bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microvolt T Wave Alternans Inducibility in Normal Newborn Puppies: Effects of Development
Authors: IDRISS SALIM F. , VAN HARE GEORGE F. , FINK DANIEL , ROSENBAUM DAVID S. 
Published: August 2003

T Wave Alternans in Normal Newborn Puppies.
Introduction: The cause of sudden infant death syndrome is unknown, but increased cardiac vulnerability due to repolarization instability may be a contributing factor. The QT interval normally is long at birth and increases further during the first few postnatal months. Although excessive QT intervals indicate increased cardiac vulnerability in the long QT syndrome, the impact of less pronounced QT prolongation during this developmental period is unclear. In adults and older children, the ease of inducing microvolt‐level T wave alternans (TWA) is used as a measure of repolarization instability and arrhythmia vulnerability. The aim of this study was to determine if TWA is inducible in normal newborn puppies. Methods and Results: Atrial pacing was performed in 15 anesthetized beagle puppies 7 to 35 days old. The pacing drive cycle length was systematically decreased in 20‐msec steps from baseline until AV conduction blocked. Pacing was performed for 8 minutes at each cycle length. Three‐lead ECGs were recorded continuously during the last 5 minutes of pacing at each cycle length. The recordings were analyzed off‐line for the presence of microvolt‐level TWA using a sensitive spectral analysis technique. Microvolt‐level TWA was present in all puppies. TWA was not present at baseline but developed and increased in amplitude as heart rate increased. The threshold heart rate for TWA did not correlate with age. However, due to age‐dependent changes in baseline heart rate, the 7‐ to 14‐day‐old animals needed a 50% to 78% increase in heart rate to reach threshold heart rate, whereas the oldest animals needed only a 5% to 25% increase. Conclusion: These data suggest that developmentally dependent dynamic repolarization instability exists in puppies as manifest by the inducibility of TWA.
Gender Differences in Various Types of Idiopathic Ventricular Tachycardia
Authors: NAKAGAWA MIKIKO , TAKAHASHI NAOHIKO , NOBE SEIKI , ICHINOSE MASASHI , OOIE TATSUHIKO , YUFU FUMIO , SHIGEMATSU SAKUJI , HARA MASAHIDE , YONEMOCHI HIDETOSHI , SAIKAWA TETSUNORI 
Published: August 2003

Gender Differences in Idiopathic VT.
Introduction: The aim of this study was to evaluate gender differences in the incidence and age distribution of various types of idiopathic ventricular tachycardia (VT). Methods and Results: We conducted a search of the medical literature on idiopathic VT. According to their site of origin, we divided the VTs into three types: right ventricular outflow tract (RVOT‐VT), left ventricular outflow tract (LVOT‐VT), and left ventricular (LV) septum (LV‐VT). We reviewed 68 articles and a total of 748 patients. Among RVOT‐VT patients, there were more females than males (311 vs 153, male/female ratio 0.49). In LV‐VT, males prevailed over females (175 vs 52, male/female ratio 3.37), whereas LVOT‐VT was distributed almost equally between males (n = 33) and females (n = 24). To determine the age distribution, we assessed 419 patients from 51 studies. In both males and females, the highest incidence of RVOT‐VT occurred in the third to fifth decade of life (males, mean 43.5 ± 18.7; females, mean 40.9 ± 13.8 years). LV‐VT occurred at a younger age in both males and females than did RVOT‐VT (mean 33.0 ± 13.9 and 25.7 ± 12.0 years, respectively, P < 0.0001 vs RVOT‐VT). LV‐VT occurred at a younger age in females than males (P < 0.005). Conclusion: Gender‐specific differences exist in the incidence and age distribution of the various types of idiopathic VT. Studies on gender‐specific differences in arrhythmia will lead to a better understanding of its mechanism(s) and provide valuable information for the development of optimal treatment strategies.
Sustained Inward Current and Pacemaker Activity of Mammalian Sinoatrial Node
Authors: ZHANG HENGGUI , HOLDEN ARUN V. , BOYETT MARK R. 
Published: August 2003

