Clinical magnetocardiography

Since the introduction, in 1982, of a Biomagnetic facility in the clinical environment, efforts were concentrated to investigate whether magnetocardiography could really provide new information of potential diagnostic use, even avoiding electromagnetic shielding to facilitate simultaneous biomagnetic and conventional cardiac investigations, including cardiac catheterization for invasive electrophysiological procedures. More than350 patients have been magnetically investigated using a single-channel second-order gradiometer. Results of 281 MCG studies, whose data have been extensively analyzed with updated software programs, are reported. Magnetocardiographic (MCG) mapping during endocardial pacing was performed to quantify the accuracy of MCG localization of intracardiac dipolar sources. MCG classification of ventricular preexcitation has been attempted in 70 patients with overt preexcitation. MCG localization of the ventricular preexcited area was accurate and reproducible, provided that during mapping a sufficient degree of ventricular preexcitation was present. MCG mapping during orthodromic A-V re-entry tachycardia has been also employed to attempt the localization of retrograde atrial preexcitation as well as the site of origin of atrial and ventricular tachyarrhythmias. For validation, the results of catheter and epicardial mappings have been used. Other applications of clinical magnetocardiography are under evaluation. The use of the Relative smoothness index needs, in our opinion, a larger experience to define its reliability as a predictor of risk for sudden death. MCG follow-up study of patients with transplanted hearts seems to be a promising application, for early detection of acute graft rejection reaction. Our reported case strongly supports this potentiality. Present work is also addressed to develop an integrated system allowing easy MCG mapping during cardiac catheterization, as a new method to guide diagnostic and therapeutic procedures as close as possible to the arrhythmogenic substrate.     

Recommended standards for fetal magnetocardiography

Fetal magnetocardiography (FMCG) is increasingly being used in research and diagnostics of fetal heart function. Currently, FMCG is the only noninvasive procedure available, comparable to postnatal ECG, which can be used to assess cardiac electrophysiology during the second and third trimester of pregnancy. For a reliable evaluation and full clinical acceptance of this new technique, large numbers of patient investigations are required which can only be obtained in multicenter studies. An international standard protocol is needed to allow pooling of sufficient data and to permit the comparison of studies performed in different centers. This article provides recommended standards for FMCG in the fields of data acquisition and data analysis.     

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.     

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.     

Reproducibility and reliability of fetal cardiac time intervals using magnetocardiography

We investigated several factors which may affect the accuracy of fetal cardiac time intervals (CTI) determined in magnetocardiographic (MCG) recordings: observer differences, the number of available recording sites and the type of sensor used in acquisition. In 253 fetal MCG recordings, acquired using different biomagnetometer devices between the 15th and 42nd weeks of gestation, P-wave, QRS complex and T-wave onsets and ends were identified in signal averaged data sets independently by different observers. Using a defined procedure for setting signal events, interobserver reliability was high. Increasing the number of registration sites led to more accurate identification of the events. The differences in wave morphology between magnetometer and gradiometer configurations led to deviations in timing whereas the differences between low and high temperature devices seemed to be primarily due to noise. Signal-to-noise ratio played an important overall role in the accurate determination of CTI and changes in signal amplitude associated with fetal maturation may largely explain the effects of gestational age on reproducibility. As fetal CTI may be of value in the identification of pathologies such as intrauterine growth retardation or fetal cardiac hypertrophy, their reliable estimation will be enhanced by strategies which take these factors into account.     

Clinical implications of the prenatal sonographic finding of fetal myocardial echogenic foci.

OBJECTIVE: The purpose of this study was to investigate the clinical implications of fetal echogenic foci limited to the myocardium of the ventricular wall (EMF) or intraventricular septum detected during prenatal sonography. METHODS: A retrospective review of fetuses found to have EMF during prenatal sonography from April 1990 through December 2003 was undertaken. Videotapes and reports were reviewed to determine the indication for sonography, gestational age, location, sonographic characteristics of the masses, and additional fetal findings. Sources of outcome data included neonatal and pediatric records and echocardiographic reports. RESULTS: Five fetuses were identified. Indications for sonographic evaluation included fetal growth (n = 4) and follow-up twin-twin transfusion syndrome (n = 1). Mean gestational age +/- SD at diagnosis was 23.7 +/- 8.0 weeks (range, 17.1-36.4 weeks). The EMF identified were within the right ventricular myocardium (n = 2), intraventricular septum (n = 1), left ventricular myocardium (n = 1), and myocardium of the cardiac apex (n = 1). All foci appeared sonographically "bright as bone." The foci ranged in size from 0.1 x 0.1 to 1.2 x 0.9 cm. Neonatal echocardiographic findings were reported as normal for each of the cases. Follow-up examinations available for up to 2.5 years of age showed normal cardiac function. CONCLUSIONS: The prenatal identification of EMF is unlikely to lead to notable short-term pathologic conditions because the fetuses in this investigation had unremarkable neonatal and pediatric echocardiograms and normal cardiac function.     

