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Loss of lag-response curvilinearity of indices of heart rate variability in congestive heart failure

BioMed Central
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Abstract ral ss BioMed CentBMC Cardiovascular Disorders Open AcceResearch article Loss of lag-response curvilinearity of indices of heart rate variability in congestive heart failure Tushar P Thakre1,2 and Michael L Smith*1 Address: 1Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth, Texas, USA and 2Lata Medical Research Foundation, Nagpur, India Email: Tushar P Thakre - [email protected]; Michael L Smith* - [email protected] * Corresponding author Abstract Background: Heart rate variability (HRV) is known to be impaired in patients with congestive heart failure (CHF). Time-domain analysis of ECG signals traditionally relies heavily on linear indices of an essentially non-linear phenomenon. Poincaré plots are commonly used to study non-linear behavior of physiologic signals. Lagged Poincaré plots incorporate autocovariance information and analysis of Poincaré plots for various lags can provide interesting insights into the autonomic control of the heart. Methods: Using Poincaré plot analysis, we assessed whether the relation of the lag between heart beats and HRV is altered in CHF. We studied the influence of lag on estimates of Poincaré plot indices for various lengths of beat sequence in a public domain data set (PhysioNet) of 29 subjects with CHF and 54 subjects with normal sinus rhythm. Results: A curvilinear association was observed between lag and Poincaré plot indices (SD1, SD2, SDLD and SD1/SD2 ratio) in normal subjects even for a small sequence of 50 beats (p value for quadratic term 3 × 10-5, 0.002, 3.5 × 10-5 and 0.0003, respectively). This curvilinearity was lost in patients with CHF even after exploring sequences up to 50,000 beats (p values for quadratic term > 0.5). Conclusion: Since lagged Poincaré plots incorporate autocovariance information, these analyses provide insights into the autonomic control of heart rate that is influenced by the non-linearity of the signal. The differences in lag

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