bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model of Contiguity for Spatial Unit Allocation
Authors: Shirabe Takeshi
Published: October 2006

We consider a problem of allocating spatial units (SUs) to particular uses to form “regions” according to specified criteria, which is here called “spatial unit allocation.” Contiguity—the quality of a single region being connected—is one of the most frequently required criteria for this problem. This is also one that is difficult to model in algebraic terms for algorithmic solution. The purpose of this article is to propose a new exact formulation of contiguity that can be incorporated into any mixed integer programming model for SU allocation. The resulting model guarantees to enforce contiguity regardless of other included criteria such as compactness. Computational results suggest that problems involving a single region and fewer than about 200 SUs are optimally solved in fairly reasonable time, but that larger problems must rely on heuristics for approximate solutions. It is also found that a problem of any size can be formulated in a more tractable form when a fixed number of SUs are to be selected or when a certain SU is selected in advance.
The Clinical Significance of Nonsustained Ventricular Tachycardia in Patients with Sustained Ventricular Tachyarrhythmias
Authors: Anderson Kelley P. , Mori Motomi ,   ESVEM Trial Investigators
Published: October 2006

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.
Interobserver Reproducibility of QT Interval Measurement and QT Dispersion in Patients After Acute Myocardial Infarction
Authors: Kautzner Josef , Gang Yi , Kishore Ravi , Copie Xavier , Janota Tomas , Nagayoshi Hirokazu , Camm A. John , Malik Marek
Published: October 2006

Background: The study evaluated interobserver differences in the classification of the T‐U wave repolarization pattern, and their influence on the numerical values of manual measurements of QT interval duration and dispersion in standard predischarge 12‐lead ECGs recorded in survivors after acute myocardial infarction.

Methods: Thirty ECGs recorded at 25 mm/s were measured by six independent observers. The observers used an adopted scheme to classify the repolarization pattern into 1 of 7 categories, based on the appearance of the T wave, and/or the presence of the U wave, and the various extent of fusion between these. In each lead with measurable QRST(U) pattern, the RR, QJ, QT‐end, QT‐nadir (i.e., interval between Q onset and the nadir or transition between T and U wave) and QU interval were measured, when applicable. Based on these measurements, the mean RR interval, the maximum, minimum, and mean QJ interval, QT‐end and/or QT‐nadir interval, and QU interval, the difference between the maximum and minimum QT interval (QT dispersion [QTD]), and the coefficient of variation of QT intervals was derived for each recording. The agreement of an individual observer with other observers in the selection of a given repolarization pattern were investigated by an agreement index, and the general reproducibility of repolarization pattern classification was evaluated by the reproducibility index. The interobserver agreement of numerical measurements was assessed by relative errors. To assess the general interobserver reproducibility of a given numerical measurement, the coefficient of variance of the values provided by all observers was computed for each ECG. Statistical comparison of these coefficients was performed using a standard sign test.

Results: The results demonstrated the existence of remarkable differences in the selection of classification patterns of repolarization among the observers. More importantly, these differences were mainly related to the presence of more complex patterns of repolarization and contributed to poor interobserver reproducibility of QTD parameters in all 12 leads and in the precordial leads (relative error of 31%–35% and 34%–43%, respectively) as compared with the interobserver reproducibility of both QT and QU interval duration measurements (relative error of 3%–6%, P < 0.01). This observation was not explained by differences in the numerical order between QT interval duration and QTD, as the reproducibility of the QJ interval (i.e., interval of the same numerical order as QTD was significantly better (relative error of 7.5%–13%, P < 0.01) than that of QTD.

Conclusions: Poor interobserver reproducibility of QT dispersion related to the presence of complex repolarization patterns may explain, to some extent, a spectrum of QT dispersion values reported in different clinical studies and may limit the clinical utility in this parameter.
Comparison of Computerized and Standard Visual Criteria of Exercise ECG for Diagnosis of Coronary Artery Disease
Authors: DelCampo Jaime , Do Dat , Umann Tianna , McGowan Vernell , Froning Jeffrey , Froelicher Victor
Published: October 2006

Objective: To review past and current studies of computerized exercise ECG criteria in order to establish which, if any, are superior to standard visual analysis for the diagnosis of coronary artery disease (CAD).

Methods: Prior studies that compared multiple computerized ECG criteria were reviewed. In addition, we investigated two sets of patients that had both exercise testing and coronary arteriography at two university‐affiliated Veteran's Affairs Medical Centers. Patients with previous myocardial infarction or coronary artery bypass surgery, valvular heart disease, left bundle branch block, or any diagnostic Q waves present on their resting ECGs were excluded from analysis. Sensitivity and specificity values were compiled for standard visual analysis and for the following computerized ECG criteria: ST0; ST60; ST slope; ST integral; ST index; R wave adjusted ST; ST/heart rate (HR) index; Hollenberg's Treadmill exercise score; and discriminant function analysis (DFA).

Results: Despite the effects of limited challenge and work‐up bias, the compiled results indicate that ST measurements recorded during the time of recovery from exercise are substantially more diagnostic than those recorded at maximal exercise. ST integral, ST60, and R wave adjusted ST60 during recovery are especially discriminating of CAD, while Hollenberg's treadmill exercise score is not. There were inconclusive results for HR adjustments to ST depression and ST index. DFA including visual analysis of the ECG consistently exhibited the greatest discriminating power of all computerized results.