Sustained Inward Current in the Sinoatrial Node.
Introduction: A novel sustained inward Na+ current ist, which sensitive to Ca2+‐antagonists and potentiated by beta‐adrenergic stimulation, has been described in pacemaker cells of rabbit, guinea pig, and rat sinoatrial node, as well as rabbit AV node. Although ist has been suggested to be an important pacemaker current, this has never been tested experimentally because of the lack of a specific blocker. In this study, we address the role of ist in the pacemaker activity of the sinoatrial node cell using computer models. Methods and Results: The newly developed models of Zhang et al. for peripheral and central rabbit sinoatrial node cells and models of Noble and Noble, Demir et al., Wilders et al., and Dokos et al. for typical rabbit sinoatrial node cells were modified to incorporate equations for ist. The conductance gst was chosen to give a current density‐voltage relationship consistent with experimental data. In the models of Zhang et al. (periphery), Noble and Noble, and Dokos et al., in which ist was smaller or about the same amplitude as other inward currents, ist increased the pacemaking rate by 0.6%, 2.2%, and 0.8%, respectively. In the models of Zhang et al. (center), Demir et al., and Wilders et al., in which ist was larger than some other inward ionic currents, ist increased the pacemaking rate by 7%, 20%, and 14%, respectively. Conclusion: ist has the potential to be a regulator of pacemaker activity, although its importance will depend on the amplitude of ist relative to the amplitude of other inward currents involved in pacemaker activity.
How to Enhance Acute Outcome of Electrical Cardioversion by Drug Therapy: Importance of Immediate Reinitiation of Atrial Fibrillation
Authors: VAN NOORD TRUDEKE , VAN GELDER ISABELLE C. , CRIJNS HARRY J.G.M. 
Published: August 2003

Electrical Cardioversion.
Introduction: In almost 20% of patients with persistent atrial fibrillation (AF), electrical cardioversion is unsuccessful because of shock failure (i.e., no single sinus beat) or immediate reinitiation of AF (IRAF; recurrence within 2 min). Relative prevalence of shock failure and IRAF are not well known because data on outcome of electrical cardioversion therapy mostly do not distinguish shock failure from IRAF. Methods and Results: In this review, the role of pretreatment with antiarrhythmic drugs on prevention of shock failure and total outcome of the cardioversion procedure are investigated. Quinidine and propafenone seem to be effective in preventing IRAF. Verapamil given in addition to Class I or III drugs may strengthen the preventive effects of these drugs than if they were given alone. Ibutilide prevents shock failure, although neither ibutilide nor dofetilide seems to be effective in preventing IRAF. Conclusion: Pretreatment with antiarrhythmic drugs may enhance cardioversion outcome predominantly by preventing IRAF. Different antiarrhythmic drugs within the same Vaughan‐Williams class have different effects on shock failure and IRAF.
Autonomic Control of the Location and Rate of the Cardiac Pacemaker in the Sinoatrial Fat Pad of Parasympathetically Denervated Dog Hearts
Authors: NAKAJIMA KOICHI , FURUKAWA YASUYUKI , KUROGOUCHI FUMIO , TSUBOI MASATO , CHIBA SHIGETOSHI 
Published: August 2003

Autonomic Regulation of Pacemaker Sites.
Introduction: Parasympathetic activity predominates over sympathetic activity not only with respect to heart rate but also with respect to the pacemaker location in the dog heart. After we removed the parasympathetic neural elements in the sinoatrial (SA) fat pad in the right atrium, we observed that cervical vagus stimulation did not decrease the atrial rate, but it did suppress the increase in rate evoked by sympathetic stimulation. We determined whether the pacemaker rate and location were affected by presynaptic or postsynaptic mechanisms. Methods and Results: We determined the earliest activation site by means of isochronic activation mapping of the right atrium of open chest, anesthetized dog hearts. An electrode array, which consisted of 48 unipolar electrodes, was used to record atrial activation. This array covered the three main pacemaker regions, including the SA node region. After parasympathetic nerve fibers in the SA fat pad had been denervated, vagus stimulation at 10 and 30 Hz did not decrease the heart rate, but it attenuated the increase in heart rate evoked by sympathetic stimulation or isoproterenol. Vagus stimulation at 10 Hz during sympathetic stimulation did not shift the earliest activation site from the superior pacemaker region to the SA node region in 11 of 18 experiments. However, vagus stimulation at 10 Hz during isoproterenol infusion shifted the earliest activation site to the SA node region in 11 of 13 experiments. More intense vagus stimulation during combined sympathetic stimulation or isoproterenol infusion shifted the earliest activation site to the SA node or the inferior pacemaker region in 15 of 18 and in all experiments, respectively. Conclusion: The results suggest that activation of parasympathetic elements not located in the SA fat pad attenuates the increase in heart rate and the shift in pacemaker location evoked by sympathetic activation. The sympathetic and parasympathetic effects interact at presynaptic and postsynaptic sites in the dog heart.
Restitution Properties and Occurrence of Ventricular Arrhythmia in LQT2 Type of Long QT Syndrome
Authors: YAMAUCHI SOU , YAMAKI MICHIYASU , WATANABE TETSU , YUUKI KOUICHI , KUBOTA ISAO , TOMOIKE HITONOBU 
Published: August 2003