Assessment of fetal rhythm in complete congenital heart block by magnetocardiography

We report high precision assessment of fetal rhythm in utero in a case of isolated congenital complete heart block using fetal magnetocardiography. The recordings reveal a remarkably strong tendency for the atria and ventricles to synchronize, which is manifested by the continual presence of ventriculophasic sinus arrhythmia and frequent episodes of accrochage and isorhythmic AV dissociation.     

Fetal diagnosis of KCNQ1-variant long QT syndrome using fetal echocardiography and magnetocardiography

A pregnant woman with KCNQ1 variant long QT syndrome (LQTS) underwent fetal magnetocardiography (fMCG) after atrioventricular (AV) block was noted during fetal echocardiogram—atypical for LQTS type 1. Concern for fetal LQTS on fMCG prompted monitoring of maternal labs, change of maternal beta blocker therapy, and frequent fetal echocardiograms. Collaboration between obstetricians, neonatologists, and pediatric cardiologists ensured safe delivery. Beta blocker therapy was initiated after birth, and postnatal evaluation confirmed genotype and phenotype positive LQTS in the infant. Our experience suggests diagnosis and evaluation of fetal LQTS can alter antenatal management to reduce risk of poor fetal and postnatal outcomes.     

Clinical magnetocardiography: Experience with a biomagnetic multichannel system

The magnetic fields caused by the human heart's electrical activity were coherently recorded with a biomagnetic multichannel system (KRENIKON®) during 1 to 10 minutes in 49 patients. 31 to 37 magnetic channels were recorded simultaneously with the ECG and respiration. Comparison of a magnetic index and the Sokolow-Lyon index to echocardiographic findings in the quantification of left ventricular hypertrophy demonstrated the superiority of the magnetocardiogram (MCG) as compared to the ECG. The magnetocardiographic investigation of patients with WPW-Syndrome, ventricular extrasystoles, ventricular tachycardia, and paced ventricular beats demonstrated that multichannel magnetocardiography permits the non-invasive three dimensional localization of arrhythmogenic tissue with high spatial accuracy.     

The effect of volume conductor modeling on the estimation of cardiac vectors in fetal magnetocardiography

Previous studies based on fetal magnetocardiographic (fMCG) recordings used simplified volume conductor models to estimate the fetal cardiac vector as an unequivocal measure of the cardiac source strength. However, the effect of simplified volume conductor modeling on the accuracy of the fMCG inverse solution remains largely unknown. Aiming to determine the sensitivity of the source estimators to the details of the volume conductor model, we performed simulations using fetal-maternal anatomical information from ultrasound images obtained in 20 pregnant women in various stages of pregnancy. The magnetic field produced by a cardiac source model was computed using the boundary-element method for a piecewise homogeneous volume conductor with three nested compartments (fetal body, amniotic fluid and maternal abdomen) of different electrical conductivities. For late gestation, we also considered the case of a fourth highly insulating layer of vernix caseosa covering the fetus. The errors introduced for simplified volume conductors were assessed by comparing the reconstruction results obtained with realistic versus spherically symmetric models. Our study demonstrates the significant effect of simplified volume conductor modeling, resulting mainly in an underestimation of the cardiac vector magnitude and low goodness-of-fit. These findings are confirmed by the analysis of real fMCG data recorded in mid-gestation.     

冠心病患者的心磁图应用

目的 评价心磁图(MCG)对冠心病(CHD)的诊断价值并筛选评价诊断指标.方法 221例胸闷胸痛患者在冠脉造影之前72 h内接受MCG检查,应用Magwird.5软件包重建磁场图与电流密度分布图,分析下述定量指标:①ACTM(average classification of total maps);②R-max/T-max,以评价MCG对CHD的诊断价值.根据冠脉造影结果,分为CHD组(至少一支主要冠脉内径减小≥50%)(n=129)和正常对照组(n=92).结果 ①ACTM在两组间差异有统计学意义(CHD组3.0±0.6,对照组2.2±0.5,P=0.000).根据ROC曲线并结合临床实际,选2.45为截断点(＞2.45为异常),其诊断的灵敏度为78.3%,特异度为75%.②R-max/T-max在两组间差异有统计学意义(CHD组5.5±2.7,对照组3.6±2.2,P=0.000).选3.65为截断点(＞3.65为异常),灵敏度为72.9%,特异度为67.4%.结论 具有精细数据分析的MCG对CHD具有较高的诊断价值.     

