bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of Electrogram Duration in Right Posteroseptal Atrium and Atrium‐Pulmonary Vein Junction on Pacing Site:
Authors: CHEN YI‐JEN , TAI CHING‐TAI , HSIEH MING‐HSIUNG , TSAI CHIN‐FENG , LIN WEI‐SHIANG , CHEN SHIH‐ANN
Published: April 2007

Right Posteroseptal Atrium and Atrium‐PV Junction. introduction: The fractionated atrial electrogram. a signal helpful in identifying the target site for radiofrequency catheter ablation of the slow AV nodal pathway, is considered to arise from nonuniform anisotropic electrical activity. However, the effects of pacing sites and radiofrequency ablation on these electrograms are not clear. Similarly, the nature of the fractionated atrial electrogram in the atrium‐pumonary vein junction has yet to be determined.

Methods and Results: Two experiments were performed in this study. Experiment 1 evaluated the fractionated atrial electrogram at target sites before and after slow AV nodal pathway ablation during sinus rhythm or during pacing from different sites, Group 1A consisted of 16 patients with dual AV nodal pathway physiology and AV nodal reentrant tachycardia who underwent successful ablation without residual slow AV nodal pathway. Group IB consisted of 7 patients who underwent successful elimination of AV nodal reentry but with residual dual AV nodal pathway physiology. Group IC consisted of 6 patients who still had AV nodal reentrant tachycardia after two applications of radiofrequency energy. In Group 1D, there were 16 patients with dual AV nodal pathway physiology, but without inducible AV nodal reentrant tachycardia. In group 1E, there were 15 patients without dual AV nodal pathway physiology. Experiment 2 investigated the fractionated atrial electrogram in the ostium of the left and right superior pulmonary veins I 18 patients with paroxysmal strial fibrillation (2A) and in 8 patients without paroxysmal atrial fibrillation (2B). Before radiofrequency ablation, eletrogram duration in the right posteroseptal atrium during pacing from the middle coronary sinus or the right posterolateral atrium was shorter than that during pacing from the high right atrium (HRA) in all group 1 patients. After the successful elimination of the slow AV nodal pathway conduction in group 1A, atrial electrogram duration during HRA pacing was shorter than that before ablation. In experiment 2 patients, electrogram duration during pacing from the proximal or distal coronary sinus was shorter than that during pacing from HRA or sinus rhythm.

Conclusion: These findings suggest that the fractionated atrial electrogrms in the right posteroseptal atrium and ostium of left or right superior pulmonary veins are potentially consistent with nonuniform anisotropic propagation. Alternations of electrogram characteristics after successful radiofrequency ablation of the slow AV nodal pathway may arise from the changes of nonuniform anisotropic activity in the right posteroseptal atrium.
Spatial and Temporal Heterogeneity of Depolarization and Repolarization May Complicate Implantable Cardioverter Defibrillator Therapy in Brugada Syndrome
Authors: STIX GUENTER , BELLA PAOLO DELLA , CARBUCICCHIO CORRADO , SCHMIDINGER HERWIG
Published: April 2007

ICD Therapy in Brugada Syndrome. Introduction: Dynamic variations in electrophysiologic phenomena inherent to the Brugada syndrome may complicate therapy with implantable cardioverter defibrillators (ICDs).

Methods and Results: Between 1997 and 1999, 3 of 7 patients with Brugada syndrome (1 man and 2 women, mean age 42 years) received an ICD. During follow‐up, 2 patients experienced multiple inappropriate shocks. Simultaneously with dynamic changes in the surface ECG, endocardial ECGs revealed a dynamic decrease in the right ventricular R wave and an increase in the corresponding T wave, resulting in T wave oversensing. With ajmaline administration, these dynamic changes in endocardial signals were reproducible at different right ventricular sites, whereas left ventricular epicardial signals remained stable. Incremental AAI pacing and exercise stress testing resulted in similar changes in right ventricular endocardial signals, but normalization of the surface ECG apart from progressively increasing S waves in leads II, V5, and V6. Orciprenaline administration had no effect on ECG phenomena. After implantation of a left ventricular epicardial lead for sensing and pacing, no inappropriate tachycardia detection recurred.

Conclusion: These findings demonstrate that, in Brugada syndrome, spontaneous or ajmaline‐induced changes in the surface ECG may be paralleled by significant variations in the right ventricular endocardial electrogram that may result in ICD malfunction. Implantation of a left ventricular epicardial lead for sensing and pacing may be the ultimate successful approach in certain patients. To assure proper ICD function, ajmaline testing during ICD implantation appears to be helpful.
Maturational Atrioventricular Nodal Physiology in the Mouse
Authors: MAGUIRE COLIN T. , BEVILACQUA LAURA M. , WAKIMOTO HIROKO , GEHRMANN JOSEF , BERUL CHARLES I.
Published: April 2007

Mouse AV Nodal Maturation. Introduction: Dual AV nodal physiology is characterized by discontinuous conduction from the atrium to His bundle during programmed atrial extrastimulus testing (A2V2 conduction curves), AV nodal echo beats, and induction of AV nodal reentry tachycardia (AVNRT). The purpose of this study was to characterize in vivo murine maturational AV nodal conduction properties and determine the frequency of dual AV nodal physiology and inducible AVNRT.

