bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Effect of β‐Adrenergic Stimulation on the Frequency‐Dependent Electrophysiologic Actions of the New Class III Antiarrhythmics Dofetilide, Ambasilide, and Chromanol 293.
Authors: SCHREIECK JÜRGEN , WANG YANGGAN , GJINI VIKTOR , KORTH MICHAEL , ZRENNER BERNHARD , SCHÖMIG ALBERT , SCHMITT CLAUS
Published: April 2007

Class III Antiarrhythmics and β‐Adrenergic Stimulation. Introduction: Blockade of the rapid delayed rectifier potassium current (IKr) as an important mechanism for current Class III antiarrhythmics is less effective in action potential prolongation during β‐adrenergic activation. We hypothesized that blockade of the increased slow IK (IKs) current during β‐adrenergic stimulation could improve action potential prolongation and tested this hypothesis by comparison of three different IK blockers: dofetilide, a selective blocker of IKr; ambasilide, a nonselective blocker of IK; and chromanol 293B, a selective blocker of IKs.

Methods and Results: Transmembrane action potential duration was determined in guinea pig papillary muscles. After equilibration with the potassium channel blockers (dofetilide 10 nM, amhasilide 10 μM, chromanol 293B 10 μM), isoproterenol (10 and 100 nM) was added. The action potential prolonging effect of dofetilide was reduced in the presence of increasing concentrations of isoproterenol whereas the effect of ambasilide was much less reduced. In contrast, the effect of chromanol 293B clearly was increased in the presence of both concentrations of isoproterenol. No afterdepolarizations were observed after application of isoproterenol in control. Following isoproterenol, but not before, dofetilide and chromanol 293B induced early afterdepolarizations in 20% and 17% of the papillary muscles, whereas ambasilide and chromanol 293B induced delayed afterdepolarizations in 27% and 17%, respectively.

Conclusion: In contrast to dofetilide, the Class III effect of ambasilide is less reduced and the effect of chromanol 293B is enhanced during β‐adrenergic stimulation. Our data support the hypothesis that IKs blockade improves the efficacy of antiarrhythmics in action potential prolongation during β‐adrenergic activation; however, this effect may increase the risk of afterdepolarizations.
Long‐Term Results of Visually Guided Left Ventricular Reconstruction as Single Therapy to Treat Ventricular Tachycardia Associated with Postinfarction Anteroseptal Aneurysm
Authors: SOSA EDUARDO , SCANAVACCA MAURICIO , D'AVILA ANDRE , FUKUSHIMA JULIA , JATENE ADIB
Published: April 2007

Visually Guided Left Ventricular Reconstruction for Recurrent VT. Introduction: Postinfarction ventricular tachycardia (VT), anteroseptal aneurysm. and ventricular dysfunction are commonly associated and predict a poor long‐term prognosis. Surgical left ventricular reconstruction, which includes double plication of the anterior and septal wall, can improve ventricular function. This article analyzes the long‐term efficacy of such a procedure to control recurrence of VT in a group of 50 consecutive patients.

Methods and Results: The study group consisted of 50 consecutive patients operated on between December 1986 and December 1994. The group comprised 44 men and 6 women. The mean age was 56 ± 11 years. All patients had spontaneous VT following an anterior myocardial infarction. Twenty‐five patients had two or more episodes of VT (eight presented as cardiac arrest, nine as syncope). Coronary artery disease was limited to the left anterior descending artery in 27 patients. An anteroseptal aneurysm was present in 49 patients. All patients had VT induced by programmed ventricular stimulation before surgery, and left ventricular reconstruction was performed without intraoperative mapping in all cases. Total mortality, VT recurrence, and sudden death rate were the endpoints of the study. In‐hospital mortality was 8%. Postoperative left ventricular ejection fraction improved from 0.38 to 0.50 (P < 0.05). Only two patients had postoperative inducible VT. Overall survival, VT recurrence rate, and sudden death rate were 73%, 12%, and 10%, respectively, after a median follow‐up period of 6.25 years (0 to 8 years).

Conclusion: Visually guided left ventricular reconstruction with septal and anterior wall plicature can he utilized effectively to treat recurrent VT associated with postinfarction anteroseptal aneurysm.
The LETR‐Principle: A Novel Method to Assess Electrode‐Tissue Contact in Radiofrequency Ablation
Authors: EICK OLAF J. , WITTKAMPE FRED H. , BRONNEBERG THOM , SCHUMACHER BURGHARD
Published: April 2007

Minimal Power RF Application. Introduction: Stable electrode‐tissue contact is crucial for successful radiofrequency ablation of cardiac tachyarrhythmias. In this in vitro study, a custom‐made radiofrequency generator was used to evaluate the correlation between tip temperature response to a minimal radiofrequency power delivery (Low Energy Temperature Response: LETR‐Principle) and electrode‐tissue contact as well as lesion size.

Methods and Results: A battery‐powered radiofrequency generator (LETR‐Box, 500 kHz, 0.1 to 0.3 W) could measure the temperature increase at the tip electrode with 0.01°C accuracy. The device was tested in vitro using isolated porcine ventricular tissue. For various electrode‐tissue settings (i.e., 0 to 0.89 N contact force), the temperature increase (δT) due to 0.1‐W power delivery for 10 seconds was recorded. Subsequently, for the same electrode‐tissue contact, a temperature‐controlled radiofrequency ablation was performed (70°C target temperature. 50‐W maximum output, 30 sec). Thereafter, the lesion size was measured histologically. To prove the safety of the applied LETR‐Principle, the tissue was inspected microscopically after continuous radiofrequency power delivery of 0.3 W for 1 hour with high contact pressure (1.33 N). The delivery of 0.1‐W radiofrequency power resulted in an average δT of 0.18° plusmn; 0.13°C. During temperature‐controlled radiofrequency ablation, the tip temperature was 59° 8.5°C, resulting in a lesion depth of 4.8 ± 0.6 mm. The correlation coefficient between δT and contact force was 0.97 and 0.81. respectively, for lesion depth. No lesion was microscopically visible after power delivery of 0.3 W for 1 hour with 1.33 N contact pressure.

