bluuebunny/crossref_metadata_2025 huggingface dataset:
A Prospective Randomized Cross‐Over Comparison of Mono‐ and Biphasic Defibrillation Using Nonthoracotomy Lead Configurations in Humans
Authors: BLOCK MICHAEL , HAMMEL DIETER , BÖCKER DIRK , BORGGREFE MARTIN , BUDDE THOMAS , ISBRUCH FRANK , WIETHOLT DETMAR , SCHELD HANS H. , BREITHARDT GUNTER
Published: May 2007

Biphasic Defibrillation with Nonthoracotomy Leads. Introduction: For current implantable defibrillators, the nonthoracotomy approach to implantation fails in a substantial number of patients. In a prospective randomized cross‐over study the defibrillation efficacy of a standard monophasic and a new biphasic waveform was compared for different lead configurations.

Methods and Results: Intraoperatively, in 79 patients receiving nonthoracotomy defibrillation leads, the defibrillation threshold was determined in the initial lead configuration for the mono‐and biphasic waveform. In each patient, both waveforms were used alternately with declining energies (20, 15,10, 5 J) until failure of defibrillation occurred. Three different initial lead configurations were tested in different, consecutive, nonrandomized patients using a bipolar endocardial defibrillation lead alone (A; n = 36) or in combination with a subcutaneous defibrillation patch (B; n = 24) or array (C; n = 19) lead. The lowest successful defibrillation energy with the biphasic waveform was less than, equal to, or higher than with the monophasic waveform in 64%, 28%, and 8% of patients, respectively, and on average significantly lower with the biphasic waveform for all three lead configurations (A: 11.3 ± 4.4 J vs 14.5 ± 4.5.); B: 9.7 ± 4.7 J vs 15.1 ± 4.5 J; C: 7.9 ± 4.5 J vs 12.4 ± 4.9 J). Defibrillation efficacy at 20 J was significantly improved by the biphasic waveform (91% vs 76%).

Conclusion: In combination with nonthoracotomy defibrillation leads, the biphasic waveform of a new implantable cardioverter defibrillator showed superior defibrillation efficacy in comparison to the standard monophasic waveform. Defibrillation thresholds were improved for lead systems with and without a subcutaneous patch or array lead.
Lack of Evidence for Low‐Dimensional Chaos in Heart Rate Variability
Authors: KANTERS JØRGEN K. , HOLSTEIN‐RATHLOU NIELS‐HENRIK , AGNER ERIK
Published: May 2007

Nonlinear Dynamics in Heart Rate. Introduction: The term chaos is used to describe erratic or apparently random time‐dependent behavior in deterministic systems. It has been suggested that the variability observed in the normal heart rate may be due to chaos, hut this question has not been settled.

Methods and Results: Heart rate variability was assessed by recordings of consecutive RR intervals in ten healthy subjects using ambulatory ECG. All recordings were performed with the subjects at rest in the supine position. To test for the presence of nonlinearities und/or chaotic dynamics, ten surrogate time series were constructed from each experimental dataset. The surrogate data were tailored to have the same linear dynamics and the same amplitude distribution as the original data. Experimental and surrogate data were then compared using various nonlinear measures. Power spectral analysis of the RR intervals showed a 1/f pattern. The correlation dimension differed only slightly between the experimental and the surrogate data, indicating that linear correlations, and not a “strange” attractor, are the major determinants of the calculated correlation dimension. A test for nonlinear predictability showed coherent nonlinear dynamic structure in the experimental data, but the prediction error as a function in the prediction length increased at a slower rate than characteristic of a low‐dimensional chaotic system.

Conclusion: There is no evidence for low‐dimensional chaos in the time series of RR intervals from healthy human subjects. However, nonlinear determinism is present in the data, and various mechanisms that could generate such determinism are discussed.
Gap Junction Protein Phenotypes of the Human Heart and Conduction System
Authors: DAVIS LLOYD M. , RODEFELD MARK E. , GREEN KAREN , BEYER ERIC C. , SAFFITZ JEFFREY E.
Published: May 2007

Connexin Phenotypes in the Human Heart. Introduction: Gap junction channels are major determinants of intercellular resistance to current flow between cardiac myocytes. Alterations in gap junctions may contribute to development of arrhythmia substrates in patients. However, there is significant interspecies variation in the types and amounts of gap junction subunit proteins (connexins) expressed in disparate regions of mammalian hearts. To elucidate determinants of conduction properties in the human heart, we characterized connexin phenotypes of specific human cardiac tissues with different conduction properties.

Methods and Results: The distribution and relative abundance of Cx37, Cx40, Cx43, Cx45, and Cx46 were studied immunohistochemically using monospecific antibodies and frozen sections of the sinoatrial node and adjacent atria, the AV node and His bundle, the bundle branches, and the left and right ventricular walls. Patterns of expression of these connexins in the human heart differed from those in previous animal studies. Sinus node gap junctions were small and sparse and contained Cx45 and apparently smaller amounts of Cx40 but no Cx43. AV node gap junctions were also small and contained mainly Cx45 and Cx40 hut, unlike the sinus node, also expressed Cx43. Atrial gap junctions were larger than nodal junctions and contained moderate amounts of Cx40, Cx43, and Cx45. Junctions in the bundle branches were the largest in size and contained abundant amounts of Cx40, Cx43, and Cx45. Gap junctions in ventricular myocardium contained mainly Cx43 and Cx45; only a very small amount of ventricular Cx40 was detected in subendocardial myocyte junctions and endothelial cells of small to medium sized intramural coronary arteries. Minimal Cx37 and Cx46 immunoreactivity was detected between occasional atrial or ventricular myocytes.

