A numerical analysis of the aortic blood flow pattern during pulsed cardiopulmonary bypass

Effects of a Short-Term Left Ventricular Assist Device on Hemodynamics in a Heart Failure Patient-Specific Aorta Model: A CFD Study

Patients with heart failure (HF) or undergoing cardiogenic shock and percutaneous coronary intervention require short-term cardiac support. Short-term cardiac support using a left ventricular assist device (LVAD) alters the pressure and flows of the vasculature by enhancing perfusion and improving the hemodynamic performance for the HF patients. However, due to the position of the inflow and outflow of the LVAD, the local hemodynamics within the aorta is altered with the LVAD support. Specifically, blood velocity, wall shear stress, and pressure difference are altered within the aorta. In this study, computational fluid dynamics (CFD) was used to elucidate the effects of a short-term LVAD for hemodynamic performance in a patient-specific aorta model. The three-dimensional (3D) geometric models of a patient-specific aorta and a short-term LVAD, Impella CP, were created. Velocity, wall shear stress, and pressure difference in the patient-specific aorta model with the Impella CP assistance were calculated and compared with the baseline values of the aorta without Impella CP support. Impella CP support augmented cardiac output, blood velocity, wall shear stress, and pressure difference in the aorta. The proposed CFD study could analyze the quantitative changes in the important hemodynamic parameters while considering the effects of Impella CP, and provide a scientific basis for further predicting and assessing the effects of these hemodynamic signals on the aorta.

How to evaluate the outflow tract of LVAD after minimally invasive implantation by 3D CT-scan

During a minimally invasive implantation technique, the outflow graft of left ventricular assist device (LVAD) is tunnelled blindly through the pericardium or left pleura, with an inability to assess for twisting or malposition. Three-dimensional computed tomography scan (CT-scan) has a role in qualitative evaluation of the different outflow tract configurations. The different surgical minimally invasive approaches include: (a) mini-sternotomy and left mini-thoracotomy, (b) right mini-thoracotomy and left mini-thoracotomy, (c) subclavian artery access and left mini-thoracotomy. The outflow graft could be anastomosed to the left axillary artery or the ascending aorta. CT-scan reconstruction using syngo InSpace4D (Siemens, Muenchen, Germany) was used to provide fast segmentation and high-resolution images. The 3D reconstructions permit an evaluation of different anastomosis configurations and to assess the route of outflow graft.

The effect of Womersley number and particle radius on the accumulation of lipoproteins in the human aorta

The purpose of this study is to compare the effects of the different physical factors on lipoproteins accumulation in the aorta artery. Results revealed that hemodynamic parameters (WSS, OSI, RRT) together affect spatial distributions of lipoproteins concentration in the human aorta. Moreover, decreasing the frequency of pulsatile flow and particle size leads to more lipoproteins accumulated on the luminal surface. In addition, given the same flow rate, the pulsatile flow could reduce lipoproteins concentration in the luminal surface of aorta relative to a steady flow condition. The present computer strategy may have great potential in predicting the local atherosclerosis lesion.

Temporary Mechanical Circulatory Support in Acute Heart Failure

Cardiogenic shock (CS) is a challenging syndrome, associated with significant morbidity and mortality. Although pharmacological therapies are successful and can successfully control this acute cardiac illness, some patients remain refractory to drugs. Therefore, a more aggressive treatment strategy is needed. Temporary mechanical circulatory support (TCS) can be used to stabilise patients with decompensated heart failure. In the last two decades, the increased use of TCS has led to several kinds of devices becoming available. However, indications for TCS and device selection are part of a complex process. It is necessary to evaluate the severity of CS, any early and prompt haemodynamic resuscitation, prior TCS, specific patient risk factors, technical limitations and adequacy of resources and training, as well as an assessment of whether care would be futile. This article examines options for commonly used TCS devices, including intra-aortic balloon pumps, a pulsatile percutaneous ventricular assist device (the iVAC), veno-arterial extra-corporeal membrane oxygenation and Impella (Abiomed) and TandemHeart (LivaNova) percutaneous ventricular assist device.

Computational fluid dynamics of a novel perfusion strategy during hybrid thoracic aortic repair

BACKGROUND AND AIM

To mitigate the risk of perioperative neurological complications during frozen elephant trunk procedures, we aimed to computationally evaluate the effects of direct cerebral perfusion strategy through a left carotid-subclavian bypass on hemodynamics in a patient-specific thoracic aorta model.