Conclusion: The LETR‐Principle safely indicates electrode‐tissue contact and lesion depth under in vitro conditions and can be useful for catheter positioning during radiofrequency ablation procedures.
Ventriculoatrial Block During Atrioventricular Nodal Reentrant Tachycardia Utilizing Multiple Retrograde Pathways
Authors: INO TAKESHI , TADERA TAKESHI , MIYAMOTO SHINJIROH , TANAKA KOTOKO , OHNO TADAAKI , NAGASAWA KOICHI , HAYAKAWA HIROKAZU
Published: April 2007

VA Block During Multiple AVNRT. A rare case of narrow QRS tachycardia continuing despite the occurrence of VA block is reported. Right ventricular stimulation suggested dual AV nodal physiology. The tachycardia was induced by ventricular premature stimulation, which failed to depolarize the atrium. Two types of tachycardia that had different retrograde conduction sequences, HA intervals, and cycle lengths were induced. The occurrence of VA block did not terminate the tachycardia but transiently prolonged the tachycardia cycle length. These findings suggest the mechanism is AV nodal reentry utilizing multiple retrograde pathways with intranodal reentry bridging the VA block and maintaining the tachycardia.
Spatiotemporal Effects of Syncytial Heterogeneities on Cardiac Far‐Field Excitations During Monophasic and Biphasic Shocks
Authors: FISHLER MATTHEW G. , VEPA KUSHAL
Published: April 2007

Far‐Field Excitation Via Syncytial Heterogeneities. Introduction: It has recently been postulated that syncytial (anatomic) heterogeneities inherent within cardiac tissue might represent a significant mechanism underlying field‐induced polarization of the bulk myocardium. This simulation study examines and characterizes the spatiotemporal excitatory dynamics associated with this newly hypothesized mechanism.

Methods and Results: Two‐dimensional regions of syncytially heterogeneous cardiac tissue were simulated with active membrane kinetics. Heterogeneities were manifested via random spatial variations of intracellular volume fractions over multiple length scales. Excitation thresholds were determined for uniform rectangular monophasic (M) and symmetric biphasic (B) far‐field stimuli, from which strength‐duration and strength‐interval relationships were constructed. For regions measuring 5.4 × 5.4 mm, baseline diastolic thresholds for longitudinal (L) and transverse (T) shocks of 5‐msec total duration averaged (in V/cm, n = 10) M‐L = 2.87 ± 0.26. M‐T = 6.71 ± 0.83, B‐L = 3.22 ± 0.25, and B‐T = 7.93 ± 0.51. These thresholds decreased by 15% to 25% when the region sizes were increased to 10.8 × 10.8 mm. Strength‐duration relationships correlated strongly with the Weiss‐Lapicque hyperbolic relationship, with rheobases and chronaxies of 2.33 V/cm and 1.15 msec for M‐L stimuli, and 2.28 V/cm and 2.04 msec for B‐L stimuli. Strength‐interval relationships for M‐I. and B‐L stimuli decreased monotonically with increasing coupling intervals, with similar minimum coupling intervals at absolute refractoriness. However, the B‐L thresholds were substantially less sensitive to changes in coupling intervals than their M‐L counterparts.

Conclusion: This study provides strong additional support for and understanding of the syncytial heterogeneity hypothesis and its manifested properties. Furthermore, these results predict that syncytial heterogeneities of even modest proportions could represent a significant mechanism contributing to the far‐field excitation process.
Conduction Properties of the Crista Terminalis in Patients with Typical Atrial Flutter: Basis for a Line of Block in the Reentrant Circuit
Authors: TAT CHING‐TAI , CHEN SHIH‐ANN , CHEN YI‐JEN , YU WEN‐CHUNG , HSIEH MING‐HSIUNG , TSAI CHIN‐FENG , CHEN CHIEN‐CHENG , DING YU‐AN , CHANG MAU‐SONG
Published: April 2007

Conduction Properties of the Crista Terminalis. Introduction: Previous mapping studies in patients with typical atrial flutter have demonstrated the crista terminalis to he a posterior harrier of the reentrant circuit forming a line of block. However, the functional role of the crista terminalis in patients with or without a history of atrial flutter is not well known. The aim of this study was to determine whether the conduction properties of the crista terminalis are different between patients with and those without a history of atrial flutter.

Methods and Results: The study population consisted of 12 patients with clinically documented atrial flutter (group 1) and 12 patients with paroxysmal supraventricular tachycardia as well as induced atrial flutter (group 2). A 7‐French, 20‐pole, deflectable Halo catheter was positioned around the tricuspid annulus. A 7‐French, 20‐pole Crista catheter was placed along the crista terminalis identified by the recording of double potentials with opposite activation sequences during typical atrial flutter. After sinus rhythm was restored, pacing from the low posterior right atrium near the crista terminalis was performed at multiple cycle length to 2:1 atrial capture. No double potentials were recorded along the crista terminalis during sinus rhythm in both groups. In group 1, the longest pacing cycle length that resulted in a line of block with double potentials along the crista terminalis was 638 ± 119 msec. After infusion of propranolol, it was prolonged to 832 ± 93 msec without change of the interdeflection intervals of double potentials. In group 2, the longest pacing cycle length that resulted in a line of block with double potentials along the crista terminalis was 214 ± 23 msec. After infusion of procainamide, it was prolonged to 306 ± 36 msec with increase of interdeflection interval of double potentials.

