Hemodynamic Implications of STABILISE Technique for Aortic Dissection Repair

BACKGROUND

The stent-assisted balloon-induced intimal disruption and relamination (STABILISE) technique for treatment of type B dissection has shown promising clinical results at mid-term. Computational modeling is a way of noninvasively obtaining hemodynamic effects, such as pressure and wall shear stress, leading to a better understanding of potential benefits. Particular areas of interest are (1) the effect of intimal disruption and re-lamination and (2) the effect of the bare metal stent in the visceral aortic segment.

METHODS

Single-center prospective case series. Data from 5 consecutive locally performed cases of STABILISE technique were analyzed. Included cases were type B aortic dissection with or without prior de-branching. The STABILISE procedure had to be performed without 30-day major complications. Preoperative and postoperative imaging data for each patient were transferred to the biomedical engineering team. Each case was reconstructed, meshed, and simulated with computational fluid dynamics using patient-specific data (heart rate, blood pressure, height, and weight). Hemodynamic parameters were then extracted from the simulations.

RESULTS

In all cases, computational analysis showed for postoperative patients: (1) a drop in pressure difference between lumina and (2) lower wall shear stress effects, compared to their preoperative status. These observations were most pronounced in the visceral aortic segment.

CONCLUSIONS

Computational modeling shows favourable changes in the flow dynamics of type B dissection treated using the STABILISE technique. This may suggest protective effects of this technique for long-term aortic healing and cicatrization.

The Role of Near Infrared Spectroscopy in Diagnosing Stump Ischaemia in Patients with Below Knee Amputation: Case Reports

Introduction

Functional near infrared spectroscopy (fNIRS) can be used to quantify stump oxygen saturation (SaO₂) as one of many possible causes of pain following major amputation. Although commonly used for cerebral perfusion monitoring during carotid or cardiac surgery, it can also be used to monitor tissue perfusion in the lower limb and predict healing following below knee amputation (BKA). The aim of this study was to measure the SaO₂ trend as there is no validated oxygen threshold to diagnose insufficient flow into the arterial collateral network currently.

Report

NIRS was used to measure SaO₂ while performing treadmill exercise. Two BKA patients with chronic stump pain were asked to perform treadmill exercise while using their prosthesis and NIRS optode applied to the posterior stump to monitor SaO₂. Cases 1 and 2 showed a decline in SaO₂ of 25% and 18%, respectively, while walking on the prosthesis. After superficial femoral artery (SFA) recanalisation and stenting, Case 1 showed improvement by maintaining SaO₂ between 54% and 60% throughout treadmill exercise. In Case 2, perfusion could not be further improved, and the patient underwent through knee amputation.

Discussion

fNIRS detected compressive ischaemia and exercise induced ischaemia as mechanisms of stump pain. Findings provided the multidisciplinary team with objective information, aiding decision making to treat stump pain.

Near infrared spectroscopy in peripheral artery disease and the diabetic foot: A systematic review

With the need for tools that assess microvascular status in diabetic foot disease (DFD) being clear, near infrared spectroscopy (NIRS) is a putative method for noninvasive testing of the diabetic foot. The use of NIRS in patients with peripheral arterial disease (PAD) has extended to its role in studying the pathophysiology of DFD. NIRS generates metrics such as recovery time, deoxygenation, oxygen consumption (VO₂ ), tissue oxygen saturation (StO₂ ), total haemoglobin (HbT), and oxyhaemoglobin area under the curve (O₂ Hb_AUC ). NIRS may potentially help the multidisciplinary team stratify limbs as high-risk, especially in diabetic patients with symptoms masked by peripheral neuropathy. NIRS may be useful for assessing treatment effectiveness and preventing deterioration of patients with PAD.

Proximal False Lumen Thrombosis is Associated with Low False Lumen Pressure and Fewer Complications in Type B Aortic Dissection

BACKGROUND

Improved risk stratification is a key priority for type B aortic dissection (TBAD). Partial false lumen thrombus morphology is an emerging predictor of complications however, partial thrombosis is poorly defined and its evaluation in clinical studies is inconsistent.

PURPOSE

This work aims to characterise hemodynamic pressure in TBAD and determine how pressure relates to false lumen thrombus morphology and clinical events.

METHODS

Retrospective admission computed tomography angiography of 69 patients with acute TBAD was used to construct three-dimensional computational models for simulation of cyclical blood flow and calculation of pressure. Patients were categorised based on false lumen thrombus morphology: minimal; proximal; distal; or extensive thrombosis. Linear regression analysis compared the luminal pressure difference between the true and false lumen for each morphology group. The impact of morphology classification on acute complications within 14 days was studied using logistic regression adjusted for clinical parameters. A survival analysis for adverse aortic events at one-year was also performed using Cox regression.

