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628 results on '"Yamazaki, Masatoshi"'

1. Deep-learning-based electrode action potential mapping (DEAP Mapping) from annotation-free unipolar electrogram

Author

Seno, Hiroshi, Kojima, Toshiya, Yamazaki, Masatoshi, Sakuma, Ichiro, Fujiu, Katsuhito, and Tomii, Naoki

Subjects
Electrical Engineering and Systems Science - Signal Processing, Electrical Engineering and Systems Science - Image and Video Processing, 92C55, 68T07, I.2.6, J.3, I.5.4
Abstract

Catheter ablation has limited therapeutic efficacy against non-paroxysmal atrial fibrillation (AF), and electrophysiological studies using mapping catheters have been applied to evaluate the AF substrate. However, many of these approaches rely on detecting excitation timing from electrograms (ECGs), potentially compromising their effectiveness in complex AF scenarios. Herein, we introduce Deep-learning-based Electrode Action Potential Mapping (DEAP Mapping), a deep learning model designed to reconstruct membrane potential images from annotation-free unipolar ECG signals. We conducted ex vivo experiments using porcine hearts (N = 6) to evaluate the accuracy of DEAP Mapping by simultaneously performing fluorescence measurement of membrane potentials and measurements of epicardial unipolar ECGs. Membrane potentials estimated via DEAP Mapping were compared with those measured via optical mapping. We assessed the clinical applicability of DEAP Mapping by comparing the DEAP Mapping's estimations from clinically measured catheter electrode signals with those from established electrode-mapping techniques. DEAP Mapping accurately estimated conduction delays and blocks in ex vivo experiments. Phase variance analysis, an AF substrate evaluation method, revealed that the substrate identified from optical mapping closely resembled that identified from DEAP Mapping estimations (structural similarity index of >0.8). In clinical evaluations, DEAP Mapping estimation observed several conduction delays and blocks that were not observed with existing methods, indicating that DEAP Mapping can estimate excitation patterns with higher spatiotemporal resolution. DEAP Mapping has a potential to derive detailed changes in membrane potential from intra-operative catheter electrode signals, offering enhanced visualisation of the AF substrate from the estimated membrane potentials., Comment: 17 pages, 7 figures, 6 supplemental movies

Published
2024

3. Millimetre-scale magnetocardiography of living rats using a solid-state quantum sensor

Author

Arai, Keigo, Kuwahata, Akihiro, Nishitani, Daisuke, Fujisaki, Ikuya, Matsuki, Ryoma, Xin, Zhonghao, Nishio, Yuki, Cao, Xinyu, Hatano, Yuji, Onoda, Shinobu, Shinei, Chikara, Miyakawa, Masashi, Taniguchi, Takashi, Yamazaki, Masatoshi, Teraji, Tokuyuki, Ohshima, Takeshi, Hatano, Mutsuko, Sekino, Masaki, and Iwasaki, Takayuki

Subjects
Physics - Medical Physics, Physics - Applied Physics, Quantum Physics
Abstract

A key challenge in cardiology is the non-invasive imaging of electric current propagation occurring in the cardiovascular system at an intra-cardiac scale. A promising approach for directly mapping the current dynamics is to monitor the associated stray magnetic field. However, in this magnetic field approach, the spatial resolution deteriorates significantly as the standoff distance between the target and the sensor increases. Existing sensors usually remain relatively far from the target and provide only centimetre-scale resolution because their operating temperature is not biocompatible. Here we demonstrate millimetre-scale magnetocardiography of living rats using a solid-state quantum sensor based on nitrogen-vacancy centres in diamond. The essence of the method is a millimetre proximity from the sensor to heart surface, which enhances the cardiac magnetic field to greater than nanoteslas and allows the mapping of these signals with intra-cardiac resolution. From the acquired magnetic images, we also estimate the source electric current vector, flowing from the right atria base via the Purkinje fibre bundle to the left ventricular apex. Our results establish the solid-state quantum sensor's capability to probe cardiac magnetic signals from mammalian animals and reveal their intra-cardiac electrodynamics. This technique will enable the study of the origin and progression of myriad cardiac arrhythmias including flutter, fibrillation, and tachycardia., Comment: 17 pages, 4 figures

