bluuebunny/crossref_metadata_2025 huggingface dataset:
Do flatland‐ and mountain‐dwelling species show different structuring of their experienced environment over latitude? A western vs. central‐eastern North America rodent multispecies comparison
Authors: Guralnick Robert
Published: October 2006

Species occurrence databases and climate databases were used to examine differences in patterns of species experienced climate across latitude for wide‐ranging rodents in the central‐eastern and western North America. The accumulated data were used to address three questions: (1) Do rodent species in the central and eastern region of North America select habitat at range edges to remain closer to climate conditions at the range core? (2) Is there a trend toward species having greater experienced climate variation consistent with smaller effects of orbitally controlled climate oscillations in the south vs. north? (3) How do species experienced temperature, precipitation, and elevation means and variation in this region compare to rodent species in the adjacent but more heterogeneous western North America? Results showed that central‐eastern North American species occur in as wide a range of environmental conditions as available throughout their ranges. These patterns are different from previous findings for rodents in the adjacent western USA and highlight major differences in current structure of species experienced environmental means and variation over latitude for species in spatially heterogeneous, mountainous areas vs. those that occupy flatter lands. The differences are likely important for determining differential response to climate changes.
Assessing the potential range expansion of the exotic monk parakeet in Spain
Authors: Muñoz Antonio‐Román , Real Raimundo
Published: October 2006

In this study we determine favourable areas for the monk parakeet,Myiopsitta monachus, in peninsular Spain to account for its current distribution and predict its future course according to its potential range. We applied a favourability function based on generalized linear models using the presence/absence of breeding colonies of the species and the values of a set of variables on the 5167 UTM 10 × 10 km squares comprising the study area. We calculated the factor of distribution change in presences predicted by the model, and grouped the variables into explanatory factors performing a variation partitioning to assess the explanatory power of each factor. Our model included six predictors to explain the presence and absence of the species. These predictors were grouped into three factors: human activity, climate, and topography. Purely human influences accounted for 63.8% of the variation of the final model, while topographical variables explained 15.2% and climate only 5.7%. We obtained a high distribution change factor in which the presences of the species were predicted to increase between two‐ and sevenfold. Taking into account highly favourable squares, we conclude that the species is still absent in more than 72% of potential settlement areas, and thus we expect a continuous increase in the distribution of the species. Human activity is the main force moulding the distribution of the species, and lies behind its fast expansion, which is not only active, but is also passive via releases and escapes. We identified the areas of likely future expansion of the exotic monk parakeet in Spain. The pest status of the species in its native range, together to its distribution trend, should be taken into account by wildlife agencies to consider options for management.
A Measurement Theory for Time Geography
Authors: Miller Harvey J.
Published: October 2006

Hägerstrand's time geography is a powerful conceptual framework for understanding constraints on human activity participation in space and time. However, rigorous, analytical definitions of basic time geography entities and relationships do not exist. This limits abilities to make statements about error and uncertainty in time geographic measurement and analysis. It also compromises comparison among different time geographic analyses and the development of standard time geographic computational tools. The time geographic measurement theory in this article consists of analytical formulations for basic time geography entities and relations, specifically, the space–time path, prism, composite path‐prisms, stations, bundling, and intersections. The definitions have arbitrary spatial and temporal resolutions and are explicit with respect to informational assumptions: there are clear distinctions between measured and inferred components of each entity or relation. They are also general ton‐dimensional space rather than the strict two‐dimensional space of classical time geography. Algebraic solutions are available for one or two spatial dimensions, while numeric (but tractable) solutions are required for some entities and relations in higher dimensional space.
Identification of Patients with Coronary Artery Disease Using a Stress‐Free Signal Variance Cardiograph Through Analysis of Temporal Heterogeneity
Authors: Deedwania Prakash C. , Carbajal Enrique V.
Published: October 2006

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.
Late Potentials Detected by Digital Holter ECG: Reproducibility, Lead Systems, and Effects of Physical Activity
Authors: Kulakowski Piotr , Biedrzycka Agnieszka , Ceremuzynski Leszek
Published: October 2006

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 during minor physical activity.
Changes of Heart Rate Variability After Coronary Bypass Grafting
Authors: Osterhues Hans‐H. , Neßlauer Thomas , Eggeling Thomas , Kochs Matthias , Hannekum Andreas , Hombach Vinzenz
Published: October 2006

Background: Heart rate variability (HRV) may serve as a follow‐up parameter in patients with coronary artery disease undergoing percutaneous transluminal angioplasty. Several studies have shown significant changes of HRV parameters in the case of restenosis. The value of this method as a prognostic parameter in patients following coronary artery bypass grafting (CABG) is unknown.

