Malperfusion syndrome in type B aortic dissection: role of the endovascular procedures

Renal artery involvement in acute aortic dissection: Prevalence and impact on renal atrophy in non-interventional treatment patients

BACKGROUND

To evaluate the frequency of renal artery dissection (RAD) and renal hypoperfusion in aortic dissection (AD) and its effect on subsequent renal atrophy in patients who did not undergo therapeutic intervention.

METHODS

Initial CT data of 155 patients with acute AD (Stanford type A = 88, B = 67) were retrospectively analyzed. The false lumen statuses were patent (n = 94), partially thrombosed (n = 25), and completely thrombosed (n = 36) (also called as intramural hematoma (IMH)). Follow-up CT images of the surviving 122 patients (6-62.6 months, median, 28.9 months) were reviewed for analysis of sequential changes in renal volume. A regional decrease of ≧20 Hounsfield units in the renal cortex was defined as a renal hypo-enhancement sign (RHS). Simplified CT estimations of renal volume and estimated glomerular filtration rates (eGFR) were calculated. The generalized estimating equations (GEE) method was used to predict renal atrophy.

RESULTS

Fifty of the 122 patients presented with 59 RAD in the current study, and a positive RHS was noted in 33.9% (20/59) of these involved kidneys. GEE analysis showed hypertension, surgical treatment for AD, presence of RAD, and positive RHS as significant risk factors for renal atrophy. Patients with RHS had the most severe form of renal atrophy. The severity of renal atrophy was mildly correlated with GFR change (γ2 = 0.044, p < 0.001).

CONCLUSION

Renal atrophy in AD was predicted by the CT findings of RAD and RHS. The severity of renal atrophy was weakly reflected by eGFR.

Percutaneous retrograde recanalization of an occluded celiac artery complicating acute aortic dissection

A 79-year-old woman with a complaint of persistent upper abdominal pain was admitted to our hospital for the treatment of thrombosed acute type B aortic dissection. Computed tomography showed the complete static occlusion of the celiac artery. Because of progressive symptom with elevation of liver enzymes and metabolic acidosis 11 h after admission, endovascular revascularization was attempted on an emergent basis. After a failed catheterization of the celiac ostium in an antegrade fashion due to a hard occlusion, we succeeded in a retrograde recanalization through the pancreaticoduodenal arcade via the superior mesenteric artery with stent placement using a pull-through technique. This technique is useful and safe when an antegrade approach seems difficult.

Evaluation of the hemodynamic effectiveness of aortic dissection treatments via virtual stenting

Aortic dissection treatment varies for each patient and stenting is one of a number of approaches that are utilized to Stabilize the condition. Information regarding the hemodynamic forces in the aorta in dissected and virtually stented cases could support clinicians in their choices of treatment prior to medical intervention. Computational fluid dynamics coupled with lumped parameter models have shown promise in providing detailed information that could be used in the clinic; for this, it is necessary to develop personalized workflows in order to produce patient-specific simulations. In the present study, a case of pre- and post-stenting (virtual stent-graft) of an aortic dissection is investigated with a particular focus on the role of personalized boundary conditions. For each virtual case, velocity, pressure, energy loss, and wall shear stress values are evaluated and compared. The simulated single stent-graft only marginally reduced the pulse pressure and systemic energy loss. The double stent-graft results showed a larger reduction in pulse pressure and a 40% reduction in energy loss as well as a more physiological wall shear stress distribution.Regions of potential risk were highlighted. The methodology applied in the present study revealed detailed information about two possible surgical outcome cases and shows promise as both a diagnostic and an interventional tool.

THE IMPACT OF THE NUMBER OF TEARS IN PATIENT-SPECIFIC STANFORD TYPE B AORTIC DISSECTING ANEURYSM: CFD SIMULATION

It is believed that the progression of Stanford type B aortic dissection is closely associated with vascular geometry and hemodynamic parameters. The hemodynamic differences owing to the presence of greater than two tears have not been explored. The focus of the present study is to investigate the impact of an additional re-entry tear on the flow, pressure and wall shear stress distribution in the dissected aorta. A 3D aorta model with one entry and one re-entry tear was generated from computed tomography (CT) angiographic images of a patient with Stanford Type B aortic dissection. To investigate the hemodynamic effect of more than two tear locations, an additional circular re-entry tear was added 24 mm above the original re-entry tear. Our simulation results showed that the presence of an additional re-entry tear provided an extra return path for blood back to the true lumen during systole, and an extra outflow path into the false lumen during diastole. The presence of this additional path led to a decrease in the false lumen pressure, particularly at the distal region. Meanwhile, the presence of this additional tear causes no significant difference on the time average wall shear stress (TAWSS) distribution except at regions adjacent to re-entry tear 2. Moderate and concentrated TAWSS was observed at the bottom region of this additional tear which may lead to further extension of the tear distally.