METHODS

Between July 2016 and March 2019, 11 consecutive patients underwent frozen elephant trunk operation using the left carotid-subclavian bypass with a side graft anastomosis and right-axillary cannulation for systemic and brain perfusion. A multiscale model realized coupling three-dimensional computational fluid dynamics was developed and validated with in vivo data. Model comparison with direct antegrade cannulation of all epiaortic vessels was performed. Wall shear stress, wall shear stress spatial gradient, and localized normalized helicity were selected as hemodynamic indicators. Four cerebral perfusion flows were tested (6 to 15 mL/kg/min).

RESULTS

Direct cerebral perfusion of the left subclavian bypass resulted in higher flow rates with augmented speeds in all epiaortic vessels in comparison with traditional perfusion model. At the level of the left vertebral artery (LVA), a speed of 22.5 vs 21 mL/min and mean velocity of 3.07 vs 2.93 cm/s were registered, respectively. With a cerebral perfusion flow of 15 mL/kg, lower LVA wall shear stress (1.596 vs 2.030 N/m² ), and wall shear stress gradient (1445 vs 5882 N/m³ ) were observed. A less disturbed flow considering the localized normalized helicity was documented. No patients experienced neurological/spinal cord damages.

CONCLUSIONS

Direct perfusion of a left carotid bypass proved to be cerebroprotective, resulting in a more physiological and stable anterior and posterior cerebral perfusion.

Aortic cannula orientation and flow impacts embolic trajectories: computational cardiopulmonary bypass

INTRODUCTION

Emboli events are associated with the aortic cannula insertion and final position in the ascending aorta. However, the impact of subtle changes in aortic cannula movement and flow influencing embolic transport throughout the aortic arch is not well understood. The present study evaluated the aortic cannula's outflow and orientation effect on emboli entering the aortic branch arteries.

METHODS

A simplified aortic computational model was anteriorly cannulated in the distal ascending aorta with a 21-French straight aortic cannula, and two orientations were analysed by injecting gaseous and solid emboli at pump flows 2, 3 and 5 L/minute. The first aortic cannula orientation (forward flow cannula) was directed towards the lesser curvature. The second aortic cannula orientation (rear flow cannula) was tilted slightly backwards by 15°, providing flow in the retrograde direction.

RESULTS

Forward flow cannula produced a primary arch flow, whereas rear flow cannula produced a secondary arch flow resulting in four times longer emboli arch resident times than forward flow cannula. The rear flow cannula had the highest percentage of gaseous emboli entering the brachiocephalic artery of 8%, 12% and 36% (at 2, 3 and 5 L/minute, respectively). Rear flow cannula provided a positive aortic branch arterial flow at all pump flows, whereas at forward flow cannula, the brachiocephalic artery experienced retrograde flows of -1.0% (3 L/minute) and -4.0% (5 L/minute), with the left common carotid -0.23% (5 L/minute). No significant number of solid emboli entered the aortic branch arteries.

CONCLUSION

This numerical study illustrated distinct trajectory behaviours between gaseous and solid emboli where slight changes in aortic cannula orientation influenced idealised emboli direction with higher pump flows magnifying the effects.

Numerical analysis of aortic hemodynamics under the support of venoarterial extracorporeal membrane oxygenation and intra-aortic balloon pump

BACKGROUND AND OBJECTIVE

A gap still exists in the hemodynamic effect of intra-aortic balloon pump (IABP), venoarterial extracorporeal membrane oxygenation (VA-ECMO), and VA-ECMO plus IABP on the blood perfusion of the coronary artery, brain, and lower limb; the relation between heart flow and ECMO flow; and the wall stress of vessels.

METHODS

A finite-element model of the aorta, ECMO, and IABP was proposed to calculate the mechanical response via fluid-structure interaction. Heart failure (HF), IABP, ECMO, and ECMO plus IABP were utilized to study the effect of support models.