Methods: In the present study we investigated changes of HRV parameters in patients undergoing CABG to prove whether this method would predict the outcome in these patients. Twenty patients (six female, 14 male, age 51–75 years, mean 62 years) with angiographically documented coronary artery disease (1 × 1‐vessel disease, 10 × 2‐vessel disease, 9 × 3‐vessel disease) were investigated. Eight patients had previous myocardial infarction: 3 × anterior infarction and 5 × inferior infarction. Before and after CABG 24‐hour measurement of HRV was performed using Holler monitoring (elapsed time between the two measurements 218 ± 92 days). All patients underwent successful CABG with complete revascularization. The following time domain parameters were calculated: SDNN, SDNN index, SDANN, r‐MSSD and pNN50.

Results: These parameters showed a significant decrease after CABG (P < 0.05) except rMSSD, which was below the statistic level. The results of the patients without previous myocardial infarction suggested that the parasympathetically influenced paramenters r‐MSSD and pNN50 were mainly involved, while in the subgroup with previous myocardial infarction the sympathetically influenced parameters (SDNN, SDANN) were significantly changed. Other variables such as ejection fraction or severity of coronary artery disease did not influence the HRV results.

Conclusions: In contratst to patients with revascularization by PTCA, HRV does not seem to be a suitable predictive parameter in patients after successful CABG. Intrinsic operative alterations with injury of cardiac nerves may be responsible for this observation.
Reproducibility and Comparability of Short‐ and Long‐Term Heart Rate Variability Measures in Healthy Young Men
Authors: Dekker Jacqueline M. , de Vries Emmy L. , Lengton Remko R. , Schouten Evert G. , Swenne Cees A. , Maan Arie
Published: October 2006

Background: In heart rate variability (HRV) studies, the duration of the electrocardiographic recordings may vary between 20 seconds and 24 hours. Little is known about the reproducibility or comparability of HRV measures calculated over observation periods of different duration.

Methods: To assess the reproducibility and comparability of HRV measures computed from short recordings under standardized conditions and from ambulatory 24‐hour recordings, 15 healthy young males were studied on three occasions.

Results: The reliability coefficient (between subject variation divided by summed between and within subject variation) for 20‐second intervals was low for all measures. For 5‐minute intervals in supine position, but not standing position, the reliability coefficients of the standard deviation, root of mean squared successive differences, proportion of successive differences > 50 ms, and the proportion low frequency power were about 70%. The reliability coefficients of the 24‐hour HRV measures were > 80% for all measures. Short‐ and long‐term measures of heart rate and HRV appeared to be correlated, implying that these measures result in similar ranking of subjects.

Conclusions: The results indicate that HRV measures based on 24‐hour monitoring during regular activities are better reproducible than short‐term measures under standardized conditions. A single 5‐minute recording may suffice to characterize a group of persons in a population study, but, because of considerable day‐to‐day variation, it is not adequate for individual characterization.
The Signal‐Averaged Electrocardiogram
Authors: Tamis Jacqueline E. , Steinberg Jonathan S.
Published: October 2006

Background: The signal‐averaged electrocardiogram (SAECG) is a useful noninvasive diagnostic tool for assessing delayed ventricular activation.

Methods: The advantage of the SAECG over standard ECGs the ability to detect very low amplitude signals indicative of areas of slowed myocardial conduction, a requirement for reentrant arrhythmias.

Results: The SAECG has been proven useful in a variety of clinical situations, particularly in risk stratification after myocardial infarction or in the patient with dilated cardiomyopathy, and in screening for the need for electrophysiological studies in the syncope patient or the patient with nonsustained ventricular tachycardia.

Conclusions: This review focuses on the currently accepted methodology of the time‐domain SAECG, and outlines the standard applications of the SAECG based on the results of important clinical research.
A hundred years of progress in electrocardiography 2: The rise and decline of vectorcardiography
Authors: Rautaharju Pentti M.
Published: October 2006

ABSTRACT: Throughout the 20th century electrocardiography has been almost exclusively preoccupied by the single dipole concept as a model to account for body surface manifestations of cardiac electrical activity. Vectorcardiography, based on the single dipole approximation as an equivalent cardiac generator, has prevailed for over one half of this century as one of the most prominent components of electrocardiographic research. In retrospect, vectorcardiography has had conceptually an important impact on the progress in electrocardiography although it never became widely used in clinical practice. Recent comparative studies have confirmed that the diagnostic information contents of the standard 12‐lead electrocardiogram and the vectorcardiogram are practically identical if adequately powerful, identical diagnostic classification procedures are used in extracting diagnostic information. After serving a useful role as a conceptual model, vectorcardiography is gradually fading away, being replaced by more realistic cardiac source models and by body surface leads supplementing in a better way the information content of the standard ECG leads.
Circadian Rhythms of Heart Rate Variability in Hypertrophic Cardiomyopathy
Authors: Guzzetti Stefano , Choudhury Lubna , Mezzetti Silvia , Cogliati Chiara , Camici Paolo G. , Malliani Alberto
Published: October 2006

Background: It has been hypothesized that an interaction between sympathetic nervous activity and an abnormal myocardium plays a role in the development and progression of hypertrophic cardiomyopathy (HCM).

