"Restitution Properties and Stability of Response Patterns in Cardiac Muscle"

Soma Sau, Wanda Krassowska (Department of Biomedical Engineering), Daniel Gauthier (Department of Physics, Duke University)


We will present experimental evidence demonstrating that the restitution properties of cardiac muscle do not
determine the stability of the response pattern to periodic stimuli as previously believed. Bullfrog ventricular
tissue is periodically paced for a fixed time interval. This is repeated as the basic cycle length (BCL) is
decrementally swept from longer to shorter values. Action potential duration (APD) and preceding diastolic
interval (DI) are measured at each BCL. It is known that the tissue initially responds to such pacing with a 1:1
pattern, but as the BCL becomes shorter, the 1:1 response becomes unstable and action potentials alternate
in amplitude and duration. From theory based on 1-d return maps, it is believed that this bifurcation occurs at
the point where the slope of the associated restitution curve (APD vs. DI) exceeds one. In our in-vitro
experiments, the tissue responded with a stable 1:1 pattern even as the slope of the restitution curve
exceeded one, indicating that tissue dynamics are not governed solely by the restitution properties of the


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Last Modified:  28-Mar-02