bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of Na+:Ca2+ Exchange Current in Cs+‐Induced Early Afterdepolarizations in Purkinje Fibers
Authors: SZABO BELA , SWEIDAN RAED , RAJAGOPALAN CADATHUR V. , LAZZARA RALPH 
Published: May 2007

Na+:Ca2+ Exchanger and EADs. Introduction: The ionic mechanisms for early afterdepolarizations (EADs) have not been fully clarified. It has been suggested that L‐type Ca2+ current (IcaL) is the primary current generating EADs that occur near the plateau level (E‐EADs) of the membrane potential (Vm) when IcaL is enhanced. The purpose of these studies was to determine accurately the range of Vm at which EADs occur in Purkinje fibers with K+ currents blocked by Cs+ and to investigate the importance of Na+:Ca2+ exchange current (INa:ca) as opposed to lCaL and other currents in the generation of EADs occurring later during repolarization (L‐EADs). Methods and Results: Shortened Purkinje strands from dogs and guinea pigs were superfused with physiologic solution containing Cs+ (3.6 mM) and a low [K+]o (3.0 or 2.0 mM) to induce EADs. The Vm of origin of EADs and their evolution were measured with the aid of phase plane plots of the rate of repolarization against Vm. L‐EADs occurred over a wide range of Vm (−35 to −90 mV), generally more negative in guinea pig than in dog. Elevation of [Ca2+]o, from 1.8 to 3.6 mM suppressed L‐EADs within a few cycles, and they returned with continued exposure. After repeated exposures to high [Ca:2+]0, L‐EADs migrated toward less negative Vm when |Ca2+]0, was reestablished to 1.8 mM in the presence of Cs+. Reduction of [Na+]0 from 147.5 to 112.5 mM by substitution with Li+ or sucrose also rapidly depressed L‐EADs. Conclusions: The observation of Cs+‐induced L‐EADs over a wide range of Vm indicates that there is not a single inward gated current as a common ionic mechanism for L‐EADs but does not exclude an important role for INa:Ca, which can operate over a wide range of Vm. The rapid suppression of L‐EADs with elevated [Ca2+]o, and reduced [Na+]o, and the migration of EADs to more positive Vm after exposures to high |Ca2+]o, are compatible with INc:Ca as the major charge carrier for L‐EADs.
Effects of Acute Volume Changes on P Wave Characteristics:
Authors: VAINER JINDRICH , CHERIEX EMILE C. , van der STELD BERT , DASSEN WILLEM R.M. , SMEETS JOEP L.R.M. , WELLENS HEIN J.J. 
Published: May 2007

Effects of Acute Volume Changes on P Wave. Introduction: This study was performed to determine the effect on the P wave of different hemodynamic loads to the heart. Methods and Results: Signal–averaged P wave ECC and atrial echocardiographic measurements were obtained from eight healthy male volunteers at rest and after infusion of 1000 mL of plasma expander (Haemaccel®) over 15 minutes. These measurements were repeated 24 hours later at rest and after 0.8 mg of nitroglycerin given sublingually. The effect of positional changes was also studied. At rest the amplitude of the P wave and the time of the maximal the P wave amplitude were reproducible. Sitting increased heart rate variability; no significant changes of the P wave were found. Volume overload decreased the heart rate and increased the atrial size on echocardiography with changes in lead V, (earlier appearance of the first positive deflection). Nitro–glycerin administration increased heart rate and decreased the echocardiographic size of the atria, the latter not reaching statistical significance. Administration of nitroglycerin induced P wave amplitude rise in leads 1 and II. The maximal power in fast Fourier transformation for calculated orthogonal leads X and Y increased as well. Conclusions: Amplitude behavior in leads I, II, and V, appears to correlate with load conditions, particularly with volume redistribution. In healthy men subtle changes in the P wave morphology after volume changes can be detected by the signal–averaged ECU. Application of these findings in patients following acute changes in circulation needs further investigation.
Immunohistochemical Localization of Gap Junction Protein Channels in Hamster Sinoatrial Node in Correlation with Electrophysiologic Mapping of the Pacemaker Region
Authors: TRABKA‐JANIK ELIZABETH , COOMBS WANDA , LEMANSKI LARRY F. , DELMAR MARIO , JALIFE JOSE 
Published: May 2007

Gap Junction Proteins in the Sinoatrial Node. Introduction: Gap junction proteins are thought to form the low resistance pathways that connect neighboring cells within the sinoatrial node, and to mediate pacemaker synchronization. Methods and Results: We have carried out microelectrode mapping experiments of the hamster sinoatrial region to localize the primary pacemaker area for subsequent light, electron, and immunofluorescence microscopic studies aimed at testing the hypothesis that the major cardiac gap junction protein (connexin43) is present in such an area. The site of earliest activation is unifocal and the pattern of activation, obtained In multiple sequential microelectrode recordings of the Sinoatrial region, is qualitatively similar to that previously described for other species. However, quantitatively, the impulse transmission time from the primary pacemaker area to the crista (sulcus) terminal's in the hamster sinoatrial node is about 50% briefer than that of the guinea pig and five times faster than that of the rabbit. Immunolocalization studies in the hamster sinoatrial node using anti‐connexin43 antisera demonstrated specific staining at the areas of cell‐to‐cell apposition and suggested that the apparently high degree of electrical coupling in this tissue is the result of abundant connexin43 expression. The immunofluorescence data were supported by light microscopic studies, which demonstrated the typical morphologic characteristics of sinus nodal cells in the pacemaker area. In addition, an electron microscopic study of the sinoatrial region revealed the presence of gap junctions in the junctional complex at areas of cell‐to‐cell contact. Conclusion: Our results demonstrate that cells in the sinoatrial region of the hamster heart are electrically well coupled and strongly suggest that such coupling is mediated by gap junctional channels formed by connexin43.
Bipolar Stimulation of Cardiac Tissue Using an Anisotropic Bidomain Model
Authors: SEPULVEDA NESTOR G. , WIKSWO JOHN P. 
Published: May 2007

Bipolar Stimulation of the Cardiac Bidomain. Introduction: One of the fundamental electrophysiologic problems that has not yet been completely elucidated is the response of cardiac tissue to externally applied electric currents. A limited number of theoretical and experimental techniques has been used to study the electric behavior of cardiac tissue in the presence of stimulating currents, and to demonstrate that the anisotropy in the passive electrical properties of the tissue plays an important role in the genesis and propagation of the activation wave‐front and the resulting potential distributions. Methods and Results: In this work we have applied the finite element method to study the electric and magnetic fields produced by cardiac tissue in response to bipolar current injection, using a linear bidomain model to represent the tissue. We found that the transmembrane potential distribution close to the stimulus electrode has a rather complex geometrical pattern, with adjacent hyperpolarized and depolarized regions. Conclusion: This behavior is consistent with previous theoretical and experimental results and may have implications in the study of electrical stimulation of cardiac tissue that are not apparent using other models.
A Prospective Randomized Comparison of Defibrillation Efficacy of Truncated Pulses and Damped Sine Wave Pulses in Humans
Authors: BARDY GUST H. , ZAGHI HEDAYATOLLAH , GARTMAN DAVID , E JEANNE , KUDENCHUK PETER K. , LEE DOLACK G. , JOHNSON GEORGE , TROUTMAN CHARLES 
Published: May 2007

Damped Sine Wave Defibrillation Pulses. Introduction: Damped sine wave pulses have been used for nearly 50 years in transthoracic defibrillation systems. The purpose of this study was to determine whether damped sine wave pulses have a role in implantable defibrillators. Methods and Results: In 21 survivors of cardiac arrest, we prospectively compared defibrillation efficacy of a standard truncated capacitor (RC) monophasic pulse with a damped sine wave inductor‐capacitor (LRC) pulse using a right ventricular‐left ventricular epicardial patch‐patch electrode system. The RC pulse was a standard 65% tilt monophasic waveform generated from a 120μF capacitor. The LRC pulse was designed to simulate the waveform currently used in transthoracic defibrillators and was generated by passing the charge stored on a 40μF capacitor through a 37‐mH inductor. Capacitor voltage, peak delivered voltage, peak delivered current, discharge pathway resistance, delivered energy, and stored energy were compared for the two waveforms at the defibrillation threshold. There was no difference in defibrillation efficacy for the two waveforms. Peak delivered voltage was similar at the defibrillation threshold: 313 ± 101 V for the RC pulse and 342 ± 119 V for the LRC pulse (P = 0.16). Similarly, no differences were found in defibrillation threshold peak delivered current: 8.6 ± 2.5 (RC) versus 9.3 ± 2.7 (LRC) amperes (A) (P = 0.20); discharge pathway resistance: 37 ± 11 (RC) versus 38 ± 13 (LRC) O (P = 0.71); delivered energy: 7.0 ± 4.5 (RC) versus 7.0 ± 4.0 (LRC) joules (J) (P = 0.88); and stored energy: 8.7 ± 5.7 (RC) versus 9.8 ± 5.4 (LRC) J (P = 0.35). Although both waveforms performed the same, it was necessary to use substantially higher stored voltages with the damped sine wave delivery system than with the truncated waveform delivery system: 356 ± 110 V for the RC pulse and 675 ± 192 V for the LRC pulse (P < 0.0001). Conclusion: This study demonstrates that RC monophasic pulses provide equally effective epicardial defibrillation as LRC pulses with respect to delivered voltage and current and stored and delivered energy. However, in order for LRC pulses to provide comparable delivered voltage, current, and energy to that of RC pulses, nearly twice the voltage must be stored on the capacitor to accomplish the same task. These findings suggest that despite the nearly 50‐year experience with damped sine wave pulses with transthoracic defibrilliitors, there is no need to begin using damped sine wave pulses for implantabte defibrillators. Moreover, these data raise a question regarding the need for inductors in transthoracic defibrillators.
Radio frequency Catheter Ablation of Sustained Intraatrial Reentrant Tachycardia in a Patient With Mirror‐Image Dextrocardia
Authors: WU TSU‐JUEY , CHEN SHIH‐ANN , CHIANG CHERN‐EN , YANG CHIN‐JUEY , CHENG CHEN‐CHUAN , WANG SHIH‐PU , CHIANG BENJAMIN N. , CHANG MAU‐SONG 
Published: May 2007

RF Catheter Ablation in Dextrocardia. Introduction: There has been limited experience with radio frequency catheter ablation in patients with Dextrocardia. This report describes a 37‐year‐oid man who had corundum type Atrial septal defect, mirror‐image Dextrocardia, and drug‐refractory Atrial tachycardia, in whom catheter‐mediated radio frequency energy successfully eliminated the tachycardia without complication. Methods and Results: On electrophysiologica study, the Atrial tachycardia could be induced and terminated by Atrial extra stimulation or rapid Atrial pacing. Mixed resetting response pattern and manifest entrainment were also demonstrated. These findings suggested that the mechanism of atrial tachycardia might be related to reentry with an excitable gap. Because of the mirrorimage dextrocardia, biplane fluoroscopy was adjusted to the right anterior oblique (RAO) 60°G and left anterior oblique (LAO) 30° positions. Inducibility of the tachycardia was completely abolished after the sixth application of radiofrequency current (30 W). It was noted that the successful electrogram preceded the onset of P wave during Atrial tachycardia by about 40 msec. Conclusion: This report presents another case in which radiofrequency catheter ablation was used in a patient with Dextrocardia. Atrial tachycardia in patients with congenital heart disease may be difficult to control pharmacologically; however, the use of radiofrequency catheter ablation could be recommended as an alternative to medication and surgery.
Spatial and Temporal Inhomogeneity of Adenosine's Effect on Atrial Refractoriness in Humans:
Authors: BOTTERON GREGORY W. , SMITH JOSEPH M. 
Published: May 2007

Adenosine's Effects on Atrial Refractoriness. Introduction: Adenosine is an antiarrhythmic agent widely used for the diagnosis and treatment of supraventricular tachyarrhythmias. Bolus administration of adenosine has been associated with transient atrial fibrillation, but the underlying mechanisms have not yet been delineated, due in part to the technical limitations resulting from adenosine's short half‐life. In this study, the rapid, repetitive activation of atrial tissue during atrial fibrillation was exploited to yield a nearly continuous estimate of atrial refractoriness, enabling a description of adenosine's action on atrial refractoriness in humans. Methods and Results: Simultaneous right and left atrial, narrow‐spaced, bipolar electro‐grams were recorded in 15 patients before, during, and after bolus administration of 12 mg of adenosine during atrial fibrillation. By estimating the local cycle length of excitation from the atrial activation frequency, a refractory period index (RPI) of local tissue was obtained. Adenosine dramatically increased the activation frequency from 6.4 ± 0.7 to 12.2 ± 12.2 Hz in the right atrium and from 6.1 ± 0.6 to 8.7 ± 1.2 Hz in the left atrium, corresponding to a decrease in the RPI from 156 to 82 msec (P < 0.0001) and from 163 to 116 msec (P < 0.0001), respectively. The magnitude of adenosine's effect was greater (47% vs 29% shortening) (P < 0.001) and the duration of adenosine's effect longer (28 vs 19 sec) (P < 0.05) in the right compared to the left atrium. Conclusion: Adenosine, at doses routinely used clinically, produces a transient, but spatially and temporally inhomogeneous, shortening of atrial refractoriness, which may explain the increased propensity toward atrial fibrillation associated with its use.
Role of Calcium Loading in Early Afterdepolarizations Generated by Cs+ in Canine and Guinea Pig Purkinje Fibers
Authors: SZABO BELA , KOVACS TIBOR , LAZZARA RALPH 
Published: May 2007

Ca2+‐Loading and EAD. introduction: Our previous observations indicate that the Na2+:Ca2+ exchange current (INa:Ca) plays an important role in early afterdepolarizations occurring at more negative Vm (L‐EAD). The purpose of these studies was to examine the role of Ca2+‐loading, which stimulates INa:Ca, in generation of L‐EAD. Methods and Results: Purkinje strands and preparations of ventricular myocardium from dogs and guinea pigs were superfused with oxygenated physiologic buffer solutions at 37°C, To induce EADs, [K+]0 was reduced to 2.0 to 3.0 mM and [Cs+]0, (3.6 to 4.0 mM) was added at slow rates of ≤ 0.3 Hz. Isometric contraction in canine Purkinje strands and guinea pig papillary muscles doubled in 1‐hour exposure to Cs+ and low [K+]0 at slow rates, and the uptake of 45Ca2+ was approximately doubled after 30 minutes. Forty‐three percent of Purkinje fibers developed L‐EAD after a latent period of 17 to 123 minutes of exposure. Ouabain (0.2 μM) suppressed LEAD within 10 minutes reversibly. Ca2+‐loading (low [Na+]0 or high [Ca2+]0 for 5 to 10 minutes before exposure to Cs+, low [K+]0, and slow rates resulted in rapid development of L‐EAD in all preparations during subsequent exposure. In Ca2+‐loaded preparations, delayed afterdepolarizations (DADs) as well as L‐EADs developed. Conclusion: Reduction of K+ currents with Cs+, low [K+]0, and slow rates induced L‐EAD in a fraction of Purkinje fibers after a latent period during which Ca2+‐loading of the sarcoplasmic reticulum occurred, while fibers preloaded with Ca2+ developed L‐EAD rapidly and uniformly. These findings indicate that Ca2+‐loading is a critical condition for the development of L‐EAD. Early suppression of L‐EAD by ouabain suggests a dependence of L‐EAD on low [Na+]1. These findings implicate INa:Ca in the generation of L‐EAD.
A Prospective Randomized Comparison in Humans of 90‐μF and 120‐μF Biphasic Pulse Defibrillation Using a Unipolar Defibrillation System
Authors: POOLE JEANNE E. , KUDENCHUK PETER J. , LEE DOLACK G. , JONES GREGORY K. , DEGROOT PAUL , JOHNSON GEORGE , BARDY GUST H. 
Published: May 2007

90‐μF and 120‐μF Biphasic Pulse Transvenous Defibrillation. Introduction: Capacitance is known to influence defibrillation. Optimal biphasic waveform capacitance for transvenous unipolar defibrillation systems in man is currently being defined. In an effort to improve defibrillation efficacy, we examined the relative defibrillation efficacy of a 65% tilt biphasic pulse from a 90‐μF capacitor compared to a 65% tilt biphasic pulse from a 120‐μF capacitor in a prospective, randomized fashion in 16 consecutive cardiac arrest survivors undergoing defibrillator surgery. Methods and Results: The transvenous unipolar pectoral defibrillation system uses a single endocardial RV anodal defibrillation coil and the shell of an 80‐cc volume (88 cm2 surface area) pulse generator (Medtronic Model 7219C PCD “active CAN”) as the cathode for the first phase of the biphasic shock: RV+→ CAN−. Defibrillation thresholds for each capacitance were determined prospectively in a randomized fashion. The defibrillation threshold results for the 90‐μF capacitance were: leading edge voltage 383 ± 132 V; stored energy 7.4 ± 5.0 J; and resistance 57 ± 10 ω. The results for the 120‐μF capacitance were: leading edge voltage 315 ± 93 V (P = 0.002); stored energy 6.5 ± 3.7 J (P = 0.21); and resistance 57.0 ± 11 ω (P = 0.87). Conclusions: We conclude that 90‐μF, 65% tilt biphasic pulses used with unipolar pectoral defibrillation systems have equivalent stored energy defibrillation efficacy compared to 120‐μF, 65% tilt pulses. Use of lower capacitance is possible in present implantable defibrillators without compromising defibrillation.
Impact of the Local Atrial Electrogram in AV Nodal Reentrant tachycardia: Abaltion Versus Modification of the Slow Pathway
Authors: TEBBENJOHANNS JÜRGEN , PFEIFFER DIETRICH , SCHUMACHER BURGHARD , MANZ MATTHIAS , LÜDERITZ BERNDT 
Published: May 2007

