ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00278.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:Normal cardiovascular control involves nonstationary complex interactions between a variety of variables such as heart rate (HR), arterial blood pressure (ABP), and respiratory activity.Methods:To account for both the complexity and transient nature of these phenomena, a closed‐loop bivariate and time‐variant (moving window) model was implemented using autoregressive parametric techniques to identify the typical HR and ABP spectral parameters of low frequency power (LF, 0.03–0.15 Hz), high frequency power (HF, 0.15–0.45 Hz), and their ratio LF/HF. In addition, cross‐parameters, such as the gain, phase, and coherent power, between HR, ABP, and changes in instantaneous lung volume (ILV) were computed in both the LF and HF regions.Results:The cross‐relations included the HR baroreflex (ABP‐HR, alpha), respiratory sinus arrhythmia (ILV‐HR), the mechanical influence of respiration (ILV‐ABP), and the mechanical feedforward of HR (HR‐ABP, beta). The analyses were performed on data from a gradual tilt protocol, which simulates the physiological nonstationarities encountered in daily life.Conclusions:The results were similar to those obtained using a bivariate batch (nonmoving window) Levinson‐Wiggins‐Robinson algorithm, but the time‐variant technique was able to provide nearly continuous parameters, allowing for a real‐time continuous monito

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00279.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:The long‐term circadian behavior of the QT interval duration was comparatively evaluated in females and in males. The corrected QT interval duration is known to be longer in females than in males, and this gender difference persists after double autonomic blockade.Methods:Our population consisted of 32 young healthy subjects (16 males). Twenty‐four‐hour ambulatory ECG recordings were processed by QT analysis software. All sinus complexes were averaged on a 30‐second time basis. The averaged template was defined by a single QT apex (QTa) interval and its mean RR interval. The circadian behavior of ventricular repolarization was assessed by the nocturnal lengthening of QTa at an identical RR interval, and by the respective diurnal and nocturnal QT/AR relationship in both genders.Results:The corrected QTa was longer in females (318 ± 20 vs 294 ± 13 ms, P = 0.0003). The correlation coefficients of the QTa/RR regression lines were>0.75, whatever the gender and the circadian period considered. In both genders, diurnal slopes were higher than nocturnal ones (0.15 ± 0.01 vs 0.09 ± 0.03 in males and 0.18 ± 0.04 vs 0.09 ± 0.05, P = NS), and the nocturnal lengthening of QTa was on the same range (25 ± 12 vs 17 ± 12 ms, P = NS).Conclusion:The longer corrected QT interval in females is not associated with a specific static or dynamic circadian behavior

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00280.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:In heart rate variability (HRV) studies, the duration of the electrocardiographic recordings may vary between 20 seconds and 24 hours. Little is known about the reproducibility or comparability of HRV measures calculated over observation periods of different duration.Methods:To assess the reproducibility and comparability of HRV measures computed from short recordings under standardized conditions and from ambulatory 24‐hour recordings, 15 healthy young males were studied on three occasions.Results:The reliability coefficient (between subject variation divided by summed between and within subject variation) for 20‐second intervals was low for all measures. For 5‐minute intervals in supine position, but not standing position, the reliability coefficients of the standard deviation, root of mean squared successive differences, proportion of successive differences>50 ms, and the proportion low frequency power were about 70%. The reliability coefficients of the 24‐hour HRV measures were>80% for all measures. Short‐ and long‐term measures of heart rate and HRV appeared to be correlated, implying that these measures result in similar ranking of subjects.Conclusions:The results indicate that HRV measures based on 24‐hour monitoring during regular activities are better reproducible than short‐term measures under standardized conditions. A single 5‐minute recording may suffice to characterize a group of persons in a population study, but, because of considerable day‐to‐day variation, it is not adequate for indivi

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00281.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:Detection of late potentials (LPs) using signal‐averaged electrocardiograms (SAECGs) is believed to help in the prediction of malignant ventricular arrhythmias and sudden cardiac death in adults. Criteria for detection of LPs in adults may not be applicable for children, as these measurements are known to be age and sex specific.Method:SAECGs were recorded using MAC 15 ECG System. Duration of filtered QRS (TQRS), duration of high frequency, low amplitude signals in the terminal portion of QRS complex that are<40 μV (HFLA), and root mean square voltage of the last 40 ms of the filtered QRS (RMS40) were determined for 535 healthy Chinese children, ages 6–17 years (268 males, 267 females).Results:Both mean TQRS and RMS40were significantly different between the male and female children (TQRS: 106 ms vs 101 ms, P<0.001; and RMS40: 62 μV vs 75 μV, P<0.001). Mean TQRS and HFLA increased significantly with age, while mean RMS40decreased with age (P<0.0001). Ninetieth percentile values of TQRS and HFLA and tenth percentile value of RMS40were used as cut‐off values for normal limits. As such, the criteria for normal TQRS, HFLA, and RMS4Owere: TQRS<117 ms; HFLA12 μV. Since TQRS and RMS40were gender specific, the criteria for male and female were: TQRS: Male<118 ms, female17 μV.Conclusion:TQRS, HFLA, and RMS40were shown to be age and sex specific in healthy Chinese children. The criteria for normal TQRS, HFLA and RMS40were different from those proposed for adults, and this may be partly due to technical differences of the recor

