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Shaun D Gregory - One of the best experts on this subject based on the ideXlab platform.

  • melt electrospun bilayered scaffolds for tissue integration of a suture less Inflow Cannula for rotary blood pumps
    Artificial Organs, 2018
    Co-Authors: Sam Liao, Shaun D Gregory, Maria A Woodruff, Christina Theodoropoulos, Keith A Blackwood
    Abstract:

    Implantation of left ventricular assist devices typically requires cardiopulmonary bypass support, which is associated with postoperative complications. A novel suture-less Inflow Cannula, which can be implanted without bypass, uses mild myocardial compression to seal the interface, however, this may lead to necrosis of the myocardium. To circumvent this issue, a bilayered scaffold has been developed to promote tissue growth at the interface between Cannula and myocardium. The bilayered scaffold consists of a silicone base layer, which mimics the seal, and a melt electrospun polycaprolactone scaffold to serve as a tissue integration layer. Biocompatibility of the bilayered scaffolds was assessed by analyzing cell viability, morphology, and metabolic activity of human foreskin fibroblasts cultured on the scaffolds for up to 14 days. There was no evidence of cytotoxicity and the cells adhered readily to the bilayered scaffolds, revealing a cell morphology characteristic of fibroblasts, in contrast to the low cell adhesion observed on flat silicone sheets. The rate of cell proliferation on the bilayered scaffolds rose over the 14-day period and was significantly greater than cells seeded on the silicone sheets. This study suggests that melt electrospun bilayered scaffolds have the potential to support tissue integration of a suture-less Inflow Cannula for cardiovascular applications. Furthermore, the method of fabrication described here and the application of bilayered scaffolds could also have potential uses in a diverse range of biomedical applications.

  • ventricular flow dynamics with varying lvad Inflow Cannula lengths in silico evaluation in a multiscale model
    Journal of Biomechanics, 2018
    Co-Authors: Benjamin Simpson, Sam Liao, Michael Neidlin, Zhiyong Li, Shaun D Gregory
    Abstract:

    Left ventricular assist devices are associated with thromboembolic events, which are potentially caused by altered intraventricular flow. Due to patient variability, differences in apical wall thickness affects Cannula insertion lengths, potentially promoting unfavourable intraventricular flow patterns which are thought to be correlated to the risk of thrombosis. This study aimed to present a 3D multiscale computational fluid dynamic model of the left ventricle (LV) developed using a commercial software, Ansys, and evaluate the risk of thrombosis with varying Inflow Cannula insertion lengths in a severely dilated LV. Based on a HeartWare HVAD Inflow Cannula, insertion lengths of 5, 19, 24 and 50 mm represented cases of apical hypertrophy, typical ranges of apical thicknesses and an experimental length, respectively. The risk of thrombosis was evaluated based on blood washout, residence time, instantaneous blood stagnation and a pulsatility index. By introducing fresh blood to displace pre-existing blood in the LV, after 5 cardiac cycles, 46.7%, 45.7%, 45.1% and 41.8% of pre-existing blood remained for insertion lengths of 5, 19, 24 and 50 mm, respectively. Compared to the 50 mm insertion, blood residence time was at least 9%, 7% and 6% higher with the 5, 19 and 24 mm insertion lengths, respectively. No instantaneous stagnation at the apex was observed directly after the E-wave. Pulsatility indices adjacent to the Cannula increased with shorter insertion lengths. For the specific scenario studied, a longer insertion length, relative to LV size, may be advantageous to minimise thrombosis by increasing LV washout and reducing blood residence time.

  • numerical prediction of thrombus risk in an anatomically dilated left ventricle the effect of Inflow Cannula designs
    Biomedical Engineering Online, 2016
    Co-Authors: Sam Liao, Benjamin Simpson, Michael Neidlin, Tim A S Kaufmann, Zhiyong Li, Maria A Woodruff, Shaun D Gregory
    Abstract:

    Implantation of a rotary blood pump (RBP) can cause non-physiological flow fields in the left ventricle (LV) which may trigger thrombosis. Different Inflow Cannula geometry can affect LV flow fields. The aim of this study was to determine the effect of Inflow Cannula geometry on intraventricular flow under full LV support in a patient specific model. Computed tomography angiography imaging of the LV was performed on a RBP candidate to develop a patient-specific model. Five Inflow Cannulae were evaluated, which were modelled on those used clinically or under development. The Inflow Cannulae are described as a crown like tip, thin walled tubular tip, large filleted tip, trumpet like tip and an inferiorly flared Cannula. Placement of the Inflow Cannula was at the LV apex with the central axis intersecting the centre of the mitral valve. Full support was simulated by prescribing 5 l/min across the mitral valve. Thrombus risk was evaluated by identifying regions of stagnation. Rate of LV washout was assessed using a volume of fluid model. Relative haemolysis index and blood residence time was calculated using an Eulerian approach. The inferiorly flared Inflow Cannula had the lowest thrombus risk due to low stagnation volumes. All Cannulae had similar rates of LV washout and blood residence time. The crown like tip and thin walled tubular tip resulted in relatively higher blood damage indices within the LV. Changes in intraventricular flow due to variances in Cannula geometry resulted in different stagnation volumes. Cannula geometry does not appreciably affect LV washout rates and blood residence time. The patient specific, full support computational fluid dynamic model provided a repeatable platform to investigate the effects of Inflow Cannula geometry on intraventricular flow.

  • Inflow Cannula design for biventricular assist devices
    Institute of Health and Biomedical Innovation; Science & Engineering Faculty, 2013
    Co-Authors: Shaun D Gregory
    Abstract:

    Cardiovascular diseases are a leading cause of death throughout the developed world. With the demand for donor hearts far exceeding the supply, a bridge-to-transplant or permanent solution is required. This is currently achieved with ventricular assist devices (VADs), which can be used to assist the left ventricle (LVAD), right ventricle (RVAD), or both ventricles simultaneously (BiVAD). Earlier generation VADs were large, volume-displacement devices designed for temporary support until a donor heart was found. The latest generation of VADs use rotary blood pump technology which improves device lifetime and the quality of life for end stage heart failure patients. VADs are connected to the heart and greater vessels of the patient through specially designed tubes called Cannulae. The Inflow Cannulae, which supply blood to the VAD, are usually attached to the left atrium or ventricle for LVAD support, and the right atrium or ventricle for RVAD support. Few studies have characterized the haemodynamic difference between the two Cannulation sites, particularly with respect to rotary RVAD support. Inflow Cannulae are usually made of metal or a semi-rigid polymer to prevent collapse with negative pressures. However suction, and subsequent collapse, of the Cannulated heart chamber can be a frequent occurrence, particularly with the relatively preload insensitive rotary blood pumps. Suction events may be associated with endocardial damage, pump flow stoppages and ventricular arrhythmias. While several VAD control strategies are under development, these usually rely on potentially inaccurate sensors or somewhat unreliable inferred data to estimate preload. Fixation of the Inflow Cannula is usually achieved through suturing the Cannula, often via a felt sewing ring, to the Cannulated chamber. This technique extends the time on cardiopulmonary bypass which is associated with several postoperative complications. The overall objective of this thesis was to improve the placement and design of rotary LVAD and RVAD Inflow Cannulae to achieve enhanced haemodynamic performance, reduced incidence of suction events, reduced levels of postoperative bleeding and a faster implantation procedure. Specific objectives were: * in-vitro evaluation of LVAD and RVAD Inflow Cannula placement, * design and in-vitro evaluation of a passive mechanism to reduce the potential for heart chamber suction, * design and in-vitro evaluation of a novel suture-less Cannula fixation device. In order to complete in-vitro evaluation of VAD Inflow Cannulae, a mock circulation loop (MCL) was developed to accurately replicate the haemodynamics in the human systemic and pulmonary circulations. Validation of the MCL’s haemodynamic performance, including the form and magnitude of pressure, flow and volume traces was completed through comparisons of patient data and the literature. The MCL was capable of reproducing almost any healthy or pathological condition, and provided a useful tool to evaluate VAD Cannulation and other cardiovascular devices. The MCL was used to evaluate Inflow Cannula placement for rotary VAD support. Left and right atrial and ventricular Cannulation sites were evaluated under conditions of mild and severe heart failure. With a view to long term LVAD support in the severe left heart failure condition, left ventricular Inflow Cannulation was preferred due to improved LVAD efficiency and reduced potential for thrombus formation. In the mild left heart failure condition, left atrial Cannulation was preferred to provide an improved platform for myocardial recovery. Similar trends were observed with RVAD support, however to a lesser degree due to a smaller difference in right atrial and ventricular pressures. A compliant Inflow Cannula to prevent suction events was then developed and evaluated in the MCL. As rotary LVAD or RVAD preload was reduced, suction events occurred in all instances with a rigid Inflow Cannula. Addition of the compliant segment eliminated suction events in all instances. This was due to passive restriction of the compliant segment as preload dropped, thus increasing the VAD circuit resistance and decreasing the VAD flow rate. Therefore, the compliant Inflow Cannula acted as a passive flow control / anti-suction system in LVAD and RVAD support. A novel suture-less Inflow Cannula fixation device was then developed to reduce implantation time and postoperative bleeding. The fixation device was evaluated for LVAD and RVAD support in cadaveric animal and human hearts attached to a MCL. LVAD Inflow Cannulation was achieved in under two minutes with the suture-less fixation device. No leakage through the suture-less fixation device – myocardial interface was noted. Continued development and in-vivo evaluation of this device may result in an improved Inflow Cannulation technique with the potential for off-bypass insertion. Continued development of this research, in particular the compliant Inflow Cannula and suture-less Inflow Cannulation device, will result in improved postoperative outcomes, life span and quality of life for end-stage heart failure patients.

