Effect of Cannula Shape on Aortic Wall and Flow Turbulence: Hydrodynamic Study During Extracorporeal Circulation in Mock Thoracic Aorta

Multidirectional Blood Flow During Cardiopulmonary Bypass Mimicking an Iatrogenic Aortic Dissection During Transesophageal Echocardiographic Examination

•IAD leads to perioperative morbidity and mortality. •TEE is sensitive and specific for the diagnosis of IAD. •Imaging artifacts are often seen during TEE evaluation of the aorta. •Multidirectional flow during CPB can resemble IAD on TEE.

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.

Clinical evaluation of a new dispersive aortic cannula

INTRODUCTION

Cerebral injury is a serious complication in open-heart surgery. Once it occurs, it causes significant disability and death. We developed a novel dispersive aortic cannula named the Stealth Flow cannula and used it as a standard aortic cannula in cardiopulmonary bypass. The aim of this study was to evaluate the efficiency of this aortic cannula.

METHODS

A total of 182 consecutive patients undergoing cardiac surgery using cardiopulmonary bypass were studied. The patients were divided into two groups: the Soft-Flow cannula group (n = 89) and the Stealth Flow cannula group (n = 93). Patients with a shaggy aortic arch were excluded from this study because the cannulae were inserted at the ascending aorta with a cannula tip directed toward the aortic root in these cases. Patients with multiple arterial perfusion sites were also excluded. Complications including early mortality, perioperative stroke, and intraoperative aortic injury were compared between the two groups.

RESULTS

Age, operative procedure, cardiopulmonary bypass time, and the Japan SCORE were not significantly different between the groups. In comparisons between the Stealth Flow and Soft-Flow groups, the incidences of early mortality, perioperative stroke, intraoperative aortic dissection, and all complications were 1.08% versus 1.12% (p = 0.98), 1.1% versus 2.2% (p = 0.53), 0% versus 1.1% (p = 0.33), and 1.1% versus 3.4% (p = 0.29), respectively. The incidence of major cardiovascular events, including early death, perioperative stroke, and aortic dissection, was not different.

CONCLUSIONS

The Stealth Flow cannula, which was designed based on our previous experimental study, contributed to reducing cerebral and aortic events as much as the Soft-Flow cannula in the present clinical study.

Computer-Simulated Fluid Dynamics of Arterial Perfusion in Extracorporeal Circulation: From Reality to Virtual Simulation

Background

Atheroembolism due to aortic manipulation remains an unsolved problem in surgery for thoracic aortic aneurysm. The goal of the present study is to create a computer simulation (CS) model with which to analyze blood flow in the diseased aorta.

Method

A three-dimensional glass model of the aortic arch was constructed from CT images of a normal, healthy person and a patient with transverse aortic arch aneurysm. Separately, a CS model of the curved end-hole cannula was created, and flow from the aortic cannula was recreated using a numerical simulation.

Results

Comparison of the data obtained by the glass model analyses revealed that the flow velocity and the vector of the flow around the exit of the cannula were similar to that in the CS model. A high-velocity area was observed around the cannula exit in both the glass model and the CS model. The maximum flow velocity was as large as 1.0 m/s at 20 mm from the cannula exit and remained as large as 0.5 to 0.6 m/s within 50 mm of the exit. In the aortic arch aneurysm models, the rapid jet flow from the cannula moved straight toward the lesser curvature of the transverse aortic arch. The locations and intensities of the calculated vortices were slightly different from those obtained for the glass model.

Conclusions

The proposed CS method for the analysis of blood flow from the aortic cannulae during extracorporeal circulation can reproduce the flow velocity and flow pattern in the proximal and transverse aortic arches.

Impact of Modified Transesophageal Echocardiography on Mortality and Stroke after Cardiac Surgery: A Large Cohort Study

The aim of this study was to investigate the impact of perioperative screening with modified transesophageal echocardiography (A-View method). We compared, in consecutive patients who underwent cardiac surgery between 2006 and 2014, 30-day mortality and in-hospital stroke incidence, operated either with perioperative modified TEE screening (intervention group) or only with conventional TEE screening (control group). Of the 8,605 study patients, modified TEE was applied in 1,391 patients (16.2%). Patients in the intervention group were on average older (71 versus 68 years, p < 0.001) and more often females (31.0% versus 28.0%, p < 0.001) and had a higher predicted mortality (EuroSCORE I: 5.9% versus 4.0%, p < 0.001). The observed 30-day mortality was 2.2% and 2.5% in both groups, respectively, with multivariable and propensity-score adjusted relative risks (RRs) of 0.70 (95% CI: 0.50–1.00, p = 0.05) and 0.67 (95% CI: 0.45–0.98, p = 0.04). In-hospital stroke was 2.9% and 2.1% in both groups, respectively, with adjusted RRs of 1.03 (95% CI: 0.73–1.45) and 1.01 (95% CI: 0.71–1.43). In patients undergoing cardiac surgery, use of perioperative screening for aortic atherosclerosis with modified TEE was associated with lower postoperative mortality, but not stroke, as compared to patients operated on without such screening.