Methods and Results: A complete transvenous in vivo electrophysiologic study was performed on 30 immature and 19 mature mice. Assessment of AV nodal conduction included (1) surface ECG and intracardiac atrial and ventricular electrograms; (2) decremental atrial pacing to the point of Wenckebach block and 2:1 conduction; and (3) programmed premature atrial extrastimuli to determine AV effective refractory periods (AVERP), construct A2V2 conduction curves, and attempt arrhythmia induction. The mean Wenckebach block interval was 73 ± 12 msec, 2:1 block pacing cycle length was 61 ± 11 msec, and mean AVERP100 was 54 ± 11 msec. The frequency of dual AV nodal physiology increased with chronologic age, with discontinuous A2V2, conduction curves or AV nodal echo heats in 27% of young mice < 8 weeks and 58% in adult mice (P = 0.03).

Conclusion: These data suggest that mice, similar to humans, have maturation of AV nodal physiology, hut they do not have inducible AVNRT. Characterization of murine electrophysiology may be of value in studying genetically modified animals with AV conduction abnormalities. Furthermore, extrapolation to humans may help explain the relative rarity of AVNRT in the younger pediatric population.
Atrial Tachycardia Masquerading as Atrial Flutter Following Ablation of the Subeustachian Isthmus
Authors: SEHRA RUCHIR , COPPESS MARK A. , ALTEMOSE GREGORY T. , MILITELLO CLAUDIO A. , MILLER JOHN M.
Published: April 2007

Pseudo‐Atrial Flutter. We report a case of atrial tachycardia masquerading as atrial flutter in a man who had previously undergone catheter ablation for atrial flutter. The recurrent arrhythmia was electrocardiographically almost identical to the prior atrial flutter; at repeat electrophysiologic study, although bidirectional conduction block was observed in the tricuspid annulus‐inferior vena caval isthmus, the atrial arrhythmia was readily initiated. Activation mapping suggested typical atrial flutter, hut entrainment techniques demonstrated intra‐atrial reentry not involving the ablated isthmus. This case illustrates the need to apply entrainment techniques even in cases of apparent “typical” atrial flutter to confirm that putative ablation targets are necessary for tachycardia perpetuation.
Prevalence and Significance of Focal Sources of Atrial Arrhythmia in Patients Undergoing Cardioversion of Persistent Atrial Fibrillation
Authors: TODD DERICK M. , FYNN SIMON P. , HOBBS W. JULIAN , FITZPATRICK ADAM P. , GARRATT CLIFFORD J.
Published: April 2007

Atrial Arrhythmias After Cardioversion of AF. Introduction: Recent reports have highlighted the importance of focal atrial arrhythmias as a curable cause fur a group of patients with frequently recurrent paroxysmal atrial fibrillation (AF). The importance of this arrhythmia mechanism in the general population of patients with persistent AF is unknown.

Methods and Results: After successful internal cardioversion of 50 consecutive patients with persistent AF (mean age 60 years, mean duration of AF 26 months), endocardial activity in the immediate postcardioversion period was analyzed for the presence of focal atria activity. Postcardioversion atrial arrhythmias were considered to be focal if there was evidence of a localized source of repetitive early atrial activation, either in the form of (1) self‐terminating monomorphic atrial tachycardia (at least five heats) or (2) recurrences of AF with an initial atrial activation sequence (first five beats) that was both monomorphic and reproducible with repeated recurrences. Evidence for a focal atrial arrhythmia was present in 20 of the total group of 50 patients (40%). Multivariate analysis of clinical characteristics revealed the diagnosis of lone AF as the only independent predictor of a focal source of AF (P = 0.028). Thirty‐nine patients were discharged from hospital in sinus rhythm. At 1‐month follow‐up. 25 (64%) of these 39 patients had suffered AF recurrence. The only significant predictor of AF recurrence was evidence of a focal source of atrial arrhythmia immediately after cardioversion, with a relative risk of 1.73 (range 1.1 to 2.7: P = 0.015).

Conclusion: Focal atrial arrhythmias are common in patients presenting with “idiopathic” persistent AF, suggesting a possible causative role in the generation of this common arrhythmia.
Successful Catheter Ablation in a Patient with Polymorphic Ventricular Tachycardia
Authors: KUSANO KENGO FUKUSHIMA , YAMAMOTO MIKA , EMORI TETSURO , MORITA HIROSHI , OHE TOHRU
Published: April 2007

Ablation of Polymorphic VT. We describe a patient with polymorphic ventricular tachycardia (PVT)/ventricular fibrillation (VF) without organic heart disease who was cured by radiofrequency catheter ablation. The patient was a 65‐year‐old woman with a l0‐year history of recurrent syncope. There was no evidence of organic heart disease, and the QT interval during sinus rhythm was borderline normal (corrected QT interval = 0.45 sec1/2). ECG, recording during syncope showed PVT. On one occasion, PVT degenerated into VF. This PVT was always induced by a premature ventricular complex (PVC) originating from the right ventricular (RV) outflow tract. Rapid pacing (220 beats/min) at the site of PVC origin reproduced polymorphic change of the QRS wave on surface ECG that was similar to PV T. This suggests that the PVT originated from a single focus in the RV outflow tract. Catheter ablation was performed at the site of PVC origin. During 18‐month follow‐up, PVT/VF was not documented.
Prevention of Atrial Fibrillation by Complete Compartmentalization of the Left Atrium Using a Catheter Technique
Authors: ERNST SABINE , OUYANG FEIFAN , SCHNEIDER BIRKE , KUCK KARL‐HEINZ
Published: April 2007

LA Compartmentalization for AF Prevention. Introduction: Right atrial compartmentalization has been demonstrated to only reduce the number of atrial fibrillation (AF) episodes: left atrial (LA) fibrillation still occurs.