Published
2021

4. Millimetre-scale magnetocardiography of living rats with thoracotomy

Author

Arai, Keigo, Kuwahata, Akihiro, Nishitani, Daisuke, Fujisaki, Ikuya, Matsuki, Ryoma, Nishio, Yuki, Xin, Zonghao, Cao, Xinyu, Hatano, Yuji, Onoda, Shinobu, Shinei, Chikara, Miyakawa, Masashi, Taniguchi, Takashi, Yamazaki, Masatoshi, Teraji, Tokuyuki, Ohshima, Takeshi, Hatano, Mutsuko, Sekino, Masaki, and Iwasaki, Takayuki

Published
2022
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6. Explainable localization of premature ventricular contraction using deep learning‐based semantic segmentation of 12‐lead electrocardiogram.

Author

Kujime, Kota, Seno, Hiroshi, Nakajima, Kenzaburo, Yamazaki, Masatoshi, Sakuma, Ichiro, Yamagata, Kenichiro, Kusano, Kengo, and Tomii, Naoki

Subjects
ARRHYTHMIA diagnosis, PHENOMENOLOGICAL biology, RECEIVER operating characteristic curves, RESEARCH funding, DESCRIPTIVE statistics, RETROSPECTIVE studies, ELECTROCARDIOGRAPHY, DEEP learning, SEMANTICS, DATA analysis software
Abstract

Background: Predicting the origin of premature ventricular contraction (PVC) from the preoperative electrocardiogram (ECG) is important for catheter ablation therapies. We propose an explainable method that localizes PVC origin based on the semantic segmentation result of a 12‐lead ECG using a deep neural network, considering suitable diagnosis support for clinical application. Methods: The deep learning‐based semantic segmentation model was trained using 265 12‐lead ECG recordings from 84 patients with frequent PVCs. The model classified each ECG sampling time into four categories: background (BG), sinus rhythm (SR), PVC originating from the left ventricular outflow tract (PVC‐L), and PVC originating from the right ventricular outflow tract (PVC‐R). Based on the ECG segmentation results, a rule‐based algorithm classified ECG recordings into three categories: PVC‐L, PVC‐R, as well as Neutral, which is a group for the recordings requiring the physician's careful assessment before separating them into PVC‐L and PVC‐R. The proposed method was evaluated with a public dataset which was used in previous research. Results: The evaluation of the proposed method achieved neutral rate, accuracy, sensitivity, specificity, F1‐score, and area under the curve of 0.098, 0.932, 0.963, 0.882, 0.945, and 0.852 on a private dataset, and 0.284, 0.916, 0.912, 0.930, 0.943, and 0.848 on a public dataset, respectively. These quantitative results indicated that the proposed method outperformed almost all previous studies, although a significant number of recordings resulted in requiring the physician's assessment. Conclusions: The feasibility of explainable localization of premature ventricular contraction was demonstrated using deep learning‐based semantic segmentation of 12‐lead ECG. Clinical trial registration: M26‐148‐8. [ABSTRACT FROM AUTHOR]

Published
2024
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9. Application of Structured Light Illumination and Compressed Sensing to High Speed Laminar Optical Fluorescence Tomography

Author

Sakuma, Ichiro, Kobayashi, Toshiki, Seno, Hiroshi, Akagi, Yuki, Nakagawa, Keiichi, Yamazaki, Masatoshi, Tomii, Naoki, Magjarevic, Ratko, Series Editor, Ładyżyński, Piotr, Associate Editor, Ibrahim, Fatimah, Associate Editor, Lackovic, Igor, Associate Editor, Rock, Emilio Sacristan, Associate Editor, González Díaz, César A., editor, Chapa González, Christian, editor, Laciar Leber, Eric, editor, Vélez, Hugo A., editor, Puente, Norma P., editor, Flores, Dora-Luz, editor, Andrade, Adriano O., editor, Galván, Héctor A., editor, Martínez, Fabiola, editor, García, Renato, editor, Trujillo, Citlalli J., editor, and Mejía, Aldo R., editor

