Blood pressure variability as sign of autonomic imbalance in patients with idiopathic dilated cardiomyopathy.

BACKGROUND: The problem of identifying idiopathic dilated cardiomyopathy (IDC) patients who are at risk of sudden death is still unsolved. The presence of autonomic imbalance in patients with IDC might predict sudden death and tachyarrhythmic events. The aim of this study was to analyze the suitability of blood pressure variability (BPV) compared to heart rate variability (HRV) for noninvasive risk stratification in IDC patients. METHODS: Continuous noninvasive blood pressure and high-resolution electrocardiogram were recorded from 91 IDC patients for 30 minutes. During a median follow-up period of 28 months (range: [17-38] months), 14 patients died due to sudden death or necessary resuscitation due to a life-threatening arrhythmia. HRV and BPV analyses were performed in time domain, frequency domain, and nonlinear dynamics. Using the Mann-Whitney U test and Cox regression, we estimated the accuracy of clinical and nonclinical parameters in discriminating high-risk from low-risk patients. RESULTS: Dynamics of blood pressure regulation was significantly changed in high-risk patients, indicating an increased BPV. BPV indexes from nonlinear symbolic dynamics revealed significant univariate (sensitivity: 85.7%; specificity 77.9%; area under receiver-operator characteristics [ROC] curve: 87.8%) differences. In an optimum multivariate set consisting of two clinical indexes (left ventricular end-diastolic diameter, New York Heart Association) and one nonlinear index (symbolic dynamics), highly significant differences between low- and high-risk IDC groups were estimated (sensitivity of 92.9%, specificity of 86.5%, and area under ROC curve of 95.3%). CONCLUSION: Diastolic BPV indexes, especially those from symbolic dynamics, appear to be useful for risk stratification of sudden death in patients with IDC.

Peripheral arterial disease alters heart rate variability in cardiovascular patients.

BACKGROUND: Autonomic regulation analysis is useful in risk stratification of ventricular tachycardia and sudden cardiac death in chronic heart failure (CHF). Heart rate variability (HRV) reflects the condition of autonomic regulation. For analyzing the autonomic control the whole cardiovascular system has to be considered. Therefore, the aim of our study was to assess the influence of peripheral arterial disease (PAD) on the autonomic regulation. METHODS: In 53 men (age: 67 +/- 11 years) from the cardiovascular unit we compared standard HRV parameters in 27 with (ankle brachial index, ABI < 0.9) and 26 patients without (ABI >0.9) PAD as well as with 12 healthy subjects as reference. High-resolution electrocardiograms were recorded over 30 minutes under resting conditions. Pulse wave velocity as well as ABI was estimated using the vascular screening system VASERA. RESULTS: In cardiac patients with PAD, we found both significant differences in linear and nonlinear HRV parameters. Higher increase of low-than high-frequency components indicated higher elevated sympathetic than vagal activation. Altered autonomic control can be interpreted as a compensatory mechanism for diminished vascular arteriolar vasodilator capacity in PAD. To maintain the arterial blood pressure, an elevated setpoint of sympathovagal balance is required. CONCLUSIONS: Our data indicate PAD alters the HRV in cardiovascular patients. PAD should be considered in the assessment of cardiac autonomic regulation especially in risk stratification.

Multivariate and multidimensional analysis of cardiovascular oscillations in patients with heart failure.

Within 5 years of first diagnosis, nearly 60% of patients with heart failure (HF) suffer from cardiac death. Early diagnosis of HF and reliable risk prediction are still required. Therefore, the objective of this study was to develop a parameter set for enhanced risk stratification in HF patients. In 43 patients suffering from HF (NYHA class > or =II, ejection fraction <45%) and 10 healthy subjects (REF), heart rate and blood pressure variability (HRV and BPV), interactions between heart rate and blood pressure (joint symbolic dynamics, JSD) and blood pressure morphology (BPM) were analysed. BPV, BPM and JSD measures revealed high significance (p<0.0001) in discriminating REF and HF. A set of three parameters from BPV, JSD and BPM was developed for risk stratification (sensitivity 76.5%, specificity 84.2%, area under the receiver operating characteristic curve 81.4%) in patients with HF.

Compression entropy contributes to risk stratification in patients with cardiomyopathy.

