bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of a Long Preshaped Sheath to Facilitate Cannulation of the Coronary Sinus at Electrophysiologic Study
Authors: PEPPER CHRIS B. , DAVIDSON NEIL C. , ROSS DAVID L.
Published: August 2003

CS Cannulation Using a Long Sheath.
Introduction: Catheterization of the coronary sinus (CS) from the femoral vein can be challenging. We tested whether use of a long preshaped sheath facilitates CS cannulation.

Methods and Results: One hundred four patients were randomized into two phases. In phase 1, consecutive patients were allocated to CS catheterization using the long sheath (n = 26) or standard 7‐French 15‐cm sheath (n = 25). If unsuccessful within 10 minutes, the alternative technique was used. Phase 2 assessed the utility of the long sheath in difficult cases. All patients initially were approached using the standard sheath. If cannulation failed after 10 minutes, patients were randomly allocated to the standard or long sheath approach. In phase 1, the standard approach failed in 4 (16%) of 25 cases. In each case, a long sheath proved successful (mean 3.2 min). The long sheath approach was successful within 10 minutes in all 26 cases. Catheter deployment was significantly quicker with the long sheath, but this was offset by the time required for sheath insertion. In phase 2, the standard approach was successful in 46 (87%) of 53 cases. Of 7 “failures,” 3 were randomized to continue the standard approach, which was successful in 1; 4 were randomized to the long sheath approach, and success was achieved in all (mean 4.4 ± 1.5 min). Overall, the CS could not be promptly catheterized in 15% of cases within 10 minutes using the standard sheath, and no failures were seen using the long sheath. No complications arose from the use of either technique.

Conclusion: The long sheath was uniformly successful in permitting catheterization of the CS from the femoral approach in both unselected and difficult cases.
Mechanisms of Transition Between Double Paroxysmal Supraventricular Tachycardias
Authors: KUO JEN‐YUAN , TAI CHING‐TAI , CHIANG CHERN‐EN , YU WEN‐CHUNG , CHEN YI‐JEN , TSAI CHIN‐FENG , HSIEH MING‐HSIUNG , CHEN CHIEN‐CHENG , LIN WEI‐SHIANG , LIN YUNG‐KUO , TSAO HSUAN‐MING , DING YU‐AN , CHANG MAU‐SONG , CHEN SHIH‐ANN
Published: August 2003

Double Paroxysmal Supraventricular Tachycardias.
Introduction: Coexistence of double tachycardias in one patient has been infrequently reported. Furthermore, the mechanisms of transition between double paroxysmal supraventricular tachycardias have not been well studied.

Methods and Results: Thirty‐five patients with two paroxysmal supraventricular tachycardias were studied. Group IA consisted of 3 patients with spontaneous transition between AV reciprocating tachycardia (AVRT) and AV nodal reentrant tachycardia (AVNRT). Group IB consisted of 13 patients without spontaneous transition between AVRT and AVNRT. Group IIA consisted of 5 patients with spontaneous transition between AVNRT and atrial tachycardia (AT). Group IIB consisted of 14 patients without spontaneous transition between AVNRT and AT. The absolute values of differences between the two tachycardia cycle lengths were significantly smaller in patients with than in those without transition between the two tachycardias (25 ± 8 msec vs 90 ± 46 msec, P < 0.05, IA vs IB; 21 ± 25 msec vs 99 ± 57 msec, P < 0.01, IIA vs IIB). The cutoff point of 25 msec had 80% positive predictive value for transition between the two tachycardias. Transition between two tachycardias occurred due to a spontaneous premature atrial complex (30%), conduction block at one limb of tachycardia (20%), or tachycardiainduced tachycardia (50%). Absence of transition between two tachycardias might be explained by the absence of a spontaneous premature atrial complex, longer cycle length of the first tachycardia, larger difference between two tachycardia cycle lengths, or induction of each tachycardia under different situations.

Conclusion: Double supraventricular tachycardias with similar tachycardia cycle lengths are vulnerable to transition between different tachycardias.
Correlation of Spontaneous and Induced Premature Atrial Complexes Initiating Atrial Fibrillation in Humans: Electrophysiologic Parameters for Guiding Therapy
Authors: SRA JASBIR , ZAIDI SYED T. , KRUM DAVID , GEORGAKOPOULOS NICHOLAS , AHMAD ARIF , AKHTAR MASOOD
Published: August 2003

Atrial Fibrillation Induction and Ablation.
Introduction: The low frequency of spontaneous premature atrial contractions (PACs) may be an impediment to mapping and ablation of atrial fibrillation (AF). It has been shown that PACs following external or internal cardioversion of AF can initiate AF. If this method could reproducibly induce PACs from the same location as spontaneous PACs, it would be clinically significant. High‐resolution noncontact mapping can map a single beat, should help identify the sites of spontaneously occurring PACs and PACs induced following cardioversion of spontaneous or induced AF, and could help correlate the trigger sites for AF induction.

Methods and Results: Twelve patients (8 men and 4 women; mean age 49 ± 10 years) with spontaneous PACs were included in the study. In all patients, AF was induced and subsequently cardioverted to assess and map isolated PACs or PACs that induced AF. Using the EnSite 3000 noncontact mapping system, mapping was performed of spontaneously occurring isolated PACs and PACs that induced AF and PACs (both with and without AF) that occurred on at least two different occasions following cardioversion. The locations of the spontaneous and the induced PACs were similar; 97% of induced PACs came from the same locations as those of spontaneous PACs (P = 0.5). Radiofrequency lesions guided by this mapping technique were delivered at 14 pulmonary vein sites. Following a single ablation attempt during a mean follow‐up of 19 ± 4 weeks, 42% of the patients were in sinus rhythm and drug‐free, whereas an additional 24% of patients could be maintained in sinus rhythm on drugs that had failed before.

