Axial Flow Left Ventricular Assist Research Articles

Machine learning based on computational fluid dynamics enables geometric design optimisation of the NeoVAD blades

The NeoVAD is a proposed paediatric axial-flow Left Ventricular Assist Device (LVAD), small enough to be implanted in infants. The design of the impeller and diffuser blades is important for hydrodynamic performance and haemocompatibility of the pump. This study aimed to optimise the blades for pump efficiency using Computational Fluid Dynamics (CFD), machine learning and global optimisation. Meshing of each design typically included 6 million hexahedral elements and a Shear Stress Transport turbulence model was used to close the Reynolds Averaged Navier–Stokes equations. CFD models of 32 base geometries, operating at 8 flow rates between 0.5 and 4 L/min, were created to match experimental studies. These were validated by comparison of the pressure-flow and efficiency-flow curves with those experimentally measured for all base prototype pumps. A surrogate model was required to allow the optimisation routine to conduct an efficient search; a multi-linear regression, Gaussian Process Regression and a Bayesian Regularised Artificial Neural Network predicted the optimisation objective at design points not explicitly simulated. A Genetic Algorithm was used to search for an optimal design. The optimised design offered a 5.51% increase in efficiency at design point (a 20.9% performance increase) as compared to the best performing pump from the 32 base designs. An optimisation method for the blade design of LVADs has been shown to work for a single objective function and future work will consider multi-objective optimisation.

Five-Year Outcomes in Patients With Fully Magnetically Levitated vs Axial-Flow Left Ventricular Assist Devices in the MOMENTUM 3 Randomized Trial

Although durable left ventricular assist device (LVAD) therapy has emerged as an important treatment option for patients with advanced heart failure refractory to pharmacological support, outcomes, including survival, beyond 2 years remain poorly characterized. To report the composite end point of survival to transplant, recovery, or LVAD support free of debilitating stroke (Modified Rankin Scale score >3) or reoperation to replace the pump 5 years after the implant in participants who received the fully magnetically levitated centrifugal-flow HeartMate 3 or axial-flow HeartMate II LVAD in the MOMENTUM 3 randomized trial and were still receiving LVAD therapy at the 2-year follow-up. This observational study was a 5-year follow-up of the MOMENTUM 3 trial, conducted in 69 US centers, that demonstrated superiority of the centrifugal-flow LVAD to the axial-flow pump with respect to survival to transplant, recovery, or LVAD support free of debilitating stroke or reoperation to replace the pump at 2 years. A total of 295 patients were enrolled between June 2019 to April 2021 in the extended-phase study, with 5-year follow-up completed in September 2021. Of 1020 patients in the investigational device exemption per-protocol population, 536 were still receiving LVAD support at 2 years, of whom 289 received the centrifugal-flow pump and 247 received the axial-flow pump. There were 10 end points evaluated at 5 years in the per-protocol population, including a composite of survival to transplant, recovery, or LVAD support free of debilitating stroke or reoperation to replace the pump between the centrifugal-flow and axial-flow pump groups and overall survival between the 2 groups. A total of 477 patients (295 enrolled and 182 provided limited data) of 536 patients still receiving LVAD support at 2 years contributed to the extended-phase analysis (median age, 62 y; 86 [18%] women). The 5-year Kaplan-Meier estimate of survival to transplant, recovery, or LVAD support free of debilitating stroke or reoperation to replace the pump in the centrifugal-flow vs axial-flow group was 54.0% vs 29.7% (hazard ratio, 0.55 [95% CI, 0.45-0.67]; P < .001). Overall Kaplan-Meier survival was 58.4% in the centrifugal-flow group vs 43.7% in the axial-flow group (hazard ratio, 0.72 [95% CI, 0.58-0.89]; P = .003). Serious adverse events of stroke, bleeding, and pump thrombosis were less frequent in the centrifugal-flow pump group. In this observational follow-up study of patients from the MOMENTUM 3 randomized trial, per-protocol analyses found that receipt of a fully magnetically levitated centrifugal-flow LVAD vs axial-flow LVAD was associated with a better composite outcome and higher likelihood of overall survival at 5 years. These findings support the use of the fully magnetically levitated LVAD. ClinicalTrials.gov Identifier: NCT02224755 and NCT03982979.