Conclusions: The relative amounts of individual connexins and the number and size of gap junctions vary greatly in specific regions of the human heart with different conduction properties. These differences likely play a role in regulating cardiac conduction velocity. Differences in the connexin phenotypes of specific regions of the human heart and experimental animal hearts must he considered in future experimental or modeling studies of cardiac conduction.
Atrial Fibrillation and Flutter: Maintaining Stability of Sinus Rhythm Versus Ventricular Rate Control
Authors: ANTMAN ELLIOTT M.
Published: May 2007

Atrial Fibrillation and Flutter. Two major treatment strategies have emerged for managing atrial fibrillation: maintaining sinus rhythm by chronic administration of suppressive antiarrhythmic agents versus controlling the ventricular rate and chronic anticoagulation. Potential benefits of maintenance of sinus rhythm include improvement of the hemodynamic profile of the patient, a decreased risk of cerebrovascular accidents, reduced symptoms, and, if atrial fibrillation is successfully suppressed, possible elimination of the need for chronic anticoagulation. When selecting long‐term antiarrhythmic drug therapy for suppression of atrial fibrillation, it should he recalled that at least 50% of patients have a recurrence of the arrhythmia within the first year and the majority of other patients have a recurrence within the next 3 to 5 years. In addition, the risk of proarrhythmia and sudden cardiac death must be considered: this has stimulated interest in nonpharmacologic approaches to maintaining sinus rhythm. Large multicenter randomized trials are now under way to compare the benefits and risks of maintaining sinus rhythm versus controlling the ventricular rate and chronically anti‐coagulating patients in atrial fibrillation. Important endpoints of these trials include mortality, functional capacity, and quality of life.
Elevated Defibrillation Threshold When Right‐Sided Venous Access is Used for Nonthoracotomy Implantable Defibrillator Lead Implantation
Authors: EPSTEIN ANDREW E. , KAY G. NEAL , PLUMB VANCE J. , LYNNETT VOSHAGE‐STAHL B.A.N. , HULL MICHAEL L.
Published: May 2007

Right/Left‐Sided ICD Implantation. Introduction: Although myriad factors influence the defibrillation threshold, the relation between the site of transvenous lead entry into the vascular system and the defibrillation threshold has not been reported. This study examines the influence that venous entry site has on defibrillation success for a transvenous implantable cardioverter defibrillator lead with two defibrillating coils.

Methods and Results: The study population comprised 345 patients. Their mean age was 61 ± 13 years and, left ventricular ejection fraction was 0.33 ± 0.13. A left‐sided approach was used in 324 (93.9%) of the patients, and a right‐sided approach was used in the remaining 21 (6.1%) patients. There was no difference in the gender, age, left ventricular ejection fraction, or underlying cardiac disease in the two groups. For all patients, with a transvenous lead used either alone or with a submuscular or subcutaneous patch, the biphasic defibrillation threshold was 9.9 ± 4.8 J when a left‐sided approach was used, and 14.0 ± 7.3 J when a right‐sided approach was used (P = 0.02). When a transvenous lead was used with a submuscular or subcutaneous patch (115 patients), the biphasic defibrillation threshold was 9.5 ± 4.3 J when a left‐sided approach was used, and 12.0 ± 10.0 J when a right‐sided approach was used (P = 0.98). When a transvenous lead was used without a submuscular or subcutaneous patch (230 patients), the biphasic defibrillation threshold was 10.1 ± 5.0 J when a left‐sided approach was used, and 14.6 ± 6.6 J when a right‐sided approach was used (P < 0.01). For the entire group of patients and for each specific lead arrangement, there was no significant difference in the defibrillating lead system impedance when right‐sided versus left‐sided approaches were compared.

Conclusion: Left‐sided approaches to implant transvenous leads with two coils for defibrillation result in lower biphasic defibrillation thresholds than when right‐sided approaches are used.
Ventricular Action Potential and L‐Type Calcium Channel in Infarct‐Induced Hypertrophy in Rats
Authors: de BRITO SANTOS PAULO EUSTÁQUIO , BARCELLOS LUCIANE CLAUDIA , MILL JOSÉ GERALDO , MASUDA MASAKO OYA
Published: May 2007

Calcium Channel in Infarct‐Induced Hypertrophied Rat Ventricle. Introduction: The present investigation was aimed at characterization of: (1) action potential parameters; and (2) L‐type calcium channels in the hypertrophied ventricular tissue surviving an extensive healed myocardial infarction in the rat.

Methods and Results: Myocardial infarction was produced in Wistar rats by ligation of the left coronary artery. One to 2 months later, their hearts were subjected to electrophysiologic study. The main difference in subendocardial transmembrane potentials recorded with intracellular microelectrodes was an increase in action potential duration (APD). In the left ventricle, the infarcted/sham‐operated APD ratio ranged from 2.7 to 7.2, whereas in the right ventricle it ranged from 1.6 to 2.3 in different regions. When compared with control ceils, ventricular myocytes from infarcted hearts were found to be larger (P < 0.01) and showed a reduction (P < 0.05) in L‐type calcium current (ICa,L) density obtained by whole cell, patch clamp (at 0 mV: 4.44 ± 0.41 in infarcted vs 8.03 ± 1.22 pA/pF in normal). The time course of decay of the currents could be fitted by two exponential functions in both normal and infarcted hearts. There was a tendency toward an increase in the time constant of the slower component of inactivation, T2, significant only at +20 mV (215 ± 25 vs 151 ± 15 msec).

