bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ventricular Fibrillation and Polymorphic Ventricular Tachycardia with Critical Coronary Artery Stenosis:
Authors: NATALE ANDREA , SRA JASBIR , AXTELL KATHI , MAGLIO CHERYL , DHALA ANWER , BLANCK ZALMEN , DESHPANDE SANJAY , JAZAYERI MOHAMMAD , AKHTAR MASOOD 
Published: May 2007

ICD Therapy and CABG for Sudden Death. Introduction: Previous studies have suggested that coronary artery bypass surgery is sufficient to prevent recurrence of sudden death in patients with critical coronary artery stenosis presenting with ventricular fibrillation or polymorphic ventricular tachycardia. We present our experience in patients with one or more episodes of sudden death associated with documented ventricular fibrillation or polymorphic ventricular tachycardia and severe operable coronary artery disease who underwent defibrillator implant at the time of bypass surgery. Methods and Results: Fifty‐eight consecutive patients (age 63 ± 8 years) were included in this study. Eighteen of the 58 patients had no evidence of previous myocardial infarction. The mean ejection fraction was 37 ± 13%. All patients underwent electrophysiologic study before and after revascularization. At the time of first defibrillator discharge, each patient was reevaluated to exclude the presence of ischemia. The benefits of defibrillator implant were estimated comparing the projected survival based upon defibrillator discharge preceded by syncope or presyncope with survival curves generated including total death and sudden plus cardiac death. After a mean follow‐up of 4.6 ± 2 years, 22 patients received appropriate shocks preceded by syncope or presyncope, and an additional 19 patients received asymptomatic shocks. At 4 years, survival free of total death was 71.2%, and the projected survival was 58.8% (P < 0.05). Multivariate analysis showed that ejection fraction lower than 30% and induction of arrhythmia with one or two extrastimuii (S2, S3) were independent predictors for defibrillator discharge. None of the remaining variables including age, gender, number of bypasses, history of myocardial infarction, and type of arrhythmias induced were predictive for death and occurrence of shocks. Conclusions: In patients with ventricular fibrillation and polymorphic ventricular tachycardia, bypass surgery does not protect from recurrence of life‐threatening arrhythmias, and, as in our population, defibrillator implant may have significant impact on survival.
Pharmacologic Properties of the Swelling‐Induced Chloride Current of Dog Atrial Myocytes
Authors: SOROTA STEVE 
Published: May 2007

Pharmacology of Swelling‐Induced Chloride Current. Introduction: Swelling‐induced chloride currents may contribute to cardiac electrical activity and cell volume regulation. Identification of selective Mockers would aid in understanding the functional contribution(s) of this current. Methods and Results: Dog atrial cells were used to investigate the pharmacologic properties of the swelling‐induced chloride current. Whole cell patch clamp was used. Swelling‐induced chloride current was activated by osmotic stress. Initially, the chloride selectivity and calcium independence of the swelling‐induced current in dog atrial cells was demonstrated. Subsequently, a number of putative chloride channel blockers were examined. Anthracene‐9‐earboxylic acid (1mM) and dideoxyforskolin (1000 μ) and extracellular cAMP (5mM) were found to partially inhibit the swelling‐induced chloride current (∼50%, 80%, and 10% inhibition, respectively). Niflumic acid (100 μ), nitrophenylpropylamino benzoate (NPPB; 10 to 40 μ), and (+) 2‐[(2‐cydopentyl‐6,7‐dichloro‐2,3‐dihydro‐2‐melhyl‐1‐oxy‐1H‐inden‐5‐yl)oxy] acetic acid (indanyloxyacetic acid; IAA‐94; 100 μ) could fully inhibit the swelling‐induced chloride current without decreasing cell size. DIDS (100 μ) and dinitrostilbene disulfonic acid (DNDS;5 mM) fully inhibited outward currents but only partially inhibited inward current. Conclusions: Niflumic acid, IAA‐94, and NPPB were identified as full blockers of cardiac swelling‐induced chloride current. Nonspecific effects were identified for each of the full blockers. Experiments that use these agents as functional antagonists should be carefully designed and interpreted with caution.
Biphasic Waveform Defibrillation Using a Three‐Electrode Transvenous Lead System in Humans
Authors: MARKS MELINDA L. , JOHNSON GEORGE , HOFER BRADLEY O. , BARDY GUST H. 
Published: May 2007

