bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cultured Adult Rabbit Myocytes:
Authors: MITCHESON JOHN S. , HANCOX JULES C. , LEVI ALLAN J. 
Published: April 2007

Effect of Supplements and Isoprenaline on Cultured Myocytes. Introduction: The aims of this study were to investigate: (1) the effect of supplementing the culture medium on preservation of L‐type calcium channel current (Ica,L) in adult rabbit ventricular myocytes cultured for 4 days; and (2) preservation of the Ica,L response in cultured myocytes to the β‐adrenergic agonist isoprenaline. Methods and Results: Adult rabbit myocytes were cultured on laminin‐pretreated glass coverslips. The basic, serum‐free culture medium was supplemented with 2 mM L‐carnitine, 5 mM creatine, and 5 mM taurine. Myocytes were whole cell patch‐clamped, and the L‐type Ca channel current was recorded selectively as Ba flux (IBa,L) via the channels, IBa,L density (i.e., IBa,L amplitude normalized to membrane capacitance) in myocytes maintained in supplemented medium did not change significantly during culture (P > 0.1). By comparison, IBa,L density in myocytes cultured in nonsupplemented medium declined by 36% after 24 hours in culture (day 1) and then recovered by the fourth day (day 4). There was no significant difference in the response to isoprenaline of acutely isolated myocytes and 4‐day cultured myocytes. Isoprenaline 100 nM increased peak IBa,L by 149%± 32% (mean ± SEM) in acutely isolated myocytes (n = 4 cells), and by 224%± 60% (n = 6 cells) and 159%± 24% (n = 8 cells) in day 1 and 4 cultured myocytes, respectively. Conclusions: Supplemented medium improved IBa,L density in cultured myocytes. β‐Adrenergic receptors and intracellular messenger pathways appear to remain intact in adult rabbit myocytes cultured for up to 4 days.
Signal‐Aver aged Intracardiac Electrograms:
Authors: BERGER RONALD D. , NSAH EMMANUEL , CALKINS HUGH 
Published: April 2007

Signal Averaged Intracardiac Electrograms. Introduction: In patients with manifest accessory pathways, Kent potentials are often difficult to identify even at sites of successful catheter ablation, due largely to signal noise and catheter instability. We hypothesized that signal averaging the intracardiac electrogram recorded from the ablation catheter over a number of beats would improve the signal‐to‐noise ratio of the electrogram and aid in the detection of Kent potentials at accessory pathway locations. Methods and Results: We retrospectively analyzed distal‐pair electrograms recorded from 9 successful, 6 transiently successful, and 10 failed ablation sites in 10 patients with manifest accessory pathways who underwent catheter ablation. We developed custom software to finely align 20 to 30 consecutive sinus beats and compute the signal average of the electrogram (SAE) for each site. Kent potentials were classified as probable, possible, or absent in the raw ablation site electrogram and the SAE base on morphologic criteria. A measure of beat‐to‐beat signal instability, the variability quotient (VQ), was also computed for each site. Probable Kent potentials were found in the raw ablation site electrogram at only 2 of the 15 successful and transiently successful sites, but were found in the SAE at 10 of these sites (P = 0.008). Eight of the 9 successful sites had VQ < 0.2, suggesting stable catheter‐tissue contact, while 3 of the 6 transiently successful sites had VQ > 0.2, indicating unstable contact. Conclusions: Signal averaging the intracardiac ablation site electrogram enhances detection of Kent potentials at accessory pathway locations. Catheter instability can be quantified by signal variability analysis and, when high, may predict lack of successful ablation even at sites where Kent potentials are present.
Azimilide (NE‐10064) Can Prolong or Shorten the Action Potential Duration in Canine Ventricular Myocytes:
Authors: YAO JIAN‐AN , TSENG GEA‐NY 
Published: April 2007

