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Synchrotron radiationVUV-photoionization based photofragment translational spectroscopywas used to identify the primary and secondary photodissociation reactions of methyl azide (CH3N3) at 157 nm under collision-free conditions. Two primary dissociation channels are identified, leading to CH3 + N3 (the radical channel) and CH3N + N2 (the molecular elimination channel). The last channel is the major dissociation pathway, but unlike work at longer photolysis wavelengths, here, the radical channel exclusively produces the higher energy isomer cyclic-N3. Product time-of-flight data for both channels were obtained and compared with earlier work on methyl azide photochemistry at 193 nm based on electron impact ionization, allowing us to estimate a product branching ratio. ... [ABSTRACT FROM AUTHOR]

The original ion imaging technique has low velocity resolution, and currently, photodissociation is mostly investigated using velocity map ion imaging. However, separating signals from the background (resulting from undissociated excited parent molecules) is difficult when velocity map ion imaging is used for the photodissociation of large molecules (number of atoms ≥ 10). In this study, we used the photodissociation of phenol at the S1 band origin as an example to demonstrate how our multimass ion imaging technique, based on modified spatial map ion imaging, can overcome this difficulty. The photofragment translational energy distribution obtained when multimass ion imaging was used differed considerably from that obtained when velocity map ion imaging and Rydberg atom tagging were used.We used conventional translational spectroscopy as a second method to further confirm the experimental results, and we conclude that data should be interpreted carefully when velocity map ion imaging or Rydberg atom tagging is used in the photodissociation of large molecules. Finally, we propose a modified velocity map ion imaging technique without the disadvantages of the current velocity map ion imaging technique. [ABSTRACT FROM AUTHOR]

The reaction C2 + C6H2 → C8H + H was investigated for the first time. Reactant C2 (C6H2) was synthesized from 1% C3F6/He (5% C2H2/He) by pulsed high-voltage discharge. We measured the translational-energy distribution, the angular distribution, and the photoionization spectrum of product C8H in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. This reaction released average translational energy of 8.5 kcal mol-1 corresponding to a fraction of 0.37 in translation. C8H was identified as octatetranyl based on the maximal translational-energy release 23 ± 2 kcal mol-1 and the ionization threshold 8.9 ± 0.2 eV. Kinematic constraints can qualitatively account for the nearly isotropic angular distribution. The quantum-chemical calculations indicate that the exothermic reactions C2 (X 1¹∑g+/a ³∏u) + HC6H → C8H + H can proceed without entrance and exit barriers, implying the importance in the cold interstellar medium. This work verifies that interstellar C8H can be formed through the C2 + C6H2 reaction. [ABSTRACT FROM AUTHOR]

The reaction C3(a³Πu ) + C2H2 → C5H + H was investigated at collision energy 10.9 kcal mol-1 that is less than the enthalpy of ground-state reaction C3(X¹Σg+) + C2H2 → C5H + H. C3(a³Πu ) radicals were synthesized from 1% C4F6/He by pulsed high-voltage discharge. The title reaction was conducted in a crossed molecular-beam apparatus equipped with a quadrupole-mass filter. Product C5H was interrogated with time-of-flight spectroscopy and synchrotron vacuum-ultraviolet ionization. Reactant C3(a³Πu ) and product C5H were identified using photoionization spectroscopy. The ionization thresholds of C3(X¹Σg+) and C3(a³Πu ) are determined as 11.6 ± 0.2 eV and 10.0 ± 0.2 eV, respectively. The C5H product is identified as linear pentynylidyne that has an ionization energy 8.4 ± 0.2 eV. The title reaction releases translational energy 10.6 kcal mol-1 in average and has an isotropic product angular distribution. The quantum-chemical calculation indicates that the C3(a³Πu ) radical attacks one of the carbon atoms of C2H2 and subsequently a hydrogen atom is ejected to form C5H + H, in good agreement with the experimental observation. As far as we are aware, the C3(a³Πu)+ C2H2 reaction is investigated for the first time. This work gives an implication for the formation of C5H from the C3(a³ nu ) + C2H2 reaction occurring in a combustion or discharge process ofC2H2. [ABSTRACT FROM AUTHOR]

We investigated the photodissociation of oxetane (1,3-trimethylene oxide) at 193.3 nm in a molecular-beam apparatus using photofragment-translational spectroscopy and selective photoionization. We measured time-of-flight (TOF) spectra and angular anisotropy parameters β(t) as a function of flight time of products at m/z=26–30 u utilizing photoionization energies from 9.8 to 14.8 eV. The TOF distributions of the products alter greatly with the employed photon energy, whereas their β(t) distributions are insensitive to the photon energy. Dissociation to H2CO+C2H4 is the major channel in the title reaction. Three distinct dissociation paths with branching ratios 0.923:0.058:0.019 are responsible for the three features observed in the distribution of kinetic energy released in the channel H2CO+C2H4. The observation of H2 and H atoms, ∼1% in branching, indicates that products H2CO and C2H4 spontaneously decompose to only a small extent. Most HCO, C2H3, and C2H2 ions originate from dissociative photoionization of products H2CO and C2H4. Except atomic H and H2, the photoproducts have large angular anisotropies, β≥-0.8, which reflects rapid dissociation of oxetane following optical excitation at 193.3 nm. The mechanisms of dissociation of oxetane are addressed. Our results confirm the quantum-chemical calculations of Palmer et al. and provide profound insight into the Paterno–Buchi reaction. [ABSTRACT FROM AUTHOR]

In a crossed molecular-beam apparatus, we reacted atomic O in states 3P and 1D with ethene (C2H4) at collision energy 3 kcal mol-1. Employing two mixtures, 20% O2+80% He and 3% O2+12.5% Ar+84.5% He, as discharge media allowed us to generate two sources of oxygen atoms that have the same mean velocity but different ratios of 1D/3P populations, 0.0017 and 0.035. We identified six reactions and recorded time-of-flight spectra of products CH2CHO, CH2CO, and CH3 as a function of laboratory angle. Reaction O(3P)+C2H4→CH2CHO+H has a fraction ft=0.43 of energy release in translation, and product CH2CHO has a maximal probability at scattering angle of 140°. For reaction O(1D)+C2H4→CH2CO+2H, ft=0.26, and the angular distribution of product CH2CO shows a backward preference. For reaction O(3P)+C2H4→CH2CO+H2, ft=0.35, and the angular distribution of product CH2CO has a slight preference for a sideways direction. In contrast, reaction O(1D)+C2H4→CH2CO+H2 has ft=0.26 and an angular distribution with forward and backward peaking and symmetry. Reactions O(3P and 1D)+C2H4→CH3+HCO have ft=0.09 and 0.08, respectively, and angular distributions with forward and backward peaking and nearly symmetric. The reactivity of O 1D with ethene is ca. 38 and 90 times that of O 3P for channels to eliminate H2 and CH3, respectively. For reactions of O 1D, the branching ratio for elimination of 2H is ca. 3.3 times that for elimination of H2. [ABSTRACT FROM AUTHOR]

We investigated the photodissociation dynamics of methyl formate-d (CH3OC(O)D) at 193.3 nm in a molecular-beam apparatus using undulator radiation as an ionization source. We measured kinetic-energy distributions, spatial angular anisotropies, and branching ratios of all photofragments. Fractions of energy release into product translation were calculated from the kinetic-energy distributions. Four primary dissociation pathways to asymptotes CH3O(X 2E)+DCO(X 2A′), CH3O(X 2E)+DCO(à 2A″), CH3OCO(X 2A′)+D(2S), and CH3OD(X 1A′)+CO(X 1Σ+) were identified; their branching ratios were determined to be 0.73, 0.06, 0.13, and 0.08, respectively. The former two dissociation paths were discernible in the time-of-flight spectra of fragment CH3O with a signal at m/z=29. Nominal products DCO (à 2A″) and CH3OCO (X 2A′) were unobservable as DCO in state à dissociated to D(2S)+CO(X 1Σ+) and internally hot CH3OCO (X 2A′) decomposed to CH3(X 2A2″)+CO2(X 1A1g). Products DCO and CH3O have angular anisotropy parameter β≈-0.37 but other products have nearly isotropic angular distributions with |β|<0.1. Nonadiabatic transitions might play an important role in fragmentation of methyl formate irradiated at 193.3 nm. [ABSTRACT FROM AUTHOR]