Methods and Results: We report successful LA compartmentalization resulting in isolation of all four pulmonary veins in a 51‐year‐old woman suffering from paroxysmal AF. Deployment of a complete encircling line resulted in dissociation of electrical activation within the isolated area from the remaining LA. Despite attempts al reinduction by pacing maneuvers inside and outside the isolated area, AF was no longer inducible. During 2l‐week follow‐up, the patient remained in stable sinus rhythm with rare atrial extrasystoles.

Conclusion: If reproducible, this ablation strategy could allow treatment of AF independent of suppression of any triggering event.
Defibrillator Challenges for the New Millennium:
Authors: FRIEDMAN PAUL A. , GLIKSON MICHAEL , STANTON MARSHALL S.
Published: April 2007

ICD Therapy. Although it has become clear that implantable cardioverter defibrillators (ICDs) are effective, important challenges remain for the physician. Due to the limitations of available risk stratification tools, patient selection for primary sudden death prevention remains controversial in many populations. Additionally, the proliferation of device choices has led to challenges in matching the appropriate device to the individual patient: device size is balanced against longevity: the advantages of dual chamber systems is weighed against their increased complexity; physician and patient preferences in device implant site are constrained by site‐dependent effects on defibrillation effectiveness and lead failure rates; and special consideration must be given to the patient with a preexisting pacemaker. After ICD placement, determination of appropriate follow‐up frequency and methodology to assess device function must be considered. This article will review patient selection, device implant site selection, device‐device interactions, single versus dual chamber ICD selection, and follow‐up.
Effect of Chronic Amiodarone Therapy on Defibrillation Energy Requirements in Humans
Authors: PELOSI FRANK , ORAL HAKAN , KIM MICHAEL H. , STICHERLING CHRISTIAN , HORWOOD LAURA , KNIGHT BRADLEY P. , MICHAUD GREGORY E. , MORADY FRED , STRICKBERGER S. ADAM
Published: April 2007

Amiodarone Effect on Defibrillation Energy Requirement. Introduction: The effect of oral amiodarone therapy on defibrillation energy requirements in patients with an implantable defibrillator has not been established.

Methods and Results: Twenty‐one consecutive patients with implantable biphasic waveform defibrillators underwent a step‐down determination of the defibrillation energy requirement 211 ± 12 days before and 73 ± 22 days after initiation of amiodarone therapy (mean total dose 26.7 ± 11.1 g). Serum amiodarone and desethylamiodarone concentrations were measured at the time of defibrillation energy requirement determination. The mean defibrillation energy requirement before amiodarone therapy was 9.9 ± 4.6 J. After initiation of amiodarone therapy, the mean defibrillation energy requirement increased to 13.7 ± 5.6 J (P = 0.004). A linear relationship between the amiodarone (P = 0.02, r = 0.6), desethylamiodarone (P = 0.02, r = 0.6), and combined amiodarone‐desethylamiodarone concentrations (P = 0.001, r = 0.6) and the defibrillation energy requirement was noted. Stepwise regression analysis demonstrated that the combined amiodarone‐desethylamiodarone concentration was the only independent predictor of increase in the defibrillation energy requirement.

Conclusion: Chronic oral amiodarone therapy increases the defibrillation energy requirement by approximately 62% in patients with an implantable defibrillator. The combined amiodarone‐desethylamiodarone concentration is directly related to the increase in the defibrillation energy requirement.
Atrial Tachycardias Originating from the Atrial Septum:
Authors: CHEN CHIEN‐CHENG , TAI CHING‐TAI , CHIANG CHERN‐EN , YU WEN‐CHUNG , LEE SHIH HUANG , CHEN YI‐JEN , HSIEH MING‐HSIUNG , TSAI CHIN‐FENG , LEE KUNG‐WEI , DING YU‐AN , CHANG MAU SONG , CHEN SHIH ANN
Published: April 2007

Atrial Tachycardia. Introduction: The characteristics of atrial tachycardia (AT) have varied widely among different reports. The anatomic locations of ATs may bias the results. We propose that septal ATs and free‐wall ATs have different characteristics.

Methods and Results: One hundred forty‐one patients with AT underwent electropharmacologic study, endocardial mapping, and radiofrequency ablation. Forty‐nine (34.7%) patients had septal AT originating from the anteroseptal, mid‐septal, and posteroseptal areas. Tachycardia cycle length was similar between septal AT and free‐wall AT (367 ± 46 msec vs 366 ± 58 msec, P > 0.05). More patients with septal AT required isoproterenol to facilitate induction (44.9% vs 31.5%, P < 0.05). Septal AT was more sensitive to adenosine than free‐wall AT (84.4% vs 67.8%, P < 0.05). Only posteroseptal AT showed a positive P wave in lead V, and negative P wave in all the inferior leads (II, III, aVF). Radiofrequency catheter ablation had a comparable success rate for septal AT and free‐wall AT (96% vs 95%) without impairment of AV conduction. During follow‐up of 49 ± 13 months (range 17 to 85), the recurrence rate was similar for septal AT and free‐wall AT (3.2% vs 4.6%, P = 0.08).

Conclusion: Septal AT has electrophysiologic characteristics that are distinct from those of free‐wait AT. Catheter ablation of the septal AT is safe and effective.
Temporal Organization of Atrial Activity and Irregular Ventricular Rhythm During Spontaneous Atrial Fibrillation:
Authors: GELZER ANNA R.M. , MOISE N. SYDNEY , VAIDYA DHANANJAY , WAGNER KARIN A. , JALIFE JOSÉ
Published: April 2007

Temporal Organization of Atrial Activity. Introduction: Atrial fibrillation (AF) is common in healthy horses. We studied the temporal organization of AF to test the hypothesis that the arrhythmia is governed by a high degree of periodicity and therefore is not random in the horse. Further, we surmised that concealed conduction of AF impulses in the AV node results in an inverse relationship between AF frequency and ventricular frequency.

