Hydrodynamic evaluation of axillary artery perfusion for normal and diseased aorta

Low-flow perfusion technique for shaggy aortic arch

BACKGROUND

The most common complication of thoracic aortic disease with shaggy aorta is cerebral infarction. We have performed "low-flow perfusion" as a method of extracorporeal circulation to prevent cerebral embolism in patients with strong atherosclerotic lesions in the aortic arch.

METHODS

"Low-flow perfusion" is a method in which cardiopulmonary bypass is started by partial blood removal, approaching deep hypothermia while maintaining self-cardiac output. We compared the outcomes of 12 patients who underwent the "low-flow perfusion" method (Group L) with those of 12 who underwent normal extracorporeal circulation (Group N) during aortic arch surgery since 2019.

RESULTS

Group L consisted of 8 males with an average age of 73 years old, and Group N consisted of 6 males with an average age of 73 years old. The average time from the start of cooling to ventricular fibrillation was 9.5 min in Group L and 3.6 min in Group N (p < 0.01). The eardrum temperature when ventricular fibrillation was reached was 28.2 °C in Group L and 32.5 °C in Group N (p = 0.01). A blood flow analysis also revealed low wall shear stress on the lesser curvature of the aortic arch.

CONCLUSION

With this method, the intracranial temperature was sufficiently low at the time of ventricular fibrillation, and there was no need to increase the total pump flow. The low-flow perfusion method can prevent cerebral embolism by preventing atheroma destruction by the blood flow jet while maintaining the self-cardiac output during the cooling process.

Two-stage hybrid surgical repair for aortic arch pathology with a shaggy aorta: a case report

BACKGROUND

The surgical treatment strategy for aortic arch pathology with a shaggy aorta must be determined on a case-by-case basis because of the risk of catastrophic complications, such as brain infarction and spinal cord injury.

CASE PRESENTATION

This report describes the surgical case of two saccular aneurysms of the arch and abdominal aorta associated with a shaggy aorta in a 63-year-old man who underwent total arch replacement and secondary thoracic endovascular aortic repair. Considering the risk of embolization during endovascular therapy, graft replacement for the abdominal aortic aneurysm was initially performed. On postoperative day 28, total arch replacement with the conventional elephant trunk was performed using the functional brain isolation technique, which involves manipulating places far from the atherosclerotic burden, such as arterial inflow for cardiopulmonary bypass and unclamping of neck vessels. On postoperative day 7 after total arch replacement, thoracic endovascular aortic repair was performed across the conventional elephant trunk in the nondiseased descending aorta. No postoperative complications, such as cerebrovascular failure, paraplegia, or embolization to abdominal viscera or lower extremities, occurred. The patient remained asymptomatic.

CONCLUSIONS

The present case suggests that total arch replacement with the conventional elephant trunk and secondary thoracic endovascular aortic repair may be an effective alternative for aortic arch pathology with a shaggy aorta. The strategy for surgical treatment in patients with aortic arch pathologies with a shaggy aorta must be judged on a case-by-case basis, considering patient characteristics, comorbidities, and preoperative evaluation using transesophageal echocardiography and computed tomography angiography, to eliminate potential determinants of intraoperative stroke.

Aortic arch isolation to reduce cerebral embolic risk during replacement of the atherosclerotic aortic arch

OBJECTIVE

To analyze the efficacy of isolating the upper body circulation from the lower body (isolation technique) in reducing the risk of embolic stroke during cardiopulmonary bypass in patients with severe atherosclerosis undergoing aortic arch surgery.

METHODS

Between 2006 and 2019, 156 patients with severe atherosclerosis undergoing total arch replacement were enrolled. Since 2017, the right axillary or innominate artery and ascending aorta were both cannulated before cardiopulmonary bypass in the isolation group (n = 30). The left common carotid artery was clamped and inserted with a 13-Fr balloon perfusion catheter. The innominate artery was clamped in succession and cardiopulmonary bypass was instituted, establishing a parallel noncommunicating circulation for the upper and lower body. Patients without atherosclerosis that were not considered at high risk of embolic complications were excluded. The no-isolation group was drawn from historically matched control patients undergoing total arch replacement.

RESULTS

The permanent stroke rate in the isolation and no-isolation groups were 3.3% (n = 1) and 15.9% (n = 15.9), respectively. After inverse-probability-of-treatment-weighting adjustment, the early mortality (P = .043), stroke (P = .044), and composite of early mortality or stroke (P = .005) rates were significantly lower in the isolation group. The logistic regression analysis after inverse-probability-of-treatment-weighting risk adjustment showed a significantly reduced composite risk of early death and stroke in the isolation group (odds ratio, 0.09; 95% confidence interval, 0.01-0.70; P = .023).

