bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.