We conducted the reaction C(3P)+SiH4 at a collision energy of 4.0 kcal mol-1 in a crossed molecular-beam apparatus measuring time-of-flight mass spectra and selective photoionization. Product ions with m/z=41–43 are associated with two product channels, H2SiCH/HSiCH2/SiCH3+H and H2SiC/HSiCH/SiCH2+H2. Apart from daughter ions and isotopic variants of reaction products, the species observed at m/z=43 is assigned to product H2SiCH/HSiCH2/SiCH3 and that at m/z=42 to product H2SiC/HSiCH/SiCH2. The signals observed at m/z=41 are due to dissociative ionization of silicon-carbon hydrides of these two types. We report time-of-flight spectra of products at specific laboratory angles and theoretical simulations, from which both kinetic-energy and angular distributions of products in the center-of-mass frame were derived. The release of kinetic energy is weakly dependent on the scattering angle for these two reactions. The channels for loss of H and H2 release average translational energies of 10.5 and 16.7 kcal mol-1, respectively. As hydrogen transfer before decomposition is facile, products H2SiCH/HSiCH2/SiCH3 and H2SiC/HSiCH/SiCH2 exhibit mildly forward/backward preferred and isotropic angular distributions, respectively. We estimate the branching ratios of these channels for loss of H and H2 to be roughly 6:4. The measurements of release of kinetic energy and ionization thresholds of products indicate that SiCH3(2A″) and SiCH2(3A2) are dominant among isomeric products. To explore the reaction mechanism, we computed the potential-energy surfaces for the reaction C(3P)+SiH4. The most likely mechanism is that atom C 3P inserts into bond Si–H of SiH4 in the entrance channel, and the reaction complex H3SiCH subsequently isomerizes to HSiCH3 followed by decomposition to SiCH3(2A″)+H and SiCH2(3A2)+H2. We observed no significant evidence for the reaction C(1D)+SiH4. [ABSTRACT FROM AUTHOR]

We report evidence that cyclic-N3 is exclusively produced in the 157-nm photolysis of ClN3. Photoproduct translational energy measurements reveal a single-peaked distribution for an N3-formation channel with maximum and minimum translational energies matching the theoretically predicted minimum and maximum binding energies of cyclic-N3, respectively. The absence of linear-N3 greatly simplifies the data analysis. The zero-Kelvin heat of formation of cyclic-N3 is derived experimentally (142±3.5 kcal/mol) and is in excellent agreement with the best existing determinations from other studies. [ABSTRACT FROM AUTHOR]

Methylazide photolysis at 248 nm has been investigated by ionizing photofragments with synchrotron radiation in a photofragmentation translational spectroscopy study. CH3N and N2 were the only observed primary products. The translational energy release suggests a simple bond rupture mechanism forming singlet methylnitrene, 1CH3N, and N2. Thus, these experiments reveal the unimolecular decomposition of this highly unstable species. We explain our observations through a mechanism which is initiated by the isomerization of 1CH3N to a highly internally excited methanimine H2C==NH isomer, which decomposes by 1,1-H2 elimination forming HNC+H2 as well as sequential H-atom loss (N–H followed by C–H bond cleavage), to form HCN. No evidence for dynamics on the triplet manifold of surfaces is found. [ABSTRACT FROM AUTHOR]

This is the last report of our extensive studies on the title reaction. Presented here are the state-to-state differential cross section determinations at 11 collision energies, ranging from 1.30 to 4.53 kcal/mol. Together with previously reported results at six lower energies (0.4–1.18 kcal/mol), this perhaps represents one of the most comprehensive set of data from a single investigation for any chemical reaction. The information contents of this set of data are examined in detail, from which the dynamical consequences of reactive resonances are elucidated. Qualitative interpretations of some of the major findings are proposed. Observations that need further theoretical investigations for better physical understanding are pointed out. [ABSTRACT FROM AUTHOR]

State-to-state differential cross sections of the title reaction are presented at four collision energies, ranging from 1.18 to 4.0 kcal/mol. Product angular distributions are predominantly backscattered at low energies and shift toward sideways (peaking near 150°) at higher energies. Experimental evidence for contributions from migratory trajectories was found in the more detailed angle-specific internal state distributions. The dynamics of this reaction is mostly governed by classical mechanics, and several major findings can qualitatively be rationalized. These “classical” behaviors serve as “references” and are to be contrasted to the attributes observed for the other isotopic product channel, HF+D, in a forthcoming paper. [ABSTRACT FROM AUTHOR]

We investigated the dissociative ionization of formaldehyde (CH2O) and ethene (C2H4) produced from photolysis of 1,3-trimethylene oxide at 193 nm using a molecular-beam apparatus and vacuum-ultraviolet radiation from an undulator for direct ionization. The CH2O (C2H4) product suffers from severe dissociative ionization to HCO+ (C2H3+ and C2H2+) even though photoionization energy is as small as 9.8 eV. Branching ratios of fragmentation of CH2O and C2H4 following ionization are revealed as a function of kinetic energy of products using ionizing photons from 9.8 to 14.8 eV. Except several exceptions, branching ratios of daughter ions increase with increasing photon energy but decrease with increasing kinetic energy. The title reaction produces CH2O and C2H4 mostly on electronic ground states but a few likely on triplet states; C2H4 (∼³ B1u) seems to have a yield greater than CH2O (ã³ A2). The distinct features observed at small kinetic energies of daughter ions are attributed to dissociative ionization of photoproducts CH2O (ã³A2) and C2H4 (ã³B1u). The observation of triplet products indicates that intersystem crossing occurs prior to fragmentation of 1,3-trimethylene oxide. [ABSTRACT FROM AUTHOR]

Photodissociation dynamics of ketene at 157.6 nm has been investigated using the photofragment translational spectroscopic technique based on photoionization detection using vacuum-ultraviolet synchrotron radiation. Three dissociation channels have been observed: CH2+CO, CH+HCO, and HCCO+H. The product translational energy distributions and angular anisotropy parameters were measured for all three observed dissociation channels, and the relative branching ratios for different channels were also estimated. The experimental results show that the direct C–C bond cleavage (CH2+CO) is the dominant channel, while H migration and elimination channels are very minor. The results in this work show that direct dissociation on excited electronic state is much more significant than the indirect dissociation via the ground state in the ketene photodissociation at 157.6 nm. [ABSTRACT FROM AUTHOR]

We present results of near-threshold photoionization of N3 photofragments produced by laser photodissociation of ClN3 at 248 nm. The time of flight of recoiling N3 is used to resolve two photochemical channels producing N3, which exhibit different translational energy release. The two forms of N3 resolved in this way exhibit different photoionization thresholds, consistent with their assignment to linear (X 2Πg) and cyclic N3. This result agrees with the existing theoretical calculations of excited and ionic states of N3 and strengthens previous experimental results which suggested that the ClN3 photolysis produces a cyclic form of N3. [ABSTRACT FROM AUTHOR]

