64-channel Magnetocardiography Research Articles

Identification of malignant early repolarization pattern by late QRS activity in high‐resolution magnetocardiography

BackgroundThe early repolarization pattern (ERP) in electrocardiography (ECG) has been considered as a risk for ventricular fibrillation (VF), but effective methods for identification of malignant ERP are still required. We investigated whether high spatiotemporal resolution 64‐channel magnetocardiography (MCG) would enable distinction between benign and malignant ERPs.MethodsAmong all 2,636 subjects who received MCG in our facility, we identified 116 subjects (43 ± 18 years old, 54% male) with inferior and/or lateral ERP in ECG and without structural heart disease, including 13 survivors of VF (ERP‐VF(+)) and 103 with no history of VF (ERP‐VF(−)). We measured the following MCG parameters in a time‐domain waveform of relative current magnitude: (a) QRS duration (MCG‐QRSD), (b) root‐mean‐square of the last 40 ms (MCG‐RMS40), and (c) low amplitude (<10% of maximal) signal duration (MCG‐LAS).ResultsCompared to ERP‐VF(−), ERP‐VF(+) subjects presented a significantly longer MCG‐QRS (108 ± 24 vs. 91 ± 23 ms, p = .02) and lower MCG‐RMS40 (0.10 ± 0.08 vs. 0.25 ± 0.20, p = .01) but no difference in MCG‐LAS (38 ± 22 vs. 29 ± 23 ms, p = .17). MCG‐QRSD and MCG‐RMS40 showed significantly larger area under the ROC curve compared to J‐peak amplitude in ECG (0.72 and 0.71 vs. 0.50; p = .04 and 0.03). The sensitivity, specificity, and odds ratio for identifying VF(+) based on MCG‐QRSD ≥ 100 ms and MCG‐RMS40 ≤ 0.24 were 69%, 74%, and 6.33 (95% CI, 1.80–22.3), and 92%, 48%, and 10.9 (95% CI, 1.37–86.8), respectively.ConclusionMagnetocardiography is an effective tool to distinguish malignant and benign ERPs.

Isolated Late Activation Detected by Magnetocardiography Predicts Future Lethal Ventricular Arrhythmic Events in Patients With Arrhythmogenic Right Ventricular Cardiomyopathy

Risk stratification of ventricular arrhythmias is vital to the optimal management in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC). We hypothesized that 64-channel magnetocardiography (MCG) would be useful to detect isolated late activation (ILA) by overcoming the limitations of conventional noninvasive predictors of ventricular tachyarrhythmias, including epsilon waves, late potential (LP), and right ventricular ejection fraction (RVEF), in ARVC patients.Methods and Results:We evaluated ILA on MCG, defined as discrete activations re-emerging after the decay of main RV activation (%magnitude >5%), and conventional noninvasive predictors of ventricular tachyarrhythmias (epsilon waves, LP, and RVEF) in 40 patients with ARVC. ILA was noted in 24 (60%) patients. Most ILAs were found in RV lateral or inferior areas (17/24, 71%). We defined "delayed ILA" as ILA in which the conduction delay exceeded its median (50 ms). During a median follow-up of 42.5 months, major arrhythmic events (MAEs: 1 sudden cardiac death, 3 sustained ventricular tachycardias, and 4 appropriate implantable cardioverter defibrillator discharges) occurred more frequently in patients with delayed ILA (6/12) than in those without (2/28; log-rank: P=0.004). Cox regression analysis identified delayed ILA as the only independent predictor of MAEs (hazard ratio 7.63, 95% confidence interval 1.72-52.6, P=0.007), and other noninvasive parameters were not significant predictors. MCG is useful to identify ARVC patients at high risk of future lethal ventricular arrhythmias.

Abstract 17191: Fragmentation Assessed by Magnetocardiography but not Electrocardiogram Can Predict Future Cardiac Events in Patients with Non-ischemic Dilated Cardiomyopathy and Narrow QRS

