The role of heart rate variability in prognosis for different modes of death in chronic heart failure

Metabolic syndrome, physical activity and cardiac autonomic function

BACKGROUND

Our primary aim was to investigate the associations that components of metabolic syndrome and physical activity have with cardiac autonomic nervous system activity as estimated by heart rate variability (HRV) in young adults free of metabolic abnormalities. We also aimed to identify predictors of 3-year changes in HRV.

METHODS

Physical activity was assessed annually in 163 healthy participants over 3 years (2008-2010). Components of metabolic syndrome measured annually were; waist circumference, systolic blood pressure, high-density lipoprotein, triglycerides, glucose, and C-reactive protein. A linear mixed regression model was used to assess associations between HRV, metabolic syndrome components and physical activity. Linear regression was used to identify predictors of changes in HRV.

RESULTS

 Metabolic syndrome components were negatively associated with HRV indices and higher heart rate, while physical activity was associated with higher HRV and lower heart rate. Physical activity and inflammation were predictors of positive and negative changes in HRV indices, respectively.

CONCLUSIONS

 In participants without significant metabolic abnormalities, metabolic syndrome components were still associated with less favourable HRV profiles. Physical activity and inflammation were both able to predict changes in HRV, albeit in different directions. It appears that the process of autonomic dysfunction starts at a young age and may be mediated in part by inflammation. Metabolic syndrome prevalence is increasing in younger populations; promoting the metabolic and autonomic benefits of exercise remains imperative.

A new approach to detect congestive heart failure using Teager energy nonlinear scatter plot of R-R interval series

A novel approach to distinguish congestive heart failure (CHF) subjects from healthy subjects is proposed. Heart rate variability (HRV) is impaired in CHF subjects. In this work hypothesizing that capturing moment to moment nonlinear dynamics of HRV will reveal cardiac patterning, we construct the nonlinear scatter plot for Teager energy of R-R interval series. The key feature of Teager energy is that it models the energy of the source that generated the signal rather than the energy of the signal itself. Hence, any deviations in the genesis of HRV, by complex interactions of hemodynamic, electrophysiological, and humoral variables, as well as by the autonomic and central nervous regulations, get manifested in the Teager energy function. Comparison of the Teager energy scatter plot with the second-order difference plot (SODP) for normal and CHF subjects reveals significant differences qualitatively and quantitatively. We introduce the concept of curvilinearity for central tendency measures of the plots and define a radial distance index that reveals the efficacy of the Teager energy scatter plot over SODP in separating CHF subjects from healthy subjects. The k-nearest neighbor classifier with RDI as feature showed almost 100% classification rate.

Depression in heart failure: biobehavioral mechanisms

The etiology, predictive value, and biobehavioral aspects of depression in heart failure (HF) are described in this article. Clinically elevated levels of depressive symptoms are present in approximately 1 out of 5 patients with HF. Depression is associated with poor quality of life and a greater than 2-fold risk of clinical HF progression and mortality. The biobehavioral mechanisms accounting for these adverse outcomes include biological processes (elevated neurohormones, autonomic nervous system dysregulation, and inflammation) and adverse health behaviors (physical inactivity, medication nonadherence, poor dietary control, and smoking). Depression often remains undetected because of its partial overlap with HF-related symptoms and lack of systematic screening. Behavioral and pharmacologic antidepressive interventions commonly result in statistically significant but clinically modest improvements in depression and quality of life in HF, but not consistently better clinical HF or cardiovascular disease outcomes. Documentation of the biobehavioral pathways by which depression affects HF progression will be important to identify potential targets for novel integrative behavioral and pharmacologic interventions.

