Methods of Non-Linear Dynamics

Noninvasive risk stratification of patients post myocardial infarction has gained renewed interest, since prophylactic therapy for sudden cardiac death has primarily to consider the expensive and invasive therapy with the implantable cardioverter/defibrillator 25. In addition to left ventricular ejection fraction and number of ventricular extrasystoles 3, measures of heart rate variability (HRV) are often used for risk stratification. HRV is usually analyzed in the time and frequency domain 4 17 22. These methods describe the linear correlations in HRV. In addition, nonlinear components in HRV have been demonstrated 20 16 7 and are being explored for improvement of risk prediction 13 29 32. In this article, we briefly review methods that have been used to describe and/or quantify nonlinear components in HRV. Methods using symbolic dynamics are presented elsewhere in this book.