bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Electroporation on the Transmembrane Potential Distribution in a Two‐Dimensional Bidomain Model of Cardiac Tissue
Authors: AGUEL FELIPE , DEBRUTN KATHERINE A. , KRASSOWSKA WANDA , TRAYANOVA NATALIA A. 
Published: April 2007

Electroporation in a Two‐Dimensional Myocardium. Introduction: Defibrillation shocks, when delivered through internal electrodes, establish transmembrane potentials (Vm) large enough to electroporate the membrane of cardiac cells. The effects of such shocks on the transmembrane potential distribution are investigated in a two‐dimensional rectangular sheet of cardiac muscle modeled as a bidomain with unequal anisotropy ratios. Methods and Results: The membrane is represented by a capacitance Cnv, a leakage conductance gv and a variable electroporation conductance G, whose rate of growth depends exponentially on the square of Vm. The stimulating current Io, 0.05–20 A/m, is delivered through a pair of electrodes placed 2 cm apart for stimulation along fibers and 1 cm apart for stimulation across fibers. Computer simulations reveal three categories of response to Io: (1) Weak Io. below 0.2 A/m, cause essentially no electroporation, and Vm: increases proportionally to Io. (2) Strong Io, between 0.2 and 2.5 A/m, electroporate tissue under the physical electrode. Vm is no longer proportional to Io; in the electroporated region, the growth of Vm is halted and in the region of reversed polarity (virtual electrode), the growth of Vm is accelerated. (3) Very strong Io, above 2.5 A/m, electroporate tissue under the physical and the virtual electrodes. The growth of Vm in ail electroporated regions is halted, and a further increase of Vo: increases both the extent of the electroporated regions and the electroporation conductance G. Conclusion: These results indicate that electroporation of the cardiac membrane plays an important role in the distribution of Vm: induced by defibrillation strength shocks.
Right Atrial Compartmentalization Using Radiofrequency Catheter Ablation for Management of Patients with Refractory Atrial Fibrillation
Authors: GARG ASHOK , FINNERAN WILLIAM , MOLLERUS MICHAEL , BIRGERSDOTTER‐GREEN ULRIKA , FUJIMURA OSAMU , TONE LINDA , FELD GREGORY K. 
Published: April 2007

Ablation of Atrial Fibrillation. Introduction: Atrial fibrillation (AF) is often refractory to antiarrhythmic drugs, and patients who are intolerant of AF may require the maze operation for cure. As a less Invasive alternative, a catheter‐based, right atrial compartmentalization procedure was evaluated. Methods and Results: Twelve patients with AF refractory to Class I and III antiarrhythmic drugs were studied. Four linear right atrial radiofrequency ablations were performed, from superior to inferior vena cava in the posterior wall and interatrial septum, anteriorly from the superior vena cava to the tricuspid annulus through the appendage, and across the tricuspid valve‐inferior vena cava isthmus. The radiofrequency catheter was dragged along each line three to four times, until the atrial electrogram amplitude decreased by 75% and there was bidirectional conduction block in the tricuspid valve‐inferior vena cava isthmus. One complication occurred: sinus node dysfunction requiring a pacemaker. Eight patients were discharged from the hospital on no antiarrhythmic drugs, and four were discharged on previously ineffective antiarrhythmic drugs. Total duration of follow‐up was 21.3 ± 11.2 months. Four patients discharged on previously ineffective antiarrhythmic drugs had no recurrence of AF. One patient discharged off antiarrhythmic drugs had no recurrence of AF. Seven patients discharged off antiarrhythmic drugs had recurrent AF by 12.6 ± 13.0 months (median 6, range 1 to 39); 3 of these 7 responded to previously ineffective antiarrhythmic drugs without further AF and 4 did not. Thus, 8 of 12 patients (67%) had suppression of AF after ablation on previously ineffective medication or no medication. Conclusion: Right atrial compartmentalization may alter the substrate for AF, thus improving the efficacy of previously ineffective antiarrhythmic drugs. Because it is relatively safe, it may be a reasonable adjunctive intervention to maintain sinus rhythm in patients with drugrefractory AF.
Intraoperative Computerized Mapping of Ventricular Tachycardia: Differences Between Anterior and Inferior Myocardial Infarctions
Authors: LACROIX DOMINIQUE , WAREMBOURG HENRI , KLUG DIDIER , DECOENE CRISTOPHE , KACET SALEM 
Published: April 2007