Conclusions: Cardiac hypertrophy of healed infarction in rats is associated with lengthening of the action potential in both ventricles. The main alteration observed in ICa,Lwas a decrease in the current density. Thus, alteration of the calcium channel is not the determinant factor of APD increase
Stability: An ICD Detection Criterion for Discriminating Atrial Fibrillation From Ventricular Tachycardia
Authors: HIGGINS STEVEN L. , LEE ROBERT S. , KRAMER RENA L.
Published: May 2007

Stability, An ICD Detection Criterion. introduction: The purpose of this study was to review a new implantable cardioverter defibrillator (ICD) detection criterion, stability, to determine if it can effectively discriminate rapid rhythms of atrial fibrillation from ventricular tachycardia. Inappropriate shocks for rapid atrial fibrillation limit the acceptance of ICDs. The advent of an additional detection criterion, stability, has been postulated to be of value in discriminating rapid atrial fibrillation, which may not warrant treatment, from ventricular tachycardia, which obviously does warrant therapy delivery.

Methods and Results: Twenty‐six patients were studied during 32 episodes of rapid atrial fibrillation and 24 episodes of monomorphic ventricular tachycardia below 220 beats/min. Each rhythm was repeatedly evaluated by the device at each of the seven stability values available (8, 16, 23, 31, 39, 47, and 55 msec) and then classified as stable or unstable. Upon completion of this acute study, 32 ICD patients bad the stability feature activated and were followed for proper arrhythmia treatment by the device. Using stability windows from 8 to 47 msec, all atrial fibrillation rhythms were appropriately classified as unstable. Three of 6 were classified correctly for the 55‐msec window. All ventricular tachycardia rhythms were appropriately classified as stable for all stability windows from 8 to 55 msec. Clinical follow‐up confirmed appropriate therapy delivery when coupled with sustained rate duration (SRD). Thirty‐two patients followed for 292 patient‐months had no episodes of untreated ventricular tachycardia with 428 successfully classified as stable and treated. Only three episodes of suspected atrial fibrillation resulted in therapy delivery as the rhythm duration exceeded the SRD of 30 seconds.

Conclusions: The CPI Ventak PRx ICD is highly reliable in appropriately classifying atrial fibrillation as unstable and monomorphic ventricular tachycardia as stable for most stability windows evaluating tachycardias below 220 beats/min. As a result, when testing of atrial fibrillation is not possible, we recommend the routine programming of this stability feature at the 31‐msec window with an SRD of 30 seconds. The reliability of this device in discriminating atrial fibrillation from monomorphic ventricular tachycardia may have important clinical implications for other tiered therapy ICDs with this feature as well as for future ICDs in development.
Nonlinear Analysis of Epicardial Atrial Electrograms of Electrically Induced Atrial Fibrillation in Man
Authors: HOEKSTRA BART P.T. , DIKS CEES G.H. , ALLESSIE MAURITS A. , De GOEDB JACOB
Published: May 2007

Nonlinear Analysis of AF in Man. Introduction: We applied methods from the theory of nonlinear dynamics to characterize unipolar epicardial right atrial electrograms of electrically induced atrial fibrillation (AF) in man.

Methods and Results: Electrograms were selected from a high‐density mapping study, which confirmed the existence of at least 3 different types of induced AF (types I, II, and III) in patients undergoing open chest surgery. We analyzed sets of 5 electrograms (4 sec, sampling frequency 1 kHz, resolution 8 bits) in 9 patients (AF type I, n = 3; type II, n = 3; type III, n = 3). The Grassberger‐Procaccia method was applied to estimate the correlation dimension and correlation entropy from the electrograms. In 2 patients (AF type I) some electrograms (2 of 5 and 3 of 5, respectively) showed scaling at normalized distances ranging from 0.2 to 0.5 in phase space. Correlation dimension D ranged from 1.8 to 3.2 and correlation entropy K from 2.2 to 3.8 nats/sec. The patients were ranked according to increasing coarse‐grained correlation dimension Dcg (range 3.7 to 7.9) and coarse‐grained correlation entropy Kcg (range 5.6 to 18.6 nats/sec). The method of surrogate data was applied to detect nonlinearity in the electrograms. Using the correlation integral as test statistic, it could be excluded that electrograms of type I AF have been generated by linear stochastic dynamics. Episodes of sinus rhythm (D ranging from 1.0 to 5.1 and K from 2.0 to 8.6 nats/sec) and induced atrial flutter (D ranging from 2.7 to 4.2 and K from 2.2 to 4.2 nats/sec) in 2 different patients showed features of low‐dimensional chaos.

Conclusion: Nonlinear analysis discriminated between electrograms during electrically induced AF in humans. The results are consistent with a classification of AF into 3 types based on the spatiotemporal complexity of right atrial activation patterns.
The Molecular Basis of Anisotropy: Role of Gap Junctions
Authors: SAFFITZ JEFFREY E. , DAVIS LLOYD M. , DARROW BRUCE J. , LEE KANTER H. , LAING JAMES G. , BEYER ERIC C.
Published: May 2007

Role of Gap Junctions in Anisotropic Conduction. Electrical activation of the heart requires transfer of current from one discrete cardiac myocyte to another, a process that occurs at gap junctions. Recent advances in knowledge have established that, like most differentiated cells, individual cardiac myocytes express multiple gap junction channel proteins that are members of a multigene family of channel proteins called connexins. These proteins form channels with unique biophysical properties. Furthermore, functionally distinct cardiac tissues such as the nodes and bundles of the conduction system and atrial and ventricular muscle express different combinations of connexins. Myocytes in these tissues are interconnected by gap junctions that differ in a tissue‐specific manner in terms of their number, size, and three‐dimensional distribution. These observations suggest that both molecular and structural aspects of gap junctions are critical determinants of the anisotropic conduction properties of different cardiac tissues. Expression of multiple connexins also creates the possibility that “hybrid” channels composed of more than one connexin protein type can form, thus greatly increasing the potential for fine control of intercellular ion flow and communication within the heart.
Evidence for Electrical Organization During Ventricular Fibrillation in the Human Heart
Authors: CLAYTON RICHARD H. , MURRAY ALAN , CAMPBELL RONALD W.F.
Published: May 2007

Electrical Organization During VF.Introduction: Ventricular fibrillation is a most dangerous cardiac arrhythmia that has received considerable attention, yet its pattern of electrical activation remains controversial. The aim of this study was to investigate the degree of organization during the clinical arrhythmia and to examine the phase relationship between deflections in independent ECG leads.

