Nonstationarity and duration of the cardiac interval time series in assessing the functional state of operator personnel

The influence of nonstationarity in the time series of cardiac intervals on the assessment of the functional state (FS) of operator personnel was analyzed with a three-factor model of heart rhythm variability (HRV). ECG recordings were made in supine position at rest and in the sedentary position before and after important operator testing. In all three cases, the FS assessments were not influenced by nonstationarity of the input data. The effect of nonstationarity was also negligible for some particular HRV indices. Reliable assessments could be obtained from relatively short samples (256 down to 32 RR intervals) with prior norming of the factor indices for the corresponding segment length. The influence of the time series duration on the HRV indices was examined in various FSs; stable indices and proper recording conditions were determined.     

Comparative Evaluation of Heart Rate Variability Based on the Data of ECG and Blood Pressure Measurements

The development of new approaches to the assessment of heart rate variability (HRV) is an important problem, since HRV reflects the functioning of cardiovascular control and is affected by various diseases. The purpose of this study was to evaluate the informative value of statistical and spectral HRV parameters calculated from pulse interval (PI) data of blood pressure as compared with those calculated from RR-interval data of electrocardiograms (ECG). We recorded ECG in conscious rats using skin adhesive electrodes simultaneously with blood pressure signal obtained through a catheter in the femoral artery. It has been found that the PI sequence can be used to calculate the statistical HRV indices that describe the HRV at time intervals about 1 min or longer, but statistical indices of the PI and RR intervals may differ in the analysis of beat-tobeat variations. The power spectra of the RR intervals and PI coincide in the low-frequency region, including the band of baroreflex cardiac rhythm oscillation. However, they can differ in the high-frequency region (at respiration frequency and above).     

Subject-specific profiles of QT/RR hysteresis

The time lag of the QT interval adaptation to heart rate changes (QT/RR hysteresis) was studied in 40 healthy subjects (18 females; mean age, 30.4+/-8.1 yr) with 3 separate daytime (>13 h) 12-lead electrocardiograms (ECG) in each subject. In each recording, 330 individual 10-s ECG segments were measured, including 100 segments preceded by 2 min of heart rate varying greater than +/-2 beats/min. Other segments were preceded by a stable heart rate. In segments preceded by variable rate, QT/RR hysteresis was characterized by lambda parameters of the exponential decay models. The intrasubject SDs of lambda values were compared with the intersubject SD of the individual means. The lambda values were also correlated to individually optimized parameters of heart rate correction. Intrasubject SDs of lambda were substantially smaller than the population SD of individual means (0.390+/-0.197 vs. 0.711, P<0.0001). The lambda values were unrelated to the QT/RR correction parameters. When compared with the corrected QT (QTc) for averaged RR intervals in 10-s ECGs and with the averaged RR intervals in 2-min history, QTc for QT/RR hysteresis led to a substantially smaller SD of QTc values (11.4+/-2.00, 6.33+/-1.31, and 4.66+/-0.85 ms, respectively, P<0.0001). Thus the speed with which the QT interval adapts to heart rate changes is highly individual with intrasubject stability and intersubject variability. QT/RR hysteresis is independent of the static QT/RR relationship and should be considered as a separate physiological process. The combination of individual heart rate correction with individual hysteresis correction of the QT interval is likely to lead to substantial improvements of cardiac repolarization studies.     

Cardiovascular evaluation,including resting and exercise electrocardiography,before participation in competitive sports: cross sectional study

Objective To evaluate the clinical usefulness of complete preparticipation cardiovascular screening in a large cohort of sports participants.Design Cross sectional study of data over a five year period.Setting Institute of Sports Medicine in Florence, Italy.Participants 30 065 (23 570 men) people seeking to obtain clinical eligibility for competitive sports.Main outcome measures Results of resting and exercise 12 lead electrocardiography.Results Resting 12 lead ECG patterns showed abnormalities in 1812 (6%) participants, with the most common abnormalities (>80%) concerning innocent ECG changes. Exercise ECG showed an abnormal pattern in 1459 (4.9%) participants. Exercise ECG showed cardiac anomalies in 1227 athletes with normal findings on resting ECG. At the end of screening, 196 (0.6%) participants were considered ineligible for competitive sports. Among the 159 participants who were disqualified at the end of the screening for cardiac reasons, a consistent proportion (n=126, 79.2%) had shown innocent or negative findings on resting 12 lead ECG but clear pathological alterations during the exercise test. After adjustment for possible confounders, logistic regression analysis showed that age >30 years was significantly associated with an increased risk of being disqualified for cardiac findings during exercise testing.Conclusions Among people seeking to take part in competitive sports, exercise ECG can identify those with cardiac abnormalities. Follow-up studies would show if disqualification of such people would reduce the incidence of CV events among athletes.     

