Inflow Stenosis Research Articles

Patency and factors related to patency after percutaneous transluminal angioplasty for inflow arterial stenosis in native arteriovenous fistula dysfunction: a single-center retrospective study

Controversy still exists regarding how much the inflow arterial percutaneous transluminal angioplasty (PTA) contributed to maintaining fistula function for hemodialysis. We aimed to analyze patency and risk factors after inflow arterial PTA. Hemodialysis patients with inflow arterial primary stenosis who were admitted to our institution from January 2017 to December 2022 were examined. One group had arterial-venous fistula with inflow artery stenosis alone (AVF + iAS) and another group had AVF with inflow artery stenosis and any vein stenosis (AVF + iAS + VS). The characteristics of patients, stenotic lesions, and PTA procedures were recorded. Kaplan–Meier analysis was used to compare primary patency, assisted primary patency, and secondary patency in the two groups. Cox proportional hazard analysis was used to identify risk factors associated with patency. We examined 213 patients, 53 in the AVF + iAS group (51 radial arterial stenosis and 2 ulnar arterial stenosis) and 160 in the AVF + iAS + VS group (159 radial arterial stenosis and 1 ulnar arterial stenosis). Kaplan–Meier analysis indicated the AVF + iAS group had better primary patency and assisted primary patency (both P < 0.05), but the groups had similar secondary patency. Cox proportional hazard analysis indicated that none of the analyzed clinical and biochemical indexes had clinically meaningful effects on primary patency, assisted primary patency, or secondary patency in either group. The patency and safety after PTA for inflow arterial stenosis were satisfactory, and none of the examined risk factors had a major clinical impact on patency. We recommend PTA as treatment for inflow stenosis of an AVF.

Exercise Transcutaneous Oxygen Pressure (Extcpo2) Measurement is a Reliable Method of Evaluation of Internal Iliac Artery flow Compromise

Clinical differentiation of buttock claudication from pseudo-claudication (neuromuscular etiology) is often challenging and cannot be diagnosed non-invasively using standard ankle-brachial index (ABI) with exercise. The aim of this study was to evaluate the reliability of exercise transcutaneous oximetry (ExTcPO2) to accurately detect significant internal iliac artery (IIA) inflow stenosis. Methods: Data from a prospectively maintained registry of consecutive patients undergoing ExTcPO2 for evaluation of buttock and hip exertional discomfort as well as arterial imaging within 12 months were retrospectively analyzed. ExTcPO2 was performed on a treadmill (10% slope; 2 mph speed); measured at buttocks, upper back and calf (rest, with exercise) to document the baseline normal, degree of change with exercise and recovery patterns. A Delta from Resting Oxygen Pressure (DROP) (buttock- back TcPO2 mmHg) ≥15 mm Hg was considered significant. A blinded physician performed aorto-iliac arterial stenosis quantification and receiver operating characteristic (ROC) curve analysis was used to determine sensitivity and specificity to diagnose severe inflow reduction (≥70%) based upon a diagnostic DROP ≥15 mm Hg. Results: One hundred and eleven patients (M:F::79:32, mean age 70, range 18-90 years) with available concomitant imaging (CTA 90, DUS 21) were included in the study. Indications for testing were suspected vascular (82), or neuromuscular (29) symptoms. ExTcPO2 study confirmed the clinical suspicion of the state of IAA inflow in 81% (91/111) of patients. DROP ≥15 mm Hg had a sensitivity, specificity, PPV, NPV of 56, 80, 70, and 68% respectively for prediction of severe IIA inflow reduction (p value &lt;0.001; OR 1.116, 95% CI 1.057-1.157; C- statistic 0.76, SE=0.03). Aorto-iliac arterial reconstruction to treat severe IIA flow compromise was performed in 16 patients. Revascularization was Direct Antegrade in 12 patients (IIA PTA /stenting – 4, aorto-ilac stenting /endarterectomy – 9), Direct Retrograde (aorto-biiliac bypass) in 1 and Indirect via increased collateral flow (profundoplasty) in 3. Post-operatively symptom relief was noted in 15/16 patients and objectively demonstrated on ExTcPo2 in 6/7 (Figure 2). One patient did not improve clinically, or on EXTcPO2 following Indirect revascularization. Conclusion: Exercise transcutaneous oximetry can reliably diagnose significant IIA inflow stenosis. It is simple, non-invasive and can serve as a valuable screening tool to differentiate buttock claudication from other neuromuscular causes of low back, buttock and hip discomfort as well as post-operatively to confirm adequacy of aorto-iliac revascularization in conjunction with standard, noninvasive vascular evaluation with ABI.