Methods and Results: Ten recordings of ventricular fibrillation were examined. Each had been provoked during routine electrophysiological study. The mean duration of ventricular fibrillation was 21 seconds (range 11 to 34). Independent and approximately orthogonal ECG leads I, aVF, and V2were recorded to computer at a sampling rate of 250 Hz. The phase relationship of each ECG lead pair was measured from the lag of peaks in their cross‐correlation function (CCF). In 61% of The 1‐second ECG epochs analyzed, CCF peak lag changed by < 20 msec compared to The previous epoch. Thus, the overall phase relationship was stable most of the time. Changes in CCF peak lag tended to be either gradual or to punctuate periods of stability.

Conclusions: This study provides evidence of organized myocardial activation during human ventricular fibrillation.
Application of an Electrocardiographic Inverse Solution to Localize Ischemia During Coronary Angioplasty
Authors: MACLEOD ROBERT S. , GARDNER MARTIN , MILLER ROBERT M. , HORÁC̆UEK B. MILAN
Published: May 2007

Localization of Ischemia. This study demonstrates the utility of an electrocardiographic Localization of Ischemia. This study demonstrates the utility of an electrocardiographic Inverse solution, coupled with body surface potential mapping (BSPM), in localizing acute ischemia in patients undergoing percutaneous transluminal coronary angioplasty (PTCA). PTCA balloon inflations produce complete occlusion and acute transient ischemia, which can be detected electrocardiographically with BSPM. Comparisons between maps recorded both during and before the inflation of the PTCA balloon allow patient‐ and artery‐specific characterizations of the resulting ischemia. Knowledge of the patient's coronary anatomy and the location of the occlusion site by coronary angiography permit an estimation based on cardiac hemodynamics of the region of myocardium most likely to suffer from PTCA‐induced ischemia. Electrocardiographic inverse solutions provide a means of predicting cardiac potentials from body surface maps. In this study, we describe an inverse solution we have developed to localize the transient ischemia produced by PTCA. To validate the procedure, we compared the locations of predicted ischemia in seven patients with a qualitative estimate of the perfusion region based on fluoroscopic examination of each patient's coronary anatomy and PTCA balloon location. In each case, the region of ischemia predicted by the model included the perfusion zone determined fluoroscopically. These results suggest that electrical changes induced by acute ischemia can be localized with an electrocardiographic inverse solution.
The Architecture of the Atrioventricular Conduction Axis in Dog Compared to Man:
Authors: YEN HO SIEW , KILPATRICK LUCIENNE , KANAI TAKAO , GERMROTH PATRICIA G. , THOMPSON ROBERT P , ANDERSON ROBERT H.
Published: May 2007

AV Node in Dog and Man. Introduction Advances in treating patients with dual atrioventricular nodal pathways have called for a better understanding of the morphology of the approaches to the atrioventricular node. In this respect, it has recently been suggested that, in dog, anatomically discrete muscle bundles originating from the sinus node represent the substrate of the dual pathways recognized electrophysiologically in patients with atrioventricular nodal reentrant tachycardia. This concept is at odds with most anatomic studies of the human specialized atrioventricular juuctional area. In this study, therefore, we studied histologically the junctional area in dog hearts, comparing them with our own findings in human heart and the descriptions of the earliest investigators.

Methods and Results: Five dog and six human hearts were prepared for histology and sectioned serially in different planes. Reconstructions were then made from each of three dog and two human hearts sectioned in orthogonal planes. Gross differences in the anatomy of the atrioveutricular junctional area and in the structure of the conduction system were obvious between dog and human hearts. The penetrating portion of the conduction axis was longer in the dog, being much more extensively embedded in the central fibrous body. The atrioventricular node, in both dog and man, was composed of a zone of transitional cells overlying a compact region. The zone of transitional cells in the dog was more extensive posteriorly than anteriorly. No bundles insulated anatomically by fibrous tissue were found either in the internodal atrial myocardium or in the approaches to the atrioventricular node. Our findings in both dog and man are comparable with the initial descriptions of the atrioventricular junctional area.

Conclusion: Although the disposition of the conduction system in dog and man is basically similar, there are important differences which relate to the gross anatomy. The anatomic substrate for functional duality of the inputs to the atrioventricular node remains unclear, since our study confirms that the concept of insulated atrionodal tracts has no morphologic basis.
Catheter Ablation of the Left Bundle Branch for the Treatment of Sustained Bundle Branch Reentrant Ventricular Tachycardia
Authors: BLANCK ZALMEN , DESHPANDE SANJAY , JAZAYERI MOHAMMAD R. , AKHTAR MASOOD
Published: May 2007

Sustained Bundle Branch Reentrant VT. Radiofrequency catheter ablation of the left bundle branch (LBB) was attempted in a patient with sustained bundle branch reentry. During sinus rhythm, the QRS had a complete LBB block pattern, and the LBB was activated retrogradely (transseptal). Ablation of the LBB eliminated inducibility of the tachycardia, while the QRS complex and the duration of the HV interval (70 msec) remained unchanged. Successful ablation of the LBB eliminated bundle branch reentry and yet maintained the anterograde conduction properties of the His‐Purkinje system, obviating implantation of a permanent pacemaker.
Effect of Isoproterenol on Accessory Pathways Without Overt Retrograde Conduction
Authors: LI HUAGUI G. , YEE RAYMOND , KLEIN GEORGE J.
Published: May 2007

Effect of Isoproterenol on Accessory Pathways. Introduction: Absence of overt retrograde accessory pathway conduction may be related to low resting sympathetic tone in patients with apparent unidirectional anterogradely conducting accessory pathways (UACAP).

