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.     

Heart Rate Variability as an Indicator of Chronic Stress Caused by Lameness in Dairy Cows

Most experimental studies on animal stress physiology have focused on acute stress, while chronic stress, which is also encountered in intensive dairy cattle farming–e.g. in case of lameness–, has received little attention. We investigated heart rate (HR) and heart rate variability (HRV) as indicators of the autonomic nervous system activity and fecal glucocorticoid concentrations as the indicator of the hypothalamic–pituitary–adrenal axis activity in lame (with locomotion scores 4 and 5; n = 51) and non-lame (with locomotion scores 1 and 2; n = 52) Holstein-Friesian cows. Data recorded during the periods of undisturbed lying–representing baseline cardiac activity–were involved in the analysis. Besides linear analysis methods of the cardiac inter-beat interval (time-domain geometric, frequency domain and Poincaré analyses) non-linear HRV parameters were also evaluated. With the exception of standard deviation 1 (SD1), all HRV indices were affected by lameness. Heart rate was lower in lame cows than in non-lame ones. Vagal tone parameters were higher in lame cows than in non-lame animals, while indices of the sympathovagal balance reflected on a decreased sympathetic activity in lame cows. All geometric and non-linear HRV measures were lower in lame cows compared to non-lame ones suggesting that chronic stress influenced linear and non-linear characteristics of cardiac function. Lameness had no effect on fecal glucocorticoid concentrations. Our results demonstrate that HRV analysis is a reliable method in the assessment of chronic stress, however, it requires further studies to fully understand the elevated parasympathetic and decreased sympathetic tone in lame animals.     

Low HRV entropy is strongly associated with myocardial infarction.

Heart rate variability (HRV) is a marker of autonomous activity in the heart. An important application of HRV measures is the stratification of mortality risk after myocardial infarction. Our hypothesis is that the information entropy of HRV, a non-linear approach, is a suitable measure for this assessment. As a first step, to evaluate the effect of myocardial infarction on the entropy, we compared the entropy to standard HRV parameters. The entropy was estimated by compressing the tachogram with Bzip2. For univariate comparison, statistical tests were used. Multivariate analysis was carried out using automatically generated decision trees. The classification rate and the simplicity of the decision trees were the two evaluation criteria. The findings support our hypothesis. The meanNN-normalized entropy is reduced in patients with myocardial infarction with very high significance. One entropy parameter alone exceeds the discrimination strength of multivariate standards-based trees.     

Autonomic cardiac control in animal models of cardiovascular diseases. I. Methods of variability analysis.

Analysis of heart rate variability (HRV) and blood pressure variability (BPV) and baroreceptor sensitivity (BRS) has become a proven tool in clinical cardiovascular diagnostics and risk stratification. In the present work, traditional and new methodological approaches for analysis of HRV, BPV, and BRS data are summarized. HRV, BPV, and BRS parameters were obtained from animal studies designed to study pathogenetic mechanisms of distinct cardiovascular diseases. Different non-linear approaches for HRV and BPV analysis are presented here, in particular measures of complexity based on symbolic dynamics. The dual sequence method (DSM) was employed for BRS analysis. In comparison to the classical measure of BRS using the average slope [ms/mm Hg], DSM offers additional information about the time-variant coupling between BPV and HRV. Since cardiovascular regulation shares common features among different species, data on HRV and BPV, as well as BRS, in animal models might be useful for understanding the pathogenetic mechanisms of cardiovascular diseases in humans and in the development of new diagnostic approaches.     

有氧锻炼对心脏自主神经调节的影响：心率变异性分析结果

为阐明有氧锻炼对心脏自主神经调节功能的影响,以及这种变化与卧位／坐位下体负压（ＬＢＮＰ）作用下的心率调节及立位耐力之间是否有一定联系,用频域、动态谱及非线性指标较全面分析了大学生有氧锻炼６个月前、后心率变异性（ＨＲＶ）的变化。结果表明：常规ＡＲ谱分析的批处理结果只能代表一段时间内ＨＲＶ信号的平均统计特性,方差大,得不出有显著意义的结果。而时变ＡＲ谱则可反映ＬＢＮＰ作用下心迷走撤除及交感激活的动态过程。非线性的β估计得不出有显著意义的结果;但ＡｐＥｎ分析则可敏感地检测出有氧锻炼关联的心率动力学细微变化,且初步揭示ΔＡｐＥｎ与立位耐力变化（ΔＤＮＰ）间显著相关。以上对阐明有氧锻炼对心率动力学调节的影响以及改进ＨＲＶ信号分析工作均有一定意义。     

