The value of magnetocardiography in patients with and without relevant stenoses of the coronary arteries using an unshielded system

BACKGROUND: The diagnostic management of patients with chest pain remains a clinical challenge. Magnetocardiography (MCG) is a noninvasive method for the recording of cardiac electromagnetic signals at multiple sites above the chest cage. Contrary to electrocardiogram (ECG) the magnetic field is unaltered by surrounding tissues. The present study aimed to analyze the diagnostic value of an unshielded four-channel MCG for the detection of coronary artery disease (CAD) in patients with chest pain. METHODS: The study included 417 subjects: 177 patients with angiographically documented CAD (stenoses > or =50%), 123 symptomatic patients without hemodynamically relevant stenosis (nCAD) and 117 healthy subjects. Twelve-lead ECG was obtained in all subjects. The magnetocardiography recordings were taken from 36 positions at rest. From these current density vector maps were generated during the ST-T interval. Each map was classified using a classification system with a scale from 0 (normal) to 4 (grossly abnormal). RESULTS: While the ECG was normal in all subjects the MCG revealed typical differences. In normals most maps were classified as category 0, 1 or 2, in nCAD and more so in CAD patients the categories 3 and 4 prevailed. Using a cut-off value of 39.2% for the discrimination between normals and CAD patients sensitivity was 73.3%, specificity 70.1%. CONCLUSION: Contrary to ECG, unshielded MCG reveals significant differences between normals and symptomatic patients with and without relevant stenoses using current density reconstruction during repolarization at rest. This method might be a suitable noninvasive tool for the management of patients with chest pain.     

QRS duration in high-resolution methods and standard ECG in risk assessment after first and recurrent myocardial infarctions

Background: Prolonged QRS duration (QRSd) is associated with increased mortality after myocardial infarction (MI). Only little data exist about its predictive ability and relationships to clinical variables in the present era of active treatment of myocardial ischemia and cardiac dysfunction. We investigated whether QRSd in high-resolution methods and standard ECG predict arrhythmic events and cardiac death in post-infarction patients with cardiac dysfunction and how it relates to clinical variables, with a special emphasis on history of previous MI.
Methods and Results: Patients (n = 158) with acute MI and cardiac dysfunction had magnetocardiography (MCG), signal-averaged ECG (SAECG), and ECG registered at discharge. Patients with a previous MI had significantly longer QRSd although their left ventricular function was almost similarly impaired. During the mean follow-up of 50 ± 15 (range 1–72) months, 32 patients died and 17 (53%) of the deaths were classified as cardiac. Eighteen patients had an arrhythmic event. QRSd >121 ms in MCG and >114 ms in SAECG were significant predictors of arrhythmic events and cardiac death, whereas QRSd in ECG predicted only cardiac death. In multivariate analysis, QRSd in MCG (hazard ratio (HR) = 3.6, P = 0.007) and SAECG (HR = 4.6, P = 0.016) predicted only arrhythmic events, whereas QRSd in ECG was an independent predictor of cardiac death.
Conclusions: Prolonged QRSd in MCG and SAECG are powerful indicators of the arrhythmia substrate in post-infarction patients with cardiac dysfunction, whereas prolonged QRSd in standard ECG associates with increased risk of cardiac death.     

Space-time database for standardization of adult magnetocardiogram-making standard MCG parameters

