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SUMMARY:Applying Nonlinear Dynamics in Medicine to Understand Cardiac Arrh
 ythmias and Epilepsy - Dr Jennifer Simonotto
DTSTART:20060519T100000Z
DTEND:20060519T110000Z
UID:TALK5010@talks.cam.ac.uk
CONTACT:vh233
DESCRIPTION:Cardiac arrhythmias and Epilepsy\, at first glance\, seemingly
  have nothing in common besides the fact that they both conditions that ar
 e characterized by a sudden onset of irregular activity in the heart and b
 rain\, respectively\, and that current treatments are not optimal at contr
 olling onset.\n\nEpilepsy affects 3-5% of the population worldwide\, affec
 ting persons indiscriminately of age\, sex or race. In the vast majority o
 f cases\, seizures arise from medial temporal structures that have been da
 maged months to years before onset of seizures. By characterizing the late
 nt development of epilepsy from traumatic insult to onset in the chronic l
 imbic epilepsy rat model (a realistic animal model for human temporal lobe
  epilepsy and epileptogenesis)\, essential relationships between onset pat
 hology and remodeling of the neural tissue can be determined. It has been 
 found that the 0-200 Hz inter-hemispherical communication is supressed in 
 stimulated\, but not non-stimulated animals.\n\nSudden cardiac death is a 
 major health issue. It accounts for more than 300\,000 deaths annually in 
 North America and is the leading cause of death in people aged 20 to 64 ye
 ars. In one sense\, sudden cardiac death can be considered an electrical a
 ccident\, representing a tragic interplay between anatomic and functional 
 substrates modulated by the transient events that perturb the balance. Mos
 t such incidents involve ventricular fibrillation (VF) with electrical def
 ibrillation its only therapy. The events surrounding the onset of fibrilla
 tion in humans\, even after 50 years of study\, remain fairly opaque. Usin
 g cardiac optical mapping\, we experimentally record defibrillation failur
 e on perfused porcine hearts to understand the underlying dynamics and dev
 elop a method of assessing orderedness for a lower energy successful defib
 rillation shock.\n\nLastly\, cardiac ablation is being increasingly used t
 o interdict the complex propagation of excitatory waves during atrial fibr
 illation. While such procedures are clearly useful\, they can often fail. 
 In order to understand this failure\, we use optical methods to observe th
 e electrical activity of an ablated porcine heart. We find that ablation l
 ines do attenuate cardiac waves\, but the attenuation is not complete. Ins
 tead a remnant of the wave incident upont the ablation barrier survives pa
 ssage through it\, albeit as a subthreshold signal. More importantly we ha
 ve found that these subthreshold signals may add constructively and thereb
 y dynamically reduce the effective attenuation\, an effect which we call d
 ynamic transmurality. We suspect this as a factor in the persistence of ar
 rhythmia after ablative procedures. 
LOCATION:Small Lecture Theature\, Cavendish Laboratory\, Department of Phy
 sics
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