Heart rate variability in childhood obstructive sleep apnea

The identification of patients with obstructive sleep apnea (OSA) is important because of morbidities associated with OSA. A previous adult study demonstrated the use of heart rate variability (HRV) as a tool to identify patients with moderate to severe OSA. Either a reduction in time parameters or an increase in LF/HF ratio was seen at overnight or 24-hr studies suggestive of increased sympathetic modulation. To study the feasibility of daytime HRV as a screening tool, a short-term recording of HRV is studied. Since it was shown in adult study that increased normalized LF, decreased normalized HF and increased LF/HF ratio could be detectable during supine rest at daytime awake period, the authors hypothesize that the differences are also detectable in children. Children who underwent sleep polysomnography for suspected OSA were recruited. Subjects were classified OSA if apnea-hypopnea index (AHI) > 1.5/hr and non-OSA if AHI ≤ 1.5/hr. Continuous 1-hr electrocardiographic monitoring was recorded in awake children during the day. Parameters from time domain and frequency domain were analyzed. Seventy-four male and 17 female snoring subjects were included in this study. Fifty-one (56%) and 40 (44%) of them were classified as "non-OSA" and "OSA," respectively. pNN50, a parameter for parasympathetic modulation, was significantly reduced in the OSA group when compared with the non-OSA group. Using multiple regression, all time domain variables were shown to be decreased in OSA group. Our results suggest that 1-hr study of HRV may be a feasible tool in identifying children with OSA.

Heart Rate and Electrocardiography Monitoring in Mice

The majority of current cardiovascular research involves studies in genetically engineered mouse models. The measurement of heart rate is central to understanding cardiovascular control under normal conditions, with altered autonomic tone, superimposed stress or disease states, both in wild type mice as well as those with altered genes. Electrocardiography (ECG) is the "gold standard" using either hard wire or telemetry transmission. In addition, heart rate is measured or monitored from the frequency of the arterial pressure pulse or cardiac contraction, or by pulse oximetry. For each of these techniques, discussions of materials and methods, as well as advantages and limitations are covered. However, only the direct ECG monitoring will determine not only the precise heart rates but also whether the cardiac rhythm is normal or not.

Effect of depression on prognosis in heart failure

Depression is a common comorbid condition in heart failure, and there is growing evidence that it increases the risks of mortality and other adverse outcomes, including rehospitalization and functional decline. The prognostic value of depression depends, in part, on how it is defined and measured. The few studies that have compared different subsets of patients with depression suggest that major (or severe) depression is a stronger predictor of mortality than is minor (or mild) depression. Whether depression is a causal risk factor for heart failure mortality, or simply a risk marker, has not yet been established, but mechanistic research has identified several plausible behavioral and biologic pathways. Further research is needed to clarify the relationships among depression, heart failure, and adverse outcomes, as well as to develop efficacious interventions for depressive disorders in patients with heart failure.

Web-enabled and improved software tools and data are needed to measure nutrient intakes and physical activity for personalized health research

Food intake, physical activity (PA), and genetic makeup each affect health and each factor influences the impact of the other 2 factors. Nutrigenomics describes interactions between genes and environment. Knowledge about the interplay between environment and genetics would be improved if experimental designs included measures of nutrient intake and PA. Lack of familiarity about how to analyze environmental variables and ease of access to tools and measurement instruments are 2 deterrents to these combined studies. This article describes the state of the art for measuring food intake and PA to encourage researchers to make their tools better known and more available to workers in other fields. Information presented was discussed during a workshop on this topic sponsored by the USDA, NIH, and FDA in the spring of 2009.

Strength and vulnerability integration: a model of emotional well-being across adulthood

The following article presents the theoretical model of strength and vulnerability integration (SAVI) to explain factors that influence emotion regulation and emotional well-being across adulthood. The model posits that trajectories of adult development are marked by age-related enhancement in the use of strategies that serve to avoid or limit exposure to negative stimuli but by age-related vulnerabilities in situations that elicit high levels of sustained emotional arousal. When older adults avoid or reduce exposure to emotional distress, they often respond better than younger adults; when they experience high levels of sustained emotional arousal, however, age-related advantages in emotional well-being are attenuated, and older adults are hypothesized to have greater difficulties returning to homeostasis. SAVI provides a testable model to understand the literature on emotion and aging and to predict trajectories of emotional experience across the adult life span.

