Joint symbolic dynamics analysis of heart rate and systolic blood pressure interactions in dilated cardiomyopathy

The dilated cardiomyopathy (DCM) induces important changes in the autonomic control. Measures of heart rate (HR) variability and systolic blood pressure (SP) variability are sensitive to those changes. The interactions between HR and SP are rather complex and strongly non-linear. We introduced the joint symbolic dynamics (JSD) as a new short-term high resolution non-linear analysis method to investigate the complex interactions between HR and SP. Continuous non-invasive 30 minutes blood pressure recordings (Portapres) of 25 patients with DCM and 27 healthy controls (CON) were analyzed. HR and SP were extracted from the blood pressure time series on a beat-to-beat basis. Using the concept of JSD, HR and SP dynamics were transformed into a bivariate symbol vector. Subsequently, this symbol vector was transformed into a word series (words consisting of three successive symbols) and the probability of occurrence of each word type was calculated and compared between both groups. We found significant differences (partly p < 0.01) in six word types between DCM and CON. JSD provides an efficient non-linear presentation of HR and SP interactions that offer rather simple physiological interpretations and seems to be particularly suitable for risk stratification in patients with dilated cardiomyopathy.