Azimilide Effects on Membrane Voltage and Current. Introduction: Azimilide (NE‐10064) has antiarrhythmic and antifibrillatory effects in canine models of ventricular arrhythmia. The goal of the present study was to examine the effects of azimilide on action potential and membrane currents of canine ventricular myocytes. Methods and Results: Membrane voltage and current were recorded using the whole cell, patch clamp method. Azimilide at 1 /μM induced a consistent prolongation of action potential duration (APD): on average APD90 was prolonged by 25% and 17% at stimulation rates of 0.33 and 1 Hz, respectively. Elevating the drug concentration to 5 μM induced APD prolongation in some cells but APD shortening in the others at 0.33 Hz, and a consistent APD shortening at 1 Hz. Azimilide suppressed the following currents (Kd in parenthesis): IKr (< 1 μM at ‐20 mV), IKs, (1.8 μM at +30 mV), L‐type Ca current (17.8 μM at +10 mV), and Na current (19 μM at ‐40 mV). Azimilide was a weak blocker of the transient outward and inward rectifier currents (Kd≥ 50 μM at +50 and ‐140 mV, respectively). Azimilide blocked IKr, IKs, and INa in a use‐dependent manner. Furthermore, azimilide reduced a slowly inactivating component of Na current that might be important for maintaining the action potential plateau in canine ventricular myocytes. Conclusion: Azimilide has variable effects on APD in canine ventricular myocytes due to Us blocking effects on multiple currents with different potencies. Its Class III antiarrhythmic action is most likely seen at low concentrations (< 5 μM).
Modulation of Procainamide's Effect on Conduction by Cellular Uncoupling in Perfused Rabbit Hearts
Authors: SPEAR JOSEPH F. , HOOK BRUCE G. , JOSEPHSON MARK E. , NET MOORE E. 
Published: April 2007

Cellular Uncoupling and Procainamide's Effect. Introduction: How cell‐to‐cell electrical coupling influences an antiarrhythmic agent's effect on conduction is largely unknown. To investigate this, we evaluated the effects of procainamide on myocardial conduction at decreasing degrees of cell‐to‐cell electrical coupling induced by graded doses of heptanol. Methods and Results: Electrograms were recorded from 50 ventricular epicardial sites in a 1 cm × 0.5 cm area during pacing to produce conduction longitudinal or transverse to myocar dial fiber orientation in Langendorff‐perfused rabbit hearts. The effects of procainamide (15 mg/L.) on conduction velocity were determined in the presence of increasing doses of heptanot (0.2, 0.5, and 1.0 mM). In addition, using standard microelectrode techniques in isolated super‐refused rabbit myocardium, intracellular potentials were recorded in the presence of 15 mg/L, procainamide and heptanol (1.0 mM). In the absence of heptanol, procainamide slowed conduction velocity. In the presence of increasing doses of heptanol, procainamide's contribution to the depressant effect on conduction velocity was attenuated and reversed at the highest dose. The latter effect was preferentially seen for conduction longitudinal to myocardial fiber orientation. Heptanol had no effect on action potential amplitude or maximum rate of depolarization in the presence of procainamide. Conclusions: Procainamide's effect on conduction velocity is influenced by the underlying degree of cell‐to‐cell electrical coupling. The present model should he useful in evaluating the relative ability of other pharmacologic agents to modulate conduction under conditions of changing cell coupling.
Vasodepressor Syncope Due to Subclinical Myocardial Ischemia
Authors: ASCHEIM DEBORAH D. , MARKOWITZ STEVEN M. , LAI HENRY , ENGELSTEIN ERICA D. , STEIN KENNETH M. , LERMAN BRUCE B. 
Published: April 2007

Vasodepressor Syncope. Introduction: Vasodepressor syncope is a common cause of syncope, but the initiating event that triggers the vasodepressor response remains incompletely understood. Although ischemia due to acute right coronary occlusion may precipitate hypotension and bradycardia through the Bezold‐Jarisch reflex, an ischemic precipitant for the common vasodepressor faint has not been previously identified. In the present study, we present evidence for a causal relationship between myocardial ischemia and vasodepressor syncope. Methods and Results: Two patients referred for evaluation of syncope underwent upright tilt table testing with either ST segment monitoring, sestamibi scintigraphy and echocardiography during the tilt test, or coronary angiography. Both patients had positive tilt table tests during the control study. Patient 1 was documented to have reproducible ischemic ECG changes during atypical chest pressure induced by upright tilt, despite a normal coronary angiogram with ergonovine provocation. Subsequent tilt testing with simultaneous sestamibi perfusion imaging and echocardiography revealed reversible anterolateral hypoperfusion corresponding with anterolateral hypokinesis during upright tilt that preceded syncope. Ischemic ECG changes during incremental rapid atrial pacing further suggested ischemia on the basis of microvascular disease. Follow‐up tilt testing on verapamil was negative. Patient 2 developed ischemic ECG changes during the recovery phase of an exercise stress test, which was followed by a vasodepressor response and frank syncope. Coronary angiography revealed a 90% distal right coronary artery stenosis that was successfully dilated, after which follow‐up tilt table testing off all other medication was negative. Conclusions: These two cases illustrate a previously unrecognized causality between myocardial ischemia and clinical vasodepressor syncope, and demonstrate that subtle manifestations of myocardial ischemia, associated with either atypical angina or silent ischemia, can provoke syncope.
Radiofrequency Ablation of Concealed Left Free‐Wall Accessory Pathways Without Coronary Sinus Catheterization:
Authors: BRUGADA JOSEP , GARCIA‐BOLAO IGNACIO , FIGUEIREDO MARCIO , PUIGFEL MARTÍ , MATAS MARIONA , NAVARRO‐LÓPEZ FRANCISCO 
Published: April 2007