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。     

Long-term implications of fetal growth restriction

Fetal growth restriction (FGR), or intrauterine growth restriction (IUGR), is a complication of pregnancy where the fetus does not achieve its genetic growth potential. FGR is characterized by a pathological retardation of intrauterine growth velocity in the curve of intrauterine growth. However, the FGR definition is still debated, and there is a lack of a uniform definition in the literature. True IUGR, compared to constitutional smallness, is a pathological condition in which the placenta fails to deliver an adequate supply of oxygen and nutrients to the developing fetus. Infants with IUGR, compared to appropriately grown gestational age infants, have a significantly higher risk of mortality and neonatal complications with long-term consequences. Several studies have demonstrated how suboptimal fetal growth leads to long-lasting physiological alterations for the developing fetus as well as for the newborn and adult in the future. The long-term effects of fetal growth retardation may be adaptations to poor oxygen and nutrient supply that are effective in the fetal period but deleterious in the long term through structural or functional alterations. Epidemiologic studies showed that FGR could be a contributing factor for adult chronic diseases including cardiovascular disease, metabolic syndrome, diabetes, respiratory diseases and impaired lung function, and chronic kidney disease. In this review we discussed pathophysiologic mechanisms of FGR-related complications and potential preventive measures for FGR.     

Clinical significance of isolated fetal pericardial effusion.

Prenatal sonographic identification of a small rim of pericardial fluid, measuring less than 2 mm in thickness, is a normal finding. Pericardial fluid 2 mm or greater in thickness may be associated with structural anomalies or hydrops, but its clinical significance in the absence of these associated findings has not been evaluated. We assessed the outcome in fetuses with isolated pericardial effusions of at least 2 mm thick. Our study population included 52 fetuses with effusions ranging from 2 to 7 mm in thickness. We compared rates of preterm delivery, cesarean section, intrauterine growth retardation, perinatal complications, Apgar scores, and length of neonatal hospital stay in these 52 cases to the overall hospital rates and found no statistically significant difference. We conclude that in the absence of other sonographic abnormalities, the finding of a fetal pericardial fluid collection 2 to 7 mm in thickness is not associated with adverse outcome.     

Clinical implications of the stress response.

A field of research that began with a curious observation in Drosophila has resulted in a new understanding of how cells respond to sudden and adverse changes in their environment. In addition through the study of the structure/function of the stress proteins, especially those which function as molecular chaperones, new insights into the details by which proteins are synthesized and acquire their final biologically active conformation have been realized. Equally exciting is the progress being made as it relates the potential diagnostic and therapeutic applications of the stress-response proteins. The use of stress proteins as the next generation of vaccines and/or their use as potentially powerful adjuvants, capable of stimulating both T and B cell responses to a particular antigen of interest appear close to becoming a reality. One wonders how many more surprises are in store for us as we continue to explore this evolutionally conserved cellular stress response.     

Clinical fetal monitoring

Abstract

Ultraviolet (UV) radiation is a notorious environmental carcinogen. Acute and chronic UV radiation exposure increase the risk for skin cancer. Protecting oneself from both UVA and UVB radiation with broad-based sunscreen can prevent certain skin cancers, their precursors, and photoaging. Although sun protection factor only measures UVB protection, it is essential to consider protection from UVA radiation when deciding on a particular sunscreen product. Awareness of particular controversies associated with sunscreen, such as vitamin D deficiency and sunscreen toxicity, is necessary to adequately counsel patients with sunscreen concerns. Additionally, all physicians should be familiar with sunscreen composition, proper use, and benefits while encouraging patient compliance.     

Changes in fetal cardiac geometry with gestation: implications for 3- and 4-dimensional fetal echocardiography.

OBJECTIVE: Three- and 4-dimensional fetal echocardiography can be performed using novel algorithms. However, these algorithms assume that the spatial relationships among cardiac chambers and great vessels are constant throughout gestation. The objective of this study was to determine whether changes in fetal cardiac geometry occur during gestation. METHODS: A cross-sectional study was conducted by reviewing 3- and 4-dimensional volume data sets from healthy fetuses obtained between 12 and 41 weeks of gestation. Volume data sets were examined using commercially available software. Parameters measured included angles between: (1) the ductal arch and fetal thoracic aorta; (2) the ductal arch and aortic arch; and (3) the left outflow tract and main pulmonary artery, as seen in the short axis of the heart. The mean angle from the left outflow tract to the short axis was calculated. Nonparametric statistics were used for analysis. RESULTS: Eighty-five fetuses were included in the study. The angle between the ductal arch and the fetal thoracic aorta decreased with gestational age (Spearman rho coefficient: -0.39; P < .001). In contrast, the angle between the ductal arch and aortic arch, and the mean angle between the left outflow tract and the short axis of the heart increased with gestational age (Spearman rho coefficients: 0.45 and 0.40, respectively; P < .001). CONCLUSIONS: (1) Changes in fetal cardiac geometry were shown with advancing gestational age. (2) Proposed algorithms for the examination of the fetal heart with 3-dimensional ultrasonography may need to be adapted to optimize visualization of the standard planes before 26 weeks of gestation.