改良HEART评分法对急诊胸痛患者分层治疗的指导价值研究

目的:研究改良HEART评分法对急诊胸痛患者分层治疗的指导价值。方法:选择我院急诊科收治的急性胸痛患者197例,根据疾病分为心源性胸痛组(n=132)和非心源性胸痛组(n=65),所有患者均行改良HEART评分和传统HEART评分,并根据评分进行危险分层,比较患者去向,建立受试者工作特征(ROC)曲线,评价HEART评分对危险分层和预后预测的价值。结果:心源性胸痛组改良HEART评分和常规HEART评分均高于非心源性胸痛组,两组改良HEART评分和常规HEART评分比较差异有统计学意义(P0.05)。改良HEART评分低危者100%未住院,中危62.71%住院,高危住院、入ICU的构成比例为73.17%、36.59%;HEART评分低危11.11%住院,中危住院、入ICU的构成比例为57.38%、6.56%,高危住院、入ICU的构成比例为68.57%、31.43%,差异有统计学意义(P0.05)。改良HEART评分用于对心源性胸痛患者分层的AUC值为0.916,敏感度为0.883,明显高于HEART评分的0.831和0.765。结论:改良HEART评分法可提高急诊胸痛患者分层的准确性,对指导患者去向和治疗价值较高。     

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.     

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.     

Approach to the asymptomatic patients with Brugada syndrome

Brugada syndrome is an arrhythmogenic disease characterized by an ECG pattern of coved-type ST segment elevation in the right precordial leads and an increased risk of sudden cardiac death (SCD) as a result of polymorphic ventricular tachyarrhythmia or ventricular fibrillation (VF). Data from large patient studies and a meta-analysis of previous reports have shown that patients with a history of syncope or SCD and a spontaneous type 1 Brugada type ECG are at high risk for SCD. However, risk stratification of asymptomatic patients with Brugada type ECG is still a challenge. In particular, the use of electrophysiological study (EPS) for risk stratification remains controversial. Although some investigators have reported the possibility of use of EPS for distinguishing between high- and low-risk patients with Brugada type ECG, no precise predictor of risk for SCD in asymptomatic patients has yet been determined. The approach to treatment of these patients is thus still unclear. Large clinical prospective studies with uniform diagnostic criteria and protocols for EPS as well as extended follow-up periods of over ten years are required for prediction of SCD.     

Differences between heart rate and blood pressure variability in schizophrenia.

Heart rate and blood pressure variability parameters were assessed to determine the risk of cardiac mortality in schizophrenia. We investigated 21 acute, unmedicated patients with paranoid schizophrenia and 21 matched controls. Cardiovascular parameters obtained included heart rate variability, blood pressure variability, cardiac output and left ventricular work index. All parameters investigated were analyzed using linear and non-linear techniques. These investigations revealed increased left ventricular work index and reduced heart rate variability. Furthermore, blood pressure was significantly higher compared to controls, whereas its variability was unchanged. We conclude that our results reflect autonomic cardiovascular dysregulation in acute schizophrenia.     

Risk stratification for sudden cardiac death

Recent advances in pharmacological and device-based therapies have provided a range of management options for patients at risk of sudden cardiac death (SCD). Since all such interventions come with their attendant risks, however, stratification procedures aimed at identifying those who stand to benefit overall have gained a new degree of importance. This review assesses the value of risk stratification measures currently available in clinical practice, as well as of others that may soon enter the market. Parameters that may be obtained only by performing invasive cardiac catheterisation procedures are considered separately from those that may be derived using more readily available non-invasive techniques. It is concluded that effective stratification is likely to require the use of composite parameters and that invasive procedures might only be justified in specific sub-groups of patients.     

The in vivo performance of small-caliber nanofibrous polyurethane vascular grafts

We evaluated the association between linear standard Heart Rate Variability (HRV) measures and vascular, renal and cardiac target organ damage (TOD). A retrospective analysis was performed including 200 patients registered in the Regione Campania network (aged 62.4 ± 12, male 64%). HRV analysis was performed by 24-h holter ECG. Renal damage was assessed by estimated glomerular filtration rate (eGFR), vascular damage by carotid intima-media thickness (IMT), and cardiac damage by left ventricular mass index. Significantly lower values of the ratio of low to high frequency power (LF/HF) were found in the patients with moderate or severe eGFR (p-value < 0.001). Similarly, depressed values of indexes of the overall autonomic modulation on heart were found in patients with plaque compared to those with a normal IMT (p-value <0.05). These associations remained significant after adjustment for other factors known to contribute to the development of target organ damage, such as age. Moreover, depressed LF/HF was found also in patients with left ventricular hypertrophy but this association was not significant after adjustment for other factors. Depressed HRV appeared to be associated with vascular and renal TOD, suggesting the involvement of autonomic imbalance in the TOD. However, as the mechanisms by which abnormal autonomic balance may lead to TOD, and, particularly, to renal organ damage are not clearly known, further prospective studies with longitudinal design are needed to determine the association between HRV and the development of TOD.     