RESULTS

For the pressure curve, VA-ECMO weakened the dicrotic notch of pressure compared with HF and the pulsatile index (0.494 vs. 0.706 vs. 0.471 vs. 0.613). IABP, ECMO, and ECMO plus IABP increased the perfusion of the coronary, brain, and renal artery compared with HF. However, ECMO and ECMO plus IABP clearly reduced the blood flow of the left arteria femoralis compared to that of the right arteria femoralis (ECMO: 194.04 vs. 730.80 mL/min; ECMO plus IABP: 342.15 vs. 947.22 mL/min). In addition, the flow of ECMO accessed the renal artery more than the left ventricular flow. Greater ventricular flow perfused to the renal artery at a diastolic period for ECMO plus IABP, especially at the time points of 2.192 s and 2.304 s. Compared to the velocity distribution with ECMO, the flow of the right arteria femoralis was increased in the process of IABP-on. According to these four cases, the stress of the vascular wall was increased for ECMO support at the systolic period. The peak wall stress of ECMO is increased by 20% at 1.68 s.

CONCLUSIONS

ECMO plus IABP is more conducive to the blood supply than other cases from the result of numerical simulation. The location of blood intersection was generated in the region of the renal artery, which is estimated carefully.

Different Blood Flow Models in Coronary Artery Diseases: Effects on hemodynamic parameters

Coronary arteries are medium-small caliber vessels, in which low shear rate values are encountered, where non-Newtonian blood effects cannot be neglected. This work aims to study a comparison between Newtonian and non-Newtonian blood behaviors in a cohort offorty-eight 3D patient-specific stenotic vessels (right (RCA), left (LAD) and circumflex (LCX) coronary artery) at different grades of stenosis. Numerical simulation was carried out by means of Computational Fluid Dynamics (CFD) Analysis to investigate the blood velocity and distribution of the shear stress indices at different times of the cardiac cycle. A statistical analysis was performed to have a prediction ofincrement or decrement ofthe various hemodynamic parameters. The results show that the non-Newtonian effects are mostly important in shear stress indices distributions.

Influence of IABP-Induced Abdominal Occlusions on Aortic Hemodynamics: A Patient-Specific Computational Evaluation

Intraaortic balloon pump (IABP) is used as temporary mechanical assistance in case of cardiovascular diseases, even if different hemodynamic problems and, thus, clinical complications may happen, such as the decrease of visceral perfusion. A computational fluid dynamic (CFD) study was carried out to investigate the effects of different IABP-induced abdominal occlusions on patient-specific aortic flow. Two possible sizes (25 and 34 cm) and two locations (2 and 3 cm) of the balloon were compared, modeling four abdominal occlusions and numerically reproducing IAB inflation/deflation behavior. The results highlighted that the perfusion in renal, mesenteric, and iliac arteries decreases when the abdominal occlusion increases with balloon inflation. The study illustrates also how the balloon size affects the flow in aorta vessels in both locations, and that the positioning is of little relevance for the 34 cm balloon, whereas it influences the aortic flow very much in case of 25 cm IAB. This analysis demonstrates how the IAB-induced occlusion may vary the abdominal circulation; therefore, the correct size and positioning are emphasized for patient's outcome.

A computational fluid dynamics comparison between different outflow graft anastomosis locations of Left Ventricular Assist Device (LVAD) in a patient-specific aortic model

Left ventricular assist devices (LVADs) are mechanical supports used in case of heart failure. Little is known as the height of the anastomosis in aorta might influence the hemodynamic. The aim of the study was to evaluate the fluid dynamic behavior due to the outflow graft placement of a continuous flow LVAD in ascending aorta and to identify the insertion site with the best hemodynamic profile. Computational fluid dynamic studies were carried out to analyze 4 different anastomosis locations in a patient-specific aorta 3D model coupled with a lumped parameters model: 1 cm (case 1), 2 cm (case 2), 3 cm (case 3) and 4 cm (case 4) above the ST junction. In cases 1 and 2, epiaortic vessels presented a steady flow, while in cases 3 and 4 the flow was whirling. Moreover, maximum velocity occurred before: brachiocephalic trunk (case 1), brachiocephalic and left carotid arteries (case 2), left carotid and left subclavian artery (case 3) and left subclavian vessel and upper wall of aortic arch (case 4). Maximum time averaged wall shear stress (TAWSS) was located in: the ascending aorta (cases 1 and 2), the inferior curvature of the arch (case 3); at the origin of epiaortic vessels (case 4). Furthermore, a flow recirculation (cases 1 and 2), a blood stagnation and chaotic flow (cases 3 and 4) occurred above the aortic valve. The results suggested that the placement of the outflow graft at 2 cm above the ST junction gave the most favorable hemodynamic profile.