Mapping of Ventricular Tachycardia. Introduction: Although direct ventricular tachycardia (VT) surgery has been shown to be effective for treatment of inferior myocardial infarction (MI), the differences in the arrhythmia substrates compared to anterior MI have not been systematically delineated. We sought to compare operative procedures and VT substrates between anterior and inferior MI locations. Methods and Results: Computerized mapping was performed in 30 patients with a 128‐electrode system using epicardial sock and transatriat left ventricular endocardial balloon arrays, followed by combined endocardial resection and cryoablation. At surgery, there were 51 and 34 different VTs in 18 patients with anterior Ml and 12 patients with inferior MI, respectively. The proportion of aneurysms was lower in inferior MI (25% vs 78%, P = 0.008). Total activation times accounted for 65%± 23% and 50%± 22% of the VT cycle length in anterior and inferior infarcts, respectively (P = 0.005). Complete superficial reentry was identified in 12 VTs related to anterior infarcts and in only two VTs associated with inferior infarction (P = 0.038). Involvement of papillary muscles occurred in two patients with inferior MI. Patients with inferior infarcts received more cryolesions and required epicardial cryolesions or mitral valve replacement more frequently, and their operative mortality was greater (2/12 vs 0/18). Noninducibility rate (89.3%) and 2‐year survival (76%± 8%) did not differ according to infarct location.Conclusion: VT associated with inferior MI can be ablated successfully; however, the substrate is more complex, with frequent participation of intramural layers rendering the ablative procedure more difficult.
Target Temperatures of 48°C versus 60°C During Slow Pathway Ablation:
Authors: STRICKBERGER S. ADAM , TOKANO TAKASHA , TSE HUNG FAT , KIM MICHAEL H. , ORAL HAKAN , FLEMMING MATTHEW , PELOSI FRANK , MICHAUD GREGORY F. , KNIGHT BRADLEY P. , GOYAL RAJIVA , MORADY FRED 
Published: April 2007

Slow Pathway Ablation. Introduction: The relationship between temperature at the electrode‐tissue interface and the loss of AV and ventriculoatrial (VA) conduction is not established, and the optimal target temperature for the slow pathway approach to radiofrequency ablation of AV nodal reentrant tachycardia (AVNRT) is unknown. Therefore, the purpose of this study was to compare target temperatures of 48°C and 60°C during the slow pathway approach to ablation of AVNRT. Methods and Results: The study included 138 patients undergoing ablation for AVNRT. Patients undergoing slow pathway ablation using closed‐loop temperature monitoring were randomly assigned to a target temperature of either 48°C or 60°C. The primary success rates were 76% in the patients assigned to 48°C and 100% in the patients assigned to 60°C (P < 0.01). The ablation procedure duration (33 ± 31 min vs 26 ± 28 min; P = 0.2), fluoroscopic time (25 ± 15 min vs 24 ± 16 min; P = 0.5), and mean number of applications (9.3 ± 6.5 vs 7.8 ± 8.1; P = 0.3) were similar in patients assigned to 48° and 60°C, respectively. The mean temperature (46.1°± 24.8°C vs 48.7°± 3.2°C; P < 0.01), the temperature associated with junctional ectopy (48.1°± 2.0°C vs 53.5°± 3.5°C, P < 0.0001), and the frequency of VA block during junctional ectopy (24.6% vs 37.2%; P < 0.0001) were less in the patients assigned to 48°C compared to 60°C. The frequency of transient or permanent AV block was similar in each group (2.8% vs 3.6%; P = 0.2). In the 60°C group, only 12% of applications achieved an electrode temperature of 60°C. During follow‐up of 9.9 ± 4.2 months, there was one recurrence of AVNRT in the 48°C group and none in the 60°C group. Conclusions: Compared to 48°C, a target temperature of 60°C during radiofrequency slow pathway ablation is associated with a higher primary success rate and a higher incidence of VA block during junctional ectopy induced by the radiofrequency energy. AV block is not more common with the higher target temperature, but only if VA conduction is aggressively monitored during applications of radiofrequency energy.
The Valve of Vieussens: An Important Cause of Difficulty in Advancing Catheters into the Cardiac Veins
Authors: CORCORAN SUSAN J. , LAWRENCE CHRISTOPHER , McGUIRE MARK A. 
Published: April 2007

