Sriram Narayanan

CFD Modelling of Abdominal Aortic Aneurysm on Hemodynamic Loads Using a Realistic Geometry with CT

The objective of this study is to find a correlation between the abdominal aortic aneurysm (AAA) geometric parameters, wall stress shear (WSS), abdominal flow patterns, intraluminal thrombus (ILT), and AAA arterial wall rupture using computational fluid dynamics (CFD). Real AAA 3D models were created by three-dimensional (3D) reconstruction of in vivo acquired computed tomography (CT) images from 5 patients. Based on 3D AAA models, high quality volume meshes were created using an optimal tetrahedral aspect ratio for the whole domain. In order to quantify the WSS and the recirculation inside the AAA, a 3D CFD using finite elements analysis was used. The CFD computation was performed assuming that the arterial wall is rigid and the blood is considered a homogeneous Newtonian fluid with a density of 1050u2009kg/m3 and a kinematic viscosity of 4 × 10−3 Pa·s. Parallelization procedures were used in order to increase the performance of the CFD calculations. A relation between AAA geometric parameters (asymmetry index (β), saccular index (γ), deformation diameter ratio (χ), and tortuosity index (ε)) and hemodynamic loads was observed, and it could be used as a potential predictor of AAA arterial wall rupture and potential ILT formation.

A Review of Computational Methods to Predict the Risk of Rupture of Abdominal Aortic Aneurysms

Computational methods have played an important role in health care in recent years, as determining parameters that affect a certain medical condition is not possible in experimental conditions in many cases. Computational fluid dynamics (CFD) methods have been used to accurately determine the nature of blood flow in the cardiovascular and nervous systems and air flow in the respiratory system, thereby giving the surgeon a diagnostic tool to plan treatment accordingly. Machine learning or data mining (MLD) methods are currently used to develop models that learn from retrospective data to make a prediction regarding factors affecting the progression of a disease. These models have also been successful in incorporating factors such as patient history and occupation. MLD models can be used as a predictive tool to determine rupture potential in patients with abdominal aortic aneurysms (AAA) along with CFD-based prediction of parameters like wall shear stress and pressure distributions. A combination of these computer methods can be pivotal in bridging the gap between translational and outcomes research in medicine. This paper reviews the use of computational methods in the diagnosis and treatment of AAA.

A Review of Arteriovenous Fistulae Creation in Octogenarians

BACKGROUNDnTo analyze the outcomes of arteriovenous fistulae (AVFs) creation in octogenarians.nnnMETHODSnA retrospective study of 47 AVFs created in patients aged 80xa0years and above from 2008 to 2014. Patient and AVF characteristics and outcomes were evaluated. Predictors of patency were analyzed with multivariate analysis and Kaplan-Meier patency, and survival analysis was performed.nnnRESULTSnForty-seven of 1,259 AVFs created were for octogenarians (4%). Mean age was 83xa0years old (range: 80-91 years), with 27 male (57%) and 35 with tunneled dialysis catheters in situ (75%). There were a total of 15 (32%) radiocephalic AVFs, 30 (64%) brachial-cephalic AVFs, and 2 (4%) brachial-basilic transposition AVFs. At 12xa0months, assisted primary patency rate was 28% (13 patients) while primary failure rate was 72% (34 patients). Subset analysis showed brachial-cephalic AVFs to have the highest assisted primary patency rate at 33%. Within 24xa0months, tunneled dialysis catheter-related sepsis rate was 31% (11 patients). Multivariate analysis did not reveal any factor to be statistically significant in predicting AVF patency. Kaplan-Meier survival curve showed a 50% survival rate at 63xa0months after AVF creation.nnnCONCLUSIONSnIn view of high AVF primary failure rate and relatively low tunneled dialysis catheter bacteremia rate, long-term tunneled dialysis catheters as the main form of hemodialysis renal access may be a viable option. However, with 50% of end-stage renal failure patients surviving up to 63xa0months after AVF creation, the risks and benefits of long-term tunneled dialysis catheters must be balanced against those of AVF creation.

Diabetic foot limb salvage – a series of 809 attempts and predictors for endovascular limb salvage failure

BACKGROUNDnTo review patient characteristics and outcomes of in-patient diabetic foot limb salvage and identify risk factors predicting for endovascular limb salvage failure.nnnMETHODSnRetrospective study of limb salvage attempts in 809 patients between August 2013 and Julyxa02015.nnnRESULTSnSixty-eight percent of our study population were male with mean age at 65 years and 73% presented with Rutherford grade 6 critical limb ischemia, with the remaining 27% Rutherford grade 5. Eighty-one percent had toe pressures of less than 50xa0mm Hg, 64% had infrainguinal trans-Atlantic inter-society consensus (TASC II) C or D lesions while 78% had infrapopliteal TASC II C or D lesions. Seven hundred seventy-seven patients (96%) underwent endovascular-first approach limb salvage, with 95% requiring infrapopliteal angioplasty, with 84% of them requiring 2-vessel or 3-vessel revascularization. Thirty-two patients (4%) underwent surgical bypass limb salvage, with 63% performed as salvage procedures for failed angioplasties. The mean in-patient stay was 12.3xa0days within the endovascular group and 31.1xa0days within the bypass group (Pxa0<xa00.01). One-year limb salvage was successful in 88% of endovascular group, as compared with 72% in bypass group (Pxa0=xa00.01). Overall 1-year survival was 93% within the endovascular group and 88% within the bypass group (Pxa0=xa00.27). The mean in-patient cost was SGD

Predictors of radio-cephalic arteriovenous fistulae patency in an Asian population.

