Noninvasive Mapping of Premature Ventricular Contractions by Merging Magnetocardiography and Computed Tomography.

OBJECTIVES: This study aimed to develop a novel premature ventricular contraction (PVC) mapping method to predict PVC origins in whole ventricles by merging a magnetocardiography (MCG) image with a cardiac computed tomography (CT) image. BACKGROUND: MCG can noninvasively discriminate PVCs originating from the aortic sinus cusp from those originating from the right ventricular outflow tract. METHODS: This study was composed of 22 candidates referred for catheter ablation of idiopathic PVCs. MCG and CT were performed the same day before ablation. Estimated origins by MCG-CT imaging using the recursive null steering spatial filter algorithm were compared with origins determined by electroanatomic mapping (CARTO, Biosense Webster, Inc., Diamond Bar, California) during the ablation procedure. Radiopaque acrylic markers for the CT scan and coil markers generating a weak magnetic field during MCG measurements were used as reference markers to merge the 2 images 3-dimensionally. RESULTS: PVC origins were determined by endocardial and epicardial mapping and ablation results in 18 (86%) patients (right ventricular outflow tract in 10 patients, aortic sinus cusp in 2 patients, interventricular septum in 1 patient, near His bundle in 1 patient, right ventricular free wall in 1 patient, and left ventricular free wall in 3 patients). Estimated origins by MCG-CT imaging matched the origins determined during the procedure in 94% (17 of 18) of patients, whereas the electrocardiography algorithms were accurate in only 56% (10 of 18). Discrimination of an epicardium versus an endocardium or right- versus left-sided septum was successful in 3 of 4 patients (75%). CONCLUSIONS: The diagnostic accuracy of noninvasive MCG-CT mapping was high enough to allow clinical use to predict the site of PVC origins in the whole ventricles.

Ability of magnetocardiography to detect regional dominant frequencies of atrial fibrillation.

BACKGROUND: Lead V1 on electrocardiography (ECG) can detect the dominant frequency (DF) of atrial fibrillation (AF) in the right atrium (RA). Paroxysmal AF is characterized by a frequency gradient from the left atrium (LA) to the right atrium (RA). We examined the ability of magnetocardiography (MCG) to detect regional DFs in both the atria. METHODS: Study subjects comprised 18 consecutive patients referred for catheter ablation of persistent AF. An MCG system with 64 magnetic sensors was used to perform MCG in the frontal, lateral, and back planes prior to the ablation procedure in each patient. DFMCG and organization index (OIMCG) were calculated using fast Fourier transformation. Intracardiac electrograms (ICEs) in both the atria and the coronary sinus (CS) were mapped at 17 sites. Regional DFsICE were also determined. RESULTS: Mean LA DFICE was higher than mean RA DFICE (6.40±0.66 versus 6.16±0.80 Hz, P=0.03). DFMCG in the channel having the highest OIMCG was 6.61±0.88 Hz in the frontal plane, 6.52±0.64 Hz in the lateral plane, and 6.42±0.62 Hz in the back plane (P=0.3). In each plane, DFMCG correlated with DFICE at the RA appendage (R=0.95, P<0.0001), the LA appendage (R=0.91, P<0.0001), and the CS (R=0.93, P<0.0001). DFECG in V5 modestly correlated with DFICE at the LA appendage (R=0.82, P<0.0001). CONCLUSIONS: MCG could more precisely detect the DFs in the LA and the CS than ECG. However, the usefulness of pre-procedural detection of the AF frequency gradient for ablation therapy needs to be evaluated in future prospective studies.

Development of a magnetocardiography-based algorithm for discrimination between ventricular arrhythmias originating from the right ventricular outflow tract and those originating from the aortic sinus cusp: a pilot study.