Conclusion: The crista terminalis forms a line of transverse conduction block during typical atrial flutter. Poor transverse conduction property in the crista terminalis may be the requisite substrate for clinical occurrence of typical atrial flutter.
Differential Effect of Adenosine on Anterograde and Retrograde Fast Pathway Conduction in Patients with Atrioventricular Nodal Reentrant Tachycardia
Authors: SOUZA JOSEPH J. , ZIVIN ADAM , FLEMMING MATTHEW , PELOSI ERANK , ORAL HAKAN , KNIGHT BRADLEY P. , GOYAL RAJIVA , MAN K. CHING , STRTCKBERGER S. ADAM , MORADY FRED
Published: April 2007

Adenosine and Retrograde Fast Pathway Conduction. Introduction: Several studies have shown that the fast pathway is more responsive to adenosine than the slow pathway in patients with AV nodal reentrant tachycardia. Little information is available regarding the effect of adenosine on anterograde and retrograde fast pathway conduction.

Methods and Results: The effects of adenosine on anterograde and retrograde fast pathway conduction were evaluated in 116 patients (mean age 47 ± 16 years) with typical AV nodal reentrant tachycardia. Each patient received 12 mg of adenosine during ventricular pacing at a cycle length 20 msec longer than the fast pathway VA block cycle length and during sinus rhythm or atrial pacing at 20 msec longer than the fast pathway AV block cycle length. Anterograde block occurred in 98% of patients compared with retrograde fast pathway block in 62% of patients (P < 0.001). Unresponsiveness of the retrograde fast pathway to adenosine was associated with a shorter AV block cycle length (374 ± 78 vs 333 ± 74 msec, P < 0.01), a shorter VA block cycle length (383 ± 121 vs 307 ± 49 msec, P < 0.001), and a shorter VA interval during tachycardia (53 ± 23 vs 41 ± 17 msec, P < 0.01).

Conclusion: Although anterograde fast pathway conduction is almost always blocked by 12 mg of adenosine, retrograde fast pathway conduction is not blocked by adenosine in 38% of patients with typical AV nodal reentrant tachycardia. This indicates that the anterograde and retrograde fast pathways may be anatomically and/or functionally distinct. Unresponsiveness of VA conduction to adenosine is not a reliable indicator of an accessory pathway.
Double‐Wave Reentry in Orthodromic Atrioventricular Reciprocating Tachycardia: Paradoxical Shortening of the Tachycardia Cycle Length with Development of Ipsilateral Bundle Branch Block
Authors: COROMILAS JAMES , KASSOTTS JOHN , DIZON JOSE , REIEFEL JAMES , COSTEAS CONSTANTINOS , LIPKA LESLIE
Published: April 2007

Double‐Wave Reentry in Orthodromic AVRT. Introduction: Attempts to terminate reentrant tachyarrhythmias by rapid pacing may accelerate the tachycardia. One mechanism for acceleration is double‐wave reentry, where two simultaneous wavefronts travel around the same circuit.

Methods and Results: We report pacing acceleration of AV reciprocating tachycardia (AVRT) due to double‐wave reentry in a patient with Wolff‐Parkinson‐White syndrome. The patient had presented with atrial fibrillation and rapid conduction across a left lateral bypass tract. Intravenous procainamide was given during electrophysiologic study because of incessant atrial fibrillation and restored sinus rhythm. Orthodromic AVRT was induced and attempts to terminate the AVRT with right ventricular pacing initiated two alternate tachycardias, both with a left bundle branch block (LBBB) morphology. The first tachycardia, as expected for bundle branch block ipsilateral to the bypass tract, had a longer cycle length (CL) than the original tachycardia (366 msec compared to 297 msec). The second tachycardia had a paradoxically shorter CL, 238 msec compared to 297 msec. Electrogram analysis revealed that the circuit traversed by the accelerated LBBB tachycardia was the same as the slower LBBB tachycardia. The activation sequence revealed two independent wavefronts, traversing this common circuit. As described previously in experimental models, double‐wave reentry was initiated when an antidromic‐stimulated impulse blocked before colliding with the previous orthodromic impulse, thus allowing two orthodromic Impulses to circulate within the circuit.

Conclusion: We speculate that conduction slowing by procainamide combined with the intrinsic AV nodal delay resulted in the necessary increase in the excitable gap required to develop double‐wave reentry. This is the first description of sustained double‐wave reentry in humans.
Electrical Proarrhythmia: Induction of Inappropriate Atrial Therapies due to Far‐Field R Wave Oversensing in a New Dual Chamber Defibrillator
Authors: WOLPERT CHRISTIAN , JUNG WERNER , SCHOLL CHRISTOPH , SPEHL SUSANNE , CYRAN JOACHIM , LÜDERITZ BERNDT
Published: April 2007

R Wave Far‐Field Sensing in Dual Chamber Defibrillators. This case report describes delivery of atrial therapies during a sinus tachycardia in a new dual chamber implantable cardioverter defibrillator inappropriately caused by far‐field oversensing of ventricular beats in the atrial channel. Upon classification of the PR interval pattern, the rate criterion for an atrial tachycardia was fulfilled, and the device initiated high‐frequency burst pacing as the first stage of programmed tiered atrial therapies. Atrial fibrillation subsequently was induced by high‐frequency burst pacing, and eventually a programmed 10‐J shock was delivered for successful termination of atrial fibrillation. The phenomenon of far‐field oversensing of ventricular beats could be repeatedly observed during exercise testing and abolished by decreasing the atrial sensitivity.
Unusual Locations for Adenosine‐Sensitive Accessory Atrioventricular Pathways with Decremental Conduction
Authors: FREY BERNHARD , KREINER GERHARD , BERGER RUDOLF , GÖSSINGER HEINZ D.
Published: April 2007

Locations of Decremental Accessory Pathways. Introduction: Accessory AV pathways with decremental conduction are uncommon and, in particular, are thought not to occur at the anterior portion of the mitral annulus.