Methods and Results: Fast Fourier transform (FFT) analysis of atrial activity was done on signal‐averaged ECGs (n = 11) and atrial electrograms (n = 3) of horses with AF at control (C), after quinidine sulfate (22 mg/kg by mouth every 2 hours) at 50% time to conversion (T50), and immediately before conversion (T90) to sinus rhythm. FFT always revealed a single dominant frequency peak. The mean dominant frequency decreased until conversion (C = 6.84 ± 0.85 Hz, T50 = 4.87 ± 1.5 Hz, T90 = 3.41 ± 1.18 Hz; P < 0.001). Mean AA intervals (n = 5WM gradually increased after quinidine. Mean RR intervals (n = 500), standard deviation of the mean ISDM), Poincaré plots, and serial autocorrelograms (SACs) of 500 RR intervals were measured at C and T90 to determine the ventricular response to AF and quinidine‐induced changes in the variability of the ventricular response. Mean RR interval and SDM were reduced after quinidine (C = 1431 ± 266 msec and 695 ± 23 msec; T90 = 974 ± 116 msec and 273 ± 158 msec, respectively: P < 0.01). Poincaré plots and SAC at C and at T90 revealed a significant correlation of consecutive RR intervals typical of a system with a deterministic behavior. At T90, the variability of RR intervals was reduced and the overall periodicity of RR intervals was increased after quinidine administration.

Conclusion: In the horse, AF is a complex arrhythmia characterized by a high degree of underlying periodicity. The inverse AA‐to‐RR interval relationship and reduced variability of RR intervals after quinidine suggest that the ventricular response during AF results from rate‐dependent concealment of AF wavelets bombarding the AV node, which nevertheless results in a significant degree of short‐term predictability of beat‐to‐beat changes in RR intervals.
Existence of Bistability and Correlation with Arrhythmogenesis in Paced Sheep Atria
Authors: OLIVER ROBERT A. , HALL G. MARTIN , BAHAR SONYA , KRASSOWSKA WANDA , WOLF PATRICK D. , TULLOCH ELLEN G. DIXON , GAUTHIER DANIEL J.
Published: April 2007

Bistability and Arrhythmogenesis in Paced Sheep Atria.Introduction:Studies of the electrical dynamics of cardiac tissue are important for understanding the mechanisms of arrhythmias. This study uses high‐frequency pacing to investigate the dynamics of sheep atria.

Methods and Results:A 504‐electrode mapping plaque was affixed to the right atrium in six sheep. Cathodal pacing stimuli were delivered to the center of the plaque. Pacing period (Tp) was decreased from 275 ± 25 msec to 75 ± 25 msec and then increased to 230 ± 70 msec in steps of either 5 or 10 msec. In all 21 trials in six sheep, the atrium responded 1:1 at longer Tps and 2:1 at shorter Tps. As Tpwas decreased, the response switched to 2:1 at a particular Tp. Conversely, as Tpwas increased, the response switched back to 1:1 at a particular Tp. Over 21 trials, the l:1‐to‐2:l and 2:l‐to‐l:l transitions occurred at 119.5 ± 18.8 msec and 130.0 ± 19.1 m.sec, respectively. This hysteretic behavior yielded bistability windows. 10.5 ± 7.2 msec wide, wherein 1:1 and 2:1 responses existed at the same Tp. In 15 trials and in all animals, idiopathic wavefronts emanating from outside the mapped region passed through the mapped region. In 13 of those trials, the idiopathic wavefronts occurred at Tps within the bistability window or within 35 msec of its upper or lower limit.

Conclusion:Bistability windows and idiopathic wavefronts were observed and found to be correlated with each other, suggesting a connection between bistability and arrhythmogenesis.
A Patient with “Atrial Torsades de Pointes”
Authors: KIRCHHOF PAULUS , ECKARDT LARS , MÖNNIG GEROLD , JOHNA ROBERT , LOH PETER , SCHULZE‐BAHR ERIC , BREITHARDT GÜNTER , BORGGREEE MARTIN , HAVERKAMP WILHELM
Published: April 2007

Atrial Torsades de Pointes. A patient with long QT syndrome and a history of palpitations underwent electrophysiologic study. Runs of polymorphic self‐terminating atrial tachyarrhythmias were easily induced and occurred spontaneously several times. Atrial monophasic action potential (MAP) durations were prolonged at short pacing cycle lengths. Premature high right atrial extrastimuli prolonged MAP duration in the low right atrium, resulting in an inverse electrical restitution curve, and increased dispersion of repolarization. MAP morphology showed gradually increasing early afterdepolarizations. When the arrhythmia was initiated, a new action potential reproducibly emerged from these afterdepolarizations. To the knowledge of the authors, this is the first reported case of “atrial torsades de pointes” in a patient.
Long QT Syndrome:
Authors: Rudy Yoram , BENNETT B.
Published: April 2007

Molecular Pharmacology of LQT3. The congenital long QT syndromes (LQTSs) are a group of inherited cardiac disorders that increase the risk of sudden death from ventricular arrhythmias. Individuals with LQTS show abnormalities in cardiac repolarization. Mutations that cause LQTSs are distributed throughout the human genome on chromosomes 3,4,7,11, and 21. Recent molecular genetic studies established that LQT3 results from mutations in the cardiac sodium ion channel gene (SCN5A). Research efforts are aimed at elucidating molecular mechanisms, determining the links between clinical phenotypes and the individual gene mutations, and pharmacologic targeting of the phenotypes. This approach will ultimately guide rational therapy. In addition, LQT3 serves as a model for inherited molecular‐based disorder, as well as a paradigm for understanding the genesis and control of other cardiac arrhythmias.
Arrhythmogenic Right Ventricular Dyspiasia/Cardiomyopathy:
Authors: CORRADO DOMENICO , FONTAINE GUY , MARCUS FRANK I. , MCKENNA WILLIAM J. , NAVA ANDREA , THIENE GAETANO , WICHTER THOMAS
Published: April 2007

Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy. Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a heart muscle disease characterized by peculiar right ventricular involvement and electrical instability that precipitates ventricular arrhythmias and sudden death. The purpose of the present consensus report of the Study Group of the European Society of Cardiology and the Scientific Council on Cardiomyopathies of the World Heart Federation is to review the considerable progress in our understanding of the etiopathogenesis, morbid anatomy, and clinical presentation of ARVD/C since its first description in 1977. This article will focus on the important hut still unanswered issues, mostly regarding risk stratification, clinical outcome, and management of affected patients. Because ARVD/C is relatively uncommon and any one center may have experience with only a few patients, an international registry is being established to accumulate information and enhance the numbers of patients that can be analyzed to answer the pending questions. The registry also will facilitate pathologic, molecular, and genetics research on the etiology and pathogenesis of the disease. Furthermore, availability of an international database will enhance awareness of this largely unrecognized condition among the medical community. Physicians are encouraged to enroll patients in the International Registry of ARVD/C.
Clinical Characteristics of Patients With Spontaneous or Inducible Ventricular Fibrillation Without Apparent Heart Disease Presenting with J Wave and ST Segment Elevation in Inferior Leads
Authors: TAKAGI MASAHTKO , AIHARA NAOHIKO , TAKAKI HIROSHI , TAGUCHI ATSUSHI , SHIMIZU WATARU , KURITA TAKASHI , SUYAMA KAZUHIRO , KAMAKURA SHIRO
Published: April 2007

Ventricular Fibrillation with J Wave in Inferior Leads. Introduction: The clinical characteristics of three patients with spontaneous or inducible ventricular fibrillation (VF) without apparent heart disease, who presented with J wave and ST segment elevation in inferior leads, are described.

Methods and Results: All patients were male and experienced syncope. Their symptoms occurred at night or early in the morning. Holter ECG revealed infrequent premature ventricular complexes. Injection with disopyramide 2 mg/kg augmented ST segment elevation.

Conclusion: These characteristics were very similar to those of patients with Brugada syndrome. These three patients with these specific features might have a variant of Brugada syndrome.
Gender and Seasonally Related Differences in Myocardial Recovery and Susceptibility to Sotalol‐Induced Arrhythmias in Isolated Rabbit Hearts
Authors: SPEAR JOSEPH F. , MOORE E. NEIL
Published: April 2007

Gender and Seasonal Differences in Rabbit Hearts. Introduction: Gender differences and seasonal variations in cardiac electrophysiology and susceptibility to arrhythmias have been described clinically. The present study was undertaken to determine if there are similar gender and seasonally related differences in the electrophysiology of the rabbit heart.

Methods and Results: We analyzed epicardial electrograms, left ventricular endocardial monophasic action potentials (MAPs), and simulated X and Y lead ECGs from 145 isolated rabbit hearts studied over a period of 41 months. Hearts from males had seasonal increases in the duration of myocardial recovery. During the months of June to September compared with October to January and February to May, epicardial activation‐recovery intervals (231.6 ± 23.4 vs 215.6 ± 19.2 and 213.5 ± 18.8 msec, P = 0.003), MAP durations (256.5 ± 25.4 vs 237.0 ± 19.6 and 230.7 ± 26.4 msec, P < 0.001), and QT intervals (278.3 ± 25.6 vs 267.3 ± 11.8 and 261.3 ± 13.0 msec, P = 0.03) were longer. Overall, hearts from females had shorter QT intervals than males (257.7 ± 15.7 vs 270.1 ± 20.3 msec, P < 0.001), and this difference was reflected in their shorter epicardial activationrecovery intervals and MAP durations. However, hearts from females showed a greater prolongation of epicardial recovery (P = 0.007) and greater incidence of arrhythmias (P < 0.001) with sotalol than males. Also, the incidence of arrhythmias was greater in the winter months October to May (P < 0.001).

Conclusion: The isolated rabbit heart provides a spontaneous model of gender and seasonally related differences in cardiac electrophysiology and arrhythmia susceptibility. These differences may be related to variation in the expression of or regulation of the membrane ion channels mediating repolarization.
Left Atrial Myocardial Extension onto Pulmonary Veins in Humans:
Authors: SAITO TSUKASA , WAKI KENJI , BECKER ANTON E.
Published: April 2007

Anatomy of Pulmonary Veins. Introduction: Electrophysiologic studies have shown that spontaneous initiation of atrial fibrillation (AF) by ectopic heats may originate from within pulmonary veins. The extensions of left atrial myocardium are considered to play a role, but there is little detailed anatomic information available. particularly in humans.

Methods and Results: Thirty‐nine human autopsy hearts were studied; 22 with AF and 17 without atrial arrhythmias. The muscle fiber arrangement of the left atrial wall and pulmonary veins was dissected. In 18 hearts, myocardial sleeves were studied microscopically; in five hearts, three‐dimensional reconstruction of the fiber arrangement in the myocardial sleeves was performed. Of 99 pulmonary veins examined, 96 contained a myocardial sleeve. The length of the sleeves was largest in the superior pulmonary veins (P < 0.01). There were no statistically significant differences between uniform and nonuniform muscle fiber arrangements. Microscopic evaluation revealed myocardial sleeves positioned on the adventitial side of the pulmonary vein, separated from the muscular media by a fibrofatty tissue plane. The most distal zone of the myocardial sleeves showed increasing fibrosis with encapsulation of small groups of myocardial cells and eventually with total disappearance of atrophic cells within fibrous tissue. Node‐like structures were not encountered. There was no relationship with presence or absence of AF.

