Patient-Specific Computational Modeling of Upper Extremity Arteriovenous Fistula Creation: Its Feasibility to Support Clinical Decision-Making

<div><h3>Introduction</h3><p>Inadequate flow enhancement on the one hand, and excessive flow enhancement on the other hand, remain frequent complications of arteriovenous fistula (AVF) creation, and hamper hemodialysis therapy in patients with end-stage renal disease. In an effort to reduce these, a patient-specific computational model, capable of predicting postoperative flow, has been developed. The purpose of this study was to determine the accuracy of the patient-specific model and to investigate its feasibility to support decision-making in AVF surgery.</p> <h3>Methods</h3><p>Patient-specific pulse wave propagation models were created for 25 patients awaiting AVF creation. Model input parameters were obtained from clinical measurements and literature. For every patient, a radiocephalic AVF, a brachiocephalic AVF, and a brachiobasilic AVF configuration were simulated and analyzed for their postoperative flow. The most distal configuration with a predicted flow between 400 and 1500 ml/min was considered the preferred location for AVF surgery. The suggestion of the model was compared to the choice of an experienced vascular surgeon. Furthermore, predicted flows were compared to measured postoperative flows.</p> <h3>Results</h3><p>Taken into account the confidence interval (25^th and 75^th percentile interval), overlap between predicted and measured postoperative flows was observed in 70% of the patients. Differentiation between upper and lower arm configuration was similar in 76% of the patients, whereas discrimination between two upper arm AVF configurations was more difficult. In 3 patients the surgeon created an upper arm AVF, while model based predictions allowed for lower arm AVF creation, thereby preserving proximal vessels. In one patient early thrombosis in a radiocephalic AVF was observed which might have been indicated by the low predicted postoperative flow.</p> <h3>Conclusions</h3><p>Postoperative flow can be predicted relatively accurately for multiple AVF configurations by using computational modeling. This model may therefore be considered a valuable additional tool in the preoperative work-up of patients awaiting AVF creation.</p> </div

Cause of Death and Predictors of All-Cause Mortality in Anticoagulated Patients With Nonvalvular Atrial Fibrillation : Data From ROCKET AF

M. Kaste on työryhmän ROCKET AF Steering Comm jäsen.Background-Atrial fibrillation is associated with higher mortality. Identification of causes of death and contemporary risk factors for all-cause mortality may guide interventions. Methods and Results-In the Rivaroxaban Once Daily Oral Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation (ROCKET AF) study, patients with nonvalvular atrial fibrillation were randomized to rivaroxaban or dose-adjusted warfarin. Cox proportional hazards regression with backward elimination identified factors at randomization that were independently associated with all-cause mortality in the 14 171 participants in the intention-to-treat population. The median age was 73 years, and the mean CHADS(2) score was 3.5. Over 1.9 years of median follow-up, 1214 (8.6%) patients died. Kaplan-Meier mortality rates were 4.2% at 1 year and 8.9% at 2 years. The majority of classified deaths (1081) were cardiovascular (72%), whereas only 6% were nonhemorrhagic stroke or systemic embolism. No significant difference in all-cause mortality was observed between the rivaroxaban and warfarin arms (P=0.15). Heart failure (hazard ratio 1.51, 95% CI 1.33-1.70, P= 75 years (hazard ratio 1.69, 95% CI 1.51-1.90, P Conclusions-In a large population of patients anticoagulated for nonvalvular atrial fibrillation, approximate to 7 in 10 deaths were cardiovascular, whereasPeer reviewe

Determination of brachial artery stiffness prior to vascular access creation: reproducibility of pulse wave velocity assessment

Background. Despite routine ultrasound mapping of upper extremity arteries and veins, early thrombosis and nonmaturation remain frequent complications following vascular access (VA) surgery. Besides vascular diameters, brachial artery stiffness is assumed to play an important role; however, reproducibility of measurements has never been established. The purpose of this study was to determine within-session and between-session variabilities of pulse wave velocity (PWV) assessment by using ultrasonography and blood pressure registration. Methods. Beat-to-beat changes in brachial artery diameter and pressure were obtained in 21 subjects in measurement sessions on Day 1 and Day 3. Each session consisted of three acquisitions. For each acquisition, systolic and diastolic diameter and pressure were determined and used for calculation of brachial artery PWV. Within-session variability of diameter and pressure, as well as the estimated PWV, was expressed using the intraclass correlation coefficient with corresponding coefficient of variation (CoV). Between-session variability was reported using Bland-Altman analysis in combination with CoV analysis. Results. Significant agreement (P <0.001) was obtained for all diameter and pressure measurements obtained on Day 1 and Day 3. Within-session CoV of pulse pressure, diastolic diameter and distension were 7.0, 1.6 and 18.3%, respectively. Subsequent estimation of local PWV resulted in a CoV of 10.6%. Between-session CoV was 15.1, 3.8 and 18.9% for pulse pressure, diastolic diameter and distension, respectively. For PWV estimation, this resulted in a CoV of 13.5%. Conclusions. Diameter and pressure can be recorded accurately over the cardiac cycle, and calculations of distensibility, pulse pressure and PWV show a slight to moderate degree of variation. Larger studies elaborating on interindividual differences need to determine the clinical efficacy of PWV measurements prior to VA creatio