Background: Fragmented QRS (fQRS) in 12-lead ECG, ascribed to myocardial scar, has been shown to predict future cardiac events in patients with both ischemic and non-ischemic dilated cardiomyopathy (NIDCM). Various definitions and low specificity of fQRS, however, limited its use. We hypothesized that the advantage of 64-channel magnetocardiography (MCG), i.e., high spatio-temporal resolution, enables more accurate detection of fragmented LV conduction (fLV), that would lead to accurate prediction of future events. Methods: In 51 patients with NIDCM and narrow QRS (LVEF, 22±7%; QRS duration, 99±11 ms), we recorded MCG. We defined, in MCG superimposed vector magnitude waveforms, fLV as distinct abnormal components (&gt;20% of maximal amplitude). In current arrow map, fLV corresponded to heterogeneous QRS currents (Figure). We predicted major adverse cardiac events (MACE), including sudden cardiac death (SCD), sustained ventricular tachyarrhythmias (VF/VT), appropriate defibrillator discharge (Def) and left ventricular assist device implantation (LVAD). Results: fLV was present in 27 (Group-F) and not in 24 (Group-N). Age, gender, ECG and echocardiographic findings, laboratory data and medications were similar irrespective of fLV. During a mean follow-up of 2.2 years, MACE occurred in 19 (4 SCD, 9 VF/VT, 2 Def, and 4 LVAD). MACE more frequently occurred with fLV (63%, 17/27) than without (8%, 2/24, Kaplan-Meier analysis, p&lt;0.001). Multivariate analysis revealed fLV as the only independent predictor of MACE (HR 4.82, p=0.015). Conclusion: MCG analysis is a promising noninvasive tool to accurately detect fragmentation and predict MACE in patients with NIDCM and normal QRS.

Spatial Repolarization Heterogeneity Detected by Magnetocardiography Correlates with Cardiac Iron Overload and Adverse Cardiac Events in Beta-Thalassemia Major

BackgroundPatients with transfusion-dependent beta-thalassemia major (TM) are at risk for myocardial iron overload and cardiac complications. Spatial repolarization heterogeneity is known to be elevated in patients with certain cardiac diseases, but little is known in TM patients. The purpose of this study was to evaluate spatial repolarization heterogeneity in patients with TM, and to investigate the relationships between spatial repolarization heterogeneity, cardiac iron load, and adverse cardiac events.Methods and ResultsFifty patients with TM and 55 control subjects received 64-channel magnetocardiography (MCG) to determine spatial repolarization heterogeneity, which was evaluated by a smoothness index of QTc (SI-QTc), a standard deviation of QTc (SD-QTc), and a QTc dispersion. Left ventricular function and myocardial T2* values were assessed by cardiac magnetic resonance. Patients with TM had significantly greater SI-QTc, SD-QTc, and QTc dispersion compared to the control subjects (all p values<0.001). Spatial repolarization heterogeneity was even more pronounced in patients with significant iron overload (T2*<20 ms, n = 20) compared to those with normal T2* (all p values<0.001). Loge cardiac T2* correlated with SI-QTc (r = −0.609, p<0.001), SD-QTc (r = −0.572, p<0.001), and QTc dispersion (r = −0.622, p<0.001), while all these indices had no relationship with measurements of the left ventricular geometry or function. At the time of study, 10 patients had either heart failure or arrhythmia. All 3 indices of repolarization heterogeneity were related to the presence of adverse cardiac events, with areas under the receiver operating characteristic curves (ranged between 0.79 and 0.86), similar to that of cardiac T2*.ConclusionsMultichannel MCG demonstrated that patients with TM had increased spatial repolarization heterogeneity, which is related to myocardial iron load and adverse cardiac events.

Usefulness of Magnetocardiography to Detect Coronary Artery Disease and Cardiac Allograft Vasculopathy

Electrophysiological information as well as anatomic information are important for the detection of coronary artery lesions. The aim of this study was to assess the efficacy of resting magnetocardiography (MCG) in stable coronary artery disease (CAD) and cardiac allograft vasculopathy (CAV). MCG and coronary angiography were performed within 1 month in 75 patients with suspected CAD and in 26 subjects after orthotopic heart transplantation (OHT). Plaque volumes were additionally measured on intravascular ultrasound in OHT recipients. The spatially distributed QT(c) interval maps were constructed with 64-channel MCG. A T-wave propagation map and QT(c) heterogeneity index including QT(c) dispersion and smoothness index of QT(c) (SI-QT(c)) were derived for ischemia detection and localization. CAD patients had higher QT(c) dispersion and SI-QT(c). Receiver operating characteristic curve analysis identified SI-QT(c) ≥9 ms, QT(c) dispersion ≥79 ms as the optimal cut-off for detecting CAD (diagnostic accuracy, 0.7953, 0.7819), better than T-wave propagation (0.6594, P<0.05). There was no significant difference of QT(c) dispersion between CAD and OHT subjects. In OHT recipients, QT(c) dispersion positively correlated with plaque volume, and SI-QT(c) progressively increased after transplantation. Using T-wave propagation mapping, regionally increased dispersion could be demonstrated in CAD patients, but increased dispersion was noted in fewer OHT recipients. MCG is clinically feasible as a non-invasive tool for diagnosis of CAD, and could be used as a surrogate marker of CAV.

Classification of AF type using Magnetocardiographic analysis

Event Abstract Back to Event Classification of AF type using Magnetocardiographic analysis Doosang Kim1*, Kiwoong Kim2, Yong-Ho Lee2 and Hyuk Ahn3 1 Seoul Veterans Hospital, South Korea 2 Korea Research Institute of Standards and Science, South Korea 3 Seoul National University Hospital, South Korea Background: Magnetocardiography (MCG) is a new, totally non-invasive, non-contact and highly sensitive method to detect atrial F-wave in AF patient than ECG. K. Kornings and M. Guillem reported three types of AF- single broad wave front, one or two wavelets, and highly fragmented wavelets, using 244 and 56 electrodes based on the complexity of atrial activation. MCG gives a good help to define the F-wave type easily. Methods: To detect weak atrial excitation, we utilized a high sensitive low-Tc 64-channel MCG system with application software KRISSMCG64. According to the F-wave activity size criteria (0.1 pTesla), we classified AF as type I (more than 0.1pT) and type II (less than 0.1pT). And we conduct the minimal AF surgery in twelve AF patients. Between the two groups, we compared their ages, sex, body weight, height, body mass index, AF duration, LA dimension, LV dimension, ejection fraction, concomitant disease, AF type, and final rhythm with t-test and Fisher’s exact test. Monthly-based ECG was used for follow-up. Results: Type I is 58% (7/12) and type II is 42% (5/12). Overall AF free rate is 71% in type I (5/7) and 100% in type II (5/5) at their last follow-up. Follow-up duration is 18 months (1-39) vs. 9 months (0-24). According to the period, AF free rates in type I and type II are 71% (5/7) vs. 80% (4/5) at postoperative time, 50% (3/6) vs. 33% (1/3) at discharge, 100% (5/5) vs. 0% (0/2) at 3 months, 80% (4/5) vs. 50% (1/2) at 6 months, 100% (4/4) vs. 50% (1/2) at 9 months, 100% (4/4) vs. 50% (1/2) at 1 year, 100% (4/4) vs. 100% (1/1) at 1.5 years, and 100% (3/3) vs. 100% (1/1) at 2 years. Between the two groups, there are statistical significance in AF duration (p=.008), age (p=.000) and body weight (p=.050). Conclusions: Classification of AF type based on MCG analysis shows different patient’s characteristics and AF free rate along period. Type I shows more recent AF history, younger age, and heavier body weight. However, the number of patients of each group is very small, the statistical significance of other characteristics is not proven yet. More case accumulation will elucidate this finding. Figure 1. AF type according to the amplitude (0.1 pT) and duration (20 ms) of F-wave activity from the MCG system. We classified F-wave as type I (bigger than 0.1 pT and longer than 20 ms) and type II (smaller than 0.1 pT and shorter than 20 ms).

Non-Invasive Magnetocardiography for the Early Diagnosis of Coronary Artery Disease in Patients Presenting With Acute Chest Pain

Accurate identification of patients with acute coronary syndrome (ACS) is often difficult especially when an electrocardiogram (ECG) does not show typical elevation of ST segment. The aim of the present study was therefore to evaluate the efficacy of magnetocardiography (MCG) for diagnosis of ACS in patients with acute chest pain presenting without ST segment elevation. In the present retrospective study 364 patients with the suspected ACS without ST segment elevation were selected. Significant coronary artery disease (CAD) was defined as a stenosis > or =50% in at least one of 16 segments of the 3 major coronary arteries and their branches. The MCG recordings were obtained at resting state using a 64-channel MCG system in a magnetically shielded room. The patients were classified on the basis of the probability distribution. The presence of significant CAD was identified with a sensitivity of 84.0% and a specificity of 85.0%, compared to 44.7% and 89.8% on ECG. In the subgroup of patients without specific findings on ECG or biomarker test, MCG had a sensitivity of 73.5% and a specificity of 82.3%. MCG was acceptably sensitive and specific in identifying patients with ACS even in the absence of specific findings on ECG and positive biomarker tests. Thus, MCG seems beneficial for the early triage of patients with acute chest pain.