Conclusion: Although DFA, ST integral during recovery, or ST60 during recovery exhibited improved predictive value, further research is necessary before we can clearly offer a superior alternative to standard visual analysis.
Vagal Influence on Deterministic Chaos of Heart Rate in Patients after Acute Myocardial Infarction
Authors: Hagerman Inger , Berglund Margareta , Ericson Mats , Sylvén Christer
Published: October 2006

Objectives

To test heart rate variability (HRV) in patients with acute myocardial infarction (AMI) for nonlinear deterministic complex behavior and for its dependence on autonomic tone.

Methods

Fifteen patients (mean age 55, 14 men) with AMI and 16 healthy individuals (mean age 41, 11 men) with ongoing beta‐adrenergic receptor blockade were investigated after intravenouse administration of atropine (0.03 mg/kg). Nonlinear indices for HRV were assessed by local sensitive dependence on initial conditions as quantitated by the Lyapunov exponent, fractal dimension (FD), and correlation dimension. Linear indices for HRV were assessed in the time domain by the standard deviation of the RR interval (SD‐RR), the coefficient of variation (CV%), and the mean successive difference (MSD). In the frequency domain, the following indices were used: very low frequency power (VLF), low frequency power (LF), high frequency power (HF), total power (TP), and the ratio between low and high frequency power (LF/HF).

Results

Surrogate data analysis revealed independent behavior of the Lyapunov exponent, the FD, and the correlation dimension, suggesting the presence of deterministic chaos in HRV. The Lyapunov exponent was positive in both groups at baseline but was significantly lower in the patient group. Following atropine, the value decreased while remaining positive, but no differences between the groups were found. The FD and the correlation dimension reacted similarly to the Lyapunov exponent. All time‐domain indices were significantly lower in the patients along with power in LF and HF bands. The differences were abolished by the administration of atropine.

Conclusions

The heart rate of patients with AMI exhibits characteristics of deterministic chaotic behavior with a positive Lyapunov exponent but with significantly less complex behavior than in healthy controls. The difference was eliminated by atropine, suggesting that vagal tone is a major cause. The nonlinear indices have a discriminating capacity for changes in HRV comparable to linear indices.
Effects of β‐Blocker Therapy on the Dynamic QT/RR Relation in Patients with Long QT Syndrome During 24‐Hour Holter ECG Monitoring
Authors: Emori Tetsuro , Ohe Tohru , Aihara Naohiko , Kurita Takashi , Shimizu Wataru , Kamakura Shiro , Shimomura Katsuro
Published: October 2006

Objective:Patients with long QT syndrome (LQTS) have an abnormality in the dynamic relationship between the QT and RR intervals (QT/RR relation) assessed by 24‐hour Holter ECG monitoring. The clinical efficacy of β‐blocker therapy in LQTS patients has been established, but its antiarrhythmic mechanism has not been fully elucidated. In the present study, the influences of β‐blocker therapy on the QT/RR relation were investigated in LQTS patients with no arrhythmic event during β‐blocker therapy.

Methods:Holter ECG recordings before and after the therapy were obtained from seven LQTS patients (all female, age range 10–45 years). The QT/RR relation was analyzed by our original computer algorithm with automatic measurement of the Q‐aT interval (time interval from the QRS onset to the T wave apex. The correlation coefficient (r), and the slope of the best fit linear regression line between the Q‐aT and RR intervals (Q‐aT/RR slope) after β‐blocker therapy were compared with those before the therapy. To determine whether the dose of β‐blockers was sufficient for suppression of the sympathetic nervous activity, a frequency‐domain analysis of the heart rate variability was performed (low frequency power [LF]: 0.04–0.15 Hz, high frequency power [HF]: 0.15–0.40 Hz).

Results:The LF component of the heart rate variability decreased and the HF component increased during the daytime after β‐blocker therapy. However, the Q‐aT/RR relation after β‐blocker therapy was the same as that before the therapy (mean slope before = 0.20 ± 0.07, mean slope after = 0.19 ± 0.08; P = not significant; mean r before = 0.82 ± 0.17; mean r after = 0.76 ± 0.15; P = not significant).

Conclusion:β‐Blocker therapy did not affect the unique Q‐aT/RR relation, which reflects an intrinsic abnormality of the ventricular repolarization in LQTS patients.
Risk Stratification of Patients After Myocardial Infarction Based on Wavelet Decomposition of the Signal‐Averaged Electrocardiogram
Authors: Sierra Gilberto , Reinhardt Lutz , Fetsch Thomas , Martínez‐Rubio Antoni , Mäkijärvi Markku , Yli‐Mäyry Sinikka , Montonen Juha , Katila Toivo , Borggrefe Martin , Breithardt Günter
Published: October 2006

Objective: The objective of this study was to investigate the prognostic significance of the wavelet decomposition (WD), when applied to single leads of the signal‐averaged ECG (SAECG) of postinfarction patients, as well as to compare it with conventional time‐domain (TD) analysis in order to optimize the utility of high resolution ECG techniques in risk stratification. Comparisons with clinical variables were also performed.

