An unusual H/D kinetic isotope effect (KIE) is described, in which isotopic selectivity arises primarily from nonstatistical dynamics in the product. In DFT-based quasiclassical trajectories of Bergman cyclization of (Z)-3-hexen-1,5-diyne (1) at 470 K, the new CC bond retains its energy, and 28% of nascent p-benzyne recrosses back to the enediyne on a vibrational time scale. The competing process of intramolecular vibrational redistribution (IVR) in p-benzyne is too slow to prevent this. Deuteration increases the rate of IVR, which decreases the fraction of recrossing and increases the yield of statistical (trapable) p-benzyne, 2. Trapable yields for three isotopomers of 2 range from 72% to 86%. The resulting KIEs for Bergman cyclization differ substantially from KIEs predicted by transition state theory, which suggests that IVR in this reaction can be studied by conventional KIEs. Leakage of vibrational zero point energy (ZPE) into the reaction coordinate was probed by trajectories in which initial ZPE in the CH/CD stretching modes was reduced by 25%. This did not change the predicted KIEs.
error). Crude expansion rates stratified by initial aortic diameter are shown (Fig). The proportion of patients with expansion to 5.5 cm during follow-up ranged from 2.3% to 53.3% when stratified by initial aortic diameter. Hierarchical regression models of AAA growth rates found statistically significant (P < .05) increased rates for female sex, smoking, and history of cardiovascular disease, whereas use of metformin, larger AAA size, and higher values of hemoglobin A 1c for patients with diabetes were associated with a lower rate of growth.Conclusions: In this large cohort of AAAs under surveillance with available patient-level data during 15 years, several risk factors for accelerated and decelerated growth are identified that have implications for risk prediction. Further analyses are ongoing to identify those at increased risk for aneurysm expansion to potentially provide targeted surveillance regimens.
experienced significant sac regression and were in the REG group (n ¼ 65; 49.2%). The REG group had smaller diameter devices and were less likely to have had concomitant chimney grafts placed (P < .05). The NON-REG group had had a greater rate of type II endoleak (35.8% vs 12.3%; P ¼ .002). Multivariate analysis identified adjunctive parallel procedures (odds ratio, 0.271; 95% confidence interval, 0.097-0.759; P ¼ .013) and type II endoleak (odds ratio, 0.180; 95% confidence interval, 0.063-0.515; P ¼ .001) as independent predictors of sac nonregression. Overall mortality was higher in the NON-REG group (3% vs 0%; P ¼ .008). Using log-rank testing, sac regression was associated with a significant mortality benefit at 72 months compared with nonregression (P < .001; Fig).Conclusions: Regression of the excluded aneurysm sac after fEVAR appears to be less common in patients with type II endoleaks and those undergoing concomitant parallel grafting. Sac regression >5 mm was associated with a significant survival benefit at the mid-term follow-up and should be used as a clinical marker for success after fEVAR.
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