bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relationship Between Ventricular Rate Variability in Nonsustained Ventricular Tachycardia and Subsequent Cardiac Events
Authors: Dabrowski Andrzej , Piotrowicz Ryszard 
Published: October 2006

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.
Frequency Response Characteristics Required for Detection of T‐Wave Alternans During Ambulatory ECG Monitoring
Authors: Hearing Bruce D. , Stone Peter H. , Verrier Richard L. 
Published: October 2006

Background: T‐wave alternans has been increasingly implicated as a potential marker of vulnerability to ventricular tachyarrhythmias in both experimental and clinical investigations. However, the suitability of ambulatory ECG (AECG) recorders for monitoring this parameter has not been systematically studied.Methods: We evaluated the frequency response characteristics and performance in monitoring a computer simulated alternans signal in three brands of amplitude‐modulated (AM) and one frequency‐modulated (FM) recorder and compared the results to those of the reference digital AECG unit.Results: A common feature of the AM recorders was distortion due to electronic head resonance, particularly at heart rates in the range of 60–100 beats/min. The maximum distortion of T‐wave morphology by the AM units was —6% to +28%.Conclusions: We conclude that digital and FM recorders are preferable for AECG monitoring of T‐wave alternans. AM recorders can be used if the distortion is not excessive.
T‐Wave Alternans During Ambulatory Ischemia in Patients with Stable Coronary Disease
Authors: Verrier Richard L. , Hearing Bruce D. , MacCallum Gail , Stone Peter H. 
Published: October 2006

Background: T‐wave alternans is a marker of vulnerability to ventricular tachyarrhythmias and has been documented during myocardial ischemia associated with angioplasty, bypass graft occlusion, and episodes of Prinzmetal's variant angina. We examined whether this phenomenon was present during ambulatory ischemia in ten patients randomly selected from the placebo phase of the Angina and Silent Ischemia Study [ASIS].Methods: The eligibility criteria for participation in the ASIS study were stable coronary disease, a positive exercise stress test, and verified ischemic episodes during ambulatory ECG (AECG) monitoring. For each patient, one ischemic episode was analyzed which met the criteria of > 2‐mm ST segment depression for > 3 minutes with a relatively stable ST segment baseline of > 1 hour preceding the index episode. T‐wave alternans was measured using the spectral analytical technique of complex demodulation.Results: In the stable coronary patients of the ASIS trial, we found that T‐wave alternans magnitude nearly tripled from 0.27 ± 0.02 mV × ms before ischemia onset to 0.77 ± 0.08 mV × ms (P < 0.01) during ischemic episodes. Heart rates ranged from 83 ± 2.9 beats/min prior to ischemia to 116 ± 2.5 beats/min during ischemia (P < 0.01). There was no statistical correlation between the magnitude of the ST segment depression > 2 mm and the ischemia‐induced increase in T‐wave alternans.Conclusions: We conclude that T‐wave alternans often occurs in association with ambulatory ischemia. Thus, risk assessment in stable coronary patients may be enhanced by monitoring both ST segment deviation and T‐wave alternans as they measure relevant but fundamentally different electrophysiological properties.
Time‐Frequency Analysis of Heart Rate Variability
Authors: Birand Ahmet , Saliu Sokol , Kudaiberdieva Gulmira Z. 
Published: October 2006

