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Background: The role of fiber orientation on a global chamber level in sustaining atrial fibrillation (AF) is unknown. The goal of this study was to correlate the fiber direction derived from Diffusion Tensor Imaging (DTI) with AF inducibility. Methods: Transgenic goats with cardiac-specific overexpression of constitutively active TGF-β1 (n = 14) underwent AF inducibility testing by rapid pacing in the left atrium. We chose a minimum of 10 minutes of sustained AF as a cut-off for AF inducibility. Explanted hearts underwent DTI to determine the fiber direction. Using tractography data, we clustered, visualized, and quantified the fiber helix angles in 8 different regions of the left atrial wall using two reference vectors defined based on anatomical landmarks. Results: Sustained AF was induced in 7 out of 14 goats. The mean helix fiber angles in 7 out of 8 selected regions were statistically different (P-Value < 0.05) in the AF inducible group. The average fractional anisotropy (FA) and the mean diffusivity (MD) were similar in the two groups with FA of 0.32±0.08 and MD of 8.54±1.72 mm2/s in the non-inducible group and FA of 0.31±0.05 (P-value = 0.90) and MD of 8.68±1.60 mm2/s (P-value = 0.88) in the inducible group. Conclusions: DTI based fiber direction shows significant variability across subjects with a significant difference between animals that are AF inducible versus animals that are not inducible. Fiber direction might be contributing to the initiation and sustaining of AF, and its role needs to be investigated further. [ABSTRACT FROM AUTHOR]

Background: Esophageal thermal injury (ETI) is a known and potentially serious complication of catheter ablation for atrial fibrillation. We intended to evaluate the distance between the esophagus and the left atrium posterior wall (LAPW) and its association with esophageal thermal injury. Methods: A retrospective analysis of 73 patients who underwent esophagogastroduodenoscopy (EGD) after LA radiofrequency catheter ablation for symptomatic atrial fibrillation and pre‐ablation magnetic resonance imaging (MRI) was used to identify the minimum distance between the inner lumen of the esophagus and the ablated atrial endocardium (pre‐ablation atrial esophageal distance; pre‐AED) and occurrence of ETI. Parameters of ablation index (AI, Visitag Surpoint) were collected in 30 patients from the CARTO3 system and compared with assess if ablation strategies and AI further impacted risk of ETI. Results: Pre‐AED was significantly larger in patients without ETI than those with ETI (5.23 ± 0.96 mm vs. 4.31 ± 0.75 mm, p <.001). Pre‐AED showed high accuracy for predicting ETI with the best cutoff value of 4.37 mm. AI was statistically comparable between Visitag lesion markers with and without associated esophageal late gadolinium enhancement (LGE) detected by postablation MRI in the low‐power long‐duration ablation group (LPLD, 25‐40 W for 10–30 s, 393.16 [308.62–408.86] vs. 406.58 [364.38–451.22], p =.16) and high‐power short‐duration group (HPSD, 50 W for 5–10 s, 336.14 [299.66–380.11] vs. 330.54 [286.21–384.71], p =.53), respectively. Conclusion: Measuring the distance between the LA and the esophagus in pre‐ablation LGE‐MRI could be helpful in predicting ETI after LAPW ablation. [ABSTRACT FROM AUTHOR]

Introduction: Esophageal injury is rare but potentially a devastating complication of atrial fibrillation (AF) ablation. The goal here was to provide insight into the short‐term natural history of esophageal thermal injury (ETI) after radiofrequency catheter ablation (RFCA) for AFby esophagogastroduodenoscopy (EGD). Methods: We screened patients who underwent RFCA for AF and EGD based on esophageal late gadolinium enhancement (LGE) in postablation magnetic resonance imaging. Patients with ETI diagnosed with EGD were included. We defined severity of ETI according to Kansas City classification: type 1: erythema; type 2: ulcers (2a: superficial; 2b deep); type 3 perforation (3a: perforation; 3b: perforation with atrioesophageal fistula [AEF]). Repeated EGD was performed within 1−14 days after the last EGD if recommended and possible until any certain healing signs (visible reduction in size without deepening of ETI or complete resolution) were observed. Results: ETI was observed in 62 of 378 patients who underwent EGD after RFCA. Out of these 62 patients with ETI, 21% (13) were type 1, 50% (31) were type 2a and 29% (18) were type 2b at the initial EGD. All esophageal lesions, but one type 2b lesion that developed into an AEF, showed signs of healing in repeated EGD studies within 14 days after the procedure. The one type 2b lesion developing into an AEF showed an increase in size and ulcer deepening in repeat EGD 8 days after the procedure. Conclusion: We found that all ETI which did not progress to AEF presented healing signs within 14 days after the procedure and that worsening ETI might be an early signal for developing esophageal perforation. [ABSTRACT FROM AUTHOR]

