Long- and short-time analysis of heartbeat sequences: Correlation with mortality risk in congestive heart failure patients

Abstract

We analyze RR heartbeat sequences with a dynamic model that satisfactorily reproduces both the long-and the short-time statistical properties of heart beating. These properties are expressed quantitatively by means of two significant parameters, the scaling ␦ concerning the asymptotic effects of long-range correlation, and the quantity 1Ϫ establishing the amount of uncorrelated fluctuations. We find a correlation between the position in the phase space (␦,) of patients with congestive heart failure and their mortality risk. The main purpose of this Brief Report is twofold. The first goal is to afford a firmer theoretical basis to the method of analysis of heartbeating proposed in an earlier publication ͓1͔. The second goal is to substantiate with more convincing arguments that this method yields an efficient criterion to estimate the mortality risk of congestive heart failure ͑CHF͒ patients.To prove this significant diagnostic property, we illustrate the relevant clinical data, missing in the earlier publication, and we limit ourselves to affording only this kind of ''experimental'' information. For other details, already adequately illustrated in the earlier publication, we refer the interested reader to Ref. ͓1͔. For this study we considered 13 male CHF patients, from a study base of 320 subjects, who experienced cardiac death during a follow-up of 26 months ͑average 19 months, median 22 months͒. Inclusion criteria were absence of pulmonary or neurological disease, absence of acute myocardial infarction or cardiac surgery within the previous six months, absence of any other disease limiting survival, stable therapy for at least two weeks, and good quality 24-h Holter recordings, with an ectopy rate less than 5%. A comparable number of control subjects ͑16 patients͒, matching for age, sex, NYHA class ͑a functional and therapeutic classification for prescription of physical activity for cardiac patients͒, and etiology, was then selected. These latter patients did not experience cardiac death after follow-up. All patients had a 24-h Holter recording at baseline, together with standard functional evaluation including measurement of left ventricular ejection fraction, peak VO2 (O 2 consumption during effort͒, and sodium ͑Na͒. Finally, RR series for 10 healthy subjects were taken from the Nonlinear Time Series Analysis ͑NOLTISALIS͒ archive ͓2͔.

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