Biphasic Transvenous Defibrillation. Introduction: Biphasic waveform defibrillation is not always more efficacious than monophasic waveform defibrillation. Methods and Results: Waveform efficacy appears to vary with the lead system used. In this prospective, randomized study, defibrillation efficacy with biphasic and monophasic single capacitor 120μF, 65% tilt pulses was compared for a lead system consisting of right ventricular (RV), chest patch (CP), and superior vena cava (SVC) electrodes. Although this lead system is commonly used with monophasic pulses in transvenous defibrillators, few studies have examined the defibrillation efficacy of this lead system in man for biphasic waveform defibrillation. Fourteen cardiac arrest survivors undergoing defibrillator implantation were included in the study using pulses delivered from a cathodal RV electrode simultaneously to anodal SVC and CP electrodes. Biphasic and monophasic waveforms were recorded oscilloscopically to acquire defibrillation threshold (DFT) data on leading edge voltage requirements and for stored energy. The monophasic DFT voltage was 661 ± 177 V compared to the biphasic DFT voltage of 451± 185 V (P < 0.0001). The monophasic DFT stored energy was 28.0 ± 13.4 J compared to the biphasic DFT stored energy of 14.1 ± 12.4 J (P ± 0.0001). The stored energy DFT was < 15 J in only 2 of 14 patients (15%) with monophasic defibrillation but < 15 J in 10 of 14 (71%) patients with biphasic defibrillation. Conclusion: These findings indicate that biphasic defibrillation with an RV, SVC, CP transvenous electrode system is substantially more efficient than monophasic defibrillation. allowing for higher numbers of patients to receive transvenous defibrillators with a relatively simple lead system at a satisfactory cutoff DFT safety margin of 15 J.
Bedside Recordings of His‐Bundle Electrograms Using Conventional Twelve‐Lead Surface Electrocardiography
Authors: GÜRSOY SINAN , STEURER GUNTER , SOUZA OLGA , BRUGADA PEDRO 
Published: May 2007

Bedside Recording of His Potentials. Introduction: Endocavitary His‐bundle electro‐grams are usually recorded using high fidelity amplifiers and special filters. Methods and Results: To evaluate whether similar recordings could be obtained using a 12‐lead surface electrocardiograph, we compared recordings obtained during an electrophysiologic study in 33 patients to those obtained by connecting the two poles of the bipolar catheter, used during the study as the His catheter, to the right and left arm leads of the surface electrocardiograph. We recorded His‐bundle electrograms using both techniques in all patients. There were no differences in measurements obtained between the two techniques. Conclusion: His‐bundle electrograms can be recorded reliably with a conventional electro‐gram without sophisticated systems.
Additions to the Wavelet Hypothesis of Cardiac Fibrillation
Authors: ABILDSKOV J.A. 
Published: May 2007

Wavelet Hypothesis. Introduction: The wavelet hypothesis of Moe relates the initiation of cardiac fibrillation to nonuniform propagation of premature responses in the presence of nonuniform recovery of excitability. Fibrillation itself is characterized by multiple spatially discrete activation fronts (wavelets) resulting in reentry at changing locations. Methods and Results: A computer model originally used to demonstrate the hypothesis has been used in further studies of fibrillation and the findings add new details to the hypothesis. The model simulated propagation, cycle length dependent recovery of excitability, and slow propagation of premature responses. Additions to the hypothesis were definition of the different mechanisms by which refractory period (RP) range and mean duration affect vulnerability, explanation of the onset of the vulnerable period later than earliest propagation, and definition of effects of conduction defects on vulnerability. They also include evidence that RP range and duration affect the degree of nonuniform excitation required for fibrillation. Conclusion: Findings indicate that mean RP duration affects vulnerability by means of the number of premature responses possible per unit time while RP range affects nonuniformity of propagation per premature response. They also suggest that effects of conduction defects on vulnerability depend on associated RPs and that the degree of nonuniform excitation required to initiate fibrillation varies with recovery properties. In addition, they provide an explanation for onset of (he vulnerable period after propagation is possible.
A Prospective Randomized Cross‐Over Comparison of Mono‐ and Biphasic Defibrillation Using Nonthoracotomy Lead Configurations in Humans
Authors: BLOCK MICHAEL , HAMMEL DIETER , BÖCKER DIRK , BORGGREFE MARTIN , BUDDE THOMAS , ISBRUCH FRANK , WIETHOLT DETMAR , SCHELD HANS H. , BREITHARDT GUNTER 
Published: May 2007