  • passive control of a biventricular assist device with compliant Inflow Cannulae
    Institute of Health and Biomedical Innovation; Science & Engineering Faculty, 2012
    Co-Authors: Shaun D Gregory, Mark J Pearcy, Daniel Timms
    Abstract:

    Rotary ventricular assist device (VAD) support of the cardiovascular system is susceptible to suction events due to the limited preload sensitivity of these devices. This may be of particular concern with rotary biventricular support (BiVAD) where the native, flow-balancing Starling response is diminished in both ventricles. The reliability of sensor and sensor-less based control systems which aim to control VAD flow based on preload have limitations and thus an alternative solution is desired. This study introduces a compliant Inflow Cannula (CIC) which could improve the preload sensitivity of a rotary VAD by passively altering VAD flow depending on preload. To evaluate the design, both the CIC and a standard rigid Inflow Cannula were inserted into a mock circulation loop to enable biventricular heart failure support using configurations of atrial and ventricular Inflow, and arterial outflow Cannulation. A range of left (LVAD) and right VAD (RVAD) rotational speeds were tested as well as step changes in systemic/pulmonary vascular resistance to alter relative preloads, with resulting flow rates recorded. Simulated suction events were observed, particularly at higher VAD speeds, during support with the rigid Inflow Cannula, while the CIC prevented suction events under all circumstances. The compliant section passively restricted its internal diameter as preload was reduced, which increased the VAD circuit resistance and thus reduced VAD flow. Therefore, a compliant Inflow Cannula could potentially be used as a passive control system to prevent suction events in rotary left, right and biventricular support.

Robert Benkowski - One of the best experts on this subject based on the ideXlab platform.

  • Preclinical Evaluation of the EVAHEART 2 Centrifugal Left Ventricular Assist Device in Bovines.
    Asaio Journal, 2019
    Co-Authors: Tadashi Motomura, Eisuke Tatsumi, Kenji Yamazaki, Robert Benkowski, Egemen Tuzun, Shunichi Yamazaki
    Abstract:

    : The EVAHEART 1 left ventricular assist device was miniaturized to the EVAHEART 2, with a new Inflow Cannula designed to mitigate the risks of malposition. To evaluate the safety of the new double-cuff tipless Inflow Cannula, in vivo studies were performed in healthy bovines. Eight consecutive studies were done: five short-term studies of hematological adaptation and three long-term studies of tissue adaptation. Each Inflow Cannula was purposefully implanted in the worst-case setting with marked malposition. Two studies terminated early: one because of an animal-specific ancillary component and one because of an accidental radial fracture. Six studies reached the study endpoint without major adverse events. One animal could not achieve proper anticoagulation because of warfarin resistance. Pump speed and power were maintained within stable, normal ranges. There were no major organ dysfunction or suction events. Necropsy results showed two cases of pannus formation around the Inflow ostium because of warfarin resistance and hyperinflammation at the Inflow cuff suture line. There was one case of trivial pannus; four cases were pannus-free, with no evidence of ventricular wall suction. No wedge thrombus formation occurred. The EVAHEART 2 tipless Inflow Cannula may reduce adverse events attributable to the Inflow Cannula, such as stroke.

  • reducing regional flow stasis and improving intraventricular hemodynamics with a tipless Inflow Cannula design an in vitro flow visualization study using the evaheart lvad
    Artificial Organs, 2019
    Co-Authors: Karen Maynewman, Tadashi Motomura, Ricardo Montes, Josue Campos, Nikolas Marquezmaya, Vi Vu, Erin Zebrowski, Robert Benkowski
    Abstract:

    : Due to the high stroke rate of left ventricular assist device (LVAD) patients, reduction of thrombus has emerged as an important target for LVAD support. Left ventricular blood flow patterns with areas of flow stasis and recirculation are associated with platelet aggregation, which is worsened by exposure to high shear stress. Previous reports of intraventricular thrombus in LVAD patients have identified the outside of the LVAD Inflow Cannula as a nidus for LV thrombus formation. Previous studies of LVAD Inflow Cannula design have shown a region of low blood velocity and pulsatility at the apex, adjacent to the Cannula. One unresolved question is whether the standard practice of inserting the LVAD Inflow Cannula several mm into the LV could be revised to reduce thrombus formation. To address this, a "tipless" Inflow Cannula was designed for the EVAHEART LVAS, and assessed in a mock circulatory loop of the LVAD-supported heart. Customized transparent silicone models of a dilated LV were connected to the EVAHEART LVAS at the apex with a clear polycarbonate Inflow Cannula for flow visualization using particle image velocimetry (PIV). The "tipless" Cannula was inserted flush with the endocardial border and did not protrude into the LV. This condition was compared to the standard Cannula position with a 1-cm insertion into the LV. The Pre-LVAD condition corresponded to a severe heart failure patient (ejection fraction of 24%) with a dilated LV (180 mL). LVAD support was provided at speeds of 1.8 and 2.3 krpm. At the lower LVAD speed, 63% of the flow passed through the LVAD, with the remainder ejecting through the aortic valve. When LVAD speed was increased, nearly all flow (98%) left the LV through the LVAD. Both LVAD speed conditions produced a vortex ring similar to the Pre-LVAD condition in diastole. However, the protruding Inflow Cannula interrupted the growth and restricted the movement of the vortex, and produced areas of low velocity and pulsatility adjacent to the Cannula. The tipless Cannula exhibited an uninterrupted pattern of the mitral jet toward the LV apex, which allowed the diastolic vortex to grow and aid in the washout of this region. In addition, the tipless Cannula increased aortic valve flow, which reduces stasis in the left ventricular outflow tract. The EVAHEART LVAS tipless Inflow Cannula design improved regional velocity, pulsatility, and vortex formation compared to the standard protruding design, which all reduce the risk of thrombus formation. The clinical significance of the differences observed in the flow field will be dependent on other factors such as the Cannula material and surface characteristics, as well as the patients' coagulation status.

  • virtual fitting and hemodynamic simulation of the evaheart 2 left ventricular assist device and double cuff tipless Inflow Cannula
    Asaio Journal, 2019
    Co-Authors: Simon J Sonntag, Tadashi Motomura, Michael Neidlin, Robert Benkowski, Erin Lipinski, Kristin Hugenroth, Tim A S Kaufmann
    Abstract:

    : Inflow malposition during surgery, postoperative pump migration, Inflow obstruction, and right ventricular compression are major contributors to low flow and adverse events in patients with ventricular assist devices (VADs). These position abnormalities can lead to adverse events including ischemic stroke. To address these problems, we conducted a virtual anatomical fitting study and hemodynamic simulation on iterative Cannula designs, resulting in the EVAHEART 2 with the novel double-cuff tipless (DCT) Inflow Cannula and smaller pump design. Anatomical fitting was based on computed tomography scans of six patients with heart failure, and a fluid-structure-integration (FSI) model of the left ventricle with a lumped parameter model of the entire cardiovascular system during VAD support was created. Using this model, the hemodynamics of three Inflow Cannula insertion lengths for two patient-specific ventricles were calculated for both full and partial VAD support. The DCT Cannula with the smaller pump housing proved resistant to obstruction even when the pump housing was adjusted. The complete system also had a smaller pump pocket size than the other designs and avoided position abnormalities that commonly lead to adverse events. Compared with conventional cadaver studies, virtual fitting and numerical simulations are more beneficial and economical for iteratively designing medical devices.

  • the effect of Inflow Cannula length on the intraventricular flow field an in vitro flow visualization study using the evaheart left ventricular assist device
    Asaio Journal, 2017
    Co-Authors: Karen Maynewman, Tadashi Motomura, Ricardo Montes, Josue Campos, Juyeun Moon, Varsha Ramesh, Brian Herold, Paul Isingoma, Robert Benkowski
    Abstract:

    : Left ventricular assist device (LVAD) Inflow Cannula malposition is a significant risk for pump thrombosis. Thrombus development is influenced by altered flow dynamics, such as stasis or high shear that promote coagulation. The goal of this study was to measure the intraventricular flow field surrounding the apical Inflow Cannula of the Evaheart centrifugal LVAD, and assess flow stasis, vortex structures, and pulsatility for a range of Cannula insertion depths and support conditions. Experimental studies were performed using a mock loop with a customized silicone left ventricle (LV) and the Evaheart LVAD. A transparent Inflow Cannula was positioned at 1, 2, or 3 cm insertion depth into the LV and the velocity field in the LV midplane was measured for 2 levels of LVAD support: 1800 and 2300 rpm. The LV velocity field exhibits a diastolic vortex ring whose size, path, and strength are affected by the flow conditions and Cannula position. During diastole, the large clockwise midplane vortex grows, but its circulation and kinetic energy are reduced with Cannula insertion depth. The counterclockwise vortex is smaller and exhibits more complex behavior, reflecting a flow split at 3 cm. Overall, the 1 cm Cannula insertion depth produces the flow pattern that exhibits the least apical flow stasis and greatest pulsatility and should correlate to a lower risk of thrombus formation.