Comparison of midterm results for the Talent and Endurant stent graft

Objective Stent graft evolution is often addressed as a cause for improved outcomes of endovascular aneurysm repair for patients with an abdominal aortic aneurysm. In this study, we directly compared the midterm result of Endurant stent graft with its predecessor, the Talent stent graft (both Medtronic, Santa Rosa, Calif). Methods Patient treated from January 2005 to December 2010 in a single tertiary center in The Netherlands with a Talent or Endurant stent graft were eligible for inclusion. Ruptured abdominal aortic aneurysms or patients with previous aortic surgery were excluded. The primary end point was the Kaplan-Meier estimated freedom from secondary interventions. Secondary end points were perioperative outcomes and indications for secondary interventions. Results In total, 221 patients were included (131 Endurant and 90 Talent). At baseline, the median aortic bifurcation was narrower for the Endurant (30 mm vs 39 mm; P <.001). Median follow-up was 64.1 ± 37.9 months and 59.2 ± 25.3 months for Talent and Endurant, respectively. The estimated freedom from secondary interventions at 30 days, 1 year, 5 years, and 7 years was 94.3%, 89.4%, 72.2%, and 64.1% for Talent and 96.8%, 89.3%, 75.2%, and 69.2% for Endurant (P =.528). The indication for secondary interventions does differ; more patients required an intervention for a proximal neck-related complication (type Ia endoleak or migration) in the Talent group (18.2% vs 4.8%; P =.001), whereas more interventions for iliac limb stenosis were seen in the Endurant group (0.0% vs 4.8%; P =.044). In a binomial regression analysis, suprarenal angulation, infrarenal neck length, and type of stent graft were independent predictors of neck-related complications. Conclusions Evolution from the Talent stent graft into the Endurant has resulted in significant reduction of infrarenal neck-related complications; on the other hand, iliac interventions increased. The overall midterm secondary intervention rate was comparable

Hemodialysis vascular access management in the Netherlands

Purpose: In the Netherlands, 86% of patients start renal replacement therapy with chronic intermittent hemodialysis (HD). Guidelines do indicate predialysis care and maintenance of a well-functioning vascular access (VA) as critical issues in the management of the renal failure patient. Referral to the surgeon and time to VA creation are important determinants of the type and success of the VA and HD treatment. Methods and Results: Data from a national questionnaire showed that time from referral to the surgeon and actual access creation is 8 weeks in 27% of the centers. Preoperative ultrasonography and postoperative access flowmetry are the diagnostic methods in the majority of centers (98%). Most facilities perform rope-ladder cannulation with occasionally the buttonhole technique for selected patients in 87% of the dialysis units. Endovascular intervention for thrombosis is practiced by 13%, surgical thrombectomy by 21% and either endovascular or surgery by 66% of the centers. Weekly multidisciplinary meetings are organized in 57% of the units. Central vein catheters are inserted by radiologists (36%), nephrologists and surgeons (32%). Conclusions: We conclude that guidelines implementation has been successful in particular regarding issues as preoperative patient assessment for VA creation and postoperative surveillance in combination with (preemptive) endovascular intervention, leading to very acceptable VA thrombosis rates

The effects of cross-hemispheric dorsolateral prefrontal cortex transcranial Direct Current Stimulation (tDCS) on task switching

Background: Task switching, defined as the ability to flexibly switch between tasks in the face of goal shifting, is a central mechanism in cognitive control. Task switching is thought to involve both prefrontal cortex (PFC) and parietal regions. Our previous work has shown that it is possible to modulate set shifting tasks using 1 mA tDCS on both the left dorsolateral prefrontal cortex and the left primary motor area. However, it remains unclear whether the effects of PFC tDCS on task switching are hemisphere-dependent.Objectives: We aimed to test the effects of three types of cross-hemispheric tDCS over the PFC (left anode right cathode [LA-RC], left cathode right anode [LC-RA] and sham stimulation) on participants' performance (reaction time) and accuracy (correct responses) in two task-switching paradigms (i.e., letter/digit naming and vowel-consonant/parity tasks).Methods: Sixteen participants received cross-hemispheric tDCS over the PFC in two task-switching paradigms.Results: The results show that cross-hemispheric tDCS over the PFC modulates task-switching ability in both paradigms. Our results were task and hemisphere-specific, such that in the letter/digit naming task, LA-RC tDCS increased switching performance, whereas LC-RA tDCS improved accuracy. On the other hand, in the vowel-consonant/parity task, LA-RC improved accuracy, and decreased switching performance.Conclusions: Our findings confirm the notion that involvement of the PFC on task switching depends critically on laterality, implying the existence of different roles for the left hemisphere and the right hemisphere in task switching.This work was supported by the Portuguese Foundation for Science and Technology with individual grants (SFRH/BD/41484/2007 and SFRH/BD/64355/2009)