Methods: SAECGs of 769 patients were analyzed (mean age 53 ± 7 years). A total of 42 arrhythmic events occurred within 54 months. For numerical calculations of WD, relative energies of the QRS complex were obtained in seven frequency bands. Conventional parameters of late potential analysis in TD were calculated at 25 and 40 Hz high pass filter.

Results: No significant correlation was found between parameters of both methods. Several parameters of the WD of single leads showed slightly higher sensitivity (e.g., 52% vs 36%) and positive predictive values (e.g., 13.3% vs 10.2%) compared with those obtained with the QRS duration of TD analysis. In multivariate analysis, combination of QRS duration with WD parameters (relative risk [rr] =4.55, P < 0.0001), followed by the WD of single leads (rr = 4.19, P < 0.0001), nonsustained ventricular tachycardia in the long‐term ECG (rr = 3.72, P = 0.0005) and the history of previous infarction (rr = 2.72, P = 0.0035) were the most significant predictors in risk stratification.

Conclusion: Time domain and wavelet transform of SAECG resulted in an improvement in postinfarction risk stratification compared with the clinical variables included in this study. Wavelet parameters may not be vastly superior to QRS duration, but they are a new index measuring intra‐QRS phenomena.
Power Spectral Changes of Spontaneous Beat‐to‐Beat Variability of the RT Interval in Patients with Coronary Artery Disease
Authors: Müller Christian , Dambacher Martin , Spadacini Giammario , Roskamm Helmut , Frey Axel W.
Published: October 2006

Objective:This study sought to evaluate the spontaneous beat‐to‐beat variability of the RT interval (RTV) as a marker of autonomic balance at the ventricle in patients with coronary artery disease (CAD), as heart rate variability (HRV) primarily reflects sympathovagal interactions at the sinus node.

Methods:ECG and peripheral blood pressure signals were analyzed in supine and passive head‐up tilt in 19 patients with CAD. RT intervals were measured between the maximum of the QRS complex and the maximum of the T wave. Power spectral analysis of RR intervals, RT intervals, systolic and diastolic pressure were performed using discrete Fourier transformation. We calculated the area under the spectral density curve in the low (LF = 0.05–0.18 Hz) and high frequency range (HF = 0.18–0.50 Hz).

Results:Tilting results in a decrease of HF in HRV to 45%± 10% (P < 0.05) and an increase of HF in RTV to 266%± 83% (P < 0.01). Total RTV was 2.4% of total HRV. In systolic blood pressure variability HF increased to 396%± 124% (P < 0.05), in diastolic blood pressure variability to 231%± 69% (P < 0.05).

Conclusion:If the transfer‐function of sympathetic activity to the ventricle and to the sinus node are similar, the increase of HF in RTV cannot be explained by the increase in sympathetic activity induced by tilting. It is most likely a mechanical phenomenon induced by respiration synchronous changes of the position of the heart in the thorax and transferred variabilities of the central venous pressure that can also be identified in systolic and diastolic pressure variabilities.
Two‐Dimensional Vector Analysis of Beat‐to‐Beat Dynamics of Ventricular Repolarization
Authors: Huikuri Heikki V. , Airaksinen K.E. Juhani , Koistinen M. Juhani , Palmgren Jan‐Erik , Linnaluoto Markku K. , Tikkanen Pauli , Sellin Lawrence
Published: October 2006

Objective: Duration of ventricular repolarization is a result of complex interaction between autonomic modulation and heart rate (HR).

Methods: To study the dynamics of ventricular repolarization of the human right ventricle, beat‐to‐beat variability of ventricular repolarization was measured by plotting the duration of each monophasic action potential at the 90% phase of repolarization (APD90) as a function of the previous APD90 both in sinus rhythm and during steady‐state atrial pacing (cycle length of 600 rns) in 12 subjects without structural heart disease.

Results: Quantitative analyses of APD90 and RR interval variability in sinus rhythm showed that the total standard deviation (SD) of APD90 was only 8% of the SD of all RR intervals. Both longterm, continuous variability (SD2) of APD90 (3.9 ± 1.5 ms) and instantaneous beat‐to‐beat variability (SD1) of APD90 (1.2 ± 0.3 ms) were smaller than the SD2 and SD1 of RR intervals (46 ± 17 ms and 15 ± 9 ms, respectively) (P < 0.001 for both), but the shapes of the APD90 and RR interval plots and the SD1/SD2 ratio did not differ. SD1 of APD90 correlated well with the SD1 of RR intervals (r = 0.64, P < 0.05) but no significant correlation was observed between the SD2 of APD90 and SD2 of RR intervals (r = 0.32, NS). During steady‐state atrial pacing, only minimal instantaneous beat‐to‐beat variability in APD90 (0.9 ± 0.3 rns) was observed but the SD2 was larger than the SD2 of RR intervals (2.3 ± 1.0 ms vs. 1.6 ± 0.8 ms, P < 0.001).

Conclusion: The results suggest that instantaneous beat‐to‐beat variability of ventricular repolarization is mainly due to beat‐to‐beat fluctuation of HR, but the long‐term dynamics of repolarization are partly influenced by other factors than the HR variability.
Quantitative Aspects of Ventricular Repolarization
Authors: Badilini Fabio , Fayn Jocelyne , Maison‐Blanche Pierre , Leenhardt Antoine , Forlini Marie Claire , Denjoy Isabelle , Coumel Philippe , Rubel Paul
Published: October 2006

Introduction:QT dispersion assesses repolarization inhomogeneity on 12‐lead standard ECG. However, the implications of the electrical cardiac vector during the repolarization phase (the T wave loop) with the genesis of this phenomenon are unknown.