A Protocol for Diagnosis and Management of Aortic Atherosclerosis in Cardiac Surgery Patients

In patients undergoing cardiac surgery, use of perioperative screening for aortic atherosclerosis with modified TEE (A-View method) was associated with lower postoperative mortality, but not stroke, as compared to patients operated on without such screening. At the time of clinical implementation and validation, we did not yet standardize the indications for modified TEE and the changes in patient management in the presence of aortic atherosclerosis. Therefore, we designed a protocol, which combined the diagnosis of atherosclerosis of thoracic aorta and the subsequent considerations with respect to the intraoperative management and provides a systematic approach to reduce the risk of cerebral complications.

Novel Straight Type Aortic Cannula with Spiral Flow Inducing Design

Aortic cannula is one of major factors leading to adverse events such as thrombosis and atherosclerosis development during open heart surgery. This is due to oxygenated blood outflow with high velocity jet from heart lung machine when exiting the cannula tip into ascending aorta. It was discovered, and validated by several researchers that blood flow out of the left ventricle into the aorta is spiral in nature. In this study, a novel design in which internal profile of the cannula was made to induce spiral flow were tested by way of numerical simulation, and compared against existing commercial cannula. Three designs were tested, which differed in number of groove employed. Among the cannula model designs, cannula design with 4 grooves yielded the lowest value of maximum wall shear stress at testing tube with 3.778 Pa and highest value of area weighted helicity density at 40 mm from cannula tips with 11.829 m/s2. Overall, spiral cannula models were showed highly potential in inducing spiral flow, and also the effect on blood hemolysis is acceptable.

Computational Analysis of the Mechanical Behaviors of Hemiarch and Total Arch Replacements

Surgery for aortic dissections or aneurysms can be extended into the aortic arch by hemiarch replacement (HAR) or total arch replacement (TAR). Although cardiovascular surgeons have been performing HAR and TAR for decades, the mechanical properties of HAR and TAR are not well understood. This study investigates the mechanical behaviors and stress distributions in HAR and TAR using a hybrid fluid-structure interaction analysis that combines computational fluid dynamics and structural static analysis. Geometrical information on the aortas of 11 subjects was extracted from contrast-enhanced computed tomography (CT) scan data. The CT images were imported into medical image processing software to reconstruct 3D models of the aortas. A 3D finite element model was employed to simulate aortas that receive HAR or TAR. The deformation of the great vessels and the stress distributions at both the vessels and the aortic grafts were calculated. The numerical results revealed that the aortas following TAR exhibited a lower level of stress than those following HAR. Higher stresses may cause arterial wall injury and increase the risk of rupture. Finite element analysis of the aortas and the aortic grafts provides useful information that helps physicians better understand the potential problems that may arise after various surgical procedures.

Hydrodynamic evaluation of aortic cardiopulmonary bypass cannulae using particle image velocimetry

The high velocity jet from aortic arterial cannulae used during cardiopulmonary bypass potentially causes a "sandblasting" injury to the aorta, increasing the possibility of embolisation of atheromatous plaque. We investigated a range of commonly available dispersion and non-dispersion cannulae, using particle image velocimetry. The maximum velocity of the exit jet was assessed 20 and 40 mm from the cannula tip at flow rates of 3 and 5 L/min. The dispersion cannulae had lower maximum velocities compared to the non-dispersion cannulae. Dispersion cannulae had fan-shaped exit profiles and maximum velocities ranged from 0.63 to 1.52 m/s when measured at 20 mm and 5 L/min. Non-dispersion cannulae had maximum velocities ranging from 1.52 to 3.06 m/s at 20 mm and 5 L/min, with corresponding narrow velocity profiles. This study highlights the importance of understanding the hydrodynamic performance of these cannulae as it may help in selecting the most appropriate cannula to minimize the risk of thromboembolic events or aortic injury.

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.

Cannula design reduces particulate and gaseous emboli during cardiopulmonary bypass for coronary revascularization

Purpose: The incidence of neurocognitive deficits after coronary bypass surgery remains problematic, with atheroembolism being one of the major causes. External manipulation of aorta and the “sandblasting” effect of the high-velocity perfusion jet can cause dislodgement of atheromatous debris.