Methods and Results: This report describes successful catheter ablation in three patients with accessory AV pathways that were adenosine sensitive and showed decremental conduction properties. The pathways were located at the anteroseptal, anteroparaseptal, and anterolateral aspects of the mitral annulus.

Conclusion: Accessory pathways with decremental conduction do occur anywhere around the mitral annulus, even in the area of fibrous continuity between the aortic leaflet of the mitral valve and the aortic valve itself.
Virtual Electrode Effects in Transvenous Defibrillation‐Modulation by Structure and Interface: Evidence from Bidomain Simulations and Optical Mapping
Authors: ENTCHEVA EMILIA , EASON JAMES , EFIMOV IGOR R. , CHENG YUANNA , MALKIN ROBERT , CLAYDON FRITZ
Published: April 2007

Virtual Electrodes, Bidomain Model, and Defibrillation. Introduction: Our goal in this combined modeling and experimental study was to gain insight into the transmembrane potential changes in defibrillation conditions, namely, when shocks are delivered by an implantable cardioverter defibrillator (ICD). Two hypotheses concerning the presence and characteristics of virtual electrode effects (VEE) during an ICD shock were tested numerically and experimentally: (H1) anisotropy‐dependent VEE are induced over a considerable portion of the “bulk” myocardium; and (H2) surface (epicardial and endocardial) VEE are generated under special tissue bath conditions and are not fully anisotropy determined.

Methods and Results: Optical mapping was performed on Langendorff‐perfused rabbit hearts (n = 4) stained with di‐4‐ANEPPS. Monophasic shocks were applied during the plateau phase of an action potential through a 9‐mm long distal electrode in the right or left ventricle and a 6‐cm proximal electrode positioned 3 cm posteriorly to the heart. We modeled the experiment using an ellipsoidal bidomain heart with transmural fiber rotation, placed in a perfusing bath, and subjected to defibrillation shocks delivered by an electrode configuration as described. Our numerical simulations demonstrated VEE occupying a significant portion of the myocardium in the conditions of unequal anisotropy ratios for the intra‐ and extracellular domains. Statistically significant differences in epicardial polarization patterns were predicted numerically and confirmed experimentally when the interface conditions varied.

Conclusion: The present study concludes that VEE are present in transvenous defibrillation. They are shaped by the combined effect of cardiac tissue characteristics and interface conditions. Because of their size, VEE might contribute significantly to defibrillation outcome.
Effect of Atrial Natriuretic Peptide on Electrical Defibrillation Efficacy
Authors: MURAKUWA YUJI , YAMASHITA TAKESHI , KANESE YUKIHIRO , OMATA MASAO
Published: April 2007

ANP and Defibrillation. Introduction: In vitro studies have suggested that human atrial natriuretic peptide (ANP) modulates the electrophysiologic properties of myocardial cells. This study assessed whether ANP could influence defibrillation efficacy.

Methods and Results: In 35 anesthetized dogs, the transcardiac defibrillation threshold (DFT) as well as hemodynamic and electrophysiologic variables were determined before and during treatment with ANP (n = 11), hydralazine (n = 11), or saline (n = 13). ANP (1.5 μg/kg + 0.2 μg/kg per min) increased the plasma concentration of cyclic GMP (a second messenger for ANP) and significantly decreased aortic blood pressure (mean 100 ± 11 mmHg to 83 ± 15 mmHg). ANP also prolonged ventricular repolarization (effective refractory period 157 ± 7 msec to 165 ± 11 msec) and markedly reduced DFT (5.4 ± 1.2 J to 3.8 ± 0.7 J [P < 0.01]) without changing pulmonary artery pressure or sinus cycle length. Neither saline nor hydralazine (1.5 mg/kg) had a significant effect on DFT (saline 4.7 ± 2.1 J to 4.6 ± 2.4 J; hydralazine 4.3 ± 2.0 J to 4.2 ± 1.9 J), although hydralazine caused pronounced hypotension (mean aortic pressure 103 ± 9 mmHg to 74 ± 13 mmHg).

Conclusion: These results suggest that ANP increases defibrillation efficacy, and that this effect is not necessarily shared by other vasodilating agents.
A Prospective Evaluation of Two Defibrillation Safety Margin Techniques in Patients with Low Defibrillation Energy Requirements
Authors: STRICKBERGER S. ADAM , MAN K. CHING , SOUZA JOSEPH , ZIVIN ADAM , WEISS RAUL , KNIGHT BRADLEY P. , GOYAL RAJIVA , DAOUD EMILE G. , MORADY FRED
Published: April 2007

Low‐Energy Defibrillation. Introduction: In patients undergoing defibrillator implantation, an appropriate defibrillation safety margin has been considered to be either 10 J or an energy equal to the defibrillation energy requirement. However, a previous clinical report suggested that a larger safety margin may be required in patients with a low defibrillation energy requirement. Therefore, the purpose of this prospective study was to compare the defibrillation efficacy of the two safety margin techniques in patients with a low defibrillation energy requirement.