Methods: In the present study we investigated cardiac autonomic function by 24‐hour spectral analysis of heart rate variability (HRV) in 18 patients with HCM, without evidence of heart failure, and 18 controls of similar age.

Results: We found a significant reduction of 24 hour variance in HCM patients relative to controls (15,000 ± 9480 ms2 vs 24,720 ± 12,450 ms2 respectively; p < 0.05). Moreover, a loss of the expected day‐night changes in the low frequency (LF) spectral component (expressed in normalized units), and LF/HF ratio (HF; high frequency component) were observed in HCM patients. Decreased day‐night changes in LF/HF ratio were previously reported in patients with mild hypertension, uncomplicated coronary disease, and after myocardial infarction, conditions in which it seems to exist a higher than normal sympathetic activity. No significant correlations were found between HRV indices and echocardiographic standard measures of systolic and diastolic function parameters.

Conclusions: These data are consistent with the presence of an alteration in neural modulation of heart period in HCM patients, noninvasively detectable by continuous 24 hour HRV analysis.
Conventional Electrocardiogram in Arrhythmogenic Right Ventricular Dysplasia‐Cardiomyopathy and Idiopathic Right Ventricular Outflow Tract Tachycardia
Authors: Peters Stefan , Weber Bettina , Reil Gert‐Hinrich
Published: October 2006

Objective: Arrhythmogenic right ventricular dysplasia up to now is a rare cardiomyopathic entity with certain difficulties in clinical definition of diagnostic criteria. In 42 patients with major and minor criteria of arrhythmogenic right ventricular dysplasia and 25 patients with idiopathic ventricular arrhythmia, the role of conventional ECG in the diagnosis of arrhythmogenic right ventricular dysplasia was reevaluated.

Methods: In standard 12‐lead ECG, QRS duration was measured in limb lead D1, and in V1‐V6. A ratio of the sum of right (V2+ V3) and left (V4+ V5) was calculated. T wave inversions, Epsilon wave, and mechanisms of advancing right bundle branch block were analyzed.

Results: In 39 out of 42 patients (93%) with the diagnosis of arrhythmogenic right ventricular dysplasia, a ratio of right and left precordial QRS duration of >1.2, a maximum right precordial QRS duration of > 100 ms in 10 cases (26%) and >110 ms in 29 cases (74%) could be found. Incomplete right bundle branch block with right precordial T inversions was found in one case. The ECG in two patients revealed a precordial R/S transition in V1 or V2; in all other cases, R/S transition was localized in V3 or V4. R peak time was normal (< 0.04 s) in all cases, a “notching” or “slurring” of the S wave was striking in 16 cases. T wave inversions were found in 27 cases and definite Epsilon wave in only one case. Although incomplete right bundle branch block and certain preforms could also be disclosed in four patients with idiopathic right ventricular outflow tract (RVOT) tachycardia, localized right precordial QRS prolongation could be excluded in all but one of these cases. Localized right precordial QRS duration prolongation in one case was probably due to a rotation of the heart with a precordial R/S transition between V1 and V2.

Conclusion: Localized right precordial QRS prolongation in a normal precordial R/S transition: (a) seems to be the most important aspect of arrhythmogenic right ventricular dysplasia at conventional ECG, with a sensitivity of 93% and a specificity of 96% in order to distinguish idiopathic RVOT tachycardia; (b) can appear with (64%) or without (36%) secondary T wave inversions; and (c) is due to a “parietal” block sparing the specialized conducting system.
Deletion Polymorphism of the Angiotensin I‐Converting Enzyme Gene Associates with Increased Risk for Late Potentials in Patients with Myocardial Infarction
Authors: Nakai Kenji , Chiba Naoki , Shobuzawa Minoru , Musha Takehiko , Shiroto Takahiro , Hosokawa Shunichi , Kamata Junya , Suzuki Tomomi , Aoki Hidehiko , Saiki Seiichi , Hiramori Katsuhiko
Published: October 2006

Background: The pathogenesis of the occurrence of late potentials (LP) has not been fully elucidated. Deletion polymorphism in the Angiotensin I‐converting enzyme (ACE) gene may relate the myocarclial remodeling after the myocardial infarction (Ml). The purpose of this study was to evaluate the significance of ACE gene polymorphism for the occurrence of LPs after Ml.

Methods: A 287 base pair (bp) insertion/deletion polymorphism in intron 16 of the ACE gene was determined by polymerase chain reaction and LPs were also examined by signal‐averaged EGC in 136 patients with Ml. Polymorphism of the ACE gene was characterized by three genotypes: II, ID, and DD. Signal‐averaged ECG were recorded using X, Y, Z leads and LP were defined by time‐domain analysis as low amplitude potentials exceeding 20 ms after the QRS‐end and filtered QRS >115 ms.