Conclusion: There is a high degree of correlation between spontaneous and induced PACs as the trigger sites for AF initiation. Cardioversion of spontaneous or induced AF could be used as an electrophysiologic parameter for guiding therapy.
Role of Right Middle Pulmonary Vein in Patients with Paroxysmal Atrial Fibrillation
Authors: TSAO HSUAN‐MING , WU MEI‐HAN , YU WEN‐CHUNG , TAI CHING‐TAI , LIN YUNG‐KUO , HSIEH MING‐HSIUNG , DING YU‐AN , CHANG MAU‐SONG , CHEN SHIH‐ANN
Published: August 2003

Right Middle Pulmonary Vein and AF.
Introduction: Elimination of the ectopic foci from pulmonary veins (PVs) has proved to be a curative therapy for focal atrial fibrillation (AF). However, information about the importance of the right middle PV (RMPV) in initiation of AF and radiofrequency ablation of AF is limited.

Method and Results: Forty‐three patients (34 men and 9 women; age 65 ± 12 years) with drugrefractory paroxysmal AF underwent electrophysiologic study and catheter ablation for treatment of AF. Three‐dimensional magnetic resonance angiography (MRA) of the PVs and left atrium (LA) was performed to determine the anatomic patterns of RMPV. Diameter of PV ostium was measured at the junction of the LA and each PV. MRA findings showed the following: (1) 36 (84%) of 43 patients had a discrete RMPV; (2) there are three drainage patterns of RMPV, including joining the proximal part (< 1 cm from the ostium) of the right superior PV (RSPV), joining the right inferior PV (RIPV), and a separate RMPV ostium in the LA wall; and (3) the ostial diameter of RMPV was significantly smaller than RSPV and RIPV (P < 0.01). Electrophysiologic studies demonstrated that five AF foci arose from RMPV. The coupling interval between the ectopic beat of AF and sinus beat was longer in RMPV than RSPV (262 ± 45 msec vs 212 ± 47 msec; P = 0.043). All AFs from RMPV were ablated successfully. PV stenosis or AF recurrence from RMPV was not found during follow‐up of 10 ± 4 months.

Conclusion: RMPV was detected by MRA in > 80% of paroxysmal AF patients. Ectopy from RMPV can initiate AF, and radiofrequency ablation of RMPV foci is feasible and safe.
QRS Complex Voltage Changes Associated with Supraventricular Tachycardia
Authors: ORETO GIUSEPPE , LUZZA FRANCESCO , BADESSA FRANCESCO , CALABRÒ MARIA PIA , MAZZONE PATRIZIO , CARERJ SCIPIONE , SAPORITO FRANCESCO , PAPPONE CARLO
Published: August 2003

QRS Voltage Changes in SVT.
 
Introduction: The aim of this study was to evaluate the changes in ventricular complex voltage associated with narrow QRS supraventricular tachycardia (SVT).

Methods and Results: One hundred forty‐five patients undergoing catheter ablation for SVT, 85 with AV nodal reentrant tachycardia (AVNRT) and 60 with AV reentrant tachycardia (AVRT) due to a concealed accessory pathway, were studied. Four consecutive tachycardia beats and four consecutive sinus beats were analyzed, excluding the last tachycardia complex and the first sinus one. For each of the 12 leads, the QRS complex voltage was measured, and the results of four beats were averaged both in SVT and in sinus rhythm (SR). The sum (∑) of the QRS voltages measured in the 12 leads during SVT (∑SVT) and SR (∑SR) were calculated, as well as the QRS axis during SVT and SR. QRS complex voltage was significantly increased during SVT, with respect to SR, in leads II, III, aVR, aVF, and V2 to V6. In addition, ∑SVT was significantly greater than ∑SR. Only lead V1 showed a significant voltage decrease during SVT. These voltage changes were almost identical in patients with AVNRT and patients with AVRT. No relationship was found between tachycardia rate and QRS voltage variation. The QRS axis showed a significant shift during SVT, from 55.8° to 64.5°.

Conclusion: QRS voltage increase occurs in reentrant SVT, independent of the underlying reentrant circuit. The phenomenon likely depends on tachycardia‐related reduced ventricular filling. This could result in displacement of the heart in such a way that the left ventricle becomes closer to the precordial electrodes (proximity effect). Alternatively, decreased intracavitary blood mass could diminish the intracardiac short‐circuiting of potentials, resulting in augmented transmission of cardiac vectors to the body surface.
Lidocaine Increases the Proarrhythmic Effects of Monophasic but not Biphasic Shocks
Authors: SIMS J. JASON , MILLER ALLISON W. , UJHELYI MICHAEL R.
Published: August 2003

Lidocaine and Shock Proarrhythmia.
Introduction: Lidocaine increases monophasic shock defibrillation energy requirement (DER) values but does not alter biphasic shock DER values. However, the mechanism of this drug/shock waveform interaction is unknown. It may be that lidocaine increases the proarrhythmic actions of monophasic shocks but not biphasic shocks. Thus, lidocaine may increase monophasic shock DER values by increasing myocardial vulnerability to shock‐induced ventricular fibrillation.