SNPs Identified as Modulators of ECG Traits in the General Population Do Not Markedly Affect ECG Traits during Acute Myocardial Infarction nor Ventricular Fibrillation Risk in This Condition

Background

Ventricular fibrillation (VF) in the setting of acute ST elevation myocardial infarction (STEMI) is a leading cause of mortality. Although the risk of VF has a genetic component, the underlying genetic factors are largely unknown. Since heart rate and ECG intervals of conduction and repolarization during acute STEMI differ between patients who do and patients who do not develop VF, we investigated whether SNPs known to modulate these ECG indices in the general population also impact on the respective ECG indices during STEMI and on the risk of VF.

Methods and Results

The study population consisted of participants of the Arrhythmia Genetics in the NEtherlandS (AGNES) study, which enrols patients with a first STEMI that develop VF (cases) and patients that do not develop VF (controls). SNPs known to impact on RR interval, PR interval, QRS duration or QTc interval in the general population were tested for effects on the respective STEMI ECG indices (stage 1). Only those showing a (suggestive) significant association were tested for association with VF (stage 2). On average, VF cases had a shorter RR and a longer QTc interval compared to non-VF controls. Eight SNPs showed a trend for association with the respective STEMI ECG indices. Of these, three were also suggestively associated with VF.

Conclusions

RR interval and ECG indices of conduction and repolarization during acute STEMI differ between patients who develop VF and patients who do not. Although the effects of the SNPs on ECG indices during an acute STEMI seem to be similar in magnitude and direction as those found in the general population, the effects, at least in isolation, are too small to explain the differences in ECGs between cases and controls and to determine risk of VF.     

Significance of the statistical characteristics of the sinus rhythm of the heart

Statistical analysis of prolonged continuous recordings of the ECG RR intervals was carried out in 64 patients with purulent surgical infection. The following indices were considered: the mean value of the RR intervals, the mean quadratic deviation (delta), the variation amplitude, the 1st and the 3rd correlation coefficients, the excess, asymmetry, the RR/delta ratio. Besides, the size and the shape of the autoregression could was analyzed. Statistically significant differences of the RR/delta ratio, of the mean quadratic deviation, and of the variation amplitude were revealed in 3 groups of patients differing by the severity of condition. These differences were reflected in the size and shape of the autoregression cloud. The results obtained suggest that statistical characteristics of prolonged recordings of the cardiac rhythm could be used for objective assessment of the severity of the patient's condition and of the therapeutic effect in the patients with a purulent surgical infection.     

Identification of patients with atrial fibrillation using HRV parameters]

Atrial fibrillation is the most common sustained cardiac rhythm disturbance. One of the most drastic complications is embolism, particularly stroke. Patients with atrial fibrillation have to be identified. This can lead to early therapy and thus avoiding strokes. The algorithm presented here detects atrial fibrillation securely and reliably. It is based on a single-channel ECG, which takes 60 min. First, the R-peaks are detected from the ECG and the RR interval is calculated. To be independent from pulse variations, the RR interval is normalized to 60 bpm. A parameter of heart rate variability is calculated in time domain (SDSD) and the so-called Poincaré plot is generated. The image analysis of the figures of the Poincaré plot is made automatically. The results from analysis in time domain, as well as image analysis, yield a risk level, which indicates the probability for the occurrence of atrial fibrillation. Even if there is no atrial fibrillation in the ECG while analyzing, it is possible to identify patients with atrial fibrillation. The sensitivity depends on the burden of atrial fibrillation. Even if a burden of 0% is assumed, the results still prove satisfactory (sensitivity of nearly 83%).     

Effect of long-term alcohol intake on the cardiovascular system of the rat

A group of rats was fed on control liquid diet, while another group was fed on liquid diet containing alcohol up to 36% of the total calories. After 4, 8 and 12 weeks of treatment ECG, haematocrit, histological structure of the heart, blood pressure, cardiac output, distribution of the organ fraction of cardiac output (by Sapirstein's method and 85Sr labelled microsphere technique), nutritive blood flow and circulatory resistance of the organs were studied. A mild repolarization disturbance was shown by the ECG record of the alcohol exposed animals. Haematocrit values and the histological structure of the heart did not change in any of the groups. Relative heart weight increased, blood pressure, total peripheral resistance and nutritive blood flow of the myocardium decreased, while myocardial vascular resistance increased. There was no significant interaction between the effects of alcohol and the duration of exposure to alcohol for any of the parameters monitored. It is concluded that chronic alcohol intake should be taken into consideration in aetiology of ischaemic heart disease.     