Methods and Results: To test this hypothesis, we studied the effect of isoproterenol on accessory pathway function and tachycardia induction in 18 patients (12 men and 6 women, ages 34 ± 16 years [mean ± SD]) with UACAP. After baseline study in the drug‐free state, electrophysiologic testing was repeated during infusion of isoproterenol (0.5 to 1.5 μg/min, titrated to increase heart rate by 20%). Isoproterenol shortened the anterograde effective refractory period (398 ± 117 vs 305 ± 63 msec; P < 0.01; basic drive cycle length 600 msec) of the accessory pathway. However, retrograde accessory pathway conduction and atrioventricular reentrant tachycardia were exposed in only 3 (17%) patients by isoproterenol infusion. All 3 patients with retrograde accessory pathway revealed after isoproterenol had clinically documented tachycardia (supraventricular tachycardia in 2, atrial fibrillation in 1) during exercise, while none of the patients with persistent absence of retrograde accessory pathway conduction had this symptom.

Conclusions: We conclude that absence of overt retrograde conduction over accessory pathways may be related to low resting sympathetic tone in some individuals. Restoration of retrograde conduction with isoproterenol is unusual and most likely to be observed in patients with clinically documented paroxysmal supraventricular tachycardia related to exercise.
Activation Time Determination by High‐Resolution Unipolar and Bipolar Extracellular Electrograms in the Canine Heart
Authors: NDREPEPA GJIN , CAREF EDWARD B. , YIN HONG , El‐SHERIF NABIL , RESTIVO MARK
Published: May 2007

Activation Time Determination by High‐Resolution Electrograms. Introduction: To identify the optimal criteria for activation time (AT) determination of bipolar electrograms from normal hearts, a high‐resolution cross electrode array comprising 128 unipolar electrodes of 500‐μm spacing was used to record extracellular potentials from the left ventricular epicardium of 12 dog hearts.

Methods and Results: Recordings were made during broad wavefront propagation (B wave) local elliptical wavefront propagation (E wave). Characteristics of 863 bipolar electrograms (1‐mm spacing) were constructed from unipolar data standardized for differences in polarity, then classified morphologically. Features for bipolar AT determination were compared to the time of the negative peak of the firrst temporal derivative of a unipolar electrogram situated mid‐way between the bipoles. During B wave, three distinct morphologies were observed: unipbasic (61%), biphasic (23%), and triphasic (16%). Peak voltage of uniphasic and triphasic signals was the best predictor of AT (error: 0.6 ± 0.6 msec and 0.6 ± 0.8 msec, respectively). During E wave, parallel orientation of the bipoles with respect to the direction of impulse propagation wavefront resulted in uniphasic signals (> 99%), while for perpendicular orientation of the bipoles, electrogram morphology was variable. For parallel orientation of the bipoles, peak negative voltage was the best predictor of AT for both longitudinal and transverse propagation, while for perpendicular bipole orientation, peak negative voltage was a less reliable predictor for propagation along both fiber axes. Increasing interpolar distance resulted in a degradation in AT accuracy for B wave (from 0.6 ± 0.6 msec at 1 mm to 1.1 ± 1.2 msec at 7 mm) and for E wave (from 0.4 ± 0.3 msec at 1 mm to 3.1 ± 2.9 msec at 7 mm).

Conclusions: (1) The accuracy of bipolar electrograms is sensitive to wavefront direction, bipole orientation, and interpolar distance; (2) peak negative voltage of uniphasic and triphasic signals is a reliable predictor of AT, but only for B wave; (3) a maximum interpolar distance of 2 mm and bipole orientation parallel to the direction of the impulse wavefront are minimally required for accurate determination of AT during impulse propagation initiated near the recording electrodes; and (4) for impulses initiated near the recording site in normal tissue, a bipbasic or triphasic morphology almost certainly indicates that the bipolar electrode is oriented perpendicular to the wavefront direction, irrespective of fiber orientation.
The Effect of Flunarizine and Ryanodine on Acquired Torsades de Pointes Arrhythmias in the Intact Canine Heart
Authors: VERDUYN S. CORA , VOS MARC A. , GORGELS ANTON P. , van der ZANDE JOLANDA , LEUNISSEN JET D.M. , WELLENS HEIN J.
Published: May 2007

Flunarizine and Ryanodine in Acquired TdP. Introduction: Ryanodine, a specific blocker of the Ca2+ release channel of the sarcoplasmic reticulum, and flunarizine, a[Ca2+], overload blocker, possess antiarrhythmic effects against delayed after depolarizations (DADs) and DAD‐dependent arrhythmias. In vitro controversy exists about their effect on early after depolarizations (EADs): no effect was reported on cesium‐induced EADs, while ryanodine did prevent EADs induced by isoproterenol. To study the possible role of intracellular Ca2+ overload in acquired EAD‐dependent torsades de pointes (TdP) arrhythmias, we tested the effects of flunarizine and ryanodine in our animal model of TdP.

