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| Wednesday, January 3 — Session 1: Cardiac Dynamics |
| 1:10-1:50 pm |
Leon Glass
Department of Physiology, McGill University
Email: glass@cnd.mcgill.ca
Predicting and Preventing Sudden Cardiac Death
Sudden cardiac death kills hundreds of thousands of North Americans each year. This number could be reduced significantly if a medical device - the implantable cardiac defibrillator - had been implanted prior to the sudden death. However, since we do not have good ways of predicting who will suffer sudden cardiac death or when, physicians face a major problem in deciding in whom to implant a cardiac defibrillator. This problem is made more severe since implantable
cardiac defibrillators are expensive, and complications, though rare, do add to the risk of using the devices in those who would not benefit. In this talk I will describe attempts to understand cardiac
arrhythmias - especially those responsible for sudden cardiac death. The methods include analysis of electrocardiographic records of patients who experienced sudden cardiac death, analysis of arrhythmias in German Shepherd dogs that experience sudden cardiac death, recording activity in tissue culture models of cardiac arrhythmias, and the formulation of mathematical models of cardiac arrhythmia employing a range of techniques from number theory to nonlinear dynamics. |
| 1:50-2:10 pm |
Carolyn Berger
Dept. of Physics and Center for Nonlinear and Complex Systems
Email: cberger@phy.duke.edu
authors: Carolyn M. Berger, Xiaopeng Zhao, Dept. of Biomedical Engineering and Center for Nonlinear and Complex Systems,David G. Schaeffer, Dept. of Mathematics and Center for Nonlinear and Complex Systems, Hana M. Dobrovolny, Dept. of Physics, Wanda Krassowska, Dept. of Biomedical Engineering and Center for Nonlinear and Complex Systems, Daniel J. Gauthier, Dept. of Physics, Dept. of Biomedical Engineering and Center for Nonlinear and Complex Systems, Duke University, North Carolina, 27708 USA
Evidence for an unfolded border-collision bifurcation in paced cardiac tissue
We investigate, both experimentally and theoretically, the bifurcation to alternans in heart tissue. Previously, this phenomenon has been modeled either as a smooth or as border-collision period-doubling bifurcation. Using a new experimental technique, we find a hybrid behavior: very close to the bifurcation point the dynamics is smooth-like, whereas further away it is border-collision-like. The essence of this behavior is captured by a model that exhibits an unfolded border-collision bifurcation. |
| 2:10-2:30 pm |
Yue-Kin Tsang
Scripps Institution of Oceanography, UCSD
Email: yktsang@ucsd.edu
authors: Emily S. C. Ching, Department of Physics, The Chinese University of Hong Kong, *Yue-Kin Tsang, Scripps Institution of Oceanography, University of California, San Diego
Multifractality in detrended human heart beat increments
We study time series b(i) of human heart beat interval (RRi) and consider the random variable S which is the sum of any n consecutive b(i)'s. We found that the shape of the probability density function (PDF) of S is independent of n. This result is used to understand a detrend procedure employed in a study of multifractality of RRi based on the PDF of heart rate increment. We also investigate the multifractality in both healthy and pathologic data set using the structure function of heart rate increment, comparison to the analysis of turbulent convection data will be made. |
| 2:30-3:10 pm |
Wanda Krassowska
Department of Biomedical Engineering, Duke University
Email: wanda.krassowska@duke.edu
authors: Wanda Krassowska, Ph.D.; Soma S. Kalb, Ph.D., Division of Physics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, Food and Drug Administration; Daniel J. Gauthier, Ph.D., Departments of Physics and Biomedical Engineering, Duke University; David G. Schaeffer, Ph.D., Department of Mathematics, Duke University
The Restitution Portrait: A Tool for Developing Models of Heart Rhythm Dynamics
An accurate model of heart rhythm dynamics is a prerequisite for the development of clinical criteria that can predict the onset of heart rhythm instabilities and thus prevent life-threatening cardiac arrhythmias. Traditionally, the stability of heart rhythm was believed to depend on electrical restitution, which relates the duration of cardiac action potential (APD) to the changes in pacing rate. However, recent studies demonstrate that stability also depends on long-term APD changes caused by memory. Our group has developed a novel method for simultaneous visualization of the rate- and memory-dependent aspects of restitution, the "restitution portrait." The restitution portrait gives a comprehensive assessment of the cardiac response to pacing and thus provides a stringent test for models of heart rhythm dynamics. Examples will show that models developed with the restitution portrait better reflect rhythm dynamics than models developed with methods used to date. The restitution portrait-based approach might also be useful for characterizing the dynamics of other biological systems with memory.
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