Cardiorespiratory phase-coupling is reduced in patients with obstructive sleep apnea

Cardiac and respiratory rhythms reveal transient phases of phase-locking which were proposed to be an important aspect of cardiorespiratory interaction. The aim of this study was to quantify cardio-respiratory phase-locking in obstructive sleep apnea (OSA). We investigated overnight polysomnography data of 248 subjects with suspected OSA. Cardiorespiratory phase-coupling was computed from the R-R intervals of body surface ECG and respiratory rate, calculated from abdominal and thoracic sensors, using Hilbert transform. A significant reduction in phase-coupling was observed in patients with severe OSA compared to patients with no or mild OSA. Cardiorespiratory phase-coupling was also associated with sleep stages and was significantly reduced during rapid-eye-movement (REM) sleep compared to slow-wave (SW) sleep. There was, however, no effect of age and BMI on phase coupling. Our study suggests that the assessment of cardiorespiratory phase coupling may be used as an ECG based screening tool for determining the severity of OSA.

Association of Holter-based measures including T-wave alternans with risk of sudden cardiac death in the community-dwelling elderly: the Cardiovascular Health Study

BACKGROUND

Sudden cardiac death (SCD) can be the first manifestation of cardiovascular disease. Development of screening methods for higher/lower risk is critical.

METHODS

The Cardiovascular Health Study is a population-based study of risk factors for coronary heart disease and stroke those 65 years or older. Forty-nine (of 1649) with usable Holters and in normal sinus rhythm had SCD during follow-up and were matched with 2 controls, alive at the time of death of the case and not experiencing SCD on follow-up. Univariate and multivariate conditional logistic regression determined the association of Holter-based information and SCD.

RESULTS

In univariate models, the upper half of ventricular premature contraction (VPC) counts, abnormal heart rate turbulence, decreased normalized low-frequency power, increased T-wave alternans (TWA), and decreased the short-term fractal scaling exponent (DFA(1)) were associated with SCD, but time domain heart rate variability was not. In multivariate models, the upper half of VPC counts (odds ratio [OR], 6.6) and having TWA of 37 muV or greater on channel 2 (OR, 4.8) were independently associated with SCD. Also, the upper half of VPC counts (OR, 6.9) and having a DFA(1) of less than 1.05 (OR, 5.0) were independently associated with SCD. When additive effects were explored, having both higher VPCs and higher TWA was associated with an OR of 8.2 for SCD compared with 2.6 for having either. Also, having both higher VPCs and lower DFA(1) was associated with an OR of 9.6 for SCD compared with 3.1 for having either.

CONCLUSIONS

Results support a potential role for 24-hour Holter recordings to identify older adults at increased or lower risk of SCD.

Limitations of oximetry to measure heart rate variability measures

Measuring heart rate variability (HRV) is widely used to assess autonomic nervous system function. It requires accurate measurement of the interval between successive heartbeats. This can be achieved from recording the electrocardiogram (ECG), which is non-invasive and widely available. However, methodological problems inherent in recording and analyzing ECG traces have motivated a search for alternative means of measuring the interval between successive heartbeats. Recording blood oxygenation pulsations (photoplethysmography-PPG) is also convenient, non-invasive and widely available, and has been suggested as an effective alternative to ECG to derive HRV. Moreover, it has been claimed that the pulse waveforms produced by oximetry may be more practicable than R-R intervals measured from the by ECG, especially for ambulatory recordings. We have therefore compared PPG with ECG recordings to measure HRV applying the same signal analysis techniques to PPG and ECG recordings made simultaneously. Comparison of 5 min recording epochs demonstrated a very high degree of correlation, in temporal, frequency domains and non-linear analysis, between HRV measures derived from the PPG and ECG. However, we found that the PPG signal is especially vulnerable to motion artifacts when compared to the ECG, preventing any HRV analysis at all in a significant minority of PPG recordings. Our results demonstrate that even though PPG provides accurate interpulse intervals to measure heart rate variability under ideal conditions, it is less reliable due to its vulnerability to motion artifacts. Therefore it is unlikely to prove a practical alternative to the ECG in ambulatory recordings or recordings made during other activities.

Moderate Exercise Training Improves Survival and Ventricular Remodeling in an Animal Model of Left Ventricular Volume Overload

Background— Exercise training has beneficial effects in patients with heart failure, although there is still no clear evidence that it may impact on their survival. There are no data regarding the effects of exercise in subjects with chronic left ventricular (LV) volume overload. Using a rat model of severe aortic valve regurgitation (AR), we studied the effects of long-term exercise training on survival, development of heart failure, and LV myocardial remodeling.