Methods and Results:The aim of this study was to explore conventional 12‐lead resting ECG QT dispersion and the corresponding morphology of the spatial three‐dimensional (3‐D) T wave loop in 25 normals subjects, 30 postmyocardial infarction (Ml) patients, and in 17 individuals with congenital long QT syndrome (LQTS). Standard and XYZ ECG leads were simultaneously digitized (250 Hz) and automatically analyzed. Ventricular repolarization dispersion was estimated by the range (RAN12o) and standard deviation (SD12o) of the 12 rate corrected QTo intervals (between the Q wave onset and the T wave offset). Spatial T wave loops were extracted from XYZ data and analyzed with a 3‐D algorithm which provides quantitative parameters related to the loop morphology. All scalar measurements of dispersion were significantly larger in the two pathological populations; however none of them could discriminate post‐MI from LQTS groups (RAN12o = 33.3, 61.4, and 62.7 ms respectively, for the three populations). Conversely, a loss of planarity and an increased roundness of the T wave loop were observed in the two pathological groups, with the former effect more pronounced in the LQTS (P = 0.04 compared to post‐MI) and the latter in the post‐MI group (P = 0.02 compared to LQTS). Furthermore, multiple regression and principal component analyses showed that planarity and roundness are independently involved with QT dispersion.

Conclusion:Changes in the morphology of the spatial T wave loop associated with QT dispersion were identified. These changes discriminate different substrates of repolarization inhomogeneity. The use of a 3‐D technique to assess repolarization inhomogeneity may bring additional information on the intrinsic nature of this disorder.
The Initial Electrocardiographic Pattern in Acute Myocardial Infarction
Authors: Birnbaum Yochai , Sclarovsky Samuel
Published: October 2006

Background: The ECG is the most widely used accessory for early diagnosis and risk stratification of patients with acute myocardial infarction (AMI). Previous studies have concentrated on the association between either the number of leads with ST segment deviation (elevation and depression) or the total amount of ST segment elevation and/or depression and prognosis. However, the results are conflicting.

Methods: A different method is to use the grades of ischemia as an estimate of infarct or size and prognosis. Grade I ischemia is defined as tall peak T waves with < 0.1 mV ST segment elevation; grade II as ST segment elevation with positive T waves, without distortion of the terminal portion of the QRS; and grade III as ST segment elevation, positive T waves, and distortion of the terminal portion of the QRS. Grade III ischemia on the admission ECG is associated with larger final infarct size and increased mortality.

Results: In patients with inferior wall AMI, especially those with prior infarction, the pattern of precordial ST segment depression is even more important and maximal ST depression in V4‐V6 is associated with high mortality. Moreover, meticulous interpretation of the initial ECG pattern provides information about the probable site of the culprit obstructive coronary lesion.

Conclusion: Thus, the admission ECG of AMI can assist not only in diagnosis, but also in estimation of infarct size, correlation with the underlying coronary anatomy and risk stratification.
Vector Quantization of T Wave Abnormalities Associated with a Predisposition to Ventricular Arrhythmias and Sudden Death
Authors: Riccio Mark L. , Moïse N. Sydney , Otani Niels F. , Belina John C. , Gelzer Anna R. M. , Gilmour Robert F.
Published: October 2006

Background

Previous studies have suggested that irregular T wave morphologies are associated with an increased risk of sudden death. However, automated characterization of T wave abnormalities has been hampered by the lack of suitable analysis techniques. In this study, we tested a new method of T wave analysis in German shepherd dogs with inherited ventricular arrhythmias and sudden death.

Methods

Sets of 24‐hour ambulatory ECG recordings obtained from unaffected (n = 6) and affected (n = 5) dogs were digitized, automatically annotated to label each R wave, and placed into a matrix with the R waves aligned. A vector quantization algorithm separated the QRS‐T complexes into classes according to T wave morphology. The existence of notched T waves was determined by assessing the number of zero crossings of the first derivative during the T wave.

Results

The duration of the QT interval was similar in affected and unaffected dogs (182 ± 14 ms vs 176 ± 16 ms, respectively). However, T wave morphology differed between the two groups. Specifically, affected dogs had a higher percentage of notched T waves than unaffected dogs (41.6%± 10.8% vs 5.0%± 1.2%, respectively). Notched T waves did not appear at all times of day, nor were they present in all leads.

Conclusion

Vector quantization and first derivative analyses were feasible and effective methods for detecting T wave abnormalities associated with the development of ventricular arrhythmias These methods ultimately may be useful for risk stratification of patients susceptible to ventricular arrhythmias and sudden death.
High Resolution Electrocardiography—Its Application for the Measurement of the QT Interval in the Presence of Low Amplitude T Waves
Authors: Sosnowski Maciej , Zbigniew Czyz M.D.  , Ĺski Jacek , Petelenz Tadeusz , Tendera Michal
Published: October 2006

Objective

We describe a computer‐interactive method for determination of QT duration in the presence of unfavorably shaped T waves. We assumed that such a method should allow to determine QT duration with the same error irrespective of the T wave amplitude.

