Multistable spatiotemporal patterns of cardiac activity

Abstract

One thing is certain. Between now and some time in the future, let's say within the next 60 years for most of you, your heart will undergo a transition from its current behavior, which is pumping adequate amounts of blood to your brain, to a different behavior that leads to inadequate pumping of blood and subsequent death. The terminal cardiac rhythm of the heart is usually ventricular fibrillation, a rhythm in which the main pumping chambers of the heart, the ventricles, do not exhibit the coordinated contractions needed to pump blood effectively. Several hundred thousand people each year in the U.S. experience unexpected “sudden cardiac death” (1). Fig. 1 is an example in an 82-year-old woman with heart failure who was wearing a portable (Holter) heart monitor recording her electrocardiogram at the time of death. Fig. 1 shows a variety of different rhythms, including normal sinus beats (N), abnormal premature ventricular ectopic beats (V), nonsustained ventricular tachycardia (NSVT) consisting of short sequences of abnormally rapid ventricular beats, and rapid sustained ventricular tachycardia (VT). Shortly after the end of this recording, there is a second transition to ventricular fibrillation, leading to the death of the individual. These data are recorded from the surface of the body, and it is not possible to know the spatiotemporal pattern of cardiac activity during these arrhythmias. The ventricular beats may arise from an abnormal localized focus, they may be associated with excitation traveling in a reentrant path, or they may arise from a combination of both mechanisms (2, 3). Recordings of cardiac activity using voltage-sensitive dyes in mammalian hearts have documented circulating reentrant spiral waves. These provide a possible physiological basis for ventricular fibrillation and for some types of ventricular tachycardia (4- …