Fibrillation of a cardiac region and the tachycardia mode of a two-oscillator system.

The interaction between two nonlinear oscillators is discussed, each one representing a region of the heart and characterized by a specific type of phase transition curve (PTC) which has been derived from human ECG-recordings. Besides the normal conduction a tachycardia mode is studied where the excitation is reflected by each oscillator (reentry). It turns out that under specific physiologically plausible conditions this tachycardia mode cannot be terminated by an external stimulus. Under periodic stimulation the response of the tachycardia mode is chaotic. Within a sheet of nonlinear oscillators the tachycardia mode serves as an ectopic focus or a region of reentry which induces fibrillation of the whole tissue.