BACKGROUND: Although several reports address characteristic 12-lead electrocardiographic findings of outflow tract ventricular arrhythmias (OT-VAs), the accuracy of electrocardiogram-based algorithms to predict the OT-VA origin is sometimes limited. OBJECTIVE: This study aimed to develop a magnetocardiography (MCG)-based algorithm using a novel adaptive spatial filter to differentiate between VAs originating from the aortic sinus cusp (ASC-VAs) and those originating from the right ventricular outflow tract (RVOT-VAs). METHODS: This study comprised 51 patients with an OT-VA as the target of catheter ablation. An algorithm was developed by correlating MCG findings with the successful ablation site. The arrhythmias were classified as RVOT-VAs or ASC-VAs. Three parameters were obtained from 3-dimensional MCG imaging: depth of the origin of the OT-VA in the anteroposterior direction; distance between the earliest atrial activation site, that is, sinus node, and the origin of the OT-VA; and orientation of the arrhythmia propagation at the QRS peak. The distance was indexed to the patient's body surface area (in mm/m2). RESULTS: Origins of ASC-VAs were significantly deeper (81 ± 6 mm/m(2) vs. 68 ± 8 mm/m(2); P < .01) and farther from the sinus node (55 ± 9 mm/m2 vs. 41 ± 9 mm/m(2); P < .01) than those of RVOT-VAs. ASC-VA propagation had a tendency toward rightward axis. Receiver operating characteristic analyses determined that the depth of the origin was the most powerful predictor, with a sensitivity of 90% and a specificity of 73% (area under the curve = 0.90; P < .01). Discriminant analysis combining all 3 parameters revealed the accuracy of the localization to be 94%. CONCLUSION: This MCG-based algorithm appeared to precisely discriminate ASC-VAs from RVOT-VAs. Further investigation is required to validate the clinical value of this technique.

Note: low temperature superconductor superconducting quantum interference device system with wide pickup coil for detecting small metallic particles.

A one-channel low temperature superconductor superconducting quantum interference device system comprising a second-order axial gradiometer with a sensing area of 10 mm × 190 mm was developed. The gradiometer was mounted in a liquid-helium dewar (450-mm diameter; 975-mm length), with a gap of 12 mm between the pickup coil and the dewar-tail surface. The magnetic field sensitivity was measured to be 16 fT/Hz(1/2) in the white noise regime above 2 Hz. The system was used to measure stainless steel particles of different sizes passing through the sensing area. A 100-µm diameter SUS304 particle was readily detected passing at different positions underneath the large pickup coil by measuring its 1.3-pT magnetic field. Thus, the system was shown to be applicable to quality control of lamination sheet products such as lithium ion batteries.

Electrogram organization predicts left atrial reverse remodeling after the restoration of sinus rhythm by catheter ablation in patients with persistent atrial fibrillation.

BACKGROUND: Despite the informative nature of atrial fibrillation (AF) electrograms, electrophysiological aspects of predicting reversal of structural remodeling of the left atrium (LA) have not been evaluated. OBJECTIVES: To identify predictors of reverse remodeling after restoration of sinus rhythm by catheter ablation in patients with persistent AF. METHODS: This study included 90 patients with persistent AF and enlarged LA (left atrial volume indexed to body surface area [LAVi] ≥32 mL/m(2)). LAVi was measured by echocardiography before ablation and 12 months after sinus rhythm restoration. We divided 73 (81%) patients free from recurrences into 2 groups according to reduction in LAVi: responders, reduction ≥23% (n = 35); nonresponders, reduction <23% (n = 38). Serological testing and electrophysiological characteristics on electrocardiogram and magnetocardiogram were analyzed. RESULTS: LAVi decreased from 43 ± 12 to 27 ± 7 mL/m(2) in responders and from 37 ± 8 to 33 ± 8 mL/m(2) in nonresponders. Higher LAVi at baseline (P = .01), lower age (59 ± 7 years vs 63 ± 7 years; P <.05), higher brain natriuretic peptide level (median = 92, interquartile range [IQR] = 98 pg/mL vs median = 60, IQR = 64 pg/mL; P = 0.01), higher atrial natriuretic peptide level (median = 73, IQR = 74 pg/mL vs median = 54, IQR = 70 pg/mL; P = .02), and higher organization index of AF signals (0.51 ± 0.11 vs 0.42 ± 0.09; P = .0001) were observed in responders. There was a linear correlation between organization index and % reduction in LAVi (R = 0.63; P <.0001). Multiple linear regression analysis showed relations between reverse remodeling and age (ß = -0.28; P = .002), atrial natriuretic peptide level (ß = 0.21; P = .03), and organization index (ß = 0.53; P <.0001). CONCLUSIONS: Electrogram organization was a robust predictor of reverse remodeling of the enlarged LA after sinus rhythm restoration by catheter ablation in patients with persistent AF.

An increase in right atrial magnetic strength is a novel predictor of recurrence of atrial fibrillation after radiofrequency catheter ablation.