Methods and Results: Area of myocardial vulnerability (AOV), defined by a two‐dimensional grid according to shock strength (y‐axis) and shock coupling interval (x‐axis), was assessed for biphasic shocks (n = 11) and monophasic shocks (n = 13) in intact swine hearts. Shocks were randomly delivered during right ventricular pacing at 10 shock strengths (50 to 500 V) and five coupling intervals (160 to 240 msec). AOV was defined as the number of points within the test grid that induced ventricular fibrillation. AOV, upper limit of vulnerability (ULV), and DER values were determined at baseline and during systemic infusion of lidocaine (10 mg/kg/hour). Lidocaine increased AOV, ULV, and DER values by 35%, 23%, and 36%, respectively, for monophasic shocks. However, lidocaine did not alter AOV, ULV, or DER values for biphasic shocks.

Conclusion: Lidocaine increases the AOV to monophasic shocks, which is directly related to changes in ULV and DER values. This implies that lidocaine increases the proarrhythmic activity of monophasic shocks but not biphasic shocks. This may explain why lidocaine increases monophasic shock DER values.
Cellular Basis for Complex T Waves and Arrhythmic Activity Following Combined IKr and IKs Block
Authors: EMORI TETSURO , ANTZELEVITCH CHARLES
Published: August 2003

Combined Congenital and Acquired LQTS.
Introduction: A growing number of cardiomyopathies have been shown to result in a reduction in both IKr and IKs, yet little is known about the electrophysiologic and ECG characteristics of combined IKr and IKs block.

Methods and Results: To address this gap in our knowledge, transmembrane action potentials (APs) from epicardial, M, and endocardial cells were recorded simultaneously, together with a transmural ECG from arterially perfused canine left ventricular wedge preparations exposed to combined IKr (d‐sotalol; 100 μmol/L) and IKs (chromanol 293B; 30 to 60 μmol/L) block. Under baseline conditions, the T wave was typically upright; epicardium repolarized first, coinciding with the peak of the T wave, and the M cells repolarized last, coinciding with the end of the T wave (Tend). Complex (inverted, biphasic, and triphasic) T waves developed following combined IKr and IKs block. M and epicardial APs prolonged dramatically, so that the endocardial AP was now the earliest to repolarize, coinciding with the first nadir of the complex T wave. In the case of biphasic/triphasic or inverted T waves, Tend coincided with repolarization of either M or epicardial cells, whichever was the last to repolarize. QT intervals prolonged from 286 ± 13 msec up to 744 ± 148 msec and transmural dispersion of repolarization (TDR) increased from 33 ± 10 msec up to 244 ± 71 msec. Early afterdepolarizations (EADs) developed in M and epicardial cells, evoking extrasystoles that precipitated polymorphic ventricular tachycardia. Acceleration‐induced EADs and T wave alternans also were observed.

Conclusion: Combined IKr and IKs block gives rise to inverted, biphasic, and triphasic T wave morphologies, a dramatic increase in TDR, and a high incidence of EADs. The diversity of T wave morphologies derives from a preferential AP prolongation of different transmural layers leading to variation in the predominance of voltage gradients on either side of the M cell region. Our study provides direct evidence linking EADs that arise in ventricular epicardial and M cells to the triggered beats that precipitate polymorphic ventricular tachycardia. Our results also suggest possible guidelines for the estimation of TDR from complex T waves appearing in the precordial leads of the surface ECG.
Mechanism for Pituitary Adenylate Cyclase‐Activating Polypeptide‐Induced Atrial Fibrillation
Authors: HIROSE MASAMICHI , LEATMANORATN ZENG , LAURITA KENNETH R. , CARLSON MARK D.
Published: August 2003

Pituitary Adenylate Cyclase‐Activating Polypeptide‐Induced AF.
Introduction: Pituitary adenylate cyclase‐activating polypeptide (PACAP), which activates intracardiac postganglionic parasympathetic nerves, has a greater profibrillatory effect than vagal stimulation. However, the mechanism responsible for this is unclear.

Methods and Results: We examined the effective refractory period (ERP), conduction time, and incidence of atrial fibrillation (AF) induced by a single premature extrastimulus at four atrial sites as well as the AF cycle length at 65 atrial sites in 12 autonomically decentralized, open chest, anesthetized dogs. These parameters were measured in the control condition, during cervical vagal stimulation, and after PACAP administration. PACAP shortened the ERP to a similar extent at all four sites. Vagal stimulation shortened the ERP primarily at the high right atrium, but not at the other three sites. Global dispersion of ERP and variation in the AF cycle length (P < 0.01) were less after PACAP than during vagal stimulation. A premature extrastimulus induced AF more frequently after PACAP than during vagal stimulation (P < 0.001). The ERP at the pacing site was shorter when AF was induced than when it was not induced regardless of the intervention and the pacing site. Conduction time following premature beats that induced AF was shorter after PACAP than during vagal stimulation (P < 0.01).

Conclusion: Global ERP shortening contributes to the greater profibrillatory effect of PACAP. In addition, the decreased conduction time following premature beats may be associated with AF induction in this model.
Different Patterns of Angiotensin II and Atrial Natriuretic Peptide Secretion in a Sheep Model of Atrial Fibrillation
Authors: WILLEMS RIK , SIPIDO KARIN R. , HOLEMANS PATRICIA , ECTOR HUGO , VAN DE WERF FRANS , HEIDBÜCHEL HEIN
Published: August 2003

Angiotensin II and Atrial Natriuretic Peptide in AF.
Introduction: It is well established that rapid atrial rates, as in atrial fibrillation (AF), cause atrial electrical and structural remodeling leading to the maintenance of AF. The role of neurohumoral changes in this pathophysiologic vicious circle remains unclear.