Background: Recent guidelines recommend a 3‐month blanking period after atrial fibrillation (AF) ablations, which are based on clinical observation. Our goal was to quantify the timeline of the radiofrequency ablation lesion maturation using serial late gadolinium enhancement‐magnetic resonance imaging (LGE‐MRI) and to develop a blanking period estimate based on visible lesion maturation. Methods: Inclusion criteria targeted patients who underwent AF ablation and at least four MRI scans: at baseline before ablation, within 24 hours after (acute), between 24 hours and 90 days after (subacute), and more than 90 days after ablation (chronic). Central nonenhanced (NE) and surrounding hyperenhanced (HE) area volumes were measured and normalized to chronic lesion volume. Results: This study assessed 75 patients with 309 MRIs. The acute lesion was heterogeneous with a HE region surrounding a central NE region in LGE‐MRI; the acute volume of the total (HE + NE) lesion was 2.62 ± 0.46 times larger than that of the chronic lesion. Acute T2‐weighted imaging also showed a relatively large area of edema. Both NE and HE areas gradually receded over time and NE was not observed after 30 days. Larger initial NE volume was associated with a significantly greater chronic scar volume and this total lesion volume receded to equal the chronic lesion size at approximately 72.5 days (95% prediction interval: 57.4‐92.2). Conclusion: On the basis of serial MRI, atrial ablation lesions are often fully mature before the typical 90‐day blanking period, which could support more timely clinical decision making for arrhythmia recurrence. [ABSTRACT FROM AUTHOR]

Polarization transfer is demonstrated as a sensitive technique for the measurement of isotopic fractionation of protonated carbons at natural abundance. This method allows kinetic isotope effects (KIEs) to be determined with substantially less material or shorter acquisition time compared with traditional experiments. Computations quantitatively reproduce the KIEs in a Diels-Alder reaction and a catalytic glycosylation. The glycosylation is shown to occur by an effectively concerted mechanism. [ABSTRACT FROM AUTHOR]

We describe a computer algorithm that searches for substitution rules on a set of triangles, the angles of which are all integer multiples of $$\pi /n$$ . We find new substitution rules admitting $$7$$ -fold rotational symmetry at many different inflation factors. [ABSTRACT FROM AUTHOR]

We present a general model for understanding the stereochemical course of intramolecular Michael reactions. We show that the addition of β-ketoester enolates to α,β-unsaturated esters and imides bearing adjacent stereocenters (X, Y = H, Me, OR) leads to high levels of asymmetric induction. Reinforcing and nonreinforcing stereochemical relationships are evaluated from the syn and anti reactant diastereomers. On the basis of synthetic, spectroscopic, and computational studies, we propose that the outcomes of these reactions can be rationalized by a dipole-minimized chair transition-state model. [ABSTRACT FROM AUTHOR]

An unusual intramolecular kinetic isotope effect (KIE) in the reaction of dichloroketene with cis-2-butene does not fit with a simple asynchronous cycloaddition transition state, but it can be predicted from trajectory studies on a bifurcating energy surface. The origin of the KIE is related to a high propensity for transition state recrossing in this system, with heavier masses recrossing less. The KIE can also be predicted by a statistical model that treats the cycloaddition as a stepwise mechanism, the rate-limiting second step being associated with an entropic barrier for formation of the second carbon-carbon bond. The relevance of this stepwise mechanism to other asynchronous but seemingly concerted cycloadditions is suggested by examination of organocatalytic Diels-Alder reactions. [ABSTRACT FROM AUTHOR]