Background: The magnetocardiogram (MCG) is a promising medical tool for detecting and visualizing abnormal cardiac electrical activation in heart-disease patients. However, there is no large-scale MCG database of healthy subjects, and there is little knowledge of gender- and age-related influences on MCG data.
Methods and Results: We obtained MCG data from 869 subjects (554 men, 315 women) using a conventional 64-channel MCG system, which covers the whole heart. Electrocardiogram (ECG) data were also obtained; 464 people (268 men, 196 women) were identified as a normal group using ECG data. Time intervals (PQ, QRS, QT, and QTc), current distributions (maximum current vector (MCV), and the total current vector (TCV)) of MCG data of the 464 normal subjects were analyzed to obtain basic MCG parameters.
Although mean values of PQ and QRS intervals of the male subjects were slightly longer than those of the female subjects, no intervals were correlated with gender or age. The correlation between PQ intervals of ECG and those of MCG was better than the correlation between QRS and QT intervals of ECG and those of MCG. Both MCV and TCV angles were much smaller than the electrical-axis angle in ECG. Although TCVs of the QRS and T waves were stable, the women's mean T-wave-TCV angles significantly increased with age. The maximum amplitude of the P wave was about 1.7 pT, and the value of the QRS complex was about 20–25 pT. Moreover, the T-wave amplitude decreases with age.
Conclusion: The MCG standard space-time parameters determined here provide a normal range for MCG parameters.     

Spatial Differences of the Duration of Ventricular Late Fields in the Signal-Averaged Magnetocardiogram in Patients with Ventricular Late Potentials

Magnetocardiography (MCG) allows one to noninvasively localize cardiac electrical activity in three dimensions. It was the purpose of this study to obtain information about the spatial variations of signal-averoged ventricular Jate magnetic fields recorded by a biomagnetic multichannel system. Biomagnetic signals of 170–600 heart cycles obtained hy the 37-channel system KRENIKON^R (Siemens Medical Engineering Group) were simultaneously averaged in all channels. The absolute values of the filtered signals (digital, bidirectional, four-pole butterworth, bandpass filter [3-dB range, 40–250 Hz]) were calculated in each channel. The noise level was determined within the TP segment. The onset of the terminal low amplitude signals (TLAS) was defined when the signals became lower than 1/23 of R_maxof the QRS complex for the channel with the largest filtered QRS complex after filtering. The TLAS ended when the signal was lower than twice the standard deviation (2 sigma) above the mean noise level. Ventricular late fields were defined as present when the TLAS had a duration of more than 39 msec. In this study, five patients with ventricular late potentials (four with sustained ventricular tachycardia) and three healthy individuals were examined. Ventricular late fields were detected in the patient group in 2–15 MCG channels with a mean length of 49.6 msec (43–60 msec). The spatial distribution of the ventricular late fields was consistently found to exhibit maximum duration in a certain area. In the normal subjects no ventricular late fields were detected. Thus, MCG is able to detect ventricular late fields and their spatial variations. In addition to the information obtained hy signal averaging from the surface ECG, averaging of biomagnetic signals with a multichannel device can reveal spatial inhomogeneity of delayed myocardial excitation.     

Noninvasive Classification of Ventricular Preexcitation with Unshielded Magnetocardiography and Transesophageal Atrial Pacing and Follow-Up

Background: Ventricular preexcitation (VPx) is usually localized noninvasively by means of electrocardiogram (ECG) algorithms, which vary in their concordance levels. Contactless magnetocardiography (MCG) has been used as an alternate 3-dimensional (3D) method of accessory pathways (AP) localization. The sensitivity of MCG can be increased for preoperative evaluations and planning of ablation procedures by combining it with transesophageal pacing (TEP) and electrophysiological (EP) studies. This study compared the accuracy of VPx localization with MCG with ECG algorithms, and examined the increment in diagnostic accuracy achievable with TEP.
Methods: Multisite mapping from the anterior chest wall was performed with a 36-channel MCG system. TEP allowed the evaluation of anterograde conduction properties and inducibility of arrhythmias. The reproducibility of the test and follow-up was examined in 88 patients with Wolff–Parkinson–White (WPW) syndrome. The accuracy of MCG localization was reevaluated during pacing-induced maximal VPx in 36 patients in whom, during MCG, the degree of VPx was highest during TEP. The gold standard for validation was effective ablation of the AP.
Results: The MCG classification of VPx was accurate in 94% of AP, versus 64% and 67% with ECG, during sinus rhythm and during pacing-induced maximal VPx, respectively. In 4.5% of cases with unclear ECG localization, MCG suggested a complex septal VPx. In all patients with successful ablations, the 3D MCG localization of the AP corresponded to the ablation site.
Conclusions: MCG was more accurate than ECG for the classification of VPx and provided additional information in the non-invasive EP assessment of patients with WPW syndrome.     