CONCLUSIONS

The isolation technique was associated with a significant reduction in early postoperative embolic stroke and mortality risks in patients with severe aortic atherosclerosis undergoing total arch replacement.

Impact of the Isolated Cerebral Perfusion Technique for Aortic Arch Aneurysm Repair in Patients with a Shaggy Aorta

Objective: Total aortic arch replacement (TAR), particularly in individuals with extensive atherosclerotic alterations, especially shaggy aortas, is more crucial and difficult. The objective of this retrospective investigation was to ascertain if patients with shaggy aortas would respond to modified isolated cerebral perfusion (ICP). Materials and Methods: Between 2015 and 2020, nine individuals with shaggy aortas who received treatment for arch aneurysms were examined. Four and five patients, respectively, who had arch replacement with traditional selective cerebral perfusion (SCP) and modified ICP, were evaluated, and their short- and long-term results were compared. Results: There were no appreciable variations in the postoperative results between patients with traditional SCP and those with modified ICP. Following surgery, one patient developed paraparesis, while two individuals with traditional SCP experienced persistent neurological damage. In patients with modified ICP, there were no postoperative neurological or other problems associated to atherosclerosis; nevertheless, one patient experienced stroke 5 months after surgery. Conclusion: Patients with shaggy aorta may not receive enough brain protection from TAR with standard SCP because single axillary artery perfusion can result in nonphysiological flow and atheroma separation. Even in patients with shaggy aortas, TAR with modified ICP is safe, but late-phase severe adverse cerebrovascular events should be taken into account.

Review of the Development of Hemodynamic Modeling Techniques to Capture Flow Behavior in Arteries Affected by Aneurysm, Atherosclerosis, and Stenting

Cardiovascular diseases (CVDs) are the leading cause of death in the developed world. CVD can include atherosclerosis, aneurysm, dissection, or occlusion of the main arteries. Many CVDs are caused by unhealthy hemodynamics. Some CVDs can be treated with the implantation of stents and stent grafts. Investigations have been carried out to understand the effects of stents and stent grafts have on arteries and the hemodynamic changes post-treatment. Numerous studies on stent hemodynamics have been carried out using computational fluid dynamics (CFD) which has yielded significant insight into the effect of stent mesh design on near-wall blood flow and improving hemodynamics. Particle image velocimetry (PIV) has also been used to capture behavior of fluids that mimic physiological hemodynamics. However, PIV studies have largely been restricted to unstented models or intra-aneurysmal flow rather than peri or distal stent flow behaviors. PIV has been used both as a standalone measurement method and as a comparison to validate the CFD studies. This article reviews the successes and limitations of CFD and PIV-based modeling methods used to investigate the hemodynamic effects of stents. The review includes an overview of physiology and relevant mechanics of arteries as well as consideration of boundary conditions and the working fluids used to simulate blood for each modeling method along with the benefits and limitations introduced.

Directing a dispersion cannula tip toward the aortic root during thoracic aortic arch surgery does not adversely affect cardiac function

INTRODUCTION

Neurologic complications of open thoracic aortic surgery are devastating problems in patients with severely diseased aortas. This study aimed to clarify whether directing the aortic cannula tip toward the aortic root affects the postoperative cardiac function in patients undergoing open thoracic aortic surgery.

METHODS

A total of 16 patients who underwent total or partial arch replacement between January 2014 and April 2019 were enrolled and divided into two groups. Ascending aorta perfusion was performed by placing the cannula tip toward the aortic root (reversed direction group, seven patients) or toward the aortic arch (standard direction group, nine patients). Intraoperative and perioperative data, including mortality, morbidity, and postoperative cardiac function, were compared between the groups.

RESULTS

There were no hospital deaths or stroke events in either group. The aortic cross-clamping time was 102.4 ± 20.3 minutes in the reversed direction group and 87.1 ± 9.9 minutes in the standard direction group (p = 0.049). Furthermore, the intubation time was 28.4 ± 12.9 hours in the reversed direction group and 12.4 ± 6.8 hours in the standard direction group (p = 0.022). Both times were significantly longer in the reverse direction group. Postoperative serum creatine kinase-MB levels were significantly lower in the reversed direction group (6.2 ± 3.3 U/L vs 13.3 ± 4.8 U/L, respectively, p = 0.006). The cardiac output and cardiac index did not significantly differ.

CONCLUSIONS

Directing the aortic cannula tip toward the aortic root does not adversely affect the postoperative cardiac function after aortic arch surgery.