Results: Positive LPs were noted in 40 of 136 patients with Ml. No differences could be detected between patients with LP‐positive and LP‐negative for the location of Ml, the success rate of reperfusion therapy, and left ventricular end‐diastolic volume (126 ± 40 vs 113 ± 43 mL/m2). In patients with LP‐positive compared with those in LP‐negative, filtered QRS was significantly higher (135 ± 8 vs 107 ± 8 ms), left ventricular ejection fraction was lower (47 ± 12 vs 54%± 11 %), and peak was higher (3602 ± 2928 vs 2614 ± 2360 IU/L). The frequency of ACE/DD genotype was associated with patients with LP‐positive (18 of DD, 18 of ID, and 4 of II for patients with LP‐positive, while 25 of DD, 42 of ID, and 29 of II for patients with LP‐negative). In the study population, the ACE / DD genotype was associated with patients with LP‐positive when compared with the ACE ID & II genotype (x2= 4.7, P = 0.03).

Conclusion: ACE/DD genotype of the ACE gene may be associated with the occurrence of LP after Ml.
The Clinical Significance of Somatic Pain Tolerance in Patients with Coronary Artery Disease
Authors: Narins Craig R. , Zareba Wojciech , Moss Arthur J. , Brown Mary W. , Case Robert B. , Case Nan , Goldstein Robert E.
Published: October 2006

Methods

Two hundred seventy‐one patients with a recent acute coronary event underwent pain tolerance testing using the tourniquet test. Baseline ambulatory and exercise electrocardiography, and stress thallium scintigraphy were performed, and patients were followed prospectively for a mean of 33 ± 8 months for the occurrence of unstable angina, nonfatal myocardial infarction (Ml), or cardiac death.

Results

Patients with lower tolerance to somatic pain were significantly older (P = 0.001), had more clinical angina (P = 0.04), and on multivariate analysis had poorer exercise tolerance (P = 0.002) than those with higher pain tolerance. Low and high pain tolerance patients demonstrated similar degrees of myocardial ischemia on noninvasive testing and had similar cardiac event rates (death, nonfatal Ml, or unstable angina) during the follow‐up period.

Conclusions

Despite demonstrating a similar frequency of myocardial ischemia and similar prognosis as patients with high pain tolerance, individuals with low pain tolerance were more likely to experience clinical symptoms and functional impairment, providing evidence that individual differences in somatic pain tolerance influence the symptomatic expression of coronary disease.
Sequential Alterations in Myocardial Lactate Metabolism, S‐T Segments, and Left Ventricular Function During Angina Induced by Atrial Pacing
Authors: PARKER JOHN O. , CHIONG MIGUEL A. , WEST ROXFOY O. , CASE ROBERT B.
Published: October 2006

Myocardial lactate metabolism was monitored before, during, and after a period of atrial pacing with a continuous automated sampling technic. The electrocardiogram was recorded, and left ventricular function was evaluated by relating left ventricular end‐diastolic pressure to left ventricular stroke work. Seventeen of 21 patients with coronary artery disease experienced angina during pacing, and 13 of these showed lactate production by the myocardium during angina. The abnormalities in lactate metabolism developed early in the pacing period, along with S‐T segment depression and impairment of left ventricular function, all of which usually occurred before the onset of pain. In the patients with angina, the mean lactate extraction was 14.1% during the control period and —15.1% during the pacing period. Abnormalities in myocardial lactate metabolism have been demonstrated with greater regularity during pacing‐induced angina than during angina precipitated by exercise or isoproterenol. This investigation has demonstrated the sequences of changes in lactate metabolism during and after a period of angina and their relation to electrocardiographic and hemodynamic events.
Comparison of the Proarrhythmic Effect of GLG‐V‐13, a Novel Class III Antiarrhythmic Compound, in Two Rabbit Models of Torsades de Pointes Ventricular Tachycardia
Authors: Fazekas Tamás , Szilvassy Zoltan , Carlsson Leif , Berlin K. Darrell , Scherlag Benjamin J. , Patterson Eugene , Lazzara Ralph
Published: October 2006

Objective: The proarrhythmic potential of a new IKr‐blocking Class III antiarrhythmic agent, GLG‐V‐13 was studied and compared in two rabbit models of torsades de pointes (TdP) ventricular tachycardia (TdP).

Methods: Chloralose‐anesthetized rabbits (n = 8) were given a concomitant infusion of GLG‐V13 (84 nmol/kg per min) and the α1‐agonist methoxamine (70 nmol/kg per min); in another set of experiments, GLG‐V‐13 was administered solely into the ear vein of electrode catheter instrumented conscious rabbits (n = 6). The doses of GLG‐V‐13, to produce maximum prolongation of the QTUc interval or the right ventricular effective refractory period (VERP), and that inducing ventricular ectopic beats (EBs) and TdP, respectively, were determined.