Methods and Results: Sixty patients who underwent implantation of a defibrillator and who had a low defibrillation energy requirement (≤ 6 J) underwent six separate inductions of ventricular fibrillation, at least 5 minutes apart. For each of the first three inductions of ventricular fibrillation, the first two shocks were equal to either the defibrillation energy requirement plus 10 J (14.6 ± 1.0 J), or to twice the defibrillation energy requirement (9.9 ± 2.3 J). The alternate technique was used for the subsequent three inductions of ventricular fibrillation. For each induction of ventricular fibrillation, the first shock success rate was 99.5%± 4.3% for shocks using the defibrillation energy requirement plus 10 J, compared to 95.0%± 17.2% for shocks at twice the defibrillation energy requirement (P = 0.02). The charge time (P < 0.0001) and the total duration of ventricular fibrillation (P < 0.0001) were each approximately 1 second longer with the defibrillation energy requirement plus 10 J technique.

Conclusion: This study is the first to compare prospectively the defibrillation efficacy of two defibrillation safety margins. In patients with a defibrillation energy requirement ≤ 6 J, a higher rate of successful defibrillation is achieved with a safety margin of 10 J than with a safety margin equal to the defibrillation energy requirement.
Specific Electrocardiographic Features of Manifest Coronary Vein Posteroseptal Accessory Pathways
Authors: TAKAHASHI ATSUSHI , SHAH DIPEN C. , JAÏS PIERRE , HOCINI MELEZE , CLEMENTY JACQUES , HAÏSSAGUERRE MICHEL
Published: April 2007

Coronary Vein Accessory Pathways. Introduction: Some posteroseptal accessory pathways (APs) can be successfully ablated by radiofrequency current only from inside the coronary sinus (CS) or its branches, because of an absolute or relatively epicardial location. The aim of this study was to identify ECG features of manifest posteroseptal APs requiring ablation in the CS or the middle cardiac veins (MCVs).

Methods and Results: One hundred seventeen consecutive patients with manifest posteroseptal APs successfully ablated: (1) ≥ 1 cm deep inside the MCV (group MCV: n = 13); (2) inside the CS, including the area adjacent to the MCV ostium (group CS: n = 10); (3) at the right (group R: n = 60); or (4) the left posteroseptal endocardial region (group L: n = 34) were included. We reviewed delta wave polarity (initial 40 msec) and QRS morphology during sinus rhythm and atrial pacing as well as electrogram characteristics in these patients. The local target site electrogram in groups MCV and CS was characterized by a longer atrial to ventricular electrogram interval, suggesting a longer course of the pathway and more frequent recording of a presumptive AP potential compared to the group ablated at the right or left endocardium. The most sensitive ECG feature for group CS or group MCV was a negative delta wave in lead II in sinus rhythm (87%), but specificity (79%) and positive predictive value (50%) were relatively low. A steep positive delta wave in aVR during maximal preexcitation possessed the highest specificity and positive predictive value (98% and 88%, sensitivity 61%) which increased to 99% and 91%, respectively, when combined with a deep S wave in V6 (R wave ≤ S wave).

Conclusion: These data suggest that posteroseptal APs ablated inside the coronary venous system have highly specific features, including the combination of a steep positive delta wave in lead aVR and a deep S wave in lead V6 (R wave ≤ S wave) during maximal preexcitation. The highest sensitivity is provided by a negative delta wave in lead II. These findings may be helpful for anticipating and planning an epicardial ablation strategy.
Relationship Between Efficacy of Defibrillation Shocks and Frequency Characteristics of Shock Waveforms
Authors: SCHUDER JOHN C. , McDANIEL WAYNE C.
Published: April 2007

Frequency Domain and Defibrillation. Introduction: Using the Fourier transform, it is possible to replace each time domain representation of a defibrillatory shock by a unique frequency domain representation in which the shock waveform is defined in terms of a complex number function of frequency and typically described as an amplitude in amperes per hertz (or, closely related, joules per hertz) and an associated frequency‐dependent phase angle.

Methods and Results: The present article describes the conceptual basis of the Fourier transform, sketches a simplified mathematical framework for deriving frequency domain parameters, considers properties crucial to interpreting defibrillatory‐type shocks when expressed in the frequency domain, and then presents a series of shock waveforms in the frequency domain. Although not definitive, knowledge of the energy distribution with frequency alone, usually presented in joules per hertz, is shown to yield considerable insight into the probable comparable efficacy of uniphasic/biphasic rectangular, untruncated/truncated uniphasic exponential, and various biphasic “single capacitor” waveforms.

Conclusion: In general, efficacy in achieving ventricular defibrillation is improved by parameter changes that shift a larger percentage of the delivered energy into a mid‐frequency range (very roughly, 40 to 160 Hz). With further study, the frequency domain approach may prove to be a useful tool in the a priori selection of optimal defibrillatory shock waveforms.
Transvenous Cold Mapping and Cryoablation of the AV Node in Dogs: Observations of Chronic Lesions and Comparison to Those Obtained Using Radiofrequency Ablation
Authors: RODRIGUEZ LUZ‐MARIA , LEUNISSEN JET , HOEKSTRA AREND , KORTELING BART‐JAN , SMEETS JOEP L.R.M. , TIMMERMANS GARL , VOS MARC , DAEMEN MAT , WELLENS HEIN J.J.
Published: April 2007

Cryoablation of the Proximal AV Node. Introduction: Radiofrequency (RF) is the most commonly used energy source for the treatment of cardiac arrhythmias. Surgical experience has shown that cryoablation also is effective for ablating arrhythmias. The aims of this study were to (I) investigate the feasibility of inducing permanent complete AV block (CAVB). (2) investigate the value of cold mapping to select the cryoablation site to produce permanent CAVB, (3) study the macro‐ and microscopic lesion characteristics 6 weeks later, and (4) compare them to those produced with RF energy.

