Biomedical subjects

Zenichi Ihara

Publications and source records attributed to Zenichi Ihara.

4 recordsLinked to original sources

PubMed2006

Adaptation of the standard 12-lead electrocardiogram system dedicated to the analysis of atrial fibrillation.

OBJECTIVE: The objective of the study was to design a lead system aimed at studying atrial fibrillation (AF), while being anchored to the standard 12-lead system. METHODS: The location of 4 of the 6 precordial electrodes was optimized while leaving the remaining 5 of the 9 electrodes of the standard 12-lead system in place. The analysis was based on episodes of 11 different variants of AF simulated by a biophysical model of the atria positioned inside an inhomogeneous thorax. The optimization criterion used was derived from the singular value decomposition of the data matrices. RESULTS: While maintaining VR, VL, VF, V1 and V4, the 4 new electrode positions increased the ratio of the eighth and the first singular values of the data matrices of the new configuration about 5-fold compared with that of the conventional electrode positions. CONCLUSION: The adapted lead system produces a more complete view on AF compared with that of the standard 12-lead system.

Atrial Fibrillation↗

PubMed2006

Vectorcardiographic lead systems for the characterization of atrial fibrillation.

OBJECTIVE: The aim of the study was to design a vectorcardiographic lead system dedicated to the analysis of atrial fibrillation (AF). METHODS: Body surface potentials during AF were simulated by using a biophysical model of the human atria and thorax. The XYZ components of the equivalent dipole were derived from the Gabor-Nelson equations. These served as the gold standard while searching for an optimal orthogonal lead system for the estimation of the heart vector while using a limited number of electrode positions. Six electrode configurations and their dedicated transfer matrices were tested by using 10 different episodes of simulated AF and 25 different thorax geometries. RESULTS: Root-mean-square-based relative estimation error of the vectorcardiogram using the Frank electrodes was 0.39. An adaptation of 4 of the 9 electrode locations of the standard electrocardiogram, with 1 electrode moved to the back, reduced the error to 0.24. CONCLUSION: The Frank lead system is suboptimal for estimating the equivalent dipole components (VCG) during AF. Alternative electrode configurations should include at least 1 electrode on the back.

Action Potentials↗

PubMed2006

Atrial repolarization as observable during the PQ interval.

OBJECTIVE: We aimed to study the involvement of atrial repolarization in body surface potentials. METHODS: Electrocardiograms of healthy subjects were recorded using a 64-lead system. The data analysis focused on the PQ intervals while devoting special attention to the low-amplitude signals during the PQ segment: the segment from the end of the P wave until onset QRS. The data were analyzed by inspecting body surface potential maps and the XYZ signals of the vectorcardiogram. RESULTS: Standard P-wave features exhibited normal values. The local potential extremes were found at positions not sampled by the standard leads. The PQ segment was found to be not isoelectric, the time course of the potential distribution being very similar to that during the P wave but for a reversed polarity and about 3-fold lower magnitudes. CONCLUSION: The results demonstrate a significant involvement of atrial repolarization during the PQ interval and essentially discordant "atrial T waves," suggesting a small dispersion of atrial action potential durations.

Atrial Function↗

PubMed2003

Study of unipolar electrogram morphology in a computer model of atrial fibrillation.

INTRODUCTION: Electrograms exhibit a wide variety of morphologies during atrial fibrillation (AF). The basis of these time courses, however, is not completely understood. In this study, data from computer models were studied to relate features of the signals to the underlying dynamics and tissue substrate. METHODS AND RESULTS: A computer model of entire human atria with a gross fiber architecture based on histology and membrane kinetics based on the Courtemanche et al. atrial model was developed to simulate paced activation and simulated AF. Unipolar electrograms were computed using a current source approximation at 256 sites in right atrium, to simulate a mapping array. The results show the following: (1) In a homogeneous and isotropic tissue, the presence of highly asymmetric electrograms is rare (<2%), although there is a marked variability in amplitude and symmetry. (2) The introduction of anisotropy increases this variability in symmetry and amplitude of the, electrograms especially for propagation across fibers. The percentage of highly asymmetric electrograms increases to 12% to 15% for anisotropy ratios greater than 3:1. (3) Multiphasic and fractionated electrograms are rarely seen in the model with uniform properties but are more common (15%-17%) in a model including regions with abrupt changes in conductivity. Beat-to-beat variations in the occurrence of multiphasic signals are possible with fixed anatomic heterogeneity, due to beat-to-beat variations in the direction of the wavefront relative to the heterogeneity. CONCLUSION: Analysis of the amplitude and symmetry of unipolar atrial electrograms can provide information about the electrophysiologic substrate maintaining AF.

Algorithms↗