Background: The heart rate variability (HRV) signal is mainly analyzed in frequency‐domain and the signal's spectrum is estimated using either Fast Fourier Transformation (FFT) or the autoregressive (AR) model. These two methods assume that the HRV signal is stationary and additionally the AR method is based on the assumption that the model is linear and the signal is monocomponent in nature. Qualities of spectral estimates are thus closely related to the validity of the above assumptions. Evidence has accumulated indicating that HRV is a multicomponent, nonlinear and nonstationary signal. Then the spectral representations currently used would yield global, approximate, and smoothed view of HRV dynamics.Methods: We applied time‐frequency (TF) analysis methods, smoothed pseudo‐Wigner distribution (SPWD), and spectrogram and complemented for validation by FT spectrum to the HRV signal of fifteen apparently healthy volunteers (mean age 27.2 ± 5.6 years). Short‐term electrocardiograms (ECG) were recorded during supine and upright tilting positions (baseline recording). After baseline recording we induced parasympathetic, sympathetic, and total autonomic blockade correspondingly to six, nine, and four subjects. In addition, in four patients ECGs were recorded during controlled respiration.Results: SPWD and spectrogram revealed strips in frequency, or TF components, corresponding to FT components. High frequency (HF) components appeared stationary (in wide sense), with slight mean frequency shifts during spontaneous respiration, concurrent with respiratory motions. Low frequency (LF) and very low frequency (VLF) components had a nonstationary character displaying activity burst in time and interrelation in frequency. Upright tilting caused a uniform reduction in intensity and bandwidth of the HF component and enhancement of intensity and burst activity of the LF component. There was a pronounced decline of HF and LF components’intensity and decrease of HF component's bandwidth after parasympathetic blockade and total autonomic blockade, while the VLF component did not change. Sympathetic blockade was accompanied by augmentation of the LF and HF components’intensity associated with an increase in the HF component's bandwidth and the spreading of it in the region between the LF and HF. The LF component exhibited less burst activity during tilting under sympathetic blockade, as compared to baseline recordings during tilt. The VLF component's behavior did not change after sympathetic, parasympathetic, and total autonomic blockades.Conclusion: Application of TF distributions to the HRV signal offers a new representation of HRV dynamics. SPWD unveiled features in the HRV signal not available in separate time‐ and frequency‐domains. TF components display idiosyncratic behavior patterns in time and were effected by physiological and pharmacological interventions. A.N.E. 1996;1(4):411–418
Predictive Value of QT Dispersion for Ventricular Tachyarrhythmias in Patients with Implantable Cardioverter Defibrillator
Authors: Grimm Wolfram , Steder Ulrike , Menz Volker , Maisch Bernhard 
Published: October 2006

Background: QT dispersion, measured as interlead variability of QT intervals in the surface electrocardiogram, has been demonstrated to provide an indirect measurement of the inhomogeneity of myocardial repolarization as a potential substrate for ventricular arrhythmias.Methods: QT dispersion was measured in the standard 12‐lead ECG in 51 patients at the time of implantation of a third generation implantable cardioverter defibrillator (ICD) with automatic electrogram storage capability for electrical events triggering device therapy. In addition, QT dispersion was measured in 100 age‐ and sex‐matched healthy controls. All 5 1 study patients with ICD were prospectively followed to determine possible associations between QT dispersion at implant and subsequent spontaneous ICD shocks for ventricular tachyarrhythmias (VT).Results: Rate‐corrected QT dispersion and adjusted QTc dispersion, which takes account of the number of leads measured, were significantly greater in ICD patients compared to controls (76 ± 25 ms vs 46 ± 11 ms, and 24 ± 7 ms vs 14 ± 3 ms respectively, P < 0.0 1). During 15 ± 8 months follow‐up, ventricular tachyarrhythmias occurred in 23 (45%) of 51 ICD patients. QTc dispersion and adjusted QTc dispersion were not significantly different between ICD patients with ventricular tachyarrhythmias and ICD patients without ventricular tachyarrhythmias during follow‐up (74 ± 19 ms versus 77 ± 29 ms, and 23 ± 6 ms vs 25 ± 8 ms respectively).Conclusion: Increased QT dispersion measured in the 12‐lead standard ECG does not appear to be a useful marker for future arrhythmic events in a mixed patient population with ICD.
Reexamination of the Roles of Beta‐Endorphin and Cardiac Autonomic Function in Exercise‐Induced Silent Myocardial Ischemia
Authors: Hikita Hiroyuki , Kurita Akira , Takase Bonpei , Nakamura Haruo 
Published: October 2006