Methods and Results: Anaesthetized dogs with chronic AV block received d‐sotalol or almokalant followed by pacing. A subset of dogs with reproducible TdP (≥ 3 times) were selected to receive flunarizine (2 mg/kg per 2 min) or ryanodine (10 μg/kg per 10 min). After dsotalol, TdP was induced at a mean cycle length of the idioventricular rhythm (CL‐IVR) of 2070 ± 635 msec and a QT(U) interval of 535 ± 65 msec. Induction of TdP was prevented by flunarizine in all experiments (8/8): electrophysiologically this was associated with a decrease in CL‐IVR, QT(U), and QTc interval (390 ± 100 to 320 ± 45, P < 0.05). Ryanodine prevented TdP induction in 4 of 5 experiments and decreased the CL‐IVR, QT(U), and the QTc interval from 385 ± 75 to 320 ± 20 msec (P < 0.05). Both drugs also suppressed the almokalant‐induced EADs and related ectopic activity. This antiarrhythmic action corresponded with the inability to reinduce TdP by pacing.

Conclusions: Blockade of the Ca2+ release channel of the sarcoplasmic reticulum by ryanodine or the reduction of [Ca2+] overload by flunarizine prevents induction of EAD‐dependent acquired TdP arrhythmias, suggesting a role for [Ca2+]i overload in acquired TdP.
Radiofrequency Ablation of Atrial Flutter
Authors: COSIO FRANCISCO G. , ARRIBAS FERNANDO , LÓPEZ‐GIL MARÍA , GONZÁLEZ H. DANIEL
Published: May 2007

RF Ablation of Atrial Flutter. Activation mapping in common atrial flutter has shown circular (reentrant) activation of the right atrium around anatomic structures and areas of functional block. The direction of rotation is counterclockwise (in a frontal view), and in the low right atrium the myocardium between the inferior vena cava (IVC) and the tricuspid valve (TV) is critical to close the activation circle. The circuit can be interrupted by radiofrequency ablation of the myocardium between the TV and the IVC, and, in some cases, by ablation between the coronary sinus and TV. Flutter interruption does not mean complete isthmus ablation, as it may remain inducible, requiring further ablation. Despite attaining noninducibility, flutter may recur, and new procedures may be needed for complete ablation. Atrial fibrillation occurs in up to 30% of the cases during follow‐up but is generally well controlled with antiarrhythmic drugs that were ineffective in treating flutter before ablation. Some noncommon atrial flutters show circular right atrial activation in a reversed (clockwise) direction, with the same critical areas in the low right atrium, and in these isthmus ablation is effective. Other noncommon flutters have different substrates in the right or left atrium, and mapping has to define specific critical isthmuses as ablation targets in each case. Left atrial flutter circuits remain inaccessible to ablation.
Variants of Preexcitation—Specialized Atriofascicular Pathways, Nodofascicular Pathways, and Fasciculoventricuiar Pathways:
Authors: KOTTKAMP HANS , HINDRICKS GERHARD , SHENASA HOSSEIN , CHEN XU , WICHTER THOMAS , BORGGREFE MARTIN , BREITHARDT GUNTER
Published: May 2007

Variants of Preexcitation. introduction: In the present report, the electrophysiiologic findings in patients with different types of variants of preeexcitwtion, i.e., atriofascicualr, nodofacicular, and fasciculoventricular fibers, and the results of radiofrequency catheter ablation using different target sites are described.

Methods and Results: Twelve patients (mean age 36 ± 17 years) with variants of the preexcitation syndromes underwent electrophysiologic study and radiofrequency catheter ablation. The atrial origin of atriofascicular pathways remote from the normal AV node was assessed by application of late atrial extrastimuli that advanced (“reset”) the timing of the next QRS complex without anterograde penetration into the AV node. In patients with atriofacicular pathways, ablation of the accessory pathway or the retrograde fast AV node pathway was attempted. Ablation of the atriofascicular pathways was guided by a stimulus‐delta wave interval mapping in the first live patients and by recording of atriofascicular pathway activation potentials in the next five patients. A nodofascicular pathway was suggested if VA dissociation occurred during tachycardia and if atrial extrastimuli failed to reset the tachycardia without anterograde penetration into the AV node. A fasciculoventricular connection was suggested if the proximal insertion of the accessory pathway was found to arise from the His bundle or bundle branches. The PR interval was expected within normal limits during sinus rhythm and the QRS complex to he slightly prolonged with a discrete slurring of the R wave, suggesting a small delta wave. Ten of the 12 patients had evidence for atriofascicular pathways and one patient each for a nodofascicular and fasciculoventricular pathway. In six patients, the atriofascicular pathways were successfully ablated, and in two patients, the retrograde fast AV node pathway. In one patient, a concealed right posteroseptal accessory AV pathway served as the retrograde limb and was successfully ablated. The nodofascicular pathway was shown to he a bystander during AV node reentrant tachycardia. After successful fast AV node pathway ablation resulting in marked PR prolongation, no preexcitation was present during sinus rhythm because of the proximal insertion of the nodofascicular pathway distal to the delay producing parts of the AV node. The proximal insertion of the fasciculoventricular pathway was suggested to arise distal to the AV node at the site of the penetrating AV bundle. The earliest ventricular activation at the His‐bundle recording site indicated the ventricular insertion of this accessory connection into the ventricular summit. The fasciculoventricular connection gave rise to a fixed ventricular preexcitation and served as a bystander during orthodromic AV reentrant tachycardia incorporating a left‐sided accessory AV pathway.
Electrocardiographic Patterns and Results of Radiofrequency Catheter Ablation of Clockwise Type I Atrial Flutter
Authors: SAOUDI NADIR , NAIR MOHAN , ABDELAZZIZ AHMED , POTY HERVE , DAOU ABDOU , ANSELME FREDERIC , LETAC BRICE
Published: May 2007

Clockwise Rotation of Atrial Flutter. Introduction: Counterclockwise right atrial propagation is usually observed in common atrial flutter, but little is known regarding flutter with clockwise right atrial rotation. The aim of this study is to describe the ECG characteristics and results of catheter ablation of atrial flutter with clockwise right atrial rotation.