5,518 within the endovascular group and SGD

Isolated abdominal aortic dissection

15,141 within the bypass group (Pxa0<xa00.01). Multivariate analysis showed that independent predictors for failure of endovascular limb salvage include end-stage renal failure (ESRF) (odds ratio [OR] 2.04, Pxa0=xa00.01), toe pressures <50xa0mm Hg (OR 2.15, Pxa0=xa00.01), infrainguinal TASC II patterns C or D (OR 1.99, Pxa0=xa00.03), and indirect angiosome revascularization (OR 2.03, Pxa0=xa00.02).nnnCONCLUSIONSnWithin our study population of Asian ethnicity, most in-patient diabetic foot peripheral arterial disease presented with Rutherford grade 6 disease, with mostly TASC II C or D lesions and required infrapopliteal revascularization. As most patients had multiple comorbidities and were poor surgical candidates, the majority underwent endovascular-first approach revascularization. Independent predictors of endovascular limb salvage failure include ESRF, toe pressures <50xa0mm Hg, infrainguinal TASC II patterns C or D, and indirect angiosome revascularization.

On the assessment of abdominal aortic aneurysm rupture risk in the Asian population based on geometric attributes

Purpose To identify predictors of arteriovenous fistula (AVF) patency in Asian patients with autogenous radio-cephalic arteriovenous fistula (RCAVF). Methods Retrospective review of 436 RCAVFs created between 2009 and 2013. Predictors of patency were identified with univariate and multivariate analysis. Kaplan-Meier survival analysis and log-rank test were used to calculate patency rates. Results Overall secondary patency rate was 72% at 12 months, 69% at 24 months, 58% at 36 months, 57% at 48 months, 56% at 60 months and 54% at 72 months. Univariate analysis showed that factors which predict for patency include male gender (p = 0.003), good diabetic control (p = 0.025), aspirin use (p = 0.031), pre-dialysis status (p = 0.037), radial artery diameter (p = 0.029) and non-calcified radial arteries (p = 0.002). Age (p = 0.866), cephalic vein diameter (p = 0.630) and surgeon grade (p = 0.472) did not predict for primary AVF failure. Multivariate analysis revealed the male gender to be an independent predictor for patency (odds ratio 1.99, p = 0.01). Subset analysis showed a significantly larger average radial artery diameter of 2.3 mm amongst males, as compared to 1.9 mm amongst females (p = 0.001) and no statistical difference in the average cephalic vein diameter. Conclusions Within our Asian study population, 12-month patency rate of RCAVF is 72%, 69% at 24 months, 58% at 36 months, 57% at 48 months, 56% at 60 months and 54% at 72 months. Male gender is an independent predictor for RCAVF patency. In females or patients with calcified radial arteries, a more proximal AVF should be considered.

Chimney Stent-Graft Repair for Concurrent Inferior Mesenteric Artery Aneurysm and Infrarenal Abdominal Aortic Aneurysm: Case Report

Isolated acute abdominal aortic dissection is a rare condition, accounting for 1.3% of all aortic dissections.1 It may be classified as iatrogenic, traumatic or spontaneous.2 To date, only 92 patients have been reported in western literature. All the reports were based on the Caucasian population, and the mean age according to the International Registry of Acute abdominal aortic dissection (IRAD) was 67.7u2005±u200513.3u2005years.1 We report a case of an isolated infrarenal abdominal aortic dissection in a middle age Asian man, and our subsequent management.

A Series of 210 Peripheral Arterial Disease Below-Knee Amputations and Predictors for Subsequent Above-Knee Amputations

This study aims to review retrospectively the records of Asian patients diagnosed with abdominal aortic aneurysm to investigate the potential correlations between clinical and morphological parameters within the context of whether the aneurysms were ruptured or unruptured. A machine-learning-based approach is proposed to predict the rupture status of Asian abdominal aortic aneurysm by comparing four different classifiers trained with clinical and geometrical parameters obtained from computed tomography images. The classifiers were applied on 312 patient data sets obtained from a regulatory-approved database. The data sets included 17 attributes under three classes: unruptured abdominal aortic aneurysm, ruptured abdominal aortic aneurysm, and normal aorta without aneurysm. Four different classification models, namely, Decision trees, Naïve Bayes, logistic regression, and support vector machines were applied to the patient data set. The models were evaluated by 10-fold cross-validation and the classifier performances were assessed with classification accuracy, area under the curve of receiver operator characteristic, and F-measures. Data analysis and evaluation were performed using the Weka machine learning application. The results indicated that Naïve Bayes achieved the best performance among the classifiers with a classification accuracy of 95.2%, an area under the curve of 0.974, and an F-measure of 0.952. The clinical implications of this work can be addressed in two ways. The best classifier can be applied to prospectively acquired data to predict the likelihood of aneurysm rupture. Next, it would be necessary to estimate the attributes implicated in rupture risk beyond just maximum aneurysm diameter.

Use of Negative Pressure Wound Therapy for Lower Limb Bypass Incisions

PURPOSEnTo report a rare case of concurrent inferior mesenteric artery (IMA) aneurysm and infrarenal abdominal aortic aneurysm (AAA) with a novel indication for the use of chimney stent-graft technique in this patient.nnnCASE REPORTnAn 82-year-old man with an asymptomatic 4.4-cm fusiform AAA and 3.6-cm IMA aneurysm, coupled with chronic occlusion of celiac artery and superior mesenteric artery at the ostia, underwent endovascular repair of both aneurysms. Preservation of the IMA and treatment of both aneurysms were achieved with IMA aneurysm stenting, aortic aneurysm stenting and IMA chimney stenting. At 1, 6, and 12 months surveillance, the grafts remained patent without endoleak.nnnCONCLUSIONSnThe IMA chimney with aortic stenting technique may be safely used in patients who require preservation of the IMA during AAA and IMA aneurysm repairs.