BACKGROUND: Differences in electrical properties between left and right atria (LA and RA) after pulmonary vein isolation (PVI) for atrial fibrillation (AF) are currently poorly understood. Magnetocardiograms were used to investigate the effect of PVI on bi-atrial magnetic field changes and their relationship to clinical outcomes. METHODS AND RESULTS: This study included 71 patients undergoing PVI for paroxysmal AF. Magnetocardiograms were recorded at baseline and 1 day, 8 weeks, and 24 weeks after ablation. Peak magnitude of LA and RA segments on P waves was separately compared before and after PVI. During a 16-month post-ablation period, 53 (75%) patients were free from AF recurrences. LA magnetic strength in patients without recurrence persistently decreased for 24 weeks and was significantly lower at 8 weeks than that in patients with recurrence (1.28±0.69 vs. 1.74±0.71 pico-Tesla, P=0.02). RA magnetic strength in patients with recurrence persistently rose for 24 weeks and was significantly higher at 8 weeks than that in patients without recurrence (2.17±0.82 vs. 3.00±1.12 pico-Tesla, P=0.001). Multivariate analysis showed RA magnetic strength at 8 weeks to be the strongest predictor of AF recurrence (odds ratio=3.335; 95% confidence interval=1.181-9.416; P=0.02). CONCLUSIONS: PVI resulted in distinct changes in magnetic strength in both the LA and the RA. A persistent rise in RA magnetic strength might be a robust predictor of AF recurrence after ablation.

Subtraction magnetocardiogram for detecting coronary heart disease.

BACKGROUND: A large-scale magnetocardiogram (MCG) database was produced, and standard MCG waveforms of healthy patients were calculated by using this database. It was clarified that the standard MCG waveforms are formed with the same shape and current distribution in healthy patients. A new subtraction method for detecting abnormal ST-T waveforms in coronary heart disease (CHD) patients by using the standard MCG waveform was developed. METHODS: We used MCGs of 56 CHD patients (63 ± 3 years old) and 101 age-matched normal control patients (65 ± 5 years old). To construct a subtracted ST-T waveform, we used standard MCG waveforms produced from 464 normal MCGs (male: 268, female: 196). The standard MCG waveforms were subtracted from each subject's measured MCGs, which were shortened or lengthened and normalized to adjust to the data length and magnitude of the standard waveform. We evaluated the maximum amplitude and maximum current-arrow magnitude of the subtracted ST-T waveform. RESULTS: The maximum magnetic field, maximum magnitude of current arrows, and maximum magnitude of total current vector increased according to the number of coronary artery lesions. The sensitivity and specificity of detecting CHD and normal control patients were 74.6% and 84.1%, respectively. CONCLUSIONS: The subtraction MCG method can be used to detect CHD with high accuracy, namely, sensitivity of 74.6% and specificity of 84.1% (in the case of maximum amplitude of total current vector). Furthermore, the subtraction MCG magnitude and its current distribution can reflect the expanse of the ischemic lesion area and the progress from ischemia to myocardial infarction.

Note: Unshielded bilateral magnetoencephalography system using two-dimensional gradiometers.

Magnetoencephalography (MEG) noninvasively measures neuronal activity with high temporal resolution. The aim of this study was to develop a new type of MEG system that can measure bilateral MEG waveforms without a magnetically shielded room, which is an obstacle to reducing both the cost and size of an MEG system. An unshielded bilateral MEG system was developed using four two-dimensional (2D) gradiometers and two symmetric cryostats. The 2D gradiometer, which is based on a low-T(c) superconducting quantum interference device and wire-wound pickup coil detects a magnetic-field gradient in two orthogonal directions, or ∂/∂x(∂(2)B(z)/∂z(2)), and reduces environmental magnetic-field noise by more than 50 dB. The cryostats can be symmetrically positioned in three directions: vertical, horizontal, and rotational. This makes it possible to detect bilateral neuronal activity in the cerebral cortex simultaneously. Bilateral auditory-evoked fields (AEF) of 18 elderly subjects were measured in an unshielded hospital environment using the MEG system. As a result, both the ipsilateral and the contralateral AEF component N100m, which is the magnetic counterpart of electric N100 in electroencephalography and appears about 100 ms after the onset of an auditory stimulus, were successfully detected for all the subjects. Moreover, the ipsilateral P50m and the contralateral P50m were also detected for 12 (67%) and 16 (89%) subjects, respectively. Experimental results demonstrate that the unshielded bilateral MEG system can detect MEG waveforms, which are associated with brain dysfunction such as epilepsy, Alzheimer's disease, and Down syndrome.