Methods

The study group comprised 20 patients following myocardial infarction and the control group, 10 healthy volunteers. ECGs were recorded from XYZ leads using a computer‐assisted low noise amplifier. After A/D conversion (16 bit, 2 kHz) fiducial points of R and T waves were determined and then the signal was aligned and averaged. A segment of 106.5‐ms duration was chosen that included either the initial portion of QRS complex or the terminal part of the T wave. This segment was scanned with a 32‐ms window every 0.5 ms. Spectrotemporal analysis was performed by use of the fast Fourier transform. The QRS onset and T wave offset were defined as points at which the percentage ratio of power in frequency range 62.7–121.6/0–121.6 Hz reached minimum. Signal‐averaged ECGs were printed out (120 mm/s, 2.1 mm/mV) for manual measurement of QT duration and T wave amplitude. Low amplitude T wave was defined as lower than 0.2 mV, otherwise normal amplitude T waves were recognized. Measurements were repeated separately by two observers for each lead.

Results

Low T waves were observed in 11 (37%) leads from controls and in 25 (42%) from post‐Ml patients. Manual measurements were possible in 82 leads (all normal and 28 low T waves), while the high resolution method allowed us to determine the QT duration in all leads. In the Ml group, the results of independent QT measurements by means of high resolution were: 412.0 ± 29.8 ms versus 411.5 ± 29.3 ms for flat, and 410.7 ± 30.4 versus 409.8 ± 30.0 ms for normal T waves. In controls, corresponding values were: 388.5 ± 32.0 versus 386.3 ± 23.8 ms and 392.9 ± 32.8 versus 392.2 ± 31.7 ms. The mean absolute error of two independent measurements was greater with use of the manual method, and reached 6.9 ms (median 5.5 ms) in normal and 12.9 ms (median 8.5 ms) in low T waves. With use of the new method, the errors were lower: 3.48 ms (median 0 ms) and 2.29 ms (median 0 ms), respectively. There was a close correlation between repeat measurements in normal T waves with both methods (r = 0.956 and r = 0.961; both P < 0.001). In low T waves the correlation was significantly lower (P < 0.05) with the manual (r = 0.879; P < 0.001), as compared with the high resolution method (r = 0.973; P < 0.001).

Conclusion

The signal‐averaged, high resolution ECG analysis allows for the determination of QT duration in the presence of a flat T wave. The described method may provide the opportunity to measure QT duration in all leads and, therefore, to calculate spatial QT dispersion in the majority of post‐Ml patients.
Characteristics of the Circadian Rhythm of Heart Rate Variability in Patients with Sudden Cardiac Death after Myocardial Infarction
Authors: Itou Tetsushi , Obata Shinichirou , Tateishi Osamu
Published: October 2006

Background: Sudden cardiac death (SCD) after myocardial infarction, most commonly caused by ventricular fibrillation, is closely associated with autonomic nervous tone. However, the mechanism of SCD and its association with autonomic nervous tone and the circadian rhythm of this tone remain obscure. We examined the characteristics of autonomic nervous tone in patients with SCD using heart rate variability (HRV) analysis.

Methods: HRV was analyzed by spectral and nonspectral methods in 46 postinfarction patients, including 6 patients who experienced SCD (SCD[+]) and 40 survivors (SCD[—]). The circadian rhythm of HRV was assessed by a nonlinear least squares method combined with the maximum entropy method (MEM) using data from 24‐hour ambulatory ECGs. The mean follow‐up period was 27 ± 12 months.

Results: Midline estimating statistic of rhythm and the amplitude of the high frequency (HF) component in the SCD(+) group were lower than those in the SCD(—) group, and differences of the circadian rhythm of the HF component between the SCD(+) group and the SCD(—) group were observed.

Conclusions: A decreased HF component indicating diminished parasympathetic nervous activity was the strongest independent predictor of SCD. These results suggest that postinfarction patients whose parasympathetic nervous activity is low and whose circadian changes are small may be susceptible to SCD.
Comparison of Body Surface Potential and Laplacian Mapping with Epicardial Mapping for Detection of Cardiac Ischemia in Pigs
Authors: Lee Yueh Z. , Belk Paul A. , Mullen Thomas J. , Rivers Samuel , Zhang Xi , Armoundas Antonis A. , Osaka Motohisa , He Bin , Aldea Gabriel , Cohen Richard J.
Published: October 2006

The standard electrocardiogram (ECG) and the body surface potential map (BSPM) are only moderately sensitive for the detection of ischemia and cannot accurately localize ischemic regions within the heart. We have previously demonstrated that the body surface Laplacian map (BSLM) does provide the capability to localize electrical activity within the heart. The objective of this study was to compare the abilities of BSLM and BSPM to detect and localize ischemic regions within the heart with reference to direct epicardial potential measurements. Ischemia was induced in six anesthetized Yorkshire swine by occluding the distal left anterior descending (LAD) coronary artery, or a diagonal branch of the LAD and the obtuse marginal coronary artery. Atrial pacing was used to incrementally increase the degree of ischemia. BSPM, BSLM, and epicardial recordings were simultaneously obtained after occlusion of each coronary artery and subsequently during atrial pacing. We used a normalized measure of ischemia (shift in the ratio: ST segment height divided by QR amplitude) measured at each electrode and created corresponding maps of the spatial distribution of this measure for the BSPM, BSLM, and epicardial potential maps. The BSLM was more sensitive than the BSPM in identifying ischemia and was capable of localizing and resolving one or more ischemic areas while the BSPM was not. The BSLM also distinguished between different levels of ischemia associated with atrial pacing at different rates. Due to its better spatial resolution and sensitivity, the BSLM promises to provide an improved means for noninvasive localization of myocardial ischemia.
Early Electrocardiographic Signs of Drug‐Induced Torsades de Pointes
Authors: Svernhage Elisabeth , Houltz Birgitta , Blomström Per , Brachmann Johannes , Crijns Harry , Jensen Steen , Vallin Hans , Swedberg Karl , Edvardsson Nils
Published: October 2006

