PHYSICAL MATHEMATICS SEMINAR

TITLE:	ORIGIN AND CONTROL OF DISCORDANT ALTERNANS, 
	A PRECURSOR TO SUDDEN CARDIAC DEATH


SPEAKER:	ALAIN KARMA
		Department of Physics and Center for 
		Interdisciplinary Research on Complex Systems
		Northeastern University

ABSTRACT: 

Cardiac fibrillation is the leading cause of death in the US. However, 
paradoxically, no good therapy exists to cope with this major health 
problem aside from the delivery of a large electrical shock after the 
onset of fibrillation. In this talk, I will describe recent experimental 
and theoretical progress made in understanding a new route to electrical 
turbulence in the heart. This route involves the spontaneous compartmentalization 
of the heart into cm scale spatial domains of different phases of alternans, 
i.e. spatial domains of different phases of period-doubling oscillations of the 
refractory period of cardiac cells, that are very analogous to ferromagnetic 
domains.  This state of "discordant alternans" is often a precursor to fibrillation 
because sharp changes of refractory periods near domain boundaries produce 
wave breaks followed by spatiotemporal chaos.  The main finding is that this state 
originates from a new type of finite-wavenumber pattern-forming linear instability.  
In particular, the natural lengthscale of out-of-phase domains of alternans emerges 
from the competition between the stabilizing effect of the local diffusive coupling 
between cells, and the nonlocal destabilizing effect of dephasing mediated by 
propagating pulses. The rest of the talk will describe how this theoretical 
understanding can be applied to design feedback control schemes to 
suppress alternans, and hence to potentially prevent the onset of fibrillation 
with low voltage stimuli. Comparisons between simulations, theory, 
and experiments will be emphasized.  


TUESDAY, NOVEMBER 25, 2003, 2:30 pm, Building 2, Room 338

Refreshments will be served at 3:30 PM in Room 2-349

Massachusetts Institute of Technology, Department of Mathematics, Cambridge, MA  02139