LVAD Flow Research Articles

FIRST ITALIAN CASE OF TRANSCATHETER TREATMENT OF AORTIC REGURGITATION IN L–VAD PATIENT WITH A DEDICATED DEVICE

Abstract In patients with L–VADs, aortic valve regurgitation is a relatively frequent complication often associated with high mortality. Surgical approaches are extremely complex and often lead to poor outcomes. TAVI can be a feasible solution but it is usually extremely challenging due to the absence of calcification and stenosis. We report the case of a 56–year–old man who underwent LVAD implantation 4years ago as destination therapy for dilated myocardiopathy and chronic multiple myeloma. During the last year, he progressively developed severe pure aortic regurgitation. Last month, he was admitted to our center for heart failure symptoms and recurrent ventricular arrhythmias (VT/VF). The patient was considered at high risk for surgery and evaluated for a transcatheter approach. Due to the absence of calcification and a relatively large annulus, we decided to use the JenaValve Trilogy prosthesis, the only THV CE approved for aortic regurgitation treatment. Unlike other types of THV (self– or balloon expandable), this is specifically designed for AR and does not require significant oversizing to allow correct anchoring. Another advantage in this setting is the possibility of avoiding the reduction of the LVAD flow due to the reduced risk of embolization and the possibility of proceeding to direct implantation without ventricular rapid pacing thanks to the direct anchoring method onto the native aortic leaflets. In this patient, a JenaValve size L bioprosthesis was implanted transfemorally under general anesthesia with an excellent result. The post–operative echocardiography showed a perfectly implanted prosthesis with no intraprosthesis regurgitation and only a mild anterior paravalvular leak with a subsequent improvement of all hemodynamic parameters. In our opinion, when feasible, the JenaValve implant can be a safe and effective therapeutic option in patients with active LVAD devices at high operative risk.

Exploring the influence of parametrized pulsatility on left ventricular washout under LVAD support: a computational study using reduced-order models

Introducing pulsatility in LVADs is known to reduce complications such as stagnation and thrombosis, but it is an ongoing topic of research on what the optimal form is. We present a framework consisting of parametrized full-order simulations, reduced-order models, and sensitivity analysis to systematically quantify the effects of parametrized pulsatility on washout. As a sample problem, we study the washout in an idealized 2D left ventricle and a parametrized sinusoidal LVAD flow rate. The framework yields speed-ups proportional to the number of samples required in the sensitivity analysis. In our setting, we find that short, intense pulses wash out the left ventricle best, while the time between consecutive pulses does not play a significant role.

Left Ventricular Assist Device Pump Obstruction Reduces Native Heart Efficiency.

Obstruction of the LVAD flow path can occur when blood clots or tissue overgrowth form within the inflow cannula, pump body, or outflow graft, and it can lead to thrombus, embolism, and stroke. The goal of this study was to measure the impact of progressive pump inflow obstruction on the pressure and flow dynamics of the LVAD-supported heart using a mock circulatory loop. Pump obstruction (PO) was produced by progressively blocking a fraction of the LVAD inlet area. Pressures, flows, and the midplane velocity field of the LV were measured for three LVAD speeds and six PO levels. Pressure and flow decreased with PO, shifting more of the flow through the aortic valve such that the total flow decreased by 6-11% and decreased the efficiency of the work of the native heart up to 60%. PO restricts diastolic flow through the LVAD, which reduces mitral inflow and decreases the strength and energy of the intraventricular vortices. The changes in flow architecture produced by PO include flow stasis and increased shear, which predispose the system to thromboembolic risk. Analysis of the contributions to external work may enable early detection, which allows time for therapeutic intervention, reducing the likelihood of pump replacement and the risk of complications.

Preservation of pulsatility with universal ventricular assist device: In vitro assessment for biventricular support.

The objective of this study was to assess the pulsatility preservation capability of the universal ventricular assist device (UVAD) when used as a biventricular assist device (BVAD). This evaluation was conducted through an in vitro experiment, utilizing a pulsatile biventricular circulatory mock loop. Two UVAD pumps were tested in a dual setup (BVAD) in the circulatory model with the simulated conditions of left heart failure (HF), right HF, and moderate/severe biventricular HF (BHF). The total flow, aortic pulse pressure, the pulse augmentation factor (PAF), the energy-equivalent pressure (EEP), and the surplus hemodynamic energy (SHE) were observed at various pump speeds to evaluate the pulsatility. The aortic pulse pressure increased from the baseline (without pump) in all simulated hemodynamic conditions. The PAF ranged from 17%-35% in healthy, left HF, right HF, and mild BHF conditions, with the highest PAF of 90% being observed in the severe BHF condition. The EEP correlated with LVAD flow in all groups (R2 = 0.87-0.97) and increased from the baseline in all cases. The SHE peaked at approximately 5-6 L/min of LVAD support and was likely to decrease at higher LVAD pump flow. The largest decrease in SHE from the baseline, 53%, was observed in the mild BHF conditions with the highest LVAD and RVAD support. The UVAD successfully demonstrated the ability to preserve pulsatility in vitro, and to optimize the cardiac output, as an isolated circulatory support device option (RVAD or LVAD) and when used for BVAD support.

An in vitro model to study suction events by a ventricular assist device: validation with clinical data.

Introduction: Ventricular assist devices (LVADs) are a valuable therapy for end-stage heart failure patients. However, some adverse events still persist, such as suction that can trigger thrombus formation and cardiac rhythm disorders. The aim of this study is to validate a suction module (SM) as a test bench for LVAD suction detection and speed control algorithms. Methods: The SM consists of a latex tube, mimicking the ventricular apex, connected to a LVAD. The SM was implemented into a hybrid in vitro-in silico cardiovascular simulator. Suction was induced simulating hypovolemia in a profile of a dilated cardiomyopathy and of a restrictive cardiomyopathy for pump speeds ranging between 2,500 and 3,200rpm. Clinical data collected in 38 LVAD patients were used for the validation. Clinical and simulated LVAD flow waveforms were visually compared. For a more quantitative validation, a binary classifier was used to classify simulated suction and non-suction beats. The obtained classification was then compared to that generated by the simulator to evaluate the specificity and sensitivity of the simulator. Finally, a statistical analysis was run on specific suction features (e.g., minimum impeller speed pulsatility, minimum slope of the estimated flow, and timing of the maximum slope of the estimated flow). Results: The simulator could reproduce most of the pump waveforms observed in vivo. The simulator showed a sensitivity and specificity and of 90.0% and 97.5%, respectively. Simulated suction features were in the interquartile range of clinical ones. Conclusions: The SM can be used to investigate suction in different pathophysiological conditions and to support the development of LVAD physiological controllers.

P19: Modeling the Effects of Heartbeat Synchronized Speed Modulation for a Pediatric LVAD

Study: Increasing the pulsatility of combined LVAD and heart output can be done by modulating the speed of the pump driver in synchrony with the heart rhythm. Increased pulsatility is closer to the physiological norm, lessens blood stagnation, and improves baroreceptor feedback for pressure regulation. This study is a first step to model the systemic response to pump speed modulation to develop the precise synchronization timing and controls for an optimized outcome and to analyze the results. Methods: A previously validated computational model of a mock circulatory loop is used as a platform to observe the hemodynamic effects of synchronized pump speed modulation on the heart. A model of a brushless DC motor used to drive the pediatric LVAD is established using the speed, torque, and inertia constants of the manufacturer specification sheet to represent the motor’s ability to change speed. The pressure and flow HQ curve of the LVAD impeller is used to calculate the pump output flow at different pressures and impeller speeds. The flow of the set speed LVAD is 3L/min, and the flow of the speed modulated LVAD varies between 1 L/min and 5 L/min at diastole and systole respectively. A PID controller is used to control the pump speed to reach the desired flow output. Results: The modulated LVAD flow results in larger changes in aortic pressure. The speed modulated LVAD had an aortic pressure difference of 20 mmHg between the minimum diastole and maximum systole values while the set speed LVAD had a difference of 7 mmHg. The set speed LVAD and the speed modulated LVAD had similar average aortic pressure values of 93mmHg and 91mmHg respectively. The changes in aortic pressure at systole and diastole resulting from the speed modulated flow show that synchronized motor speed modulation results in physiologic conditions closer to the norm.Figure 1. Overview of the Mock Circulatory Loop model and LVAD motor speed controller.Figure 2. Left Ventricular and Aortic Pressure with a set speed LVAD and a speed modulated LVAD.

P16: Dual Continuous-Flow Ventricular Assist Devices Operation With a Single Controller: Early Assessment for Biventricular Support

Objective: The biventricular assist device (BVAD) is a treatment option for severe biventricular heart failure (BHF). For left and/or right ventricular assist device (LVAD and/or RVAD), a standalone controller unit is required for operation and control. In this work we sought to evaluate the feasibility of dual-device setup using continuous-flow (CF) universal ventricular assist device (UVAD, Fig. 1A) operation using a single controller unit. Methods: Two pneumatic pumps (Abiomed AB5000™, Danvers, MA, USA incorporated into the biventricular circulatory mock loop were used for simulation) driven by a dual-output driver (Thoratec Model 2600, Pleasanton, CA, USA) were used to simulate the left and right heart failure conditions. Systolic BHF conditions were simulated and two UVAD configurations (LVAD - primary controller mode, RVAD - secondary controller mode, set at 80% of LVAD work) were tested at various speeds for performance. Custom user interface software was developed to enable intuitive control and monitoring of the device (Fig. 1B). Results: The hemodynamic requirements were met in both RVAD and LVAD arrangement (Fig. 1C,D). The LVAD flow values provided guidance for RVAD control. In all simulated BHF conditions, both LVAD and RVAD (UVADs) provided optimal performance and demonstrated stable hemodynamics. Conclusion: The feasibility of a single controller system architecture for dual CF device operation has been shown. Both UVAD’s demonstrated optimal performance and communication for dual-device support configurations in BHF. Future direction should consist of technology characterization and optimizations.Figure 1. A - UVAD design; B - BVAD controller interface. Red window, LVAD (primary); Blue window, RVAD (secondary); C- LVAD performance; D –RVAD performance.

Abstract 10041: Cardiopulmonary Performance Among Heart Failure Patients Before and After Left Ventricular Assist Device Implantation

Introduction: Continuous-flow left ventricular assist devices (CF-LVAD) improve survival and subjective assessments of health-related quality-of-life (HRqOL) when implanted into patients with advanced heart failure with reduced ejection fraction (HFrEF). However, functional capacity remains severely reduced. Hypothesis: LVAD flow during exercise contributes minimally to overall functional capacity. Exercise tolerance depends on intrinsic factors such as cardiac output (Qc) and arteriovenous oxygen difference (avo2 diff ). Methods: Ten patients (9 male, 60±10 years), underwent three invasive cardiopulmonary exercise tests on upright cycle ergometry. Visits were arranged 1) before (median, IQR: 0.3, 0.1-0.05 months) implantation, 2) after (4.2, 3.1-5.3 months) implantation with CF-LVAD speed held constant, and 3) with increases in pump speed during exercise (2.3, 1.9-3.0 months) after Visit 2. Submaximal functional capacity was measured by six-minute hall walk (6MHW). Fick Qc was measured via pulmonary artery catheter and gas exchange parameters determined by indirect calorimetry. Subjective assessments of HRqOL were obtained prior to and following implantation. Results: Following implantation, HRqOL and 6MHW improved. The avo2 diff and Qc predicted Watts achieved during exercise testing pre-implantation. The avo2diff, but not LVAD flow or Qc, predicted Watts achieved on multivariable analysis with both fixed and variable pumps speeds ( Table 1 ). Conclusions: Submaximal exercise performance and subjective HFrEF severity improved post implantation. The primary determinant of workload achieved during exercise testing, regardless of whether participants exercised at a fixed pump speed or with increases in pump speed, was the (A-V)O2 difference. LVAD flow contributes minimally to functional capacity.

Self-care behaviors of patients with implanted left-ventricular assist device in Israel: a comparative study before and during COVID-19 pandemic

Funding AcknowledgementsType of funding sources: None.Background/IntroductionLeft ventricular assist devices (LVADs) support the heart of patients with advanced heart failure. Following LVAD implantation, patients face a complex regimen of self-care behaviors including self-care maintenance, self-care monitoring and self-care management. During the COVID-19 pandemic, the self-care might be inadequate because of the disease occurrence as well as social constraints, transportation restrictions, social distancing, and psychosocial stress. Little is known on how comparable specific self-care behaviors are among LVAD-implanted patients before and during COVID-19 pandemic.PurposeTo describe and compare self-care behaviors among patients with an implanted LVAD in Israel before and during the COVID-19 pandemic and explore factors related to self-care behaviors change.MethodsA prospective observational cross-sectional study design. A convenience sample of 28 Israeli LVAD-implanted patients (mean age 62.4 ± 9, 86% male, 78.6% lived with a partner) completed an LVAD Self-Care Behavior Scale before (data collection: March, 2017- February, 2020) and again, following the onset of COVID-19 pandemic in Israel in March 2020 (data collection: April, 2020 – September, 2020). The patients responded to 33 statements about how they perform self-care behaviors on a 5-point Likert scale ranging from 1 (never) to 5 (always). Statistical analyses included paired t-test and one-way repeated measures ANOVA.ResultsAttending scheduled clinic visits (M=4.93) and keeping the exit site and the driveline clean and dry (4.89) were two highly prevalent behaviors that did not change during the COVID-19 pandemic. The significant decrease in adherence during the COVID-19 pandemic was found in checking and recording LVAD speed, flow, power and PI (Mbefore=3.88±1.48 vs Mduring=3.08±1.55, t=2.02, p=.05), checking INR (Mb=5.0±0 vs Md=4.78±.42, t=2.73, p=.01), and weighing daily (Mb=4.54±.71 vs Md=3.92±1.06, t=3.19, p<.01). Adherence to the following behaviors increased most prominently, but not statistically significantly: talking to an LVAD team when feeling sad or worried (Mb=3.13±1.65 vs Md=3.71±1.55, t=1.39, p=.18) and contacting the LVAD team in case of symptoms (Mb=4.52±.96 vs Md=4.80±.5, t=1.37, p=.18).Compared to patients with a partner, those without a partner tended to worsen their adherence to some of the self-care behaviors e.g. taking medicines as prescribed (Mb=5.00±0 and Md=5.0±0 vs Mb=5.0±0 and Md=4.6±.89, F=4.85, p=.04, respectively).ConclusionsPriorities in self-care behaviors among patients with implanted LVAD may differ before and during a pandemic. In several crucial behaviors in self-care maintenance and management (checking and recording LVAD and INR, and taking medicines) and self-care monitoring (daily weighing) the adherence decreased significantly. The current results may guide further research on identifying behaviors at risk of not being maintained in a time of emergency.

Design and execution of a verification, validation, and uncertainty quantification plan for a numerical model of left ventricular flow after LVAD implantation.

Left ventricular assist devices (LVADs) are implantable pumps that act as a life support therapy for patients with severe heart failure. Despite improving the survival rate, LVAD therapy can carry major complications. Particularly, the flow distortion introduced by the LVAD in the left ventricle (LV) may induce thrombus formation. While previous works have used numerical models to study the impact of multiple variables in the intra-LV stagnation regions, a comprehensive validation analysis has never been executed. The main goal of this work is to present a model of the LV-LVAD system and to design and follow a verification, validation and uncertainty quantification (VVUQ) plan based on the ASME V&V40 and V&V20 standards to ensure credible predictions. The experiment used to validate the simulation is the SDSU cardiac simulator, a bench mock-up of the cardiovascular system that allows mimicking multiple operation conditions for the heart-LVAD system. The numerical model is based on Alya, the BSC's in-house platform for numerical modelling. Alya solves the Navier-Stokes equation with an Arbitrary Lagrangian-Eulerian (ALE) formulation in a deformable ventricle and includes pressure-driven valves, a 0D Windkessel model for the arterial output and a LVAD boundary condition modeled through a dynamic pressure-flow performance curve. The designed VVUQ plan involves: (a) a risk analysis and the associated credibility goals; (b) a verification stage to ensure correctness in the numerical solution procedure; (c) a sensitivity analysis to quantify the impact of the inputs on the four quantities of interest (QoIs) (average aortic root flow [Formula: see text], maximum aortic root flow [Formula: see text], average LVAD flow [Formula: see text], and maximum LVAD flow [Formula: see text]); (d) an uncertainty quantification using six validation experiments that include extreme operating conditions. Numerical code verification tests ensured correctness of the solution procedure and numerical calculation verification showed a grid convergence index (GCI)95% <3.3%. The total Sobol indices obtained during the sensitivity analysis demonstrated that the ejection fraction, the heart rate, and the pump performance curve coefficients are the most impactful inputs for the analysed QoIs. The Minkowski norm is used as validation metric for the uncertainty quantification. It shows that the midpoint cases have more accurate results when compared to the extreme cases. The total computational cost of the simulations was above 100 [core-years] executed in around three weeks time span in Marenostrum IV supercomputer. This work details a novel numerical model for the LV-LVAD system, that is supported by the design and execution of a VVUQ plan created following recognised international standards. We present a methodology demonstrating that stringent VVUQ according to ASME standards is feasible but computationally expensive.

CARD21: In Vitro Investigation Of The Timing Of The LVAD Pulsatility Event On Intraventricular Hemodynamics

Background: To reduce in-pump thrombosis and potentially improve left ventricular (LV) washout, pulsatility events (i.e., periodic LVAD speed modulation) have been introduced in 3rd generation LVADs. However, this pseudo-pulsatility of the centrifugal continuous flow pumps is not synchronized with native LV residual contractility. This study investigates the effect of timing of pulsatility events, with respect to LV pressure variations along the cardiac cycle, on intraventricular hemodynamics. Methods: Time-resolved stereo particle image velocimetry measurements were performed in a patient-derived quasirigid LV silicon model implanted with an LVAD. The residual LV contractility was modelled as a periodic variation in intraventricular pressure (IVP). Velocity fields in two orthogonal planes were measured for 7.5 cardiac cycles (including 3 occurrences of the pulsatility events, which happen every two seconds), for 3 LVAD speeds and 4 different synchronicities of pulsatility: at maximum/ minimum IVP and during increasing/decreasing IVP. Instantaneous measurements of the flowrate through the LVAD, with a time-resolution of 1 ms, were collected during the entire experiment. Ventricle stagnation index (VSI) was computed for each measurement plane and all experimental conditions studied. Results: Despite maintaining a constant average flowrate, the synchronicity of the LVAD pulsatility with the oscillatory IVP strongly influenced the flow rate waveforms, especially the peak and minimum instantaneous flow rates. A strong effect of the timing of pulsatility was also observed on intraventricular hemodynamics: pulsatility events taking place during decreasing IVP (diastole) resulted in higher VSI than other timing of pulsatility. Overall, these high resolution, instantaneous measurements of LVAD flow rate and pressure also highlighted the complex interrelations between LVAD speed, peripheral resistance, IVP and flow rate. Conclusion: This in vitro study elucidates the effect of LVAD pulsatility event synchronicity with the cardiac cycle on flowrate and LV flow patterns.

A NOVEL METHOD TO DETECT CHANGING LEFT VENTRICULAR ASSIST DEVICE PUMP FLOW USING A WIRELESS, WEARABLE DOPPLER ULTRASOUND: PROOF-OF-CONCEPT

TYPE: Late Breaking Abstract TOPIC: Critical Care PURPOSE: A proof-of-concept study to assess the accuracy of common carotid artery Doppler ultrasonography for detecting clinically-significant changes in continuous-flow left ventricular assist device (LVADCF) pump speed. METHODS: LVADCF outpatients were enrolled; written and informed consent was obtained and the study was approved by the Research Ethics Board of the Mayo Clinic. Each patient underwent a 6-minute protocol while sitting – 2 minutes at their baseline LVAD pump speed (T1), 2-minutes with pump speed decreased by 5% (T2) and 2-minutes with pump speed increased to 5% above baseline (T3). The patients wore an FDA-cleared, wireless, wearable Doppler ultrasound (Flosonics Medical, Sudbury, Ontario, Canada) over the common carotid artery. Both total velocity time integral per 5-seconds (VTI5-SEC) and a corrected VTI for the non-pulsatile fraction of the VTI (VTICORR) were investigated (Figure 1). Sensitivity and specificity for both VTI measures were compared for their ability to distinguish clinically-insignificant pump speed change (i.e., T1-to-T2, 5% decrease) from a significant one (i.e., T2-to-T3, 10% increase). RESULTS: Exploratory analysis was performed on two patients; results are shown in Figure 1. CONCLUSIONS: Changing LVADCF flow, induced by pump speed change, was accurately detected by a wireless, wearable Doppler ultrasound. Novel measures that correct for the non-pulsatile fraction of the cardiac cycle may improve diagnostic accuracy. CLINICAL IMPLICATIONS: Caring for the critically-ill patient with a LVADCF is challenging given that pump flow is afterload sensitive and that mean arterial pressure can be labile. Therefore, an automated method to detect changing LVAD flow from a wearable Doppler ultrasound is promising. DISCLOSURE: JSK, ME, ZY, AME, JKE work for Flosonics Medical, a start-up building the wearable Doppler ultrasound. PS, BDJ, MLC report no conflicts KEYWORD: left ventricular assist device

Metabolic and Hemodynamic Determinants of Exercise with the HeartMate 3 LVAD

<h3>Purpose</h3> Several studies have reported that peak oxygen consumption (pVO2) is diminished after continuous flow (CF) LVAD support and recent data shows that pVO2 post LVAD predicts outcomes. It has been suggested that augmentation of native cardiac output (NCO) and not LVAD flow supports exercise. Using simultaneous metabolic and hemodynamic measures, we further studied the determinants of maximal exercise with the Heartmate 3 (HM3) LVAD. <h3>Methods</h3> Subjects underwent maximal upright bicycle exercise testing utilizing a 10-15 W ramp protocol with hemodynamic measurements from a right heart and radial arterial catheter, and CPET testing with a metabolic cart (Metalyzer 3B, Cortex, Germany). Mid-point hemodynamics were acquired to plot pressure/flow relationships. NCO was calculated by subtracting LVAD flow from Fick cardiac output (FCO). Arterial lactate and regional tissue oxygenation (rSO2) with the NIRS SenSmart™ were also measured. <h3>Results</h3> Six HM3 subjects (43-76 yrs) were studied at least 12 weeks post implant, all were on at least 2 neurohormonal agents. All patients performed maximal exercise (RER 1.10-1.34). Most did not demonstrate chronotropic incompetence; achieving median 80.8 (63.5- 90.9) % of predicted heart rate. We saw robust oxygen extraction, with median peak A-VO2 difference 14.2 (10.5-15.8) mL/100mL with no change in rSO2 and median peak lactate 6.5 (3.5-9.9) mmol/L. However, 5/6 subjects achieved pVO2 ≤14 ml/kg/min. During exercise, there was minimal augmentation of LVAD flow (0.4-1.6 L/min) while NCO increased by 2.0-7.1 L/min. Mean pulmonary artery (mPA)/FCO relationships were available for 5 subjects (Fig.1), demonstrating abnormal rate of rise of mPA in all patients (slope 3.7-7.0, normal < 3). <h3>Conclusion</h3> Neither chronotropic response nor peripheral extraction appeared to limit exercise. Steep rise in mPA suggests either impaired pulmonary vasoreactivity and or cardiac reserve may be the key determinants of exercise capacity during HM3 support. Further study will clarify these factors.

The Effect of Multiple Outflow Graft Stenting on Hemodynamics in the Treatment of Left Ventricular Assist Device Outflow Graft Stenosis

<h3>Introduction</h3> Outflow graft stenosis is a potential complication of durable left ventricular assist device implantation. It presents with reduced LVAD flow, increased power requirement and decompensated left heart failure. Percutaneous intervention for OFG stenosis with single OFG stenting has been described. We present a case of decompensated heart failure due to LVAD OFG stenosis successfully managed with multiple OFG stenting. <h3>Case Report</h3> A 31 year old male with nonischemic cardiomyopathy underwent LVAD implantation 6 years ago with 20cm PTFE graft covering the OFG. He presented with acute decompensated left heart failure due to decreased LVAD flow on prior settings. Contrast CT showed OFG stenosis. Cardiac catheterization demonstrated 130mmHg pressure gradient. OFG angiography revealed 80% stenosis inside the PTFE graft. Four overlapping OFG stents were placed reducing gradient to 10mmHg. There was significant hemodynamic improvement with return of LVAD flow to baseline. <h3>Summary</h3> LVAD OFG stenosis may be caused by exudate overlying OFG covered by PTFE graft or the original bend relief. Successful surgical and percutaneous intervention for this complication has been reported. We observed the hemodynamic impact of multiple OFG stenting on OFG stenosis with return of LVAD flow to baseline. Multiple stents may be needed for long OFG covering since the exudate outside the OFG may worsen stenosis next to the stent. Our case of LVAD dysfunction due to OFG stenosis successfully managed with multiple OFG stenting affirms the essential role of this percutaneous intervention in managing this complication.

Three-Dimensional CT Reconstruction for Diagnosis of LVAD Outflow Graft Twist

<h3>Introduction</h3> Third generation LVAD, HeartMate3 (HM3) are associated with favorable prognosis. A rare life-threatening adverse event is a sudden outflow graft obstruction due to a rotational twist. There is limited data regarding the natural history of this complication. <h3>Case Report</h3> A 70-year-old male with dilated cardiomyopathy was implanted with an HM3 LVAD on September 2019. Echocardiography and cardiac CT immediately following the implantation showed appropriate left ventricular (LV) unloading and normal outflow cannula flows and patency. On April 2021 the patient complained of weakness. Clinical examination was normal, but LVAD interrogation identified decline of LVAD flow. Laboratory tests revealed INR in therapeutic range and normal LDH. An echocardiography revealed impaired unloading of the LV and opening of the aortic valve. A CTA showed a large irregular filling defect sized 7cm at the proximal outflow cannula. Differential diagnosis included outflow cannula twist or thrombosis. Three-dimensional CT volume rendering demonstrated a full rotational twist of the outflow cannula. An untwist operation using a lateral thoracotomy approach identified a >270º twist of the outflow graft. The cannula was untwisted and using a fixation device, the cannula was fixed, resulting in immediate improvement of the flow rate. Repeated transient low flow events at the end of the procedure mandated a repeat CTA to confirm the adequacy of cannula untwisting. Four months following the untwist procedure, the patient is well with stable LVAD flows. <h3>Summary</h3> This is the first case of an outflow graft twist obstruction with comprehensive CTA imaging at 3 critical time points: immediately after LVAD implantation, at twist occurrence and after surgical repair. We believe that it is very important to maintain a high degree of active awareness that a sudden drop in pump flow without signs of pump thrombosis may indicate outflow graft obstruction due to a twist, which is best recognized by three-dimensional CT reconstruction of the outflow graft.

Dynamic LVAD Inflow Cannula Obstruction Due to Mobile Thrombi

<h3>Introduction</h3> While LVAD outflow cannula obstructions are commonly described, we present a rare case of fulminant heart failure secondary to dynamic inflow cannula obstruction due to mobile thrombi within the left ventricular cavity. <h3>Case Report</h3> A 65 year old man with a history of ischemic cardiomyopathy and chronic kidney disease (CKD) underwent implantation of a continuous flow left ventricular assist device (LVAD; HeartWare™ HVAD™, Medtronic plc) as a bridge to transplantation. Three years following implantation, he presented with progressive fulminant right heart failure (RHF) followed by a sudden decrease in LVAD flow from 3.5 to 1.5 liters/min (Figure 1A). INR was 2.6, lactate dehydrogenase (LDH) level was normal and transthoracic echocardiogram showed a midline septum and the aortic valve opening with every beat. On admission, flows did not improve despite inotropic support. Outflow graft obstruction was suspected, however imaging was not pursued due to the risk of further renal injury with intravenous contrast, and that ultimately definitive treatment strategy remained heart transplantation. His UNOS listing status was upgraded from 4 to 2E. Anticoagulation was not escalated beyond aspirin and warfarin due to recurrent gastrointestinal bleeding. He continued to experience recurrent abrupt changes in LVAD flows (Figure 1B) without additional evidence to support pump thrombosis. Five weeks later, at the time of heart-kidney transplant, a partially obstructive thrombus within the inflow cannula as well as a mobile thrombus attached to the endocardium, prolapsing intermittently into the inflow cannula were visualized (Figure 1C-1D). <h3>Summary</h3> Dynamic inflow cannula obstruction should be suspected in the setting of heart failure and sudden changes in LVAD pump power consumption even when a lack corroborating imaging and laboratory evidence exists.

Left Ventricular Assist Device Graft Obstruction Relieved by Transcutaneous Stenting in a Teenage Patient

<h3>Introduction</h3> We describe a case of LVAD outflow graft stenosis from external outflow graft compression in a teenage patient successfully treated with percutaneous stenting. <h3>Case Report</h3> 17-year-old female with a continuous flow left ventricular assist device implanted 3 years prior for heart failure secondary to cardiomyopathy due to a TTN gene mutation. She presented with 1 week of worsening shortness of breath and 3 kilogram weight gain. LVAD flows were 3 liters-per-minute (L/min). The patient was referred for transcatheter stent therapy due to concern for outflow cannula obstruction. Hemodynamics during initial catheterization showed a gradient of 30 mmHg across the conduit. A stent was deployed in the distal aspect of the outflow cannula. A second stent was placed to reinforce the area of persistent stenosis. Post-intervention hemodynamics showed an improvement in the gradient to 13 mmHg. She re-presented 3 months later due to LVAD low flow alarm, decreased flows to 0.3 L/min, and decreased wattage of 2.9 watts (Figure 1). CT angiography (CTA) demonstrated 80% narrowing of the outflow conduit, proximal to previously placed outflow graft stents (Figure 2a-b). Low density material between the outflow graft and circumferential wrap was identified by radiology. The previously placed stents were first re-dilated. Three additional stents were placed within the LVAD outflow cannula. We placed the stents from aortic end toward LVAD inflow. In total, the outflow graft was stented for a length of approximately 7.5cm (Figure 3). Angiography showed mild residual narrowing at the anastomotic site. LVAD flows improved to 3.5L/min. Repeat CTA showed no residual evidence of stenosis. <h3>Summary</h3> To our knowledge this is the first reported case of external compression of an LVAD outflow graft from an overwrap treated with successful transcatheter stent treatment in the pediatric population. By stenting the outflow graft we believe we pushed the built-up material into the mediastinum, relieving the obstruction.

The Hemodynamic Impact of Mitral Regurgitation on Aortic Insufficiency in the LVAD-Supported Heart

Aortic valve incompetence (AI) is a serious complication that develops in 20% of LVAD patients within 12 months of implantation. Many LVAD patients with AI also develop mitral regurgitation (MR). Our goal in this study was to measure systemic flow (Qsys) and LVAD flow (QLVAD) during AI, MR and AI+MR. A mock circulatory loop with a dilated silicone LV and bioprosthetic valves was attached to a HeartMate II LVAD (Abbott Labs), and pressure and flow measured in the LV, LVAD and aorta. A Pre-LVAD ejection fraction of 20% without any valve dysfunction was established, followed LVAD support at speeds of 8, 9.4 and 11krpm. AI and MR were created with small stents that were non-obstructive to forward flow but prevented the leaflets from fully closing. Four conditions were tested: Normal, AI, MR and AI and MR combined. Average flow was obtained from ten cycles of data, and Q calculated as QLVAD/Qsys. Pre-LVAD AI, MR and AI+MR produced a 28%, 12% and 45% reduction in Qsys, respectively. LVAD support at 9.4krpm increased Normal Qsys to 3.6 L/min with 95% of flow through the LVAD. MR reduced Qsys by 16% and QLVADby 21%; AI reduced by Qsys by 24% but QLVADby only 5%; and AI+MR reduced Qsys by 25% and QLVADby 7%, which was comparable to AI alone. In all conditions except AI+MR, Q increases with LVAD speed indicating that QLVAD increases faster than Qsys. This trend reverses when MR is present, reducing the impact of AI as LVAD speed is increased. The major finding of these studies is that MR does not worsen Qsys when it coincides with AI and LVAD support. AI and MR occur during different phases of the cardiac cycle and sum in the absence of LVAD support. When an LVAD is added without valve dysfunction, QLVADis evenly distributed across systole and diastole. AI and MR reduces systolic and increases diastolic QLVAD, but AI+MR restores the original distribution. AI+MR produces the same overall Qsys but QLVADoccurs more evenly throughout the cardiac cycle resulting in a greater sensitivity to LVAD speed changes.

Incidence, Clinical Relevance and Treatment Options for Outflow Graft Stenosis after LVAD Implantation

LVAD outflow graft stenosis (OGS) is increasingly recognized after left ventricular assist device implantation. We analyzed our institutional experience with (OGS) in order to better understand the clinical significance and treatment options for this new form of pump pathology. We retrospectively reviewed our institutional experience with OGS in patients with contemporary centrifugal LVAD. Study endpoint were incidence and outcomes of LVAD OGS. From March 2006 to October 2019, 284 consecutive patients (183 (64.4%) HVAD and 101 (35.6%) HeartMate3) underwent primary LVAD implantation. Median follow up was 456 (range 1-2921) days. OGS was identified in 17 patients (total incidence 5.0%, 95% CI 3.5%-9.4%; HVAD: 5.5%, 95% CI 2.7%-9.8% vs. HeartMate3 6.9%, 95% CI 2.8%-13.8%, p=0.611). Median time to OGS development was 911 (range 281-2811) days. In all cases, OGS was located within covered segments of the outflow graft (bend relief (Heartmate 3 only) or protective Gore-Tex cover). In 13 patients (76.5%) OGS impaired LVAD flow and necessitated interventions (surgical revision n=2, endovascular stent placement n=9, surgery after failed stent placement n=1, death before intervention n=1). Two patients (11.8%) died following intervention and outflow graft stenosis recurred in two patients (11.8%) after initially successful treatment. Kaplan-Meier estimate of survival free from outflow graft stenosis is depicted on Figure 1. Outflow graft stenosis is a potentially lethal late complication of LVAD implantation. Surgical or interventional treatment is indicated when LVAD flows are impaired. Modification of pump design may be warranted as outflow graft stenosis preferentially occur in covered portions of outflow grafts.

Outflow Graft Obstruction Causing Recurrent Heart Failure after Left Ventricular Assist Device Implantation

Outflow graft obstruction is a poorly described complication following continuous flow-left ventricular assist device (CF-LVAD) surgery. We sought to define the incidence of CF-LVAD outflow graft obstruction and assess clinical outcomes with a percutaneous treatment strategy. From January 2012 to June 2019, 252 CF-LVAD patients were managed at our institution. Patients with suspected LVAD outflow graft obstruction underwent comprehensive evaluation with Doppler echocardiography, cardiac computed tomography with angiography and invasive hemodynamic assessment followed by percutaneous intervention. Fourteen patients (5.6%) developed hemodynamically significant LVAD outflow graft obstruction at a rate of 0.03 events per patient-year. Outflow graft obstruction presented a mean of 34±18 months after surgery. Patients presented with heart failure (HF; 86%), low LVAD pump flow (93%), or both (79%). LVAD flow declined by an average of 2.1±0.8L/min (p<0.001). Outflow graft obstruction was caused by external graft compression (77%), stenosis of the aortic anastomosis (46%) and discrete kinking of the outflow cannula (46%); most patients presented with 2 or more lesions (69%). There were no cases of outflow graft thrombosis. External graft compression was uniformly due to build-up of fibrinous material between the outflow cannula and the protective external GoreTex graft. Outflow graft stenting was 100% successful and reduced the gradient from 80mmHg (IQR 58-100mmHg) to 13mmHg (IQR 10-20mmHg, Figure). There was no in-hospital mortality and few complications. Outflow graft stenting was durable; over a mean follow-up of 13±7 months, no patients had recurrent outflow graft obstruction. LVAD outflow graft obstruction is a relatively common and underappreciated cause of recurrent HF and LVAD dysfunction. Outflow graft stenting can be achieved with low morbidity and provides a long-term solution to this complication.