Biphasic Defibrillation with Nonthoracotomy Leads. Introduction: For current implantable defibrillators, the nonthoracotomy approach to implantation fails in a substantial number of patients. In a prospective randomized cross‐over study the defibrillation efficacy of a standard monophasic and a new biphasic waveform was compared for different lead configurations. Methods and Results: Intraoperatively, in 79 patients receiving nonthoracotomy defibrillation leads, the defibrillation threshold was determined in the initial lead configuration for the mono‐and biphasic waveform. In each patient, both waveforms were used alternately with declining energies (20, 15,10, 5 J) until failure of defibrillation occurred. Three different initial lead configurations were tested in different, consecutive, nonrandomized patients using a bipolar endocardial defibrillation lead alone (A; n = 36) or in combination with a subcutaneous defibrillation patch (B; n = 24) or array (C; n = 19) lead. The lowest successful defibrillation energy with the biphasic waveform was less than, equal to, or higher than with the monophasic waveform in 64%, 28%, and 8% of patients, respectively, and on average significantly lower with the biphasic waveform for all three lead configurations (A: 11.3 ± 4.4 J vs 14.5 ± 4.5.); B: 9.7 ± 4.7 J vs 15.1 ± 4.5 J; C: 7.9 ± 4.5 J vs 12.4 ± 4.9 J). Defibrillation efficacy at 20 J was significantly improved by the biphasic waveform (91% vs 76%). Conclusion: In combination with nonthoracotomy defibrillation leads, the biphasic waveform of a new implantable cardioverter defibrillator showed superior defibrillation efficacy in comparison to the standard monophasic waveform. Defibrillation thresholds were improved for lead systems with and without a subcutaneous patch or array lead.
Lack of Evidence for Low‐Dimensional Chaos in Heart Rate Variability
Authors: KANTERS JØRGEN K. , HOLSTEIN‐RATHLOU NIELS‐HENRIK , AGNER ERIK 
Published: May 2007

Nonlinear Dynamics in Heart Rate. Introduction: The term chaos is used to describe erratic or apparently random time‐dependent behavior in deterministic systems. It has been suggested that the variability observed in the normal heart rate may be due to chaos, hut this question has not been settled. Methods and Results: Heart rate variability was assessed by recordings of consecutive RR intervals in ten healthy subjects using ambulatory ECG. All recordings were performed with the subjects at rest in the supine position. To test for the presence of nonlinearities und/or chaotic dynamics, ten surrogate time series were constructed from each experimental dataset. The surrogate data were tailored to have the same linear dynamics and the same amplitude distribution as the original data. Experimental and surrogate data were then compared using various nonlinear measures. Power spectral analysis of the RR intervals showed a 1/f pattern. The correlation dimension differed only slightly between the experimental and the surrogate data, indicating that linear correlations, and not a “strange” attractor, are the major determinants of the calculated correlation dimension. A test for nonlinear predictability showed coherent nonlinear dynamic structure in the experimental data, but the prediction error as a function in the prediction length increased at a slower rate than characteristic of a low‐dimensional chaotic system. Conclusion: There is no evidence for low‐dimensional chaos in the time series of RR intervals from healthy human subjects. However, nonlinear determinism is present in the data, and various mechanisms that could generate such determinism are discussed.
Gap Junction Protein Phenotypes of the Human Heart and Conduction System
Authors: DAVIS LLOYD M. , RODEFELD MARK E. , GREEN KAREN , BEYER ERIC C. , SAFFITZ JEFFREY E. 
Published: May 2007