Catheterization of Cardiac Veins. Introduction: The coronary sinus and cardiac veins are useful conduits for the passage of electrode catheters for mapping the origin of cardiac arrhythmias. However, sometimes it is difficult to advance catheters an adequate distance into the cardiac veins. The aim of this study was to determine the reasons for this. Methods and Results: In 50 cadaveric hearts, a deflectable 7‐French electrode catheter was passed from the right atrium into the coronary sinus and advanced to the anterior interventricular portion of the great cardiac vein (GCV). Causes of obstruction were determined. The catheter was obstructed by the valve of Vieussens in 23 of 50 hearts (46%). Once the valve was negotiated, obstruction was caused by an acute bend in the GCV in 28 of 50 hearts (56%). Clinical studies were undertaken in 10 patients in whom electrode catheters could not be advanced as far as required. Using contrast venography, the most frequent cause of obstruction was determined to be the valve of Vieussens in 8 of 10 cases (80%). An acute bend in the GCV caused obstruction in 2 cases (20%). Conclusions: The valve of Vieussens is a frequent cause of obstruction to passage of a catheter in postmortem and in vivo studies. An acute bend in the vein, with or without lodgment in a tributary, is the other common cause. In adults, venous luminal diameter is not a cause of obstruction to the passage of a 7‐French catheter in the coronary sinus or proximal GCV.
Functional Effects of Mutations in KvLQT1 that Cause Long QT Syndrome
Authors: WANG Z. , TRISTANI‐FIROUZI M. , XU Q. , LIN M. , KEATING M.T. , SANGUINETTI M.C. 
Published: April 2007

Mutations in KvLQT1. Introduction: The long QT syndrome (LQT) is caused by mutations in genes encoding ion channels that modulate the duration of ventricular action potentials. One of these genes, KVLQT1, encodes an α subunit that coassembles with another subunit, hminK, to form the cardiac slow delayed rectifier (IKs) K+ channel. Methods and Results: The functional effects of seven mutations in KVLQT1 were assessed using two‐microelectrode voltage clamp and the Xenopus oocyte expression system. Most mutations in KVLQT1 caused loss of function when expressed alone. Oocytes were also injected with equal amounts of wild‐type (WT) KVLQT1 and mutant KVLQT1 cRNA (with or without coinjection of hminK) and the resulting currents compared to currents induced by WT KvLQT1 alone. A341V, RI90Q, or G189R KVLQT1 subunits did not affect expression of WT KvLQT1. The other mutations in KVLQT1 caused a variable degree of dominant‐negative suppression of IKs. The order of potency for this effect was G345E > G306R = V254M > A341E. Conclusions: LQTl‐associated mutations in KVLQT1 caused a spectrum of dysfunction in IKs and KvLQT1 channels. The degree of IKs dysfunction did not correlate with the QTc interval or the presence of symptoms in the respective gene carriers. In contrast to previous reports, we found that loss of function mutations are not exclusive to recessiveiy inherited LQT.
Gene Expression of the Natriuretic Peptide System in Atrial Tissue of Patients with Paroxysmal and Persistent Atrial Fibrillation
Authors: TUINENBURG ANTON E. , BRUNDEL BIANCA J.J.M. , Van GELDER ISABELLE C. , HENNING ROBERT H. , Van Den BERG MAARTEN P. , DRIESSEN CÉCILE , GRANDJEAN JAN G. , Van GILST WIEK H. , CRIJNS HARRY J.G.M. 
Published: April 2007