Quantitative physical examination indicators to detect patients with stenosis at a high risk of thrombosis at hemodialysis vascular access sites: A retrospective case-control study.

Quantitative physical examination (PE) indicators, including palpable pulsatility length and outflow scores, can be used to quantify stenosis severity at hemodialysis vascular access sites. It is known that the risk of high-shear-related thrombosis is increased when the minimal luminal diameter (MLD) of stenosis decreases. At present, MLD is measured using sonography or angiography. This study sought to determine the relationship between quantitative PE indicators and MLD and report their diagnostic performance in detecting patients with stenosis at a high risk of thrombosis. We performed a retrospective case-control study using routinely collected data. We used the post-stenosis palpable pulsatility length (sPPL) and pulse-and-thrill based outflow score to assess the severity of AVF inflow and outflow stenosis, respectively. We recorded paired quantitative PE indicators and MLD before and after angioplasty in patients enrolled over a 4-month period. A total of 249 paired PE indicators and MLD measurements were obtained from 163 patients. A receiver operating characteristic curve analysis showed that an MLD cutoff value of <1.55 mm and an MLD of <1.95 mm discriminated sPPL = 0 and PESOS (physical examination significant outflow stenosis)/1- of the outflow score, respectively, from all other measurements, with the area under the curve values of 0.8922 and 0.9618, respectively. With sPPL = 0 and PESOS/1- of the outflow score as diagnostic tools to detect inflow stenosis with an MLD of ⩽1.5 mm and outflow stenosis with an MLD of ⩽1.9 mm at vascular access sites, sensitivity = 86.00% and 88.46%; specificity = 97.67% and 92.11%; positive predictive values of 97.73% and 92.00% and negative predictive values of 85.71% and 88.61%, respectively, were observed. Our preliminary results showed that physical examination can potentially be a diagnostic tool in detecting patients with stenosis who are at a high risk of thrombosis at hemodialysis vascular access sites with high diagnostic accuracy.

Cerebral venous steal equation for intracranial segmental perfusion pressure predicts and\xa0quantifies reversible\xa0intracranial to extracranial flow diversion

Cerebral perfusion is determined by segmental perfusion pressure for the intracranial compartment (SPP), which is lower than cerebral perfusion pressure (CPP) because of extracranial stenosis. We used the Thevenin model of Starling resistors to represent the intra-extra-cranial compartments, with outflow pressures ICP and Pe, to express SPP = Pd–ICP = FFR*CPP–Ge(1 − FFR)(ICP–Pe). Here Pd is intracranial inflow pressure in the circle of Willis, ICP—intracranial pressure; FFR = Pd/Pa is fractional flow reserve (Pd scaled to the systemic pressure Pa), Ge—relative extracranial conductance. The second term (cerebral venous steal) decreases SPP when FFR < 1 and ICP > Pe. We verified the SPP equation in a bench of fluid flow through the collapsible tubes. We estimated Pd, measuring pressure in the intra-extracranial collateral (supraorbital artery) in a volunteer. To manipulate extracranial outflow pressure Pe, we inflated the infraorbital cuff, which led to the Pd increase and directional Doppler flow signal reversal in the supraorbital artery. SPP equation accounts for the hemodynamic effect of inflow stenosis and intra-extracranial flow diversion, and is a more precise perfusion pressure target than CPP for the intracranial compartment. Manipulation of intra-extracranial pressure gradient ICP–Pe can augment intracranial inflow pressure (Pd) and reverse intra-extracranial steal.