This article presents information regarding factors affecting relative efficiency of general acid catalysis. Proton transfer catalysis by Bronsted acids and bases is a recurring theme in organic reaction mechanisms. This form of catalysis has received considerable attention in physical- organic chemistry for its mechanistic role not only in standard transformations but also in enzymatic reactions. Organic reactions often proceed simultaneously through multiple mechanisms towards the same products. Acetal hydrolysis (6, 7), for example, may occur through a SAG or GAG mechanism. Although in certain cases thermodynamic or stereoelectronic considerations allow a priori prediction of one dominant mechanism, distinguishing SAG from GAG is challenging in general. Increasing the SAC-to -GAC rate constant ratio reduces the effective pH range for GAG. Moderate strength general acids are most effective for GAG and higher total buffer concentrations considerably enhance the relative rate and acceptable pH range for GAG.

Introduction: Atrial fibrillation (AF) is related to numerous electrophysiological changes, however the timeline and extent of these changes are not well characterized. Hypothesis: Using a chronic canine paced AF model, we investigated not only structual remodeling but also electrophysiological remodeling which is changes in electrogram amplitude, dominant frequency (DF). Methods: Eight dogs were implanted with a neurostimulator set to pace at 50 Hz every other second in the high right atrium. Electroanatomical mapping during sinus rhythm was done prior to and following more than 6 months of pacing. Animals were euthanized and tissue samples in several areas (Panel A) were acquired for histological analysis. Results: The maximum number of days of AF duration between studies was 412, with a mean of 183±122 days. About structual remodeling, a significant change was seen in the LA as chamber volume increased fro 22.25±12.60 cm3 to 34.00±12.23 cm3 among all animals (p=0.01).Bipolar amplitude in roof area at baseline was significantly higher than other areas. Here we report a significant decrease in mean bipolar EGM amplitude in the left atrium (LA) from 5.64±0.84 mV at baseline to 3.14±0.89 mV (p<0.01) after AF. Also, the significant bipolar amplitude decrease occurred in each segments but the amount of change was not significantly different among each areas (Panel B). Additionally, the average of dominant frequency increased from 7.02±0.37 Hz to 10.12±0.28 Hz (p<0.001) in the LA. Panel C showed Masson's trichrome stained microscope images of LA tissue samples. The percentage of fibrosis in chronic AF animals was also significaltly larger in each lesions (Panel B). Conclusions: Chronic AF of dog is accompanied by a small but significant decrease in intracardiac bipolar amplitudes. These EGM values were higher than traditional values associated with scarred tissue. However, changes in DF and tissue fibrosis show significant remodeling despite EGM values indicating healthy tissue. [ABSTRACT FROM AUTHOR]

The discorhabdin natural products are a large subset of pyrroloiminoquinone alkaloids with a myriad of biological activities. Despite garnering much synthetic attention, few members have thus far been completed, particularly those featuring a bridging carbon‐nitrogen bond that is found in numerous discorhabdins, including discorhabdin V. Herein we report the first total synthesis and full stereochemical assignment of (+)‐discorhabdin V. To access the pyrroloiminoquinone we developed a convergent N‐alkylation/oxidative aminocyclization/bromination cascade that joins two key components, which are both made on multigram scale. An intramolecular Heck reaction then forms the quaternary carbon center in an intermediate containing the carbon‐nitrogen bridge, and a reductive N,O‐acetal cyclization sequence introduces the final piperidine ring. Furthermore, we have established the relative configuration of (+)‐discorhabdin V through experimental NOESY data and DP4 NMR probability calculations. The absolute configuration of the natural product has also been determined by circular dichroism and the use of an amino acid derived chiral starting material. Our work represents one of only two reports of a total synthesis of a nitrogen‐bridged discorhabdin and paves the way for future biological evaluation of such compounds. [ABSTRACT FROM AUTHOR]