Signal Amplitude Ratio of Magnetocardiogram Between Sensor Assembly and Chest Surface

Magnetocardiography (MCG) using a superconducting quantum interference device (SQUID) sensor has been known for a noninvasive, noncontact, and safe diagnostic tool to detect ischemic heart disease such as angina and myocardial infarction. The magnetic distribution generated by the electrical activation of the heart reveals the abnormality of the myocardial status. The bust depth of people in 20s and 70s are much different, and the greatest difference is up to 154 mm. The purpose of this study is to identify whether MCG signals and parameter values are changed at the different locations of the SQUID sensor assembly. It would be an important reference for the standard measurement. Four healthy male subjects (33.3 plusmn 6.3 years) participated in this study. The distance between the chest surface and the bottom of the sensor assembly was 20, 40, 60, and 80 mm. Recording was made using 64-channel MCG system (axial type, first-order gradiometer) developed by Korea Research Institute of Standards and Science (KRISS). MCG were recorded for 30 s in a magnetically shielded room. As the sensor location is getting away from the chest surface, the each mean amplitude of R- and T-wave peak decreases to 70% (at 40-mm distance), 51% and 50% (at 60 mm), and 38% and 35% (at 80 mm) of the reference amplitude measured at 20-mm distance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> = -0.000002* <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> + 0.0003* <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> - 0.0308* <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> + 1.4961, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> =1.00; where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> = average amplitude remained after reduction}, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> = distance between the chest surface and sensor location). Interindividual difference was less than 5%. The regression equations may be used as a good reference to calculate how much strength will be decreased by the distance. In MCG parameters, most parameters decreased when the distance increased. As an example, the current moment at T-wave peak reduced to 52% (at 40-mm distance), 33% (at 60 mm), and 19% (at 80 mm). Results showed how MCG signal and parameter values decreased rapidly when the sensor assembly was located far from the signal source. The study results may be used as a useful reference to design MCG system and analysis program.

Detection of non-ST-elevation myocardial infarction using magnetocardiogram: New information from spatiotemporal electrical activation map

Background and aim. Non-ST-segment elevation myocardial infarction (NSTEMI) cannot be easily detected in the emergency room. We evaluate a method to detect NSTEMI using 64-channel magnetocardiography (MCG).Methods. MCG recordings were made in 20 NSTEMI patients (aged 59.7±12.4 years), 15 young (aged 26.8±3.4 years), and 13 age-matched control subjects (aged 57.3±3.6). We evaluated three approaches to analysis, including 1) determination when individual subjects’ MCG results fell outside normal ranges for ten MCG parameters, 2) the magnetic field map at the T-wave peak (T-MFM), and 3) a pair of spatiotemporal activation graphs (STAGs) showing two projections of electrical excitation during repolarization.Results. Significant differences were found between normal controls and patients for all MCG parameters. None of the healthy controls had more than four MCG abnormal parameters, whereas 19 NSTEMI patients (95%) were abnormal in more than four parameters. STAGs and T-MFM also showed clear differences between healthy controls and NSTEMI patients.Conclusions. These results suggest that the MCG is sensitive to changes in the cardiac electrical pathway after myocardial infarction as described by these graphs and parameters, and therefore MCG may be a useful tool to detect severe ischemic patients.

Assessment of Fetal Autonomic Nervous System Activity by Fetal Magnetocardiography

Aim: To clarify the significance of heart rate variability for the evaluation of an autonomic nervous system (ANS) in the normal fetus using fetal magnetocardiography (FMCG). Methods: Subjects consisted of normal pregnancy (n = 35) at 28–39 weeks gestation. FMCG was recorded using 64-channel magnetocardiography (MCG) in a magnetically shielded room. The QRS interval was derived from signal-averaged MCG. The R–R interval variability induced by an R-wave trigger was eventually adopted to calculate for time-domain and frequency domain analysis. The power spectrum in the frequency domain was derived from frequency-field components using the maximum entropy method of fetal heart rate variability. Based on frequency analysis, the ranges of the LF and HF domains were defined as 0.01–0.15 and 0.15–0.4 Hz, respectively. We defined a coeffi cient of variance (CVRR) as an index of parasympathetic activity, and defined a low frequency/high frequency (LF/HF) ratio as a sympathetic activity. Results: The value of CVRR in the normal pregnancy group displayed a slight increasing trend with gestational age (y = 1.77 + 0.10x; r = 0.32). In contrast, the LF/HF ratio in the normal pregnancy group clearly increased over the gestational period (one-way ANOVA: P = 0.003). Conclusions: Analyses based on the time and frequency domains of heart rate variability using FMCG enable an evaluation of fetal ANS activity. Sympathetic nervous activity increased with gestational age in the normal pregnancy group.