Published
2020
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11. Statistical Guideline of Threshold Determination for Cardiac Spiral Wave Center Detection Using Phase Variance Analysis

Author

Tomii, Naoki, Yamazaki, Masatoshi, Shibata, Nitaro, Honjo, Haruo, Sakuma, Ichiro, Magjarevic, Ratko, Editor-in-Chief, Ładyżyński, Piotr, Series Editor, Ibrahim, Fatimah, Series Editor, Lacković, Igor, Series Editor, Rock, Emilio Sacristan, Series Editor, Lhotska, Lenka, editor, Sukupova, Lucie, editor, and Ibbott, Geoffrey S., editor

Published
2019
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12. Cardiac macrophages prevent sudden death during heart stress

Author

Sugita, Junichi, Fujiu, Katsuhito, Nakayama, Yukiteru, Matsubara, Takumi, Matsuda, Jun, Oshima, Tsukasa, Liu, Yuxiang, Maru, Yujin, Hasumi, Eriko, Kojima, Toshiya, Seno, Hiroshi, Asano, Keisuke, Ishijima, Ayumu, Tomii, Naoki, Yamazaki, Masatoshi, Kudo, Fujimi, Sakuma, Ichiro, Nagai, Ryozo, Manabe, Ichiro, and Komuro, Issei

Published
2021
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15. Cardiac Spiral Wave Termination by Linear Regional Cooling Toward the Anatomical Boundary of the Heart

Author

Seno, Hiroshi, Tomii, Naoki, Yamazaki, Masatoshi, Honjo, Haruo, Shibata, Nitaro, and Sakuma, Ichiro

Abstract

Purpose: We hypothesized that linear regional cooling (LRC) toward the atrio-ventricular groove (AV-G) can move the spiral wave (SW) center to the AV-G effectively and terminate SW. The effectiveness of LRC in ex vivo 2D ventricle rabbit experiments was tested. Methods: We developed an experimental system to operate LRC and optical mapping simultaneously. To realize simultaneous cooling and optical mapping, a transparent cooling device was developed. LRC for 60 s toward 2D subepicardial ventricular myocardium of Langendorff-perfused rabbit hearts (n = 4) was conducted during constant pacing and persistent ventricular tachyarrhythmias (VTs). Results: Action potential duration at 90% repolarization (APD90) at the cooling area was prolonged by LRC from 187 to 228 ms. 41% of persistent VTs were terminated by LRC (12/29 cases). Cases where the original SW center moved toward the AV-G were observed via optical mapping. However, there were some cases where VT was not terminated by LRC. When the action potential duration (APD) of VT sustained cases were analyzed, LRC prolonged APD, but the APD prolonged area did not move toward the AV-G in most VT sustained cases Conclusion: Proper LRC toward the AV-G near the original SW center could move this center toward the AV-G and terminate SW excitation.

Published
2024
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16. Biobank-driven genomic discovery yields new insight into atrial fibrillation biology

Author

Nielsen, Jonas B., Thorolfsdottir, Rosa B., Fritsche, Lars G., Zhou, Wei, Skov, Morten W., Graham, Sarah E., Herron, Todd J., McCarthy, Shane, Schmidt, Ellen M., Sveinbjornsson, Gardar, Surakka, Ida, Mathis, Michael R., Yamazaki, Masatoshi, Crawford, Ryan D., Gabrielsen, Maiken E., Skogholt, Anne Heidi, Holmen, Oddgeir L., Lin, Maoxuan, Wolford, Brooke N., Dey, Rounak, Dalen, Håvard, Sulem, Patrick, Chung, Jonathan H., Backman, Joshua D., Arnar, David O., Thorsteinsdottir, Unnur, Baras, Aris, O’Dushlaine, Colm, Holst, Anders G., Wen, Xiaoquan, Hornsby, Whitney, Dewey, Frederick E., Boehnke, Michael, Kheterpal, Sachin, Mukherjee, Bhramar, Lee, Seunggeun, Kang, Hyun M., Holm, Hilma, Kitzman, Jacob, Shavit, Jordan A., Jalife, José, Brummett, Chad M., Teslovich, Tanya M., Carey, David J., Gudbjartsson, Daniel F., Stefansson, Kari, Abecasis, Gonçalo R., Hveem, Kristian, and Willer, Cristen J.

