Detection of spatial repolarization abnormalities in patients with LQT1 and LQT2 forms of congenital long-QT syndrome

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.

Electrocardiographic interventricular dispersion of repolarization during autonomic adaptation in LQT1 subtype of long QT syndrome

OBJECTIVES

In LQT1 subtype of inherited long QT syndrome, repolarization abnormalities originating from defective I(Ks) render patients vulnerable to ventricular arrhythmia during sudden sympathetic activation. Experimental studies show lower I(Ks) density and longer action potential duration in left (LV) than in right (RV) ventricle. We studied interventricular dispersion of repolarization in patients with I(Ks) defect during autonomic tests.

DESIGN

We measured interventricular (difference of QT intervals between LV and RV type leads) and transmural electrocardiographic dispersion of repolarization from 25-lead electrocardiograms in nine asymptomatic KCNQ1 mutation carriers (LQT1) and eight controls during rest, Valsalva maneuver, mental stress, sustained handgrip and supine exercise.

RESULTS

LQT1 carriers showed increased interventricular dispersion of repolarization (13+/-9 ms vs. 4+/-4 ms, p=0.03) during all tests. Valsalva strain increased the difference between the study groups. In LQT1 carriers, interventricular dispersion of repolarization correlated weakly with electrocardiographic transmural dispersion of repolarization.

CONCLUSIONS

Asymptomatic KCNQ1 mutation carriers exhibit increased and by abrupt sympathetic activation augmented interventricular difference in electrocardiographic repolarization times. Interventricular and transmural repolarization dispersion behave similarly in patients with I(Ks) defect.

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.

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.

Pseudo current density maps of electrophysiological heart, nerve or brain function and their physical basis

Background

In recent years the visualization of biomagnetic measurement data by so-called pseudo current density maps or Hosaka-Cohen (HC) transformations became popular.

Methods

The physical basis of these intuitive maps is clarified by means of analytically solvable problems.

Results

Examples in magnetocardiography, magnetoencephalography and magnetoneurography demonstrate the usefulness of this method.

Conclusion

Hardware realizations of the HC-transformation and some similar transformations are discussed which could advantageously support cross-platform comparability of biomagnetic measurements.

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.

Magnetocardiography for pharmacology safety studies requiring high patient throughput and reliability

Recent guideline drafts of the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) underline the necessity to test nonantiarrhythmic drugs for their potential to prolong the QT or the corrected QT (QTc) interval. The implementation of these guidelines requires a large amount of ECG measurements on animals and humans in preclinical and clinical phases of the drug development process. We propose the use of magnetocardiography (MCG) as a complementary method with particular advantages in high-throughput studies, where signal quality and reliability are key factors. Our proposal is based on a review of recent MCG studies investigating the repolarization phase and results of methodological work assessing QT interval parameters from the MCG. The applicability of MCG for pre-clinical in-vivo studies is demonstrated by the ease of measurement in unrestrained non-anesthetized rabbits, guinea pigs, and hamsters..

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.

Identifying patterns of spatial current dispersion that characterise and separate the Brugada syndrome and complete right-bundle branch block

The aim of the study was to detect patterns of spatial-current distribution in the late QRS and early ST-segments that distinguish Brugada-syndrome cases from complete right-bundle branch block (CRBBB). Magnetocardiograms (MCGs) were recorded from Brugada-syndrome patients (n = 6), CRBBB patients (n = 4) and the members of a control group (n = 33). The current distributions at six time points from Q-onset were estimated by producing current-arrow maps (CAMs). The angle of the current arrow of maximum amplitude at each time point was calculated. In the Brugada cases, the characteristic ST elevation was seen above the upper right chest, and abnormal currents appeared to be present in the right-ventricular outflow tract (RVOT). The angles of the abnormal arrows were -78 degrees +/- 51 degrees at 100 ms and -50 degrees +/- 61 degrees at 110 ms. In the cases of CRBBB, wide S- and R-waves were recorded above the upper right and lower right chest, respectively. The angles of the abnormal arrows for CRBBB were 152 degrees +/- 19 degrees at 100 ms, 159 degrees +/- 20 degrees at 110 ms, and 157 degrees +/- 19 degrees at 120 ms. The findings suggest that an abnormal current from the RVOT to the upper left chest may be a feature of the Brugada syndrome, and that the direction of this current is completely different from that seen in CRBBB.