Blood pressure and heart rate variability are linked with hyperphosphatemia in chronic kidney disease patients

ABSTRACT

Hyperphosphatemia is a common complication of chronic kidney disease (CKD) and is associated with cardiovascular disease (CVD), which has contributed to an increase in mortality of CKD patients. The onset of CVD often varies by time-of-day. Acute myocardial infarction or ventricular arrhythmia occurs most frequently during early morning. Blood pressure (BP) and heart rate circadian rhythms account for the diurnal variations in CVD. Preservation of normal circadian time structure from the cardiomyocyte level to the whole organ system is essential for cardiovascular health and CVD prevention. Independent risk factors, such as reduced heart rate variability (HRV) and increased BP variability (BPV), are particularly prevalent in patients with CKD. Analysis of HRV is an important clinical tool for characterizing cardiac autonomic status, and reduced HRV has prognostic significance for various types of CVD. Circadian BP rhythms are classified as extreme dipper, dipper, non-dipper or riser. It has been reported that nocturnal riser BP pattern contributes to cardiovascular threats. Previous studies have indicated that the circadian rhythm of serum phosphate in CKD patients is consistent with the general population, with the highest diurnal value observed in the early morning hours, followed by a progressive decrease to the lowest value of the day, which occurs around 11:00 am. Rhythm abnormalities have become the main therapeutic target for treating CVD in CKD patients. It has been reported that high levels of serum phosphate are associated with reduced HRV and increased BPV in CKD patients. However, the mechanisms related to interactions between hyperphosphatemia, HRV and BPV have not been fully elucidated. This review focuses on the evidence and discusses the potential mechanisms related to the effects of hyperphosphatemia on HRV and BPV.     

Clinical correlates of non-linear indices of heart rate variability in chronic heart failure patients.

We assessed the clinical correlates of a comprehensive set of non-linear heart rate variability (HRV) indices computed from 24-h Holter recordings for 200 stable chronic heart failure (CHF) patients [median age (lower quartile, upper quartile) 54 (47, 58) years, LVEF 23% (19%, 28%)]. A total of 19 non-linear indices belonging to six major families, namely symbolic dynamics, entropy, empirical mode decomposition, fractality-multifractality, unpredictability and Poincaré plots, were considered. Most indices showed a significant association with ejection fraction and with the severity of symptoms, while only two (one each from the fractality and Poincaré plot families) showed an association with aetiology. Only one symbolic dynamics variable was associated with the presence of non-sustained ventricular tachycardia and two symbolic dynamics variables were associated with the rate of ventricular ectopic events. Our results demonstrate the existence of selective links between non-linear indexes of HRV and the clinical status and functional impairment of CHF patients. This indicates that further studies should be designed to investigate the physiopathological mechanisms involved in such links.     

Patients with left bundle branch block pattern and high cardiac risk myocardial SPECT: does the current management suffice?

Introduction

Myocardial perfusion SPECT (MPS) is frequently used for cardiovascular risk stratification. The significance of MPS in patients with abnormal electrical ventricular activation is often questionable. This review assesses the value of MPS for risk stratification of patients with intrinsic left bundle branch block or that due to right ventricular apical pacing.

Methods

We reviewed the literature by a search of the MEDLINE database (January 1980 to September 2010). The terms prognosis or prognostic value were combined with SPECT and LBBB or pacing or pacemakers. MPS was categorised as low and high risk according to the original definitions.

Results

We identified 11 studies suitable for review. A low-risk MPS is associated with a low risk of cardiac events whereas high-risk MPS carries a 4.8-fold increased risk, 95% CI [3.2 – 7.2] (p < 0.0001). Despite secondary prevention and an improved medical and interventional care, these figures have hardly changed over time.

Conclusion and clinical implications

A low-risk MPS permits a policy of watchful waiting whereas a high-risk MPS requires further analysis and treatment. The persistent high cardiac death and acute myocardial infarction rate after a high-risk MPS suggest that the current management of these patients does not suffice and needs reconsideration.     

Normal ranges and reproducibility of statistical, geometric, frequency domain, and non-linear measures of 24-hour heart rate variability.