Detection of atrial arrhythmia in superconducting quantum interference device magnetocardiography; preliminary result of a totally-noninvasive localization method for atrial current mapping

Map-guided surgery is the goal for treatment of atrial fibrillation (AF), because it minimizes unnecessary incisions or procedures. We propose a totally-noninvasive and even non-contact method to detect atrial arrhythmia with a superconducting quantum interference device magnetocardiography (MCG) system, and report the first clinical application case of MCG map-guided AF surgery. To detect weak atrial excitation, we utilized a high sensitive 64-channel MCG system measuring tangential magnetic field components, which is known to be more sensitive to a deeper current source. We measured the MCG signals from eight patients with chronic AF. Then, we separated the f-wave from the other components by using independent component analysis. The extracted f-wave caused by reentrant myocardial excitation was three-dimensionally localized on the mesh model of a human heart by a novel beamformer technique having a surface action potential activity as its filter output. We localized the abnormal stimulation source of an atrial arrhythmia non-invasively and visualized the current source distribution corresponding to the atrial excitation successfully on the three-dimensional atrial surface, which was separated from the ventricular excitation. Using this atrial mapping, we underwent minimal AF surgery in three patients and converted their AF to sinus rhythm successfully.

Development of a Signal-Averaged Vector-Projected 187-Channel High-Resolution Electrocardiogram for the Evaluation of the Spatial Location of High-Frequency Potentials and Abnormal Ventricular Repolarization

Noninvasive risk stratification is important for screening for lethal arrhythmia. We developed a 187-channel signal-averaged vector-projected high-resolution electrocardiograph (187-ch SAVP-ECG) for detecting abnormalities in the spatial location of ventricular high-frequency late potentials (HFLPs) and ventricular repolarization. The subjects consisted of 30 normal controls (CONTROL) and 13 patients with HFLPs (6 with myocardial infarction [MI], 6 with cardiomyopathy, and 1 with Brugada syndrome). The modified X, Y, Z-lead ECG and the synthesized signals from vector-projected 187-channel ECGs were amplified and passed through a digital filter. We calculated the integration of the HFLPs area between QRS(end) and 30 ms before QRS(end). The integrated HFLPs map was superimposed on the corrected recovery time (RTc) and Tpeak-end dispersion maps composed by 187-ch SAVP-ECG. All patients received an examination by 64-channel magnetocardiography (64-ch MCG) on the same day. The spatial distribution of HFLPs by the 187-ch SAVP-ECG map was in agreement with the location of increased RT dispersion in MI. The spatial distribution of HFLPs in DCM demonstrated a wide variety of patterns. Interestingly, the spatial distribution of HFLPs in cases with ARVC was located at around a right ventricular outflow region. The spatial distribution of HFLPs by 187-ch SAVP-ECG was in agreement with those determined by 64-ch MCG. The 187-ch SAVP-ECG might be useful for evaluating the spatial distribution of nonuniform conduction and ventricular repolarization heterogeneity.

AB22-4: Magnetocardiography as a new noninvasive tool for Brugada syndrome

The differential diagnosis of Brugada syndrome (BS) remains a clinical challenge. Magnetocardiography (MCG) is a noninvasive method for the recording of cardiac electromagnetic signals at multiple sites above the chest cage. The present study aimed to analyze the diagnostic value of a 64-channel MCG for the detection of BS.

Three-dimensional recovery time dispersion map by 64-channel magnetocardiography may demonstrate the location of a myocardial injury and heterogeneity of repolarization