Results: In anesthetized rabbits, GLG‐V‐13 increased QTUc from 125 ± 3 to 161 ± 6 ms after a cumulative dose of 0.84 μmol/kg (P < 0.001) and caused EBs at a mean cumulative dose of 3.9 ± 1.1 μmol/kg. In five of the rabbits, the EBs turned into TdP at a dose of 5.2 ± 3.2 μmol/kg. In conscious rabbits, maximum prolongation of the VERP (27%± 4.3%; P < 0.01) by GLG‐V‐13 was seen at a dose of 1.2 ± 0.54 μmol/kg, whereas EBs and TdP were induced after 6.3 ± 1.4 (6/6) and 8.1 ± 1.4 μmol/kg (6/6), respectively.

Conclusion: (1) The dose‐dependent “torsadogenic” potential of IKr‐blockers can be evaluated in conscious rabbits without concomitant methoxamine administration; (2) in the conscious state, the EB‐ and TdP‐inducing dose of GLG‐V‐13 is about 50% higher than in the chloralose‐anesthetized animal; and (3) irrespective of the chemical nature of the compound applied, blockade of the cardiac IKr potassium channel is associated with proarrhythmic effect.
Gender Specificities in Risk Stratification After Myocardial Infarction
Authors: Copie Xavier , Hnatkova Katerina , Fei Lü , Staunton Anne , Camm A. John , Malik Marek
Published: October 2006

Objective: Although gender specificities of various risk factors have been well documented, risk stratification after myocardial infarction has never been compared in women and men.

Methods: The power of left ventricular ejection fraction, heart rate variability, and mean RR interval computed from 24‐hour Holter recordings, was compared in women and men for the prediction of cardiac mortality after an acute myocardial infarction. The study population consisted of 456 patients (108 women, 348 men) aged 50–75 years.

Results: During a follow‐up of 3 years, there were 41 cardiac deaths (13 women vs 28 men, P = NS). The positive predictive accuracy of left ventricular ejection fraction, heart rate variability, and mean RR interval at all sensitivity levels was higher in women than in men. For a 40% sensitivity, positive predictive accuracy of left ventricular ejection fraction was 46% in women and 16% in men (P < 0.05), positive predictive accuracy of mean RR interval was 90% in women and 28% in men (P < 0.05), and positive predictive accuracy of heart rate variability was 61% in women and 43% in men (P = NS). Mean RR interval had the highest positive predictive accuracy for cardiac mortality in women, but its superiority over heart rate variability was not statistically significant. In men, heart rate variability was the strongest predictor of mortality that was significantly more powerful than mean RR interval and left ventricular ejection fraction (P < 0.05).

Conclusion: Increased 24‐hour mean heart rate is the strongest predictor of cardiac mortality in women in whom it performs significantly better than in men. While in men, heart rate variability is a significantly better predictor of postinfarction cardiac mortality than 24‐hour mean heart rate, this is not the case in women.
Hemodynamic Determinants of Silent ST Segment Depression in Patients with Hypertrophic Cardiomyopathy Treated with Verapamil
Authors: Dimitrow Paweł Petkow , Surdacki Andrzej , Kakol Janusz , Jasiriski Tomasz , Dubiel Jacek Stefan , Janicki Kazimierz
Published: October 2006

Objective: The aim of the study was to establish mechanisms of ischemic type, painless ST segment depression in nine patients with nonobstructive hypertrophic cardiomyopathy (HC) treated effectively by verapamil.

Methods: Simultaneous 24‐hour Holter and blood pressure monitoring (measurements every 15 minutes) was performed to determine approximate indices of myocardial oxygen demand (double product), myocardial oxygen supply (diastolic blood pressure), and ST segment level during each minute when blood pressure measurements were obtained. According to ST segment level, all recordings were divided into four subgroups (one without and three with gradually increasing magnitude of ST segment depression) in which average double product and diastolic blood pressure were calculated.

Results: Increasing ST segment depression coincided with gradual rises in double product indicating increasing myocardial oxygen consumption. Diastolic blood pressure was low in the group without ST segment deviation whereas it was significantly higher only in groups with ST segment depression of more than 2 mm.

Conclusion: Verapamil‐induced, excessive fail of diastolic blood pressure was not associated with exacerbating ST segment depression. On the other hand, occasionally verapamil insufficiently prevented increases of double product, which coincided with the prescence of painless ST segment depression episodes.
Sleep Related Cardiovascular Risk
Authors: Verrier Richard L. , Stone Peter H. , Pace‐Schott Edward F. , Hobson J. Allan
Published: October 2006