Methods and Results— One hundred sixty male adult rats were divided in 3 groups: sham sedentary (n=40), AR sedentary (n=80), and AR trained (n=40). Training consisted in treadmill running for up to 30 minutes, 5 times per week for 9 months, at a maximal speed of 20 m/minute. All sham-operated animals survived the entire course of the protocol. After 9 months, 65% of trained animals were alive compared with 46% of sedentary ones ( P =0.05). Ejection fractions remained in the normal range (all above 60%) and LV masses between AR groups were similar. There was significantly less LV fibrosis in the trained group and lower LV filling pressures and improved echocardiographic diastolic parameters. Heart rate variability was also improved by exercise.

Conclusion— Our data show that moderate endurance training is safe, does not increase the rate of developing heart failure, and most importantly, improves survival in this animal model of chronic LV volume overload. Exercise improved LV diastolic function, heart rate variability, and reduced myocardial fibrosis.

T-type Ca2+ channel blockade prevents sudden death in mice with heart failure

BACKGROUND

Pharmacological interventions for prevention of sudden arrhythmic death in patients with chronic heart failure remain limited. Accumulating evidence suggests increased ventricular expression of T-type Ca(2+) channels contributes to the progression of heart failure. The ability of T-type Ca(2+) channel blockade to prevent lethal arrhythmias associated with heart failure has never been tested, however.

METHODS AND RESULTS

We compared the effects of efonidipine and mibefradil, dual T- and L-type Ca(2+) channel blockers, with those of nitrendipine, a selective L-type Ca(2+) channel blocker, on survival and arrhythmogenicity in a cardiac-specific, dominant-negative form of neuron-restrictive silencer factor transgenic mice (dnNRSF-Tg), which is a useful mouse model of dilated cardiomyopathy leading to sudden death. Efonidipine, but not nitrendipine, substantially improved survival among dnNRSF-Tg mice. Arrhythmogenicity was dramatically reduced in dnNRSF-Tg mice treated with efonidipine or mibefradil. Efonidipine acted by reversing depolarization of the resting membrane potential otherwise seen in ventricular myocytes from dnNRSF-Tg mice and by correcting cardiac autonomic nervous system imbalance. Moreover, the R(-)-isomer of efonidipine, a recently identified, highly selective T-type Ca(2+) channel blocker, similarly improved survival among dnNRSF-Tg mice. Efonidipine also reduced the incidence of sudden death and arrhythmogenicity in mice with acute myocardial infarction.

CONCLUSIONS

T-type Ca(2+) channel blockade reduced arrhythmias in a mouse model of dilated cardiomyopathy by repolarizing the resting membrane potential and improving cardiac autonomic nervous system imbalance. T-type Ca(2+) channel blockade also prevented sudden death in mice with myocardial infarction. Our findings suggest T-type Ca(2+) channel blockade is a potentially useful approach to preventing sudden death in patients with heart failure.

The effect of biofeedback on function in patients with heart failure

Decreased HRV has been consistently associated with increased cardiac mortality and morbidity in HF patients. The aim of this study is to determine if a 6-week course of heart rate variability (HRV) biofeedback and breathing retraining could increase exercise tolerance, HRV, and quality of life in patients with New York Heart Association Class I-III heart failure (HF). Participants (N = 29) were randomly assigned to either the treatment group consisting of six sessions of breathing retraining, HRV biofeedback and daily practice, or the comparison group consisting of six sessions of quasi-false alpha-theta biofeedback and daily practice. Exercise tolerance, measured by the 6-min walk test (6MWT), HRV, measured by the standard deviation of normal of normal beats (SDNN), and quality of life, measured by the Minnesota Living with Congestive Heart Failure Questionnaire, were measured baseline (week 0), post (week 6), and follow-up (week 18). Cardiorespiratory biofeedback significantly increased exercise tolerance (p = .05) for the treatment group in the high (>or=31%) left ventricular ejection fraction (LVEF) category between baseline and follow-up. Neither a significant difference in SDNN (p = .09) nor quality of life (p = .08), was found between baseline and follow-up. A combination of HRV biofeedback and breathing retraining may improve exercise tolerance in patients with HF with an LVEF of 31% or higher. Because exercise tolerance is considered a strong prognostic indicator, cardiorespiratory biofeedback has the potential to improve cardiac mortality and morbidity in HF patients.