The discorhabdin natural products are a large subset of pyrroloiminoquinone alkaloids with a myriad of biological activities. Despite garnering much synthetic attention, few members have thus far been completed, particularly those featuring a bridging carbon‐nitrogen bond that is found in numerous discorhabdins, including discorhabdin V. Herein we report the first total synthesis and full stereochemical assignment of (+)‐discorhabdin V. To access the pyrroloiminoquinone we developed a convergent N‐alkylation/oxidative aminocyclization/bromination cascade that joins two key components, which are both made on multigram scale. An intramolecular Heck reaction then forms the quaternary carbon center in an intermediate containing the carbon‐nitrogen bridge, and a reductive N,O‐acetal cyclization sequence introduces the final piperidine ring. Furthermore, we have established the relative configuration of (+)‐discorhabdin V through experimental NOESY data and DP4 NMR probability calculations. The absolute configuration of the natural product has also been determined by circular dichroism and the use of an amino acid derived chiral starting material. Our work represents one of only two reports of a total synthesis of a nitrogen‐bridged discorhabdin and paves the way for future biological evaluation of such compounds. [ABSTRACT FROM AUTHOR]

Background: Atrial fibrillation (AF) is related to numerous electrophysiological changes; however, the extent of structural and electrophysiological remodeling with long‐term AF is not well characterized. Methods: Dogs (n = 6) were implanted with a neurostimulator in the right atrium (AF group). No implantation was done in the Control group (n = 3). Electroanatomical mapping was done prior to and following more than 6 months of AF. Magnetic resonance imaging was also done to assess structural remodeling. Animals were euthanized and tissue samples were acquired for histological analysis. Results: A significant increase was seen in the left atrial (LA) volume among all AF animals (22.25 ± 12.60 cm3 vs 34.00 ± 12.23 cm3, P = .01). Also, mean bipolar amplitude in the LA significantly decreased from 5.96 ± 2.17 mV at baseline to 3.23 ± 1.51 mV (P < .01) after chronic AF. Those significant changes occurred in each anterior, lateral, posterior, septal, and roof regions as well. Additionally, the dominant frequency (DF) in the LA increased from 7.02 ± 0.37 Hz to 10.12 ± 0.28 Hz at chronic AF (P < .01). Moreover, the percentage of fibrosis in chronic AF animals was significantly larger than that of control animals in each location (P < .01). Conclusions: Canine chronic AF is accompanied by a significant decrease in intracardiac bipolar amplitudes. These decreased electrogram amplitude values are still higher than traditional cut‐off values used for diseased myocardial tissue. Despite these "normal" bipolar amplitudes, there is a significant increase in DF and tissue fibrosis. [ABSTRACT FROM AUTHOR]

A response by Eugene E. Kwan to a letter to the editor about his article "Factors Affecting the Relative Efficiency of General Acid Catalysis" is presented.

A full account of our total synthesis of the galbulimima alkaloids GB 13 and himgaline is provided. Using a strategy adapted from the proposed biosynthesis of the GB alkaloid family, a linear precursor underwent successive intramolecular Diels-Alder, Michael, and imine aldol cyclizations to form the polycyclic alkaloid core. We now show that modification of this strategy can also deliver an advanced intermediate en route to the related alkaloid himandridine. The success of the key imine aldol cyclization is acutely sensitive to substrate structure and solvent, including a case in which cyclization was spontaneous in protic solvents. A detailed computational investigation of the course of the reaction closely correlates with, and suggests a rationale for, the observed patterns of imine aldol reactivity. [ABSTRACT FROM AUTHOR]