Although 20% of myocardial infarctions (MIs) and 15% of sudden cardiac deaths (SCD) occur between midnight and 6:00 A.M., nocturnal cardiac death remains an underappreciated and poorly understood phenomenon. The risk of nocturnal SCD may be‐especially high in patients with coronary disease confounded by apnea, heart failure, recent Ml, pause‐dependent Torsade de Pointes, and near miss victims of sudden infant death syndrome (SIDS) or siblings of SIDS vistims. During rapid eye movement (REM) sleep and dreaming, significant bursts in sympathetic nervous system activity may compromise coronary flow and trigger life‐threatening arrhythmia in susceptible individuals. In non‐REM or slow wave sleep, hypotension may lead to malperfusion of the heart and brain as a result of a lowered pressure gradient through stenosed vessels. Obstructive sleep apnea, which afflicts 1.5 million Americans, can generate reductions in arterial oxygen saturation, which may lead to hypertension and greatly increased risk of myocardial infarction. Cardiac medications which cross the blood‐brain barrier have the potential to alter sleep structure and provoke nightmares with severe cardiac autonomic discharge. Recently, new streamlined technology has been developed for tracking of sleep state. Among the most promising is the Nightcap, an unobtrusive, low cost device which accurately detects sleep state from eyelid and head movement with algorithms which could be incorporated into the circuity of ambulatory ECG recorders. Sleep states present unique autonomic, hemodynamic, and respiratory challenges to the diseased myocardium which cannot be replicated by daytime diagnostic tests. Because of the magnitude of the problem of nocturnal death and the availability of new practical technology for combined monitoring of sleep state and ECG, more widespread nighttime monitoring of the cardiac patient seems warranted.
Can Dispersion of the QT Interval Identify Inducible Monomorphic Versus Polymorphic Ventricular Tachycardia?
Authors: Clay Anthony , Dreifus Leonard S. , Zaim Sina , Kutalek Steven P.
Published: October 2006

Background

Dispersion of QT interval has been utilized to stratify patients who may be at risk for lethal ventricular arrhythmias. This study attempted to evaluate the value of QT dispersion in patients undergoing electrophysiological studies (EPSs) to predict inducible monomorphic ventricular tachycardia (MVT) or polymorphic ventricular tachycardia or ventricular fibrillation (PMVT/VF).

Methods

EPSs were performed on 33 patients with a history of symptomatic MVT and PMVT/VF. Seventeen patients were induced by EPS to MVT and 13 patients to PMVT/VF; three other patients could not be induced. The QT limb (QTL, QTCL), precordial (QTP, QTcP) and dispersion measurements, and limb (QTLd, QTcLd, JTLd) and precordial (QTpd, QTcPd, JTPd), were analyzed by two independent observers. Except for the QTP which appeared longer in patients with PMVT/VF than in patients with MVT (468 ± 124 vs 410 ± 41.8 ms, P < 0.05), there was no statistical difference between the QT, QTc, QTd, JTd and induced MVT vs PMVT/VF.

Conclusion

Our data suggest that QT dispersion considering limb leads, precordial leads, or a combination of all leads did not predict inducible MVT vs PMVT/VF in patients presenting with serious index ventricular arrhythmias. A.N.E. 1998; 3(1):20–24
The Long QT Syndrome
Authors: Schwartz Peter J. , Priori Silvia G.
Published: October 2006

Major progress has taken place, and at a very rapid pace, in the understanding of the congenital long QT syndrome (LQTS). This has been the direct consequence of the identification of several of the genes responsible for LQTS and of the studies that have followed, at both basic and clinical levels. A key issue is represented by the fact that all LQTS genes identified so far encode for ionic channels involved in the control of repolarization. The expression studies of the mutated genes have allowed identification of the specific electrophysiologic consequences of the specific mutations and have demonstrated alterations in the NA+ and in K+ currents sufficient to explain the prolongation of action potential duration and, hence, of the QT interval.

Ongoing studies in the selected LQTS patients, for whom the specific mutations are known, are allowing a unique understanding of the complex genotype‐phenotype correlation. These studies indicate the existence of what appear to be gene‐specific patterns in many clinically important features such as the response to therapeutic interventions, the response to increases in heart rate, and in the factors that precipitate the life‐threatening arrhythmias typical of this intriguing disease.
The Association Between Residual Myocardial Ischemia and Heart Rate Variability Early After Acute Myocardial Infarction
Authors: Quintana Miguel , Lindvall Kaj , Storck Niklas
Published: October 2006

Background

Residual myocardial ischemia and decreased heart rate variability (HRV) are common findings during the acute phase of acute myocardial infarction. Both signs have been associated with a poor prognosis. The present study investigated the association between residual myocardial ischemia and HRV in the early phase after AMI.

Patients and Methods

Seventy‐four patients were monitored with ambulatory electrocardiography during 23 ± 1 hours, 4 ± 1 days after AMI. In addition, 24 healthy individuals (controls) with similar age and gender were also monitored. HRV was computed in time and frequency domains. Residual myocardial ischemia was defined as the presence of ST‐segment depression during ambulatory electrocardiography, defined as a 0.1 mV horizontal or downsloping ST‐segment deviation from the reference level, elapsing 1 minute or longer, measured 80 ms after the J point.

Results

Residual myocardial ischemia was found in 22 (30%) patients. Some time‐domain and all frequency‐domain measures of HRV were lower in patients showing residual myocardial ischemia compared with those without residual myocardial ischemia. All time‐ and frequency‐domain measures of HRV were higher in controls compared with patients with residual myocardial ischemia. Only SDNN and low frequency band values were lower in patients without residual myocardial ischemia compared with healthy controls. Both residual myocardial ischemia and a decreased HRV were associated with poor in‐hospital outcome.