Methods and Results: A new steerable 8.5‐French bipolar electrode catheter having a thermocouple with a 3‐mm tip using N2O as the refrigerant controlled by a cryoconsole was used. Six mongrel dogs were anesthetized, and the catheter was positioned via the femoral vein across the tricuspid valve to record a large low right atrial and a small His‐bundle potential. After cold mapping (‐15° to ‐20°C tip temperature) resulted in ECG modifications, cryothermia (‐70°C) was given twice, lasting 5 minutes each, to create permanent CAVB (Cryo group). Additionally, RF catheter ablation of the AV node was performed in two anesthetized mongrel dogs (RF group). In the Cryo group, a permanent proximal CAVB was created in four dogs (block occurred within 10 to 20 sec of cryothermia). Permanent right bundle branch block was obtained in one dog and transient CAVB in the remaining dog. In both dogs of the RF group, permanent CAVB was obtained. The cryolesions consisted of well‐circumscribed, homogeneous areas of fibrotic tissue without viable cardiomyocytes. Lesions produced with RF were less circumscribed and inhomogeneous, with clear evidence of viable cardiomyocytes and cartilage formation (patchy lesions).

Conclusions: (1) Permanent CAVB can he created by using a steerable cryoablation catheter. (2) Histologically, cryoablated sites were homogeneous and showed fibrotic tissue without signs of chronic inflammation and no evidence of viable myocytes. (3) Lesions created with RF were less homogenous and still contained viable myocytes within the lesion and cartilage formation. (4) The arrhythmogenic significance of these differences requires further study. (5) The technology of using reversible cold mapping has the potential to identify the successful ablation site and warrants further clinical study.
Severe and Early Alteration of Action Potential During Acute Cardiac Rejection in Rats
Authors: BABUTY DOMINIQUE , OJEDA CARLOS , MACHET MARIE‐CHRISTINE , AUPART MICHEL , COSNAY PIERRE , FAUCHIER JEAN‐PAUL , GARNIER DIDIER
Published: April 2007

Alteration of Cardiac Action Potential. Introduction: Alteration of cardiac action potential and its adaptation to heart rate could contribute to cardiac dysfunction and arrhythmias during acute cardiac rejection.

Methods and Results: Heterotopic heart transplantation was performed in allogeneic and syngeneic rats in which the action potentials of right and left ventricles were measured at 1, 2.5, 3.3, and 5.7 Hz successively using standard microelectrode techniques and compared with nontransplanted hearts. For each frequency, we measured action potential amplitude, action potential duration, transmembrane resting potential, and Vmax. In the right ventricle, at 1 Hz in the presence of rejection (n = 40), a significant increase was observed in action potential duration at 20%, 50%, and 70% repolarization (82.5%, 75.6%, and 70.8%, respectively) and in action potential amplitude (+17.9 mV), and the resting potential was decreased (‐5.3 mV). A lack of adaptation of action potential duration to the driving frequency was observed in the rejecting heart group in contrast to controls (n = 20) and nourejecting hearts (n = 13). Similar results were observed in the left ventricle and surprisingly in the native hearts (n = 11) of recipients with allografted rejecting hearts in the abdominal position.

Conclusion: Action potential and its adaptation to the driving frequency is considerably altered during acute rejection. A humoral factor could contribute to cardiac dysfunction.
Atrial Tachycardia Originating from a Single Site with Exit Block Mimicking Atrial Fibrillation Eliminated with Radiofrequency Applications
Authors: MECCA ANDREW L. , GUO HONGSHENG , TELFER ANDREW , OLSHANSKY BRIAN
Published: April 2007

Atrial Tachycardia from a Single Site. We describe the case of a patient who has a right atrial tachycardia and atrial fibrillation who was found to have a single site responsible for both. We recorded a tachycardia from this site with exit block into the remainder of the atria.
Entrance Site of the Slow Conduction Zone of Verapamil‐Sensitive Idiopathic Left Ventricular Tachycardia:
Authors: LAI LING‐PING , LIN JTUNN‐LEE , HWANG JUEY‐JEN , HUANG SHOEI K.STEPHEN
Published: April 2007

Entrance Site in ILVT. The entrance site of the slow conduction zone was identified by entrainment study in an 18 year‐old woman with verapamil‐sensitive idiopathic left ventricular tachycardia. Radiofrequency catheter ablation at this site eliminated the tachycardia. The entrance site was at a mid‐septal location and was more than 2 cm away from the exit site. Electrophysiologic findings suggested macroreentry in the Purkinje system as the mechanism of idiopathic left ventricular tachycardia.
Incessant Tachycardia Using a Concealed Atrionodal Bypass Tract
Authors: ZIVIN ADAM , MORADY FRED
Published: April 2007

Atrionodal Bypass Tract. A case of incessant supraventricular tachycardia continuing despite AV block is reported. Atrial tachycardia and AV nodal reentrant tachycardia were excluded, as was orthodromic tachycardia using a concealed accessory AV pathway. The earliest retrograde atrial activation was at the posterolateral tricuspid annulus, and the tachycardia was eliminated by ablation at this site. The findings in this case are explained only by a concealed atrionodal pathway.
Sinus Tachycardia with Atrioventricular Block:
Authors: SRA JASBIR , SINGH BALBIR , BLANCK ZALMEN , DHALA ANWER , AKHTAR MASOOD
Published: April 2007

Sinus Tachycardia with AV Block During VVS. Introduction: Neurocardiogenic (vasovagal) syncope is characterized by hypotension and bradycardia. The presence of sinus tachycardia along with AV block during syncope in patients with neurocardiogenic syncope has not been described previously.

Methods and Results: Two female patients (18 and 16 years old) with recurrent syncope and documented sinus tachycardia at the time of syncope are described. Patient 1 had recurrent episodes of syncope. During one of these episodes, which occurred while she was being monitored, sinus tachycardia along with high‐grade AV block was seen at the time of syncope and hypotension. Patient 2 had a history of recurrent syncope and seizure. During one of these episodes, she was documented to have ventricular asystole lasting for about 39 seconds. The sinus rate was 480 msec at the beginning, before slowing down to 960 msec prior to restoration of sinus rhythm with 1:1 AV conduction. The same scenario was repeated during head‐up tilt testing. Both patients were treated successfully with oral disopyramide and, during a follow‐up of 28 months and 9 months, have remained symptom‐free.