BackgroundAnginal pain perception has been reported to be modulated by endogenous opiates, or peripherally as a result of neuropathy. However, whether these factors can contribute to the mechanisms of silent myocardial ischemia remains unclear.MethodsBased on the results of previous exercise testing, a total of 140 patients (39 diabetic and 101 nondiabetic) with exercise‐induced myocardial ischemia were divided into the following four groups: 19 diabetics with silent myocardial ischemia; 49 nondiabetics with silent myocardial ischemia; 20 diabetics with anginal symptoms; and 52 nondiabetics with anginal symptoms. All patients underwent treadmill exercise testing and 24‐hour ambulatory electrocardiographic recording. Plasma beta‐endorphin levels and tactile thresholds were measured before and during exercise. With regard to the ambulatory electrocardiographic recording, the mean of the standard deviations (SDNNIDX) of all normal sinus RR intervals during successive 5‐minute recording periods over 24 hours was analyzed and considered as an index of the autonomic function.ResultsThe plasma beta‐endorphin level during exercise was significantly greater in nondiabetic patients with silent myocardial ischemia than in diabetics with silent myocardial ischemia and in nondiabetics with anginal symptoms. The SDNNIDX mean was significantly less in diabetics with silent myocardial ischemia than in diabetics with anginal symptoms; in nondiabetics with anginal symptoms; and in nondiabetics with silent myocardial ischemia.ConclusionsWe confirm that elevated beta‐endorphin levels are associated with silent myocardial ischemia in nondiabetic patients and that abnormalities in autonomic function seen in diabetes are associated with the silent form of myocardial ischemia. A.N.E. 1997;2(4):319–325
Signal‐Averaged Electrocardiogram: Update 1997
Authors: Mäkijärvi M. , Breithardt G. , Reinhardt L. , Fetsch T. , Borggrefe M. , Martinez‐Rubio A. 
Published: October 2006

BackgroundDuring the last 10 years, the signal‐averaged electrocardiographic (SAECG) method has been proposed for a growing amount of clinical applications. As a screening method for increased risk of life‐threatening ventricular arrhythmias it has demonstrated its value especially in risk stratification after myocardial infarction (Ml) and in the evaluation of patients with unexplained syncope. Its value in risk prediction is now also proven in patients treated with thrombolytic therapy.MethodsIn patients with dilated cardiomyopathy, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy, the SAECG is helpful for detecting propensity to spontaneous ventricular tachycardia. P wave signal averaging has been demonstrated to identify patients with propensity to atrial arrhythmias, especially atrial fibrillation. Also, the diagnosis of sick sinus syndrome can be enhanced using this method.ResultsSo far, the use of SAECG in other patient populations except coronary heart disease has been very limited. However, the results of the recent studies recommend the utilization of this technique also in children and in the elderly, adjusting the findings with the effects of body size and age on the SAECG.ConclusionsThe SAECG has a definite independent role in improving the predictive accuracy of conventional risk‐evaluation techniques in patients with Ml or cardiomyopathy. New patient populations like children and the elderly enlarge the number of patients benefiting of this method. New clinical applications of the SAECG method, such as detection of the propensity to atrial arrhythmias, ischemia and drug effects, are currently merging. Combining the time‐ and frequencydomain analysis of the SAECG with other methods relevant for the clinical problem is the way to optimize the use of this sophisticated noninvasive technique in clinical practice.
Effect of Repetitive, Transient Coronary Occlusions During Percutaneous Transluminal Angioplasty on Autonomic Cardiac Control
Authors: Limbruno Ugo , Strata Giancarlo , Petronio Anna Sonia , Baglini Roberto , Di Santo Domenica , Amoroso Giovanni , Zucchi Riccardo , Balbarini Alberto , Mariani Mario 
Published: October 2006