Conclusions

Patients showing residual myocardial ischemia during ambulatory electrocardiography performed early after AMI had lower values of HRV compared with those without residual myocardial ischemia. The causality between these findings are not still defined and deserve further research.
Normal Dispersion of Ventricular Repolarization in Patients with Kawasaki Disease Who Develop Coronary Artery Abnormalities
Authors: Berul Charles I. , Hill Sharon L. , Fulton David R.
Published: October 2006

Background

Kawasaki disease (KD) is complicated by coronary artery abnormalities (CAA) in 3%‐25% of patients, depending on acute therapy. ECG markers of ventricular vulnerability such as QT and JT dispersion, SAECG, and ambulatory monitoring have been shown to have predictive value in disparate diseases such as long QT syndrome, postmyocardial infarction, and atherosclerotic coronary artery disease. The aim of this study was to evaluate the association between QT and JT dispersion and the occurrence of CAA in KD.

Methods

Over the past 15 years, we evaluated 814 children with acute KD, of which 24 (3%) developed significant CAA (aneurysms, stenoses). An additional 40 children (5%) developed milder CAA (4–5 mm dilation). Multivariate analysis was used to compare QTc, JTc, and dispersion in the 24 patients who developed significant CAA with three other groups: 40 patients with mild CAA, 750 KD patients without evidence of CAA, and 1000 normal control children. A small prospective study included additional noninvasive ECG markers using ambulatory (Holter) monitoring and SAECG.

Results

There were no significant differences in any ECG measures of ventricular repolarization among any of the three KD groups and the normal control pediatric ECGs.

Conclusions

Increased dispersion of ventricular repolarization is not associated with coronary‐artery abnormalities in KD.
Spontaneous Variability of Ventricular Ectopic Activity in Patients with Sustained Ventricular Tachycardia and in Survivors of Cardiac Arrest
Authors: Anastasiou‐Nana Maria I. , Karagounis Labros A. , Anderson Jeffrey L. , Mason Jay W.
Published: October 2006

Background: Spontaneous variability of ventricular arrhythmia has been described in patients with chronic stable ventricular arrhythmias and in patients with chronic heart failure. However, no data are available on spontaneous variability in patients with sustained ventricular tachyarrhythmias. Thus, the present study was designed to prospectively determine the extent of spontaneous variability of ventricular arrhythmia in patients with sustained ventricular tachyarrhythmias and in survivors of cardiac arrest.

Methods: Ventricular arrhythmia variability was determined in 470 patients (413 men, 57 women), age (mean ± SD) 64.6 ± 9.5 years with documented ventricular tachycardia (VT), cardiac arrest, or syncope who were prospectively enrolled in a randomized trial of the comparison of electrophysiological testing with Holter monitoring to predict antiarrhythmic drug efficacy. Coronary artery disease was present in 398 (85%) patients, and the mean left ventricular ejection fraction was 0.32 ± 0.13. They underwent two 24‐hour ambulatory recordings separated by 1 day. Spontaneous variability was determined for total premature ventricular complexes (PVCs), pairs, and VT events.

Results: Arithmetic mean of hourly total PVCs on day 1 was 315 ± 425. The 95% confidence limit of spontaneous reduction in total PVC count was 71%. Corresponding values for pairs, VT events of 3–15 beats, < 15 beats, or < 15 seconds were 72%, 80%, 94%, and 95%, respectively. The percentage increases in total PVCs, pairs, and VT events 3–15 beats, < 15 beats, and < 15 seconds were 243%, 259%, 397%, 1553%, and 1756%, respectively. The percentage reduction required to show a true drug effect was 63% for patients with an ejection fraction > 0.32 and 76% for those with an ejection fraction ltm 0.32 (P = 0.024). Patients who presented with unmonitored syncope showed less spontaneous variability than either patients with documented, sustained VT or cardiac arrest.

Conclusions: Marked spontaneous variability of ventricular arrhythmias is observed in patients with sustained ventricular tachyarrhythmias. Variability is affected by the degree of left ventricular dysfunction. The lowest variability was observed in patients presenting with unmonitored syncope. Thus, large changes in arrhythmia frequency must be observed in this population, as in others, to be ascribed to drug effect.
Slowed Conduction with Antiarrhythmic Drugs Reduces High Frequency Energy of the Signal‐Averaged Electrocardiogram
Authors: Bloomfield Daniel M. , Freedman Roger A. , Steinberg Jonathan S.
Published: October 2006

Background: We have previously demonstrated that high frequency QRS energy decreases after experimental myocardial infarction (Ml) and is lower in patients who have had MI compared to controls. The mechanism for this decrease in high frequency QRS energy is unclear. The objective of this study was to evaluate the effect of slowed myocardial conduction on high frequency QRS energy measured on the signal‐averaged SAECG. We hypothesized that slowed conduction in the infarcted ventricle may be responsible for the decrease in high frequency QRS energy. In order to test this hypothesis, we examined antiarrhythmic drug therapy known to slow conduction (propafenone) compared to drug therapy with minimal effects on conduction (sotalol).