Diabetic cardiovascular autonomic neuropathy (CAN) carries an increased risk of mortality. The early detection and characterization of CAN has traditionally been based on the results of autonomic reflex tests (AFTs). A variety of different measures to quantify 24-hour heart rate variability (HRV) have recently been introduced, but their normal ranges, reliability, and validity in patients with CAN have not been adequately studied. We established the normal ranges of statistical (SDNN index, CV, SNN50, RMSSD), geometric (triangular index (TI), triangular interpolation (TINN), top angle index [TAI]), frequency domain (spectral power in the VLF, LF, and HF bands, LF/HF ratio, LF in normalized units [NU]), and non-linear measures (CV1 and CV2 of the Poincaré plot) of 24-hour HRV in 94 healthy control subjects. Day-to-day reproducibility was evaluated on two occasions in 17 healthy subjects and 9 diabetic patients. The parameters of HRV were computed over time periods representing the day (6:00-24:00 hours), night (00:00-6:00 hours), and 24 hours in total. The results of all indexes, except for the LF/HF ratio and LF-NU, declined significantly with increasing age (p<0.05), but were independent of sex and BMI. The statistical, geometric, and non-linear measures (p<0.05), but not the frequency-domain parameters decreased significantly with increasing heart rate. Since the HRV data showed log normal distribution, log transformation was used to define the age-related lower limits of normal at the 2.5th centile. Intraindividual reproducibility was highest for the geometric measures. The nonlinear and statistical parameters also showed high reliability, except for the SNN50. The repeatability of the frequency domain measures was somewhat lower but still satisfactory. Reproducibility was lower in the diabetic than in the control group, higher during the day than during the night, and better than that reported previously for the AFTs. In conclusion, in healthy subjects the measures of 24-h HRV are not related to sex or BMI, but strongly dependent on age and heart rate, the latter except for the frequency domain measures. The majority of the HRV measures, in particular the geometric parameters, show a relatively high intraindividual reproducibility which underlines their suitability for the use in prospective studies.     

Diagnostic accuracy of the TIMI risk score in patients with chest pain in the emergency department: a meta-analysis

Background

The Thrombolysis in Myocardial Infarction (TIMI) risk score uses clinical data to predict the short-term risk of acute myocardial infarction, coronary revascularization or death from any cause. It was originally developed for use in patients with unstable angina or non–ST-elevation myocardial infarction. We sought to expand the clinical application of the TIMI risk score by assessing its prognostic accuracy in patients in the emergency department with potential acute coronary syndromes.

Methods

We searched five electronic databases, hand-searched reference lists of included studies and contacted content experts to identify articles for review. We included prospective cohort studies that validated the TIMI risk score in emergency department patients. We performed a meta-regression to determine whether a linear relation exists between TIMI risk score and the cumulative incidence of cardiac events.

Results

We included 10 prospective cohort studies (with a total of 17 265 patients) in our systematic review. Data were available for meta-analysis in 8 of the 10 studies. Of patients with a score of zero, 1.8% had a cardiac event within 30 days (sensitivity 97.2%, 95% CI 96.4–97.8; specificity 25.0%, 95% CI 24.3–25.7; positive likelihood ratio 1.30, 95% CI 1.28–1.31; negative likelihood ratio 0.11, 95% CI 0.09–0.15). Meta-regression analysis revealed a strong linear relation between TIMI risk score (p < 0.001) and the cumulative incidence of cardiac events.

Interpretation

Although the TIMI risk score is an effective risk stratification tool for patients in the emergency department with potential acute coronary syndromes, it should not be used as the sole means of determining patient disposition.Chest pain is a common presenting complaint in the emergency department that requires efficient risk stratification, timely initiation of treatment in high-risk patients and safe determination of patient disposition. Several studies have been published that stratify the risk of patients in the emergency department with chest pain.^1–5 However, only the Thrombolysis in Myocardial Infarction (TIMI) risk score, which was initially developed for use in patients with unstable angina or non–ST-segment elevation myocardial infarction or both,⁶ has been broadly validated in several independent emergency department populations with chest pain and thus constitutes the highest level of evidence available.The TIMI risk score assigns each of seven predictors a value of one point, allowing stratification of patients into one of eight prognostic categories (Box 1).⁶ The clinical end points are acute myocardial infarction, coronary revascularization and death from any cause.