心磁图测量心脏复极时间对冠心病患者心功能预后的评估

背景有近50%的冠心病患者在第1次发生心肌梗死前没有心脏病的征兆,因此尽早可靠地检测到冠心病、心肌缺血尤为重要.目的采用心磁图对冠心病患者心脏复极时间变异进行测量,探讨无创的心磁图检查对冠心病患者心功能的评估作用.设计病例-对照观察.单位德国埃森Philippustift医院心内科.对象选择1998-03/2002-12在德国埃森Philippustift医院心内科住院,怀疑为冠心病的患者52例,另选择10例确诊为陈旧性心肌梗死的患者作为心肌梗死组,以上患者均知情同意.对照组为32例年龄大于40岁的自愿参与观察的健康人.方法所有患者均进行普通12导联的心电图、负荷心电图、超声心动图、冠状动脉造影检查、血生化检查及心磁图检查;对照组只行普通12导联心电图及心磁图检查,比较患者与对照组间心磁图、心电图QT离散度的变异程度.冠心病的诊断标准为冠状动脉造影检查发现冠状动脉有1支狭窄≥75%.对于心脏复极时间变异的指标,采用心磁图QT离散度及离散度均一性指数(每个心磁图探头信号与周围探头QT离散度的平均数)进行测量.主要观察指标各组观察对象的心电图QT离散度、心磁图QT离散度及QT离散度均一性指数.结果怀疑为冠心病的患者52例、陈旧性心肌梗死组10例及对照组32例全部进入结果分析.怀疑为冠心病的患者分为2组,冠心病组27例,无冠心病组25例.[1]心电图QT离散度的比较各组差异无显著性意义(P＞0.05).[2]心磁图QT离散度的比较心肌梗死组显著高于对照组[81.3±21.5,52.4±13.6(f=13.113,P＜0.05)].[3]QT离散度均一性指数的比较心肌梗死组与冠心病组均显著高于对照组[15.6±4.2,14.9±4.1,10.2±2.7(f=2.403,3.332,P＜0.01)].结论心磁图能更好地反映冠心病患者心脏复极时间均一性的变异,优于普通心电图,而离散度均一性指数优于QT离散度.因为心磁图对心切线电流更为敏感,而当心肌缺血、梗死时心肌电流在心前区表现为切线电流.     

Concentric Remodeling Detection by Magnetocardiography in Patients with Recent Onset Arterial Hypertension

The aim of this work was to evaluate a number of magnetocardiographic (MCG) indices in their predictive ability for left ventricular (LV) concentric remodeling. Twenty-five male patients affected by essential hypertension for no longer than 15 months and presenting signs of LV remodeling participated in the study; 25 normal men volunteers of comparable age were evaluated as controls. All participants underwent echocardiography (ECHO), electrocardiography (ECG), and magnetocardiography (MCG). Several MCG based indices were evaluated, namely the QRS Integral, T Integral, QRS-T Integral, T/QRS Integral, RS Index, and the variations of the electrical cardiac axis (ECA) orientation. MCG indices were compared with ECHO parameters, i.e., left ventricular mass index (LVMI) and relative wall thickness (RWT), and with ECG parameters, i.e., 12-lead standard ECG LVH Sokolow-Lyon and Cornell voltages. QRS Integral values for patients and controls were significantly different (P = 0.03), whereas T Integral values showed only a tendency to differentiate between patients and controls (P = 0.15). No significant correlation between MCG and echocardiographic indices in patients was found; RWT showed a tendency to correlate with QRS Integral (r = 0.34, P = 0.17) and with RS Index (r = 0.49, P = 0.15), and LVMI showed a tendency to correlate with the variations of the ECA orientation (r = 0.38, P = 0.10). Our findings, also supported by preliminary results on patients affected by hypertension induced LV hypertrophy, suggest a potential role of MCG in the evaluation of early electrophysiological alterations due to LV concentric remodeling. (PACE 2004; 27[Pt. I]:709–718)     