Chaotic signatures of heart rate variability and its power spectrum in health, aging and heart failure

A paradox regarding the classic power spectral analysis of heart rate variability (HRV) is whether the characteristic high- (HF) and low-frequency (LF) spectral peaks represent stochastic or chaotic phenomena. Resolution of this fundamental issue is key to unraveling the mechanisms of HRV, which is critical to its proper use as a noninvasive marker for cardiac mortality risk assessment and stratification in congestive heart failure (CHF) and other cardiac dysfunctions. However, conventional techniques of nonlinear time series analysis generally lack sufficient sensitivity, specificity and robustness to discriminate chaos from random noise, much less quantify the chaos level. Here, we apply a ‘litmus test’ for heartbeat chaos based on a novel noise titration assay which affords a robust, specific, time-resolved and quantitative measure of the relative chaos level. Noise titration of running short-segment Holter tachograms from healthy subjects revealed circadian-dependent (or sleep/wake-dependent) heartbeat chaos that was linked to the HF component (respiratory sinus arrhythmia). The relative ‘HF chaos’ levels were similar in young and elderly subjects despite proportional age-related decreases in HF and LF power. In contrast, the near-regular heartbeat in CHF patients was primarily nonchaotic except punctuated by undetected ectopic beats and other abnormal beats, causing transient chaos. Such profound circadian-, age- and CHF-dependent changes in the chaotic and spectral characteristics of HRV were accompanied by little changes in approximate entropy, a measure of signal irregularity. The salient chaotic signatures of HRV in these subject groups reveal distinct autonomic, cardiac, respiratory and circadian/sleep-wake mechanisms that distinguish health and aging from CHF.

Cardiac and autonomic nerve function after reduced-intensity stem cell transplantation for hematologic malignancy in patients with pre-transplant cardiac dysfunction

Recent reports have shown that cardiomyopathy caused by hemochromatosis in severe aplastic anemia is reversible after reduced-intensity allogeneic stem-cell transplantation (RIST). We comprehensively evaluated cardiac and autonomic nerve function to determine whether cardiac dysfunction due to causes other than hemochromatosis is attenuated after RIST. In five patients with cardiac dysfunction before transplant, we analyzed the changes in cardiac and autonomic nerve function after transplant, using electrocardiography (ECG), echocardiography, radionuclide angiography (RNA), serum markers, and heart rate variability (HRV), before and up to 100 days after transplant. There was no significant improvement in cardiac function in any patient and no significant alteration in ECG, echocardiogram, RNA, or serum markers. However, on time-domain analysis of HRV, the SD of normal-to-normal RR intervals (SDNN) and the coefficient of variation of the RR interval (CVRR) decreased significantly 30 and 60 days after transplant (P = 0.04 and 0.01, respectively). Similarly, on frequency-domain analysis of HRV, low and high frequency power (LF and HF) significantly and temporarily decreased (P = 0.003 and 0.03, respectively). Notably, in one patient who had acute heart failure after transplantation, the values of SDNN, CVRR, r-MSSD, LF, and HF at 30 and 60 days after transplantation were the lowest of all the patients. In conclusion, this study suggests that (a) RIST is well-tolerated in patients with cardiac dysfunction, but we cannot expect improvement in cardiac dysfunction due to causes other than hemochromatosis; and (b) monitoring HRV may be useful in predicting cardiac events after RIST.

Standard Deviation of normal interbeat intervals as a risk marker in patients with left ventricular systolic dysfunction: a meta-analysis

Our aim was to evaluate the Standard Deviation of Normal-Normal (SDNN) interbeat interval as a risk marker in left ventricular systolic dysfunction (LVSD) patients through a meta-analysis. We searched PubMed for studies that evaluated SDNN as a predictor of all-cause-death, cardiac death, transplantation, and progressive clinical deterioration using a search strategy validated for MEDLINE. Mean values and SD for SDNN in sixteen studies included were 115+/-48 ms in survivors versus 87+/-40 ms in non-survivors, resulting in a statistically significant standardized mean difference (0.594, 95%CI 0.385 to 0.803). In conclusion, SDNN may be a useful prognostic marker in LVSD. Additional studies must evaluate if SDNN may be used to subsidize therapeutic decisions.