Sunil M Prasad - One of the best experts on this subject based on the ideXlab platform.

  • sternal sparing approach for lvad implantation allows for a more consistent Inflow Cannula angle
    Journal of Heart and Lung Transplantation, 2020
    Co-Authors: Brian C Ayers, T Marini, K Wood, M Croake, Wendy K Bernstein, Eugene Storozynsky, M Tallman, C Cheyne, Bryan Barrus, Sunil M Prasad
    Abstract:

    PURPOSE Prior study has suggested an association between angulation of the Inflow Cannula and outcomes following left ventricular assist device (LVAD) implantation. A potential benefit of the sternal-sparing LVAD implantation technique is superior visualization of the apex in its natural anatomic position. Our hypothesis was the sternal-sparing technique would result in more consistent angle of LVAD implantation. METHODS This single-center, retrospective review included consecutive patients implanted from September 2015 through September 2019. Patients were stratified via surgical technique: sternal-sparing or median sternotomy. The coronal angle of the Inflow Cannula relative to the horizontal line was measured on the first available postoperative anterior-posterior chest radiograph (Figure 1). All measurements were calculated by trained radiologists. A randomly selected subgroup of patients was repeated by multiple readers to assess interrater reliability. RESULTS Of the 161 patients included in the study, 102 (63%) were implanted via the sternal-sparing approach. Preoperative patient characteristics were similar between cohorts. The Inflow Cannula angle was significantly different between cohorts (Figure 1, p=0.020). The sternal-sparing cohort had a more consistent angle (median [IQR], 18 [6-29] degrees) compared to the sternotomy patients (25 [10-42] degrees, p=0.020). Significantly more sternal-sparing patients had an angle ≤65 degrees (100% vs 93%, p=0.017), which has previously been associated with improved patient outcomes with a different model pump. CONCLUSION Our data suggests the angle of the Inflow Cannula after LVAD implantation is more consistently reproduced when utilizing the sternal-sparing approach compared to median sternotomy. Further research is needed to examine the relationship between Inflow Cannula angle and patient outcomes to determine the ideal Inflow Cannula angle for the fully magnetically levitated pump.

Tadashi Motomura - One of the best experts on this subject based on the ideXlab platform.

  • surgical techniques for implanting the evaheart 2 double cuff tipless Inflow Cannula
    Asaio Journal, 2019
    Co-Authors: Tadashi Motomura, Brian Kelly
    Abstract:

    : The EVAHEART 2 (Sun Medical Technology Research Corporation, Nagano, Japan) is an investigational centrifugal ventricular assist device in the United States, introduced a new type Inflow, named "double cuff tipless" Inflow Cannula intended to mitigate the risks of Cannula malposition and subsequent ischemic stroke events associated with thrombi around the Inflow Cannula. To achieve these performance benefits of the "tipless" design, however, it is crucial to adhere to the recommended surgical procedure. We introduced a polymer-based patient model that mimics a dilated cardiomyopathy apex for Inflow Cannula implantation training. Here, we used the model to simulate appropriate and inappropriate techniques for Inflow suturing. With the appropriate technique, the Inflow ostium is aligned on the endocardial plane, and the cut myocardial surface is not exposed to the bloodstream. By contrast, with the inappropriate technique, which is represented as a worst-case suturing scenario, the Inflow ostium is misaligned, thus exposing the cut myocardial cross-section to the bloodstream. This misalignment can predispose to platelet deposition, thrombus formation, and pannus formation with long-term support. Repeated training with this human apex model is important to confirm the Inflow position and intraventricular finish before moving on to human cases. Along with rigorous preclinical training, technical adherence will help to ensure better clinical outcomes.