Background: The aim of the present analysis was to identify early changes in the surface ECG predicting development of torsades de pointes (TdP) during treatment with almokalant, a Class III antiarrhythmic compound.

Methods and Results: In two studies with identical protocols, five patients were reported to have developed TdP. The proarrhythmia occurred 43–137 minutes after start of infusion of almokalant, a selective IKr‐blocking substance. Precordial ECG leads V1–V6 were continuously recorded on tape and analyzed for ECG changes during the first 40 minutes of infusion. The tape recording for one patient was, however, technically insufficient for analysis. Each of the remaining four patients was compared with two control patients from the same study and matched for gender, age, conversion to sinus rhythm, and plasma drug concentration. Prolongation of the QTtop interval, i.e., from the beginning of the Q wave to the first identifiable top of the TU complex, was significantly greater during the 40‐minute period (P = 0.009) among the TdP cases compared with controls. Remarkably, the increase was twice that seen in controls within the first 10 minutes of infusion. A significantly greater increase in the interlead QT dispersion (P = 0.0496) and the intralead QT variability were also observed over the 40 minutes.

Conclusion: Our analysis indicates that a rapidly developing and pronounced increase in QTtop duration, a significant increase in interlead QT dispersion, as well as an increased intralead QT variability, characterized patients who developed TdP when treated with an IKr channel‐blocking substance, as compared to identically treated patients without TdP.
Physiological Background Underlying Short‐Term Heart Rate Variability
Authors: Hedman Antti , Hartikainen Juha , Martti Hakumäki M.D., Ph.D.
Published: October 2006

A large number of papers has been published on heart rate variability (HRV) based on the assumption that the specific components of HRV provide specific information about cardiac parasympathetic or sympathetic efferent nerve activity. However, neural control of the cardiorespiratory system is very complex, and the physiological phenomenon underlying HRV in different conditions are far from being fully understood. This review summarizes, in the light of current literature, a series of studies focused on the mechanisms by which fluctuations in neural outflows are transferred into HRV. In the interpretation of HRV analyses, it should be taken into account that: (1) HRV seems to be strongly influenced by the parasympathetic nervous system at all the frequency components; (2) due to sympathovagal interactions, sympathetic outflow is able to reduce the variations generated by vagal modulation also in the high frequency band; and (3) the variations in heart rate reflect fluctuations in the neural activity rather than the mean level of sympathetic or parasympathetic neural activity. Thus, we should be cautious in interpreting a specific component of HRV as a specific marker of sympathetic or parasympathetic cardiac control. Furthermore, due to the complexity of the cardiorespiratory control system, the analysis of short‐term HRV should be performed in well‐controlled conditions, in which the behavior of the autonomic nervous system is well documented.
Detection of AAI, R Pacemaker Syndrome by Holter Monitoring: A Case Report
Authors: Böhm Ádám , Lehoczky Dezsö , Pintér Arnold , Préda István
Published: October 2006

The authors present the case of a patient with symptomatic sinus bradycardia. Implantation of a rate responsive atrial pacemaker improved the exercise capacity of the patient, but exercise intolerance was still intermittently present. Only Holter monitoring could reveal the development of AAI, R pacemaker syndrome that led to the symptoms. Reprogramming of the pacemaker eliminated the phenomenon.
Efficacy of Intravenous Atenolol for Prevention of Neurally Mediated Syncope Induced by Head‐Up Tilt Testing
Authors: Ortega Javier , Madrid Antonio H. , Seara Javier G. , Rebollo José M. Gonzalez , Lozano Fernando , Parra Javier , Palma José Luis , Moro Concepción
Published: October 2006

Background

In our hospital we performed a prospective, randomized, double‐blind, and controlled study on the efficacy of oral atenolol in patients with neurocardiogenic syncope. Fifty patients with clinically diagnosed vasovagal syncope were included.A complete study to discard other possible causes of syncope was performed in all patients. In the first part of this study, before the patients were randomized in two groups to receive either atenolol or placebo, a baseline tilt test with a protocol of 80° during 45 minutes was performed.

Methods

All patients with a positive response (18) underwent an infusion of intravenous atenolol and the test was repeated. Four patients with a positive baseline test did not accept the infusion of that drug and, therefore, were not included in this protocol. Atenolol prevented a second positive tilt in 5 of 18 patients (27.8%).

Results

There were no significant differences between both groups with respect to age, gender, blood pressure, heart rate, and number of episodes of syncope. Thirteen patients had a recurrent positive response in spite of atenolol. Eleven of these subjects had a syncope during the first tilt test. In seven of these patients (63.6%) atenolol prevented severe symptoms 'syncope) in the second test. In patients with a significant cardioinhibitory response in the first test, atenolol did not prevent a second positive response in any of the patients.