Flow analysis during mock circulation in normal and aortic arch aneurysm models through an aortic cannula toward the aortic arch and root

The aim of this study was to elucidate flow patterns of two different types of aortic cannulas inserted from the ascending aorta toward the aortic arch and root by mock circulation in a normal aortic arch and an aortic arch aneurysm model. Extracorporeal circulation was established using a centrifugal pump, a transparent glass normal aortic arch model, and an aortic arch aneurysm model for measurement by particle image velocimetry. The Stealthflow and Dispersion cannulas were used to elucidate the characteristics of the flow pattern and velocity under the condition of the cannula tip toward the aortic arch and aortic root. In the normal aortic arch model, high-velocity exit flow ranging from 0.7 to 0.8 m/s was detected in the proximal aortic arch by directing the cannula tip toward the aortic arch, whereas flow velocity in the aortic arch was < 0.2 m/s by directing the cannula tip toward the aortic root. In the aortic arch aneurysm model, high-velocity exit flow ranging from 0.5 to 0.8 m/s was detected in the aortic arch by directing the cannula tip toward the aortic arch, whereas flow velocity in the aortic arch was decreased to less than 0.2 m/s by directing the cannula tip toward the aortic root. Directing the aortic cannula tip toward the aortic root allowed the high-velocity exit flow to attenuate in velocity, so that flow velocity in the aortic arch was sufficiently reduced by reversed flow and vortex formation in both the normal and aortic arch aneurysm models.

Numerical simulation of blood flow in femoral perfusion: comparison between side-armed femoral artery perfusion and direct femoral artery perfusion

Computational numerical analysis was performed to elucidate the flow dynamics of femoral artery perfusion. Numerical simulation of blood flow was performed from the right femoral artery in an aortic model. An incompressible Navier-Stokes equation and continuity equation were solved using computed flow dynamics software. Three different perfusion models were analyzed: a 4.0-mm cannula (outer diameter 15 French size), a 5.2-mm cannula (18 French size) and an 8-mm prosthetic graft. The cannula was inserted parallel to the femoral artery, while the graft was anastomosed perpendicular to the femoral artery. Shear stress was highest with the 4-mm cannula (172 Pa) followed by the graft (127 Pa) and the 5.2-mm cannula (99 Pa). The cannula exit velocity was high, even when the 5.2-mm cannula was used. Although side-armed perfusion with an 8-mm graft generated a high shear stress area near the point of anastomosis, flow velocity at the external iliac artery was decreased. The jet speed decreased due to the Coanda effect caused by the recirculation behind sudden expansion of diameter, and the flow velocity maintains a constant speed after the reattachment length of the flow. This study showed that iliac artery shear stress was lower with the 5.2-mm cannula than with the 4-mm cannula when used for femoral perfusion. Side-armed graft perfusion generates a high shear stress area around the anastomotic site, but flow velocity in the iliac artery is slower in the graft model than in the 5.2-mm cannula model.

VALIDATION OF LOSS-COEFFICIENT-BASED OUTLET BOUNDARY CONDITIONS FOR SIMULATING AORTIC FLOW

Flow in a polyurethane model of a human aorta, driven by a heart-lung machine, is analyzed experimentally and computationally for antegrade and retrograde perfusion. The purpose of the analysis is the validation of the previously proposed loss-coefficient-based outlet boundary condition for aortic branches. This model is claimed to be commonly applicable to different perfusion modes of the aorta, unlike the alternative straightforward constant-pressure outlet boundary condition. First, the antegrade perfusion is analyzed computationally and experimentally. This step delivers the loss-coefficients that are to be used in any other perfusion mode of the aorta. Subsequently, a retrograde perfusion is applied to the same aorta, where the flow rates at the outlets of the aortic branches are measured and predicted by applying the loss-coefficient-based outlet boundary conditions. A very good agreement of the predictions with the measurements is observed. The predictions delivered by the standard constant-pressure outlet boundary condition are observed, on the contrary, to be highly in error. Thus, the advocated loss-coefficient-based outlet boundary condition is experimentally validated. It is shown that it is applicable to different perfusion modes with a quite good accuracy, which is much higher compared to the straightforward constant-pressure outlet boundary condition.

Blood flow analysis of the aortic arch using computational fluid dynamics

OBJECTIVES

To obtain predictive information regarding aortic disease, we evaluated how blood flow inside the aortic arch was influenced by thoracic aortic aneurysms. In addition, to reveal the optimal intraoperative management in these cases, we examined blood flow during right subclavian arterial (rSCA) perfusion using computational fluid dynamics (CFD).

METHODS

Patient-specific models of the aortic arch were made with six different patterns based on the computed tomographic images. CFD models with finite volume methods were created to simulate the physiological pulsatile flow including the peripheral reflection wave, characteristic impedance and autonomous regulation system. Flow stream patterns, wall shear stress (WSS) and the oscillatory shear index (OSI) were calculated during one cardiac cycle. Furthermore, flow streamlines during rSCA perfusion were simulated under different perfusion flows.