Photodissociation dynamics of 1,2-butadiene at 157 nm has been investigated using a molecular beam apparatus based on photoionization using vacuum ultraviolet synchrotron radiation. Six dissociation pathways have been observed. The observed channels are C4H5+H, C4H4+H2, C3H3+CH3, C2H3+C2H3, C2H4+C2H2, and C4H4+H+H. Among all the dissociation channels, the C3H3+CH3 channel is found to be the dominant process. The product kinetic energy distributions of all dissociation channels have been determined from simulating the experimental time-of-flight spectra. Relative branching ratios for all observed dissociation channels were also estimated based on all detected products. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We investigated the photodissociation of ethylene and its isotopomers at 157 nm in a molecular-beam apparatus using photofragment translational spectroscopy combined with synchrotron-based photoionization. The time-of-flight TOF spectra of all photofragments H, H2, C2H2, C2H3, and their deuterium isotopic variants were recorded, from which kinetic-energy distributions P(Et) and branching ratios were obtained. Most C2H3 spontaneously dissociates to C2H2+H and only C2H3 with small internal energy survives. The C2H2 fragment due to H2 elimination is observed leading the C2H2 fragment due to 2H elimination in TOF distribution because the former process has more kinetic-energy release. An analogous result is observed for C2D4 photolysis. That elimination of molecular hydrogen is site-specific and is revealed from photolysis of three dideuterated ethylene isotopomers, in which an isotopic effect plays a significant role. Observations of C2D2+2H and C2H2+2D product channels in the photolysis of 1,1-CH2CD2 provide evidence for migrations of H and D atoms. A comparison with previous experimental and theoretical results is made. [ABSTRACT FROM AUTHOR]

In a preceding paper [Lee et al., J. Chem. Phys. 119, 827 (2003)], we measured the kinetic-energy distributions P(Et) and branching ratios of products from photolysis of propene at 157 nm using time-of-flight spectroscopy combined with photoionization. In the present work, hydrogen migration before fragmentation and a site effect on P(Et) and branching ratios were revealed from the photodissociation of CD3CHCH2. Labeling of the methyl group with deuterium enabled us to differentiate between elimination of atomic and molecular hydrogen from the vinyl moiety and from the methyl moiety; the P(Et) and relative yields for the formation of H, D, H2, HD, and D2 were measured. Deuterium labeling allowed us to also differentiate the fragmentation after hydrogen transfer from that before hydrogen migration. The observation of isotopic variants of CD3 and C2H3 radicals in the C—C bond cleavage provides evidence for hydrogen transfer of propene because of site specificity. The fraction of fragmentation after hydrogen transfer is estimated to be 25%. The isotope-specific branching ratios for five dissociation pathways of CD3CHCH2 were evaluated. [ABSTRACT FROM AUTHOR]

Examines the effects of spin-orbit and rotational states on state-specific excitation function for Cl([sup 2]P)+ H[sub 2]. Effect of the rotation of the H[sub 2] reagent on reactivity at low collision energies; Role of the H[sub 2] rotation in promoting the reaction at higher E[sub c]'s; Ratio of the cross sections for a rotating H[sub 2] to a nonrotating one.

Background: Gastrointestinal bleeding is a hemorrhagic complication after primary percutaneous coronary intervention in patients with ST-segment elevation myocardial infarction (STEMI). Objectives: To determine predictors of gastrointestinal bleeding and the impact of gastrointestinal bleeding on outcomes in STEMI patients undergoing primary percutaneous coronary intervention. Methods and Results: Gastrointestinal bleeding occurred in 18 (3.5%) of 519 consecutive patients with STEMI undergoing primary percutaneous coronary intervention. Univariate predictors of gastrointestinal bleeding were previous gastrointestinal bleeding (33% vs 4%, P < .001), impaired renal function (89% vs 37%, P<.001), Killip class IV at presentation (61% vs 18%, P<.001), higher peak creatinine kinase level (mean [SD], 3801.6 [3280.2] vs 2721.3 [2286.6] IU/L, P=.05), and mechanical ventilator support (44% vs 12%, P<.001). Coprescription of proton-pump inhibitors did not reduce the risk of gastrointestinal bleeding (22.2% vs 13.4%, P=.22). Multivariate analysis showed an odds ratio (95% confidence interval) for gastrointestinal bleeding of 22.1 (5.6-86.89, P<.001) for previous gastrointestinal bleeding, 6.74 (1.30-34.89, P=.02) for impaired renal function, and 4.68 (1.35-16.2, P=.01) for Killip class IV at presentation. Gastrointestinal bleeding was associated with longer intensive care unit stay (mean [SD], 5.4 [6.7] vs 3.6 [3.6] days, P=.04), and higher in-hospital (44% vs 9%, P<.001) and overall (44% vs 13%, P<.001) mortality rate. Conclusions: Although rare, gastrointestinal bleeding in patients with STEMI significantly prolongs intensive care unit stay and increases mortality. Previous gastrointestinal bleeding, impaired renal function, and Killip class IV at presentation are associated with higher incidence of gastrointestinal bleeding. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the predictor of long-term outcomes in patients after stent implantation for unprotected left main coronary artery (LMCA) disease. Coronary stenting has recently been advocated as an alternative procedure for LMCA disease. Information on the predictors of long-term outcomes in patients after stent implantation for unprotected LMCA disease is not clear. Seventy six patients (51 men and 25 women, age 68 ± 10 years) with medically refractory angina received coronary stenting for unprotected LMCA disease. During a follow-up period of 40 ± 26 months, 7 patients (9%) died because of cardiovascular disease in 5 (7%) and noncardiovascular disease in 2 (3%). In the other 69 patients, 19 patients (25%) needed repeated percutaneous coronary intervention (PCI) and/or coronary artery bypass grafting (CABG). In a univariate analysis, only female sex was related to the repeated PCI and/or CABG ( P = 0.04). A history of cerebral vascular attack (CVA) ( P = 0.005), anemia ( P = 0.03) and lower left ventricular ejection fraction (LVEF) ( P = 0.008) were related to the cardiovascular mortality. A history of myocardial infarction ( P = 0.03), a history of CVA ( P = 0.02), anemia ( P = 0.02), and lower LVEF ( P = 0.002) were related to the total mortality. In a multivariate analysis, female sex ( P = 0.007; odds ratio 5.29, 95% confidence interval [CI] 1.57–17.80) and young age ( P = 0.025; odds ratio 3.92, 95% CI 1.19–12.98) could predict the repeated PCI and/or CABG. Only a history of CVA could predict the cardiovascular mortality ( P = 0.027; odds ratio 34.18, 95% CI 1.49–783) and only lower LVEF could predict the total mortality ( P = 0.027; odds ratio 13.26, 95% CI 1.34–131). Female sex and young age could predict the repeated PCI and/or CABG in patients after stent implantation for unprotected LMCA disease. Furthermore, a history of CVA could predict the cardiovascular mortality and lower LVEF could predict the total mortality. [ABSTRACT FROM AUTHOR]

Objective We studied the response of the superior vena cava (SVC) myocardial sleeve to atrial fibrillation (AF). Methods and results We examined adult male dogs without pacing (N=6) and after rapid atrial pacing (600 bpm) for 2 weeks (P2w; N=5) and 6-8 weeks (P6-8w; N=5). After pacing, the sleeve was increased in thickness (non-paced vs. either paced group, both P<0.05). This was associated with an increase in proliferative activity, which was higher in the P2w than the P6-8w animals (P < 0.05). In addition, collagen content increased, and the component cardiomyocytes become more unevenly oriented and shorter and narrower in shape (non-paced vs. either paced group, both P < 0.05). Pacing had different effects on connexin40 (Cx40) and Cx43 gap junctions. There was a 98% increase in Cx43 signal in P2w, and a 74% increase in P6-8w animals (non-paced vs. each paced group, both P < 0.05). In contrast, Cx40 signal decreased 47% in P2w but increased 44% in P6-8w animals (nonpaced vs. each paced group, both P < 0.05). Conclusions Rapid atrial pacing results in a specific pattern of remodeling of the canine SVC sleeve, including changes in size and shape, spatial orientation, and gap junction expression profile of the component cardiomyocytes. These changes may co-operatively affect the electrical properties and contribute to the formation and maintenance of the arrhythmogenic substrate of AF [ABSTRACT FROM AUTHOR]