Connexin Phenotypes in the Human Heart. Introduction: Gap junction channels are major determinants of intercellular resistance to current flow between cardiac myocytes. Alterations in gap junctions may contribute to development of arrhythmia substrates in patients. However, there is significant interspecies variation in the types and amounts of gap junction subunit proteins (connexins) expressed in disparate regions of mammalian hearts. To elucidate determinants of conduction properties in the human heart, we characterized connexin phenotypes of specific human cardiac tissues with different conduction properties. Methods and Results: The distribution and relative abundance of Cx37, Cx40, Cx43, Cx45, and Cx46 were studied immunohistochemically using monospecific antibodies and frozen sections of the sinoatrial node and adjacent atria, the AV node and His bundle, the bundle branches, and the left and right ventricular walls. Patterns of expression of these connexins in the human heart differed from those in previous animal studies. Sinus node gap junctions were small and sparse and contained Cx45 and apparently smaller amounts of Cx40 but no Cx43. AV node gap junctions were also small and contained mainly Cx45 and Cx40 hut, unlike the sinus node, also expressed Cx43. Atrial gap junctions were larger than nodal junctions and contained moderate amounts of Cx40, Cx43, and Cx45. Junctions in the bundle branches were the largest in size and contained abundant amounts of Cx40, Cx43, and Cx45. Gap junctions in ventricular myocardium contained mainly Cx43 and Cx45; only a very small amount of ventricular Cx40 was detected in subendocardial myocyte junctions and endothelial cells of small to medium sized intramural coronary arteries. Minimal Cx37 and Cx46 immunoreactivity was detected between occasional atrial or ventricular myocytes. Conclusions: The relative amounts of individual connexins and the number and size of gap junctions vary greatly in specific regions of the human heart with different conduction properties. These differences likely play a role in regulating cardiac conduction velocity. Differences in the connexin phenotypes of specific regions of the human heart and experimental animal hearts must he considered in future experimental or modeling studies of cardiac conduction.
Elevated Defibrillation Threshold When Right‐Sided Venous Access is Used for Nonthoracotomy Implantable Defibrillator Lead Implantation
Authors: EPSTEIN ANDREW E. , KAY G. NEAL , PLUMB VANCE J. , LYNNETT VOSHAGE‐STAHL B.A.N. , HULL MICHAEL L. 
Published: May 2007

Right/Left‐Sided ICD Implantation. Introduction: Although myriad factors influence the defibrillation threshold, the relation between the site of transvenous lead entry into the vascular system and the defibrillation threshold has not been reported. This study examines the influence that venous entry site has on defibrillation success for a transvenous implantable cardioverter defibrillator lead with two defibrillating coils. Methods and Results: The study population comprised 345 patients. Their mean age was 61 ± 13 years and, left ventricular ejection fraction was 0.33 ± 0.13. A left‐sided approach was used in 324 (93.9%) of the patients, and a right‐sided approach was used in the remaining 21 (6.1%) patients. There was no difference in the gender, age, left ventricular ejection fraction, or underlying cardiac disease in the two groups. For all patients, with a transvenous lead used either alone or with a submuscular or subcutaneous patch, the biphasic defibrillation threshold was 9.9 ± 4.8 J when a left‐sided approach was used, and 14.0 ± 7.3 J when a right‐sided approach was used (P = 0.02). When a transvenous lead was used with a submuscular or subcutaneous patch (115 patients), the biphasic defibrillation threshold was 9.5 ± 4.3 J when a left‐sided approach was used, and 12.0 ± 10.0 J when a right‐sided approach was used (P = 0.98). When a transvenous lead was used without a submuscular or subcutaneous patch (230 patients), the biphasic defibrillation threshold was 10.1 ± 5.0 J when a left‐sided approach was used, and 14.6 ± 6.6 J when a right‐sided approach was used (P < 0.01). For the entire group of patients and for each specific lead arrangement, there was no significant difference in the defibrillating lead system impedance when right‐sided versus left‐sided approaches were compared. Conclusion: Left‐sided approaches to implant transvenous leads with two coils for defibrillation result in lower biphasic defibrillation thresholds than when right‐sided approaches are used.
Ventricular Action Potential and L‐Type Calcium Channel in Infarct‐Induced Hypertrophy in Rats
Authors: de BRITO SANTOS PAULO EUSTÁQUIO , BARCELLOS LUCIANE CLAUDIA , MILL JOSÉ GERALDO , MASUDA MASAKO OYA 
Published: May 2007