Determination of heart rate and heart rate variability in the equine fetus by fetomaternal electrocardiography

Heart rate is an important parameter of fetal well-being. We have analyzed fetal heart rate (HR) and heart rate variability (HRV) by fetomaternal electrocardiography (ECG) in the horse (Equus caballus) from midpregnancy to foaling. It was the aim of the study to detect changes in the regulation of fetal cardiac activity over time and to establish normal values in undisturbed pregnancies. A total of 22 mares were available for the study. Fetomaternal electrocardiography was a reliable technique to detect cardiac signals in fetuses between Day 173 of gestation and foaling. Fetal HR decreased from 115 ± 4 beats/min (Days 170 to 240 of gestation) to 83 ± 3 beats/min (Day 320) to 79 ± 1 beats/min (1 d before foaling; P < 0.001). Mean beat to beat (RR) interval and standard deviation of the RR interval (SDRR) increased (P < 0.001). Gestational age thus affects RR interval and HR in the equine fetus. From Days 270 to 340 of gestation, SDRR increased from 11.4 ± 1.3 msec on Day 270 to 27.8 ± 3.6 msec on Day 340 (P < 0.05), and the root mean square of successive RR differences (RMSSD) tended to increase (P = 0.07), indicating maturation of the fetal autonomous nervous system. For the last 10 d before foaling, fetal HR and HRV remained constant and did not allow predicting the onset of parturition in the horse. Only during the last 30 min before the foal was born, in 4 of 5 fetuses, HR decreased and RR interval increased. Accelerations and decelerations in HR were detectable at all times, but neither their number nor duration changed over time.     

L-arginine mitigates radiation-induced early changes in cardiac dysfunction: the role of inflammatory pathways

Our earlier studies demonstrated the ability of L-arginine (L-Arg) to reverse radiation-induced immune dysfunction. The aim of the present study was to investigate cardiac dysfunction up to 24 h after 2 Gy of total-body irradiation (TBI) and its mitigation by L-Arg. The current studies also explore the association of radiation-induced inflammation and electrocardiographic (ECG) abnormalities. TBI-induced cardiac iNOS and kinin B1 R, changes in the ECG profile like bradycardia, increased RR interval, ST elevation and increased QRS duration at 4 h and 24 h after TBI. TBI with 2 Gy induced inflammatory responses in spleen and cardiac tissue. L-Arg administered 2 h after TBI (TBI+L-Arg) mitigated the entire inflammatory response and ECG profile toward normalcy. L-Arg administered just before TBI (L-Arg +TBI) could not reverse the above-mentioned changes. Radiation-induced inflammatory responses at +4 h and +24 h after TBI in spleen and cardiac tissue correlated with the changes in ECG profile at the corresponding time. The results suggest the ability of L-Arg administered at the correct therapeutic window to mitigate radiation-induced cardiac dysfunction at 4 and 24 h after TBI.     

Is monomorphic tachycardia indeed monomorphic?

The dependence of some ECG characteristics on the excitation threshold was studied by mathematical modeling of cardiac arrhythmia in a 2D homogeneous excitable medium. It is shown that monomorphic tachycardias can arise both at elevated and at lowered excitability but the ECG characteristics in these cases are different.     

Open source model for generating RR intervals in atrial fibrillation and beyond

Background  

Realistic modeling of cardiac inter-beat (RR) intervals is highly desirable for basic research in cardiac electrophysiology, clinical management of heart diseases, and developing signal processing tools for ECG analysis.     

Non-linear dynamic analysis of the cardiac rhythm during transient myocardial ischemia.

Coronary artery occlusions related to myocardial ischemia drive cardiac control system reactions that may lead to heart failure. The purpose of this study was to assess the autonomic nervous system (ANS) response during prolonged percutaneous transluminal coronary angioplasty (PTCA). Continuous ECG data were acquired from 50 patients before and during PTCA, with occlusions in the left anterior descending, left circumflex or right coronary artery. Heart rate variability (HRV) was analyzed for 3-min segments of the R-R interval signal obtained from ECG data. The ANS behavior was evaluated by HRV analysis using fractal-like indices. The fractal scalar exponent alpha(1) and power-law slope beta decreased considerably during PTCA. This indicates that significant reactions of autonomic control of the heart rate occurred during coronary artery occlusions, with a reduction in complexity of the ANS.     