Conclusion: The observation that the peripheral zones of myocardial sleeves are associated with increasing connective tissue deposition between myocardial muscle groups suggests a degenerative change that, from the histologic viewpoint, fits with progressive ischemia. These changes could provide a basis for microreentry and, hence, for atrial arrhythmias.
Computer Model for Study of Cardiac Repolarization
Authors: BERNARDO DIEGO di , MURRAY ALAN
Published: April 2007

Computer Model for Cardiac Repolarization. Introduction: We propose a new and simple method to model repolarization in the left ventricle and the corresponding T waves on the surface ECG.

Methods and Results: We modeled the cardiac cell action potentials (APs) in the left ventricle (LV) with differences in only the duration of the plateau phase. Using published experimental data on the epicardial and endocardial repolarization sequences, or each point on the left ventricular surface we set a different AP repolarization starting time, determined by the duration of the plateau phase. The surface source model was used to compute potentials on the surface of the torso, generated by repolarization of the LV. Both the torso and the LV had homogeneous and isotropic conductivity. We simulated T waves on the 12‐lead ECG and compared our results with measured T waves from five normal subjects. The orientation and shape in each lead were reproduced. In each lead we computed the root mean square error between simulated and measured T waves. The average error across the 12 leads was small, with a mean value of 0.11 mV across all the subjects.

Conclusion: Repolarization of the LV can be modeled independently of the depolarization sequence and AP duration gradients. This method is an easy and powerful tool to describe the ECG features of repolarization.
Marked Reduction of Ventricular Defibrillation Threshold by Application of an Auxiliary Shock to a Catheter Electrode in the Left Posterior Coronary Vein of Dogs
Authors: KENKNIGHT BRUCE H. , WALKER ROBERT G. , IDEKER RAYMOND E.
Published: April 2007

Ventricular Defibrillation with Coronary Venous Electrode. Introduction: For endocardial shocks near the defibrillation threshold (DFT), postshock activity originates from the lateral left ventricular apex, where the shock field is weak. This study tested the hypothesis that an auxiliary shock (AS) delivered between an electrode at this site and a superior vena cava (SVC) electrode before the primary endocardial shock (PS) would reduce the DFT.

Methods and Results: In six pentobarbital‐anesthetized dogs (26 to 36 kg), catheter electrodes were placed in the right ventricular (RV) apex and the SVC. To simulate transvenous introduction, a small electrode was inserted into the posterior cardiac vein using an epicardial approach. For dual shock treatments. AS (2‐m.sec monophasic) was applied to the coronary vein electrode at different time intervals before a biphasic PS (4 msec/3 msec) to the RV‐SVC electrodes. The mean DFT energy for dual shocks treatments were significantly reduced (P < 0.05) in comparison to the control treatment (no AS, 26.5 ± 8.8 J). Mean DFT energy after 10 seconds of electrically induced ventricular fibrillation for dual shocks, in which AS and PS were separated by 1, 5, 10, and 20 msec, were 10.2 ± 4.1 J, 10.9 ± 5.5 J, 11.3 ± 6.3 J, and 15.4 ± 7.2 J, respectively. These values were all significantly lower than the PS alone (26.5 ± 8.8 J).

Conclusion: Addition of an AS from the posterior cardiac vein before an endocardial PS reduces DFT energy by more than 50%. Such DFT reduction could improve therapeutic safety margin or permit reduction in volume of implantable cardioverter defibrillators.
New Approach to Biphasic Waveforms for Internal Defibrillation:
Authors: YAMANOUCHI YOSHIO , FISHLER MATTHEW G. , MOWRHY KENT A. , WILKOFF BRUCE L. , MAZGALEV TODOR N. , TCHOU PATRICK J.
Published: April 2007

Internal Defibrillation with Fully Discharging Capacitors. Introduction: The use of two independent, fully discharging capacitors for each phase of a biphasic defibrillation waveform may lead to the design of a simpler, smaller, internal defibrillator. The goal of this study was to determine the optimal combination of capacitor sizes for such a waveform.

Methods and Results: Eight full‐discharge (95/95% tilt), biphasic waveforms produced by several combinations of phase‐1 capacitors (30, 60, and 90 μF) and phase‐2 capacitors (1/3, 2/3, and 1.0 times the phase‐1 capacitor) were tested and compared to a single‐capacitor waveform (120 μF, 65/65% tilt) in a pig ventricular fibrillation model (n = 12, 23 ± 2 kg). In the full‐discharge waveforms, phase‐2 peak voltage was equal to phase‐1 peak voltage. Shocks were delivered between a right ventricular lead and a left pectoral can electrode. E50s and V50s were determined using a ten‐step Bayesian process. Full‐discharge waveforms with phase‐2 capacitors of ≥40 μF had the same E50 (6.7 ± 1.7 J to 7.3 ± 3.9 J) as the single‐capacitor truncated waveform (7.3 ± 3.7 J), whereas waveforms with phase‐2 capacitors of ≥60 μF had an extremely high E50 (14.5 ± 10.8 J or greater, P < 0.05). Moreover, of the former set of energy‐efficient waveforms, those with phase‐1 capacitors of ≥60 μF additionally exhibited V50s that were equivalent to the V50 of the single‐capacitor waveform (344 ± 65 V to 407 ± 50 V vs 339 ± 83 V).