Repolarization spatial-time current abnormalities in patients with coronary heart disease.

BACKGROUND: Magnetocardiography (MCG) is a new technique for visualizing a current distribution in the myocardium. In recent years, current distribution parameters (CDPs) have been developed based on the distribution. The CDPs reflect spatial-time current abnormalities in patients with coronary heart disease (CHD). However, the criteria and scoring method of the abnormalities using CDPs are still controversial. METHOD: We measured MCG signals for 101 normal controls and 56 CHD patients (single-, double-, and triple-vessel diseases) using a MCG system. The CDPs (maximum current vector [MCV], total current vector [TCV], current integral map, and current rotation) during ventricular repolarization were analyzed. To evaluate the CDPs that are effective in distinguishing between normal controls and CHD patients, the areas under the receiver operating characteristic curve (A(z)) are calculated. Furthermore, the total scores ("0" to "4") of four CDPs with high A(z) values are also calculated. RESULTS: MCV and TCV angles at the T-wave peak had the highest A(z) value. Furthermore, TCV angular differences between the ST-T segment also had high A(z) values. Using the four CDPs, the averaged total score for patients with triple-vessel disease was the highest ("2.67") compared to the other groups (normal controls: 0.53). Furthermore, based on the assumption that subjects with a total score over "1" were suspected of having CHD, sensitivity and specificity were 85.7% and 74.3%, respectively. CONCLUSION: We concluded that the score and criteria using MCV and TCV during repolarization in CHD patients can reflect lesion areas and time changes of electrical activation dispersion due to ischemia.

Standard template of adult magnetocardiogram.

BACKGROUND: We need to know the magnetocardiogram (MCG) features regarding waveform and two-dimensional current distribution in normal subjects in order to classify the abnormal waveform in patients with heart disease. However, a standard MCG waveform has not been produced yet, therefore, we have first made the standard template MCG waveform. METHODS AND RESULTS: We used data from 464 normal control subjects' 64-channel MCGs (268 males, 196 females) to produce a template MCG waveform. The measured data were averaged after shortening or lengthening and normalization. The time interval and amplitude of the averaged data were adjusted to mean values obtained from a database. Furthermore, the current distributions (current arrow maps [CAMs]) were calculated from the produced templates to determine the current distribution pattern. The produced template of the QRS complex had a typical shape in six regions that we defined (M1, M2, M3, M4, M5, and M6). In the P wave, the main current arrow in CAMs pointing in a lower-left direction appeared in M1. In the QRS complex, the typical wave appeared in each region, and there were two main current arrows in M2 and M5. There were negative T waves in M1, M4, and M5, and positive T waves in M3 and M6, and the main current arrow pointing in a lower-left direction appeared in M2. CONCLUSION: Template MCG waveforms were produced. These morphologic features were classified into six regions, and the current distribution was characterized in each region. Consequently, the templates and classifications enable understanding MCG features and writing clinical reports.

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.

Integral value of JT interval in magnetocardiography is sensitive to coronary stenosis and improves soon after coronary revascularization.

BACKGROUND: Magnetocardiography (MCG) is sensitive to minute cardiac electric abnormalities, but its clinical utility in diagnosing ischemic heart disease (IHD) has not been established. The present study examined the usefulness of an integral MCG value of ventricular repolarization in patients with IHD. METHODS AND RESULTS: MCG was performed at rest in 14 patients with coronary stenosis >75% confirmed by coronary angiography (IHD group) using a 64-channel system, and then the sum of the 64-channel integral values of the QRS or JT intervals (QRSi and JTi, respectively) was calculated. The JTi/QRSi value indicated the total power of currents in JT compared with those in QRS. These measurements were repeated within 2 weeks after coronary revascularization. The Control group comprised 30 healthy volunteers. The baseline value of JTi/QRSi was significantly smaller in the IHD than in the Control group, but after revascularization it increased and did not significantly differ from the Control group. No significant difference in ST deviation was identified by electrocardiography (ECG) before and after coronary revascularization. Analysis of the Control group revealed that JTi/QRSi was not affected by age. CONCLUSIONS: The JTi/QRSi of the MCG is more sensitive to coronary stenosis than ECG, and this parameter improves soon after coronary revascularization.