Arteriovenous shunt stenosis assessment based on empirical mode decomposition and 1D-convolutional neural network: Clinical trial stage

Patients suffering from end-stage renal disease usually receive dialysis therapy. The arteriovenous (AV) shunt is a vital vascular access for achieving sufficient blood flow in the vein during hemodialysis and can be either an arteriovenous fistula (AVF) or an arteriovenous graft (AVG). However, the lumens of dialysis accesses are frequently narrowed by thrombosis, resulting in stenosis at the venous anastomosis site or progression of inflow stenosis at the arterial anastomosis site. A narrowed vascular wall will produce abnormal physical stress and cause turbulent flow and high blood pressure. Hence, murmur sounds will occur around the stenotic site. The auscultation method is a noninvasive technique to detect these sounds as phonoangiograph (PAG) signals. The empirical mode decomposition (EMD) method is used to decompose intrinsic fast and slow oscillation components from PAG signals. In this study, the slow oscillation component containing key spectral energy distributions (< 100, 100–300 Hz, and > 300 Hz) will be used to identify the normal and abnormal conditions for further stenosis level assessment. After extracting key frequency-based features using EMD, 1D convolutional and pooling processes, feature patterns can be extracted from spectral patterns, which can distinguish distinct feature patterns and reduce the dimensions of feature patterns and the number of feature datasets for training the classifier. Next, a convolutional neural network-based classifier is used to assess the stenosis levels at a near venous anastomosis site. Its model can solve nonlinear mapping applications and nonlinear separable classifications, including the normal condition, AVG stenosis, and AVF stenosis. The experimental tests with cross-validation will indicate that the proposed method provides a promising result in clinical trials, including mean recall (%), mean precision (%), mean accuracy (%), and a mean F1 score of 95.35 %, 89.49 %, 86.82 %, and 0.9232, respectively, by offering an automatic procedure for AV shunt stenosis assessment without the need for manual feature extraction and classification.

Measuring the palpable pulsatility length as a physical examination test in defining the severity of inflow stenosis for hemodialysis fistulas

BackgroundPulsatility is an important property of hemodialysis arteriovenous fistulas (AVF) and can be perceived by the fingers as a gradual decrease in strength downstream from the anastomosis along the main trunk of the fistula. The distance from the point at which the pulse becomes imperceptible to the anastomosis is termed the palpable pulsatility length (PPL); we considered this length may play a role in assessing the severity of inflow stenosis for hemodialysis fistulas.MethodsThis study was performed by retrospective analysis of routinely collected data. Physical examinations and fistula measurements were performed in a selected population of 76 hemodialysis patients with mature fistulas during half a year. Fistula measurements included the PPL before and after treatment and the distance between the anastomosis and the arterial cannulation site (aPump length). The aPump index (API) was calculated by dividing the PPL by the aPump length. Angiograms were reviewed to determine the location and severity of stenosis. PPL and API were used to detect the critical inflow stenosis, which indicates severe inflow stenosis of an AVF.ResultsReceiver operating characteristic analysis showed that the area under the curve was 0.895 for API and 0.878 for PPL. A cutoff value of API < 1.29 and PPL < 11.0 cm were selected to detect the critical inflow stenosis. The sensitivity was 96.0% versus 80.0% and specificity was 84.31% versus 84.31% for API and PPL, respectively.ConclusionsPPL and API are useful tools in defining the severity of pure inflow stenosis for mature AVFs in the hands of trained examiners with high sensitivity and specificity.

Effect of Etiology and Inflow on Outcomes of Endovascular Recanalization for Nonmalignant Inferior Vena Cava Occlusion

The aim of this study was to determine factors affecting outcomes of inferior vena cava (IVC) recanalization for nonmalignant obstruction, with focus on venous inflow and etiology of IVC occlusion. Data from consecutive patients undergoing IVC recanalization between January 2001 and December 2017 were retrospectively reviewed. Patients were grouped by etiology of IVC obstruction, including post-thrombotic (PT), retroperitoneal fibrosis (RPF), and hypoplasia (HP). Patency of the femoral, deep femoral, and great saphenous veins was evaluated; the venous inflow was graded, assigning a point to each for stenosis or occlusion, for a total possible unilateral score of 3 and a composite score of 6. A score of 6 indicated no inflow stenosis or occlusion, whereas a score of 0 indicated disease of all 6 inflow veins. Primary outcomes included primary, primary assisted, and secondary patency rates. There were 114 patients during the 18-year period (64% male; mean age, 42 ± 15 years). Etiology was PT in 96 (84%), RPF in 5 (5%), and HP in 13 (11%) patients. Clinical, Etiology, Anatomy, and Pathophysiology classes included 3, 4a, 4b, 5, and 6 in 23, 17, 3, 11, and 23 patients, respectively. Forty-four (38%) patients had an IVC filter, all of whom had PT etiology, and 33 (29%) had a thrombophilia. Inflow grading was 6 in 20 (18%), indicating no disease; 4 in 36 (32%); and 3 or less in 32 (30%). There was no mortality related to the procedure. Periprocedural complications occurred in 11% of patients. Median follow-up was 15.2 months (interquartile range, 6.4-35.8 months; maximum, 141.6 months). Kaplan-Meier analysis of primary, primary assisted, and secondary patency in the entire cohort at 1 year and 5 years was 78%, 85%, and 95% and 66%, 85%, and 95%, respectively. Early failures occurred in 12 PT, 2 HP, and 0 RPF patients (P = .94) No factors studied, including female sex, etiology of IVC occlusion, or thrombophilia, affected patency (P > .05). Median venous inflow in PT, RPF, and HP was 4, 5.5, and 5, respectively. Patients with grade 0 to 3 had patency rates similar to those of patients with grade 4 to 6 (P > .05). Presence of an IVC filter crushed aside during IVC stenting did not adversely affect stent patency. Midterm results of endovascular recanalization are excellent regardless of the etiology of IVC occlusion. This cohort was predominantly PT with small numbers of RPF and HP, resulting in insufficient statistical power to demonstrate the effect of venous inflow on patency.