QT dispersion reveals heterogeneities in the repolarization time in the three-dimensional (3D) structure of the ventricular myocardium. In this study, we report on a 3D function map of recovery time (RT) dispersions as measured by 64-channel magnetocardiography (MCG). MCG were simultaneously recorded in 29 controls and 21 patients with previous myocardial infarction (MI). The 3D current density was calculated from 64-channel MCG data in the Bz component using a space filter. The heart outline, reconstructed from the integrated the current density, revealed both the atrium and ventricle. The RT for the intervals between QRS onset and the time of the maximum dT/dt of T wave, and the peak to the end of the T wave (T(peak)-negative dT/dt) were automatically measured by means of a computer from 3D MCG data. The corrected RT (RTc) and corrected T(peak)-negative dT/dt were then calculated using Bazett's formula. The 3D RTc and the corrected T(peak)-negative dT/dt dispersion map were superimposed on the heart outline generated by MCG. The RTc was significantly longer for the MI group than in the control group (67+/-25 ms1/2 vs. 16+/-6 ms1/2) (p<0.0001). The corrected T(peak)-negative dT/dt dispersions in each patient was also significantly longer for the MI group than in the control group (35+/-27 ms1/2 vs. 10+/-5 ms1/2) (p<0.0001). Furthermore, the 3D RTc and T(peak)-negative dT/dt dispersion maps corresponded with the space location of MI, as defined by Tc-99m tetrofosmin myocardial imaging 3D RTc and T(peak)-negative dT/dt dispersion maps in the ST segment, obtained by 64-channel MCG may be used demonstrate the location of a myocardial injury and heterogeneities of repolarization.

Construction of a Three-dimensional Outline of the Heart and Conduction Pathway by Means of a 64-channel Magnetocardiogram in Patients with Atrial Flutter and Fibrillation

Magnetocardiography (MCG) has the potential for collecting three-dimensional (3D) intracardiac electric information, because the magnetic field is unaffected by the shape of the lungs and torso. In the present study, we report on the generation of a 3D heart outline and conduction pathway by means of a current density map using a 64-channel SQUID system, and an evaluation of its significance in patients with atrial flutter (AFL) and atrial fibrillation (AFIB). The subjects consisted of 20 healthy volunteers, and 3 patients with AFL and 4 patients with AFIB. A 64-channel MCG was recorded after digitization at 500 Hz, and a 3D current density was reconstructed from the magnetic fields using a space filter in conjunction with the minimum normalization method of Tikhonov. A 3D heart outline was generated from the integrated current density by the space filter. The conduction pathway was superimposed on a heart outline generated by a magnetic field. The heart outline was verified by the silhouette on the magnetic resonance (MR) images. An MCG was recorded pre- and post interventional therapy, and therapeutic efficacy was evaluated. The 3D heart outline of the atrium and ventricle corresponded to the silhouette of the right atrium and left ventricle, respectively, on an MR image. The serial conduction pathway of the QRS segment superimposed on the 3D heart outline map demonstrated the conduction pattern generated within the heart. The MCG revealed a counter-clockwise rotation in patients with AFL, and random micro-reentry in the case of AFIB. After interventional therapy, restoration of the sinus rhythm was verified in patients with both AFL and AFIB. A 64-channel MCG was used to evaluate the 3D heart outline and conduction pathway in patients with AFL and AFIB without the need for MR images. Condensed Abstract A 64-channel MCG was used to evaluate the 3D heart out line and conduction pathway in patients with AFL and AFIB.

A new screening method to diagnose coronary artery disease using multichannel magnetocardiogram and simple exercise.

Magnetocardiography (MCG) is a non-contact mapping technique to record cardiac action currents. The Master's two-step electrocardiogram (ECG) test is a simple exercise method for screening coronary artery disease (CAD), but it is inadequate concerning the sensitivity. Our aim was to develop a new screening method using multichannel MCG instead of ECG. Thirty subjects (aged 54 +/- 16 years, 27 males), 17 of whom had CAD confirmed by coronary angiography, underwent the Master's exercise ECG test. After the exercise, MCG signals were acquired every minute during recovery with a 64-channel MCG system (MC-6400, Hitachi Ltd). We integrated tangential components of the MCG signals within QRS (during 20, 40, 80, and 120 ms centering on R-wave peak) immediately after exercise (Iex) and 5 minutes after exercise (Irec). The exercise-induced change of currents [(Iex-Irec)/Irec] was determined and normalized for each channel, and the maximal change among 64 channels, maximal QRS integral change, was used as a diagnostic index for myocardial ischemia. The maximal QRS integral change during 40 ms was significantly higher in the CAD group than in the control group (0.81 +/- 0.51 vs. 0.36 +/- 0.19, p < 0.01). A sensitivity and specificity for predicting CAD by the change > 0.44 were 82 % and 85 %, respectively, yielding a diagnostic accuracy of 83 %. The conventional Master's ECG test identified the CAD patients with a diagnostic accuracy of 63 % (sensitivity 47 %, specificity 85 %). The Master's two-step exercise test with a 64-channel MCG system showed the high diagnostic accuracy, despite of non-contact recording and simple exercise. The magnetic field in the depolarization process has the potential to detect the subtle myocardial ischemia induced by exercise.