Natriuretic Peptide System in AF. Introduction: Circulating cardiac natriuretic peptides play an important role in maintaining volume homeostasis, especially during conditions affecting hemodynamics. During atrial fibrillation (AF), levels of plasma atrial natriuretic peptide (ANP) becomes elevated. The aim of this study was to gather information about gene expression of the natriuretic peptide system on the atrial level in patients with AF. Methods and Results: Right atrial appendages of 36 patients with either paroxysmal or persistent AF were compared with 36 case matched controls in sinus rhythm for mRNA expression of pro‐ atrial natriuretic peptide (pro‐ANP), pro‐brain natriuretic peptide (pro‐BNP), and their natriuretic peptide receptor type‐A (NPR‐A). We investigated patients without (n = 36) and with (n = 36) valvular disease. Persistent AF was associated with higher mRNA expression of pro‐BNP (+66%, P = 0.04, in patients without valvular disease, and +69%, P < 0.01, in patients with valvular disease) and lower mRNA expression of NPR‐A (‐58%, P = 0.02, in patients witbout valvular disease, and ‐62%, P < 0.01, in patients with valvular disease). The mRNA content of pro‐ANP was only increased in patients with valvular disease (+12%, P = 0.03). No changes were observed in patients with paroxysmal AF. Conclusion: This study demonstrates that persistent, but not paroxysmal, AF induces alterations in gene expression of pro‐BNP and NPR‐A on the atrial level. Although AF generally is associated with an increase of plasma ANP level, a change in mRNA content of pro‐ANP is only observed in the presence of concomitant valvular disease and is of minor magnitude.
Ablation of Ventricular Tachycardia with a Saline‐Cooled Radiofrequency Catheter:
Authors: DELACRETAZ ETIENNE , STEVENSON WTLLIAM G. , WINTERS GAYLE L. , MITCHELL RICHARD N. , STEWART SARAH , LYNCH KRISTIN , ERIEDMAN PETER L. 
Published: April 2007

Saline‐Irrigated RF Catheter Ablation. Introduction: In animal models, active cooling of the electrode during radiofrequency (RF) ablation allows creation of larger lesions, presumably by increasing the power that can be delivered without coagulum formation. These RF lesions have not been characterized in human myocardium in regions of infarction and scarring. Methods and Results: Cooled‐tip RF catheter ablation of ventricular tacbycardias (VTs) was performed in two patients who had severe congestive heart failure and subsequently underwent cardiac transplantation. The first patient bad four different monomorphic VTs. RF applications along the inferoseptal margin of a scarred region abolished all inducible VTs. The second patient had sarcoidosis involving the myocardium and four different inducible VTs. RF current applied at an inferobasal VT exit and at the right and left septa failed to abolish the VTs. The explanted hearts were examined at the time of cardiac transplantation 18 and 21 days later, respectively. Lesions extended to depths up to 7 mm, reaching clusters of myocardial cells deep to regions of fibrosis. Microscopically, the ablation sites contained coagulation necrosis with hemorrhage, surrounded by a rim of granulation tissue. Conclusion: Saline‐irrigated RF catheter ablation produces relatively large lesions capable of penetrating deep into scarred myocardium.
Value of Programmed Ventricular Stimulation in Patients with Congenital Heart Disease
Authors: ALEXANDER MARK E. , WALSH EDWARD P. , SAUL J. PHILIP , EPSTEIN MICHAEL R. , TRIEDMAN JOHN K. 
Published: April 2007