Background: Previous findings suggest that transient myocardial ischemia and reperfusion may elicit changes in the autonomic balance. In this study, a spectral analysis of heart rate variability was used to assess the modifications of sympathovagal balance induced by coronary angioplasty and their relationship with the occlusion site.Methods: We studied 23 patients (17M, 6F, age 58 ± 10 years) with left anterior descending and 19 patients (15M, 4F, age 56 ± 9 years) with right coronary artery stenosis. Spectral analysis of heart rate variability was performed, by autoregressive model, in basal conditions and during each balloon inflation. At least two inflations of 90–120 seconds were performed in each patient.Results: In patients with left anterior descending artery stenosis, the first occlusion induced marked changes in the autonomic balance, which moved toward a sympathetic predominance. The low frequency component of the spectrum and the low‐to‐high frequency ratio increased from 59 ± 10 normalized units (NU) to 75 ± 10 NU (P < 0.001) and from 2.4 ± 1.4 to 7.3 ± 4.7 (P < 0.001) respectively, while the high frequency component decreased from 30 ± 11 NU to 14 ± 7 NU (P < 0.001). These changes showed a progressive attenuation during repetitive occlusions, and were significantly correlated with the entity of myocardial ischemia assessed by the ST‐segment shift measured on the intracoronary electrocardiographic lead. On the contrary, in patients with right coronary artery stenosis the first occlusion was ineffective with regard to the spectral parameters whereas the third occlusion induced a significant increase in the high frequency component (from 31 ± 9 NU to 41 ± 10 NU, P < 0.01) and decrease in the low‐to‐high frequency ratio (from 2.1 ± 0.9 to 1.3 ± 0.5, P < 0.05) suggesting a vagal activation. The entity of vagal activation was not correlated with the ST‐segment shift.Conclusions: Our data indicate that repetitive coronary occlusions induce significant changes in the autonomic balance. The direction and the time course of these changes are related to the occlusion site.
Circadian Variation and Waking Hour Dynamics of the QT Interval
Authors: Singh Jagmeet P. , Johnston Jim , Sleight Peter , Marinho Maria F. , Kulangara Sara , Casadei Barbara , Hart George 
Published: October 2006

Background: The incidence of sudden cardiac death is maximal in the morning hours. Although ventricular arrhythmias have been implicated as a potential mechanism, and several neurohumoral factors affecting myocardial excitability have been shown to be raised in the early morning hours, it is not known if there is any circadian variation in the dynamics of ventricular repolarization when studied on a beat‐to‐beat basis. The objective of this study was to examine the range, diurnal variations, and circadian distribution of the variability of the QT interval in healthy subjects.Method: We developed and validated a new method for continuous measurement of QT intervals from 24‐hour Holter recordings. The QT intervals measured semi‐automatically were corrected by a linear regression formula derived independently for each patient from his own QT and RR values in 32 healthy males (20 ± 0.4 years). QT variability was assessed by the mean standard deviation of the average of consecutive uncorrected QT intervals (SDA‐QT Index) and corrected QT intervals (SDA‐QTc index) over 5‐minute segments. The rate‐dependent changes of the QT interval were studied as a function of the slope of the regression line between the QT and RR values.Results: The average QTc range was mean (SD) 79 (± 28) ms; the average maximal QTc interval was 481 (± 24) ms. The 95% upper confidence limit for the mean 24‐hour QTc interval was 443 ms. The RR, QT, and QTc intervals were longer, while the SDA‐QT and SDA‐QTc indices were shorter during sleep. Hourly averages of the SDA‐QT and SDA‐ QTc index revealed a sudden increase in QT variability in the first hour of waking (P < 0.0001 and P = 0.006).Conclusion: The dynamic behavior of the QT interval shows significant diurnal variations. The maximal QTc interval over 24 hours is longer than previously assumed. The period shortly following awakening is characterized by a peak in the variability of the QT interval. These changes may be indicative of autonomic instability during the early waking hours and correspond with the peak incidence of sudden arrhythmic death.
Twelve‐Lead QT Dispersion Is Smaller In Women Than In Men
Authors: Challapalli Sridevi , Lingamneni Rajeswari , Horvath George , Parker Michele , Goldberger Jeffrey J. , Kadish Alan H. 
Published: October 2006