RESULTS

44 patients experienced acute complications and 45 had an adverse aortic event at one-year. Mean (±standard deviation) age was 62.6 (±12.6) years and 75.4% were male. Compared to patients with minimal thrombosis, those with proximal thrombosis had reduced false lumen pressure by 10.1mmHg (95% CI 4.3-15.9mmHg, p=.001). Individuals that did not experience an acute complication had reduced relative false lumen pressure (-6.35mmHg vs -0.62mmHg, p=.03). Proximal thrombosis was associated with fewer acute complications (OR 0.17, 95% CI 0.04-0.60 p=.01) and one-year adverse aortic events (HR 0.36, 95% CI 0.16-0.80, p=.01).

CONCLUSIONS

Proximal false lumen thrombosis is a marker of reduced false lumen pressure. This may explain how proximal false lumen thrombosis appears protective of acute complications (refractory hypertension or pain, aortic rupture, visceral or limb malperfusion and acute expansion) and adverse aortic events within the first year.

Availability and service provision of multidisciplinary diabetes foot units in Australia: a cross-sectional survey

BACKGROUND

With growing global prevalence of diabetes mellitus, diabetes-related foot disease (DFD) is contributing significantly to disease burden. As more healthcare resources are being dedicated to the management of DFD, service design and delivery is being scrutinised. Through a national survey, this study aimed to investigate the current characteristics of services which treat patients with DFD in Australia.

METHODS

An online survey was distributed to all 195 Australian members of the Australian and New Zealand Society for Vascular Surgery investigating aspects of DFD management in each member's institution.

RESULTS

From the survey, 52 responses were received (26.7%). A multidisciplinary diabetes foot unit (MDFU) was available in more than half of respondent's institutions, most of which were tertiary hospitals. The common components of MDFU were identified as podiatrists, endocrinologists, vascular surgeons and infectious disease physicians. Many respondents identified vascular surgery as being the primary admitting specialty for DFD patients that require hospitalisation (33/52, 63.5%). This finding was consistent even in centres with MDFU clinics. Less than one third of MDFUs had independent admission rights.

CONCLUSIONS

The present study suggests that many tertiary centres in Australia provide their diabetic foot service in a multidisciplinary environment however their composition and function remain heterogeneous. These findings provide an opportunity to evaluate current practice and, to initiate strategies aimed to improve outcomes of patients with DFD.

Management of acute type B aortic dissection

BACKGROUND

The best management of acute uncomplicated type B aortic dissection is currently a controversial area. Recent advances in endovascular intervention have begun to establish pre-emptive thoracic endovascular aortic repair as a potential strategy. A review about the management for type B aortic dissection has been conducted.

METHODS

A narrative review consisting of 157 original articles, meta-analyses and guidelines was conducted. The findings were synthesized and summarized using 70 articles.

RESULTS

There are clear guidelines directing surgical management of acute complicated type B aortic dissection. However, the best management of acute uncomplicated disease is more ambiguous, which is especially concerning in a condition which is associated with significant morbidity and mortality. Medical management alone is generally favoured. Endovascular intervention is now being considered by some surgeons, but it can be technically difficult, while exposing the patient to potential surgical risks.

CONCLUSIONS

Clinical and anatomical risk factors have been identified to help vascular surgeons make decisions about treatment in acute uncomplicated type B aortic dissection. New endovascular strategies are being developed to reduce surgical risk and address technical challenges. Registry data should be used to support future best management.

The application of computational modeling for risk prediction in type B aortic dissection

OBJECTIVE

New tools are urgently needed to help with surgical decision-making in type B aortic dissection (TBAD) that is uncomplicated at the time of initial presentation. This narrative review aims to answer the clinical question, Can computational modeling be used to predict risk in acute and chronic Stanford TBAD?

METHODS

The review (PROSPERO 2018 CRD42018104472) focused on risk prediction in TBAD. A comprehensive search of the Ovid MEDLINE database, using terms related to computational modeling and aortic dissection, was conducted to find studies of any form published between 1998 and 2018. Cohort studies, case series, and case reports of adults (older than 18 years) with computed tomography or magnetic resonance imaging diagnosis of TBAD were included. Computational modeling was applied in all selected studies.

RESULTS

There were 37 studies about computational modeling of TBAD identified from the search, and the findings were synthesized into a narrative review. Computational modeling can produce numerically calculated values of stresses, pressures, and flow velocities that are difficult to measure in vivo. Hemodynamic parameters-high or low wall shear stress, high pressure gradient between lumens during the cardiac cycle, and high false lumen flow rate-have been linked to the pathogenesis of branch malperfusion and aneurysm formation by numerous studies. Considering the major outcomes of end-organ failure, aortic rupture, and stabilization and remodeling, hypotheses have been generated about inter-relationships of measurable parameters in computational models with observable anatomic and pathologic changes, resulting in specific clinical outcomes.

CONCLUSIONS

There is consistency in study findings about computational modeling in TBAD, although a limited number of patients have been analyzed using various techniques. The mechanistic patterns of association found in this narrative review should be investigated in larger cohort prospective studies to further refine our understanding. It highlights the importance of patient-specific computational hemodynamic parameters in clinical decision-making algorithms. The current challenge is to develop and to test a risk assessment method that can be used by clinicians for TBAD.