Conclusion: Defibrillation efficacy can be maintained in a full‐discharge, two‐capacitor waveform with the proper choice of capacitors.
Use of Multisite Electroanatomic Mapping to Facilitate Ablation of Intra‐Atrial Reentry Following the Mustard Procedure
Authors: SOKOLOSKI MARY C. , PENNINGTON JOSEPH C. , WINTON GEORGE J. , MARCHLINSKI FRANCIS E.
Published: April 2007

Multisite Electroanatomic Mapping. Ablation of intra‐atrial reentrant tachycardia following Mustard or Senning procedures has low success rates. The Biosense Carto system was used to map intra‐atrial reentry in a 22‐year‐old woman who had undergone a Mustard procedure. A line of block was created connecting a Mustard baffle suture line to the tricuspid valve annulus, which terminated the arrhythmia and prevented its reinitiation. Multisite electoanatomic mapping was invaluable in defining atrial anatomy and the intra‐atrial reentrant pathway, and in creating a contiguous line of block. This mapping may improve ablation success rates in patients following the Mustard or Senning repair.
Premature Depolarization Concealed in Two Pulmonary Veins
Authors: SCHWARTZMAN DAVID
Published: April 2007

Pulmonary Vein Premature Depolarization. A case is presented in which a premature depolarization emanated from a partially activated left inferior pulmonary vein, activated the entire left superior pulmonary vein, but did not activate the atria (“concealed”). The site of conduction block between each vein and the left atrium was the anatomic atriovenous junction. At times, the same depolarization would activate the atria and initiate atrial fibrillation. The shortest depolarization coupling interval that activated the atria was significantly longer than the atrial fibrillation cycle length recorded in either vein. Observations in this case support two concepts: (I) the existence of myocardial “tracts,” extending into and between pulmonary veins; and (2) a “mismatch” between pulmonary vein activation ingress and egress.
Mini‐Maze Suffices as Adjunct to Mitral Valve Surgery in Patients with Preoperative Atrial Fibrillation
Authors: TUINENBURG ANTON E. , VAN GELDER ISABELLE C. , TIELEMAN ROBERT G. , GRANDJEAN JAN G. , HUET ROLE C.G. , VAN DER MAATEN JOOST M.A.A. , PIEPER ELS G. , DE KAM PIETER J. , EBELS TJARK , CRIJNS HARRY J.G.M.
Published: April 2007

Mini‐Maze and Mitral Valve Surgery. Introduction: After mitral valve (MV) surgery, preoperative atrial fibrillation (AF) often recurs while cardioversion therapy generally fails. Additional Cox maze surgery improves postoperative arrhythmia outcome, but the extensive nature of such an approach limits general appliance. We investigated the clinical outcome of a simplified, less extensive Cox maze procedure (“mini‐maze”) as adjunct to MV surgery.

Methods and Results: Thirteen patients with MV disease and preoperative AF were treated with combined surgery (group 1). Nine control patients without previous AF underwent isolated MV surgery (group 2). We retrospectively compared the results to findings in 23 patients with preoperative AF who had undergone isolated MV surgery (group 3). In group 1, mini‐maze took an additional 46 minutes of perfusion time. One 75‐year‐old patient died of postoperative multiple organ failure. Seven patients showed spontaneously converting (within 2 months) postoperative AF. After 1 year, 82% were in sinus rhythm (SR). No sinus node dysfunction was observed. In group 2, all patients were in SR after 1 year. In group 3, only 53% were in SR after 1 year, despite serial cardioversion and antiarrhythmic drug therapy. Exercise tolerance and heart rate were comparable for groups 1 and 2. Left atrial function was present in all but one patient in group 1 and in all patients in group 2 (after MV reconstruction).

Conclusion: Adding a relatively simple mini‐maze to MV surgery improves arrhythmia outcome in patients with preoperative AF without introducing sinus node dysfunction or persistent absence of left atrial function. The results of this type of combined surgery are encouraging and deserve further attention.
Mechanism for Site‐Dependent Differences in the Shape of the Resetting Response Curve in Fixed Barrier Reentry
Authors: INGELMO CHRISTOPHER , FRAME LAWRENCE H.
Published: April 2007

Site Dependence of Resetting Response Curves. introduction: We investigated whether the site of stimulation within a reentrant circuit affects the resetting response curve (RRC). RRCs are used to characterize the excitable gap of reentrant circuits, including the duration of the fully excitable gap and the presence of partially excitable tissue.

Methods and Results: We reset proximal and distal to a site of interval‐dependent conduction (IDC) in canine in vitro atrial tricuspid rings. Adjustable reentry allowed changes in the cycle length and direction of reentry. In nine preparations we reset 26 tachycardias. In the 16 tachycardias with one site of IDC, RRCs were significantly different when stimulating distal and proximal to a site of interval‐dependent conduction. For the distal curves, the duration of the flat portion was 42 ± 26 msec greater (P < 0.001), the slope of the increasing portion was 0.20 ± 0.17 less (P < 0.02), and the increase in the return cycle was 14 ± 9 msec less (P < 0.001). These differences resulted from early activation of the site of IDC by the antidromic premature impulse when stimulating from distal sites. As a result, the coupling interval of the orthodromic impulse at the site of IDC was the same or greater than at the stimulation site. In 10 tachycardias with multiple sites of IDC, significant differences in the resetting responses did not occur even when the antidromic impulse penetrated one site of IDC.