Published
2018
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20. Heavy Ion Irradiation Reduces Vulnerability to Atrial Tachyarrhythmias ― Gap Junction and Sympathetic Neural Remodeling ―

Author

Amino, Mari, primary, Yamazaki, Masatoshi, additional, Yoshioka, Koichiro, additional, Kawabe, Noboru, additional, Tanaka, Sachie, additional, Shimokawa, Takashi, additional, Niwa, Ryoko, additional, Tomii, Naoki, additional, Kabuki, Shigeto, additional, Kunieda, Etsuo, additional, Yagishita, Atsuhiko, additional, Ikari, Yuji, additional, and Kodama, Itsuo, additional

Published
2022
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29. Magnetocardiography imaging of living rats using NV centers in Diamond

Author

Matsuki, Ryoma, Arai, Keigo, Kuwahata, Akihiro, Nishitani, Daisuke, Fujisaki, Ikuya, Nishio, Yuki, Xin, Zonghao, Cao, Xinyu, Hatano, Yuji, Shinobu, Onoda, Shinei, Chikara, Miyakawa, Masashi, Taniguchi, Takashi, Yamazaki, Masatoshi, Teraji, Tokuyuki, Takeshi, Ohshima, Hatano, Mutsuko, Sekino, Masaki, and Iwasaki, Takayuki

Abstract

The study on Magnetocardiography imaging of living rats using NV centers in Diamond, The 4th International Forum on Quantum Metrology and Sensing

Published
2021

33. B-PO05-081 SIMULTANEOUS ULTRA-HIGH RESOLUTION OPTICAL MAPPING AND CATHETER MAPPING IN A LANGENDORFF-PERFUSED SWINE HEART MODEL TO IDENTIFY ATRIAL FIBRILLATION ROTORS BY CATHETER MAPPING

Author

Nakagawa, Hiroshi, primary, Yamazaki, Masatoshi, additional, Tomii, Naoki, additional, Seno, Hiroshi, additional, Kuroda, Shunsuke, additional, Basu, Shubhayu, additional, Bar-tal, Meir, additional, Takamiya, Nobuteru, additional, Malinaric, Jamie L., additional, Tsukihra, Hiroyuki, additional, Hussein, Ayman A., additional, Saliba, Walid I., additional, Wazni, Oussama M., additional, Sakuma, Ichiro, additional, and Jackman, Warren M., additional

Published
2021
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37. Contributors