Conclusion: Sinus acceleration along with high‐grade AV block during syncope and hypotension can occur in some patients with neurocardiogenic syncope. The exact mechanism of this phenomenon is unclear.
Influence of Filtering Techniques on the Time‐Domain Analysis of Signal‐Averaged P Wave Electrocardiogram
Authors: VALVBRDE ESTEBAN R. , QUINTEIRO RICARDO A. , BERTRAN GUILLERMO C. , ARINI PEDRO D. , GLENNY PATRICIO , BIAGETTI MARCELO O.
Published: April 2007

Differences in P Wave Filtering Techniques. introduction: The advent of signal‐averaged ECG (SAECG) systems for P wave analysis has made it important to determine if the use of different filtering techniques in these systems is diagnostically equivalent.

Methods and Results: Three different high‐pass filtering techniques and two cutoff frequency values were used: 29‐ and 40‐Hz Butterworth bidirectional filter (BB29, BB40), 29‐and 40‐Hz Butterworth unidirectional filter (UB29, UB40), and 29‐ and 40‐Hz least mean square filter (LIV1S29, LMS40). Normal healthy volunteers (n = 36) and patients with documented paroxysmal atrial fibrillation (n = 23) were analyzed. A custom‐built SAECG system and standard bipolar orthogonal leads were used. Noise was reduced to < 0.3 μV. P wave total duration, root mean square voltage of the terminal 20, 30, and 40 msec of the filtered vector magnitude, and the area under the curve between the onset and offset of averaged unfiltered and filtered P wave vector magnitude were analyzed. Only the duration of the P wave showed statistically significant differences between groups, being longer in the PAF group for all filters and cutoff frequencies studied. A bias increment of ‐20 msec was detected in unidirectional and least mean square filters as compared to the bidirectional filter. Sensitivity, specificity, and predictive accuracy were > 70% for all filters; the BB40 filter yielded the best performance.

Conclusion: The normality limits derived from one filter cannot be applied directly to recordings obtained from the other filters. Critical limits must be established individually for different software settings.
AV Nodal Reentrant Tachycardia with Unusual Characteristics:
Authors: CHEN SHIH‐ANN , TAI CHING‐TAI , LEE SHIH‐HUANG , CHANG MAU‐SONG
Published: April 2007

AV Nodal Reentrant Tachycardia. There are still some AV nodal reentrant tachycardias with unusual AV nodal properties that need further study to understand these complexities. Accordingly, the two‐dimensional model with alpha and beta pathways in the AV nodal reentrant tachycardia circuit certainly is an oversimplification and does not explain adequately the anatomic and physiologic complexity of the AV junctional area. The modern concept suggests that this arrhythmia takes place in a highly complex three‐dimensional model with nonuniform anisotropy and discontinuous conduction property in the AV junctional area. Application of radiofrequency energy within the AV Junctional area should always he performed carefully to achieve a successful ablation procedure and to minimize possible injury of AV nodal conduction.
Divergent Effect of Acute Ventricular Dilatation on the Electrophysiologic Characteristics of d,I‐Sotalol and Flecainide in the Isolated Rebbit heart
Authors: ECKARDT LARS , HAVERKAMP WILHELM , GOTTKER ULRICH , MADEJA MICHAEL , JOHNA ROBERT , BORGGREFE MARTIN , BREITHARDT GUNTER
Published: April 2007

Ventricular Dilatation and d,l‐Sotalol/Flecainide in Isolated Rabbit Heart. Introduction: The interaction between acute ventricular dilatation (AVD) as one aspect of ventricular dysfunction and Class I and III antiarrhythmic drugs is uncertain. We therefore investigated the effects of AVD on the electrophysiologic properties of d,l‐sotalol and flecainide.

Methods and Results: The isolated rabbit heart was used as a model of AVD. The ventricular size and, therefore, the diastolic pressure were modified by sudden volume changes of a fluid‐filled balloon placed in the left ventricle. Pacing was performed alternately using epi‐ and endocardial monophasic action potential (MAP)‐pacing catheters at cycle lengths from 1,000 to 300 msec. d,l‐Sotalol (10 μM) resulted in a significant (P < 0.05) lengthening of refractoriness (+13.5%± 3.1%), MAP duration (+14.9%± 3.2%), and QT interval (+15.5%± 4.1%) (mean ± SEM at 1,000 msec). These effects had a reverse rate‐dependence. AVD to a diastolic pressure of 30 mmHg reduced refractoriness and left ventricular MAP duration. In comparison with the control group with the same extent of WD, d,l‐sotalol still led to a significant prolongation of repolarization for all cycle lengths except 300 msec, so that its effects were not absolutely but relatively preserved. In contrast, flecainide (2μM) had no significant effects on refractoriness or MAP duration. It led to a significant, rate‐dependent increase of pacing thresholds (+47.6%± 8.2%), prolongation of QRS (+48.8%± 5.6%), and conduction time (+78.6%± 8.6%) (mean ± SEM at 300 msec). In the flecainide group, AVD significantly increased the normal rate‐dependent prolongation of QRS (+16.7%± 5.5%) and conduction time (+17.1%± 4.3%).