Background The superior vena cava (SVC) might serve as the trigger and/or substrate for paroxysmal atrial fibrillation (AF). However, the electrophysiological properties of the SVC with chronic AF are unknown. The purposes of this study were to investigate the electrophysiological properties of the SVC and the electropharmacological effects of intravenous dl-sotalol on the canine SVC after chronic rapid atrial pacing (RAP). Methods and results In the control group, the effective refractory period (ERP), conduction velocity, and AF inducibility of the SVC were assessed in 6 normal dogs before and after an infusion of dl-sotalol. In the experimental group, the ERP, conduction velocity, and AF inducibility of the SVC were assessed before and after dl-sotalol administration in 10 dogs after 8 weeks of RAP. The SVC showed a shorter ERP, decreased slope of rate-adaptation of the ERP, increased ERP dispersion, a decreased conduction velocity, and increased inducibility and duration of AF initiated from the SVC in the RAP dogs. In the RAP dogs, intravenous dl-sotalol significantly increased the ERP, but dlsotalol did not change the slope of rate-adaptation of the ERP, dispersion of the ERP, conduction velocity, inducibility, or duration of AF initiated from the SVC. Conclusions The present study demonstrates that the canine SVC shows significant electrical remodeling and increased AF vulnerability after chronic RAP. Intravenous dl-sotalol was unable to decrease the inducibility or duration of AF initiated from the SVC. [ABSTRACT FROM AUTHOR]

Introduction: The outcome of patients with early recurrence of atrial fibrillation (AF) (within one month) after ablation procedure is controversial. Furthermore, the predictors of early and late (up to mean follow-up 30 months) recurrence of AF are not investigated in depth.Aims of the Study: The aim of the present study was to investigate the predictors of early and late recurrence of AF after catheter ablation of arrhythmogenic foci initiating AF in patients with paroxysmal AF.Methods and Results: The study included 207 patients (155 men; mean age 62 ± 13 years) who received catheter ablation of paroxysmal AF. Eighty-one (39%) patients had early recurrence of AF. Five clinical variables were related to the early recurrence of AF: (1) old age (≥65 years) (P = 0.004); (2) presence of associated cardiovascular disease (P = 0.01); (3) presence of multiple AF foci (P = 0.004); (4) presence of AF foci from left atrial free wall (P = 0.039); (5) left atrial enlargement (P = 0.038). Multivariate analysis demonstrated that presence of multiple AF foci could predict early recurrence of AF (P = 0.013; ratio = 2.24; 95% CI 1.18 to 4.25). During the follow-up period (30 ± 11 months), 70 (34%) patients had late recurrence of AF, and two clinical variables were related to the late recurrence of AF: (1) presence of early recurrence of AF (P = 0.025); (2) presence of multiple AF foci (P = 0.034). Multivariate analysis found that presence of early recurrence of AF could predict late recurrence of AF (P = 0.046; hazard ratio = 1.62; 95% CI 1.01 to 2.59). Late recurrence of AF happened in 35 (43%) of the 81 patients with early recurrence of AF, and in 35 (28%) of the 126 patients without early recurrence of AF.Conclusions: Early AF recurrence could predict late AF recurrence. [ABSTRACT FROM AUTHOR]

The aim of the study was to define the factors that may predict the outcomes of radio frequency ablation from the right ventricular outflow tract (RVOT) in patients with idiopathic VT with a QRS morphology of LBBB. Endocardial mapping and RF ablation from the RVOT were performed in 35 patients (14 men, wean age 41 ± 14 years), and VT was successfully ablated in 30 patients, There was no significant difference with regard to clinical characteristics and electrophysiological findings between patients with successful and failed ablation. The VTs with successful ablation showed an rS (n = 16) or QS (n = 14) pattern in lead V1, and all five VTs with failed ablation showed an rS pattern in lead V,. Although the absence of an R wave in lead V; did not differ between patients with successful and failed ablation (P = 0.13). the absence of an R wave in lead V1 predicted VT successfully ablated from the RVOT (positive predictive value 100%: negative predictive value 24 %). The VTs with successful ablation had a median precordial transitional zone at lead V4 (range V3-V6), whereas all five VTs with failed ablation had precordial transition zones at lead V, (P = 0.004). Furthermore, a presence of an R wave in lead V1 associated with a precordial transition zone at lead V1, predicted VT not successfully ablated from the RVOT (positive predictive value 100%: negative predictive value 100%). In conclusion, some VTs with LBBB and inferior or normal axis cannot be ablated from the RVOT. The presence of an R wave in lead V1 associated with a precordial transition zone at lead V3, suggest that some VTs may not arise from the RVOT. [ABSTRACT FROM AUTHOR]

Introduction: The precise role of irregular ventricular response in atrial fibrillation (AF) has not been fully elucidated. This study examined the independent effects of rhythm regularity in patients with chronic AF. Methods and Results: This study included 50 patients who had chronic lone AF and a normal ventricular rate. Among these patients, 21 who underwent AV junction ablation and implantation of a VVIR pacemaker constituted the ablation group; the other 29 patients were the medical group. Acute hemodynamic findings were measured in 21 ablation patients before ablation (during AF, baseline) and 15 minutes after ablation (during right ventricular pacing). Compared with baseline data, ablation and pacing therapy increased cardiac output (4.7 ± 0.8 vs 5.2 ± 0.9 L/min; P = 0.05), decreased pulmonary capillary wedge pressure (16 ± 5 vs 13 ± 4 mmHg; P = 0.001), and decreased left ventricular end-diastolic pressure (14 ± 4 vs 11 ± 3 mmHg; P < 0.05). After 12 months, the ablation group patients showed lower scores in general quality of life (-20%; P < 0.001), overall symptoms (-24%; P < 0.001), overall activity scale (-23%; P = 0.004), and significant increase of left ventricular ejection fraction (44% ± 6% vs 49% ± 5%; P = 0.02) by echocardiographic examination. Conclusion: AV junction ablation and pacing in patients with chronic AF and normal ventricular response may confer acute and long-term benefits beyond rate control by eliminating rhythm irregularity. [ABSTRACT FROM AUTHOR]

Discusses the research about the induction of changes in atrial electrophysiological properties due to tachycardia. Detection of shortening of atrial effective refractory period (ERP) on animals due to rapid atrial pacing; Consideration of tachycardia induced ERP shortening as not a specific response to atrial fibrillation; Reduction in atrial ERP at the right atrial appendage and lower right atrium.