Methods and Results: We followed the concentrations of angiotensin II (AT II) and atrial natriuretic peptide (ANP) in a sheep model of AF. The sheep were atrially paced at 600 beats/min for 15 weeks. Electrophysiologic study was performed at regular intervals, and venous blood samples were taken. There was a slow increase in the vulnerability for AF. The cumulative incidence of sustained AF was 80% after 15 weeks of pacing. This increased vulnerability for AF was accompanied by atrial electrical remodeling and an increase in atrial pressure. AT II increased rapidly and stayed elevated: 17 ± 4 pg/mL at baseline, and 40 ± 11 and 39 ± 7 pg/mL after 1 and 12 weeks of pacing, respectively. ANP rose more progressively: 35 ± 7 pg/mL at baseline, and 72 ± 17, 95 ± 10, and 106 ± 23 pg/mL after 1, 3, and 12 weeks, respectively. ANP levels correlated with atrial pressure and inducibility of AF. There was no relation between these parameters and AT II levels.

Conclusion: AT II and ANP increased significantly in this animal model of AF. Elevation of AT II occurs early and seems to be dependent on rapid atrial rate rather than the presence of AF. ANP increased more progressively. It paralleled the inducibility of AF and atrial stretch. Both neurohumoral pathways may form a potential therapeutic target for treatment of patients with AF.
Electroporation in a Model of Cardiac Defibrillation
Authors: ASHIHARA TAKASHI , YAO TAKENORI , NAMBA TSUNETOYO , ITO MAKOTO , IKEDA TAKANORI , KAWASE AYAKA , TODA SUNAO , SUZUKI TORU , INAGAKI MASASHI , SUGIMACHI MASARU , KINOSHITA MASAHIKO , NAKAZAWA KAZUO
Published: August 2003

Electroporation in a Model of Cardiac Defibrillation.
Introduction: It is known that highstrength shock disrupts the lipid matrix of the myocardial cell membrane and forms reversible aqueous pores across the membrane. This process is known as “electroporation.” However, it remains unclear whether electroporation contributes to the mechanism of ventricular defibrillation. The aim of this computer simulation study was to examine the possible role of electroporation in the success of defibrillation shock.

Methods and Results: Using a modified Luo‐Rudy‐1 model, we simulated two‐dimensional myocardial tissue with a homogeneous bidomain nature and unequal anisotropy ratios. Spiral waves were induced by the S1‐S2 method. Next, monophasic defibrillation shocks were delivered externally via two line electrodes. For nonelectroporating tissue, termination of ongoing fibrillation succeeded; however, new spiral waves were initiated, even with high‐strength shock (24 V/cm). For electroporating tissue, high‐strength shock (24 V/cm) was sufficient to extinguish ongoing fibrillation and did not initiate any new spiral waves. Weak shock (16 to 20 V/cm) also extinguished ongoing fibrillation; however, in contrast to the highstrength shock, new spiral waves were initiated. Success in defibrillation depended on the occurrence of electroporation‐mediated anodal‐break excitation from the physical anode and the virtual anode. Some excitation wavefronts following electrical shock used a deexcited area with recovered excitability as a pass‐through point; therefore, electroporation‐mediated anodal‐break excitation is necessary to block out the pass‐through point, resulting in successful defibrillation.

Conclusion: The electroporation‐mediated anodal‐break excitation mechanism may play an important role in electrical defibrillation.
Electrical Remodeling and Atrial Dilation During Atrial Tachycardia are Influenced by Ventricular Rate: Role of Developing Tachycardiomyopathy
Authors: SCHOONDERWOERD BAS A. , VAN GELDER ISABELLE C. , VAN VELDHUISEN DIRK J. , TIELEMAN ROBERT G. , GRANDJEAN JAN G. , BEL KLAAS J. , ALLESSIE MAURITS A. , CRIJNS HARRY J.G.M.
Published: August 2003

Atrial Remodeling in Tachycardiomyopathy.
Introduction: Atrial fibrillation (AF) and congestive heart failure (CHF) are two clinical entities that often coincide. Our aim was to establish the influence of concomitant high ventricular rate and consequent development of CHF on electrical remodeling and dilation during atrial tachycardia.

Methods and Results: A total of 14 goats was studied. Five goats were subjected to 3:1 AV pacing (A‐paced group, atrial rate 240 beats/min, ventricular rate 80 beats/min). Nine goats were subjected to rapid 1:1 AV pacing (AV‐paced group, atrial and ventricular rates 240 beats/min). During 4 weeks, right atrial (RA) and left ventricular (LV) diameters were measured during sinus rhythm. Atrial effective refractory periods (AERP) and inducibility of AF were assessed at three basic cycle lengths (BCL). After 4 weeks of rapid AV pacing, RA and LV diameters had increased to 151% and 113% of baseline, whereas after rapid atrial pacing alone, these parameters were unchanged. Right AERP (157 ± 10 msec vs 144 ± 16 msec at baseline with BCL of 400 msec in the A‐paced and AV‐paced group, respectively) initially decreased in both groups, reaching minimum values within 1 week. Subsequently, AERP partially recovered in AV‐paced goats, whereas AERP remained short in A‐paced goats (79 ± 7 msec vs 102 ± 12 msec after 4 weeks; P < 0.05). Left AERP demonstrated a similar time course. Inducibility of AF increased in both groups and reached a maximum during the first week in both groups, being 20% and 48% in the A‐paced and AV‐paced group, respectively.