Author

Abriel, Hugues, primary, Adkisson, Wayne O., additional, Agullo-Pascual, Esperanza, additional, Ajijola, Olujimi A., additional, Al-Ahmad, Amin, additional, Alli, Oluseun, additional, Altman, Robert K., additional, Anter, Elad, additional, Antzelevitch, Charles, additional, Anumonwo, Justus M.B., additional, Armaganijan, Luciana, additional, Ashikaga, Hiroshi, additional, Atienza, Felipe, additional, Avula, Uma Mahesh R., additional, Backx, Peter H., additional, Balse, Elise, additional, Barrett, Conor D., additional, Benditt, David G., additional, Berenfeld, Omer, additional, Bers, Donald M., additional, Berul, Charles I., additional, Blank, A. Christian, additional, Bloise, Raffaella, additional, Bogun, Frank Matthias, additional, Borggrefe, Martin, additional, Boyle, Noel G., additional, Breithardt, Günter, additional, Brini, Marisa, additional, Brink, Peter R., additional, Brugada, Josep, additional, Brugada, Pau, additional, Brugada, Pedro, additional, Brugada, Ramon, additional, Brugada, Victoria, additional, Buch, Eric, additional, Bukauskas, Feliksas F., additional, Burkhardt, J. David, additional, Bursac, Nenad, additional, Calkins, Hugh, additional, Callans, David J., additional, Campuzano, Oscar, additional, Caples, Sean M., additional, Carafoli, Ernesto, additional, Castellanos, Augustin, additional, Catterall, William, additional, Cerrone, Marina, additional, Chen, Lan S., additional, Chen, Lei, additional, Chen, Peng-Sheng, additional, Chin, Ashley, additional, Chugh, Aman, additional, Cohen, Ira S., additional, Connolly, Stuart J., additional, Constantino, Jason, additional, Crotti, Lia, additional, Cuoco, Frank A., additional, Curtis, Anne B., additional, Damiano, Ralph J., additional, Darbar, Dawood, additional, Das, Mithilesh K., additional, Delmar, Mario, additional, Delpón, Eva, additional, Di Biase, Luigi, additional, Dixit, Sanjay, additional, Dobrev, Dobromir, additional, Dosdall, Derek J., additional, Dyer, John W., additional, Eckardt, Lars, additional, Edwards, Andrew G., additional, Efimov, Igor R., additional, Ellenbogen, Kenneth A., additional, Ellinor, Patrick T., additional, Entcheva, Emilia, additional, Estes, N.A. Mark, additional, Fischmeister, Rodolphe, additional, Fisher, John D., additional, Fishman, Glenn I., additional, Frankel, David S., additional, Franz, Michael R., additional, Friedman, Paul A., additional, Froelicher, Victor F., additional, Gami, Apoor S., additional, George, Alfred L., additional, Gerstenfeld, Edward P., additional, Gold, Michael R., additional, Goldberger, Jeffrey J., additional, Grandi, Eleonora, additional, Gray, Richard A., additional, Groh, William J., additional, Grubb, Blair P., additional, Haissaguerre, Michel, additional, Hake, Johan, additional, Halperin, Henry R., additional, Harris, Louise, additional, Hatem, Stéphane, additional, Hayes, David L., additional, Hocini, Meleze, additional, Hohnloser, Stefan H., additional, Holmes, David Richard, additional, Hoshijima, Masahiko, additional, Hu, Yuxuan, additional, Hund, Thomas J., additional, Hutchinson, Mathew D., additional, Hwang, Hye Jin, additional, Ideker, Raymond E., additional, Ilkhanoff, Leonard, additional, Ingles, Jodie, additional, Jackman, Warren M., additional, Jais, Pierre, additional, Jalife, José, additional, Jhun, Bong Sook, additional, John, Roy M., additional, Jongbloed, Monique, additional, Josephson, Mark E., additional, Kadish, Alan H., additional, Kalifa, Jérôme, additional, Kalman, Jonathan M., additional, Kamp, Timothy J., additional, Kanj, Mohamed Hani, additional, Karabin, Beverly, additional, Kass, Robert S., additional, Katritsis, Demosthenes G., additional, Kaur, Kuljeet, additional, Kim, Jong J., additional, Kirchhof, Paulus, additional, Kléber, André G., additional, Klein, George J., additional, Kohl, Peter, additional, Kolandaivelu, Aravindan, additional, Krahn, Andrew D., additional, Krumerman, Andrew, additional, Kumar, Saurabh, additional, Kuck, Karl-Heinz, additional, Lakatta, Edward G., additional, Latchamsetty, Rakesh, additional, Lau, Dennis