The association of overhydration with megafistulas in hemodialysis patients

Objectives: Diffuse enlargements of arteriovenous dialysis fistulas customarily attributed to either excessive arterial inflow or central outflow stenosis. The relationship between volume status and clinically enlarged (arteriovenous) fistula (CEF) formation in end-stage renal disease (ESRD) patients is not well understood.Methods: We assessed the pre-dialysis bioimpedance spectroscopy-measured percentage of overhydration (OH%) in 13 prevalent dialysis patients with CEF development and negative angiography and compared the results with those of 52 control dialysis patients (CONTR). All patients were prevalent ESRD patients receiving thrice-weekly maintenance hemodiafiltration at an academic outpatient dialysis unit.Results: 10/13 CEF patients had OH% ≥15% as compared to 20/52 control patients (Chi square p: .02). The degree of OH% was 20.2 ± 7.4% among the CEF vs. 14.4 ± 7.1% in the control group (Student’s t-test p: .01), representing 4.2 ± 3.2 vs. 2.8 ± 1.6 L of excess fluid pre-dialysis (p: .03). Patients with CEF development took an average of 1.7 ± 1.4 vs. 0.8 ± 0.8 (p: .002) antihypertensive medications compared to the CONTR patients, yet their blood pressure was higher: 156/91 vs. 141/78 mmHg (systolic/diastolic p: .03<.0001). We found no difference in fistula vintage, body mass index, age, diabetes status, or diuretic use. The odds ratio of having a CEF in patients with ≥15% OH status was 5.3 (95% CI: 1.3–21.7; p: .01), the Number Needed to Harm with overhydration was 4.Conclusions: There is an association between bioimpedance spectroscopy-measured overhydrated clinical state and the presence of CEF; either as an increased volume capacitance or as a potential cause.

Outcome of endovascular salvage of immature hemodialysis arteriovenous fistulas.

To assess the causes of immature hemodialysis arteriovenous fistula and the outcome of endovascular salvage. The outcome of 207 endovascular salvage procedures in 139 patients after the first successful cannulation was analyzed retrospectively from January 2011 to December 2017 in the Catholic University of Korea, Seoul St. Mary's Hospital. Of the 139 patients aged 62 ± 13 years, 45% were women, 59% had diabetes, and 71% were maintained on hemodialysis using central venous catheters. Mean interval between arteriovenous fistula creation and referral to angiography was 87 ± 63 days. While inflow stenosis (54.4%) was the most common cause of immature forearm fistulas (n = 76), both inflow (38.6%) and mixed stenosis (35.1%) were the main causes of immature upper arm fistulas (n = 63). Endovascular salvage procedures included percutaneous transluminal angioplasty (n = 174) and accessory vein obliteration (n = 30). The overall technical and clinical success rates were 97% and 93.4%, respectively. Mean interval between endovascular procedure and the first successful cannulation of the fistula was 28 ± 35 days. At 3, 6, and 12 months following the first successful cannulation, the primary patency rates were 81%, 69.5%, and 57.6%, respectively, and the secondary patency rates were 97.2%, 96%, and 94.8%, respectively. Mixed stenosis was the only determinant of secondary patency rate of immature arteriovenous fistula (hazard ratio = 6.334, confidence interval = 1.364-29.423, p = 0.018), and patients with mixed stenosis had poorer access outcomes (p = 0.016). Immature arteriovenous fistulas can be successfully salvaged by aggressive and timely endovascular intervention. Mixed stenosis is associated with poor access outcomes.