Conclusion: Nature and time course of atrial electrical remodeling and dilation during atrial tachycardia are influenced by concurrent high ventricular rate and consequent development of CHF.
Electrophysiology and Anatomic Characterization of an Epicardial Accessory Pathway
Authors: SAPP JOHN , SOEJIMA KYOKO , COUPER GREGORY S. , STEVENSON WILLIAM G.
Published: August 2003

Epicardial Accessory Pathway. Pericardial access permitted epicardial catheter mapping and ablation of a rapidly conducting posteroseptal accessory pathway (AP) that had failed repeated ablation attempts. Transient block was achieved at the site of an AP potential. The AP was visible at surgery and resected. Histologic examination revealed cells typical of specialized cardiac conduction tissue. The location, size, and presence of conduction tissue likely account for failure of catheter ablation and resistance to drug therapy.
Transvenous Cryothermal Catheter Ablation of a Right Anteroseptal Accessory Pathway
Authors: KIMMAN GEERT‐JAN P. , SZILI‐TOROK TAMAS , THEUNS DOMINIC A.M.J. , JORDAENS LUC J.
Published: August 2003

Transvenous Cryothermal Catheter Ablation. In patients with Wolff‐Parkinson‐White syndrome, right anteroseptal accessory pathways are uncommon and run from the atrium to the ventricle in close anatomic proximity to the normal AV conduction system. Radiofrequency catheter ablation is the first‐line therapy for elimination of these accessory pathways. Although the initial success rate is high, there is a potential risk of inadvertent development of complete heart block, and the recurrence rate is relatively high. The capability of cryothermal energy to create reversible lesions (ice mapping) at less severe temperatures provides a potential benefit in ablation of pathways located in a complex anatomic area, such as the mid‐septum and anteroseptum.
Paradoxic Abbreviation of Repolarization in Epicardium of the Right Ventricular Outflow Tract During Augmentation of Brugada‐Type ST Segment Elevation
Authors: SHIMIZU WATARU , AIBA TAKESHI , KURITA TAKASHI , KAMAKURA SHIRO
Published: August 2003

ST Elevation in Brugada Syndrome. We report the case of a 53‐year‐old Japanese man with a typical Brugada‐like ECG in whom epicardial and endocardial activation‐recovery intervals (ARI) in the right ventricular outflow tract (RVOT) were simultaneously measured by recording unipolar electrograms from the Pathfinder catheter introduced in the great cardiac vein as well as from the multielectrode basket catheter deployed in the RVOT. Epicardial ARI in the RVOT was abbreviated paradoxically at the beat of augmented ST segment elevation in lead V2 after a long pause or after pilsicainide injection. Endocardial ARI in the RVOT and epicardial ARI in the left ventricle were prolonged or were not changed. Our data support the hypothesis that heterogenous response of repolarization across the ventricular wall in the RVOT is responsible for accentuation of ST segment elevation in the right precordial leads.
Exploding Implantable Cardioverter Defibrillator
Authors: SWEENEY MICHAEL O.
Published: August 2003

Exploding Implantable Cardioverter Defibrillator. A 79‐year‐old man with a pectoral implantable cardioverter defibrillator (ICD) system underwent periodic defibrillation threshold testing 18 months after implant. Attempted delivery of a 15‐J shock caused a light flash above the pocket and a loud “pop.” High‐voltage lead impedance was < 20 Ω. Pocket exploration revealed insulation abrasion of the high‐voltage portion of the single‐coil right ventricular lead. The outer shield of the active can pulse was perforated and scorched due to arcing. Device analysis confirmed a shorted transistor in the high‐voltage output circuit. Unsuspected physical contact between high‐voltage electrodes of opposite polarity within the pocket can cause catastrophic ICD system failure.
Improved Fermi operator expansion methods for fast electronic structure calculations
Authors: Liang WanZhen , Saravanan Chandra , Shao Yihan , Baer Roi , Bell Alexis T. , Head-Gordon Martin
Published: August 2003

Linear scaling algorithms based on Fermi operator expansions (FOE) have been considered significantly slower than other alternative approaches in evaluating the density matrix in Kohn–Sham density functional theory, despite their attractive simplicity. In this work, two new improvements to the FOE method are introduced. First, novel fast summation methods are employed to evaluate a matrix polynomial or Chebyshev matrix polynomial with matrix multiplications totalling roughly twice the square root of the degree of the polynomial. Second, six different representations of the Fermi operators are compared to assess the smallest possible degree of polynomial expansion for a given target precision. The optimal choice appears to be the complementary error function. Together, these advances make the FOE method competitive with the best existing alternatives.
Anharmonic effects on the structural and vibrational properties of the ethyl radical: A path integral Monte Carlo study
Authors: López-Ciudad Telesforo , Ramı́rez Rafael , Schulte Joachim , Böhm Michael C.
Published: August 2003