Nonfluoroscopic Localization of an Amagnetic Stimulation Catheter by Multichannel Magnetocardiography

This study was performed to: (1) evaluate the accuracy of noninvasive magnetocardiographic (MCG) localization of an amagnetic stimulation catheter; (2) validate the feasibility of this multipurpose catheter; and (3) study the characteristics of cardiac evoked fields. A stimulation catheter specially designed to produce no magnetic disturbances was inserted into the heart of five patients after routine electrophysiological studies. The catheter position was documented on biplane cine x-ray images. MCG signals were then recorded in a magnetically shielded room during cardiac pacing. Noninvasive localization of the catheter's tip and stimulated depolarization was computed from measured MCG data using a moving equivalent current-dipole source in patient-specific boundary element torso models. In all five patients, the MCG localizations were anatomically in good agreement with the catheter positions defined from the x-ray images. The mean distance between the position of the tip of the catheter defined from x-ray fluoroscopy and the MCG localization was 11 +/- 4 mm. The mean three-dimensional difference between the MCG localization at the peak stimulus and the MCG localization, during the ventricular evoked response about 3 ms later, was 4 +/- 1 mm calculated from signal-averaged data. The 95% confidence interval of beat-to-beat localization of the tip of the stimulation catheter from ten consecutive beats in the patients was 4 +/- 2 mm. The propagation velocity of the equivalent current dipole between 5 and 10 ms after the peak stimulus was 0.9 +/- 0.2 m/s. The results show that the use of the amagnetic catheter is technically feasible and reliable in clinical studies. The accurate three-dimensional localization of this multipurpose catheter by multichannel MCG suggests that the method could be developed toward a useful clinical tool during electrophysiological studies.     

Computer analysis of mechanocardiograms in patients with acute respiratory insufficiency

Spectral analysis of mechanocardiograms (MCG) has been performed, using the method of fast Fourier analysis, in patients with acute respiratory failure (ARF) of various etiology. Two time intervals of the cardiac cycle have been investigated: 160 ms after the R wave on the ECG (interval A) and 160 ms after the T wave (interval B). It has been shown that patients with ARF reveal the appearance of high-frequency oscillations (31-32 and 37-38 Hz) in interval A and low-frequency oscillations (7-8 Hz) in interval B. It is assumed that one of the reasons for MCG spectrum alterations may be cardiohemodynamic resetting, as well as changes in the myocardial function and pulmonary hypertension.     

Evaluation of the non-invasive localization accuracy of cardiac arrhythmias attainable by multichannel magnetocardiography (MCG)

The accuracy of multichannel magnetocardiography (MCG) for the non-invasive localization of cardiac arrhythmias was investigated. A non-magnetic catheter was used in phantom studies and for cardiac pacing of 6 patients. In a clinical setting, 32 patients with WPW-syndrome, 37 patients with premature ventricular complexes and 12 patients with ventricular tachycardia were studied and the MCG results compared to reference methods, including invasive electrophysiological mapping. Phantom and pacing studies demonstrated the spatial localization accuracy to be better than 15 mm for a dipole-to-dewar distance below 15 cm. In all patients with structural cardiac disease, the ectopic focus was localized at the margin of the damaged area, serving as a proof of MCG localization. Invasive mapping confirmed the MCG result whenever performed (42 patients). In 11 patients (9 WPW, 2 VT) the MCG localization result was verified by successful HF catheter ablation as a gold standard. MCG permits the non-invasive localization of cardiac arrhythmias with high spatial accuracy. MCG guided HF catheter ablation constitutes a new concept of non-invasive localization and minimally invasive causal therapy.     