RESULTS

Aortic dilatation caused vortical disturbed flow in a dilated space, resulting in turbulent flow not only inside the aneurysm but also in the proximal and/or distal normal aortic portion. In patients with a dilated thoracic aorta, there was a helical spiral flow with a circumferential vortex in systole. In patients with an arch aneurysm, turbulent flow inside the aneurysm caused a high OSI at the tip of the aneurysm. A high OSI was detected at the orifice of the supra-aortic branches, sinotubular junction, posterior lateral side of the ascending aorta and lesser curvature of the proximal descending aorta. rSCA perfusion revealed that the right common carotid artery was perfused by blood flow from rSCA throughout the cardiac cycle. With 75% of the flow from the rSCA, blood flow from the heart reached the left common carotid and subclavian artery only during a short period during the peak of systole.

CONCLUSIONS

A dilated aorta causes a turbulent flow pattern in the aortic arch. The high OSI site was similar to the favourite entry site for acute aortic dissection, indicating the causal relationship between mechanical stress and acute aortic dissection. rSCA cannulation might be cerebroprotective from ascending aortic plaque.

Efficacy of right axillary artery perfusion for antegrade cerebral perfusion in open total arch repair

OBJECTIVE

Right axillary artery (RAxA) perfusion was introduced for selective antegrade cerebral perfusion in total aortic arch repair to prevent cerebral embolism derived from arterial cannulation. However, the strategic benefits and long-term results regarding the cannulation site remain controversial. We retrospectively compared the outcomes between propensity score-matched patients with and without using RAxA cannulation.

METHODS

Between 2006 and 2012, 260 consecutive patients underwent total arch repair with antegrade cerebral perfusion and moderate hypothermia at a single institution. RAxA cannulation was added in 142 patients (54.6%), and 70 propensity score-matched pairs were obtained.

RESULTS

There were no significant differences in 30-day (2.9% [2 of 70] vs 5.7% [4 of 70]; P = .415 and in-hospital death (5.7% [4 of 70] vs 5.7% [4 of 70]; P = 1.000) between matched pairs. Although there was no significant difference in the occurrence of postoperative stroke (8.6% [6 of 70] vs 8.6% [6 of 70]; P = 1.000), the new rate of new occurrence of postoperative paraparesis was lower in patients with RAxA perfusion (0% [0 of 70] vs 4.3% [3 of 70]; P = .067). With a mean follow-up period of 1057 ± 686 days, the overall 5-year survival was 90.6% and was 89.6% for patients with RAxA perfusion. Thee difference in survival between patients with and without RAxA perfusion was not significant.

CONCLUSIONS

RAxA perfusion is a useful option for total aortic arch repair, and the midterm outcomes were satisfactory. However, RAxA perfusion did not completely prevent stroke in patients with an atherothrombotic aorta.

Investigation of risks for cerebral embolism associated with the hemodynamics of cardiopulmonary bypass cannula: a numerical model

Cerebral emboli originating in the ascending aorta are a major cause of noncardiac complications following cardiac surgery. The hemodynamics of the aortic cannula has been proven to play a significant role in emboli generation and distribution. The aim of the current study was to perform a thorough numerical investigation in order to examine the effect of the design and orientation of the cannula used during cardiopulmonary bypass on the risk to develop cerebral embolism. Hemodynamic analyses compared numerical models of 27 cases consisting of six different cannula orientations, four aortic anatomies, and three cannula designs. The cannula designs included a straight-tip (ST) cannula, a moderately curved tip cannula (TIP1 ), and a sharp-angle curved cannula (TIP2 ). Outcome measures included hemodynamic parameters such as emanating jet velocity, jet velocity drop, maximal shear stress, aortic wall reaction, emboli pathlines and distribution between upper and lower vessels, and stagnation regions. Based on these parameters, the risks for hemolysis, atheroembolism, and cerebral embolism were evaluated and compared. On one hand, the jet emerging from the ST cannula generated large wall-shear stress at the aortic wall; this may have triggered the erosion and distribution of embolic atheromatous debris from the aortic arch. On the other hand, it diverted more emboli from the clamp region to the descending aorta and thus reduced the risk for cerebral embolism. The TIP1 cannula demonstrated less shear stress on the aortic wall and diverted more emboli from the clamp region toward the upper vessels. The TIP2 cannula exhibited a stronger emanating jet, higher shear stress inside the cannula, and highly disturbed flow, which was more stagnant near the clamp region. Current findings support the significant impact of the cannula design and orientation on emboli generation and distribution. Specifically, the straight tip cannula demonstrated a reduced risk of cerebral embolism, which may be pivotal in the clinical setting.