The structural and vibrational properties of the ethyl radical have been investigated by a series of finite temperature simulations that treat the nuclei as quantum particles. The potential energy surface of the electronic ground state has been described by a nonorthogonal tight-binding Hamiltonian that provides results in reasonable agreement with ab initio methods. The quantum nature of the nuclei has been described by path integral Monte Carlo simulations at temperatures between 25 and 1000 K. Special interest deserves the determination of anharmonic and tunneling effects in the zero-point vibrational structure. In particular, we have studied the influence of anharmonic effects both on the mean value and the quantum fluctuations of equilibrium bond lengths and bond angles. The local structure of the radical center is found to be planar as a result of the zero-point motion of the atomic nuclei, even though the minimum energy configuration exhibits a pyramidal structure for this center. Anharmonic effects in the fundamental vibrational modes of the molecule are studied by a nonperturbative approach based on the centroid density. This function is a path integral concept that provides information on the static response of the system to applied external forces. Our study reveals a softening of the stretching modes associated with the C–H bonds and a hardening of the out-of-plane rocking motion of the methylene group. Both effects are in good agreement with experimental and ab initio data. The softening of the C–C stretching mode predicted by our simulations suggests a revision of the currently accepted experimental assignment for two fundamental vibrations of the ethyl radical. The tunneling of an H atom between the methyl and methylene groups has been investigated. These simulations should contribute to the open question whether or not this process is responsible for the changes in the electron spin resonance spectrum at low temperatures.
Theoretical studies on the variational transitional state theory rate constants for the hydrogen abstraction reaction of O (3P) with CH3Cl and CH2Cl2
Authors: Zhang Qingzhu , Gu Yueshu , Wang Shaokun
Published: August 2003

The hydrogen abstraction reactions of atomic O (3P) with CH3Cl and CH2Cl2 have been studied theoretically using ab initio molecular orbital theory for the first time. In the Cs symmetry, both reactions proceed over two potential-energy surfaces, A″3 and A′3 generated by the pseudo-Jahn–Teller effect. Two nearly degenerate transition states of A″3 and A′3 symmetries have been located for each hydrogen abstraction reaction from the C–H bonds. Geometries of the reactants, transition states, and products have been optimized at the second-order Møller–Plesset (MP2) level with the 6-311G(2d,p) basis set. The single-point energy calculations have been carried at the [QCISD(T)]/6-311+G(3df,2p) level. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction paths are discussed and compared. The total thermal rate constants were obtained from the sum of the calculated rate constants for the two surfaces using canonical variational transition-state theory (CVT) with small curvature tunneling effect (SCT). The results show that the variational effect is small and in the lower-temperature range, the small curvature tunneling contribution is important for each reaction. The calculated CVT/SCT rate constants show reasonable agreement with the recent experimental values, with a more pronounced curvature in the Arrhenius plot than in the experimental data.
Ab initio molecular dynamics study on the excitation dynamics of psoralen compounds
Authors: Nakai H. , Yamauchi Y. , Nakata A. , Baba T. , Takahashi H.
Published: August 2003

Ab initio molecular dynamics (AIMD) simulations are performed for studying the S0→T1 excitation dynamics of psoralen compounds; namely, nonsubstituted psoralen, 5-methoxypsoralen (5-MOP), and 8-methoxypsoralen (8-MOP). The density functional theory calculations at the B3LYP/D95V level are used for evaluating the atomic forces in every AIMD step. The specific behavior of 8-MOP in the T1 state, which has been reported by the experimental study, is found to be due to a unique open-ring structure, which leads to a different spin distribution in comparison with the cases of psoralen and 5-MOP and further to a crossing between the S0 and T1 states.
High-rank quantum topological electrostatic potential: Molecular dynamics simulation of liquid hydrogen fluoride
Authors: Liem S. Y. , Popelier P. L. A.
Published: August 2003

Five bulk properties of liquid hydrogen fluoride were obtained by a molecular dynamics simulation at five temperatures between 203 and 273 K. The rigid-body interaction potential was designed with emphasis on the electrostatic contribution. The potential was expanded in spherical tensor multipole moments, and its corresponding Ewald summations, containing all possible interaction up to L=5 (i.e., monopole–hexadecapole, dipole–octopole, quadrupole–quadrupole). The moments were generated by a quantum chemical topological analysis of the electron density of the geometry-optimized monomer at the MP2/aug-cc-pVTZ level. Only two parameters in the Lennard-Jones part of the potential were adjusted to the experimental density and radial distribution functions. Agreement with experiment is excellent for the total energy and the density, and reasonable (with even overall performance) for the diffusion coefficient, the isobaric heat capacity and the thermal expansion coefficient. Chains of hydrogen-bonded HF monomers up to 10 molecules are quite common in the liquid and they more or less retain the relative orientation of the HF monomers in the gas-phase dimer.
Librational modes of ice. I
Authors: Severson Mark W. , Devlin J. Paul , Buch Victoria
Published: August 2003

A joint spectroscopic–computational study was carried out of molecular librations in ice. The measured Fourier transform infrared spectra included H2O and HDO isolated in D2O ice and D2O and HDO isolated in H2O ice. Isotopic isolation greatly simplifies the spectra. The observed bands were assigned to hindered rotations around different molecular principal axes. Intermolecular coupling results in remarkable broadening of the librational spectrum, however hindered rotations around the respective axes appear to retain their frequency ordering. Diffusion Monte Carlo investigation was carried out of anharmonic effects. Anharmonic shifts of up to several tens of inverse centimeters are negative for high frequency modes and positive for low frequency ones (with the exception of one HDO frequency in H2O), and affect the ordering of the frequencies.
Quantum chemistry using the density matrix renormalization group II
Authors: Mitrushenkov A. O. , Linguerri Roberto , Palmieri Paolo , Fano Guido
Published: August 2003