Prediction of vascular access stenosis: Blood temperature monitoring with the Twister versus static intra-access pressure ratio.

BackgroundThe Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines recommend intra-access flow (Qa) measurement as the preferred vascular access surveillance method over static intra-access pressure ratio (SIAPR). Recently, it has become possible to perform Qa measurement during hemodialysis using thermodilution method called blood temperature monitoring (BTM) with the Twister device. The aim of this study was to investigate the correlation between Qa by BTM and SIAPR and to compare the performance of two tests in prediction of vascular access stenosis.MethodsThe study was performed from January 2016 to November 2017 and included 97 patients with arteriovenous fistulas (AVF). Qa by BTM and SIAPR were simultaneously measured every 1~3 months with a total of 449 measurements during study period.ResultsIn our study population, mean age was 59.9±10.0 years and 61.9% were diabetes. The mean Qa obtained by BTM was 1186±588 mL/min. There was no correlation between Qa by BTM and venous SIAPR (r = 0.061, P = 0.196). Angiography identified 36 stenotic AVFs (37.1%) among the study subjects. They included 13 cases with only inflow stenosis, 6 with only outflow stenosis, and 17 with stenosis on both sides. Receiver-operating characteristic (ROC) curve analysis showed that Qa by BTM had higher discriminative ability to diagnose vascular access stenosis compared to SIAPR (P <0.001). The Qa less than 583 mL/min showed the highest diagnostic accuracy in vascular stenosis prediction.ConclusionIntradialytic measurement of Qa by BTM showed better diagnostic power over venous SIAPR in prediction of vascular access stenosis.

Normal Ultrasound Doppler Parameters for Functioning AV Fistulas

Doppler ultrasound (DUS) is a highly sensitive and specific test for assessment of the morphology of stenoses and measure blood flow within arteriovenous fistulas (AVFs). Retrospective review of 150 Doppler studies (121 patients) performed by a single radiologist were analyzed in conjunction with contemporaneous clinical dialysis function. Volume flow in the brachial artery, peak systolic velocity (PSV), and size of the anastomosis (diameter and intimal thickness) were recorded. Volume flow in the brachial artery of ≈&gt;1000 mL/min is a predictor of good fistula function. Volume flow in the brachial artery negatively correlates with both the reduction in perianastomotic diameter and increased intimal thickness ( P = .02) and positively correlates with increased diameter of the perianastomotic vein (PAV) ( P &lt; .0001). Measurements of PSV across the PAV do not correlate with fistula dysfunction or a significant stenosis. Volume flow of &gt;1000 mL/min in the brachial artery and a PAV diameter of ≥3.5 mm are predictive of a well-functioning fistula. Intimal thickening at the anastomosis can be measured on ultrasound and may be another useful parameter in the assessment of a failing fistula. These parameters could be used to exclude a significant inflow stenosis.

Generalized Regression Estimator Improved the Accuracy Rate of Estimated Dialysis Accesses Stenotic Condition on In-Vitro Arteriovenous Graft Experimental Model

Dialysis vascular accesses are critical for patients receiving hemodialysis treatment. However, dialysis access stenosis and further dysfunction are engendered by thrombosis or outflow (venous anastomosis site) stenosis and the progression of inflow (arterial anastomosis site) stenosis. Thus, any narrowed access causes vibrations, turbulent flow, and murmur sounds around stenosis sites. Auscultation and frequency-based techniques are employed to detect these sounds, and frequency components are also validated on the basis of the degree of stenosis (DOS). In this paper, a biophysical experimental model employing an in vitro arteriovenous graft model was established to produce various acoustic signals associated with single stenosis and multiple stenoses. By analyzing various combinations of stenoses, this paper selected suitable features of the frequency and power spectra using the Burg autoregressive method. A multiple regression model applying a higher number of explanatory variables and response variables, as a generalized regression neural network, was employed to identify DOS levels at inflow and outflow sites. The experimental results indicated that the proposed screening model provided a higher average hit rate of >90%, average true-positive rate of >90%, and true-negative rate of 100% in single and multiple stenosis screening, compared with the multiple linear regression model.