Calcium Channel in Infarct‐Induced Hypertrophied Rat Ventricle. Introduction: The present investigation was aimed at characterization of: (1) action potential parameters; and (2) L‐type calcium channels in the hypertrophied ventricular tissue surviving an extensive healed myocardial infarction in the rat. Methods and Results: Myocardial infarction was produced in Wistar rats by ligation of the left coronary artery. One to 2 months later, their hearts were subjected to electrophysiologic study. The main difference in subendocardial transmembrane potentials recorded with intracellular microelectrodes was an increase in action potential duration (APD). In the left ventricle, the infarcted/sham‐operated APD ratio ranged from 2.7 to 7.2, whereas in the right ventricle it ranged from 1.6 to 2.3 in different regions. When compared with control ceils, ventricular myocytes from infarcted hearts were found to be larger (P < 0.01) and showed a reduction (P < 0.05) in L‐type calcium current (ICa,L) density obtained by whole cell, patch clamp (at 0 mV: 4.44 ± 0.41 in infarcted vs 8.03 ± 1.22 pA/pF in normal). The time course of decay of the currents could be fitted by two exponential functions in both normal and infarcted hearts. There was a tendency toward an increase in the time constant of the slower component of inactivation, T2, significant only at +20 mV (215 ± 25 vs 151 ± 15 msec). Conclusions: Cardiac hypertrophy of healed infarction in rats is associated with lengthening of the action potential in both ventricles. The main alteration observed in ICa,Lwas a decrease in the current density. Thus, alteration of the calcium channel is not the determinant factor of APD increase
Stability: An ICD Detection Criterion for Discriminating Atrial Fibrillation From Ventricular Tachycardia
Authors: HIGGINS STEVEN L. , LEE ROBERT S. , KRAMER RENA L. 
Published: May 2007

Stability, An ICD Detection Criterion. introduction: The purpose of this study was to review a new implantable cardioverter defibrillator (ICD) detection criterion, stability, to determine if it can effectively discriminate rapid rhythms of atrial fibrillation from ventricular tachycardia. Inappropriate shocks for rapid atrial fibrillation limit the acceptance of ICDs. The advent of an additional detection criterion, stability, has been postulated to be of value in discriminating rapid atrial fibrillation, which may not warrant treatment, from ventricular tachycardia, which obviously does warrant therapy delivery. Methods and Results: Twenty‐six patients were studied during 32 episodes of rapid atrial fibrillation and 24 episodes of monomorphic ventricular tachycardia below 220 beats/min. Each rhythm was repeatedly evaluated by the device at each of the seven stability values available (8, 16, 23, 31, 39, 47, and 55 msec) and then classified as stable or unstable. Upon completion of this acute study, 32 ICD patients bad the stability feature activated and were followed for proper arrhythmia treatment by the device. Using stability windows from 8 to 47 msec, all atrial fibrillation rhythms were appropriately classified as unstable. Three of 6 were classified correctly for the 55‐msec window. All ventricular tachycardia rhythms were appropriately classified as stable for all stability windows from 8 to 55 msec. Clinical follow‐up confirmed appropriate therapy delivery when coupled with sustained rate duration (SRD). Thirty‐two patients followed for 292 patient‐months had no episodes of untreated ventricular tachycardia with 428 successfully classified as stable and treated. Only three episodes of suspected atrial fibrillation resulted in therapy delivery as the rhythm duration exceeded the SRD of 30 seconds. Conclusions: The CPI Ventak PRx ICD is highly reliable in appropriately classifying atrial fibrillation as unstable and monomorphic ventricular tachycardia as stable for most stability windows evaluating tachycardias below 220 beats/min. As a result, when testing of atrial fibrillation is not possible, we recommend the routine programming of this stability feature at the 31‐msec window with an SRD of 30 seconds. The reliability of this device in discriminating atrial fibrillation from monomorphic ventricular tachycardia may have important clinical implications for other tiered therapy ICDs with this feature as well as for future ICDs in development.