BackgroundAlthough gender differences in the corrected QT interval (QTc) have been described, gender differences in QT dispersion (QTd) have not been carefully evaluated. This study was designed to measure QTd in 22 young healthy women and in 20 healthy men.Methods and ResultsTwelve‐lead ECGs were recorded at rest and following double autonomic blockade with atropine 0.04 mg/kg and propranolol 0.2 mg/kg during the menstrual, follicular, and luteal phases of the menstrual cycle, which was confirmed by hormone levels. Men were studied during three separate visits as controls. In women, there was no difference in QTd among the three phases of the menstrual cycle, and thus all three visits were pooled for comparison with men. The 12‐lead QT dispersion (maximum — minimum QT) was larger in men than in women at baseline (41 ± 17 ms vs 35 ± 16 ms), and this difference tended to decrease after double autonomic blockade (35 ± 14 ms vs 32 ± 11 ms). The standard deviation of the QT interval across the 12 leads was larger in men than in women at baseline (12.6 ± 4.5 vs 10.8 ± 4.1), and this difference was no longer significant after double autonomic blockade (10.4 ± 4.4 vs 10.1 ± 3.5). QT dispersion was significantly reduced by autonomic blockade (P < 0.05).Conclusions(1) Double autonomic blockade slightly reduces QTd. (2) QTd is higher in men than in women at baseline but more similar after autonomic blockade. These findings may contribute to the gender difference in the corrected QT interval. (3) Increased female QTd is not the mechanism of increased female susceptibility to torsade de pointes. The clinical implications of gender differences in QTd and QTc remain to be defined. A.N.E. 1998; 3(1):25–31
Spatial Dispersion of the Magnetocardiographically Determined QT Interval and Its Components in the Identification of Patients at Risk for Arrhythmia after Myocardial Infarction
Authors: Hailer Birgit , Van Leeuwen Peter , Lange Silke , Gronemeyer Dietrich , Wehr Michael 
Published: October 2006

BackgroundAim was the examination of the spatial distribution of QT interval in patients after Ml with and without VT. Analysis of the QT interval components was undertaken to identify those repolarization patterns that contribute essentially to heterogeneity of recovery times.MethodsMultichannel magnetocardiography was performed in 10 healthy subjects as well as in 18 patients after Ml of whom 8 had experienced clinical episodes of sustained VT in a period up to 4 years after Ml. For each subject, the temporal dispersion of the intervals QT, QRS, JT apex, T apex‐T offset, and QT apex was calculated as the difference between its minimal and maximal value. The spatial dispersion of each interval was examined visually by plotting the deviations of each channel from the minimal value with respect to its position. Local and global spatial variability was quantified using two smoothness indices, SI and Sin.ResultsDispersion and smoothness values for all intervals were generally significantly lower in the control group. When comparing patients with and without VT, dispersion values could not separate between patient groups. In contrast, SI and Sin values were significantly different, the VT group demonstrating higher values for QT, JT apex, and QT apex (P < 0.05).ConclusionSpatial analysis of the dispersion of cardiac time intervals is a better marker for increased risk for malignant arrhythmia than the strictly temporal approach using standard dispersion measures. In particular the results suggest that the heterogeneity of repolarization is the greatest during the interval between QRS offset and T apex.
The Potential Impact of Prehospital Electrocardiography and Telemetry on Time to Thrombolysis in a United Kingdom Center
Authors: Melville Martin R. , Gray David , Hinchley Malcolm 
Published: October 2006

BackgroundDespite efforts to modify patient attitudes, prehospital, and in‐hospital factors, the median symptom‐to‐needle and door‐to‐needle time to thrombolysis remains unacceptably long for patients experiencing the symptoms of acute myocardial infarction (AMI) in University Hospital, Nottingham.In order to circumvent avoidable in‐hospital delays, we evaluated the use of equipment undergoing field tests with the Nottingham ambulance crew that can record and transmit 12‐lead ECGs to the Coronary Care Unit (CCU) from the patient's home, and so enable the identification of patients with AMI who might be appropriate for direct admission to the unit.MethodsFrom November 1996, for 3 months, ambulance crews recorded ECGs on all patients with chest pain suggestive of AMI. These were transmitted to and assessed by coronary care nursing staff who decided whether they satisfied existing criteria for thrombolysis, and arranged direct admission to CCU. Door‐to‐needle times were recorded for those patients thrombolysed as a result.ResultsOne hundred consecutive ECGs were transmitted. Twenty‐two showed evidence of AMI resulting in direct admission. Of these, 17 (61%) had a final diagnosis of AMI. Eleven (65%) were eligible for thrombolysis, their median door‐to‐needle time being reduced by 60 minutes. The remaining 78 patients were taken to the Casualty Department for further assessment.ConclusionsECG 12‐lead telemetry could make a significant reduction on chest pain to needle time, reducing delay by at least 1 hour, and has the potential to facilitate out‐of‐hospital thrombolysis.