Pulmonary Vein Electrogram in Paroxysmal AF. Introduction: The major source of ectopic heats initiating paroxysmal atrial fibrillation (AF) is from pulmonary veins (PS's). However, the electrogram characteristics of PVs are not well defined. Methods and Results: Group I consisted of 129 patients with paroxysmal AF. Group II consisted of II) patients with a concealed left-sided freewall accessory pathway. All group 1 patients had spontaneous AF initiated by ectopic beats, including 169 ectopic foci originating from the PVs. We analyzed PV electrograms from the 169 ectopic foci during sinus heats and ectopic beats. During AF initiation, most (70%) ectopic beats showed PV spike potential followed by atrial potential; 16% of ectopic beats showed PV fragmented potential followed by atrial potential; and 14% showed fusion potentials. The coupling interval between the sinus beat and the ectopic beat was significantly shorter in the inferior PV's than in the superior PV's (171 ± 48 msec vs 222 ± 63 msec, P = 0.001) and was significantly shorter in the distal foci than in the ostial foci of PVs (206 ± 52 msec vs 230 ± 56 msec, P = 0.01). The incidence of conduction block in the PVs during AF initiation was significantly higher in the inferior PS's than in the superior PVs (12/24 vs 371145, P = 0.03) and was significantly higher in the distal foci than in the ostial foci of PV's (43/121 vs 6/48, P = 0.04). The maximal amplitude of PV potential was significantly larger in the left PS's than in the right PV's, and the maximal duration of PV's potential was significantly longer in the superior PV's than in the inferior PV's during sinus beats in both group 1 and II patients. Conclusion: PV electrogram characteristics were different among the four PV's, Detailed mapping and careful interpretation are the most important steps in ablation of paroxysmal AF originating [ABSTRACT FROM AUTHOR]

Introduction: The characteristics of atrial tachycardia (AT) have varied widely among different reports. The anatomic locations of ATs may bias the results. We propose that septal ATs and freeewall ATs have different characteristics. Methods and Results: One hundred forty one patients with AT underwent electropharmacologic study, endocardial mapping, and radiofrequency ablation. Forty-nine (34.7%) patients had septal AT originating from the anteroseptal, midseptal, and posteroseptal areas. Tachycardia cycle length was similar between septal AT and freewaIl AT(367±46 msec vs 366 ± 58 msec, P > 0.05). More patients with septal AT required isoproterenol to facilitate induction (44.9% vs 31.5%, P <0.05). Septal AT was more sensitive to adenosine than free-wall AT (84.4% vs 67.8%, p <0.05). Only posteroseptal AT showed a positive P wave in Lead V1 and negative P wave in all the inferior leads (II, Ill, aVF). Radiofrequency catheter ablation had a comparable success rate for septal AT and free-wall AT (96% vs 95%) without impairment of AV conduction. During follow-up of 49 ± 13 months (range 17 to 85), the recurrence rate was similar for septal AT and free-wall AT (3.2% vs 4.6%, P = 0.08). Conclusion: Septal AT has electrophysiologic characteristics that are distinct from those of free-wall AT. Catheter ablation of the septal AT is sale and effective. [ABSTRACT FROM AUTHOR]

Introduction: Use of endocardial atrial activation sequences from recording catheters in the right atrium, His bundle, and coronary sinus to predict the location of initiating foci of atrial fibrillation (AF) before an atrial transseptal procedure has not been reported. The purpose of the present study was to develop an algorithm using endocardial atrial activation sequences to predict the location of initiating foci of AF before transseptal procedure. Methods and Results: Seventy-five patients (60 men and 15 women, age 68 ± 12 years) with frequent episodes of paroxysmal AF were referred for radiofrequency ablation. By retrospective analysis, characteristics of the endocardial atrial activation sequences of right atrial, His-bundle, and coronary sinus catheters from the Initial 37 patients were correlated with the location of Initiating foci of AF which were confirmed by successful ablation. The endocardial atrial activation sequences of the other 38 patients were evaluated prospectively to predict the location of initiating foci of AF before transseptal procedure using the algorithm derived from the retrospective analysis. Accuracy of the value <0 msec (obtained by subtracting the time interval between high right atrium and His-bundle atrial activation during atrial premature beats from that obtained during sinus rhythm) for discriminating the superior vena cava or upper portion of the crista terminalis from the pulmonary vein (PV) foci was 100%. When the Interval between sinai activation of ostial and distal pairs of the coronary sinus catheter of the atrial premature beats was <0 msec, the accuracy for discriminating left PV foci from right PV foci was 92% In the 24 foci from the left PVs and 100% in the 19 foci from the right PVs. Conclusion: Endocardial atrial activation sequences from right atrial, His-bundle, and coronary sinus catheters can accurately predict the location of initiating foci of Al before transseptal procedure. This may facilitate mapping and radiofrequency ablation of paroxysmal AF. [ABSTRACT FROM AUTHOR]

Introduction: The characteristics of atrial tachycardia (AT) have varied widely among different reports. The anatomic locations of ATs may bias the results. We propose that septal ATs and free-wall ATs have different characteristics. Methods and Results: One hundred forty-one patients with AT underwent electropharmacologic study, endocardial mapping, and radiofrequency ablation. Forty-nine (34.7%) patients had septal AT originating from the anteroseptal, midseptal, and posteroseptal areas. Tachycardia cycle length was similar between septal AT and freewaIl AT(367 ± 46 msec vs 366 ± 58 msec, P> 0.05). More patients with septal AT required isoproterenol to facilitate induction (44.9% vs 31.5%, P < 0.05). Septal AT was more sensitive to adenosine than free-wall AT (84.4% vs 67.8%, p < 0.05). Only posteroseptal AT showed a positive P wave in lead V1 and negative P wave in all the inferior leads (II, III, aVF). Radiofrequency catheter ablation had a comparable success rate for septal AT and free-wall AT (96% vs 95%) without impairment of AV conduction. During follow-up of 49 ± 13 months (range 17 to 85), the recurrence rate was similar for septal AT and free-wall AT (3.2% vs 4.6%, P = 0.08). Conclusion: Septal AT has electrophysiologic characteristics that are distinct from those of free-wall AT. Catheter ablation of the septal AT is sale and effective. [ABSTRACT FROM AUTHOR]

To compare the safety and efficacy of anterior versus posterior approach for atrioventricular (AV) junction modification, 40 patients with medically refractory paroxysmal (PAF) or chronic atrial fibrillation (AF) were randomly assigned to receive AV junction modification with an anterior or posterior approach. If the ablation session had taken more than 1 hour without success, the alternative ablation approach was attempted. Among the 18 patients assigned to receive the anterior approach, 14 (78%) had a primary success. One (5%) patient had complete AV block after ablation. Three patients crossed over to the posterior approach and had a successful outcome. Fourteen (64%) of 22 patients initially treated with the posterior approach had primary success. One (4%) patient developed complete AV block. Seven patients crossed over to the anterior approach and had a successful outcome. The primary success rate (14/18 vs 14/22, P = NS), incidence of transient AV block (3/18 vs 3/22, P = NS), and complete AV block (1/18 vs 1/22, P = NS) were similar between the anterior approach and posterior approach. The major differences between the two groups showed more radiofrequency pulses (10 ± 4 vs 6 ± 3 pulses, P < 0.01), longer procedure duration (50 ± 24 vs 28 ± 18 minutes, P < 0.01), and longer fluoroscopy exposure time (28 ± 17 vs 16 ± 8 minutes, P < 0.01) in the patients who had primary success with the posterior approach. In conclusion, this study demonstrated that (1) the two techniques had similar efficacies; (2) if one approach was ineffective, switching to the other approach might be safe; (3) combining these two approaches resulted in overall improvement in the success rate of this procedure, and (4) the posterior approach needed more radiofrequency pulses, longer procedural time, and longer fluoroscopy exposure time. [ABSTRACT FROM AUTHOR]

The authors developed a canine model of pacing induced cardiomyopathy to study the possible mechanisms of ibutilide induced torsades de pointes (TPj in heart failure. Thirteen dogs received intravenous ibutilide after acute A V block for 60 minutes, and after implantation of a VVI pacemaker, with a rate of 270 beats/min for 2-3 weeks. Twelve-lead ECG and right and left ventricle monophasic action potentials were recorded at different right ventricle pacing cycle lengths from 600 ms to 1200 ms during the study. The results showed ibutilide could significantly prolong ventricular repolarization and increase the dispersion in a dose dependent and reverse use dependent manner. Furthermore, after ibutilide administration, cardiomyopathic dogs had a greater dispersion of ventricular repolarization, and also had higher incidences of early after depolarizations and spontaneous or pacing induced TP than acute AV block dogs. [ABSTRACT FROM AUTHOR]