Ablation of Concealed Accessory Pathways. Introduction: Feasibility of radiofrequency (RF) ablation using a two‐catheter technique without coronary sinus catheterization was studied in 100 consecutive patients with a single concealed left free‐wall accessory path‐way. Methods and Results: Tachycardia was induced by electrical stimulation in the right atrium/right ventricle, and the presence of a concealed left free‐wall accessory pathway was suggested electrocardiographically (negative P wave in leads I and/or a VL during orthodromic tachycardia) or by earlier atrial activation in the pulmonary artery compared to the high right atrium. Mapping of the mitral annulus was performed during right ventricular pacing or orthodromic tachycardia, and RF energy was applied at the site with the earliest retrograde atrial activation. Ablation was considered effective if tachycardia could not be induced, and if VA dissociation or exclusive retrograde nodal conduction was observed. Ablation was initially successful in 98 of 100 patients. Mean number of radiofrequency pulses were 3.2 ± 2. Mean fluoroscopy time and total procedure time was 14 ± 9 and 107 ± 32 minutes, respectively. There were no complications related to the procedure. At a mean follow‐up of 22 ± 13 months, two patients experienced tachycardia recurrence and required a second procedure, which was successful. Conclusions: Our results suggest that RF catheter ablation of concealed left free‐wall accessory pathways can be safely, effectively, and rapidly performed using a simplified two‐catheter technique with no need for coronary sinus catheterization.
Defibrillation Efficacy Using High‐Frequency Switching to Proportion Current Among Simultaneous Shock Pathways
Authors: SWEENEY ROBERT J. , GILL ROBERT M. , REID PHILIP R. 
Published: April 2007

High‐Frequency Current‐Proportioned Defibrillation. Introduction: Multiple‐pathway electrode configurations generally allow improved current distribution over the heart and lower defibrillation thresholds than single‐pathway systems. However, current distributions using multiple pathways are largely determined by electrode type and location. We hypothesized that switching the current among multiple pathways at high frequency (HF) could allow the switching duty cycle to control the proportion of time‐averaged current flowing in each pathway, thus permitting altered (possibly improved) defibrillation efficacy using the same electrodes and shock waveform. Methods and Results: In dogs, we measured the current (I50) for 50% defibrillation success using catheter electrodes in the right ventricular apex (cathode) and superior vena cava (A‐pathway anode) and a subcutaneous patch on the left chest wall (B‐pathway anode). In group 1 (N = 7), we measured I50s for shocks that used HF to proportion 10% to 90% of the current to the A‐pathway. Shocks with 10% to 30% of the current in the A‐pathway had significantly lower I50s than nonproportioned shocks using all three electrodes. However, the resistance differed among single and simultaneous pathways so energy did not necessarily parallel these changes. In group 2 (N = 6), we measured I50s for shocks to the B‐pathway alone, for nonproportioned shocks to A and B, and for shocks that proportioned 80% of the current to the B‐pathway using either HF, sequential, or amplitude proportioning methods. All proportioning methods had similar ISUs that were significantly lower than the I50 for nonproportioned shocks to A and B and that were comparable to shocks to the B‐pathway alone. Conclusions: Shocks with most current proportioned to the B‐pathway had lower defibrillation currents than nonproportioned shocks using both pathways. Thus, defibrillation efficacy was changed by HF proportioning without changing the electrodes or shock waveform. These findings suggest that HF proportioning may be a method to improve defibrillation.
Paced Activation Mapping Reveals Organization of Myocardial Fibers:
Authors: MUZIKANT ADAM L. , HENRIQUEZ CRAIG S. 
Published: April 2007