  • Preclinical Evaluation of the EVAHEART 2 Centrifugal Left Ventricular Assist Device in Bovines.
    Asaio Journal, 2019
    Co-Authors: Tadashi Motomura, Eisuke Tatsumi, Kenji Yamazaki, Robert Benkowski, Egemen Tuzun, Shunichi Yamazaki
    Abstract:

    : The EVAHEART 1 left ventricular assist device was miniaturized to the EVAHEART 2, with a new Inflow Cannula designed to mitigate the risks of malposition. To evaluate the safety of the new double-cuff tipless Inflow Cannula, in vivo studies were performed in healthy bovines. Eight consecutive studies were done: five short-term studies of hematological adaptation and three long-term studies of tissue adaptation. Each Inflow Cannula was purposefully implanted in the worst-case setting with marked malposition. Two studies terminated early: one because of an animal-specific ancillary component and one because of an accidental radial fracture. Six studies reached the study endpoint without major adverse events. One animal could not achieve proper anticoagulation because of warfarin resistance. Pump speed and power were maintained within stable, normal ranges. There were no major organ dysfunction or suction events. Necropsy results showed two cases of pannus formation around the Inflow ostium because of warfarin resistance and hyperinflammation at the Inflow cuff suture line. There was one case of trivial pannus; four cases were pannus-free, with no evidence of ventricular wall suction. No wedge thrombus formation occurred. The EVAHEART 2 tipless Inflow Cannula may reduce adverse events attributable to the Inflow Cannula, such as stroke.

  • reducing regional flow stasis and improving intraventricular hemodynamics with a tipless Inflow Cannula design an in vitro flow visualization study using the evaheart lvad
    Artificial Organs, 2019
    Co-Authors: Karen Maynewman, Tadashi Motomura, Ricardo Montes, Josue Campos, Nikolas Marquezmaya, Vi Vu, Erin Zebrowski, Robert Benkowski
    Abstract:

    : Due to the high stroke rate of left ventricular assist device (LVAD) patients, reduction of thrombus has emerged as an important target for LVAD support. Left ventricular blood flow patterns with areas of flow stasis and recirculation are associated with platelet aggregation, which is worsened by exposure to high shear stress. Previous reports of intraventricular thrombus in LVAD patients have identified the outside of the LVAD Inflow Cannula as a nidus for LV thrombus formation. Previous studies of LVAD Inflow Cannula design have shown a region of low blood velocity and pulsatility at the apex, adjacent to the Cannula. One unresolved question is whether the standard practice of inserting the LVAD Inflow Cannula several mm into the LV could be revised to reduce thrombus formation. To address this, a "tipless" Inflow Cannula was designed for the EVAHEART LVAS, and assessed in a mock circulatory loop of the LVAD-supported heart. Customized transparent silicone models of a dilated LV were connected to the EVAHEART LVAS at the apex with a clear polycarbonate Inflow Cannula for flow visualization using particle image velocimetry (PIV). The "tipless" Cannula was inserted flush with the endocardial border and did not protrude into the LV. This condition was compared to the standard Cannula position with a 1-cm insertion into the LV. The Pre-LVAD condition corresponded to a severe heart failure patient (ejection fraction of 24%) with a dilated LV (180 mL). LVAD support was provided at speeds of 1.8 and 2.3 krpm. At the lower LVAD speed, 63% of the flow passed through the LVAD, with the remainder ejecting through the aortic valve. When LVAD speed was increased, nearly all flow (98%) left the LV through the LVAD. Both LVAD speed conditions produced a vortex ring similar to the Pre-LVAD condition in diastole. However, the protruding Inflow Cannula interrupted the growth and restricted the movement of the vortex, and produced areas of low velocity and pulsatility adjacent to the Cannula. The tipless Cannula exhibited an uninterrupted pattern of the mitral jet toward the LV apex, which allowed the diastolic vortex to grow and aid in the washout of this region. In addition, the tipless Cannula increased aortic valve flow, which reduces stasis in the left ventricular outflow tract. The EVAHEART LVAS tipless Inflow Cannula design improved regional velocity, pulsatility, and vortex formation compared to the standard protruding design, which all reduce the risk of thrombus formation. The clinical significance of the differences observed in the flow field will be dependent on other factors such as the Cannula material and surface characteristics, as well as the patients' coagulation status.

  • virtual fitting and hemodynamic simulation of the evaheart 2 left ventricular assist device and double cuff tipless Inflow Cannula
    Asaio Journal, 2019
    Co-Authors: Simon J Sonntag, Tadashi Motomura, Michael Neidlin, Robert Benkowski, Erin Lipinski, Kristin Hugenroth, Tim A S Kaufmann
    Abstract:

    : Inflow malposition during surgery, postoperative pump migration, Inflow obstruction, and right ventricular compression are major contributors to low flow and adverse events in patients with ventricular assist devices (VADs). These position abnormalities can lead to adverse events including ischemic stroke. To address these problems, we conducted a virtual anatomical fitting study and hemodynamic simulation on iterative Cannula designs, resulting in the EVAHEART 2 with the novel double-cuff tipless (DCT) Inflow Cannula and smaller pump design. Anatomical fitting was based on computed tomography scans of six patients with heart failure, and a fluid-structure-integration (FSI) model of the left ventricle with a lumped parameter model of the entire cardiovascular system during VAD support was created. Using this model, the hemodynamics of three Inflow Cannula insertion lengths for two patient-specific ventricles were calculated for both full and partial VAD support. The DCT Cannula with the smaller pump housing proved resistant to obstruction even when the pump housing was adjusted. The complete system also had a smaller pump pocket size than the other designs and avoided position abnormalities that commonly lead to adverse events. Compared with conventional cadaver studies, virtual fitting and numerical simulations are more beneficial and economical for iteratively designing medical devices.