Methods and Results: Among the 38 patients with type I atrial flutter in this study population, right atrial impulse propagation was counterclockwise in 20 and clockwise in 8. In the remaining 10 patients, both clockwise and counterclockwise patterns were seen. Clinical and ECG parameters associated with clockwise flutter were compared to those of 28 cases of counterclockwise atrial flutter. Ablation was performed in 11 of 18 cases using a technique identical to that used for counterclockwise flutter. A classical “sawtooth” pattern of the flutter wave was observed in 28 of 28 counterclockwise and 14 of 18 clockwise flutter. A shorter plateau phase, a widening of the negative component of the F wave in the inferior leads, and a negative F wave in V1 were the most consistent findings in clockwise flutter. Coronary sinus recording always showed septal to lateral left atrial impulse propagation. Ablation was successful in 11 of 11 cases of clockwise flutter in whom this procedure was performed, with 9.5 ± 11.6 radiofrequency pulses delivered between the tricuspid valve and the coronary sinus ostium (n = 5) or the inferior vena cava (n = 5), and in the proximal coronary sinus (n = 1). After a follow‐up of 46.6 weeks, two recurrences of clockwise flutter were encountered, which were successfully treated with a second session.

Conclusion: Contrary to commonly accepted concepts, clockwise rotation of atrial flutter Ls not an infrequent phenomenon and can mimic counterclockwise rotation. It can also be successfully ablated by radiofrequency pulses.
Alternation of Atrioventricular Nodal Conduction Time During Atrioventricular Reentrant Tachycardia:
Authors: AMELLAL FARID , HALL KEVIN , GLASS LEON , BILLETTE JACQUES
Published: May 2007

AV Nodal Conduction Time Alternation. Introduction: Alternation of atrial cycle length and AV nodal conduction time (NCT) is often observed during AV reentrant tachycardia. Both AV nodal dual pathway and rate‐dependent function have been postulated to be involved in this phenomenon. This study was designed to determine the respective role of these two mechanisms in the alternation observed in an in vitro model of orthodromic AV reentrant tachycardia.

Methods and Results: The tachycardia was produced by detecting each His‐bundle activation and stimulating the atrium after a retrograde delay, thereby simulating retrograde pathway conduction, in six isolated rabbit heart preparations. After a 5‐minute stabilization period at a fast rate, the retrograde delay was decremented by 2 msec every minute until nodal blocks occurred. We observed a sequential alternation of the cycle length and NCT in four preparations in the short retrograde delay range. The magnitude of the alternation gradually increased as the retrograde delay was decreased and reached 4.6 ± 0.5 msec during 1:1 conduction. The alternation increased further just prior to termination of the tachycardia by an AV nodal block. None of the preparations showed discontinuous AV nodal recovery curves. Moreover, an electrode positioned over the endocardial surface of the node showed that the alternation developed distally to the nodal inputs, which are believed to constitute a major component of dual pathways. A mathematical model predicted the alternation from known characteristics of rate‐dependent nodal functional properties.

Conclusions: NCT and cycle length alternation can arise during orthodromic AV reentrant tachycardia when the retrograde delay is sufficiently short. The characteristics of the alternation, presence of continuous recovery curves, intranodal location of the alternation, and mathematical modeling suggest that the alternation is predictahle from the known functional properties of the AV node without postulating dual pathway physiology.
Polymorphic Ventricular Tachycardia Induced by Intracoronary Injection of Ioxaglate in a Patient with Borderline QT Prolongation
Authors: EMORI TETSURO , FUJIEDA HIROYUKT , OHE TOHRU
Published: May 2007

Ioxaglate‐Induced Polymorphic VT. A 68‐year‐old female patient with borderline QT prolongation developed polymorphic ventricular tachycardia soon alter intracoronary injection of ioxaglate. There was no coronary stenosis or vasospasm. To investigate abnormality of the ventricular repolarization, we recorded the monophasic action potential (MAP) during coronary angiography. Ioxaglate prolonged the MAP duration regionally in the perfused area and produced temporal dispersion of ventricular repolarization.
Autonomic Influences in Atrial Tachyarrhythmias
Authors: COUMEL PHILIPPE
Published: May 2007

Atrial Tachyarrhythmias. The electrophysiologic characteristics of atrial cells (action potential duration and refractoriness, conduction speed) are modulated differently by vagal and sympathetic influences. The former tend to favor macroreentry phenomena, whereas the latter favor abnormal automaticity and triggered activity. In normal hearts, vagal influences are predominant, thus explaining why the Clinical pattern of vagally mediated paroxysmal atrial fibrillation is preferentially observed in the absence of detectable heart disease, in young male adults, with an ECG pattern of common flutter alternating with fibrillation. Sympathetically mediated atrial fibrillation is observed in the presence of any heart disease, the first effect of which is to provoke a vagal withdrawal. The clinical history is a reliable guide for determining which type of physiologic autonomic predominance contributes to destabilization of the arrhythmogenic substrate, but observing the behavior of sinus rate variability just preceding the onset of the arrhythmia only permits documentation of the mechanism. The role of autonomic influences should be taken into consideration every time conventional antiarrhythmic treatment is insufficient. Beta blockers as well as digitalis may be either beneficial or detrimental, depending on the causal mechanism, so the choice of their use as a single or a combined therapy should be appropriate.
Dimension and Related Anatomical Distance of Koch's Triangle in Patients with Atrioventricular Nodal Reentrant Tachycardia
Authors: UENG KWO‐CHANG , CHEN SHIH‐ANN , CHIANG CHERN‐EN , TAI CHING‐TAI , LEE SHIH‐HUANG , CHIOU CHUEN‐WONG , WEN ZU‐CHI , TSENG CHI‐JEN , CHEN YI‐JEN , YU WEN‐CHUNG , CHEN CHUNG‐YIN , CHANG MAU‐SONG
Published: May 2007