Box 1.?Predictor variables included in the TIMI risk score^*

• Age of more than 65 years
• Three or more risk factors for atherosclerosis
• Known coronary artery disease
• Two or more episodes of anginal chest pain in the preceding 24 hours
• Acetylsalicylic acid use in the seven days before hospitalization
• ST-segment deviation of 0.05 mV or more
• Elevated cardiac markers

A robust estimate of the performance of the TIMI risk score obtained from a systematic review may prove useful to both clinicians and researchers. Clinicians would have a reliable quantitative estimate of a patient’s short-term risk of a cardiac event. This could be used as an adjunct to clinical acumen and as a tool to communicate risk to patients in a shared decision-making model of care.⁷ Researchers would also have an estimate of the prognostic accuracy of the TIMI risk score derived from different practice settings and patient populations that represent a wide variety of ethnic backgrounds. This estimate may serve as a useful baseline for comparison as emerging clinical prediction rules and imaging modalities continue to refine our approach to diagnosis and risk stratification in patients in the emergency department with potential acute coronary syndromes.We conducted a comprehensive systematic review and meta-analysis to assess the methodological quality and prognostic performance of studies that had prospectively validated the TIMI risk score in patients in the emergency department.     

Heart Rate Variability as an Alternative Indicator for Identifying Cardiac Iron Status in Non-Transfusion Dependent Thalassemia Patients

Background

Iron-overload cardiomyopathy is a major cause of death in thalassemia patients due to the lack of an early detection strategy. Although cardiac magnetic resonance (CMR) T2* is used for early detection of cardiac iron accumulation, its availability is limited. Heart rate variability (HRV) has been used to evaluate cardiac autonomic function and found to be depressed in thalassemia. However, its direct correlation with cardiac iron accumulation has never been investigated. We investigated whether HRV can be used as an alternative indicator for early identification of cardiac iron deposition in thalassemia patients.

Methods

Ninety-nine non-transfusion dependent thalassemia patients (23.00 (17.00, 32.75) years, 35 male) were enrolled. The correlation between HRV recorded using 24-hour Holter monitoring and non-transferrin bound iron (NTBI), hemoglobin (Hb), serum ferritin, LV ejection fraction (LVEF), and CMR-T2* were determined.

Results

The median NTBI value was 3.15 (1.11, 6.59) μM. Both time and frequency domains of HRV showed a significant correlation with the NTBI level, supporting HRV as a marker of iron overload. Moreover, the LF/HF ratio showed a significant correlation with CMR-T2* with the receiver operating characteristic (ROC) curve of 0.684±0.063, suggesting that it could represent the cardiac iron deposit in thalassemia patients. HRV was also significantly correlated with serum ferritin and Hb.

Conclusions

This novel finding regarding the correlation between HRV and CMR-T2* indicates that HRV could be a potential marker in identifying early cardiac iron deposition prior to the development of LV dysfunction, and may be used as an alternative to CMR-T2* for screening cardiac iron status in thalassemia patients.     

Heart rate variability dynamics for the prognosis of cardiovascular risk

Statistical, spectral, multi-resolution and non-linear methods were applied to heart rate variability (HRV) series linked with classification schemes for the prognosis of cardiovascular risk. A total of 90 HRV records were analyzed: 45 from healthy subjects and 45 from cardiovascular risk patients. A total of 52 features from all the analysis methods were evaluated using standard two-sample Kolmogorov-Smirnov test (KS-test). The results of the statistical procedure provided input to multi-layer perceptron (MLP) neural networks, radial basis function (RBF) neural networks and support vector machines (SVM) for data classification. These schemes showed high performances with both training and test sets and many combinations of features (with a maximum accuracy of 96.67%). Additionally, there was a strong consideration for breathing frequency as a relevant feature in the HRV analysis.     

Evaluation of receiver operator characteristics — optimum time of day for the assessment of heart rate variability after acute myocardial infarction

The study reports a mathematical method for deciding which clinical data are of importance for treatment decisions in a given clinical setting. The method comprises the following steps: (A) the receiver operator characteristic (ROC) functions of the compared sets of data are computed; (B) the design and aim of the clinical study is expressed as an integral measure on the space of sensitivity values (this reflects the preference of low or high sensitivity values dependent on the clinical targets); (C) the sets of data being compared are characterised by the non-linear integrals of their ROC functions. The approach has been used to compare mean heart rate (HR) and heart rate variability (HRV) data calculated in 5113 different portions of 24-h ECG recordings and assessed in 365 patients surviving acute myocardial infarction, in order to evaluate the utility of Holter recording of varying lengths and starting times for the prediction of sudden cardiac death and/or serious arrhythmic events. The results of the study show that this approach is capable of evaluating and comparing the sets of medical data used for identification of patients who are at increased risk. The experimental part of the study showed that the optimum recording interval for the assessment of HR and HRV data in patients who survived acute myocardial infarction depends on the aim of the identification of increased risk patients. The optimum interval of recording is different for an identification which requires a low number of false negative cases and permits a higher number of false positive cases, than for the situation where a low number of false positive cases are required and a higher number of false negative cases are permissible.