Mechanisms of Ventricular Arrhythmia in LQT2 Heart.
Introduction: The aim of this study was to clarify the ventricular tachyarrhythmia mechanism induced by the IKr‐blocking agent E4031, simulating the LQT2 form. Electrophysiologic properties were examined in 13 canines before and after administration of E4031. Method and Results: Thirty‐six needle electrodes were inserted into the anterior left ventricular wall. From each needle, local unipolar electrograms were obtained from four intramural sites. Activation time (AT) and activation‐recovery interval (ARI) were measured. To evaluate the susceptibility to ventricular arrhythmia, intramural ARI dispersions and the restitution relationship between ARI and diastolic interval were calculated. After E4031 administration, ARI prolonged uniformly in each myocardial layer. However, ARI dispersion was not augmented compared with control. The slope of the ARI restitution curve after E4031 was significantly steeper than control. A steep slope may result from augmented ARI alternans. In 11 of the 13 canines, ventricular tachyarrhythmia was induced by programmed stimulation after E4031, whereas no arrhythmia was induced by the same protocol in control. Conclusion: Steepness of electrical restitution may play a major role in arrhythmogenicity in LQT2 hearts.
Advanced Rhythm Discrimination for Implantable Cardioverter Defibrillators Using Electrogram Vector Timing and Correlation
Authors: GOLD MICHAEL R. , SHOROFSKY STEPHEN R. , THOMPSON JULIE A. , KIM JAEHO , SCHWARTZ MARK , BOCEK JOE , LOVETT ERIC G. , HSU WILLIAM , MORRIS MILTON M. , LANG DOUGLAS J. 
Published: August 2003

Electrogram Vector Timing and Correlation.
Introduction: Discrimination of ventricular and supraventricular arrhythmias remains one of the major challenges for appropriate implantable defibrillator (ICD) therapy delivery. The electrogram vector timing and correlation (VTC) algorithm was developed for such rhythm discrimination. The VTC algorithm differentiates normally conducted supraventricular beats from abnormally conducted ventricular beats by comparing the timing and correlation of rate and shock channel electrograms. Methods and Results: Rate and shock channel electrograms of sinus rhythm and induced arrhythmias were collected from 93 patients during ICD placement. The algorithm was developed using data from 50 patients and prospectively tested in a software model with the remaining 43 patients. A sinus rhythm reference was formed by averaging complexes of the shock channel signal aligned by the peak amplitude of the rate channel. Eight features measuring the amplitude and timing of shock channel signal characteristics were extracted from the reference for comparison. When a high‐rate rhythm was detected, the VTC algorithm computed the correlation of the arrhythmia complex features with the reference. Rhythms with a sufficient number of uncorrelated beats were classified as ventricular tachycardia (VT). In a dual‐chamber implementation, the VTC algorithm is integrated with ventricular and atrial rate comparison (V > A) and stability above an atrial fibrillation rate threshold. The test set consisted of 117 arrhythmias. Dual‐chamber sensitivity was 100% (81/81 VT) and specificity was 97% (35/36 supraventricular tachycardia). Single‐chamber analysis demonstrated 99% sensitivity and 97% specificity. Conclusion: The VTC algorithm demonstrated high sensitivity and specificity in discriminating between ventricular and supraventricular arrhythmias.
Inducible Ventricular Flutter and Fibrillation Predict for Arrhythmia Occurrence in Coronary Artery Disease Patients Presenting with Syncope of Unknown Origin
Authors: LINK MARK S. , SAEED MOHAMMAD , GUPTA NEERA , HOMOUD MUNTHER K. , WANG PAUL J. , ESTES N.A. MARK 
Published: August 2003

