy can be of great clinical impact.     

血管迷走性晕厥儿童心室晚电位变化

目的探讨血管迷走性晕厥（VVS）儿童心室晚电位（VLP）的变化。方法直立倾斜试验（HUTT）阳性的VVS儿童45例（研究组），用广东中山SR-1000A心电综合自动分析仪通过体表叠加方法检测VLP。匹配健康儿童45例（对照组）。结果与对照组比较，研究组高频低幅时限（LAS40）明显延长（P〈0．05），心率、总QRS时间（TQRS）、均方根值（RMS40）差异无统计学意义（P〉0．05）。结论VVS儿童心肌电活动异常，存在心脏事件发生的危险性。     

Serum antioxidant activity in normal and abnormal subjects

Serum oxidant activity (AOA) was correlated with the serum caeruloplasmin and serum copper concentration and with the total and available serum iron-binding capacity in 313 normal and abnormal subjects. In all groups except in patients with Wilson's disease (hepatolenticular degeneration) there was a highly significant direct correlation between serum AOA and serum caeruloplasmin concentration. A statistically significant direct correlation between serum AOA and the available iron-binding capacity of serum was found only in normal subjects and in children with thalassemia major and iron overload. There was no correlation between serum AOA and the serum tocopherol concentration in any of the groups studied.     

Evaluation of reduced activity galactose-1-phosphate uridyl transferase by combined radioisotopic assay and high-resolution isoelectric focusing

Fifty-nine patients referred for testing of galactose-1-phosphate uridyl transferase (GALT) activity were evaluated by a combination of radioisotopic assay and an improved high-resolution isoelectric focusing (IEF) method for determination of individual genotypes. The majority of evaluations (43 of 59) were undertaken because of an abnormal fluorometric GALT screening assay conducted as part of a state newborn galactosemia screening program or as a diagnostic test for an infant with one or more clinical signs of galactosemia. Only 12 of the 43 patients with an abnormal fluorometric screening test were found to have less than 3% GALT activity by quantitative assay, no GALT-staining by IEF, and a clinical history consistent with classical galactosemia. The majority of the remainder (24 of 43) were found to be heterozygotes for galactosemia, the Duarte variant, or both. IEF was found to be a fast and accurate technique for assignment of GALT genotypes in conjunction with quantitative enzymatic assay.     

Prognosis of early pre-discharge and late left ventricular dilatation by cardiac magnetic resonance imaging after acute myocardial infarction

The International Journal of Cardiovascular Imaging - To study the long-term prognosis of early pre-discharge and late left ventricular (LV) dilatation in patients with first ST-elevation...     

Iatrogenic ventricular tachycardia from endocardial pacemaker late after repair of tetralogy of Fallot

A 34-year-old woman, who had undergone radical repair for tetralogy of Fallot at the age of 8 years, was left with moderate-to-severe pulmonary regurgitation. VT developed after endocardial pacing for symptomatic pauses and atrial flutter. The possibility that the new VT originated from the apical endocardial lead was suggested by the unusual morphology of the VT, which was similar to paced. Surgical removal of the lead, which was deeply embedded at the same time as a pulmonary valve was replaced, cured the arrhythmia. This unusual cause of VT highlights possible risks associated with setting up a dangerous reentry circuit by inserting a right ventricular endocardial pacemaker lead.     

Effect of abnormal levels of serum components on antibiotic activity.

Antibiotic activity in serum from a model for type II diabetes was similar to that in normal sera or media containing cholesterol but lacking glucose, insulin, or both. The ratio of effects of broth plus obese-rat serum to effects of broth plus lean-rat serum supplemented with cholesterol approached or equaled 1.