Issues related to renal artery angioplasty and stenting.

Renal artery stenosis may play a significant role in the pathogenesis of secondary hypertension, renal dysfunction, and flash pulmonary edema. Currently correction of renal arterial inflow stenosis is reserved for resistant hypertension patients who have failed maximal medical therapy, have worsening renal function and/or unexplained proximal congestive failure. With the recent advances in minimally invasive percutaneous stent placement techniques, open surgical revascularization has been largely replaced by renal artery stenting. The potential benefit of revascularization seemed intuitive; however, the initial enthusiasm and rise in the number of percutaneous interventions have been tempered by many subsequent negative randomized clinical trials that failed to prove the proposed benefits of the percutaneous intervention. The negative randomized trial results have fallen under scrutiny due to trial design concerns and inconsistent outcomes of these studies compared to pivotal trials undertaken under US Food and Drug Administration scrutiny. Treatment of atherosclerotic renal artery occlusive disease has become one of the most debatable topics in the field of vascular disease. The results from recent randomized clinical trials of renal artery stenting have basically limited the utilization of the procedure in many centers, but not every clinical scenario was covered in those trials. There are potential areas for improvement focusing mainly on procedural details and patient selection with respect to catheter based treatment of atherosclerotic renal artery stenosis. We believe, limiting patient selection, enrollment criteria and outcomes measured functioned to reduce the benefit of renal artery stenosis stenting by not enrolling patients likely to benefit. Future studies incorporating potential procedural improvements and that include patients more likely to benefit from renal stenting than were included in ASTRAL and CORAL are needed to more carefully examine specific patient subgroups so that "the baby is not thrown out with the bath water." We also discuss several other concerns related to renal artery stenting which include diagnostic, procedure, indication, and reimbursement issues.

Assessment of inflow and outflow stenoses using big spectral data and radial‐based colour relation analysis on in vitro arteriovenous graft biophysical experimental model

Dialysis vascular accesses are critical for dialysis therapy, but they frequently suffer from stenotic complications. Higher patency rates and thrombosis rates are a concern to nephrology nurses and patients. These complications are complex events, including inflow stenosis, outflow stenosis, and coexistence of both. Therefore, a biophysical experimental model is employed to mimic the various combinations of stenoses and dialysis circulation circuits on a virtual adult hand. Considering the suggested signal preprocessing specifications, auscultation method and frequency analysis technique are used to extract the key frequency components from sufficient big spectral data. Key frequency components, depending on the degree of stenosis (DOS) (positive correlation), are validated using multiple regression models with multiple explanatory variables and response variables. A new machine learning method, radial-based colour relation analysis, is employed to identify the level of DOS at the inflow and outflow sites. In contrast to the multiple linear regression and traditional machine learning method, the experimental results indicated that the proposed screening model had higher accuracy (hit rate), true-positive rate, and true-negative rate in clinical indication.

Right Ventricle-to-Pulmonary Artery Shunt in Pulmonary Atresia with a Ventricular Septal Defect: A Word of Caution.

The management of pulmonary atresia with a ventricular septal defect (PA/VSD) depends on the anatomy of the pulmonary artery or on the surgical strategy used at individual institutions. In our institution, we adopted a right ventricle-to-pulmonary artery (RV-PA) shunt in 2011 as a palliative procedure for PA/VSD to overcome the disadvantages of a Blalock-Taussig shunt. We evaluated the results of the RV-PA shunt as initial palliative surgery for PA/VSD. Thirteen patients with ductus-dependent PA/VSD from August 2011 to August 2015 were enrolled. The mean age at surgery was 17.9 ± 15.3 (range 5-60) days, and the mean body weight was 2.9 ± 0.6 (range 2.2-4.0) kg. A Gore-Tex tube graft was used in all patients. We retrospectively observed intra- and postoperative complications, early and late mortality, and palliation duration to definitive repair. Left pulmonary artery angioplasty was performed as a concomitant procedure in three patients. There were no early hospital mortalities, although two inter-stage deaths occurred 34 and 47days postoperatively: one patient died of aspiration and the other of right ventricular outflow tract (RVOT) pseudoaneurysm rupture. Two patients (15.4%) required the extracorporeal membrane oxygenation support postoperatively: one because of failure to wean from a bypass caused by persistent hypoxemia and the other because of sudden massive bleeding from the RVOT suture line in the intensive care unit 2 days postoperatively. These two patients underwent second-stage definitive repair successfully. Five patients (41.7%) required catheter intervention, for juxtaductal left pulmonary artery stenosis in three patients, right pulmonary artery stenosis in one, and shunt inflow stenosis in one. Two patients (15.4%) required re-operation because of shunt inflow stenosis and RVOT pseudoaneurysm, respectively. All patients who survived the RV-PA shunt underwent total correction at a mean interval of 13.1 months. A RV-PA shunt is an option for the initial palliation of ductus-dependent PA/VSD. Major complications can occur, including RVOT pseudoaneurysm, shunt inflow stenosis, persistent hypoxemia during the immediate postoperative period, and dehiscence of the shunt anastomosis site. Caution should be taken when performing the RV-PA shunt for palliation of PA/VSD.