Pacing and Atrial Electrophysiology. Introduction: Patients receiving VVI pacemakers have a higher incidence of paroxysmal atrial fibrillation (AF) than those receiving DDD pacemakers. However, the mechanism behind the difference is not clear. The purpose of this study was to investigate whether atrial electrophysiology and the autonomic nervous system play a role in the occurrence of AF during AV pacing. Methods and Results: The study population consisted of 28 patients who had (group I, n = 15) or did not have (group II, n = 13) AF induced by a single extrastimulus during pacing with different AV intervals. Atrial pressure, atrial size, atrial effective refractory periods, and atrial dispersion were evaluated during pacing with different AV intervals. Twenty-four-hour heart rate variability and barorefiex sensitivity also were examined. Atrial pressure, atrial size, effective refractory periods in the right posterolateral atrium and distal coronary sinus, and atrial dispersion increased as the AV interval shortened from 160 to 0 msec. During AV pacing, group I patients had greater minimal (52 ± 17 vs 25 ± 7 msec; P < 0.005) and maximal (76 ± 16 vs 36 ± 9 msec; P < 0.005) atrial dispersion than group II patients. The differences in atrial size and atrial dispersion among different AV intervals were greater in patients with AF than in those without AF. Baroreflex sensitivity (6.6 ± 1.7 vs 3.9 ± 1.0; P < 0.00005), but not heart rate variability, was higher in patients with AF than in those without AF. Conclusion: Abnormal atrial electrophysiology and higher vagal reflex activity can play important roles in the genesis of AF in patients receiving pacemakers. [ABSTRACT FROM AUTHOR]

Introduction: Antiarrhythmic drugs have been reported to promote the conversion of atrial fibrillation to atrial flutter In patients with paroxysmal atrial fibrillation. However, information about the electrophysiologic mechanism and response to radiofrequency ablation of these drug-induced atrial flutters is limited. Furthermore, the determinants of the development of persistent atrial flutter in patients treated for atrial fibrillation with antiarrhythmic drugs are still unknown. Methods and Results: Among the 136 patients treated for atrial fibrillation with amiodarone (n = 96) or propafenone (n = 40), 15 (11%, mean age 65.5 ± 12.3 years) were identified to have subsequent development of persistent atrial flutter based on surface ECG characteristics during antiarrhythmic drug treatment. The mean interval between the beginning of drug treatment and the onset of atrial flutter was 5.0 ± 55 months. Intracardiac mapping and entrainment studies revealed that 11 patients had counterclockwise typical atrial flutter, and 4 had clockwise typical atrial flutter. All 15 patients underwent successful ablation with creation of complete bidirectional isthmus conduction block. After a mean follow-up of 123 ± 4.2 months, 14(93%) of 15 patients who underwent successful ablation and continued taking antiarrhythmic drugs have remained in sinus rhythm. Univariate analysis of clinical variables demonstrated that only atrial enlargement was significantly related to the occurrence of persistent atrial flutter. Conclusion: In patients with atrial fibrillation, persistent typical atrial flutter might occur during antiarrhythmic drug treatment, and atrial enlargement was a risk factor for the development of such an arrhythmia. Radiofrequency ablation and continuation of pharmacologic therapy offered a safe and effective means of achieving and maintaining sinus rhythm. [ABSTRACT FROM AUTHOR]

Introduction: Gender difference is known to be associated with the occurrence of arrhythmia. However, the effects of female sex hormone on atrial electrophysiology, and on the occurrence of torsades de pointes (TdP) induced by cisapride have been unclear. Methods and Results: Two experiments were included in this study, in experiment 1, effective refractory periods (ERPs) from five epicardial atrial sites were measured before and after rapid atrial pacing at 800 beats/min for 30 minutes in dogs with pretreatment of verapamil (n = 10), 17β-estradiol (n = 10), or without pretreatment (n = 10, control group). In experiment 2, limb-lead ECG and monophasic action potentials in the left and right ventricles were recorded before and after each dose of cisapride (2 to 6 mg/kg) during different ventricular rates in dogs with (n = 9) and without (n = 14) concomitant administration of 17β-estradiol (0.3 μg/kg). After 17β-estradiol administration, there were greater atrial ERPs in the study dogs than in the control group. The atrial ERPs were shortened significantly after rapid atrial pacing, but the degree was greater In the control group titan In the dogs pretreated with verapamil or 17β-estradiol. Moreover, the recovery of atrial ERPs was faster in dogs pretreated with verapamil or 17β-estradiol than in the control group. In experiment 2, cisapride prolonged the QT interval and biventricular APD90 and induced early afterdepolarizations (EADs) in a dose-dependent manner. However, dogs receiving cisapride combined with 17β-estradiol had a greater increase of ventricular repolarization and a higher incidence of EADs than those receiving cisapride only. Moreover, dogs receiving cisapride combined with 17β-estradiol (3/9, 33%) had a greater incidence of TdP than those receiving cisapride only (0/14, 0%, P < 0.05). Conclusions: 17β-estradiol has a significant effect on atrial electrophysiology, which may be related to the prevention of atrial fibrillation. However, the high incidence of TdP in dogs receiving cisapride combined with 17β-estradiol suggests that the female sex hormone is an important risk factor of cisapride-induced proarrhythmia. [ABSTRACT FROM AUTHOR]

It Is unknown whether there are regional differences in the change of atrial effective refractory period (EBP) after a short duration of rapid atrial pacing. Furthermore, the effects of calcium channel and potassium channel on this phenomenon have not been extensively investigated. In opened-chest dogs, the endocardial monophasic action potential duration at 90% repolarization (APD90) from the right atrial appendage, and ERP from seven atrial sites were measured before and after rapid atrial pacing at 800 beats/min for 30 minutes. Both atrial ERP and APD90 significantly shortened after rapid atrial pacing. The postpacing atrial ERP and APD90 shortening persisted for 119 ± 3 and 123 ± 4 seconds after cessation of pacing, respectively. There was no significant difference in the magnitude or recovery course of atrial ERP shortening after pacing among the seven atrial sites. Pretreatment with nicorandil and d-sotalol had no effects on the magnitude or recovery course of atrial ERP shortening after pacing. However, the degree of ERP and APD90 shortening after pacing was significantly attenuated in the verapamil and ryanodine groups; furthermore, the recovery of ERP and APD90 after cessation of pacing was faster in the two groups. In conclusion, shortening of atrial EBP induced by short-duration rapid atrial pacing was uniform in both atria. Both the adenosine triphosphatase (ATP) dependent potassium current and rapid component of the delayed rectifier did not significantly influence this phenomenon, but both the verapamil and ryanodine could significantly attenuate the degree of atrial ERP and APD90 shortening. [ABSTRACT FROM AUTHOR]

Although pacing technique has demonstrated that the most common site of conduction block in a manifest accessory pathway (AP) was between the AP and the ventricle, most of the block sites have been found to be between the atrium and AP after successful radiofrequency ablation. Furthermore, the block site in a concealed AP after successful radiofrequency catheter ablation has not been reported in the literature, and comparisons between a manifest and concealed AP have not been performed. This study included 219 consecutive patients undergoing successful radiofrequency catheter ablation of a single AP. AP potential was recorded at the successful target site in 76 of 92 (82.6%) patients with manifest APs, and in 99 of 127 (77.9%) patients with concealed APs. All the left-sided APs (including left posteroseptal APs) were ablated by a ventricular approach, and right-sided APs (including anteromidseptal and right posteroseptal APs) were ablated by an atrial approach. The site of conduction block was determined by analyzing and comparing the local electrograms recorded before and after radiofrequency ablation at successful ablation sites. Conduction block of manifest APs was between the atrial-AP (A-AP) in 69 patients (75%) and between the AP-ventricle (AP-V) interface in 7 patients (7.6%), whereas the conduction block of concealed APs occurred between the AP-V in 90 patients (70.9%) and between the A-AP interface in 9 patients (7.1%). Neither the preablation electrogram nor electrophysiologic characteristics of APs predicted the site of conduction block. Furthermore, neither the location of the APs nor the position of the ablation catheter affected the block site. It was concluded that the most common site of conduction block during successful radiofrequency catheter ablation of a manifest and concealed AP was between the A-AP and AP-V interface, respectively, and the impedance mismatch theory explained only part of the findings. [ABSTRACT FROM AUTHOR]