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00282.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:The purpose of this trial was to evaluate a patient actuated transtelephonic cardiac monitoring system in order to document cardiac arrhythmias and cardiac pacemaker function.Material:Eighty‐two patients were prospectively evaluated, 69 with pacemaker (group I) and 13 with symptomatic arrhythmias (group II). Two different recorders were used: a memory loop‐recorder (KH) and a wrist‐worn recorder (HW). Both of them were implemented using a small, portable, battery‐powered transmitter, which monitors a modified V5 in KH and a lead 1 with the HW over regular nondigital pulse telephone lines.Results:In group I, 54 patients used single chamber pacemakers, 2 VDDR, and 13 used dual chamber devices. In group II, all patients included referred palpitations as their symptom. In group I, 248 registers were made using the KH and 50 with the HW. Recordings were made with KH had a 96% accuracy in the diagnosis of the ECG, while HW recordings failed to detect the QRS and the spike in 52% of the cases. Arrhythmia patients (group II) made 65 recordings with KH, all symptomatic: 28 were ventricular ectopic beats (23 isolated, 4 bigeminy, and 1 coupled ventricular ectopic beats); 9 supraventricular ectopic beats (isolated); 18 episodes of sinus tachycardia; and 10 normal sinus rhythm. Artifact was present partially in 6 other recordings, but did not affect the diagnosis. Two patients made no recordings and were excluded from the trial (group I).Conclusions:The loop‐recording transtelephonic monitoring system is an excellent tool for the evaluation of patients with symptomatic arrhythmias and pacemaker. The memory KH had an excellent performance, even over regular telephone lines. The accuracy of the HW recordings was low and failed to evaluate the QRS, probably due to the direction of the AQ

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00283.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:Frequency‐domain techniques presently used for micropotential analysis in the signal averaged ECG (SAECC) have several inherent shortcomings. For example, they depend on sensitive determination of the I‐point, which becomes inaccurate in the presence of noise, or derivation of multiple, complicated statistical parameters to quantify spectral characteristics in a three‐dimensional “spectral temporal map.” While these techniques are not as well accepted clinically as the conventional time‐domain Simson method, the latter is not without limitations either. Although time‐domain SAECG analysis has a very high negative predictive value, it has low positive predictive accuracy. Furthermore, it cannot be used to analyze SAECC data in patients with conduction delay problems, such as bundle branch block. Hence, the goal of this new frequency‐domain technique is to address and solve some of these shortcomings.Methods:The Fourier transform of the second derivative signal, or “acceleration spectrum,” extracts the frequency‐domain “signature” of damaged myocardium throughout the entire QRS complex, rather than from only the late potential region. The technique i s not dependent on precise endpoint or other fiducial point determination. A “spectral change index” (SCI) for quantifying variation from 50‐300 Hz in the acceleration spectrum i s calculated. The characterization of the cut‐off values for the SCI was based on results from a study including 50 postmyocardial infarction (post‐MI) patients (25 of whom were inducible to sustained ventricular tachycardia), and 10 normal controls.Results:An SCI<20, typical of a normal, “flat” acceleration spectrum in the 50‐ to 300‐Hz band width, may indicate undamaged myocardium, while an SCI 220 corresponding to a higher degree of spectral “fragmentation” in the same bandwidth, may indicate increased myocardial tissue damage. Using this cutoff, the sensitivity, specificity, and positive and negative predictive values for this initial study were 72%, 84%, 82%, and 75%, respectively.Conclusions:Acceleration spectrum analysis (ASA) using the SCI shows promise in predicting inducibility in post‐MI patients, including those with conduction delay problems. Since it is well documented that time‐domain SAECG has a high negative predictive value and a low positive predictive value, the high positive predictive value of the newly develope

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00284.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:The signal‐averaged electrocardiogram (SAECG) is a useful noninvasive diagnostic tool for assessing delayed ventricular activation.Methods:The advantage of the SAECG over standard ECGs the ability to detect very low amplitude signals indicative of areas of slowed myocardial conduction, a requirement for reentrant arrhythmias.Results:The SAECG has been proven useful in a variety of clinical situations, particularly in risk stratification after myocardial infarction or in the patient with dilated cardiomyopathy, and in screening for the need for electrophysiological studies in the syncope patient or the patient with nonsustained ventricular tachycardia.Conclusions:This review focuses on the currently accepted methodology of the time‐domain SAECG, and outlines the standard applications of the SAECG based on the results of important clinical resea

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00285.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00286.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:Throughout the 20th century electrocardiography has been almost exclusively preoccupied by the single dipole concept as a model to account for body surface manifestations of cardiac electrical activity. Vectorcardiography, based on the single dipole approximation as an equivalent cardiac generator, has prevailed for over one half of this century as one of the most prominent components of electrocardiographic research. In retrospect, vectorcardiography has had conceptually an important impact on the progress in electrocardiography although it never became widely used in clinical practice. Recent comparative studies have confirmed that the diagnostic information contents of the standard 12‐lead electrocardiogram and the vectorcardiogram are practically identical if adequately powerful, identical diagnostic classification procedures are used in extracting diagnostic information. After serving a useful role as a conceptual model, vectorcardiography is gradually fading away, being replaced by more realistic cardiac source models and by body surface leads supplementing in a better way the information content of the standard ECG lead

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00287.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY