bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dual Morphology of Idiopathic Ventricular Tachycardia
Authors: LOKHANDWALA YASH Y. , VORA AMIT M. , NAIK AJAY M. , NABAR ASHISH , KAVTHALE SANTOSH 
Published: April 2007

Dual Morphology of Idiopathic VT. Introduction: Idiopathic ventricular tachycardia (VT) typically has a single morphology originating either in the right ventricular outflow tract (RVOT)or near the posterior fascicle of the left ventricle (LV) in most instances. We present our observations in six patients with idiopathic VT in whom two morphologies were present. Methods and Results: Of 55 patients with idiopathic VT who underwent radiofrequency (RF) ablation. 44 had LV “fascicular” tachycardia, whereas 11 had RVOT tachycardia. During RF energy delivery, there was a change in VT morphology in two patients with idiopathic LV tachycardia. This second morphology was not ablated initially, recurred at follow‐up, and was reablated successfully. In two additional patients with idiopathic LV tachycardia, a second VT was inducible after ablation of the “clinical” VT. This second morphology recurred at follow‐up and was ablated successfully in one patient. The site where the second VT was ablated in all the three patients was remote from that of the first VT. In two patients with RVOT tachycardia, a second VT, originating from a different area of the RVOT, was induced after RF ablation of the “clinical” VT. This second VT recurred at follow‐up and was reablated successfully in one patient. Conclusion: Idiopathic VT is a more heterogenous entity than hitherto believed. A second VT was seen in 11% of patients during or after RF ablation of the “clinical” VT. The appearance of a second VT suggests either a different exit site of the same circuit or another site of origin.
Amiodarone Reduces the Prevalence of T Wave Alternans in a Population with Ventricular Tachyarrhythmias
Authors: GROH WILLIAM J , SHINN TIMOTHY S. , ENGELSTEIN ERICA E. , ZIPES DOUGLAS P. 
Published: April 2007

Amiodarone and the Presence of TWA. Introduction: Testing for the presence of microvolt T wave alternans (TWA) is useful for arrhythmic risk stratification. Whether antiarrhythmic pharmacotherapy affects the presence of TWA is unknown. We tested whether patients with known ventricular tachyarrhythmias who were receiving amiodarone were less likely to manifest TWA as compared with those not receiving amiodarone. Methods and Results: Forty‐four patients with a history of ventricular tachyarrhythmias and an implantable cardioverter defibrillator (ICD) implanted at least 1 month earlier underwent TWA testing. In this group, 14 patients were receiving amiodarone and 30 were not. Indeterminate test results occurred in 13 patients without a significant difference in those receiving or not receiving amiodarone. In the 31 patients with determinate TWA testing, a positive test was less likely in those receiving amiodarone (1 of 9 [11%]) as compared with those not receiving amiodarone (14 of 22 [64%]; P = 0.04). During a follow‐up period averaging 0.9 ± 0.2 years, the presence of TWA (P = 0.04) and decreased left ventricular ejection fraction (P = 0.05) predicted appropriate ICD therapy for ventricular tachyarrhythmias. Conclusion: The prevalence of TWA was decreased in a chronic ventricular tachyarrhythmic population receiving amiodarone as compared with a population not receiving amiodarone.
Accuracy and Limitations of Published Algorithms Using the Twelve‐Lead Electrocardiogram to Localize Overt Atrioventricular Accessory Pathways
Authors: BASIOUNY TAREK , DE CHILLOU CHRISTIAN , FAREH SAMIR , KIRKORIAN GILBERT , MESSIER MARC , SADOUL NICOLAS , CHEVALIER PHILLIPE , MAGNIN‐POULL ISABELLE , BLANKOFF IVAN , CHEN JIAN , TOUBOUL PAUL , ALIOT ETIENNE 
Published: April 2007

Accessory Pathway Localization. Introduction: The purpose of this study was to evaluate the accuracy and limitations of published algorithms using the 12‐lead ECG to localize AV accessary pathways (APs). Methods and Results: The 11 relevant algorithms found in the literature (MEDLINE database and major scientific sessions) were tested on a series of 266 consecutive patients who successfully underwent radiofrequency catheter ablation of a single overt AV AP. The positive predictive values (PPV) of the algorithms in applicable patients were significantly lower for algorithms with > 6 accessory location sites (40.6%± 10.9% vs 61.2%± 8.0%; P < 0.03) and show a tendency for algorithms not relying on delta wave polarity but on QRS polarity only (36.6%± 11.2% vs 52.3%± 13.1%; P = 0.09). The PPV in applicable patients is related to the AP location (P < 0.001) and ranked from the highest to the lowest as follows: left lateral (mean PPV = 86.3%), posteroseptal (mean PPV = 65.2%), right anteroseptal (mean PPV = 45.2%), and right posterolateral (mean PPV = 23.4%). Conclusion: Our study suggests that the accuracy of algorithms relying on the 12‐lead ECG depends on AP locations as defined in the algorithms and on the number of AP sites. The accuracy tends to be lower when delta wave polarity is not included in the algorithm's architecture. This should be considered when using these algorithms or when building new ones.
Cardiac Conduction Abnormalities in Mice Lacking the Gap Junction Protein Connexin40
Authors: VERHEULE SANDER , Van BATENBURG CHRISTEL A.J.A.C. , COENJAERTS FRANK E.J. , KIRCHHOFE SUSANNE , WILLECKE KLAUS , JONGSMA HABO J. 
Published: April 2007

Cardiac Conduction in C×40−/− Mice. Introduction: The gap junction protein connexin40 (C×40) normally is expressed in the murine atrial myocardium and ventricular conduction system. In mice lacking C×40, several changes in the surface ECG have been described. In this study, we analyzed cardiac conduction in more detail. Methods and Results: In open chest mice under urethane anesthesia, epicardial electrodes were used to determine a number of atrial and ventricular pacing parameters. The corrected sinus node recovery time was significantly longer in C×40−/− mice than in C×40+/+ mice (44.4 ± 7.2 msec vs 35.5 ± 8.0 msec). In addition, the Wenckebach period was longer in C×40−/− mice compared with the wild type (84.6 ± 5.4 msec vs 78.8 ± 3.6 msec), with the AV node probably limiting AV conduction in both cases. Whereas arrhythmias could not be induced by ventricular burst pacing in any of the mice, atrial burst pacing induced atrial tachyarrhythmias in 5 of 10 C×40−/− mice, but not in any of 9 Cx40−/− mice. Conduction velocities were measured in vivo using an array of unipolar recording electrodes. Ventricular conduction velocity did not differ between the groups, but atrial conduction velocity was reduced by 30% in C×40−/− mice compared with the wild type. Heterozygous C×40+/− mice did not differ significantly from the wild type in any respect. Conclusion: These findings indicate that in the atria and the AV conduction system, C×40 is an important determinant of conduction.
Evidence of Three‐Dimensional Scroll Waves with Ribbon‐Shaped Filament as a Mechanism of Ventricular Tachycardia in the Isolated Rabbit Heart
Authors: EFIMOV IGOR R. , SIDOROV VENIAMIN , CHENG YUANNA , WOLLENZIER BRIAN 
Published: April 2007

Scroll Waves in the Heart. Introduction: Rotating vortices have been observed in excitable media of different nature. Vortices may sustain life or kill in different species, by underlining morphogenesis in Dictiostelium discoideum during starvation, or arrhythmias during sudden cardiac death in mammals. Investigation of vortices in the heart has been limited by two‐dimensional experimental techniques. In contrast, three‐dimensional (3D) Belousov‐Zhabotinsky excitable medium and mathematical models have been shown to sustain scroll‐shaped waves. The heart is a 3D structure; therefore, scroll waves may underlie cardiac arrhythmias. Methods and Results: We used potentiometric dye and optical mapping techniques to study vortices during ventricular arrhythmias. The core of all observed vortices were linearly shaped and ≥ 9 mm (48 episodes, six hearts). As shown by Allessie et al. in the rabbit atrium, ventricular signals recorded within 1 to 2 mm from the line of block were dual humped, suggesting there is electrotonic interaction across the line of block. We hypothesized that the line of block represents epicardial intersection of ribbon‐shaped filaments, which in some cases may be oriented under an angle or parallel to the epicardium. In 14 episodes we observed dualhumped optical recordings at one side of the line of block at a distance up to 12 mm. The two humps may represent the signatures of two activation wave fronts propagating above and below the filament, which in this area is close to the epicardial surface. The activation sequence of the two waves is consistent with the idea of a scroll wave with ribbon‐like filament. Conclusion: Our data provide new insights into the shape and dynamics of the filament of the 3D scroll wave, which underlies the mechanism of ventricular tachycardia in the rabbit heart. The filament of the scroll wave may be ribbon shaped, with a significant width ≥ 9 mm and a thickness of 1 to 2 mm. No evidence of fully excitable cells in the core of vortex was observed.
High‐Resolution Mapping and Histologic Examination of Long Radiofrequency Lesions in Canine Atria
Authors: TAYLOR GREGG W. , WALCOTT GREGORY P. , HALL JEFFREY A. , BISHOP SANFORD , KAY G. NEAL , IDEKER RAYMOND E. 
Published: April 2007

High‐Resolution Mapping and Histologic Examination. Introduction: Catheter ablation may prevent conduction of multiple atrial wavefronts and/or reduce the critical mass of atrial myocardium required to sustain fibrillation. The purpose of this study was to examine the effect of radiofrequency (RF) energy application on conduction in canine atria by performing high‐density epicardial mapping and careful histologic examination of the ablation zone. Methods and Results: RF energy was applied to the right atrial endocardium in nine anesthetized mongrel dogs in an attempt to create a line of conduction block spanning; the vertical length of a 504‐cbannel epicardial mapping plaque. The mean length and width of the histologically determined ablation zone was 34 ± 4 and 7.3 ± 2.6 mm, respectively. No thrombus was present. Conduction block that spanned the mapping plaque in 6 of 9 animals was matched histologically by continuous transmural necrosis in five. In one, only a portion of the ablation zone was transmural; the remainder was wide but nontransmural. In 2 of 3 animals with conduction, a narrow region was present where continuous transmural necrosis was absent. In the other animal, conduction was present despite continuous transmural necrosis. Conclusion: Conduction block usually occurred when continuous transmural necrosis was present, and conduction usually persisted when continuous transmural necrosis was absent. However, important exceptions were observed, including block when the ablation zone was wide but nontransmural, and conduction despite a thin line of continuous transmural necrosis.
Anatomy of the Left Atrium:
Authors: YEN HO SIEW , SANCHEZ‐QUINTANA DAMIAN , CABRERA JOSE ANGEL , ANDERSON ROBERT H. 
Published: April 2007

Anatomy of the Left Atrium. Introduction: The feasibility of treating atrial fibrillation with radiofrequency ablation has revived interest in the structure of the left atrium, a chamber that has been neglected in many textbooks of anatomy. Methods and Results: We reviewed the gross structure of the left atrium by examining the septum, the appendage, and insertions of the pulmonary veins in normal hearts. The limited extent of the true septal component is relevant to procedures using the transseptal approach. On gross examination, the musculature of the atrial wall is composed of overlapping bundles of aligned fibers that, in the majority of hearts, are arranged in characteristic patterns with only minor individual variations. Muscular sleeves extend into the walls of the pulmonary veins to varying distances. The longest sleeves are in the left upper veins. Bachmann's bundle anteriorly, and other smaller bundles superiorly and posteriorly, bridge the septal raphe to blend with musculature of the right atrium. Tongues of left atrial musculature from the posterior wall also extend into the wall of the coronary sinus. Conclusion: The left atrium is more complex than usually conceived. Understanding its structure, and the arrangement of its musculature, will help in improving strategies for linear lesions when attempting to compartmentalize the chamber, or when placing focal lesions for ablating ectopic sources.
Sinusoidal Stimulation of Myocardial Tissue:
Authors: MEUNIER JASON M. , TRAYANOVA NATALIA A. , GRAY RICHARD A. 
Published: April 2007

Sinusoidal Stimulation of Cardiac Cells. Introduction: Cardiac tissue subjected to sinasoidal stimulus Is characterized by action potentials (APs) that have extended plateau phases, sustained for the duration of the stimulus. Extended action potential durations (APDs) are beneficial because they disrupt wandering wavelets in the fibrillating heart. To investigate the mechanisms by which periodic stimulus affects cardiac tissue, particularly the development of sustained depolarization, computer simulations of single cardiac cells exposed to alternating current (AC) are performed. Methods and Results: Two modes of stimulation of the cell are examined: external field stimulation and transmembrane current injection. Several membrane models, including Luo‐Rudy I and II, are used in the simulations. External AC field stimuli increase the APD of the single cell. The extended plateau of the cellular AP is characterized by periodic oscillations that are 1:2 phase locked with the applied stimulus. This specific behavior is due to the variations in stimulus magnitude and polarity along the cell border, which elicit opposite electrical responses from the cell sides. These pointwise responses are averaged in the macroscopic cellular response and result in sustained oscillatory depolarization that lasts for the duration of the stimulus. In contrast, the cell undergoing current injection does not develop an extended APD. Conclusion: The simulations demonstrate that variation of membrane potential within a cell is of paramount importance to the formation of an extended AP plateau in response to AC stimulation.
The Effect of Procainamide on T Wave Alternans
Authors: KAVESH NEAL G. , SHOROFSKY STEPHEN R. , SARANG SAMANTHA B. , GOLD MICHAEL R. 
Published: April 2007

Procainamide and T‐Wave Alternans. Introduction: The measurement of microvolt level T wave alternans (TWA) is a technique for detecting arrhythmia vulnerability. Previous studies demonstrated that the magnitude of TWA is dependent on heart rate. However, the effects of antiarrhythmic drugs on TWA are unknown. Methods and Results: This was a prospective evaluation of intravenous procainamide on TWA in 24 subjects with inducible sustained ventricular tachycardia (VT). Measurements of TWA were performed at baseline in the drug‐free state and after procainamide loading (1,204 ± 278 mg). Recordings were made in normal sinus rhythm, and during atrial pacing at 100 heats/min and 120 heats/min. The magnitude of TWA in the vector magnitude lead was decreased by procainamide at all heart rates: 0.6 ± 0.8 to 0.3 ± 0.4 μV in sinus rhythm, 2.0 ± 1.6 to 0.7 ± 0.7 μV at 100 beats/min, and 3.0 ± 2.0 to 1.7 ± 1.8 μV at 120 beats/min (P < 0.001 by analysis of variance). The sensitivity of TWA for the induction of VT at baseline was 5% in sinus, 60% at 100 beats/min, and 87% at 120 beats/min, while it decreased with procainamide to 5%, 19%, and 60%, respectively. Decreases in TWA in response to procainamide were independent of the antiarrhythmic effects on VT inducibility. Conclusions: These results indicate that the magnitude of TWA decreases with acute procainamide loading and this effect decreases the sensitivity of TWA for the induction of sustained VT.
Separation Between Virtual Sources Modifies the Response of Cardiac Tissue to Field Stimulation
Authors: SUSIL ROBERT C. , A ERIC , TUNG LESLIE 
Published: April 2007

Source Separation and Field Stimulation. Introduction: While it is now understood that the tissue geometry and the electric field distribution are important in generating virtual electrodes, the effects of interaction between a collection of electrodes have not been examined. To develop a basis for understanding such interactions, we have studied a single pair of oppositely polarized virtual sources. Although such oppositely polarized pairs of virtual electrodes can be generated by a variety of field distributions and tissue geometries, we examine one simple system that incorporates the salient features of source interaction. Methods and Results: Our model system is a homogeneous tissue strip stimulated by a uniform extracellular field. To clarify virtual source interaction, we show that field stimulated tissue can be equivalently polarized by a set of intracellular current sources with magnitude and distribution defined by the generalized activating function. In our model system, an intracellular current source is produced at one edge of the tissue and an Intracellular current sink at the other. Therefore, the tissue length acts to modulate the overlap, or interaction, between the polarizations arising from each source. To quantify the effects of source interaction, the chronaxie and rheobase values of the strength‐duration relation were determined for source separations varying between 1.0 cm and 100 μm (active membrane dynamics were modeled with the Luo‐Rudy phase I formulation). At all separations > 3.0 mm, the chronaxie was constant at 3.09 msec and the rheobase was 0.38 V/cm. Under 0.2 mm, the chronaxie decreased to 0.55 msec while the rheobase increased linearly with the inverse of source separation. The dependence of these parameters on separation primarily reflects passive electrotonic interactions between the two virtual electrodes. However, the exact values are strongly dependent upon active tissue properties—largely the inward rectifier potassium channel and activation of the sodium current. Conclusion: Tissue excitation in response to field stimulation is strongly modulated by the proximity of, and therefore the interaction between, oppositely polarized virtual electrode sources.
Intraoperative Radiofrequency Ablation of Chronic Atrial Fibrillation: A Left Atrial Curative Approach by Elimination of Anatomic “Anchor” Reentrant Circuits
Authors: KOTTKAMP HANS , HINDRICKS GERHARD , HAMMEL DIETER , AUTSCHBACH RÜDIGER , MERGENTHALER JÖRG , BORGGREFE MARTIN , BREITHARDT GÜNTER , MOHR FRIEDRICH‐WILHELM , SCHELD HANS H. 
Published: April 2007

Intraoperative Ablation of Atrial Fibrillation. Introduction: The percutaneous approach to radiofrequency (RF) catheter ablation for curative treatment of atrial fibrillation (AF) is an investigational technique, and the optimal composition of lesion lines is unknown. We tested an intraoperative RF ablation concept with elimination of left atrial anatomic “anchor” reentrant circuits. Methods and Results: In 12 patients with an indication for valve surgery and chronic AF, a right atrial‐transseptal approach was chosen for access to the left atrium. AF had been present for 4.3 ± 3.9 years; the left atria measured 56 ± 7 mm. Under direct vision, contiguous lesion lines were placed endocardially with temperature‐guided RF energy applications for treatment of AF with a specially designed probe. The lesion lines were placed between the mitral annulus and the left lower pulmonary vein, further to the left upper pulmonary vein, from there to the right upper pulmonary vein, and finally to the right lower pulmonary vein. The antiarrhythmic ablation procedure lasted 19 ± 4 minutes. One patient died postoperatively of low cardiac output. During follow‐up of 11 ± 6 months, chronic AF was ablated successfully in 9 of 11 patients (82%). Six patients were in stable sinus rhythm or intermittent pacemaker rhythm, and three patients were in sinus rhythm with intermittent atypical atrial flutter. Conclusions: Intraoperative RF energy application for induction of contiguous lesion lines is feasible. Elimination of anatomically defined “anchor” reentrant circuits within the left atrium prevented chronic AF in > 80% of the patients treated. Intraoperative validation of lesion line concepts for curative treatment of AF may he transferred to percutaneous ablation techniques.
Muscarinic Receptor Stimulation with Edrophonium Hydrochloride Does Not Elevate Ventricular Fibrillation Thresholds in Humans
Authors: MITRANI RAUL D. , KLOOSTERMAN E. MARTIN , HUIKURI HEIKKI , DYLEWSKI JOHN , ATAPATTU SURESH , INTERIAN ALBERTO , CASTELLANOS AGUSTIN , MYERBURG ROBERT J. 
Published: April 2007

Edrophonium Hydrochloride Effect on VE Threshold. Introduction: Although decreased vagal tone, as measured by heart rate variability is a risk factor for ventricular fibrillation (VF) and sudden cardiac death, it is unknown whether increasing vagal tone has an antiarrhythmic effect. The purpose of this study was to determine whether edrophonium hydrochloride (HCl), a vagomimetic agent, increases VF threshold. Methods and Results: Twenty‐eight consecutive patients with previously implanted defibrillators had two inductions of VF by monophasic direct‐current shocks delivered at 10 to 30 msec after the T wave peak, escalating energies (0.4, 1, then 3 J) until VF was induced. If VF was not induced, this protocol was repeated at the T wave peak and then at 10 to 30 msec before the T wave until VF was induced. Patients were randomized to receive edrophonium HCl (12 to 18 mg) or no drug before repeating the protocol for the second VF induction. The mean sinus cycle length increased from 782 to 872 msec in the group receiving edrophonium HCl (P = 0.006). In the control group, the mean sinus cycle length remained unchanged (838 vs 858 msec). The mean energy to induce VF, coupling interval relative to the T wave, and the number of attempts to induce VF were not different between VF induction attempts 1 and 2, and they were not different between the group receiving edrophonium HCl and the control group. Conclusion: In a sedated patient population with implantable defibrillators, edrophonium HCl infusion prolongs sinus cycle length but does not change inducibility of VF using T wave shocks.