A twin study of metabolic syndrome and autonomic tone

INTRODUCTION

One possible mechanism of higher cardiovascular mortality associated with the metabolic syndrome (MetS) may be through abnormal modulation in autonomic tone.

METHODS AND RESULTS

We examined the association between the MetS and autonomic tone as measured by heart rate variability (HRV) among 288 twins from the Twins Heart Study (THS). Of the 288 participants, 151 (52%) had the MetS. The MetS was associated with decreased HRV across all frequency ranges, and each additional MetS risk factor was associated with lower HRV. After adjustment for several potential confounders, very-low frequency (P < 0.001), low frequency (P < 0.001), and total power (P = 0.02) spectra of HRV remained significantly lower in twins with a progressively higher number of MetS components (18-50% decrease comparing twins with 5 risk factors to those with no risk factors). Among 87 twin pairs who were discordant for the number of MetS components, a one-unit increment in MetS components was associated with an 8% smaller very-low frequency (p = 0.03) and a 15% smaller low frequency spectrum (P = 0.002) comparing each twin with his brother.

CONCLUSION

MetS was associated with lower HRV in a well-characterized sample of middle-aged male twins. This association persisted even after controlling for genetic and shared environmental factors accounted for by comparison within twin pairs. Abnormalities of autonomic tone, as evidenced by lower HRV, may be partly responsible for the higher rate of atrial fibrillation, coronary heart disease, cardiac death, and overall mortality seen in patients with the MetS.

Psychological predictors of prognosis in chronic heart failure

BACKGROUND

Chronic heart failure (CHF) is an increasingly prevalent condition with high mortality and morbidity rates. This review examines the role of depression, anxiety, and social support on prognosis in CHF.

METHOD AND RESULTS

Prospective studies that examined mortality as an outcome, and assessed depression, anxiety, or social support as associates were included. Methodological qualities were evaluated. In total, 25 studies were identified. Concerning depression, 6 of 15 studies of inpatients, 10 of 11 studies of outpatients, and 1 study of a mixed sample found associations between depression and prognosis, with greater associations rendered by depressive symptomatology in outpatients. Anxiety was not associated with prognosis in one inpatient study and one outpatient study. There was a univariable trend in one outpatient study for anxiety to be associated with prognosis. In two of six studies of inpatients and in two of four studies of outpatients, social support was associated with prognosis. On the basis of methodological quality, studies on depression showed mixed results, no conclusions could be drawn for anxiety because this association was not investigated soundly, and the quality of the social network was not associated with outcome.

CONCLUSION

Evidence suggests that depressive symptoms and social support might be associated with prognosis in CHF outpatients, independently of biomedical risk factors. With respect to anxiety, no conclusions can be drawn. Future studies are warranted to disentangle associations with psychological factors.

Treatment of chronic systolic heart failure secondary to Chagas heart disease in the current era of heart failure therapy

The treatment of chronic heart failure secondary to Chagas disease has been based on extrapolation of data achieved in the treatment of non-Chagas disease heart failure. Because beta-blockers decrease the incidence of sudden cardiac death in non-Chagas disease heart failure and sudden cardiac death occurs preferentially in patients with mild Chagas disease heart failure, beta-blockers may be administered first to class I/II patients with Chagas disease heart failure. In advanced Chagas disease heart failure, angiotensin-converting enzyme inhibitor and diuretics may be given at first to compensate for congestive symptoms. After clinical status improvement, beta-blockers should be given at targeted doses, if necessary reducing angiotensin-converting enzyme inhibitor doses. Primary and secondary prevention of sudden cardiac death may be accomplished with implantable cardioverter defibrillators because of the high recurrence of life-threatening arrhythmias despite amiodarone administration. In refractory heart failure, heart transplantation is the treatment of choice.

Autonomic response to cardiac dysfunction in chronic heart failure: a risk predictor based on autonomic information flow

BACKGROUND

Chronic heart failure (CHF) is associated with a complex dysfunction of cardiac, cardiovascular, autonomic, and other mechanisms. Autonomic information flow (AIF) characteristics calculated from heart rate patterns were recently found as promising predictors of outcome in several cardiovascular diseases.

AIM

To assess the prognostic value of AIF indices in CHF patients.