Motion analysis of grip and release with fingers using simple magnetic detection system.

We have developed a magnetic grip-and-release motion detection system to measure time differences among fingers during motion. We designed a magnetic sensing system consisting of a magnetic oscillation coil, sensing coil, and circuit unit. We measured wave forms of grip-and-release motion (15 s) of seven healthy volunteers using the system. To provide the grip-and-release timing of each finger, we used the reference voltage of each subject in the state of grasping a rod with a 30 mm diameter. Using the reference voltage, the time differences in the finger movements of all volunteers were detected. The detected grip-and-release time difference of both dominant and nondominant hands had a main tendency in which the closing movement of the little finger is fast, within 10 ms, and the opening movement is slow, within 13 ms. Our data suggest that the new magnetic sensing system has the potential to detect the quantitative value of the time difference in grip-and-release motion among fingers.

Visualization of three-dimensional cardiac electrical excitation using standard heart model and anterior and posterior magnetocardiogram.

Our aim in this study is to obtain novel three-dimensional (3-D) images of cardiac electrical excitation that include morphological information on the whole heart. We obtain these 3-D images by projecting anterior and posterior two-dimensional (2-D) current-arrow maps (CAMs) onto a 3-D standard heart model. This standard heart model is adjusted to the individual subject's heart position by using the coordinates of the sinus node, which are obtained from magnetocardiogram (MCG) signals. The anterior and posterior CAMs are calculated by taking the orthogonal partial derivatives of the normal component of the anterior and posterior MCGs. After adjusting the base current values of the anterior and posterior CAMs, the adjusted CAMs are projected onto the standard heart model. We generated the projected CAMs (PCAMs) of the six phases (atrial, and ventricular, excitation) for seven healthy subjects. The validity of PCAM was evaluated by extracting the maximal current directions and positions from the PCAMs. The maximal current directions and positions during each excitation phase were almost in the same in the seven healthy subjects. Therefore, the PCAMs give us a clear view of the anterior and posterior myocardial excitation for the respective electrophysiological phases.

Electrical space-time abnormalities of ventricular depolarization in patients with Brugada syndrome and patients with complete right-bundle branch blocks studied by magnetocardiography.

BACKGROUND: Both ventricular depolarization abnormalities (QRS complex) and repolarization ones (ST/T) are still controversial in literature. The objective of this study was to clarify the space-time variations that occur in patients carriers of Brugada syndrome using Magnetocardiography and also compare them with cases of complete right-bundle branch block (CRBBB) and individuals without any dromotropic disorder (control group). METHODS AND RESULTS: Magnetocardiograms (MCGs) of Brugada syndrome patients (n = 16), CRBBB patients (n = 14), and members of a control group (n = 46) at rest were recorded. The MCGs were used to produce a whole-heart electrical-activation diagram (W-HEAD), which can visualize the spatial time-variant activation in the whole heart. In the W-HEAD pattern, three activations were located in the left ventricle, and CRBBB patients had a wide peak with about 65-ms delay on the right anterior side. While the Brugada syndrome pattern has a posteromedian left-ventricle excitation, that is half the amplitude that occurs in CRBBB patients, the electrical conduction rate to the posterosuperior septum area was low. CONCLUSIONS: The W-HEAD data made it possible to visualize space-time depolarization abnormalities. These findings suggest that the electrical conduction rate to the posterosuperior septum area in Brugada syndrome cases is low, and this low activation may be a feature of typical Brugada syndrome.

Standardization of the PQRST waveform and analysis of arrhythmias in the fetus using vector magnetocardiography.