Ventricular Fibrillation and Syncope.
Introduction: Ventricular fibrillation and ventricular flutter (cycle length ≤230 msec) induced at electrophysiologic studies are thought to be nonspecific findings in patients presenting with syncope of unknown origin. However, there are limited data on the prognosis of these patients in long‐term follow‐up. Methods and Results: We followed 274 consecutive patients with coronary artery disease presenting with syncope or presyncope who underwent electrophysiologic studies from January 1992 to June 1999 and assessed the risk of subsequent arrhythmias stratified by the electrophysiologic result at the time of their presentation with syncope. Ventricular fibrillation was induced in 23 patients (8%); ventricular flutter in 24 (9%), sustained ventricular tachycardia in 41 (15%); and nonsustained ventricular tachycardia 42 (15%). In 37 ± 25 months of follow‐up, there have been ventricular arrhythmias in 34 patients, including 3 (13%) of 23 who had induced ventricular fibrillation, and 7 (30%) of 24 with induced ventricular flutter, compared to 13 (32%) of 41 with sustained ventricular tachycardia, 7 (17%) of 42 with nonsustained ventricular tachycardia, and only 4 (3%) of 144 noninducible patients (P < 0.001 for induced ventricular fibrillation and ventricular flutter vs noninducible patients). The inducibility of ventricular fibrillation and ventricular flutter were independent risk factors for arrhythmia occurrence in follow‐up. Conclusion: Ventricular fibrillation and ventricular flutter induced at electrophysiologic studies have prognostic significance for arrhythmia occurrence in patients presenting with syncope. These induced arrhythmias may not be as nonspecific as previously thought and treatment should be considered for these patients.
Three‐Dimensional Mapping of Right Atrial Activation During Sinus Rhythm and Its Relationship to Endocardial Architecture
Authors: BETTS TIM R. , HO SIEW YEN , SANCHEZ‐QUINTANA DAMIAN , ROBERTS PAUL R. , ANDERSON ROBERT H. , MORGAN JOHN M. 
Published: August 2003

Right Atrial Activation.
Introduction: Previous mapping studies of right atrial (RA) activation during sinus rhythm have been limited by the use of epicardial electrode plaques in open chest subjects or microelectrodes in the excised heart. This study describes global RA endocardial activation patterns using high‐density mapping and compares the results with underlying endocardial architecture. Methods and Results: Noncontact mapping of the RA was performed in 21 anesthetized swine. Isopotential and isochronal maps were superimposed upon three‐dimensional reconstructions of RA geometry. Hearts were excised and endocardial dissection performed. Two patterns of RA activation were recorded. The site of earliest endocardial activation occurred either laterally at a position consistent with the terminal crest or superiorly at the junction between the superior caval vein and RA appendage. The subsequent spread of depolarization followed the longitudinal orientation of muscle fibers. Areas of conduction delay and block were seen at the junction between the terminal crest and posterior wall, the cavotricuspid isthmus, and around the margins of the triangle of Koch. Endocardial dissection at these sites demonstrated complex fiber orientation. A lateral site of earliest activation demonstrated a more prominent display of conduction delay or block. Conclusion: The spread of the sinus impulse follows endocardial myofiber orientation and is dictated by the site of earliest activation. Even during sinus rhythm, anisotropic conduction results in areas of conduction block or delay. These findings have implications in the development of reentrant arrhythmias and may influence surgical or electrophysiologic procedures.
Nod Factor Inhibition of Reactive Oxygen Efflux in a Host Legume
Authors: Shaw Sidney L. , Long Sharon R. 
Published: August 2003