Introduction: The dromotropic effects of intracardiac parasympathetic nerve stimulation have not been well studied; furthermore, the effects of radiofrequency ablation lesions on parasympathetic nerve stimulation are not clear. Methods and Results: Group I: intracardiac electrical stimulation in the right posteroseptal and anteroseptal areas under different stimulation strengths; group II: intracardiac electrical stimulation before and 10 minutes after intravenous propranolol; group III; intracardiac electrical stimulation before and 5 minutes after intravenous atropine. Among the 10 patients with AV nodal reentrant tachycardia (group IV) and the 10 patients with atrial flutter (group V), atrial fibrillation was induced before and after successful ablation, and intracardiac electrical stimulation in the right posteroseptal area was performed before and after successful ablation. The maximal response and complete decay of the response occurred within 2 to 6 seconds of initiation or termination of parasympathetic nerve stimulation. This negative dromotropic effect disappeared after atropine was administered, but not after propranolol. After successful ablation, parasympathetic stimulation still induced negative dromotropic effects. Conclusion: Electrical stimulation of parasympathetic nerve fibers near the posteroseptal and anteroseptal areas could induce a negative dromotropic effect, and this effect was preserved after successful radiofrequency ablation of slow pathway and isthmus conduction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

RF Catheter Ablation for Atrial Flutter. Introduction: Little is known about the predictors of recurrent atrial flutter or fibrillation after successful radiofrequency ablation of typical atrial flutter. In addition, there is only limited evidence suggesting that elimination of atrial flutter would modify the natural history of atrial fibrillation in patients who experienced both of these arrhythmias. The aims of the present study were to investigate the long-term results of radiofrequency catheter ablation and to examine the predictors for late occurrence of atrial fibrillation in a large population with typical atrial flutter. Methods and Results: The study population consisted of 144 patients (mean age 56 ± 18 years) with successful ablation of clinically documented typical atrial flutter. In the first 50 patients, successful ablation was defined as termination and noninducibility of atrial flutter; for the subsequent 94 patients, successful ablation was defined as achievement of bidirectional isthmus conduction block and no induction of atrial flutter. The clinical and echocardiographic variables were analyzed in relation to the late occurrence of atrial flutter or fibrillation. Over the follow-up period of 17 ± 13 months, 14 (9.7%) patients had recurrence of typical atrial flutter. In the first 50 patients, 8 (16%) had recurrence of atrial flutter, compared with only 6 (6%) of the following 94 patients. Patients with incomplete isthmus block had a significantly higher incidence of recurrent atrial flutter than those with complete isthmus block (6/16 vs 0/78, P < 0.0001) in the following 94 patients. There was no predictor for recurrence of atrial flutter after successful ablation as determined by univariate and multivariate analysis. Although successful ablation of atrial flutter eliminated atrial fibrillation in 45 % of patients with a prior history of atrial fibrillation, 31 (21.5%) of 144 patients undergoing this procedure developed atrial fibrillation during the followup period. Univariate analysis revealed that three clinical variables were related to the occurrence of atrial fibrillation: (1) the presence of structural heart disease; (2) a history of atrial fibrillation before ablation; and (3) inducible sustained atrial fibrillation after ablation. By multi- variate analysis, only a history of atrial fibrillation and inducible sustained atrial fibrillation could predict the late development of atrial fibrillation after atrial flutter ablation. Conclusion: Radiofrequency catheter ablation of typical atrial flutter is highly effective and associated with a low recurrence rate of atrial flutter, but atrial fibrillation continues to be a long-term risk for patients undergoing this procedure. The presence of structural heart disease and prior spontaneous or inducible sustained atrial fibrillation increases the risk of developing atrial fibrillation. [ABSTRACT FROM AUTHOR]

We present a case of cardiac asystole Induced by radiofrequency catheter ablation of a left anterolateral accessory pathway in a 28-year-old woman with Wolff-Parkinson-White syndrome who was experiencing recurrent palpitation. Radiofrequency current applied on the ventricular aspect of the mitral annulus corresponding to the aforementioned site provoked profound slowing of the sinus rate preceded by disappearance of the preexcitation, and then asystole ensued. The proposed causal mechanism was a reflexogenically mediated hypotension-bradycardia syndrome (Bezold-Jarisch-like phenomenon) through stimulation of either nearby vagal afferent pathways or sensory terminal receptors at the ablation site. [ABSTRACT FROM AUTHOR]

Introduction: Detailed electrophysiologic study of AV nodal reentrant tachycardia (AVNRT) with 2:1 AV block has been limited. Methods and Results: Six hundred nine consecutive patients with AVNRT underwent electrophysiologic study and radiofrequency catheter ablation of the slow pathway. Twenty-six patients with 2:1 AV block during AVNRT were designated as group I, and those without this particular finding were designated as group II. The major findings of the present study were: (1) group I patients had better anterograde and retrograde AV nodal function, shorter tachycardia cycle length (during tachycardia with 1:1 conduction (307 ± 30 vs 360 ± 58 msec, P < 0.001), and higher incidence of transient bundle branch block during tachycardia (18/26 vs 43/609, P < 0.001) than group II patients: (2) 21 (80.8%) group I patients had alternans of AA intervals during AVNRT with 2:1 AV block. Longer AH intervals (264 ± 26 vs 253 ± 27 msec, P = 0.031) were associated with the blocked beats. However, similar HA intervals (51 ± 12 vs 50 ± 12 msec. P = 0.363) and similar HV intervals (53 ± 11 vs 52 ± 12, P = 0.834) were found in the blocked and conducted beats; (3) ventricular extrastimulation before or during the His-bundle refractory period bundle could convert 2:1 AV block to 1:1 AV conduction. Conclusions: Fast reentrant circuit, rather than underlying impaired conduction of the distal AV node or infranodal area, might account for second-degree AV block during AVNRT. Slow pathway ablation is safe and effective in patients who have AVNRT with 2:1 AV block. [ABSTRACT FROM AUTHOR]

Introduction: Although the mechanism and radiofrequency catheter ablation of counterclockwise (typical) atrial flutter have been studied extensively, information about the electrocardiographic and electrophysiologic characteristics and effects of radiofrequency ablation in patients with clockwise atrial flutter is limited. Methods and Results: Thirty consecutive patients with clinically documented paroxysmal clock-wise atrial flutter were studied. Endocardial recordings and entrainment study using a "halo" catheter with 10 electrode pairs in the right atrium were performed. Radiofrequency energy was applied to the inferior vena cava-tricuspid annulus (IVC-TA) and/or coronary sinus ostium-tricuspid annulus (CSO-TA) isthmus to evaluate the effects of linear catheter ablation. Eighteen patients had both counterclockwise and clockwise atrial flutters, and 12 patients had only clockwise atrial flutter. Both forms of atrial flutter had similar flutter cycle lengths (232 ± 30 vs 226 ± 25 msec, P = 0.526) but reverse activation sequences. Right atrial pacing at a cycle length 20 msec shorter than the flutter cycle length from the CSO-TA isthmus, IVC-TA isthmus, and the area between the two isthmuses revealed concealed entrainment with stimulus-to-P wave intervals of 32 ± 19, 95 ± 14, and 50 ± 17 msec (P = 0.022) in the counterclockwise form, and 110 ± 12, 40 ± 20, and 60 ± 15 msec (P = 0.018) in the clockwise form. In clockwise atrial flutter, 20 patients with biphasic P waves in the inferior leads had the presumed exit site of slow conduction area located at the low posterolateral right atrium; 10 patients with positive P waves in the inferior leads had the presumed exit site located at the mid-high posterolateral right atrium. Among the 18 patients with both forms of atrial flutter, linear ablation lesions directed at the IVC-TA isthmus eliminated both forms of atrial flutter in 14 patients; in the remaining 4 patients. CSO-TA linear lesions eliminated the counterclockwise form and IVC-TA lesions eliminated the clockwise form. Among the 12 patients with the clockwise form only, CSO-TA linear lesions eliminated flutter in 2 and IVC-TA linear lesions eliminated flutter in 10 patients. Successful ablation was confirmed by creation of bidirectional conduction block in the IVC-TA and/or CSO-TA isthmus during pacing from the proximal coronary sinus and right posterolateral atrium sandwiching the linear lesions. During the follow-up period of 17 ± 8 months. 2 patients had recurrence clockwise atrial flutter, 1 patient had new onset of atypical atrial flutter, and 2 patients had new onset of atrial fibrillation. Conclusions: Counterclockwise and clockwise atrial flutters may have overlapping slow conduction areas with different exit sites. Radiofrequency catheter ablation using the linear method directed at the IVC-TA and CSO-TA isthmuses was feasible and effective in treating both forms of atrial flutter. [ABSTRACT FROM AUTHOR]