Ventricular Stimulation in Congenital Heart Disease, introduction: The role of programmed ventricular stimulation (VSTIM) for risk stratification in congenital heart disease is unclear. We analyzed the results of VSTIM in selected congenital heart disease survivors at a single center lo determine whether it improved the ability to predict a serious outcome. Methods and Results: Between July 1985 and September 1996. 140 primary VSTIM studies were performed on 130 patients (median age 18.1 years, range 0 to 51). Tetralogy of Fallot (33%), d‐transposition of the great arteries (25%), and left ventricular outflow tract obstruction (12%) accounted for the majority of patients. Indications included spontaneous ventricular tachycardia (VT) of ≥ 3 beats (72%) and/or symptoms (68%). Sustained VT was induced in 25% of the studies, and nonsustained VT in 12%. Atrial flutter or other supraventricular tachycardia was documented in 32% and bradyarrhythmias in 26%. By univariate analysis, mortality was increased in patients with positive VSTIM versus negative VSTIM (18% vs 7%, P = 0.04). Using multivariate analysis, positive VSTIM was associated with a sixfold increased risk of decreased survival and a threefold increased risk of serious arrhythmic events, allowing up to 87% sensitivity in predicting mortality. However, 7 (33%) of 21 patients with documented clinical VT had false‐negative studies. Conclusion: VSTIM in a large, selected group of congenital heart disease patients identified a subgroup with significantly increased mortality and sudden arrhythmic events. Failure to induce VT was a favorable prognostic sign, but the frequency of false‐negative studies was high. Frequent supraventricular tachycardia further complicated risk stratification. Although VSTIM appears to be a reasonable tool for evaluation of this population, a larger, multicenter trial is recommended to clarify its utility.
Characterization of Sinoatrial Parasympathetic Innervation in Humans
Authors: QUAN KARA J. , LEE JAI H. , GEHA ALEXANDER S. , BIBLO LEE A. , VAN HARE GEORGE F. , MACKALL JUDITH A. , CARLSON MARK D. 
Published: April 2007

Sinoatrial Parasympathetic Innervation. Introduction: The response to sinoatrial parasympathetic nerve stimulation (shortened atrial refractoriness) was used to determine the atrial distribution of these nerve fibers in humans. We hypothesized that, in humans, parasympathetic nerves that innervate the sinoatrial node also innervate the right atrium and that the greatest density of innervation is near the sinoatrial nodal fat pad. Methods and Results: Temporary epicardial wire electrodes were sutured in pairs in the sinoatrial nodal fat pad, high right atrium, and right ventricle by direct visualization during coronary artery bypass surgery in nine patients. Appropriate electrode placement was confirmed by electrically stimulating the fat pad in the operating room to prolong sinus cycle length by 50%. Experiments were performed in the electrophysiology laboratory 1 to 5 days after surgery. Programmed atrial stimulation was performed via an endocardial electrode catheter advanced to the right atrium. The catheter tip electrode was moved in 1‐cm concentric zones around the epicardial wires by fluoroscopic guidance. Atrial refractoriness was determined in the presence and absence of sinoatrial parasympathetic nerve stimulation at each cutheter site. In 8 of 9 patients, parasympathetic nerve stimulation reproducibly prolonged sinus cycle length by 50%. There was no effect on AV nodal conduction (no prolongation of PR interval) and no change in AV nodal refractoriness. Atrial effective refractory periods reproducibly shortened in response to parasympathetic nerve stimulation in 1‐cm zones up to 3 cm surrounding the fat pad, by a mean (± SEM) of 26.6 ± 4.3 msec (zone 1), 11.4 ± 1.8 msec (zone 2), and 10.0 ± 2.5 msec (zone 3), respectively (P = 0.0001). At distances > 3 cm from the fat pad, the effective refractory period did not shorten. Conclusion: Stimulation of parasympathetic nerves that innervate the sinoatrial node shortened atrial refractoriness in humans.
Parasympathetic Inhibition of Sympathetic Effects on Pacemaker Location and Rate in Hearts of Anesthetized Dogs
Authors: MIYASHITA YUSUKE , FURUKAWA YASUYUKI , NAKAJIMA KOICHI , HIROSE MASAMICHI , KUROGOUCHI FUMIO , CHIBA SHIGETOSHI 
Published: April 2007

