Characterization of heart rate variability using a nonlinear model

The heart rate variability is investigated using a two dimensional nonlinear model. The time series of the RR-intervals as obtained from 24-h-Holter-ECG monitoring is transferred to a trajectory in a 2D phase space. This trajectory is centered along the bisector in the case of healthy subjects, but covers the main part of the quadrant, if patients with complex arrhythmias are investigated. The box dimension is a quantitative measure of the geometric complexity of the trajectory and reflects the underlying heart dynamics. Patients with absolute arrhythmias in combination with atrial flutter have box dimensions greater than 1.68 whereas healthy subjects exhibit values less than 1.68.