Conclusion: In a fixed anatomic barrier reentrant circuit with one site of IDC, resetting distal to this site misrepresents the properties of the excitable gap of the entire circuit.
Prediction of Defibrillation Outcome by Epicardial Activation Patterns Following Shocks Near the Defibrillation Threshold
Authors: CHATTIPAKORN NIPON , FOTUHI PARWIS C. , IDEKER RAYMOND E.
Published: April 2007

Activation Patterns and Defibrillation Outcome. Introduction: Ventricular defibrillation is probabilistic and shock strength dependent. We investigated the relationship between defibrillation outcome and postshock activation patterns for shocks of the same strength (‐50% probability of success for defibrillation [ED50] to yield an equal number of successful and failed shocks).

Methods and Results: In five pigs, 10 shocks of ED50 strength (right ventricle‐superior vena cava, biphasic, 6/4 msec) were delivered after 10 seconds of ventricular fibrillation (VF). Epicardial activation sequences following shocks were mapped with a 504‐electrode stock and analyzed by animating dV/dt of the electrograms. Intercycle interval (ICI. time between the onset of successive postshock cycles), wavefront conduction time (WCT, time between the earliest and latest activation of a cycle), and overlapping index (WCT of cycle[n]/ICI of cycle[n+1]) were determined for the first five postshock cycles. An overlapping index > 1 indicates overlap between successive cycles. Of 50 defibrillation attempts, 25 were successes. There was no difference between successful and failed episodes for both ICI (68 ± 9 msec vs 62 ± 10 msec) and WCT (97 ± 24 msec vs 100 ± 14 msec) of cycle 1. However, starting at cycle 2, the ICI was longer, and the WCT was shorter for successful than failed episodes (P < 0.01). Overlapping cycles (index > 1) were found during the transition from cycles 2 through 5 in all failed (index >1) and in no successful episodes.

Conclusions: (1) Defibrillation outcome cannot be determined during the first postshock cycle. (2) At least three rapid successive cycles with overlap of cycles 2 and 3 are present in all failed and in no successful episodes. (3) The overlapping index is a marker to predict defibrillation outcome.
Pacing Following Shocks Stronger than the Defibrillation Threshold:
Authors: CHATTIPAKORN NIPON , FOTUHI PARWIS C. , IDEKER RAYMOND E.
Published: April 2007

VF Induction After Defibrillation Shocks. Introduction: A recent study of shocks near defibrillation threshold (DFT) strength demonstrated that at least three rapid cycles always occur after failed shocks but not after successful shocks, suggestion that the number and rapidity of postshock cycles are important in determining defibrillation success. To test this hypothesis, rapid pacing was performed following a shock stronger than the DFT that by itself did not induce rapid cycles and ventricular fibrillation (VF).

Methods and Results: Epicardial activation was mapped in six pigs using a 504‐electrode sock. The DFT was determined by an up/down protocol with SI shocks (right ventricle‐superior vena cava, biphasic). Ten shocks that were 100 to 200 V above the DFT (aDFT) were delivered after 10 seconds of VF to confirm they always defibrillated. Then, S2, S3, etc., pacing at 5 to 10 times diastolic threshold was performed from the left ventricular apex after aDFT shocks during VF. First, the postshock interval after aDFT shocks was scanned with an S2 stimulus to find the shortest S1‐S2 coupling interval (CI) that captured. This was repeated for S3, S4, etc., until VF was induced. To induce VF after aDFT shocks, three pacing stimuli (S2, S3, S4) with progressively shorter CIs were always required; S2 or S2, S3 never induced VF. For the S2‐S4 cycles, the intercycle interval was shorter (P < 0.01), and the wavefront conduction time was longer (P < 0.0l) for episodes in which VF was induced (n = 57) than for episodes in which it was not (n = 60). Following the S4 cycle that induced VF, two types of spontaneous activation patterns appeared: focal (88%) and reentrant (12%).

Conclusion: VF induction after aDFT shocks always required at least three rapid successive paced‐induced cycles. Thus, the number and rapidity of the first several postshock cycles rather than just the first postshock cycle may be determining factors for defibrillation outcome.
Ablation of Atypical Atrial Flutter Guided by the Use of Concealed Entrainment in Patients Without Prior Cardiac Surgery
Authors: BOGUN FRANK , BENDER BIRGIT , LI YI‐GANG , HOHNLOSER STEFAN H.
Published: April 2007

Ablation of Atypical Atrial Flutter. Introduction: Mapping techniques have not been systematically evaluated with respect to atypical atrial flutter (AF) not involving the inferior vena cava isthmus. The purpose of this study was to assess prospectively the use of concealed entrainment (CE) in mapping of AF and to assess the clinical benefit of ablation of clinically relevant atypical AF.

Methods and Results: In seven consecutive patients without prior cardiac surgery presenting with atypical AF, mapping was performed in the right and, if necessary, left atrium. At sites with CE, radiofrequency energy was delivered. In a posthoc analysis, the endocardial activation time, stimulus‐flutter wave (F) interval, presence of split potentials and diastolic potentials, and postpacing Interval were assessed, and effective sites were compared to ineffective sites. A total of 22 forms of atypical AE either could be induced or were present at the time of the study. Eleven of the 13 targeted atypical AFs (85%) were successfully ablated. The positive predictive value of CE increased from 45% to 75% in the presence of matching electrogram‐F and stimulus‐F intervals or if flutter terminated during entrainment pacing, and to 88% in the presence of split atrial electrograms or diastolic potentials. During short‐term clinical follow‐up, none of the patients had recurrence of the ablated AE. However, the majority of patients required either medication for atrial fibrillation or repeated interventions for new forms of AF.

Conclusion: Mapping and ablation of atypical AF is feasible if sites with CE can be identified. However, the clinical benefit of successful ablations in patients with atypical flutter appears to be limited.