Koch's Triangle in AVNRT. Introduction: The dimension of Koch's triangle in patients with AV nodal reentrant tachycardia has not been well described. Understanding the dimension and anatomical distance related to Koch's triangle might be useful in avoiding accidental AV block during ablation of the slow pathway. The purposes of this study were to define the dimension of Koch's triangle and its related anatomical distance and correlate these parameters with the successful ablation sites in patients with AV nodal reentrant tachycardia.

Methods and Results: We studied 218 patients with AV nodal reentrant tachycardia. The distance between the presumed proximal His‐bundle area and the base of the coronary sinus orifice (DHis‐Os) measured in the right anterior oblique view was used to define the dimension of Koch's triangle. The distance of the proximal His‐bundle recording site from the successful ablation site (DHis‐Ab) and the distance as a fraction of the entire length of Koch's triangle (DHis‐Ab/DHis‐Os) were determined. The mean DHis‐Os, and DHis‐Ab were 25.9 ± 7.9 and 13.4 ± 3.8 mm, respectively. DHis‐os negatively correlated with patient age (r = ‐0.41, P < 0.0001) and body mass index (r = ‐0.18, P = 0.004). Among the patients with successful ablation sites in the medial area, DHis‐Os was longer (27.2 ± 6.6 vs 24.6 ± 8.4 mm, P < 0.005), DHis–Ab was similar (12.9 ± 3.1 vs 13.9 ± 4.0, P > 0.05) and DHis‐Ab/DHis‐Os was smaller (0.48 ± 0.04 vs 0.74 ± 0.11, P < 0.05). Furthermore, the patients with successful ablation sites in the medial location needed more radiofrequency pulse numbers than those in the posterior location (6 ± 4 vs 4 ± 3, P < 0.05).

Conclusion: The site of successful slow pathway ablation was consistently about 13 mm from the site recording the proximal His‐bundle deflection in patients with AV nodal reentrant tachycardia despite marked variability in the dimensions of Koch's triangle: therefore, patients with large triangles required ablation in the medial region rather than the posterior region. Care should be taken when delivering radiofrequency energy to the posteroseptal area in patients with shorter DHis‐Os to avoid injury to AV node.
Effect of Coronary Perfusion of Heptanol on Conduction and Ventricular Arrhythmias in Infarcted Canine Myocardium
Authors: CALLANS DAVID J. , MOORE E. NEIL , SPEAR JOSEPH F.
Published: May 2007

Effect of Heptanol in Healed Infarction. Introduction: Abnormal cellular coupling is a major constituent of the slow, dissociated conduction that supports ventricular tachycardia (VT) following myocardial infarction. Agents that modulate cellular coupling may exert either proarrhythmic or antiarrhythmic effects.

Methods and Results: The effects of modulating cellular coupling on conduction and susceptibility to inducible VT were studied in 11 dogs with healed left anterior descending (LAD) infarction. The LAD circulation was isolated and supplied with arterial blood via a constant‐flow bypass system. Localized intracoronary infusion of heptanol, an agent with relatively specific effects on intracellular coupling, was performed using this bypass system. Heptanol produced dose‐dependent changes in cardiac conduction, assessed by delayed local activation times in sinus rhythm (0.5 mM: 11.9%± 11.0% change, P = 0.005; 1.0 mM: 45.8%± 25.5% change, P = 0.0004) and slowed conduction velocity both transverse and longitudinal to fiber orientation. Sustained VT was not induced in any of the control animals. During infusion of 0.5 mM heptanol, uniform sustained VT was inducible in 4 of 11 animals (P = 0.027). During infusion of 1.0 mM heptanol, sustained VT was induced in only 1 of 9 animals.

Concltisions: In the canine model of healed myocardial infarction, heptanol had a bimodal effect on susceptibility to inducible VT. Low‐dose heptanol facilitated the induction of sustained VT, and high‐dose heptanol had an antiarrhythmic effect. This suggests that agents that modulate coupling may significantly modify susceptibility to VT following myocardial infarction.
Electrophysiologic Study and Radiofrequency Ablation in Patients with Intracardiac Tumors and Accessory Pathways:
Authors: VAN HARE GEORGE E. , PHOON COLIN K. , MUNKENBECK FRAN , PATEL CHANDRAKANT R. , FINK DANIEL L. , SILVERMAN NORMAN H.
Published: May 2007

Ablation with Intracardiac Tumors.Introduction: There is a strong association of cardiac rhabdomyomas with the Wolff‐Parkinson‐White syndrome. This report describes the results of investigations in two patients with accessory pathway‐mediated AV reciprocating tachycardia coexisting with intracardiac tumors.

Methods and Results: Two patients with intracardiac tumors had mapping of the accessory pathway. Echocardiograms obtained in the electrophysiology laboratory while the ablation catheter was at the site of successful radiofrequency ablation demonstrated a close correspondence between the site of intracardiac tumor and the location of the accessory pathway.

Conclusions: These results lend support to the hypothesis that accessory pathways in patients with intracardiac tumors, such as rhabdomyomas, are not typical Kent bundles, hut instead are either part of the intracardiac tumor or are closely related to the tumor. Ablation is possible in at least some patients with accessory pathways associated with intracardiac tumors.