Fetal magnetocardiography (fMCG) is useful for analysis of fetal cardiac events. However, fetal presentation and movement affect the fMCG waveform, making it difficult to standardize the waveform. The aim of this study was to investigate whether the use of vector magnetometers can compensate for these limitations. We studied 59 fetuses (gestational age, 22-40 wk, median, 32), including 41 with uncomplicated pregnancies and 18 with fetal cardiac disease. fMCG was recorded twice in each case, and the two waveforms were compared with each other in uncomplicated subjects to investigate the effects of fetal presentation. The superconducting quantum interference device (SQUID) system used in this study was a 12-channel vector magnetometer, by which the three components of the magnetic field (Bx, By, Bz) could be detected simultaneously at four recording points. By constructing the three components, a composite waveform (Bxyz) was obtained. The configuration of the composite waveforms was similar among normal fetuses always with positive polarity, independent of fetal presentation and movement. The difference in the time intervals (PR, QRS, and ventricular activation time [VAT]) between the first and second measurements was minimal in the composite waveforms (Bxyz) compared with that in each channel (Bx, By, Bz). Even before signal averaging, waveforms with high time resolution were recorded in at least one of the three components, making it possible to analyze fetal arrhythmias precisely. Our results indicate that vector magnetocardiography is potentially useful for standardization of the fMCG waveforms and to provide a more complete and accurate analysis of fetal arrhythmias.

Magnetocardiography study on ventricular depolarization-current pattern in patients with brugada syndrome and complete right-bundle branch blocks.

BACKGROUND: The objective of this study is to use magnetocardiography to determine the existence of a small abnormal current during ventricular depolarization in patients with Brugada syndrome. To understand this small difference in abnormal current during ventricular depolarization, we compared abnormal currents of patients with cases of complete right-bundle-branch block (CRBBB). METHODS AND RESULTS: We developed a whole-heart electrical bull's eye map (WHEBEM) that uses magnetocardiograms (MCGs) to visualize the current distribution in a circular map. MCGs of Brugada syndrome patients (n = 16), CRBBB patients (n = 10), and controls (n = 12) at rest were recorded. In the WHEBEMs of Brugada syndrome patients, the magnitude of the S-wave current in the upper-right direction of the anterior side is larger than that of the controls. In addition, the R-wave current direction is similar to that of the controls, and the R-wave vector is distributed over a larger area than that of the controls. On the other hand, the CRBBB patients have a distribution of R-wave currents over a larger area in the left anteromedian region and the left posteromedian region. Moreover, in all CRBBB patients, S-wave currents with a large magnitude have the same direction distributed over a small area. CONCLUSIONS: The WHEBEM findings suggest that there is an abnormal current in the direction to the upper right (in the S-wave) in the anterosuperior region of Brugada syndrome patients. We thus conclude that a WHEBEM has the potential to detect characteristics of heart disease.

Reconstruction of action potential of repolarization in patients with congenital long-QT syndrome.

A method for reconstructing an action potential during the repolarization period was developed. This method uses a current distribution-plotted as a current-arrow map (CAM)--calculated using magnetocardiogram (MCG) signals. The current arrows are summarized during the QRS complex period and subtracted during the ST-T wave period in order to reconstruct the action-potential waveform. To ensure the similarity between a real action potential and the reconstructed action potential using CAM, a monophasic action potential (MAP) and an MCG of the same patient with type-I long-QT syndrome were measured. Although the MAP had one notch that was associated with early afterdepolarization (EAD), the reconstructed action potential had two large and small notches. The small notch timing agreed with the occurrence of the EAD in the MAP. On the other hand, the initiation time of an abnormal current distribution coincides with the appearance timing of the first large notch, and its end time coincides with that of the second small notch. These results suggest that a simple reconstruction method using a CAM based on MCG data can provide a similar action-potential waveform to a MAP waveform without having to introduce a catheter.

Quantitative magnetic detection of finger movements in patients with Parkinson's disease.

To develop a new measurement tool for quantitatively detecting the finger movement of a patient with Parkinson's disease (PD), we designed a magnetic sensing system consisting of a magnetic induction coil, a sensing coil, and a circuit unit. The sensing coil detects the inducted magnetic field that varies with the distance between the two coils, and the detected signals are demodulated in the circuit unit in order to obtain the variation voltage from the oscillation frequency. To obtain a coefficient for converting voltage to distance, we measured the output voltages for seven fixed finger positions of 12 normal volunteers. The voltage differences corresponding to the finger movement in 20 PD patients, six age-matched controls, and 12 normal volunteers were then recorded for 30s. To investigate the velocity and acceleration of the finger movement, we calculated their waveforms from the measured displacement waveform. We also detected the main frequency of the tapping rhythm by using a fast Fourier transform (FFT). The averaged amplitude of each waveform decreased with the disorder in the Hoehn-Yahr (HY) stage, while the averaged tapping frequency of PD patients did not have any correlation with this stage. It can be concluded that this magnetic sensing system can assess finger movement quantitatively.