Noise Effects on the Complex Patterns of Abnormal Heartbeats
  Patients at high risk for sudden death often exhibit complex heart rhythms in which abnormal heartbeats are interspersed with normal heartbeats. We analyze such a complex rhythm in a single patient over a 12-hour period and show that the rhythm can be described by a theoretical model consisting of two interacting oscillators with stochastic elements. By varying the magnitude of the noise, we show that for an intermediate level of noise, the model gives best agreement with key statistical features of the dynamics. 
Verena Schulte-Frohlinde (1), Yosef Ashkenazy (1), Plamen Ch. Ivanov   (1), Leon Glass (2), Ary L. Goldberger (3), and H. Eu...