Routine use of an aortic balloon to resolve possible inflow stenosis induced by the inflatable ring fixation mechanism of the Ovation endograft.

To investigate if the routine use of an aortic balloon within 15-30min after Ovation stent graft ring inflation would resolve any inflow stenosis, which may reach 60%, at the level of the sealing rings. Moreover, we estimated the potential hemodynamic compromise in these patients during rest and exercise. Following 3-dimensional reconstruction of AAA models, cross-sectional area of the infrarenal aorta just proximal the sealing mechanism (A aort, R aort, respectively) and internal area at the site of stenosis (A int, R int, respectively) were measured for 83. Forty-nine patients were managed without and 34 with an aortic balloon use. Pressure drop during rest and exercise was estimated. Technical success was 98% and there were no perioperative deaths, one type-I endoleak, and 12 (14.5%) type-II endoleaks. Median A int and R int were significantly reduced compared to A aort [55% reduction, 143 (range 28-380) mm2 vs 314 (range 177-531) mm2, P value <0.001] and R aort [42% reduction, 6.75 (range 3-11) mm vs 10 (range 7.5-13) mm, P value <0.001]. The observed stenosis was significantly less for patients in whom an aortic balloon was used intraoperatively (area reduction 36 vs 59%, P value=0.009). This stenosis caused a statistically significant, but clinically insignificant ΔP in both groups during rest (0.13 vs 0.06mmHg, P value=0.02) and exercise (1 vs 0.5mmHg, P value=0.02). The advantages of the unique sealing mechanism of the Ovation device seem to be accompanied by an inflow stenosis which is significantly reduced when neck molding with an aortic balloon is used. Overall, the hemodynamic impact of this abnormality seems to be clinically insignificant at 1-month follow-up.

Bilateral photoplethysmography for arterial steal detection in arteriovenous fistula using a fractional-order decision-making quantizer.

As inflow and outflow stenoses worsen, both flow resistance and pressure increase in the stenotic vascular access. During dialysis, when blood flow decreases, it may retrograde from the peripheral artery through the palmar arch to the arterial anastomosis site. Arterial steal syndrome (ASS) causes distal hypoperfusion, resulting in hand ischemia or extremity pain and edema. Hence, this study proposes the bilateral photoplethysmography (PPG) for ASS detection in arteriovenous fistulas. The decision-making quantizer utilizes the fractional-order feature extraction method and a non-cooperative game (NCG) framework to evaluate the ASS risk level. Bilateral asynchronous PPG signals have significant differences in the rise time and amplitude in relation to the degree of stenosis. The fractional-order self-synchronization error formulation is a feature extraction method used to quantify bilateral differences in blood flow changes between the dexter and sinister PPG signals. The NCG model as a method of decision-making is then employed to evaluate the ASS risk level. Using an acoustic Doppler measurement, the resistive (Res) index is also used to evaluate the vascular access stenosis at the arterial anastomosis site. In contrast with alternative methods including the high-sensitivity C-reactive protein level or Res index, our experimental results indicate that the proposed decision-making quantizer is more efficient in preventing ASS during hemodialysis treatment.

