ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00255.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:The triggering role of the autonomic nervous system in the initiation of ventricular tachycardia has not been established. To investigate the relationship between changes in autonomic activity and the occurrence of nonsustained ventricular tachycardia (NSVT) we examined heart rate variability (HRV) during the 2‐hour period preceding spontaneous episodes of NSVT. Twenty‐four subjects were identified retrospectively as having had one episode of NSVT during 24‐hour Holter ECG recording.Methods:We measured the mean interval between normal beats (meanRR), the standard deviation of the intervals between beats (SD), the percentage of counts of sequential intervals between normal beats with a change of>50 ms (%RR50), the logarithms of low‐ and high‐frequency spectral components (InLF, InHF) of HRV for sequential 10‐minute segments preceding NSVT. The correlation dimension (CDim) of HRV was calculated similarly for sequential 20‐minute segments. We assessed the significance of the time‐course change of each marker over the 120‐minute period prior to NSVT onset.Results:MeanRR (P<0.05), InLF (P<0.0001), InHF (P<0.0001), the natural logarithm of the ratio of LF to HF (ln[LF/HF]; P<0.05), and CDim (P<0.05) showed significant time‐course changes during that period, while SD and %RR50 did not. MeanRR, InLF, InHF, and CDim all decreased prior to the onset of NSVT, whereas ln(LF/HF) increased. We divided the subjects into two groups: one consisting of 12 patients with coronary artery disease; and the second group of 12 patients without known coronary artery disease. Both groups showed significant changes (P<0.05) of CDim, InLF, and InHF preceding the episodes of NSVT.Conclusions:Changes in the pattern of HRV prior to the onset of episodes of NSVT suggest that changes in autonomic activity may commonly play a role in the triggering of spontaneous episodes of NSVT in susceptible patients. The measured changes suggest a reduction in parasympathetic activity, perhaps in conjunction with an increase in sympathetic activit

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00256.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

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

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00257.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

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 detec

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00258.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

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 sub

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00259.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

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 ch

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00260.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

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 QTcinterval. 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

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00261.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:The aim of this study was to analyze the characteristics of stable patients with resting ST segment depression on the resting electrocardiogram (ECG) following an acute ischemic event (i.e., infarction or unstable angina) to better understand its association with subsequent cardiac death and nonfatal infarction. The recent Multicenter Study of Myocardial Ischemia (MSMI) demonstrated that the resting ST segment depression had an independent prognostic value.Methods:We studied clinical features, noninvasive test results and coronary arteriography findings in 99 patients with ST depression on the resting ECG and 837 patients without ST segment depression with respect to endpoints of cardiac death and hospitalization for acute myocardial infarction or unstable angina.Results:Our results showed that patients with resting ECG ST depression were significantly older with a higher incidence of hypertension, angina, claudication, and tobacco use. ST depression on the resting ECG correlated closely with ST segment depression on the 24‐hour ambulatory ECG and the exercise ECG but not with redistribution on the thallium perfusion scan. Left ventricular diastolic pressure was higher and exercise duration less in patients with ST depression. Although not achieving statistical significance, patients with ST depression did show more extensive coronary disease and a lower ejection fraction.Conclusions:ECG ST depression was associated with cardiac death and nonfatal reinfarction over the follow‐up period only in patients originally admitted with an acute infarction but not in patients hospitalized for unstable angina. The reason for this appears to be an association of ST depression with increased age, the presence of hypertension, the presence of more severe coronary disease, and more extensive myocardial dam

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00262.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:The nonstationary conditions of unrestricted ambulatory ECG monitoring preclude any meaningful detection of short‐term transient events by conventional time series methods. Time‐frequency analysis offers a unique approach that tracks the frequency content of the signal as it is changing in time.Methods:We compared the ability of three methods: time‐frequency, RR interval time series, and global HR power spectra to detect the occurrence of silent ischemia (ST depression>1.5 mm × 80 ms for at least 2 min) among 17 Holter records. The records were obtained from five patients (age 52 ± 2 years) with angiographic coronary artery stenosis>70%. Individual segments were analyzed in a blinded fashion by three of the authors (MK, EF, AM).Results:Neither changes in the RR interval series nor sequential 2.2‐minute power spectra was significantly predictive of ischemia. Conversely, an abrupt loss of variance in the time‐frequency plot was associated with ST depression 82.3% of the time (Chi square = 3.41; P<0.055). There was a weaker correspondance between the duration of ST depression and loss of autospectral power.Conclusions:Although a significant correlation (r2= 0.863) was seen between the maximum low frequency power (sympathetic modulation) and sudden decreases in RR interval, there were at least three instances where no detectable change in HR occurred during episodes of ischemia. These preliminary observations offer hope that time‐frequency methods may prove useful in the detection of transient events in the ambulato

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00263.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Background:We sought to assess reproducibility, effects of various lead systems, and influence of physical activity on the results of signal‐averaged ECG obtained from the digital Holter system. Late potentials are routinely recorded using specially designed electrocardiographic devices. It has been shown recently that late potentials can also be recorded and analyzed from Holter tapes, which enables to examine possible dynamic changes of late potentials in relation to transient ischemia and spontaneous ventricular arrhythmias. However, there are some technical limitations of the signal‐averaged ECG analysis from Holter tapes that may be overcome by the use of digital, solid‐state Holter recorders where the ECG signal is acquired directly by the computer system and analyzed in real time.Methods:The signal‐averaged ECG was recorded at rest from XYZ leads and from lead system suggested by the manufacturer (Holter leads), and during moderate physical activity in 34 postin‐farction patients, using a new solid‐state Holter recorder. From each of these 20 minutes of recording, four consecutive ECG segments, lasting 5 minutes, were averaged, combined into vector magnitude, and analyzed using a Butterworth bidirectional filter between 40 and 250 Hz.Results:Reproducibility of signal‐averaged ECG was high; the P values (ANOVA) ranged from 0.93–0.99. Of the individual signal‐averaged ECG variables, reproducibility of the total QRS duration was superior to that of the terminal QRS measurements (the standard deviations of the mean relative errors were 6.3% vs 22.3% and 24.4%, respectively). There were no signifcant differences in signal‐averaged ECG variables when results obtained using orthogonal XYZ leads were compared with those obtained from Holter leads. Modest physical activity (slow walk) did not alter significantly signal‐averaged ECG variables. The values of the total QRS duration were more consistent than the terminal QRS measurements when two lead confgurations and recordings obtained during rest and physical activity were compared.Conclusions:Reproducibility of signal‐averaged ECG analysis obtained from a digital Holter system is high, the results are similar using XYZ or Holter leads, and the signal‐averaged ECG can be recorded and analyzed durin

ISSN:1082-720X    

DOI:10.1111/j.1542-474X.1996.tb00264.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY