Left Ventricular Assist Devices Outflow Cannula Research Articles

Outflow cannula alignment in continuous flow left ventricular devices is associated with stroke.

We sought to evaluate whether differences in left ventricular assist device (LVAD) canula alignment are associated with stroke. There is a paucity of clinical data on contribution of LVAD canulae alignment to strokes. We conducted a retrospective analysis of patients who underwent LVAD implantation at Houston Methodist hospital from 2011 to 2016 and included those who had undergone cardiac computed tomography (CT) with contrast. LVAD graft alignment using X-ray, echocardiography, and cardiac CT was evaluated. The primary outcome was stroke within 1 year of LVAD implantation. Of the 101 patients that underwent LVAD Implantation and cardiac CT scan during the study period, 78 met inclusion criteria. The primary outcome occurred in 12 (15.4%) patients with a median time to stroke of 77 days (interquartile range: 42-132 days). Of these, 10 patients had an ischemic and two had hemorrhagic strokes. The predominant device type was Heart Mate II (94.8%). Patients with LVAD outflow cannula to aortic angle lesser than 37.5° and those with outflow graft diameter of anastomosis less than 1.5 cm (assessed by cardiac CT) had significantly higher stroke risk (p < 0.001 and p = 0.01 respectively). In HMII patients, a lower LVAD speed at the time of CT scan was associated with stroke. Further studies are needed to identify optimal outflow graft configuration to mitigate stroke risk.

The Effect of Spiral Inducing Chamber to Left Ventricular Assist Device Outflow Cannula

The rise of heart failure in the setting of shortage heart donor had brought to the emergence of development of left ventricular assist device (LVAD). However, patients are still encountering severe complications such as stroke and device thrombosis due to the hemodynamic changes. This study aimed to compare the hemodynamic characteristic between the standard and spiral LVAD outflow cannula. Two different anastomosis sites (2cm and 3cm) from sino-tubular junction are used and a spiral inducing chamber is attached to the cannula to promote spiral flow. The result showed that spiral LVAD cannula exhibit a lower output velocity with 37% percentage difference and lower region of low WSS value.

Left Ventricular Assist Device Flow Pattern Analysis Using Computational Fluid Dynamics at the Time of Invasive Hemodynamic Ramp Study: Using Patient-Specific Data to Optimize the Ramp Study

<h3>Purpose</h3> Invasive hemodynamic ramp studies have been shown to decrease the rates of left ventricular assist device (LVAD) complications however hemocompatibility related adverse events (HRAE) still remain unacceptably high. Computational fluid dynamics (CFD) allows for a more thorough analysis of shear rate (SR) and shear stress (SS) which influences endothelial function and thrombotic potential. <h3>Methods</h3> An invasive hemodynamic ramp study was performed on a patient with a HeartMate 3 (HM3). An anatomical model of the patient was reconstructed from computed tomography (CT) images, and the LVAD outflow cannula was used as the inflow boundary. The LVAD flow was calculated separately using a lumped-parameter-model (LPM) of the circulation. Ventricular volumes were reconstructed from CT and the patient's hemodynamic tracings. The contribution of flow from the HM3 was implemented in the LPM via published H-Q curves. CFD simulations were then carried out over the entire clinical operating condition of the HM3 from 4600 to 6400 RPM. SS and SR were quantified in the outflow cannula, ascending aorta, aortic arch and cerebral circulation. <h3>Results</h3> As speed was increased from 4600 to 5500, and then to 6400 RPM, blood volume exposed to a SR greater than 500 s⁻¹ increased, respectively, by 1.46 fold and 2.18 fold (2.00 to 2.93 to 4.37 cm³). Increase of SS in the cannula was 1.37 fold and 1.74 fold (1.88 to 2.56 to 3.26 Pa), in the ascending aorta was 1.44 fold and 1.92 fold (0.60 to 0.86 to 1.14 Pa), and in the aortic arch and cerebral circulation was 1.40 fold and 1.88 fold (0.46 to 0.65 to 0.87 Pa). <h3>Conclusion</h3> Hemodynamic optimization during ramp studies needs to be balanced with increased rates of SS and SR that occur with incremental speed increases. CFD when applied to a ramp study can provide additive patient-specific information that may further mitigate HRAE.

Combining Invasive Cardiopulmonary Exercise Testing with Computational Fluid Dynamics to Better Understand LVAD Fluid Mechanics during Exercise

<h3>Purpose</h3> Invasive cardiopulmonary exercise testing (iCPET) is helpful in evaluating dyspnea but is infrequently utilized in patient supported by left ventricular assist devices (LVAD). Computational fluid dynamics (CFD) allows for a more thorough analysis of fluid mechanics including shear stress (SS) and shear rate (SR). The additive information from iCPET and CFD may allow for optimal understanding of the pump-patient interaction during exercise. <h3>Methods</h3> Hemodynamic and ventilatory gas measurements were recorded as part of an iCPET study on a patient with a HeartMate 3 (HM3). Exercise using a bicycle ergometer by increments of 20 watts every 2 minutes was performed. An anatomical model of the vasculature was reconstructed from computed tomography (CT) images, and the LVAD outflow cannula was used as the inflow boundary. The LVAD outflow was calculated separately using a lumped-parameter-model (LPM) of the circulation. Ventricular volumes were reconstructed from CT and the patient's hemodynamic tracings. The contribution of flow from the HM3 was implemented in the LPM via published H-Q curves. CFD simulations were then carried out over the stages of exercise. Blood velocities, SS and SR were quantified in the vascular beds. <h3>Results</h3> Compared to rest, blood volume exposed to SR >1000 s⁻¹ increased 2.8 fold (0.47 to 1.31 cm³), while average SS increased 1.45 fold (2.61 to 3.79 Pa) in the cannula, 1.48 fold (0.89 to 1.31 Pa) in the ascending aorta, and 1.61 fold (0.67 to 1.08 Pa) in the aortic arch and cerebral circulation. Compared to rest, peak velocities increased nearly 5 fold in the aortic arch. <h3>Conclusion</h3> CFD applied to iCPET provides valuable information about variations in flow to the vasculature with exercise as well as shear rate and shear stress augmentation. This patient-specific information may help with optimization of LVAD speeds to meet the physiological needs of exercise.

Outflow Cannula Systolic Slope as a Predictor of Myocardial Recovery Leading to Successful LVAD Decommission: A Case Series

In patients implanted with durable left ventricular assist device (LVAD), the incidence of myocardial recovery leading to device explant or decommission is low, and reliable predictors of myocardial recovery remain lacking. Here, we investigate the potential of outflow cannula systolic slope as a non-invasive predictor of successful LVAD liberation amongst select cohort of patients with high recovery potential. We first identified a cohort of patients with high recovery likelihood by querying all LVAD patients at our institution who underwent reverse ramp test, a protocol developed to assess native myocardial contractility with sequential LVAD turn-down to minimal support. We then queried all echocardiographic studies of these patients within one year of the reverse ramp tests. In the subset of patients with adequate Doppler images of the outflow cannula, the systolic slope, a load-independent marker of contractility, was measured as previously described, and the clinical outcomes were correlated. Between September 1, 2015 and August 23, 2019, a total of 10 patients underwent reverse ramp test at our institution per published protocol. Of these, 4 patients had adequate echocardiographic window of the LVAD outflow cannula, and the systolic slope was calculated. 3 of the 4 patients had outflow cannula systolic slope of <1200 cm/s2 (813 ±148 cm/s2, range 651-1010 cm/s2; top figure), and none was able to achieve sustainable recovery (1 was bridged to transplant, 1 remains on LVAD support, and 1 was deceased). 1 out of the 4 patients had outflow cannula systolic slope >1200 cm/s2 (1788 cm/s2), and she underwent successful percutaneous decommission of her LVAD device (bottom figure). In a small case series of 4 patients from reverse ramp database with available echocardiographic images of the outflow cannula, high systolic slope value (>1200 cm/s2) identified the patient with clinical recovery leading to successful LVAD decommission.

Percutaneous Deactivation of Left Ventricular Assist Devices

Left ventricular assist device (LVAD) deactivation may be considered in cases of left ventricular recovery, pump thrombosis, infection, and end-of-life palliation. Surgical pump explantation remains the principal method, but percutaneous deactivation presents a safe and effective alternative. We have developed a formal program for percutaneous LVAD deactivation within our advanced heart failure program including patient selection criteria, preprocedure testing, a procedural algorithm, and a postprocedure care plan. Patient selection for percutaneous LVAD deactivation required review by an interdisciplinary heart transplant team including reason for deactivation, cardiac function, surgical risk, and patient preference. All candidates underwent LVAD ramp studies with both transthoracic echocardiography and right heart catheterization assessment. Deactivation was performed under general anesthesia with transesophageal echocardiography guidance. Three Amplatzer Vascular Plug IIs (Abbott, St. Paul, MN) were deployed in the LVAD outflow cannula with the proximal edge of the third plug aligned with the aortic anastomosis of the graft as guided by angiography and 3-dimensional transesophageal echocardiography. In a separate procedure, the LVAD drive line was transected below the skin, which was closed surgically over the driveline stump. Anticoagulation was continued for at least 3 months. Since initiation in January 2017, our program has performed 7 percutaneous LVAD deactivation procedures. All procedures have been successful, 5 of the patients remain medically managed, and 2 have proceeded to heart transplant. Percutaneous LVAD deactivation provides an alternative to surgical explantation. A percutaneous LVAD deactivation program is an important component of an advanced heart failure program.

Association of LVAD Outflow Cannula Position with Stroke Risk

Background Stroke remains a major cause of morbidity and mortality in patients with left ventricular assist devices (LVAD). Although several studies have delineated clinical risk factors for development of stroke, it is not entirely clear whether changes in position/orientation of the LVAD cannula impact incidence of subsequent stroke. Hypothesis We hypothesized that variations in surgical implant techniques for LVAD inflow and outflow cannula positions impact the subsequent risk of stroke. Methods We conducted a retrospective review of all patients that underwent LVAD implantation at our institute between 2011 and 2016. All patients that underwent multi detector cardiac computed tomography (MDCT) were included in the analysis. Patients with non-contrast CT scans and poor imaging quality were excluded. Baseline demographic as well as clinical parameters were obtained for all patients. Inflow and outflow cannula positions were assessed by various MDCT parameters outlined in table 1. The incidence of stroke from time of implantation to one year post-LVAD implantation was obtained. Results A total of 311 continuous-flow LVADs were implanted at our hospital from 2011-2016, of which 75 patients met inclusion criteria for the study. The study population was predominantly HM II with only 3 HVAD and 1 HM 3 patients. 11 patients had stroke within 1 year of LVAD implantation. There were no significant differences in baseline demographic or clinical characteristics between patients that had stroke versus those that did not. Patients with stroke had more acute angulation of outflow cannula relative to the aorta compared to patients without stroke (42⁰ versus 65⁰ respectively, p= 0.026). In addition, patients with stroke had a smaller diameter of anastomosis of the outflow cannula compared to those without stroke (1.3 cm versus 1.5 cm respectively, p= 0.013). The inflow cannula position did not impact incidence of stroke. Conclusions Our study shows that LVAD outflow cannula orientation and size of anastomosis portend a higher risk of subsequent stroke. Therefore, it is imperative to optimize LVAD surgical implant techniques and device manufacturing to allow larger anastomosis site and less acute angulation of the outflow cannula.

Outflow Cannula Systolic Slope in Patients With Left Ventricular Assist Devices: A Novel Marker of Myocardial Contractility.

Left ventricular (LV) unloading with a LV assist device (LVAD) reverse remodels the heart and may lead to favorable changes in cellular architecture and LV geometry promoting myocardial recovery. Currently, there are no standardized methods for evaluating myocardial recovery. This study assesses the systolic slope of the LVAD outflow cannula as a marker for myocardial contractility. Doppler echocardiography (transthoracic echocardiogram [TTE]) of the LVAD outflow cannula and TTE of the LV cavity were prospectively collected in 57 patients with LVADs. Systolic acceleration of the LVAD outflow cannula was measured in each patient as the peak change of velocity over time (dv/dt) during systole from continuous-wave Doppler signal acquired from the LVAD outflow cannula. Ventricular volumes were concurrently measured by TTE. In a subset of 10 patients, the systolic slope was measured during each stage of a ramp study to study the properties of this parameter across a variety of loading conditions. The systolic slope of the LVAD outflow cannula was successfully measured in 53 of 57 patients (93%). Systolic slope strongly correlated with ejection fraction (EF) (R = 0.92). Analysis of systolic slope stratified by EF (EF >30%, EF 20-30%, EF 10-20%, and EF <10%) revealed systolic slopes that were significantly different between the groups (1,371 cm/s ± 324; 983 cm/s ± 122; 578 cm/s ± 139; and 495 cm/s ± 107, respectively; p < 0.001). Systolic slope did not change significantly across variable preload and afterload conditions during a ramp study. Systolic slope of the LVAD outflow cannula strongly correlates with EF and can be used to assess underlying myocardial contractility across a variety of LVAD loading conditions.

Intravascular Ultrasound-Guided Percutaneous Stenting for Treatment of LVAD Outflow Graft Obstruction

Introduction Left ventricular assist device (LVAD) outflow graft obstruction is a well-known and significant complication. The typical management involves treatment of presumed thrombosis of the graft with intensified anticoagulation or surgery. More recently, endovascular stenting has been reported as a possible treatment option. We describe the management of a LVAD outflow cannula obstruction with never reported intravascular ultrasound (IVUS)-guided covered endovascular stenting. Case report A 68 year-old female with non-ischemic cardiomyopathy status-post LVAD implantation in March 2016 presented with persistent symptomatic low flow alarms and clinical signs of heart failure. Symptoms seemed to worsen when she laid on her right side. She was compliant with her anticoagulation and lactate dehydrogenase level was found to be near her baseline. A CT scan with IV contrast revealed intraluminal obstruction of the LVAD outflow graft secondary to a kinked portion of the outflow cannula near the bend relief with a possible thrombotic component. The severe angulation of the cannula likely developed due to the patient's gradual weight gain of 28kg in the 24 months since LVAD implantation. Given the patient's risk profile, a percutaneous endovascular stenting approach was taken. IVUS was used to visualize the obstruction and kinking of the graft. A balloon-expandable covered stent was deployed at the stenotic site while the LVAD was briefly stopped to avoid stent/balloon migration. A covered stent was used to minimize the risk of thrombus migration/extrusion. IVUS was used again after post-dilation of the stent to confirm placement with no thrombus extrusion. Several hours later the patient had recurrent low-flow alarms. A repeat CT scan revealed that the kink had migrated and been transmitted within the outflow cannula towards the LVAD. The patient returned to the angiography suite where 2 balloon expandable stents were deployed more proximally within the outflow cannula and in an overlapping fashion with the original covered stent. Non-covered stents were used for the second procedure as there was no suspected thrombotic component. IVUS showed no significant residual kinking post-stenting. This was confirmed with a repeat CT scan. The patient recovered without any hemodynamic or neurologic sequelae. Conclusion Percutaneous endovascular stenting is an emerging option for treatment of outflow tract obstruction in LVAD patients that are not candidates for surgery. IVUS can be a valuable tool during intervention to confirm proper stent position, thrombus isolation, and outflow cannula geometry.

Echocardiographic Predictors of Hemodynamics in Patients Supported With Left Ventricular Assist Devices

The assessment of hemodynamics in patients supported with left ventricular assist devices (LVADs) is often challenging. Physical examination maneuvers correlate poorly with true hemodynamics. We assessed the value of novel transthoracic echocardiography (TTE)-derived variables to reliably predict hemodynamics in patients supported with LVAD. A total of 102 Doppler-TTE images of the LVAD outflow cannula were obtained during simultaneous invasive right heart catheterization (RHC) in 30 patients supported with continuous-flow LVADs (22 HMII, 8 HVAD) either during routine RHC or during invasive ramp testing. Properties of the Doppler signal though the outflow cannula were measured at each ramp stage (RS), including the systolic slope (SS), diastolic slope (DS), and velocity time integral (VTI). Hemodynamic variables were concurrently recorded, including Doppler opening pressure (MAP), heart rate (HR), right atrial pressure, pulmonary artery pressure, pulmonary capillary wedge pressure (PCWP), Fick cardiac output (CO) and systemic vascular resistance (SVR). Univariate and multivariate regression analyses were used to explore the dependence of PCWP, CO, and SVR on DS, SS, VTI, MAP, HR, and RS. Multivariate linear regression analysis revealed significant contributions of DS on PCWP (PCWPpred = 0.164DS + 4.959; R = 0.68). Receiver operating characteristic (ROC) curve analysis revealed that PCWPpred could predict an elevated PCWP ≥18 mm Hg with a sensitivity (Sn) of 94% and specificity (Sp) of 85% (area under the ROC curve 0.88). CO could be predicted by RS, VTI, and HR (COpred = 0.017VTI + 0.016HR + 0.12RS + 2.042; R = 0.61). COpred could predict CO ≤4.5 L/min with Sn 73% and Sp 79% (AUC 0.81). SVR could be predicted by MAP, VTI, and HR (SVRpred = 15.44MAP - 5.453VTI - 6.349HR + 856.15; R = 0.84) with Sn 84% and Sp 79% (AUC 0.91) to predict SVR ≥1200 dyn-s/cm5. Doppler-TTE variables derived from the LVAD outflow cannula can reliably predict PCWP, CO, and SVR in patients supported with LVADs and may mitigate the need for invasive testing.

Screening for Outflow Cannula Malfunction of Left Ventricular Assist Devices (LVADs) With the Use of Doppler Echocardiography: New LVAD-Specific Reference Values for Contemporary Devices

BackgroundEchocardiographic assessment of left ventricular assist devices (LVADs) is used as a screening tool to evaluate the integrity and mechanics of the pump and circuit. We aimed to 1) establish the normal range and upper reference limit of peak velocity of the outflow cannula for the modern era of LVADs and 2) assess the clinical performance of the currently cited and newly proposed reference limits in patients with continuous-flow LVADs as a screening tool for cannula malfunction. MethodsLVAD outflow peak CW velocities were measured with the use of Doppler transthoracic echocardiography (TTE) in 57 patients with LVADs (44 with Heartmate II (HM2), 13 with Heartware (HW)). The average velocity and the upper and lower normal reference limits (defined as ±2 standard deviations from the mean) for each LVAD type was calculated. The upper reference limit was then used as a screening threshold for cannula malfunction. ResultsThe average outflow cannula peak velocity for the normal HM2 cohort was 1.86 ± 0.44 m/s with upper and lower reference limits of 2.73 m/s and 0.98 m/s, respectively. The average outflow cannula peak velocity for the normal HW cohort was 2.36 ± 0.53 m/s with upper and lower reference limits of 3.42 m/s and 1.3 m/s, respectively, which was significantly higher than the HM2 cohort (P = .004). ConclusionsIn both HM2 and HW LVADs, the average peak outflow velocity and reference limit for the normal population, as measured by Doppler TTE, was markedly higher than the currently used LVAD reference limits of 2 m/s and are significantly different between devices. Patients with peak outflow velocities above our upper reference limits should be evaluated for LVAD outflow cannula malfunction.

Abstract 16514: Screening for Outflow Cannula Malfunction of Left Ventricular Assist Devices Using Doppler Echocardiography: Establishing New Reference Values

Background: Echocardiographic assessment of left ventricular assist devices (LVAD) is used as a screening tool to evaluate the integrity and mechanics of the pump and circuit. We aimed to 1) establish the normal range and upper reference limit of peak velocity of the outflow cannula for the modern era of LVADs and 2) assess the performance of the current reference limit and our new reference limit in patients with continuous flow LVADs as a screening tool for cannula malfunction. Methods: LVAD outflow peak velocities were measured with Doppler echocardiography (TTE) in 57 patients with LVADs (HeartMate II (HMII) = 44, HeartWare (HW) = 13). The average velocity and the upper and lower normal reference limits (defined as +/- two standard deviations from the mean) for each LVAD type was then calculated. The upper reference limit was then used as a screening threshold for cannula malfunction. Results: The average outflow cannula peak velocity for the HMII cohort was 1.94 m/sec +/- 0.42 with an upper and lower reference limit of 2.78 m/sec and 1.10 m/sec, respectively. The average outflow cannula peak velocity for the HW cohort was 2.36 +/- 0.53 with an upper and lower reference limit of 3.42 m/sec and 1.3 m/sec, respectively, which was significantly higher than the HMII cohort (p=0.004). Velocities from both cohorts were dramatically higher than the commonly citied upper reference limit velocities of 2 m/sec. Use of the previously cited reference limit poorly discriminated between normal and malfunctioning LVAD cannulas whereas our new reference limit identified all four patients with outlet cannula malfunction (Figure1). Conclusions: In both HeartMate II and HeartWare LVADs, the average peak outflow velocity and reference limit for the normal population as measured by Doppler-TTE was markedly higher than currently cited LVAD reference limits. Patients with peak outflow velocities above our upper reference limit should be evaluated for LVAD outflow cannula malfunction.

Computational fluid dynamics analysis of surgical adjustment of left ventricular assist device implantation to minimise stroke risk

Background. Currently, mechanical support is the most promising alternative to cardiac transplantation. Ventricular assist devices (VADs) were originally used to provide mechanical circulatory support in patients awaiting planned heart transplantation (‘bridge-to-transplantation’ therapy). The success of short-term bridge devices led to clinical trials evaluating the clinical suitability of long-term support (‘destination’ therapy) with left ventricular assist devices (LVADs). The first larger scale, randomised trial that tested long-term support with an LVAD reported a 44% reduction in the risk of stroke or death in patients with an LVAD. In spite of the success of LVADs as bridge-to-transplantation and long-term support, patients managed by these devices are still at risk of several adverse events. The most devastating complication is caused by embolisation of thrombi formed within the LVAD or inside the heart into the brain. Prevention of thrombi formation is attempted through anticoagulation management and by improving LVADs design; however, there is still significant occurrence of thromboembolic events in patients. Investigators have reported that the incidence of thromboembolic cerebral events ranges from 14% to 47% over a period of 6–12 months.Methods and approach. An alternative method to reduce the incidence of cerebral embolisation is proposed by the co-authors, and the hypothesis is that it is possible to minimise the number of thrombi flowing into the carotid and vertebral arteries by an optimal placement of the LVAD outflow conduit, with or without the addition of aortic bypass connecting the ascending aorta and the innominate artery (IA), or left carotid artery. This paper presents the computational fluid dynamics (CFD) analysis of the aortic arch haemodynamics using a representative geometry of the human aortic arch with or without an alternative aortic bypass. In order to study the trajectory of the thrombi within the aortic arch bed, the CFD code, Fluent 6.3, is utilised to resolve the flow field and to solve the Lagrangian particle tracking of thrombi released randomly at the inlet of the LVAD cannula.Results. Results are presented for simulations of thrombi in the range of 2–5 mm. The percentage of individual diameter as well as aggregate diameter thrombi flowing to the carotid and vertebral arteries as a function of LVAD conduit placement and aortic bypass implantation is reported. The influence of the LVAD conduit implantation and bypass reveals a nearly 50% variation in predicted cerebral embolism rates.Conclusions. The adjustment of the location of the anastomosis of the LVAD outflow cannula as well as its angle of incidence plays a significant role in the level of thromboembolisms. By proper adjustment in this CFD study of a synthetic model of an aortic arch bed, we found that nearly a 50% reduction in cerebral embolism could be achieved for a configuration consisting of a shallow angle of implantation over a baseline normal incidence of the LVAD cannula. Within the limitations of our model, we have established that the LVAD implantation geometry is an important factor and should be taken into consideration when implanting an LVAD. It is possible that other parameters such as distance of the LVAD outflow cannula to the root of the IA could affect the thrombi embolisation probabilities. However, the results of this study suggest that the risk of stroke may be significantly reduced by as much as 50% by tailoring the VAD implantation by a simple surgical manoeuvre. The results of this line of research may ultimately lead to techniques that can be used to estimate the optimal LVAD configuration in a patient-specific manner by pre-operative imaging.

Case 1–2003 The use of intraoperative echocardiography during insertion of ventricular assist devices

Transesophageal echocardiography (TEE) assists in the intraoperative decision-making process during cardiac anesthesia and cardiac surgery. Mechanical ventricular support may be necessary to support the circulatory system temporarily or serve as a bridge to heart transplantation. A left ventricular assist device (LVAD) is most commonly used.1 Biventricular failure necessitates the use of an LVAD along with a right ventricular assist device (RVAD) to form a biventricular assist device (BIVAD) (Fig 1). TEE plays a vital role in evaluating effective mechanical assistance of the circulation.1-3 This case describes a BIVAD placement in a patient and shows the roles and limitations of TEE in this scenario.

Markers of thromboembolization in a bovine ex vivo left ventricular assist device model.

The production of blood microemboli (BME) was studied using an ex vivo exteriorized left ventricular assist device (LVAD) model in calves. Each of eight calves received a series of three LVADs, each operating for 24 hr. Blood microemboli were measured directly by a laser (624 nm and 828 nm) light scattering microemboli detection (LSMD) system through the LVAD outflow cannula and by constant pressure filtration (CPF) of blood samples from the LVAD outflow cannula. Hematologic parameters were also measured. After LVAD removal, perivalvular thrombi were evaluated using polar coordinate mapping. The average LSMD and CPF results correlated. For example, in one series of three calves, one ventricle exhibited significantly greater thrombogenesis than did the other ventricles, as indicated by both the LSMD and CPF results. In a series of five calves, one calf developed an abnormally high activated thromboplastin time (APTT), even in the absence of heparin. For two of the three ventricles tested in that calf, microemboli concentration (CPF), Factor XII activity, level of fibrin degradation products (FDP), and accumulated thrombus were significantly lower than for the other calves. The whole blood viscosity (WBV, at 230 s-1) in this calf also decreased to lower values than were seen with the other calves.