We have compared different strategies for ab initio quantum chemistry density matrix renormalization group treatments. The two starting orbital blocks include all valence and active orbitals of the reference complete active space self consistent field wave function. To generate the remaining blocks, we propose following the order of the contributions to the correlation energy: a posteriori using approximate occupation numbers or a priori, using a Møller–Plesset type of arguments, by explicit evaluation of second-order interactions. We have compared two different schemes for orbital localization to identify the important and less important orbital interactions and simplify the generation of the orbital blocks. To truncate the expansion we have compared two approaches, keeping constant the number m of components or the threshold λ to fix the residue of the expansion at each step. The extrapolation of the energies is found to provide accurate estimates of the full configuration interaction energy, making the expansion independent on the actual values of the two parameters m and λ. We propose to generate the factors for the two blocks from ground and excited eigenvectors of the Hamiltonian matrix.
Nonthermal transport of small sorbates in zeolites: Chaotic dynamics and long jumps
Authors: Kopelevich Dmitry I. , Chang Hsueh-Chia
Published: August 2003

In some molecular systems, the dominant driving force for transport is not thermal noise from lattice vibration or other sources, but low-dimensional deterministic chaos. We consider this deterministic transport for an example of diffusion of methane sorbate in zeolite AlPO4-5. In this system, the chaotic motion of the sorbate is due to nonlinear coupling between its longitudinal and azimuthal degrees of freedom. Assuming ergodicity of the sorbate motion, we develop a quantitative RRKM-type theory for the sorbate transport. The theoretical predictions for the escape rate of the sorbate from the zeolite cage are in good agreement with molecular dynamics simulations. We observe that, in addition to ergodic mixing of the sorbate degrees of freedom when the sorbate is trapped inside a zeolite cage, long ballistic flights are an important aspect of the sorbate dynamics. We investigate the complicated interplay between the ergodic trapping and the multisite flights, where the ergodicity assumption breaks down, with a kinetic Monte Carlo scheme which offers a diffusivity estimate that includes contribution from ballistic flights.
Ab initio calculation of the ground (1A′) potential energy surface and theoretical rate constant for the Si+O2→SiO+O reaction
Authors: Dayou F. , Spielfiedel A.
Published: August 2003

The entrance channel of the Si+O2→SiO+O reaction has been investigated for collinear and perpendicular approach of the silicon atom to the O2 molecule by ab initio electronic structure calculations using the multireference configuration interaction (MRCI) method and Davidson correction (MRCI+Q). Results show that the reaction can proceed through the ground singlet (1A′) and first triplet (3A′) electronic states at low temperatures. The ground A′1 three-dimensional potential energy surface (PES) which correlates the Si(3P)+O2(X 3Σg−) reactants to the SiO(X 1Σ+)+O(1D) products was computed at the MRCI+Q level of theory using the Woon and Dunning cc-pVTZ basis sets. The reaction was found barrierless and three minima have been characterized on the A′1 PES with energy ordering: linear OSiO(1Σg+)<triangular OSiO(1A1)<linear SiOO(1Σ+). About 2500 ab initio data points have been fitted to a many body expansion using the method of Aguado and Paniagua, with a global root-mean-square of 1.49 kcal/mol. The analytical A′1 PES has been used to determine the thermal rate constants in the temperature range 15–300 K by quasiclassical trajectory calculations. Comparison with experimental results shows a quite good agreement for temperature dependence of the rate constants when the spin–orbit structure of the reactants is taken into account. The rate constants are also compared with earlier results of adiabatic capture calculations. The excellent agreement between both theoretical results for temperatures above 50 K points out an increasing contribution of the first triplet state to reactivity when temperature increases.
The electronic spectra of aryl olefins: A theoretical study of phenylacetylene
Authors: Serrano-Andrés Luis , Merchán Manuela , Jabłoński Mirosław
Published: August 2003

The electronic absorption and emission spectra of phenylacetylene have been studied by means of a multiconfigurational second-order perturbation method and its multistate extension. The low-lying valence singlet and triplet π→π* excited states together with 3s3p3d members of the two lowest Rydberg series have been computed in the vertical spectrum. By optimization of the geometries of the ground and low-lying excited states and the calculation of transition energies and properties, the obtained results lead to a detailed analysis and assignment of the available experimental absorption spectrum and to the description of the basic features of the emission processes in phenylacetylene. Vibrational frequencies for the two lowest singlet and triplet excited states have also been computed. The spectroscopy of phenylacetylene is finally related to that of other aryl olefins such as styrene and benzaldehyde. Differences and similarities of their excited state structures are discussed.
Microscopic diffusion model applied to C60 fullerene fractals in carbon disulphide solution
Authors: Bokare Alok D. , Patnaik Archita
Published: August 2003

Using Positronium (Ps) atom as a fundamental probe that maps changes in the local electron density of the microenvironment and high resolution transmission electron microscopy, C60 aggregation in neat CS2 solvent is reported over a concentration range 0.02 to 2.16 g/dm3. Spontaneous formation of stable spherical C60 aggregates in the colloidal range (∼90–125 nm) was observed over a critical concentration range of 0.06–0.36 g/dm3, beyond which the clusters broke. Specific interactions of the Ps atom with the surrounding revealed the onset concentration for stable aggregate formation in this solvent to be 0.06 g/dm3. The solution phase C60 structure in the critical concentration range was analyzed to be a spherical fractal aggregate with a fractal dimension of 1.9 and the growth mode followed a diffusion limited cluster aggregation mechanism. At concentrations beyond 0.36 g/dm3, an entropy driven phase change was noticed leading to the formation of irregular, but oriented crystalline components. A microscopic diffusion model was applied to calculate the o-Ps lifetime density function and diffusion coefficients of o-Ps and the C60 aggregates in the solution. With randomly distributed C60 fractal clusters, the o-Ps density function resulted in a good agreement between the calculated and the experimental o-Ps lifetimes, revealing the diffusion coefficients of C60 fractal cluster and the o-Ps to be 2.27×10−6 cm2/s and 25.1×10−5 cm2/s respectively.
Infrared spectra of CH3F(ortho-H2)n clusters in solid parahydrogen
Authors: Yoshioka Kazuki , Anderson David T.
Published: August 2003