Hemodynamic impact of abdominal aortic aneurysm stent-graft implantation-induced stenosis

The current study aims to computationally evaluate the hemodynamic impact of a novel sealing mechanism employed by a recently developed endograft (Ovation TriVascular Stent-Graft System) for endovascular aneurysm repair. The exploitation of two inflatable O-rings to achieve sealing may be advantageous in terms of accommodating challenging anatomies, but comes at a price of a marked inflow stenosis. Here, four representative patient cases of inflow stenosis ranging from 30 to 80% were analyzed. Lumen surface models were constructed from 1 month post-operative computed tomography images and then used to numerically compute the complex endograft flow field. Our results highlight coexistence of stenotic wall regions exposed to high shear rate and post-stenotic recirculation zones. These conditions may implicate platelet activation and predispose thrombus formation and thromboembolic complications. A clinically insignificant cycle-averaged pressure drop along the inflow stenosis and further in the endograft main body legs was predicted (range 0.01-1.72mmHg) which was, however, notable at peak systole (range 3.52-19.73mmHg). Although the functional impact of the endograft stenosis at rest flow conditions may appear insignificant, increased flow rate during exercise is expected to strongly accentuate the observed effects. Pressure drop in the endograft legs was attributed to suboptimal, based on Murray's scaling law, cross-sectional area ratio between trunk and legs of the device.

Series of Noncontrast Time-of-Flight Magnetic Resonance Angiographies to Identify Problems with Arteriovenous Fistula Maturation

Successful maturation of arteriovenous fistulas (AVFs) remains a challenge for those managing patients with end-stage renal disease. Time-of-flight magnetic resonance angiography (TOF-MR) can be used to evaluate AVFs without the risk of radiation exposure, intravenous contrast, or reliance on the operator-dependent modality of color Doppler ultrasonography (CDUS). The objective of our study was to assess the utility of TOF-MR in the evaluation of nonmaturing AVFs and to identify the best clinical situations to use this technology. Consecutive patients with abnormal findings on CDUS or physical examination after AVF creation underwent 3-dimensional (3D) TOF-MR. Imaging was performed at 3 T with a scan acquisition time of approximately 15 min. The technique was similar to head and neck magnetic resonance angiography (MRA), except presaturation bands were not used, thereby allowing simultaneous visualization of both arterial and venous flow. A total of 19 TOF-MR studies were performed. Nineteen patients underwent imaging and were the focus of this study. Seventeen of 19 TOF-MR studies were of diagnostic quality and yielded findings which enabled the vascular surgeon to take corrective measures. Findings included inflow stenosis, anastomotic narrowing, venous outflow stenosis, and hemodynamically significant venous tributaries. Twelve of 17 patients required conventional digital subtraction angiography (DSA). The congruence rate between TOF-MR and DSA was 83.3%. Four patients (21%) avoided DSA and went directly to definitive surgical treatment including branch ligation (3) or new access (1). This is the first report in the literature of successful implementation of 3D TOF-MR to assist in identifying AVF maturation problems. This unique noninvasive imaging modality provides actionable images without contrast or radiation exposure and can obviate the need for invasive diagnostic procedures or provide an anatomic map for planning corrective intervention.

Dysfunction Screening in Experimental Arteriovenous Grafts for Hemodialysis Using Fractional-Order Extractor and Color Relation Analysis.

In physical examinations, hemodialysis access stenosis leading to dysfunction occurs at the venous anastomosis site or the outflow vein. Information from the inflow stenosis, such as blood pressure, pressure drop, and flow resistance increases, allows dysfunction screening from the stage of early clots and thrombosis to the progression of outflow stenosis. Therefore, this study proposes dysfunction screening model in experimental arteriovenous grafts (AVGs) using the fractional-order extractor (FOE) and the color relation analysis (CRA). A Sprott system was designed using an FOE to quantify the differences in transverse vibration pressures between the inflow and outflow sites of an AVG. Experimental analysis revealed that the degree of stenosis (DOS) correlated with an increase in fractional-order dynamic errors (FODEs). Exponential regression was used to fit a non-linear curve and can be used to quantify the relationship between the FODEs and DOS (R (2) = 0.8064). The specific ranges were used to evaluate the stenosis degree, such as DOS: <50, 50-80, and >80%. A CRA-based screening method was derived from the hue angle-saturation-value color model, which describes perceptual color relationships for the DOS. It has a flexibility inference manner with color visualization to represent the different stenosis degrees, which has average accuracy >90% superior to the traditional methods. This in vitro experimental study demonstrated that the proposed model can be used for dysfunction screening in stenotic AVGs.