Description: A new arterial cannula features a tip configuration that diffuses the flow through multiple outlets, providing reduced velocity and shear with one central and three diverted flow streams.

Evaluation: Between March 2007 and July 2008 twenty patients having isolated coronary artery bypass operations were instrumented with an Embolus Detection and Classification transducer. These data were compared to 43 patients from a previous study using similar techniques except for a standard open-tip arterial cannula. Total embolic counts were markedly lower in the new cannula group (20±25 vs 174±378) as were both gaseous (11±15 vs 95±211) and particulate counts (9±11 vs 80±194).

Conclusions: The select 3D cannula design reduces the sandblasting effect of the perfusion jet and, also, may direct emboli from the heart and cardiopulmonary bypass equipment away from the cerebral circulation.

Comparative Study of Continuous and Pulsatile Left Ventricular Assist Devices on Hemodynamics of a Pediatric End-to-Side Anastomotic Graft

Although there are many studies that focus on understanding the consequence of pumping mode (continuous vs. pulsatile) associated with ventricular assist devices (VADs) on pediatric vascular pulsatility, the impact on local hemodynamics has been largely ignored. Hence, we compare not only the hemodynamic parameters indicative of pulsatility but also the local flow fields in the aorta and the great vessels originating from the aortic arch. A physiologic graft anastomotic model is constructed based on a pediatric, patient specific, aorta with a graft attached on the ascending aorta. The flow is simulated using a previously validated second-order accurate Navier-Stokes flow solver based upon a finite volume approach. The major findings are: (1) pulsatile support provides a greater degree of vascular pulsatility when compared to continuous support, which, however, is still 20% less than pulsatility in the healthy aorta; (2) pulsatile support increases the flow in the great vessels, while continuous support decreases it; (3) complete VAD support results in turbulence in the aorta, with maximum principal Reynolds stresses for pulsatile support and continuous support of 7081 and 249 dyn/cm2, respectively; (4) complete pulsatile support results in a significant increase in predicted hemolysis in the aorta; and (5) pulsatile support causes both higher time-averaged wall shear stresses (WSS) and oscillatory shear indices (OSI) in the aorta than does continuous support. These findings will help to identify the risk of graft failure for pediatric patients with pulsatile and continuous VADs.

Hydrodynamics of aortic cannulae during extracorporeal circulation in a mock aortic arch aneurysm model

This study was designed to analyze flow pattern, velocity, and strain on the aortic wall of a glass aortic arch aneurysm model during the extracorporeal circulation, and to elucidate the characteristics of flow pattern in three different aortic cannulae. Different patterns of large vortices and helical flow were made by each cannula. With the curved end-hole cannula, the high velocity flow (approximately 0.6-0.8 m/s) was blowing to the aneurismal wall without attenuating the strain rate tensor (approximately 0.2-0.25/s). With the dispersion cannula and the Soft-Flow cannula, cannular jet was attenuated in the ascending aorta creating a large vortex at a velocity less than 0.5 m/s, and the strain rate tensor on the aneurismal wall was small (less than 0.15/s). In conclusion, end-hole cannula should not be used in the operation of aortic arch aneurysm. Dispersion-type aortic cannulae were less invasive on the aortic arch aneurismal wall, but particular attention to alternative cannulation sites should be paid in cases with severe atherosclerosis on the ascending aortic wall.

Numerical Study of Blood Flow at the End-to-Side Anastomosis of a Left Ventricular Assist Device for Adult Patients

We use an implicit large eddy simulation (ILES) method based on a finite volume approach to capture the turbulence in the anastomoses of a left ventricular assist device (LVAD) to the aorta. The order-of-accuracy of the numerical schemes is computed using a two-dimensional decaying Taylor–Green vortex. The ILES method is carefully validated by comparing to documented results for a fully developed turbulent channel flow at Reτ=395. Two different anastomotic flows (proximal and distal) are simulated for 50% and 100% LVAD supports and the results are compared with a healthy aortic flow. All the analyses are based on a planar aortic model under steady inflow conditions for simplification. Our results reveal that the outflow cannulae induce high exit jet flows in the aorta, resulting in turbulent flow. The distal configuration causes more turbulence in the aorta than the proximal configuration. The turbulence, however, may not cause any hemolysis due to low Reynolds stresses and relatively large Kolmogorov length scales compared with red blood cells. The LVAD support causes an acute increase in flow splitting in the major branch vessels for both anastomotic configurations, although its long-term effect on the flow splitting remains unknown. A large increase in wall shear stress is found near the cannulation sites during the LVAD support. This work builds a foundation for more physiologically realistic simulations under pulsatile flow conditions.