Introduction: Information about temperature and impedance monitoring during radiofrequency catheter linear ablation of atrial flutter has not been reported. We proposed that a radiofrequency catheter ablation system using a closed-loop temperature control model could decrease the incidence of coagulum formation and shorten the radiation exposure and procedure times compared with those found in a power control model. Methods and Results: Forty patients (8 women and 32 men; mean age 64 ± 7 years) with atrial flutter were referred for radiofrequency ablation. The patients were randomized into two groups: group I patients underwent radiofrequency catheter linear ablation of atrial flutter using a power control of energy output model; and group II patients underwent the closed-loop temperature control model with a target electrode temperature of 70°C. As compared with group II, group I patients had a higher incidence of coagulum formation (12% vs 2%, P < 0.05), temperature shutdown (11% vs 0%, P < 0.01), and impedance shutdown (16% vs 3%, P < 0.01), more radiofrequency applications (7 ± 3 vs 4 ± 2, P < 0.01), and longer procedure time (100 ± 25 vs 75 ± 23 minutes, P < 0.05) and radiation exposure time (31 ± 10 vs 20 ± 7 minutes, P < 0.05) required for successful ablation. Larger deviations of temperature (9.0° ± 2.4°C vs 5.0° ± 1.2°C, P < 0.0001) and impedance (9.2 ± 2.6 Ω vs 5.3 ± 1.6 Ω, P < 0.0001) were also found in group I patients compared with those in group II. Conclusions: This study demonstrated that a closed-loop temperature control model could facilitate the effects of radiofrequency catheter ablation of the atrial flutter circuit by decreasing coagulum formation, temperature and impedance shutdown, and procedure and radiation exposure times. [ABSTRACT FROM AUTHOR]

Introduction: The dimension of Koch's triangle in patients with AV nodal reentrant tachycardia has not been well described. Understanding the dimension and anatomical distance related to Koch's triangle might be useful in avoiding accidental AV block during ablation of the slow pathway. The purposes of this study were to define the dimension of Koch's triangle and its related anatomical distance and correlate these parameters with the successful ablation sites in patients with AV nodal reentrant tachycardia. Methods and Results: We studied 218 patients with AV nodal reentrant tachycardia. The distance between the presumed proximal His-bundle area and the base of the coronary sinus orifice (DHis-OS) measured in the right anterior oblique view was used to define the dimension of Koch's triangle. The distance of the proximal His-bundle recording site from the successful ablation site (DHis-Ab) and the distance as a fraction of the entire length of Koch's triangle (DHis-Ab/DHis-OS) were determined. The mean DHis-OS and DHis-Ab were 25.9 ± 7.9 and 13.4 ± 3.8 mm, respectively. DHis-OS negatively correlated with patient age (r = -0.41, P < 0.0001) and body mass index (r = -0.18, P = 0.004). Among the patients with successful ablation sites in the medial area, DHis-OS was longer (27.2 ± 6.6 vs 24.6 ± 8.4 mm, P < 0.005), DHis-Ab was similar (12.9 ± 3.1 vs 13.9 ± 4.0, P > 0.05) and DHis-Ab/DHis-OS was smaller (0.48 ± 0.04 vs 0.74 ± 0.11, P < 0.05). Furthermore, the patients with successful ablation sites in the medial location needed more radiofrequency pulse numbers than those in the posterior location (6 ± 4 vs 4 ± 3, P < 0.05). Conclusion: The site of successful slow pathway ablation was consistently about 13 mm from the site recording the proximal His-bundle deflection in patients with AV nodal reentrant tachycardia despite marked variability in the dimensions of Koch's triangle: therefore, patients with large triangles required ablation in the medial region rather than the posterior region. Care should be taken when delivering radiofrequency energy to the posteroseptal area in patients with shorter DHis-OS to avoid injury to AV node. [ABSTRACT FROM AUTHOR]

Introduction: Catheter ablation may eliminate anterograde and retrograde accessory pathway conduction at closely adjacent but anatomically discrete sites. However, the mechanisms of this discrepancy, the electrophysiologic and anatomical characteristics, and information about systematic study from a large patient population are not available. The purpose of this study was to investigate the electrophysiologic characteristics and anatomical complexities of the accessory pathway in which anterograde and retrograde conduction was successfully ablated at different sites. Methods and Results: Thirty-eight (10.9%) patients (19 men and 19 women; mean age 37 ± 2.4 years) fulfilling the criteria of having separate ablation sites for anterograde and retrograde conduction were designated as group I, and the other 310 patients (215 men and 95 women: mean age 47 ± 0.6 years) were designated as group II. The patients with right-sided free-wall pathways had the highest incidence (18.6%) of separate ablation sites. The anatomical distance between anterograde and retrograde directions (left anterior oblique view, 13 ± 0.6 vs 8 ± 0.9 mm, P < 0.01; right anterior oblique view, 17 ± 0.6 vs 5 ± 0.7 mm, P < 0.01), and incidence of conduction impairment in one direction after successful ablation of another direction (15% vs 78%, P < 0.05) differed significantly between left and right free-wall pathways. The mean distances obtained from left (7 ± 0.4 vs 14 ± 0.4 mm, P < 0.05) and right (7 ± 1.1 vs 15 ± 0.9 mm, P < 0.05) anterior oblique views were shorter in patients who had impairment of conduction properties than those in patients without impaired conduction after successful ablation of one direction. Conclusions: This study showed that anatomical and functional dissociation of the accessory pathway into anterograde and retrograde components was possible. Further study on the relation between electrophysiologic and pathologic characteristics would be helpful to confirm these findings. [ABSTRACT FROM AUTHOR]

Catheter Ablation. Application of radiofrequency energy to arrhythmogenic substrates after careful cardiac mapping could ensure a high success rate in eliminating certain types of tachyarrhythmias. Future studies of catheter ablation will focus on how to improve ablation efficacy and achieve a better result in various types of tachyarrhythmias. More information about the arrhythmogenic mechanisms will be provided to improve the knowledge of diagnostic and interventional electrophysiology. [ABSTRACT FROM AUTHOR]

Idiopathic left ventricular tachycardia is a distinct clinical entity with a typical ECG of right bundle branch block and left axis deviation. We presented a 39-year-old man with idiopathic left ventricular tachycardia, which demonstrated change in the configuration of QRS complex during successive radiofrequency catheter ablation. We proposed that this idiopathic left ventricular tachycardia may have alternative pathways within the reentrant circuit leading to different exits. [ABSTRACT FROM AUTHOR]