Introduction: The VisiTag Module, in CARTO, can be a useful tool in marking areas that will result in scar but the optimal setting that best predicts scar is unknown. Hypothesis: Our goal was to find out the optimal VisiTag settings for predicting scar by correlating the areas marked by VisiTag with scar as seen in left atrial LGE-MRI. Methods: We retrospectively identified 70 consecutive patients who experienced pulmonary vein isolation using CARTO with VisiTag and also had a 3-month post-ablation LGE-MRI for assessment of chronic LA scar. The electro-anatomical map was used to retrospectively tag ablated area for six different VisiTag settings varying the minimum force, stability range and duration, force over time and impedance drop (panel A). The LA surface area covered by the automated tags was measured semiautomatically in CARTO. The LGE-MRI done 3 months post ablation was segmented and the LA surface covered with scar was computed. We then compared the LA surface area deemed ablated as marked by VisiTag with the surface area covered with scar in the MRI. Results: The mean LA surface area ablated by VisiTag varied from 21.0% (n=70) for the most liberal setting (Set 1) to 8.5% for the most stringent setting (Set 3-2). The mean scarred area in LGE-MRI was 13.3%. Area deemed ablated with Settings 1, 3 and 3-2 was significantly different (p<0.05) from the scar area in the MRI (B and C). Settings 1-2, 2 and 2-2 were much closer (12.8, 14.7 and 12.3 respectively) in predicting the ablated area and statistically not different form the scar area in MRI. Also, the contact force data were shown in Non Scar Tag and Scar Tag. Average Force was not significantly different in these groups but catheter duration time was significantly longer in Scar Tag. According to that, force time integral (FTI) was also higher in Scar Tag. Conclusions: VisiTag settings with a minimum force of 5 grams, stability duration of 3 to 6 secs, force over time of 40%, catheter stability range of 2 mm provides the best match for scar for LA ablation. Moreover, catheter duration time was more important than average contact force and FTI more than 180 gs would help make chronic durable scar. [ABSTRACT FROM AUTHOR]

Introduction: Radiofrequency (RF) and cryoablation are routinely used to treat arrhythmias, but the extent and time course of edema associated with the two different modalities is unknown. Our goal was to follow the lesion maturation and edema formation after RF and cryoablation using serial magnetic resonance imaging (MRI). Methods and Results: Ventricular ablation was performed in a canine model (n = 11) using a cryo or an irrigated RF catheter. T2‐weighted (T2w) edema imaging and late gadolinium enhancement (LGE)‐MRI were done immediately (0 day: acute), 1 to 2 weeks (subacute), and 8 to 12 weeks (chronic) after ablation. After the final MRI, excised hearts underwent pathological evaluation. As a result, 45 ventricular lesions (cryo group: 20; RF group: 25) were evaluated. Acute LGE volume was not significantly different but acute edema volume in cryo group was significantly smaller (1225.0 ± 263.5 vs 1855.2 ± 520.5 mm3; P = 0.01). One week after ablation, edema still existed in both group but was similar in size. Two weeks after ablation there was no edema in either of the groups. In the chronic phase, the lesion volume for cryo and RF in LGE‐MRI (296.7 ± 156.4 vs 281.6 ± 140.8 mm3; P = 0.73); and pathology (243.3 ± 125.9 vs 214.5 ± 148.6 mm3; P = 0.49), as well as depth, was comparable. Conclusions: When comparing cryo and RF lesions of similar chronic size, acute edema is larger for RF lesions. Edema resolves in both cryo and RF lesions in 1 to 2 weeks. [ABSTRACT FROM AUTHOR]

Carbohydrates are involved in nearly all aspects of biochemistry, but their complex chemical structures present long-standing practical challenges to their synthesis. In particular, stereochemical outcomes in glycosylation reactions are highly dependent on the steric and electronic properties of coupling partners; thus, carbohydrate synthesis is not easily predictable. Here we report the discovery of a macrocyclic bis-thiourea derivative that catalyzes stereospecific invertive substitution pathways of glycosyl chlorides. The utility of the catalyst is demonstrated in the synthesis of trans-1,2-, cis-1,2-, and 2-deoxy-β-glycosides. Mechanistic studies are consistent with a cooperative mechanism in which an electrophile and a nucleophile are simultaneously activated to effect a stereospecific substitution reaction. [ABSTRACT FROM AUTHOR]

A summary is presented of an article published online at http://dx.doi.org/10.1126/science.aaw2872 examining the role of passenger mutation events that can accumulate during tumorigenesis but do not provide an advantage to cancer cells and the role of DNA substrates and hairpin structures in mutations found in cancer genomes.