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  • 1
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Coronary artery disease (CAD) is associated with a small but measurable amount of electrical disorganization, which may appear as temporal electrical heterogeneity on the electrocardiogram and is not visible with the low resolution, 12-lead electrocardiogram. A newly developed, multilead, high-fidelity variance cardiograph captures the heterogeneity component of the electrocardiograph signal. The subsequent analysis produces an electrical heterogeneity index (EHI) by quantifying phase-invariant electrical disorganization, which represents cardiac abnormalities that are modulated onto the measured high frequency electrocardiogram. A prospective investigation was conducted to determine the predictive accuracy of the variance cardiograph to detect clinically important CAD.Methods: Sixty-five patients (group I) with documented CAD were given the variance cardiography test, as well as 21 normal volunteers (group II). An EHI 〉; 75 from the variance cardiograph was determined to best represent a positive test for clinically important CAD.Results: Group I had a mean EHI of 89.5 ± 19.7, while group II had a mean EHI of 61.1 ± 19.1 (P 〈 0.001). The variance cardiograph had a sensitivity of 79%, a specificity of 76%, a positive predictive value of 91%, and a negative predictive value of 55%.Conclusions: These results demonstrate that analysis of the temporal electrical heterogeneity component of the electrocardiographic signal obtained by the variance cardiograph provides a new and reliable stress-free test For the detection of CAD.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Clinical and experimental observations indicate that reduced beat-to-beat changes in the cycle length of nonsustained ventricular tachycardia (NSVT) may portend malignant ventricular tachyarrhythmias and sudden cardiac death. The purpose of the study was to test the hypothesis that measures of ventricular rate variability during NSVT (VRV-NSVT) may be useful in identifying patients at high risk of life-threatening arrhythmic events.Methods: The study group consisted of 326 patients who had NSVT on 24-hour ECG recordings. Temporal changes in up to 10 beat-to-beat intervals of NSVT runs (V-V) were assessed. The following parameters of VRV-NSVT were calculated: (1) average value of successive differences in V-V intervals (ADVV); and (2) normalized average value of successive differences in V-V intervals (nADVV).Results: During a mean follow-up of 4 years, 52 (16%) patients had a documented episode of sustained VT or ventricular fibrillation. Patients with these arrhythmic events had significantly (P 〈 0.001) lower values of ADVV and nADVV variables in comparison to patients without arrhythmic events. The relative risk of malignant arrhythmic events for patients with ADW 〈 40 ms was 4.9 (P 〈 0.001), for patients with nADVV 〈 6%, the risk was 3.9 (P 〈 0.001).Conclusions: The results of this study indicate a strong and significant relationship between NSVT and the risk of subsequent malignant ventricular tachycardia. The assessment of VRV-NSVT may be useful for identifying patients at high and low risk for subsequent arrhythmic events.
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  • 3
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Depressed heart rate variability (HRV) is associated with increased risk for sudden cardiac death after myocardial infarction. Beta-blocker therapy reduces the risk of sudden cardiac death in patients with recent infarction. There is also evidence that beta-blockers improve HRV in postinfarction patients. In this study, we investigated whether the association between HRV and cardiac mortality in postinfarction patients is different in those who, on clinical grounds are and are not discharged on beta-blocker therapy.Methods: HRV was assessed from 24-hour ambulatory electrocardiograms before hospital discharge in 438 survivors of acute myocardial infarction. After the recordings, 147 patients were prescribed beta-blockers and 291 were discharged without beta-blocker therapy. The patients were followed for at least 2 years using cardiac death and arrhythmic death as clinical endpoints. Patients were dichotomized to depressed and normal HRV at the lowest 30 percentile.Results: Multivariate logistic regression analysis showed that HRV was a sigificant determinant of cardiac (P 〈 0.001) and arrhythmic mortality (P 〈 0.001) in patients who were not on beta-blocker therapy, whereas it was not a predictor of cardiac or arrhythmic mortality in patients who were taking beta-blockers. Beta-blocker therapy was associated with a significantly lower total cardiac mortality and arrhythmic mortality in patients with depressed HRV (P 〈 0.01 and P 〈 0.05, respectively). In patients with normal HRV, the reduction of mortality was smaller and remained nonsignificant.Conclusion: HRV was not a predictor of cardiac mortality in postinfarction patients who were prescribed beta-blockers before hospital discharge. In addition, beta-blocker therapy was associated with a lower cardiac mortality, particularly in patients with depressed HRV. Thus, depressed HRV might be considered as an additional indication for beta-blocker therapy in postinfarction patients.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: Nonsustained ventricular tachycardia (NSVT) predicts mortality in several disorders but its significance in patients with sustained ventricular tachyarrhythmias is unknown. We analyzed the clinical features and outcome associated with NSVT (〉; 3 beats at 〉; 100 beats/min) recorded on a 48-hour Holter in the absence of antiarrhythmic drugs.Methods: Patients enrolled in the ESVEM trial (n = 486) were grouped according to the duration of the longest recorded episode of NSVT, and in the second analysis, according to frequency of recorded episodes. Assessments were on an intention-to-treat basis.Results: Patients without NSVT were more likely to have ischemic heart disease and had significantly lower frequencies of single and paired premature ventricular complexes (PVCs). There were no significant differences with respect to age, sex, presenting arrhythmia, years since last myocardial infarction, functional class, or present ejection fraction. The cumulative probabilities of arrhythmia recurrence and all-cause mortality at 4 years in patients without NSVT (60%± 7% and 32%± 6%, respectively) were not significantly different than those of patients with NSVT (63%± 3% and 41%± 3%, respectively). Cox regression models indicated that ejection fraction and functional class were significant predictors of outcome, but variables based on the presence, duration, and frequency of recorded episodes of NSVT were not.Conclusions: NSVT is common in patients with spontaneous and inducible sustained ventricular tachyarrhythmias and at least 10 PVCs/hour (ESVEM enrollment criteria), but is not a significant predictor of arrhythmia recurrence, sudden death, or all-cause mortality in patients with these characteristics.