Time delays in ultrasound systems can result in fallacious measurements

Even short time delays (less than 30 ms) in cardiac motion pattern may have clinical relevance. These delays can be measured with echocardiography, using techniques such as flow and tissue Doppler and M-mode together with external signals (e.g., ECG and phonocardiography). If one or more of these signals are delayed in relation to the other signals (asynchronous), an incorrect definition of cardiac time intervals can occur, the consequence of which is invalid measurement. To determine if this time delay in signal processing is a problem, we tested three common ultrasound (US) systems using the ECG as the reference signal. We used a digital ECG simulator and a Doppler string phantom to obtain test signals for flow and tissue pulsed Doppler, M-mode, phonocardiography, auxiliary and ECG signals. We found long time delays of up to 90 ms in one system, whereas delays were mostly short in the two other systems. The time delays varied relative to system settings. Consequently, to avoid these errors, precise knowledge of the characteristics of the system being used is essential.     

Biomagnetic multi-channel systems. Principles and application in cardiology

Summary The non-invasive measurement of the extremely weak magnetic fields generated by heart and brain is motivated by the possibility of obtaining quantitative diagnostic information about electric function. Magnetic signals (MCG, MEG) are significantly less influenced by body tissue than the corresponding electric signals (ECG, EEG). Measurement of biomagnetic signals is performed by superconducting sensors consisting of pickup coils and SQUIDs (superconducting quantum interference device) operating in liquid Helium. For clinical investigations a biomagnetic multi-channel system (KRENIKON^R) has been designed. It uses a flat array of 37 magnetic field sensors and is operated inside a shielded room. Evaluation of biomagnetic signals by use of simple source and body models and in combination with anatomical data from 3D MR- or CT-images yields sequences of locations of electrical function with a spatial resolution of some millimeters and a time resolution better than one millisecond. More than three years of clinical studies have demonstrated the value of the method primarily in cases with localized functional pathologies. In cardiology this is pathologies of the cardiac conductive pathway, ectopies, and arrhythmias. Validation has been performed by catheter stimulation in volunteers, and by catheter mapping and nuclear medical methods in patients. Extension of modelling and evaluation to cases with distributed activity, e.g. ventricular excitation, is under investigation.     

Spatial distribution of repolarization times in patients with coronary artery disease

The potential clinical value of QT dispersion (QTd), a measure of the interlead range of QT interval duration in the surface 12-lead ECG, remains ambiguous. The aim of the study was the temporal and spatial analysis of the QT interval in healthy subjects and in patients with coronary artery disease (CAD) using magnetocardiography (MCG) and surface ECG. Standard 12-lead ECG and 37-channel MCG were performed in 20 healthy subjects, 23 patients with CAD without prior myocardial infarction (MI), 31 MI patients and 11 MI patients with ventricular tachycardia (VT). QTd was increased in CAD without MI compared to normals (ECG 46.1 +/- 6.0 vs 42.8 +/- 5.0, P < 0.05; MCG 66.8 +/- 20.3 vs 49.7 +/- 10.8, P < 0.01) and in VT compared to MI (ECG 66.8 +/- 16.5 vs 51.9 +/- 16.6, P < 0.05; MCG 93.6 +/- 29.6 vs 66.8 +/- 20.8, P < 0.005). In MCG, spatial distribution of QT intervals in patient groups differed from those in healthy subjects in three ways: (1) greater dispersion, (2) greater local variability, and (3) a change in overall pattern. This was quantified on the basis of smoothness indexes (SI). Normalized SI was higher in CAD without MI compared to normals (3.8 +/- 1.1 vs 2.7 +/- 0.6, P < 0.001) and in VT compared to MI (6.4 +/- 1.6 vs 4.2 +/- 1.4, P < 0.0005). For the normal-CAD comparison a sensitivity of 74% and a specificity of 80% was obtained, for MI-VT, 100% and 77%, respectively. The results suggest that examining the spatial interlead variability in multichannel MCG may aid in the initial identification of CAD patients with unimpaired left ventricular function and the identification of post-MI patients with augmented risk for VT.     