Conclusion: Our data demonstrate that, during AVD, the Class III effect of d,l‐sotalol is preserved, whereas flecainide's effect of slowing conduction is exaggerated. This may contribute to flecainide‐related proarrhythmia in certain clinical situations.
Functional Communication Between Cardiac ATPSensitive K+ Channel and Na/K ATPase
Authors: TSUCHIYA KUNIHIKO , HORIE MINORU , HARUNA TETSUYA , AI TOMOHIKO , NISHIMOTO TOSHIHISA , FUJIWARA HISAYOSHI , SASAYAMA SHIGETAKE
Published: April 2007

KATP Channel and Na/K ATPase. Introduction: Functional interaction between KATP channel and Na/K ATPase was studied in single guinea pig ventricular myocytes because both membrane molecules are known to he involved in ischemic episodes.

Methods and Results: KATP channel currents were recorded at 36°C by using whole cell, cell attached, inside‐out, and open cell‐attached modes of patch clamp techniques on enzymatically isolated ventricular myocytes. In the whole cell mode, ouabain (1 μM) reversibly inhibited the KATP currents induced by metabolic stress (ATP‐free pipette solution and 1 mM NaCN), but not those activated by cromakalim (100 μM), a KATP channel opener. In the cell‐attached mode, ouabain concentration dependently inhibited KATP, channel opening induced by metabolic suppression (5.5 μM 2‐deoxyglucose and 1 mM CN). Half‐inhibition concentration for ouabain was 21.0 ± 5.5 nM and the Hill coefficient was 0.8 ± 0.1 (n = 26). However, ouabain did not have an effect on the channel activity induced by cromakalim (100 μM). In the inside‐out mode, ouabain applied to the internal side of membrane did not affect the channel. In the open cell‐attached mode made by preincubation with streptolysin‐0 (0.08 U/mL), the KATP channels were not activated by the metabolic inhibitors but were by reducing extracellular ATP concentrations, because subsarcolenimal ATP concentration could he controlled through tiny membrane holes. The channels thus activated were not suppressed by ouabain.

Conclusion: The inhibition of Na/K ATPase by ouahain appeared to block the KATP channels by accumulating subsarcolemmal ATP caused by a decrease of the transition from ATP to ADP. In the presence of ischemic episodes, the administration of digitalis compounds may affect the opening of KATP channels, which is primarily protective against the development of irreversible myocardial damage.
Lack of Benefit of Very Short Basic Drive Train Cycle Length or Repetition of Extrastimulus Coupling Intervals for Induction of Ventricular Tachycardia
Authors: LEE CHEE‐STONG , WAN SIU‐HONG , COOPER MARK J. , ROSS DAVID L.
Published: April 2007

Stimulation Protocol for VT Induction. Introduction: There are considerable variations of uncertain importance in basic drive train cycle lengths and degree of repetition of extrastimuli used in programmed ventricular stimulation protocols in different laboratories. We compare prospectively three different stimulation protocols to examine the influence of a short basic drive train cycle length and repetition of extrastimuli on induction of ventricular tachycardia.

Methods and Results: Thirty consecutive patients who had documented ventricular tachycardia or fibrillation based on underlying coronary artery disease underwent programmed ventricular stimulation with each of the three study protocols. Protocol A used a basic drive train cycle length of 400 msec with each extrastimulus coupling interval delivered only once. Protocol B used the same basic drive train cycle length, but with each extrastimulus coupling interval repeated three times before decrementing. Protocol C used 300 msec as the cycle length of basic drive trains without repetition of extrastimuli. Sixty‐three percent, 67%, and 63% of the study patients bad ventricular tachycardia inducible with protocols A, B, and C, respectively (P = NS). Ventricular fibrillation was induced in 23% of the 30 patients in all three protocols. There were no significant differences in the mean cycle lengths of induced ventricular tachycardia, the number of extrastimuli used, and the coupling interval of the last extrastimulus inducing ventricular tachycardia among the three protocols.

Conclusion: This study showed no clinical benefit for repetition of extrastimuli that have failed to induce a ventricular tachyarrhythmia during programmed ventricular stimulation. A short basic cycle length of 300 msec was not superior to 400 msec for induction of ventricular tachyarrhythmias. We recommend the use of basic cycle length 400 msec with delivery of each extrastimulus interval only once as the initial protocol for programmed ventricular stimulation.
Antibodies Against Myosin in Sera of Patients with Idiopathic Paroxysmal Atrial Fibrillation
Authors: MAIXENT JEAN‐MICHEL , PAGANELLI FRANCK , SCAGLIONE JORGE , LÉVY SAMUEL
Published: April 2007

Myosin Antibodies in Atrial Fibrillation. Introduction: Circulating autoantibodies against myosin heavy chain have been detected in patients with ventricular myocarditis and in patients with dilated cardiomyopathy. This study investigated the presence of antibodies against myosin in sera of healthy control persons as compared with patients with idiopathic paroxysmal atrial fibrillation refractory to antiarrhythmic therapy.

Methods and Results: An SDS‐PAGK (sodium dodecylsulfate polyacrylamide gel electrophoresis) procedure, followed by Western blotting with homogenates and membrane fractions of human left ventricular and atrial specimen as antigens, was used to analyze sera of 10 patients with idiopathic paroxysmal atrial fibrillation and 10 age‐matched healthy control subjects. Circulating immunoglobulin G reactivity against cardiac myosin heavy chain was detected in 6 patients (60%) as compared with 1 control subject (10%). This difference was statistically significant (P < 0.05). All patients with idiopathic paroxysmal atrial fibrillation who showed reactivity against myosin heavy chain also had specific reactivity in their sera that exhibited reactivities to both ventricular and atrial cardiac myosin heavy chain isoforms.

Conclusion: This study demonstrates the presence of circulating autoantibodies against myosin heavy chain in a significant percentage of patients with idiopathic paroxysmal atrial fibrillation and raises the possibility of an autoimmune process in some patients with paroxysmal atrial fibbrillation.