Abstract
Hydrogen peroxide (H2O2) efflux was measured from Medicago truncatula root segments exposed to purified Nod factor and to poly-GalUA (PGA) heptamers. Nod factor, at concentrations &gt; 100 pm, reduced H2O2 efflux rates to 60% of baseline levels beginning 20 to 30 min after exposure, whereas the PGA elicitor, at &gt; 75 nm, caused a rapid increase in H2O2 efflux to &gt;200% of baseline rates. Pretreatment of plants with Nod factor alters the effect of PGA by limiting the maximum H2O2 efflux rate to 125% of that observed for untreated plants. Two Nod factor-related compounds showed no ability to modulate peroxide efflux, and tomato (Lycopersicon esculentum), a nonlegume, showed no response to 1 nm Nod factor. Seven M. truncatula mutants, lacking the ability to make nodules, were tested for Nod factor effects on H2O2 efflux. The nfp mutant was blocked for suppression of peroxide efflux, whereas the dmi1 and dmi2 mutants, previously shown to be blocked for early Nod factor responses, showed a wild-type peroxide efflux modulation. These data demonstrate that exposure to Nod factor suppresses the activity of the reactive oxygen-generating system used for plant defense responses.
Expression Profiling of Cytokinin Action in Arabidopsis
Authors: Rashotte Aaron M. , Carson Susan D.B. , To Jennifer P.C. , Kieber Joseph J. 
Published: August 2003

Abstract
The phytohormone cytokinin is an important regulator of plant growth and development; however, relatively few genes that mediate cytokinin responses have been identified. Genome-wide analyses of Arabidopsis seedlings using the approximately 8,300-element Affymetrix Arabidopsis GeneChips (Affymetrix, Santa Clara, CA) to examine cytokinin-responsive genes were conducted, revealing at least 30 genes whose steady-state level of mRNA was elevated and at least 40 that were down-regulated at multiple time points after application of cytokinin. The cytokinin up-regulated genes include the type-A Arabidopsis response regulators (ARRs), which had been shown previously to be cytokinin primary response genes, cytokinin oxidase, which encodes an enzyme that degrades cytokinins, and several transcription factors. Cytokinin down-regulated genes include several peroxidases and kinases and an E3 ubiquitin ligase. We identified a common sequence motif enriched in the upstream regions of the most consistently cytokinin up-regulated genes. This motif is highly similar to the optimal DNA-binding sites for ARR1/ARR2, type-B ARRs that have been implicated in the transcriptional elevation of the type-A ARRs. Additionally, genome-wide analyses of cytokinin receptor mutants (wol/cre1) revealed large-scale changes in gene expression, including down-regulation of the type-A ARRs and several meristem and cell cycle genes, such as CycD3. Mutations in CRE1 reduced but did not eliminate the effect of cytokinin on gene expression for a subset of cytokinin-responsive genes and had little or no effect on others, suggesting functional redundancy among the cytokinin receptors.
Hyperphosphorylation of a Mitochondrial Protein, Prohibitin, Is Induced by Calyculin A in a Rice Lesion-Mimic Mutant cdr1
Authors: Takahashi Akira , Kawasaki Tsutomu , Wong Hann Ling , Suharsono Utut , Hirano Hisashi , Shimamoto Ko 
Published: August 2003

Abstract
The rice (Oryza sativa) lesion-mimic mutants, cell death and resistance (cdr), show spontaneous cell death on the entire leaf and exhibited significant resistance to the rice blast fungus. Our previous studies showed that CDR1 and CDR2 genes negatively regulated the phosphorylation steps leading to the activation of NADPH oxidase, which is associated with oxidative burst. To identify novel factors involved in the phosphorylation steps, the phosphorylation level of total proteins was compared between cdr mutants and wild type using two-dimensional gel electrophoresis. Here, we show that the phosphorylation level of four proteins in cdr1 was increased as compared with the wild type after calyculin A treatment. Partial amino acid sequences revealed that one of the four proteins is homologous to prohibitin (PHB), which has been shown to be associated with senescence and cell death and to function as a chaperone in the assembly of mitochondrial respiratory chain complex in yeast and mammals. Analysis of green fluorescent protein fusions indicated that rice PHB (OsPHB1) was targeted to mitochondria as found in yeast and mammals, suggesting a possibility that PHB is involved in defense response and/or programmed cell death through the mitochondrial function.