Pacing Reveals Fiber Orientation in 3D Bidomain. Introduction: A three‐dimensional bidomain model of a block section of both the right and left ventricular walls that included rotational anisotropy and fiber curvature was used to investigate potential distributions generated during paced activation mapping. Unlike previous large‐scale tissue models, the extracellular stimulus was included. Methods and Results: The model was used to test the hypothesis that information about the underlying tissue structure (surface fiber angle gradients, amount of fiber rotation per unit depth, and anisotropy) can be extracted from surface potential distributions during stimulation. Results from distributions during stimulation were compared to those obtained using the distributions during activation. To better correlate results to possible experimental measurements, the analysis was performed using a 21 × 21 grid of “electrode” sites, each separated by 1 mm. Fiber orientation was estimated from the surface data by: (1) curve‐fitting the elliptical shape of the epicardial potential distribution during stimulation: (2) identifying the location of the potential maxima leading the wavefront during early activation: and (3) for epicardial stimuli, curve‐fitting the elliptical shape of the activation isochrones. Results show that surface potential distributions from the stimulus can be used to estimate fiber orientation: however, the accuracy of the reconstruction is highly dependent on the amount of fiber rotation per unit depth. Conclusions: Extracellular potential data during and after stimulation is shown to reflect the organization of myocardial fibers and, as such, could be used to characterize the three‐dimensional anisotropic electrical properties in situ.
Mitral Valve Prolapse and Ventricular Arrhythmias: Observations in a Patient with a 20‐Year History
Authors: WILDE ARTHUR A.M. , DÜREN DONALD R. , HAUER RICHARD N.W. , de BAKKER JACQUES M.T. , BAKKER PATRICIA F.A. , BECKER ANTON E. , JANSE MICHIEL J. 
Published: April 2007

Ventricular Arrhythmias in MVP. Introduction: Ventricular arrhythmias are a common feature in patients with mitral valve prolapse. In an attempt to determine the origin and underlying electrophysiologic mechanism, we describe a patient with ventricular fibrillation, exercise‐induced ventricular tachycardia (VT), and, at the time of diagnosis, prolapse of the posterior mitral valve leaflet without mitral regurgitation. Methods and Results: Treatment with β‐blockade and diphenyihydantoin prevented the occurrence of malignant ventricular arrhythmias for more than 17 years. Discontinuation of the therapy resulted in an immediate reappearance of the VT, which, despite the marked enlargement of the left ventricle (secondary to development of severe mitral valve regurgitation), had a strikingly similar morphology. For hemodynamic reasons, the patient was finally selected for valve replacement. Detailed pre‐, peri‐, and postoperative studies were performed, including administration of flunarizine, body surface mapping, construction of perioperative epicardial and endocardial maps, and studies of the excised muscles in vitro. Conclusions: Delayed afterdepolarization‐induced triggered activity is the mechanism of VT in this mitral valve prolapse patient. The trigger is provided by Isolated ventricular premature complexes elicited by a different electrophysiologic mechanism, possibly reentry, which is related to stretch and presumably to fibrosis of the papillary muscles.
Delivery of Noncommitted Shocks for Nonsustained Ventricular Arrhythmias by a New Implantable Cardioverter Defibrillator with Abortive Shock Capability
Authors: BLANCK ZALMEN , BIEHL MICHAEL , SRA JASBIR , DHALA ANWER , AKHTAR MASOOD 
Published: April 2007

Shock Delivery Despite Abortive Shock Capability. Introduction: To describe the delivery of noncommitted implantable cardioverter defibrillator (ICD) shocks despite self‐termination of ventricular arrhythmias. Abortive shock capability should eliminate the delivery of shocks for self‐terminating ventricular arrhythmias. The delivery of noncommitted shocks despite abortive shock capability is, therefore, unexpected and previously unreported. Methods and Results: Among 118 patients who received the Transvene nonthoracotomy lead system and the Jewel ICD (model 7219D), three patients (1.7%) experienced spurious, noncommitted shocks for self‐terminating arrhythmias. Only one detection zone (i.e., ventricular fibrillation) had been programmed in the defibrillator in each patient. In all three patients, the ventricular arrhythmias self‐terminated during the charging period. One patient received seven shocks during periods of asystole, and the other two patients received one shock each. Two different mechanisms for shock delivery in this setting were identified: one occurring in the absence of electrical activity at the end of the bradycardia escape interval (i.e., associated with bradyarrhytbmias), and the other when two sensed electrical events (i.e., escape beats) occurred during the so‐called “synchronization” window of the defibrillator. Conclusions: In rare patients with the Jewel defibrillator, shocks may be delivered for self‐terminating arrhythmias despite abortive shock capability. Patients who are dependent upon pacing from their implanted defibrillator are at particular risk for shock in the aftermath of self‐terminating ventricular arrhythmias. Defibrillator programming strategies aimed at eliminating or diminishing the incidence of this problem are discussed.
Preferential Locations for Critical Reentry Circuit Sites Causing Ventricular Tachycardia After Inferior Wall Myocardial Infarction
Authors: HADJIS TOMY A. , STEVENSON WILLIAM G. , HARADA TOMOO , ERIEDMAN PETER L. , SAGER PHILIP , SAXON LESLIE A. 
Published: April 2007