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: This study was designed to evaluate the effects of autonomic tone on the QT interval, using conventional and heart rate independent analysis. Effects of autonomic tone on the QT interval have been studied either using rate correction formulae or during fixed rate atrial pacing, both of which have been associated with problems. Since most autonomic interventions are associated with heart rate changes, separation of “true” autonomic effects from rate related effects on the QT interval is essential.Methods: Electrocardiographic recordings were performed in 14 healthy volunteers during: (1) sympathetic stimulation (tilt, epinephrine infusion, isoproterenol infusion, and exercise); (2) β-adrenergic blockade; (3) parasympathetic blockade; (4) autonomic blockade; (5) tilt following autonomic blockade; (6) parasympathetic stimulation (phenylephrine infusion); and (7) isolated α-adrenergic stimulation (phenylephrine infusion following atropine). The QT interval was adjusted for heart rate using Bazett's formula. Heart rate independent analysis was performed between conditions with similar cycle lengths.Results: QT interval measurements were reproducible and exhibited the typical QT-RR relationship. Sympathetic stimulation decreased the RR interval and prolonged the QTc interval. Parasympathetic blockade also increased the QTc. Heart rate independent analysis of the effects of β-blockade showed a shortening of the QT (from 368.5 ± 20.5 ms to 355.9 ± 17.9 ms; n = 8). Alpha-adrenergic stimulation also decreased the QT interval from 302.4 ± 16.8 ms to 294.3 ± 17.7 ms (n = 7).Conclusion: Sympathetic stimulation prolongs the QT interval, while β-blockade shortens it. Alpha-adrenergic stimulation also shortens the QT interval. Autonomic effects on the QT interval as assessed by heart rate independent analysis may help separate the true autonomic effects from rate related effects.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: The signal-averaged ECG is a widely used and accepted technique for analysis of low-level cardiac signals. This article reviews a new and enhanced form of ECG signal averaging: the time-frequency plane Wiener (TFPW) filter.Methods: The TFPW filter accelerates the process of noise reduction. It facilitates use of signal averaging in settings previously unexplored with the technique, where a limited number of beats may be available.Conclusion: Example applications of the TFPW filter include improved analysis of ventricular late potentials and analysis of dynamic events, such as transient ischemia.
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  • 7
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 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 developed ASA increases the overall value of the SAECG test.
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  • 8
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 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 AQRS vector.
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  • 9
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: We evaluated classification accuracy of ECG criteria at varying levels of left ventricular hypertrophy (LVH) severity according to echocardiographically measured left ventricular mass (LVM) adjusted to body size.Methods: The test population was derived from the Cardiovascular Health Study (CHS), a population-based sample of 5201 men and women aged 65 and older, and consisted of 1844 women and 1119 men with adequate quality ECGs and echocardiograms for LVM determination. The criteria evaluated were Sokolow-Lyon, Cornell voltage, Cornell product, Framingham modification of the Cornell voltage, and the left ventricular mass index (LVMI) of the Novacode ECG program.Results: With LVH thresholds at upper 95% normal limit for weight adjusted LVM for the CHS population and ECG thresholds adjusted for 95% specificity in normal weight and overweight subgroups, the sensitivity of ECG criteria for LVH was relatively low. It was highest (40.8%) for the Novacode LVMI in normal weight men and for the Framingham criteria (30.9%) in normal weight women, but it deteriorated for both of these criteria in the presence of obesity. The overall performance of the Cornell product and Cornell voltage criteria was least influenced by obesity. The Framingham adjustment for the Cornell voltage criteria for obesity substantially reduced their sensitivity.Conclusion: The choice of echocardiographic standard, LVH severity level and overweight in the test groups have a strong influence on ECG evaluation results.
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  • 10
    Electronic Resource
    Electronic Resource
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2XG , UK . : Blackwell Publishing, Inc.
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The recognition of the ubiquitous role of short coupled ectopics in the initiation of paroxysmal atrial fibrillation has renewed interest in their localization with the ultimate aim of facilitating their neutralization by catheter ablation. The P-waves resulting from such ectopics are partly or completely concealed by the QRST of the preceding beat and therefore their morphology has been underutilized for localization purposes. Subtraction has been the most commonly used technique for QRST suppression and though an averaged template offers a higher signal-to-noise ratio, the immediately preceding QRST provides the best match between template and target and allows simple, nearly real-time, and accurate subtraction without distorting the underlying P-wave. Algorithms derived from clinical tachycardias as well as pacemapping have permitted a rational analysis and accurate prediction (81%) of the correct pulmonary vein of origin. Other nonpulmonary sources may also be similarly localized, particularly with the help of a catalogue of pacemaps from various sites. Incessant arrhythmia and frequent aberrancy limit the effectiveness of QRST suppression by subtraction. Further improvements in the localizing resolution of the P-wave may depend upon knowledge of the relationship between recording electrodes and the underlying atria.
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