Reentrant arrhythmias in cardiac tissue

In the healthy heart, electrical stimuli are generated at the sinus node in the right atrium, propagate over the heart, and cause the heart to contract uniformly.  Then the heart rests until the sinus node generates the next stimulus.  During a reentrant arrhythmia, electrical waves move around in the heart in a circular fashion.  The heart does no more contract uniformly and it also does not rest as a whole anymore. Reentrant arrhythmias in the ventricles are dangerous and often fatal, in the atria they constitute a serious disease. 

We study reentrant arrhythmias in experiments and simulations.  In experiments, we isolate cardiac tissue from animals and make electrical excitation visible using a dye.  Then we record the surface activity with cameras.  In simulations, we use mathematical models of cardiac cells to create virtual networks of heart cells or even virtual pieces of tissue.  Mathematical models provide perfect data acquisition and complete control, allowing us to test hypotheses on the mechanisms of arrhythmias that we derive from experiments. 

           

A spiral-shaped wave of exciation in a sheep heart, made visible using a fluorescent dye.

 

   Simulation of Defibrillation in a block of cardiac tissue. Initially, a single scroll wave is rotating around its filament (red). The shock destabilizes the wave and changes the filament. After the shock, the filament contracts until it finally disappears.