METHODS

We analyzed 24-hour Holter recordings from 200 consecutive CHF patients in sinus rhythm and computed AIF over the shortest possible interval of an interbeat series, namely over one heart beat interval (BDnn), and over longer intervals (12.5-166.7 seconds, PDmVLF), which reflect slower heart rate modulations. End-point for survival analysis over three years (Cox model) was total cardiac death. A prognostic model was built (backward elimination) considering known clinical and functional risk factors, and the ability of AIF indices to add prognostic information to this model assessed.

RESULTS

Out of candidate predictors, New York Heart Association class, left ventricular ejection fraction, peak VO(2,) and systolic pressure were selected as the variables with the highest joint predictive value. When entered into this model, both BDnn and PDmVLF added prognostic information (HR (95%CI): 1.76 (1.00-3.09), P = 0.05, 1.73 (1.05-2.85), P = 0.031 respectively). High risk was associated with reduced fast AIF and increased slower AIF.

CONCLUSION

In CHF patients, AIF indices provide prognostic information independent of known risk factors.

Using devices for physiologic monitoring in heart failure

Heart failure (HF) is a complex and costly disease process associated with high morbidity and mortality. Implanted cardiac rhythm management devices are increasingly used in the HF population to provide therapies such as protection from sudden death and cardiac resynchronization therapy. Device-based diagnostic monitoring provides clinicians with information that can assist in identifying patients at risk for HF decompensation and subsequent hospitalization. This article will review the evidence for using diagnostic information from cardiac rhythm management devices in the management of HF patients. Future advanced monitoring devices will also be discussed.

Heart rate chaos as a mortality predictor in mild to moderate heart failure

Linear and nonlinear indices of heart rate variability (HRV) have been shown to predict mortality in congestive heart failure (CHF). However, most nonlinear indices describe only the fractality or complexity of HRV but not the intrinsic chaotic properties. In the present study, we performed linear (time- and frequency-domain), complexity (sample entropy), fractal (detrended fluctuation analysis) and chaos (numerical titration) analyses on the HRV of 50 CHF patients from the United Kingdom heart failure evaluation and assessment of risk trial database. Receiver operating characteristic and survival analysis yielded the chaos level to be the best predictor of mortality (followed by low/high frequency power ratio, LF/HF), such that these indices were significant in both univariate and multivariate models. These results indicate the power of heart rate chaos analysis as a potential prognostic tool for CHF.

Heart rate variability in mice: a theoretical and practical guide

The mouse is the animal model principally used to study biological processes in mammals. The mutation, overexpression or knockout of one or several genes can provide insight into human disease. In cardiovascular research, evaluation of autonomic nervous function is an essential tool for a better understanding of the pathophysiological conditions in which cardiomyopathy arises and develops. Analysis of heart rate variability is the least invasive method to evaluate the sympathovagal balance on the sino-atrial level. The need to perform this technique on freely moving mice emerged in the 1990s, but despite previous studies it has been difficult to set up and standardize a common protocol. The multitudes of techniques used, plus subtle differences in methodology, impede the comparison and clear interpretation of results. This article aims to make a survey of heart rate variability analysis and to establish a standardized protocol for the assessment of the autonomic neural regulation of heart rate in mice.

SCD in patients with cardiomyopathy: use of microvolt T-wave alternans and other noninvasive tests for risk stratification and prevention of SCD

Based on current guidelines, most electrophysiologists today are implanting cardioverter-defibrillators (ICDs) using a low left ventricular ejection fraction alone as the sole stratifier for the risk of sudden cardiac death. However, left ventricular ejection fraction is a better marker of total mortality than sudden death. As a result, this strategy is flawed because it exposes many patients to the risk and cost of ICD therapy without its benefits. Primary prevention trials based on this strategy show that the rate of appropriate ICD shocks is only 5% to 10% per year. We believe that the effectiveness of ICD therapy can be improved by the use, in addition to ejection fraction, of one or more of the noninvasive tests, which are reviewed in this article. Such tests are more adequate to evaluate the arrhythmogenic substrate of the patient than the left ventricular ejection fraction alone. Whether any of these tests can help us identify the patients at the lowest risk of sudden death, who could safely avoid ICD implant, remains to be determined.