Reentrant VT Post MI. Introduction: For relatively slow monomorphic ventricular tachycardia (VT) after myocardial infarction, entrainment can be used to identify reentry circuit “isthmus sites” (exit sites and sites proximal to the exit) where radioifrequency (RF) catheter ablation has the greatest likelihood of interrupting reentry. Similarities in coronary and ventricular anatomy may cause such sites to form in preferential locations. The objective of this study is to determine if there are preferential locations for reentry circuit isthmus regions in chronic inferior wall infarctions causing VT. Methods and Results: Catheter mapping and RF catheter ablation was performed in 21 patients with an old inferior wall myocardial infarction and VT. The inferior wall was divided into 9 anatomic regions: 3 apical, 3 mid, and 3 basal segments. Of 46 different VTs, an endocardial isthmus site was identified in one or more zones in 28 (61%), with 10 VTs having isthmus sites in two or more adjacent regions. Isthmus zones were found in a basal region of the left ventricle in 24 (86%) of 28 VTs, in a mid segment in 9 (32%) VTs, and in an apical segment in 1 (4%) (P = 0.002). Of 30 RF current applications that terminated VT, 21 (70%) were at basal isthmus sites. Conclusion: The high prevalence of endocardial isthmus zones near the base of the left ventricle suggests that the mitral annulus often plays a role in defining the margins of reentry circuits that cau.se relatively slow VTs after inferior wall myocardial infarction.
Mapping of the Coronary Sinus and Great Cardiac Vein Using a 2‐French Electrode Catheter and a Right Femoral Approach
Authors: CAPPATO RICCARDO , SCHLÜTER MICHAEL , WEISS CHRISTIAN , WILLEMS STEPHAN , MEINERTZ THOMAS , KUCK KARLHEINZ 
Published: April 2007

Coronary Sinus Mapping. Introduction: Local electrogranis recorded from the coronary sinus and great cardiac vein provide important information for the diagnosis of various arrhythmias and identification of target sites for ablation of left‐sided accessory pathways. One limitation of present techniques is the inability, in many cases, to probe the great cardiac vein at the anterior mitral annulus. We tested the feasibility of a new technique for catheterization of the coronary sinus and great cardiac vein by means of a small‐diameter electrode catheter advanced via a right femoral approach through an angiography catheter. Methods and Results: Of 22 patients (12 men and 10 women; ages 44.5 ± 13.4 years) undergoing radiofrequency ablation of a supraventricular tachycardia, cannulation of the coronary sinus orifice using a 6‐French 1L or 2L Amplatz catheter was achieved in 20 patients (91%) within 0.9 ± 0.6 minutes; after cannulation, a 2‐French octapolar electrode catheter with a soft radiopaque tip and a 3‐mm interelectrode distance could he advanced in all 20 patients through the guiding catheter to the great cardiac vein in the anterior region of the AV sulcus within 0.8 ± 0.7 minutes. Atrial and ventricular local potentials were recorded all along the mitral annulus during sinus rhythm, atrial and ventricular pacing, or supraventricular tachycardia. Variation of local potential amplitude never exceeded 20% of the mean and presented similar stability at all annular regions. The arrhythmogenic substrate was identified in all patients. Of 18 patients with 21 left‐sided accessory pathways, an accessory pathway potential could he recorded at the ablation site by one or more adjacent epicardial electrode pairs in 10 pathways. No procedure‐related complications were observed. Conclusions: The technique introduced in this study proved feasible in 91% of patients. Its main advantages are the simplicity and rapidity of coronary sinus cannulation and the ability to advance the electrode catheter to the anterior cardiac vein. In addition, closely spaced bipolar electrograms resulted in enhanced atrial, ventricular, and accessory pathway potential resolution.