H., additional, Lerman, Bruce B., additional, Leroy, Jérôme, additional, Lewis, William R., additional, Lin, Shien-Fong, additional, Link, Mark S., additional, Liu, Christopher F., additional, Lockwood, Deborah J., additional, Loh, Peter, additional, Lopatin, Anatoli N., additional, Lopshire, John C., additional, Lubitz, Steven A., additional, Madias, Christopher, additional, Mahajan, Aman, additional, Makielski, Jonathan C., additional, Malik, Marek, additional, Maltsev, Victor A., additional, Marchlinski, Francis E., additional, Marelli, Ariane J., additional, Markowitz, Steven M., additional, Maron, Barry J., additional, Martens, Jeffrey R., additional, Marx, Steven O., additional, McCulloch, Andrew D., additional, Metzner, Andreas, additional, Michailova, Anuska P., additional, Miller, John Michael, additional, Milstein, Michelle Lynne, additional, Mohler, Peter, additional, Morady, Fred, additional, Myerburg, Robert J., additional, Nakagawa, Hiroshi, additional, Napolitano, Carlo, additional, Narayan, Sanjiv M., additional, Natale, Andrea, additional, Nattel, Stanley, additional, Nazarian, Saman, additional, Nerbonne, Jeanne M., additional, Ng, Fu Siong, additional, Nogami, Akihiko, additional, Noujaim, Sami F., additional, Olshansky, Brian, additional, Oral, Hakan, additional, O-Uchi, Jin, additional, Ouyang, Feifan, additional, Ozcan, Cevher, additional, Packer, Douglas L., additional, Pahlm, Olle, additional, Pandit, Sandeep V., additional, Park, David S., additional, Pitt, Geoffrey S., additional, Po, Sunny S., additional, Priori, Silvia G., additional, Rappel, Wouter-Jan, additional, Reddy, Vivek Y., additional, Robertson, Jason O., additional, Robinson, Richard B., additional, Roden, Dan M., additional, Rose, Robert A., additional, Rosen, Michael R., additional, Rosso, Raphael, additional, Rudy, Yoram, additional, Ruskin, Jeremy N., additional, Sabbah, Hani N., additional, Sachse, Frank B., additional, Saint, Lindsey L., additional, Saiz, Javier, additional, Sánchez-Chapula, José A., additional, Sanders, Prashanthan, additional, Sanguinetti, Michael C., additional, Santangeli, Pasquale, additional, Sarquella-Brugada, Georgia, additional, Satin, Jonathan, additional, Schalij, Martin Jan, additional, Scherlag, Benjamin J., additional, Schimpf, Rainer, additional, Schmidt, Georg, additional, Schwartz, Peter J., additional, Semsarian, Christopher, additional, Shah, Ashok J., additional, Shaw, Robin, additional, Sheu, Shey Shing, additional, Shivkumar, Kalyanam, additional, Skanes, Allan C., additional, Somers, Virend K., additional, Stambler, Bruce S., additional, Stein, Adam B., additional, Stevenson, Lynne Warner, additional, Stevenson, William G., additional, Sun, Jian, additional, Sutton, Richard, additional, Sweeney, Michael O., additional, Swerdlow, Charles, additional, Tamargo, Juan, additional, Tandri, Harikrishna, additional, Tawil, Rabi, additional, Tedrow, Usha, additional, Terrenoire, Cecile, additional, Tobón, Catalina, additional, Towbin, Jeffrey A., additional, Trayanova, Natalia A., additional, Tristani-Firouzi, Martin, additional, Trohman, Richard G., additional, Tseng, Zian H., additional, Turakhia, Mintu P., additional, Vaidyanathan, Ravi, additional, Valdivia, Héctor H., additional, Valiunas, Virginijus, additional, van der Heyden, Marcel A.G., additional, van der Werf, Christian, additional, Van, George F., additional, Vaseghi, Marmar, additional, Veltmann, Christian, additional, Vetter, Victoria L., additional, Viskin, Sami, additional, Voigt, Niels, additional, Vos, Marc A., additional, Wagner, Galen S., additional, Wang, Paul J., additional, Weerasooriya, Rukshen, additional, Wilde, Arthur A.M., additional, Wilkoff, Bruce L., additional, Wissner, Erik, additional, Woo, Y. Joseph, additional, Yamazaki, Masatoshi, additional, Yang, Felix, additional, Yaniv, Yael, additional, Yap, Sing-Chien, additional, Yee, Raymond, additional, Zarzoso, Manuel, additional, Zeppenfeld, Katja, additional, and Zipes, Douglas P., additional