Methods: In patients with sustained ventricular tachyarrhythmias undergoing serial drug testing, SAECGs were obtained before and after antiarrhythmic therapy. After filtering the leads with a spectral band‐pass (15–40 Hz, 40–80 Hz, and 80–300 Hz) filter, the vector magnitude was con structed, and the energy (in μV sec) was calculated for the entire QRS by integrating the area under the filtered QRS complex.

Results: Propafenone significantly prolonged QRS duration (+17%, P > 0.001) and significantly reduced QRS energy (‐16.1% to 21.8%, P > 0.0001) in all three band widths. Sotalol did not have either effect (P = ns). There was a strong correlation between the prolongation of the filtered QRS and the drop in QRS energy for all three band widths (r values ranging from 0.64–0.90, all P > 0.05). When the changes in QRS energy were corrected for QRS duration, the results did not change.

Conclusion: The Class IC antiarrhythmic drug propafenone, known to decrease myocardial conduction velocity, significantly reduced QRS energy in all three band widths, whereas the Class III drug sotalol did not. These data are consistent with the hypothesis that decreases in low and high frequency QRS energy after Ml result in part from slowed conduction.
Spectral Analysis of RR and R‐T Variabilities in Patients with Coronary Artery Disease
Authors: Sandrone G. , Torzillo D. , Fundarò C. , Porta A. , Danna P. , Polese A. , Malliani A. , Lombardi F.
Published: October 2006

Background: As the duration of the Q‐T interval is dependent upon the length of the preceding cardiac cycle, changes in QT interval duration mainly reflect, in normal subjects, the physiological beat‐by‐beat variability of the sinus node. However, little information is available on short‐term Q‐T variability in patients with an abnormal neural modulation of the sinus node.

Methods: We analyzed, with autoregressive techniques, RR and R‐Tapex, and R‐Tend variabilities in 12 patients after myocardial infarction, in 13 patients before and after percutaneous transluminal coronary angioplasty (PTCA), and in 10 age‐matched controls.

Results: No significant differences in mean value and variance of RR, R‐Tapex, and R‐Tend interval among the three groups of subjects were observed. Spectral analysis of RR variability was characterized by signs of sympathetic activation with a predominance of low frequency (LF) component in patients after myocardial infarction (69 ± 5 nu) and before PICA (74 ± 5 nu) in comparison to controls (50 ± 4 nu). Instead, spectral energy was equally distributed within LF and HF (high frequency) components of RTapex and R‐Tend variabilities in the three groups of subjects.

Conclusions: These data indicate that the predominance of LFRR in normalized units, indicating an increase of sympathetic modulation of sinus node activity in patients with coronary artery disease, are not accompanied by a parallel predominance of the LF component of R‐Tapex and R‐Tend variabilities. This difference reflects, in our opinion, a minor dependency of duration of ventricular repolarization from the preceding cardiac cycle in patients with coronary artery disease.
Absence of Increased Systemic Vascular Resistance During Syncopal Episodes in Patients with Tilt‐Positive Neurocardiogenic Syncope
Authors: Perl Shira , Weitzman Shimon , Battler Alexander , Katz Amos
Published: October 2006

Background

The purpose of this study was to elucidate the mechanism of syncope in patients with neurocardiogenic syncope (NCS) by measuring hemodynamic parameters continuously during a head‐up tilt (HUT) test.

Methods

Twenty‐three adults (mean age 22.6 ± 9.8, range 15–62) participated in the study: 16 with a history of syncope suggesting NCS and 7 healthy volunteers who served as controls. The subjects underwent a 45‐minute 60° tilt test. Heart rate and blood pressure were monitored continuously. The stroke volume was measured every minute by noninvasive impedance cardiography, and systemic vascular resistance was calculated from these measurements. The test was terminated when syncope occurred or after 45 minutes in an upward position.

Results

Eight of the 16 patients had a positive HUT, while all control subjects had a negative HUT. Decreased stroke volume and cardiac index were observed in all subjects and subgroups in the upward position, compared to the rest position (P < 0.01). Systemic vascular resistance rose in patients with a negative HUT and all controls (P < 0.03), but did not change in the HUT‐positive patients (P = 0.25), during the HUT. Systemic vascular resistance was significantly lower in the upward position in the positive HUT than in the other groups (P < 0.04), but there were no differences in the cardiac index.

Conclusions

Failure to achieve an appropriate increase in systemic vascular resistance may be an important mechanism in some cases of NCS and should be taken in account when considering therapeutic options. Impedance cardiography is a noninvasive technique for the detection of this abnormal response and can be used to assess the effect of drug therapy on systemic vascular resistance. A.N.E. 1999; 4(2):121–129