Assessment of diagnostic accuracy of SanketLife – A wireless,pocket-sized ECG biosensor,in comparison to standard 12 lead ECG in the detection of cardiovascular diseases in a tertiary care setting

BackgroundThe SanketLife is a low cost, portable, pocket sized 12 lead ECG mechanised by SanketLife app running on compatible iOS and Android phones that connect wirelessly via Bluetooth technology to the device.ObjectiveThe current study was conducted to assess the diagnostic accuracy of SanketLife ECG in comparison to standard 12 lead ECG (GE-2000) in detection of cardiovascular diseases.Research design and methodsThis was a prospective diagnostic test accuracy trial conducted in outpatient settings of a tertiary cardiac care centre in India. A total of 100 patients, attended cardiology OPD, were included in the study. Consecutive ECGs were taken by 12 lead standard ECG as well as by SanketLife ECG. Diagnostic accuracy variables such as sensitivity, specificity, negative and positive predictive value, negative and positive likelihood ratios were estimated. Ethical permission was taken from the Institutional ethical committee.Results & conclusionThe analysis showed a high degree of agreement and accuracy of SanketLife in detecting major cardiovascular conditions (Major Minnesota codes) such as Left and right bundle branch block, ST-segment elevation and ST-segment depression, AV conduction block. SanketLife showed high sensitivity (98.15%) and specificity (100%) in diagnosing major cardiovascular conditions.     

Breathing cardiovascular variability and baroreflex in mechanically ventilated patients

Heart rate and blood pressure variations during spontaneous ventilation are related to the negative airway pressure during inspiration. Inspiratory airway pressure is positive during mechanical ventilation, suggesting that reversal of the normal baroreflex-mediated pattern of variability may occur. We investigated heart rate and blood pressure variability and baroreflex sensitivity in 17 mechanically ventilated patients. ECG (RR intervals), invasive systolic blood pressure (SBP), and respiratory flow signals were recorded. High-frequency (HF) amplitude of RR and SBP time series and HF phase differences between RR, SBP, and ventilatory signals were continuously computed by Complex DeModulation (CDM). Cross-spectral analysis was used to assess the coherence and the gain functions between RR and SBP, yielding baroreflex sensitivity indices. The HF phase difference between SBP and ventilatory signals was nearly constant in all patients with inversion of SBP variability during the ventilator cycle compared with cycling with negative inspiratory pressure to replicate spontaneous breathing. In 12 patients (group 1), the phase difference between RR and ventilatory signals changed over time and the HF-RR amplitude varied. In the remaining five patients (group 2), RR-ventilatory signal phase and HF-RR amplitude showed little change; however, only one of these patients exhibited a RR-ventilatory signal phase difference mimicking the normal pattern of respiratory sinus arrhythmia. Spectral coherence between RR and SBP was lower in the group with phase difference changes. Positive pressure ventilation exerts mainly a mechanical effect on SBP, whereas its influence on HR variability seems more complex, suggesting a role for neural influences.     

The effect of NADP+ on cardiomyocyte electrophysiological properties of C57BL/6 and mdx mice

We have studied the influence of NADP⁺ on routine electrocardiography (ECG) in 6-month-old C57BL/6 and mdx mice. The animals were anesthetized by ether before ECG recording. ECG registration was carried out at a speed of 100 mm/s. The first ECG recording was made before intraperitoneal NADP⁺ injection in a dose of 13 or 80 mg/kg. The second ECG recording was made 10 min after NADP⁺ injection. Anesthesia was then terminated. The mice were occasionally anesthetized 45–60 min later, and the third ECG was recorded 1 h after injection of NADP⁺. ECG recording was carried out at a speed of 100 mm/s in standard leads I, II, and III and unipolar leads AvR, AvL, and AvF. Values of standard ECG characteristics, such as the P wave and the intervals PQ, QT, RR, and the QRS complex, were measured in milliseconds in standard lead II. We did not observe any differences between ECG magnitudes of 2- to 3-month-old C57BL/6 and mdx mice during trial experiments. Mice of both strains had a sinus rhythm in their heart rate. The QRS complex in mdx mice had a tendency to be larger than in C57BL/6 mice. Heart rates fluctuated between 722 ± 22 and 681 ± 21 beats per minute. The effect of NADP⁺ was studied in 6-month-old male mice. The increase in the RR interval and the decline in heart rate from 697 ± 21 to 461 ± 23 and 491 ± 28 beats per min for C57BL/6 mice (p < 0.01) and from 722 ± 28 beats per minute to 454 ± 31 beats per min for mdx mice were registered 10 min after NADP⁺ injection at a dose of 80 mg/kg. The increase in the RR interval can be explained by an increase in the QT interval. A statistically significant reduction in the QT interval leading to a diminished RR interval was observed in mdx mice 1 h after NADP⁺ injection. NADP⁺ at a dose of 13 mg/kg did not significantly change the ECG properties in mdx mice. ECG of mdx mice was characterized by negative repolarization of the T wave in 37% of all leads. The amount of leads with negative T-wave repolarization decreased up to 3% 1 h after NADP⁺ injection in dose of 80 mg/kg. The results have shown that cytomembranes of ventricular cardiac myocytes and the degree of oxidative stress are the main targets of the action of NADP⁺ in C57BL/6 and mdx mouse hearts.     