Published
2014
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42. Enhancement of piscine orthoreovirus-2 DNA vaccine potency by linkage of antigen gene to a trigger factor gene or signal peptide genes

Author

Matsuyama, Tomomasa, primary, Takano, Tomokazu, additional, Honjo, Miho, additional, Kikuta, Takumi, additional, Nawata, Akatsuki, additional, Kumagai, Akira, additional, Honda, Ryo, additional, Sakai, Takamitsu, additional, Kurita, Jun, additional, Terashima, Sachiko, additional, Yamazaki, Masatoshi, additional, Matsuura, Yuta, additional, Nishizawa, Yuko, additional, and Nakayasu, Chihaya, additional

Published
2021
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43. Moderate hypothermia increases the chance of spiral wave collision in favor of self-termination of ventricular tachycardia/fibrillation

Author

Harada, Masahide, Honjo, Haruo, Yamazaki, Masatoshi, Nakagawa, Harumichi, Ishiguro, Yuko S., Okuno, Yusuke, Ashihara, Takashi, Sakuma, Ichiro, Kamiya, Kaichiro, and Kodama, Itsuo

Subjects
Hypothermia -- Risk factors, Hypothermia -- Measurement, Ventricular fibrillation -- Risk factors, Ventricular fibrillation -- Care and treatment, Ventricular fibrillation -- Prevention, Ventricular fibrillation -- Research, Biological sciences
Abstract

In cardiac arrest due to ventricular fibrillation (VF), moderate hypothermia (MH,33[degrees]C) has been shown to improve defibrillation success compared with normothermia (NR, 37[degrees]C) and severe hypothermia (SH, 30[degrees]C). The underlying mechanisms remain unclear. We hypothesized that MH might prevent reentrant excitations rotating around functional obstacles (rotors) that are responsible for the genesis of VF. In two-dimensional Langendorff-perfused rabbit hearts prepared by cryoablation (n = 13), action potential signals were recorded by a high-resolution optical mapping system. During basic stimulation (2.5-5.0 Hz), MH and SH caused signifcant prolongation of action potential duration and significant reduction of conduction velocity. Wavelength was unchanged at MH, whereas it was shortened significantly at SH at higher stimulation frequencies (4.0-5.0 Hz). The duration of direct current stimulation-induced ventficular tachycardia (VT)/VF was reduced dramatically at MH compared with NR and SH. The spiral wave (SW) excitations documented during VT at NR were by and large organized, whereas those during VT/VF at MH and SH were characterized by disorganization with frequent breakup. Phase maps during VT/VF at MH showed a higher incidence of SW collision (mutual annihilation or exit from the anatomical boundaries), which caused a temporal disappearance of phase singularity points (PS-0), compared with that at NR and SH. There was an inverse relation between PS-0 period in the observation area and VT/VF duration. MH data points were located in a longer PS-0 period and a shorter VT/VF duration zone compared with SH. MH causes a modification of SW dynamics, leading to an increase in the chance of SW collision in favor of self-termination of VT/VF. optical mapping; ventricular fibrillation

Published
2008

44. Altered expression of connexin43 contributes to the arrhythmogenic substrate during the development of heart failure in cardiomyopathic hamster

Author

Sato, Takashi, Ohkusa, Tomoko, Honjo, Haruo, Suzuki, Shinsuke, Yoshida, Masa-aki, Ishiguro, Yuko S., Nakagawa, Harumichi, Yamazaki, Masatoshi, Yano, Masafumi, Kodama, Itsuo, and Matsuzaki, Masunori

Subjects
Membrane proteins -- Health aspects, Membrane proteins -- Genetic aspects, Arrhythmia -- Development and progression, Arrhythmia -- Risk factors, Phosphorylation -- Health aspects, Phosphorylation -- Evaluation, Biological sciences
Abstract