Conclusions

In our study, intravenous atenolol was not an efficient drug to prevent a second positive tilt test in patients with clinically diagnosed vasovagal syncope and a first positive tilt‐table test. Only 5 of 18 patients (27.8%) had a negative response in the second test after the infusion of that drug. This drug was more effective in patients with a vasodepressor or mixed response in the first tilt test. A.N.E. 1999; 4(2):130–136
Circadian Pattern of QT/RR Adaptation in Patients with and Without Sudden Cardiac Death after Myocardial Infarction
Authors: Yi Gang , Guo Xiao Hua , Gallagher Mark M. , Hnatkova Katerina , Reardon Michael , Poloniecki Jan , Camm A. John , Malik Marek
Published: October 2006

Background:Abnormalities in the adaptation of the QT interval to changes in the RR interval may facilitate the development of ventricular arrhythmias.

Methods:This study sought to evaluate the dynamic relation between the QT and RR intervals in patients after acute myocardial infarction. The study population consisted of 14 patients after myocardial infarction (age 60 ± 7 years, 12 men) who died suddenly (SCD victims) within 1 year after the myocardial infarction and 14 pair‐matched age, sex, left ventricular ejection fraction, infarct site, thrombolytic therapy) patients who remained event‐free after myocardial infarction (Ml survivors) for at least 3 years. Fourteen normal subjects were studied as controls (age 55 ± 9 years, 11 men). QT and RR intervals were measured on a beat‐to‐beat basis automatically with a visual control from 24‐hour ambulatory ECGs using Reynolds Pathfinder 700. Mean hourly values of the QT/RR slope (QT =α+βRR) and corrected QT interval at 1000 ms of RR interval (QT1s) were derived for each subject using an inhouse program (QT1s=α+1000β). The dynamics of the QT/RR slope and QT1s were assessed on the basis of hourly mean values. The circadian rhythm of ventricular repolarization (QT1s and QT/RR slope) was examined by harmonic regression analysis.

Results:There was a trend towards a significant difference in 24‐hour mean value of QT1s between study groups (408 ± 26 ms vs 381 ± 43 ms and 386 ± 22 ms, P = 0.06), and a significant difference was found between SCD victims and normal subjects (408 ± 26 vs 386 ± 22 ms, P = 0.02). The QT1s differed significantly between study groups (P = 0.038) only during the day time (09:00–19:00 hour), when QT1s was significantly longer in SCD victims than in normal subjects (409 ± 33 vs 380 ± 27 ms, P = 0.02) and tended to be longer than in Ml survivors (409 ± 33 vs 379 ± 42 ms, P = 0.08). The 24‐hour mean value of QT/RR slope was significantly different between study groups (P = 0.04), with a significantly steeper slope in SCD victims than in normal subjects (0.15 ± 0.07 vs 0.09 ± 0.02, P = 0.008). During day time, the QT/RR slope differed significantly between study groups (P = 0.04), while the difference was less marked at night (P = 0.08). The slope was significantly steeper in SCD victims than in normal subjects during both day and night (P < 0.05). A marked circadian variation of QT1s was observed in normal subjects, which was blunted in Ml survivors and SCD victims.

Conclusions:Abnormal repolarization behaviors, characterized by longer QT1s and impaired adaptation of QT to variations in RR intervals, were found in SCD victims. Hence, lethal ventricular tachyarrhythmias might be provoked by the altered repolarization dynamics in patients after myocardial infarction. A.N.E. 1999;4(3):286–294
Occurrence and Prognosis of Ventricular Arrhythmia in Men With and Without Asymptomatic Leg Artery Disease: Results from a Prospective Population Study “Men Born in 1914,” Malmö, Sweden
Authors: Hedblad B. , Janzon L. , Ögren M.
Published: October 2006

Background:The occurrence of frequent or complex ventricular arrhythmia in apparently healthy men during ambulatory ECG recording has been shown to be associated with an increased incidence and mortality in ischemic heart disease. Similar risk has been documented for individuals with asymptomatic leg artery disease. The objective of this follow‐up of 450 men from the prospective cohort study “Men born in 1914” in Malmö, Sweden has been to assess whether there is any relationship between the occurrence of ventricular arrhythmia and asymptomatic leg artery disease and whether the prognosis with regard to survival and incidence of myocardial infarction is different in men with and without asymptomatic leg artery disease.

Methods:The ECG was recorded during 24 hours. Mortality and incidence of cardiac events (i.e., acute myocardial infarction and death in chronic ischaemic heart disease) during the 10 years following the baseline examination 1982–1983 has been related to occurrence of frequent or complex ventricular arrhythmia (i.e., Lown class 2–5) and prevalence of asymptomatic leg artery disease (i.e., ankle‐arm blood pressure index, ABPI < 0.9 at rest).