Electrogram in AVNRT. Introduction: The purpose of this study was to determine the predictors of successful ablation versus modification sites of the slow pathway in patients with AV nodal reentrant tachycardia. Complete elimination of slow pathway conduction (“ablation”) is considered to be an appropriate endpoint during radiofrequency (RF) current delivery, whereas the persistence of residual slow pathway conduction with or without single echo beats (“modification”) may be indicative of tachycardia recurrence. Methods and Results: Of 131 patients, 71 consecutive patients were followed for 15.1 ± 7.6 months. After elimination of inducible AV nodal reentrant tachycardia in all patients, residual slow pathway conduction (modification) persisted in 38 patients, whereas complete elimination of slow pathway conduction (ablation) was documented in 33 patients. Including electrophysiologic study after 5 to 7 days and after 3 to 6 months, 6 (8.4%) patients had recurrences: 5 with residual slow pathway conduction after the procedure and 1 with complete elimination of slow pathway conduction (P < 0.05). As compared with modulated sites, ablation sites of the slow pathway were characterized as follows: (1) duration of the local atrial electrogram (AEGM) (66.7 ± 10.2 vs 54.1 ± 12.6 msec, P < 0.01); (2) interval from the end of the AEGM to onset of His‐bundle deflection (4.4 ± 8.2 vs 16.1 ± 9.3 msec, P < 0.01); and (3) number of peaks of the AEGM as an indicator of fractionation (4.1 ± 0.7 vs 3.0 ± 0.8, P < 0.01). The rate of junctional tachycardias (103.4 ± 12.1 vs 102.1 ± 16.9 per min), the AV ratio (0.4 ± 0.5 vs 0.5 ± 0.5), the number of RF current deliveries (4.1 ± 4.4 vs 4.5 ± 4.4), the duration of the procedure (124.1 ± 45.3 vs 125.6 ± 42.3 min), and the fluoroscopy time (15.5 ± 10.8 vs 16.6 ± 9.6 min) as well as power and total energy of RF current deliveries and the anatomically calculated catheter position at the successful site were not statistically different. A subset analysis in patients who received only a single RF application showed the same results for both groups. Patients without recurrence (n = 65) were found to have longer duration of the AEGM (61.9 ± 14.6 msec) and a shorter interval from the end of AEGM to the onset of His‐bundle deflection (10.1 ± 12.2 msec) than patients with recurrence (n = 6) (47.5 ± 7.5 msec and 20.8 ± 12.8 msec, respectively). Conclusion: Complete ablation of the slow pathway resulted in a lower recurrence rate. The complete ablation approach is feasible using precisely analyzed local AEGMs to guide RF current in AV nodal reentrant tachycardia in a short procedure time.
Ventricular Fibrillation Is Not Always Due to Multiple Wavelet Reentry
Authors: JANSE MICHIEL J. , WILMS‐SCHOPMAN FRANCIEN J.G. , CORONEL RUBEN 
Published: May 2007

Mechanisms of VF. Introduction: It is not known whether ventricular fibrillation (VF) is always caused by multiple wavelet reentry, or if it could also be caused by a single wandering reentrant wavefront. Activation mapping of the entire ventricles during VF is practically impossible. Methods and Results: We studied VF in a two‐dimensional sheet of left ventricular subepicardial tissue of isolated. Langendorff‐perfused pig hearts. Left and right endocardial cryoablation via probes tilled with liquid nitrogen caused coagulation necrosis of the right ventricle, interventricular septum, and most of the left ventricular wall, leaving a thin subepicardial layer intact. Left ventricular epicardial activation patterns were constructed based on simultaneous recording of 128 unipolar extracellular electrograms. Regular pacing through a central electrode before and after freezing revealed that, following cryoablation, the activation pattern no longer showed evidence of involvement of the Purkinje system, and that it was compatible with propagation through a two‐dimensional anisotropic tissue sheet. VF was induced by burst pacing. When the mass of surviving subepicardium was < 10 g, no VF could be induced: when it was between 10 and 20 g, VF was nonsustained; when it was > 20 g. VF was sustained. Unipolar extracellular electrograms during VF before and after cryoablation could not be distinguisbed from each other; however, epicardial activation patterns were markedly different. In the intact left ventricle, up to six different wavefronts were simultaneously present during a 100‐msec time window. In the “frozen heart.” during a period of about 0.5 seconds, at most two wandering reentrant waves were simultaneously present; sometimes only one reentrant wave was seen in a 100‐msec time window. Conclusion: The extracellular waveform during VF can be caused by different forms of reentry: multiple wavelet reentry (on the order of six different wavefronts), two independent wandering reentrant waves, and a single wandering reentrant wave.