"Suppressing Alternans in Small Pieces of Periodically-Paced
Daniel J. Gauthier and G. Martin Hall
Duke University, Department of Physics, Department of Biomedical Engineering,
and Center for Nonlinear and Complex Systems, Durham, North Carolina 27708,
Alternans is a periodic rhythm in which the action potential duration alternate;
spcifically, a short action potential is followed by a long action potential.
It is important to understand the suppression of alternans in myocardium
because the myocardium is the primary substrate for fibrillation and it
is believed that alternans can trigger the onset of fibrillation.
In a systematic approach to controlling heart muscle dynamics, we have
developed an in vitro animal model of alternans consisting of a small piece
of periodically-paced bullfrog (Rana catesbeiana) myocardium and use it
to test and optimize closed-loop feedback methods controlling alternans.
We demonstrate that alternans can be suppressed experimentally by making
minute adjustments to the pacing period using a pacing protocal motivated
by chaos control techniques. The size of the adjustments is determined
by comparing real-time measurements of the action potential duration with
the duration of previous action potentials. We map out the range
of feedback parameters that stabilize the desired state, demonstrate the
adaptability of the controller to adjust to tissue-parameter drift, and
consider restrictions to the control algorithm that may be important for
Last Modified: 28-Mar-02