Heart rate complexities assessed by short binary symbolic patterns

On large time scales the heart rate dynamics of healthy subjects is more complex than in patients with congestive heart failure (CHF). On a beat-to-beat basis reflecting acceleration and deceleration of heart rate the healthy heart rate dynamics can also be regular whereas CHF patients show less regularity. In this study, we investigated the impact of two pattern lengths on symbolic dynamics analysis. Holter ECGs from 30 healthy subjects and 15 CHF patients were analyzed with respect to the regularity of binary sequences of length 4 and 8. The regularity of the binary patterns was quantified using Approximate Entropy (ApEn). In essence, both pattern lengths showed similar results. Regular binary patterns were observed more often in healthy subjects whereas CHF patients showed mostly one particular regular binary pattern. Hence, even very short binary patterns can be used to assess dynamical aspects of heart rate variability.