Heart failure is known to predispose to life-threatening ventricular tachyarrhythmias even before compromising the systemic circulation. but the underlying mechanism is not well understood. The aim of this study was to clarify the connexin43 (Cx43) gap junction remodeling and its potential role in the pathogenesis of arrhythmias during the development of heart failure. We investigated stage-dependent changes in Cx43 expression in UM-X7.1 cardiomyopathic hamster hearts and associated alterations in the electrophysiological properties using a high-resolution optical mapping system. UM-X7.1 hamsters developed left ventricular (LV) hypertrophy by ages 6-10 wk and showed a moderate reduction in LV contractility at age 20 wk. Appreciable interstitial fibrosis was recognized at these stages. LV mRNA and protein levels of Cx43 in UM-X7.1 were unaffected at age 10 wk but significantly reduced at 20 wk. The expression level of Ser255-phosphorylated Cx43 in UM-X7.1 at age 20 wk was significantly greater than that in control golden hamsters at the same age. In UM-X7.1 at age 10 wk, almost normal LV conduction was preserved, whereas the dispersion of action potential duration was significantly increased. UM-X7.1 at age 20 wk showed significant reduction of cardiac space constant, significant decrease in conduction velocity, marked distortion of activation fronts, and pronounced increase in action potential duration dispersion. Programmed stimulation resulted in sustained ventricular tachycardia or fibrillation in UM-X7.1. LV activation during polymorphic ventricular tachycardia was characterized by multiple phase singularities or wavebreaks. During the development of heart failure in the cardiomyopathic hamster, alterations of Cx43 expression and phosphorylation in concert with interstitial fibrosis may create serious arrhythmogenic substrate through an inhibition of cell-to-cell coupling. cardiomyopathy; ventricular arrhythmia; optical mapping; phosphorylation

Published
2008

46. Mechanisms of destabilization and early termination of spiral wave reentry in the ventricle by a class III antiarrhythmic agent, nifekalant

Author

Yamazaki, Masatoshi, Honjo, Haruo, Nakagawa, Harumichi, Ishiguro, Yuko S., Okuno, Yusuke, Amino, Mari, Sakuma, Ichiro, Kamiya, Kaichiro, and Kodama, Itsuo

Subjects
Potassium channels -- Research, Ventricular tachycardia -- Causes of, Anti-arrhythmia drugs -- Usage, Biological sciences
Abstract

Nifekalant (NF) is a novel class III antiarrhythmic agent that is effective in preventing life-threatening ventricular tachycardia/ fibrillation (VT/VF). We investigated mechanisms of destabilization and early termination of spiral-type reentrant VT by NF in a two-dimensional subepicardial myocardial layer of Langendorff-perfused rabbit hearts (n = 21) using a high-resolution optical action potential mapping system. During basic stimulation, NF (0.1 [micro]M) caused uniform prolongation of action potential duration (APD) without affecting conduction velocity and an increase of APD restitution slope. VTs induced by direct current stimulation in the presence of NF were of shorter duration (VTs > 30 s: 2/54 NF vs. 19/93 control). During VTs in control (with visible rotors), the wave front chased its own tail with a certain distance (repolarized zone), and they seldom met each other. The average number of phase singularity (PS) points was 1.31 [+ or -] 0.14 per 665 ms (n = 7). In the presence of NF, the wave front frequently encountered its own tail, causing a transient breakup of the spiral wave or sudden movement of the rotation center (spatial jump of PS). The average number of PS was increased to 1.63 [+ or -] 0.22 per 665 ms (n = 7, P < 0.05) after NF. The mode of spontaneous termination of rotors in control was in most cases (9/10, 90.0%) the result of mutual annihilation of counterrotating wave fronts. With NF, rotors frequently terminated by wave front collision with the atrioventricular groove (12/19, 63.2%) or by trapping the spiral tip in a refractory zone (7/19, 36.8%). Destabilization and early termination of spiral wave reentry induced by NF are the result of a limited proportion of excitable tissue after modulation of repolarization. potassium channel blocker; optical mapping; ventricular tachycardia

Published
2007

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