Echocardiography and cardiac resynchronisation therapy,friends or foes?

Echocardiography is used in cardiac resynchronisation therapy (CRT) to assess cardiac function, and in particular left ventricular (LV) volumetric status, and prediction of response. Despite its widespread applicability, LV volumes determined by echocardiography have inherent measurement errors, interobserver and intraobserver variability, and discrepancies with the gold standard magnetic resonance imaging. Echocardiographic predictors of CRT response are based on mechanical dyssynchrony. However, parameters are mainly tested in single-centre studies or lack feasibility. Speckle tracking echocardiography can guide LV lead placement, improving volumetric response and clinical outcome by guiding lead positioning towards the latest contracting segment. Results on optimisation of CRT device settings using echocardiographic indices have so far been rather disappointing, as results suffer from noise. Defining response by echocardiography seems valid, although re-assessment after 6 months is advisable, as patients can show both continuous improvement as well as deterioration after the initial response. Three-dimensional echocardiography is interesting for future implications, as it can determine volume, dyssynchrony and viability in a single recording, although image quality needs to be adequate. Deformation patterns from the septum and the derived parameters are promising, although validation in a multicentre trial is required. We conclude that echocardiography has a pivotal role in CRT, although clinicians should know its shortcomings.     

Assessment of Interaction Between Cardio-Respiratory Signals Using Directed Coherence on Healthy Subjects During Postural Change

PurposeTo detect and quantify the directional interaction changes between cardio-respiratory system during postural change.MethodTraditional frequency domain analysis based on power spectrum and coherence are insufficient to quantify nonlinear structures and complexity of physiological subsystems. Recently, Granger causality is found as preferable method for evaluation of causality i.e., directional interaction. Frequency domain Granger causality based on directed coherence has been used in this study to identify directional interaction between cardiac and respiratory signal during postural change from supine to standing for healthy subjects.ResultECG and respiration signal are recorded for this study. The beat-to-beat variability series from ECG provides heart rate (RR) and the respiration amplitude corresponds to RESP time series. It was observed that respiration is responsible for the changes in ECG signal during supine position as compared to standing. The outflow of information from RESP to RR increases during supine results in stronger interaction but reduces during standing result in reduction of interaction. Similarly, the effect of RR on RESP is found significant only during standing.ConclusionThe proposed directed coherence approach detects the cardio-respiratory regulation during postural change and provide information about coupling changes during this transition.     

Noninvasive cardiac psychophysiology as a tool for translational science with marmosets

The importance of marmosets for comparative and translational science has grown in recent years because of their relatively rapid development, birth cohorts of twins, family social structure, and genetic tractability. Despite this, they remain understudied in investigations of affective processes. In this methodological note, we establish the validity of using noninvasive commercially available equipment to record cardiac physiology and compute indices of autonomic nervous system activity—a major component of affective processes. Specifically, we recorded electrocardiogram and impedance cardiogram, from which we derived heart rate, respiration rate, measures of high‐frequency heart rate variability (indices of parasympathetic autonomic nervous system activity), and ventricular contractility (an index of sympathetic autonomic nervous system activity). Our methods produced physiologically plausible data, and further, animals with increased heart rates during testing were also more reactive to isolation from their social partner and presentation of novel objects, though no relationship was observed between reactivity and specific indices of parasympathetic or sympathetic nervous system activity.     

Grammatic representation of beat sequences for fuzzy arrhythmia diagnosis

The final stage of a system for automatic monitoring of cardiac arrhythmias is the diagnosis of the rhythm or arrhythmia present in the patient during the monitoring process. In this paper we approach the detection process by means of the analysis of the electrocardiographic signal (ECG) on a surface lead produced by those arrhythmias which can be recognized by identifying specific beat sequences and taking into account contextual information, mainly rhythm information. We have developed a diagnosis process for arrhythmias which uses a fuzzy classification of beats according to their etiology or focus of origin. The process we describe permits a more adequate consideration by the user of the arrhythmias diagnosed by the system, mainly in those cases in which the information derived from ECG analysis is not determinant.