Results:There was no association between the prevalence (14% vs 13%) or severity of leg artery disease and the occurrence of ventricular arrhythmia. History of cardiovascular disease was related to both conditions. In men without leg artery disease, occurrence of arrhythmia was associated with an increased mortality rate, from 29.1 to 41.5 per 1000 person‐years (P = 0.046) and cardiac event rate, from 15.6 to 27.1 per 1000 person‐years (P = 0.023). The increased incidence of cardiac events and death associated with arrhythmia was modified by the presence of leg artery disease. There was a low ABPI in the group with arrhythmia associated with an increase in mortality rate from 41.5 to 95.8 per 1000 person‐years and an increase of the cardiac event rate from 27.1 to 76.1 per 1000 person‐years. These associations remained statistically significant after adjustment in the analysis with regard to history of cardiovascular disease and other potential confounders.

Conclusions:Occurrence of ventricular arrhythmia is a common condition in apparently healthy elderly men. Although it seems to be equally common in men with and without asymptomatic leg artery disease, with regard to the incidence of cardiac events and death it is associated with a more serious prognosis in men with leg artery disease.A.N.E. 1999;4(3):309–315
Changes in High Frequency QRS Energy in the Signal‐Averaged Electrocardiogram After Acute Experimental Infarction
Authors: Bloomfield Daniel M. , Lander Paul , Steinberg Jonathan S.
Published: October 2006

Background: The effect of Ml on the high frequency content of the QRS complex in the SAECG remains a matter of controversy. The purpose of this study was (1) to characterize the changes in the high frequency QRS energy that occur after experimental Ml in dogs, (2) to evaluate the change in QRS energy in a number of frequency bandwidths, and (3) to evaluate the relationship between the change in QRS energy and infarct size and location, as well as the inducibility of VT.

Methods: MIs were created in 21 dogs by balloon occlusion of the left circumflex (n = 10) or left anterior descending (n = 11) coronary arteries. SAECGs, using three orthogonal leads (X, Y, Z), were obtained before and 4–6 days after the Ml. The vector magnitude was calculated. Using a spectral filter, we calculated the energy in û Vs) of the entire QRS as the integrated area of the signal voltage within a low frequency bandwidth (15–40Hz) and two high frequency bandwidths (40–80 Hz, 80–300 Hz). QRS energy was log transformed to achieve a normal distribution.

Results: There was a significant decrease in QRS energy after Ml in the low and high frequency bandwidths in the 21 dogs that was primarily detected in the Y lead. This decrease in high frequency energy after Ml occurred primarily in the dogs with anterior infarction where there was a 13–21% drop in QRS energy in all three bandwidths in the vector magnitude as well as the Y and Z leads (all P > 0.05). This drop in QRS energy after anterior wall Ml was moderately correlated with increasing infarct size in all three bandwidths. There were no consistent changes in QRS energy in the dogs with posterior infarction. The drop in QRS energy after Ml was not associated with inducible VT. The change in QRS energy after Ml in all three bandwidths were highly correlated.

Conclusions: The process of Ml produced a decrease in QRS energy, in both low and high frequency bandwidths, that was most consistent in dogs with anterior wall Ml. The decrease in QRS energy after Ml was not associated with inducible VT. Ml produced similar changes in QRS energy in low and high frequency bandwidths. A.N.E. 1999;4(1):72–82
Evaluation of Patients with Palpitations: Cardiac Event Recorder Versus 48‐hour Holter Monitoring
Authors: Makowska Ewa , Szymot Joanna , Soszyriska Malgorzata , Kulakowski Piotr
Published: October 2006

Objectives: (1) To compare a diagnostic yield of cardiac event recorders with that of 48‐hour Holler monitoring, (2) to determine the etiologies of palpitations, and (3) to assess an optimal duration of using an event recorder by a patient.

Background: Palpitation is a common symptom which accounts for 16% of total complaints reported by patients in general medical settings. An ambulatory Holter ECG monitoring or an event recorder can be used to establish the cause of palpitations.

Methods: (1)The study group consisted of 33 consecutive patients (24 females, 9 males, mean age 50 ± 32 years) with undiagnosed attacks of palpitations, occurring at least once per month. Each patient was randomly allocated to use either an event monitor or 48‐hour Holler monitoring. The patient kept the event monitor for 4 weeks. After the first monitor was returned, the patient was given the other device.

Results: Holter monitoring determined the etiology of palpitations in 11 (33%) patients, and the event recorder in 21 (64%) patients (P = 0.0138). In the whole study group, the etiology of palpitations was disclosed in 23 (70%) patients. The diagnosis was possible using Holler ECG monitoring in only 2 (9%) patients, whereas the event recorder revealed the underlying mechanism of palpitations in 12 (52%) patients (P = 0.0007). In nine (39%) patients both methods were able to disclose the eliology of palpitations. The findings of 117 recordings obtained using an event recorder during palpitations were atrial fibrillation in 10 (9%), narrow QRS tachycardia in 4 (3%), frequent supraventricular eclopy in 17 (15%), frequent ventricular eclopy in 6 (5%), and episodes of palpitations sinus rhythm were recorded in the remaining 80 (68%). Of patients who experienced episodes of palpitations while using an event recorder, the earliest recording was obtained on the first day of the study, and the latest on the 18 day of using the event recorder.

Conclusions: (1) The cardiac event recorders yield more diagnoses than 48‐hour Holter monitoring in patients with palpitations occurring at least once per month, (2) in this group of patients the event recorder provided a diagnostic ECG recording during the first 18 days of using the device, and (3) in the majority (57%) of patients a normal sinus rhythm was recorded during episodes of palpitations. A.N.E. 2000;5(4):315–321