Sudden cardiac death (SCD) is a leading cause of mortality with an incidence of 3 million cases per year worldwide. Therapies for patients who have survived an SCD episode or have a high risk of developing lethal ventricular arrhythmia are well established and depend mainly on risk stratification. In this study we investigated the suitability of the non-linear measure compression entropy (Hc) for improved risk prediction in cardiac patients. We recorded 24-h Holter ECG for 300 patients with congestive heart failure (CHF). During a mean follow-up period of 12 months, 32 patients died due to a cardiac event. Hc depends on the compression parameters window length w and buffer length b, which were optimised by analysing a subgroup of patients. Compression entropies based on the beat-to-beat interval (BBI) were subsequently calculated and compared with standard heartrate variability parameters. Statistical analysis revealed significant differences between high- and low-risk CHF patients in standard HRV measures, as well as compression entropy based on the BBI (cardiac death, p = 0.005; SCD, p = 0.02). In conclusion, the implementation of non-linear compression entropy analysis in multivariate analysis seems to be useful for enhanced risk stratification of cardiac death, especially SCD, in ischaemic cardiomyopathy patients.

Short- and long-term joint symbolic dynamics of heart rate and blood pressure in dilated cardiomyopathy.

Autonomic cardiovascular control involves complex interactions of heart rate and blood pressure. In patients with dilated cardiomyopathy (DCM), this control is impaired and parameters for its quantification might be of prognostic importance. In this paper, we introduce methods based on joint symbolic dynamics (JSD) for the enhanced analysis of heart rate and blood pressure interactions. To assess the coarse-grained dynamics beat-to-beat changes of heart rate and blood pressure are encoded in symbol strings. Subsequently, the distribution properties of short symbol sequences (words) as well as the scaling properties of the whole symbol string are assessed. The comparison of joint symbolic heart rate and blood pressure dynamics in DCM (n = 75) with those in healthy controls (n = 75) showed significant changes. Both, the distribution of words and the scaling properties indicate a loss in heart rate dynamics associated with blood pressure regulation in DCM. In conclusion, the analyses of short- and long-term JSDs provide insights into complex physiological heart rate and blood pressure interactions and furthermore reveal patho-physiological cardiovascular control in DCM.

Cardiovascular variability before and after delivery: recovery from arterial stiffness in women with preeclampsia 4 days post partum.

OBJECTIVE: We studied the short-term response of autonomic control to delivery in normal pregnancies and pregnancies with preeclampsia (PE). METHODS: Fourteen healthy pregnant women and 13 women with PE were monitored within four days before and four days after delivery and compared to values of 14 non-pregnant women as controls using high-resolution electrocardiogram and noninvasive continuous blood pressure monitoring. RESULTS: In PE, blood pressure remained elevated four days postpartum, but markers for arterial stiffness normalized. In contrast, none of heart rate variability and baroreflex sensitivity parameters, altered due to either pregnancy or disease, were normalized 96 h after delivery. CONCLUSION: Four days after delivery, the maternal cardiovascular system is still strongly affected by pregnancy independent of the health status.

Comparison of nonlinear methods symbolic dynamics, detrended fluctuation, and Poincare plot analysis in risk stratification in patients with dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) has an incidence of about 20100 000 new cases per annum and accounts for nearly 10 000 deaths per year in the United States. Approximately 36% of patients with dilated cardiomyopathy (DCM) suffer from cardiac death within five years after diagnosis. Currently applied methods for an early risk prediction in DCM patients are rather insufficient. The objective of this study was to investigate the suitability of short-term nonlinear methods symbolic dynamics (STSD), detrended fluctuation (DFA), and Poincare plot analysis (PPA) for risk stratification in these patients. From 91 DCM patients and 30 healthy subjects (REF), heart rate and blood pressure variability (HRV, BPV), STSD, DFA, and PPA were analyzed. Measures from BPV analysis, DFA, and PPA revealed highly significant differences (p<0.0011) discriminating REF and DCM. For risk stratification in DCM patients, four parameters from BPV analysis, STSD, and PPA revealed significant differences between low and high risk (maximum sensitivity: 90%, specificity: 90%). These results suggest that STSD and PPA are useful nonlinear methods for enhanced risk stratification in DCM patients.