Autonomic Effect on Pacemaker Location. introduction: The site of impulse origin in the right atrium generally is considered to be a single static locus within the sinoatrial (SA) node. Previous investigators showed that the pacemaker site may shift due to changes in sympathetic or parasympathetic neural activity. We investigated the interactions between sympathetic and parasympathetic influences on the site of impulse initiation in the right atrium in anesthetized dogs. Methods and Results: We determined the site of impulse initiation and the spread of excitation over the anterior and posterior regions of the right atrium by a matrix of 48 unipolar recording electrodes. We assessed the spread of excitation at 3‐nisec intervals by constructing isochronal activation sequence maps. Sympathetic stimulation increased the frequency of atrial excitation (i.e., the heart rate), but also shifted the earliest activation region (EAR) from a locus in the SA node to a locus in the superior vena cava (the superior pacemaker site). Vagus stimulation decreased the heart rate and shifted the EAR to a lower site in the SA node or a site in the interior right atrium along the sulcus terminalis (the inferior pacemaker site). A short period of vagus stimulation during a more prolonged sympathetic stimulation elicited a larger decrease in rate than did vagus stimulation alone and shifted the EAR from the superior site to the SA node or to the inferior site. After atropine, combined stimulation shifted the EAR to the superior site, but propranolol did not change EAR location. Conclusion: Our results suggest that parasympathetic activity predominates over sympathetic activity not only on heart rate, but also on the location of the EAR in the anesthetized dog.
Validation of a Noninvasive Measure of Local Myocardial Repolarization in a Conscious Human Model:
Authors: DOUGLAS LEE S. , DORIAN PAUL , GEIST MICHAEL , DAVIES EDWARD , BARR AIALA , DUNNE CATHERINE , PAQUETTE MINEY , NEWMAN DAVID 
Published: April 2007

Rate Adaptation of Myocardial Repolarization. Introduction: A commercial pacemaker sensor measure of the unipolar endocardial stimulus to T wave interval may accurately reflect changes in the monophasic action potential duration at 90% repolarization (APD90). This sensor system was used to study the kinetics of adaptation of repolarization duration to changes in heart rate in humans. Methods and Results: Patients were studied using an external pacemaker capable of displaying all stimulus to T wave intervals for each paced beat. Right ventricular stimulation was delivered via the pacemaker and compared simultaneously to APD90. Steady‐state pacing was simulated by 60 seconds of pacing at cycle lengths (CLs) 350 to 700 msec. Adaptation to a new ventricular rate was analyzed with a sudden 200‐msec decrease in CL. The relation between repolarization measure and steady‐state CL (n = 16) was linear with a slope of 0.16 and 0.19 for APD90 and stimulus to T wave interval, respectively (P = NS). The adaptation of both repolarization measures to a sudden change in rate were best modeled by a biexponential function. Stimulus to T wave interval exhibited a parallel course to APD90, and an analysis of normalized differences between APD90 and stimulus to T wave interval followed an approximately normal distribution, with 93.5% of the paired differences within 2 SD of the mean. Conclusion: A pacemaker sensor measure of stimulus to T wave interval accurately parallels APD90, during both steady‐state and sudden changes in rate. Repolarization in human endocardium follows a linear relation to steady‐state CL and adapts to a new rate with a biexponential function. This model represents a novel method for studying human cardiac repolarization.