The formation of CH3F(ortho-H2)n clusters in rapid vapor deposited solid molecular hydrogen containing low concentrations of CH3F and ortho-H2 has been investigated using high-resolution Fourier transform infrared spectroscopy of the C–F stretching mode (ν3) of the CH3F chromophore. Distributions of CH3F(ortho-H2)n clusters ranging in size from n=0 to n=12 are synthesized in para-H2 crystals by systematically varying the ortho-H2 concentration between 100 to 20 000 parts per million. The rotational motion of CH3F is quenched in solid para-H2; this simplifies the spectrum such that a single sharp transition is observed for each cluster. In the fundamental ν3 region, the spectrum consists of a series of well-separated peaks shifted toward lower energy with increasing numbers of nearest neighbor orthohydrogen molecules. The CH3F(ortho-H2)n clusters are also investigated in the ν3 overtone region and for analogous transitions of the CD3F(ortho-H2)n. Theoretical calculations based on an electrostatic interaction potential qualitatively reproduce the measured vibrational and isotopomer dependence of the spectra.
Observation of a HI leaving group following ultraviolet photolysis of CH2I2 in water and an ab initio investigation of the O–H insertion/HI elimination reactions of the CH2I–I isopolyhalomethane species with H2O and 2H2O
Authors: Li Yun-Liang , Zhao Cunyuan , Kwok Wai Ming , Guan Xiangguo , Zuo Peng , Phillips David Lee
Published: August 2003

We report an experimental observation of H+ and I− being formed following ultraviolet photolysis of CH2I2 in liquid water. The concentration of H+ and I− are about the same and suggest a reaction that produces a HI leaving group. A preliminary ab initio investigation is reported for the O–H insertion reactions of the isodiiodomethane (CH2I–I) carbenoid species with H2O and 2H2O and these are compared to the related reactions for the dichlorocarbene (:CCl2) species. The CH2I–I carbenoid reacts with water via an O–H insertion/HI elimination reaction mechanism. These reactions produce a HI leaving group whereas the dichlorocarbene O–H insertion reaction has no need for a leaving group. The differing structures and properties of the CH2I–I and the :CCl2 species can account for the differences in their O–H insertion reactions. The CH2I–I species O–H insertion/HI elimination reactions can be catalyzed by a second water molecule when two water molecules are available and this occurs in a way similar to that previously observed for the reaction of :CCl2 with two water molecules. These results suggest that isopolyhalomethane molecules (like CH2I–I and others) are noticeably reactive towards O–H bonds like those found in water and can likely account for the strong acid formation observed experimentally after ultraviolet photolysis of polyhalomethanes in water. Possible implications for the photochemistry of polyhalomethanes in the atmosphere and oceans are briefly discussed.
Thermal expansion models of viscous fluids based on limits of free energy
Authors: Bechtel S. E. , Forest M. G. , Rooney F. J. , Wang Q.
Published: August 2003

Many viscous flows are mechanically incompressible, yet thermally expand and shrink. Approximations of the compressible Navier–Stokes equations are routinely utilized to model diverse phenomena that share these properties, with a primary goal to remove rapid timescales associated with sound waves. Most models are derived from thermodynamic assumptions coupled with application-specific, scale separation assumptions in time and space. The Boussinesq model for laboratory-scale, buoyancy-driven thermal convection patterns [Spiegel and Veronis, Astrophys. J. 131, 442 (1960)] and the anelastic model for atmospheric-scale, density-stratification phenomena [Emanuel, Atmospheric Convection (Oxford University Press, New York, 1994)] are two important examples. Some engineering models of thermal expansion are fluid specific, e.g., for molten glasses and polymers, and rest upon thermodynamic assumptions alone. These models postpone specification of flow conditions, since applications range from slow confined flows for mold filling, to film flows, to high-speed, free surface fiber flows. The aims of this paper are to systematize the implementation of thermodynamic assumptions to derive thermal expansion models; to benchmark this class of models with respect to near-equilibrium physical behavior; and to pose candidate models for thermal expansion which may be used for a diverse set of flow conditions. By casting thermodynamic assumptions as limits of free energy, we reduce the full Navier–Stokes system in a straightforward way, and parametrize the limits of linearized compressible modes and their propagation properties. The thermodynamic assumptions are uncoupled from flow-dependent scale separation conditions, which can be subsequently augmented for specific applications. Indeed, one conclusion of this analysis is that the traditional thermal expansion assumption, where density is slaved to the temperature field, must be coupled with additional flow or thermal assumptions or else the model equations possess unphysical properties (e.g., instability of thermodynamic equilibrium or negative specific heat). Two new models for thermal expansion are deduced solely from a limit condition on free energy, which pass the minimal benchmark of non-negativity of bulk modulus, squared sound speed, and specific heat. We close with an indication of viscous flow applications of one of the new thermal expansion models.
Controlled steady-state switching in optical bistability
Authors: Brown Andy , Joshi Amitabh , Xiao Min
Published: August 2003

Optical switching has been achieved between two steady states of optical bistability generated in a system with three-level atoms inside an optical cavity. The optical power switching is controlled by adding short positive (switching up) or negative (switching down) pulses to the input intensity. The coupling laser beam in the three-level atomic system is used to control the threshold value and the width of the hysteresis cycle, which can adjust and optimize the optical switching process.