Magnetocardiographic QT Interval Dispersion in Postmyocardial Infarction Patients with Sustained Ventricular Tachycardia: Validation of Automated QT Measurements

T dispersion is a measure of heterogeneity in ventricular repolarization. Increased ECG QT dispersion is associated with life-threatening ventricular arrhythmias. We studied if magnetocardiographic (MCG) measures of QT dispersion can separate postmyocardial infarction patients with and without susceptibility to sustained VT. Manual dispersion measurements were compared to a newly adapted automatic QT interval analysis method. Ten patients with a history of sustained VT (VT group) and eight patients without ventricular arrhythmias (Controls) were studied after a remote myocardial infarction. Single-channel MCGs were recorded from 42 locations over the frontal chest area and the signals were averaged. QT dispersion was defined as maximum — minimum or standard deviation of measured QT intervals. VT group showed significantly more QT and JT dispersion than Controls. QT_apex dispersions were 127 ± 26 versus 83 ± 21 ms (P = 0.004) and QT_end dispersions 130 ± 37 versus 82 ± 37 ms (P = 0.013), respectively. Automatic method gave comparable values. Their relative differences were 9% for QT_apex and 27% for QT_end dispersion on average. In conclusion, increased MCG QT interval dispersion seems to be associated with a susceptibility to VT in postmyocardial infarction patients. MCG mapping with automated QT interval analysis may provide a user independent method to detect nonhomogeneity in ventricular repolarization.     

Successful detection of the fetal electrocardiogram waveform changes during various states of singletons

Accurate assessment of fetal well-being is one of the most important tasks for obstetricians. It is still difficult to measure fetal electrocardiogram (ECG) during fetal movements. Recently, a new method, blind source separation with reference signals, was proposed for stable measurements. This method distinguishes weak signals from noisy mixed signals with little information about the sources. The aim of this study is to estimate the ability of this method for fetal ECG monitoring and to establish standard fetal ECG electrocardiogram values of normal singletons including during fetal movement. The subjects enrolled were 167 pregnant women with normal single pregnancy from 18- to 41-week gestation, who regularly visited Tohoku University Hospital, and 12 pregnant women with fetal abnormality. Fetal signals were successfully separated in 163 of 179 subjects at 91.1% success rate regardless of fetal movements. Time intervals of ECG (P, PR and QRS intervals and QTc) were measured. The standard curves of each interval through the gestational period were obtained. The data in active phase were compared to that in rest phase and the data obtained from normal and abnormal fetuses were investigated. PR intervals in the rest phase were prolonged compared to those in the active phase. Fetal ECG showed anomalous values such as PR interval or QTc prolongation in the abnormal fetuses. The fetal ECG was measured by the new method with or without fetal movements, and the standard fetal ECG values have been established. This study provides a foundation for further detailed clinical studies.     

Adaptive filtering of ECG interference on surface EEnGs based on signal averaging

An external electroenterogram (EEnG) is the recording of the small bowel myoelectrical signal using contact electrodes placed on the abdominal surface. It is a weak signal affected by possible movements and by the interferences of respiration and, principally, of the cardiac signal. In this paper an adaptive filtering technique was proposed to identify and subsequently cancel ECG interference on canine surface EEnGs by means of a signal averaging process time-locked with the R-wave. Twelve recording sessions were carried out on six conscious dogs in the fasting state. The adaptive filtering technique used increases the signal-to-interference ratio of the raw surface EEnG from 16.7 +/- 6.5 dB up to 31.9 +/- 4.0 dB. In addition to removing ECG interference, this technique has been proven to respect intestinal SB activity, i.e. the EEnG component associated with bowel contractions, despite the fact that they overlap in the frequency domain. In this way, more robust non-invasive intestinal motility indicators can be obtained with correlation coefficients of 0.68 +/- 0.09 with internal intestinal activity. The method proposed here may also be applied to other biological recordings affected by cardiac interference and could be a very helpful tool for future applications of non-invasive recordings of gastrointestinal signals.     