Development of a patient-specific simulation tool to analyse aortic dissections: assessment of mixed patient-specific flow and pressure boundary conditions

Aortic dissection has high morbidity and mortality rates and guidelines regarding surgical intervention are not clearly defined. The treatment of aortic dissection varies with each patient and detailed knowledge of haemodynamic and mechanical forces would be advantageous in the process of choosing a course of treatment. In this study, a patient-specific dissected aorta geometry is constructed from computed tomography scans. Dynamic boundary conditions are implemented by coupling a three element Windkessel model to the 3D domain at each outlet, in order to capture the essential behaviour of the downstream vasculature. The Windkessel model parameters are defined based on clinical data. The predicted minimum and maximum pressures are close to those measured invasively. Malperfusion is indicated and complex flow patterns are observed. Pressure, flow and wall shear stress distributions are analysed. The methodology presented here provides insight into the haemodynamics in a patient-specific dissected aorta and represents a development towards the use of CFD simulations as a diagnostic tool for aortic dissection.

Simultaneous Surgical Treatment of Type B Dissection Complicated With Visceral Malperfusion and Abdominal Aortic Aneurysm: Role of Aortic Fenestration

Aortic dissection occurs in about 5% of patients with coexistent abdominal aortic aneurysm (AAA); combined type B dissection complicated with visceral malperfusion and AAA is an uncommon aortic emergency and patients presenting with complications of thoracic aortic dissection have a dismal prognosis related to difficulties in treatment strategies. Despite tremendous improvement of endovascular techniques, surgical aortic fenestration represents a quick, safe, and effective procedure able to restore flow in an otherwise malperfused aorta. This procedure has to be kept in mind because subsets of patients cannot be treated conventionally due to either prohibitive risk of aortic replacement, anatomic contraindication, or limitations of percutaneous procedures. Herein we report a case of a patient presenting with type B aortic dissection complicated by visceral malperfusion and AAA which was successfully treated simultaneously by open AAA repair and surgical fenestration. We focus on the mechanism of malperfusion and on the role of surgical fenestration.

[Malperfusion in aortic dissection: diagnostic problems and therapeutic procedures]

Malperfusion of the thoracoabdominal aorta and its side branches is a common complication of aortic dissection, often proving fatal. Vital organ malperfusion accompanying acute aortic dissection is a major cause of mortality and morbidity and requires timely reperfusion of the ischemic organs as well as adequate management of the aortic dissection. Ischemic damage to vital organs supplied by the thoracoabdominal aorta greatly increases the overall risk of aortic dissection. As initial symptoms may be subtle, malperfusion tends to be recognized late, and therefore accounts for a considerable percentage of fatalities.Effective reperfusion is not readily achieved by central aortic surgery alone in a certain number of patients. Various strategies have been used, including entry closure by central aortic surgery or stent grafting, surgical or catheter fenestration, bypass grafting and percutaneous stenting.Endovascular bare-metal stent placement is an attractive and promising treatment option since it is readily available, is less invasive and presents fewer risks to the patient.

Acute Complex Type A Dissection associated with peripheral malperfusion syndrome treated with a staged approach guided by lactate levels

Acute type A aortic dissection can be complicated by visceral malperfusion and is associated with a significant surgical morbidity and mortality. We describe a case of successful management of a complex acute type A dissection with mesenteric and lower limb ischemia treated with endovascular thoracic stenting and femoro-femoral crossover bypass grafting followed by aortic arch repair. To accomplish this, we applied a staged therapeutic approach using serial lactate measurements to assess the adequacy of peripheral perfusion and metabolic status prior to surgical repair of the proximal dissection.