  • the effect of Inflow Cannula length on the intraventricular flow field an in vitro flow visualization study using the evaheart left ventricular assist device
    Asaio Journal, 2017
    Co-Authors: Karen Maynewman, Tadashi Motomura, Ricardo Montes, Josue Campos, Juyeun Moon, Varsha Ramesh, Brian Herold, Paul Isingoma, Robert Benkowski
    Abstract:

    : Left ventricular assist device (LVAD) Inflow Cannula malposition is a significant risk for pump thrombosis. Thrombus development is influenced by altered flow dynamics, such as stasis or high shear that promote coagulation. The goal of this study was to measure the intraventricular flow field surrounding the apical Inflow Cannula of the Evaheart centrifugal LVAD, and assess flow stasis, vortex structures, and pulsatility for a range of Cannula insertion depths and support conditions. Experimental studies were performed using a mock loop with a customized silicone left ventricle (LV) and the Evaheart LVAD. A transparent Inflow Cannula was positioned at 1, 2, or 3 cm insertion depth into the LV and the velocity field in the LV midplane was measured for 2 levels of LVAD support: 1800 and 2300 rpm. The LV velocity field exhibits a diastolic vortex ring whose size, path, and strength are affected by the flow conditions and Cannula position. During diastole, the large clockwise midplane vortex grows, but its circulation and kinetic energy are reduced with Cannula insertion depth. The counterclockwise vortex is smaller and exhibits more complex behavior, reflecting a flow split at 3 cm. Overall, the 1 cm Cannula insertion depth produces the flow pattern that exhibits the least apical flow stasis and greatest pulsatility and should correlate to a lower risk of thrombus formation.

Eisuke Tatsumi - One of the best experts on this subject based on the ideXlab platform.

  • Preclinical Evaluation of the EVAHEART 2 Centrifugal Left Ventricular Assist Device in Bovines.
    Asaio Journal, 2019
    Co-Authors: Tadashi Motomura, Eisuke Tatsumi, Kenji Yamazaki, Robert Benkowski, Egemen Tuzun, Shunichi Yamazaki
    Abstract:

    : The EVAHEART 1 left ventricular assist device was miniaturized to the EVAHEART 2, with a new Inflow Cannula designed to mitigate the risks of malposition. To evaluate the safety of the new double-cuff tipless Inflow Cannula, in vivo studies were performed in healthy bovines. Eight consecutive studies were done: five short-term studies of hematological adaptation and three long-term studies of tissue adaptation. Each Inflow Cannula was purposefully implanted in the worst-case setting with marked malposition. Two studies terminated early: one because of an animal-specific ancillary component and one because of an accidental radial fracture. Six studies reached the study endpoint without major adverse events. One animal could not achieve proper anticoagulation because of warfarin resistance. Pump speed and power were maintained within stable, normal ranges. There were no major organ dysfunction or suction events. Necropsy results showed two cases of pannus formation around the Inflow ostium because of warfarin resistance and hyperinflammation at the Inflow cuff suture line. There was one case of trivial pannus; four cases were pannus-free, with no evidence of ventricular wall suction. No wedge thrombus formation occurred. The EVAHEART 2 tipless Inflow Cannula may reduce adverse events attributable to the Inflow Cannula, such as stroke.

  • development of a novel tissue compatible apical Inflow Cannula for an implantable vad
    Journal of Heart and Lung Transplantation, 2013
    Co-Authors: Toshihide Mizuno, Tomonori Tsukiya, Y Takawa, Eisuke Tatsumi
    Abstract:

    Purpose Clinical application of VAD is a potent therapeutic option for treating the patients with heart failure. However, as the VAD support period prolonged, the incidence of device-related complication, such as wedge thrombus, has been increasing. We already reported on new axial flow blood pump featuring a hydrodynamically levitated impeller with superior mechanical durability and anti-thrombogenesity. However, a measure against device-related complication occurred in the other components was not considered sufficiently. In this study, we developed a novel tissue-compatible polyester velour covered Inflow Cannula for preventing the wedge thrombus, and evaluated its performance in a series of animal tests. Methods and Materials Eight calves (BW: 62-99 kg) underwent VAD implantation with our new axial flow blood pump. In the first two animals, a titanium-made Inflow Cannula with a smooth surface was used. In the following six animals, the outside of the cylindrical Inflow Cannula tip was wrapped with tissue-compatible polyester velour material. Outer diameters of the Cannula tip was 20 mm, respectively, and the length of the Cannula tip was 30 mm. The portion of the velour protruding from the apex was made to be 20 mm in length. Results All animals were sacrificed on 90-92 POD on schedule. At autopsies, first two animals with smooth surface titanium Inflow Cannula demonstrated wedge thrombus formation at the Cannula insertion site of the ventricular apex. The granulomatous tissue covered and partially occluded the tip of the Inflow Cannula. In contrast, six cases with newly developed Cannula revealed no wedge thrombus formation around the outside of the Inflow Cannulas, and the polyester velour was completely enveloped with the neointimal tissue presumably grown from the ventricular endocardium. Conclusions In conclusion, our newly developed tissue-compatible Inflow Cannula with polyester velour material successfully reduced the wedge thrombus formation in a series of 3 months animal implantation.

  • Neointima-inducing Inflow Cannula with titanium mesh for left ventricular assist device
    Journal of Artificial Organs, 2011
    Co-Authors: Yukiko Yamada, Tomohiro Nishinaka, Toshihide Mizuno, Yoshiyuki Taenaka, Eisuke Tatsumi, Kenji Yamazaki
    Abstract:

    The formation of wedge thrombus is a crucial problem in any left ventricular assist device (LVAD) with a left ventricle apical Inflow Cannula. We therefore developed a new titanium mesh wrapped Inflow Cannula expecting to induce autologous neointima to avoid such wedge thrombus formation. We performed animal experiments to evaluate the feasibility of this newly developed Inflow Cannula with titanium mesh for the induction of autologous neointima. Four calves were implanted with the Inflow Cannula as well as an EVAHEART centrifugal pump LVAD (Sun Medical Technology Research Corp., Nagano, Japan) for a duration of about 2 months. The titanium mesh was enveloped with neointimal tissue grown from the ventricular endocardium. There was no thrombus formation in any of the blood pumps or around the outside of the Inflow Cannulas. The histological findings showed that the neointimal tissue consisted of a layer of endothelial cells and fibroblasts. The newly developed Inflow Cannula using a titanium mesh induces autologous neointima formation, avoiding wedge thrombus formation.

  • Computational fluid dynamic analysis of the flow field in the newly developed Inflow Cannula for a bridge-to-decision mechanical circulatory support
    Journal of Artificial Organs, 2011
    Co-Authors: Tomonori Tsukiya, Yoshiyuki Taenaka, Hirohito Sumikura, Koichi Toda, Yoshiaki Takewa, Fumikazu Watanabe, Eisuke Tatsumi
    Abstract:

    The flow field of the newly developed Inflow Cannula designed for a bridge-to-decision circulatory support was numerically analyzed by computational fluid dynamics. This new Cannula has elastic struts at the tip that enable minimal invasive insertion into the left ventricle while maintaining a wide Inflow area by its lantern-like tip. The Cannula’s hydrodynamic loss, including change in pressure loss due to deformation, and its thrombus potential were numerically examined. Hydraulic resistance of the Cannula with blood analog fluid was 31 mmHg at the flow rate of 5.0 L/min. There were regions on the inner surface of the struts where the shear rate was

  • computational fluid dynamic analysis of the flow field in the newly developed Inflow Cannula for a bridge to decision mechanical circulatory support
    Journal of Artificial Organs, 2011
    Co-Authors: Tomonori Tsukiya, Yoshiyuki Taenaka, Hirohito Sumikura, Koichi Toda, Yoshiaki Takewa, Fumikazu Watanabe, Eisuke Tatsumi
    Abstract:

    The flow field of the newly developed Inflow Cannula designed for a bridge-to-decision circulatory support was numerically analyzed by computational fluid dynamics. This new Cannula has elastic struts at the tip that enable minimal invasive insertion into the left ventricle while maintaining a wide Inflow area by its lantern-like tip. The Cannula’s hydrodynamic loss, including change in pressure loss due to deformation, and its thrombus potential were numerically examined. Hydraulic resistance of the Cannula with blood analog fluid was 31 mmHg at the flow rate of 5.0 L/min. There were regions on the inner surface of the struts where the shear rate was <100 s−1, and these regions can be a potential for thrombus formation, especially at low flow rates or under limited anticoagulant therapy.