Carmeli's S index assesses motion and muscle artefact reduction in rowers' electrocardiograms

Electrocardiograms (ECG) suffer high perturbations from motion and muscle activities when measured on the chest of rowers. However, for cardiac assessment and sport performance measures, ECG complexes and their time occurrences contain information of great value. We thus propose to use electromyogram (EMG) sensors placed on the distal pectoral muscle to provide a reference signal for motion and muscle activity cancellation. The low frequencies of the EMG signal are conserved for motion cancellation. A combination of band-pass and adaptive filters allows us to recover ECG complexes. This specific scheme is intended to be used for advanced ECG sensors with on-board digital signal processing which requires low-power electronics. A validation of the method is performed based on a nonlinear dynamic model of the ECG and linear frequency modulated rowing movement for various input and output signal-to-noise ratios and adaptive filter gain parameters. Results show a good motion tracking cancellation of the adaptive filter. Finally, assessments of the method on the real recorded data from five subjects are presented. To this end, we have first computed estimates of the signal-to-noise ratio gain between the original and noise-reduced signals. Second, we have developed a modified synchronization index first proposed by Carmeli et al between a QRS template and the original and noise-reduced signals. Both assessment measures are complementary to each other.     

Errors in repolarization measurement using magnetocardiography

Multichannel magnetocardiography (MCG) noninvasively measures variations in magnetic field strength from many sites at the body surface, potentially providing useful regional information about ventricular repolarization. MCGs contain features similar to ECGs, and although errors associated with repolarization measurement have been quantified for ECGs, no comparative data exists for MCGs. In this study, errors in manual measurement of repolarization interval in the MCG were determined. Sixteen MCG channels and three ECG leads were recorded simultaneously in eight healthy subjects. Each recording was displayed in a random order on a computer screen, in presentations with different noise levels, time display widths, and amplitude display heights. In total, manual measurement of repolarization intervals in 2,048 (eight subjects x 16 channels x eight presentations x two repeats) MCGs were made by each of four analysts. Measured repolarization intervals were reduced by 3 ms when noise was added and by a further 3 ms when this noise was doubled. Intervals were shortened by 9 ms when the time display width was doubled and by a further 10 ms when the display width was doubled again. Measurements increased by 7 ms for a doubling of amplitude display height, equivalent to a doubling of T wave height. There were also consistent differences between analysts; amounting to a greatest mean difference of 24 ms. Display characteristics, added noise, and different analysts thus affect manual repolarization interval measurements in MCG. The errors detected demonstrate the importance of a standard presentation for repolarization measurement in the MCG.     

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.     

Capecitabine-associated coronary vasospasm: a case report

Capecitabine (Xeloda) is an oral 5-fluorouracil pro-drug used in the treatment of two of the commonest cancers: breast and colorectal. This report concerns a 43-year-old woman with metastatic cancer of the sigmoid colon who developed cardiac chest pain 5 days after starting capecitabine therapy. Capecitabine-induced cardiac symptoms have previously been reported but infrequently. In the main they have documented pain and electrocardiogram (ECG) changes associated with exercise. This case report is of a patient with minimal cardiac risk factors, who had ischaemic cardiac pain with widespread ECG changes at rest that resolved with a nitrate infusion. Coronary vasospasm is proposed as the probable mechanism for the cardiac ischaemia and dramatic ECG changes. Capecitabine is now in widespread use and so physicians will encounter an increasing number of patients using this therapy. In the light of this, it is important that doctors in emergency and acute medicine are aware of its treatable cardiac side effects.