CARC19: Endovascular Axial Flow Left Ventricular Assist Device as a Bridge to Orthotopic Heart Transplantation

CARC19: Endovascular Axial Flow Left Ventricular Assist Device as a Bridge to Orthotopic Heart Transplantation

Simulation of Axial Flow Left Ventricular Assist Device’s Control Algorithm Used to Assist Different Levels of Heart Failure Based on the Circuit Model

Modelling blood circulation is difficult. Due to the similarity of blood circulation and circuit loop, a numerical model coupled with the cardiovascular system and the left ventricular assist device is used to study the control algorithm of left ventricular assist devices in this study. According to severity, heart failure can be divided into three levels, and is simulated by varying the time-varying capacitance. Most of the left ventricular assist devices adopt the control algorithm of constant speed, which can reduce the pulsation of aortic pressure, and it is especially obvious in level III heart failure. We compare the positive pulse mode and the constant speed mode, and the results show that the positive pulse could increase systolic blood pressure and reduce diastolic blood pressure, which is more in line with the human aortic pulsation, and is more suitable for patients with high level of heart failure.

Acoustic Properties of Axial and Centrifugal Flow Left Ventricular Assist Devices and Prediction of Pump Thrombosis

ObjectiveTo characterize the properties of the audible tones produced by current left ventricular assist device (LVAD) pumps approved for use, and to ascertain if changes in those may be present in the setting of pump thrombosis. Patients and MethodsFrom August 31, 2016, to January 16, 2020, LVAD recipients consented to have surface recordings obtained using a high-fidelity digital stethoscope. Audio data were analyzed using digital recording and editing software to produce an acoustic spectrogram by Fast Fourier transformation. ResultsRecordings were obtained in 53 patient encounters (27 HeartMate II, 19 HeartWare and 7 HeartMate 3). In 12 patients (9 HeartMate II, 3 HeartWare) there was a clinical concern for pump thrombosis. In all patients and pump models, a fundamental frequency was noted, and the second and third harmonics were also clearly detectable. Where thrombosis occurred in the HeartMate II pump, the absolute (normal -46.9 [-57.5,-42.9] dB vs thrombosis -41.4 [-49.8,-26.8] dB; P=.08) and relative (normal 0.72 [0.62, 0.92] vs thrombosis 0.95 [0.86, 1.24]; P=.01) third harmonic frequencies were increased in amplitude. Where paired data were available, an increase in the absolute and relative third harmonic frequencies was observed in all patients. In the case of the HeartWare device, a consistent difference in harmonic amplitudes in the setting of thrombosis could not be identified. ConclusionA consistent pattern of fundamental and harmonic frequencies is common to all LVADs currently approved for use. Alterations in the amplitude of higher order harmonics may signal the onset of pump thrombosis in axial flow LVADs.

Comparison of Exercise Hemodynamics in Patients Supported with Centrifugal and Axial Flow Left Ventricular Assist Devices

Comparison of Exercise Hemodynamics in Patients Supported with Centrifugal and Axial Flow Left Ventricular Assist Devices

Axial Flow Left Ventricular Assist Device is Associated with Progression of Aortic Valve Insufficiency

Aortic Valve Insufficiency (AI) in patients with Left Ventricular Assist Device (LVAD) can increase re-circulation causing inefficient forward blood flow, exacerbate RV failure and subsequently demand strict LV afterload control which may adversely affect on other end-organ function. Moreover, careful attention is required for moderate or more AI potentially necessitating valvular intervention or earlier heart transplant. However, risk factors for progression of AI in patients supported with LVAD are not well understood.

Heat Generation in Axial and Centrifugal Flow Left Ventricular Assist Devices.

Despite increasing use of left ventricular assist devices (LVADs) as a surgical treatment for advanced heart failure in an era of improved outcomes with LVAD support, the mechanical interactions between these pumps and the cardiovascular system are not completely understood. We utilized an in vitro mock circulatory loop to analyze the heat production incurred by operation of an axial flow and centrifugal flow LVAD. A HeartMate II and a HeartWare HVAD were connected to an abbreviated flow loop and were implanted in a viscoelastic gel. Temperature was measured at the surface of each LVAD. Device speed and fluid viscosity were altered and, in the HeartMate II, as artificial thrombi were attached to the inflow stator, impeller, and outflow stator. The surface temperatures of both LVADs increased in all trials and reached a plateau within 80 minutes of flow initiation. Rate of heat generation and maximum system temperature were greater when speed was increased, when viscosity was increased, and when artificial thrombi were attached to the HeartMate II impeller. Normal operation of these two widely utilized LVADs results in appreciable heat generation in vitro. Increased pump loading resulted in more rapid heat generation, which was particularly severe when a large thrombus was attached to the impeller of the HeartMate II. While heat accumulation in vivo is likely minimized by greater dissipation in the blood and soft tissues, focal temperature gains with the pump housing of these two devices during long-term operation may have negative hematological consequences.

(923) - Differences in Heat Generation Between Axial and Centrifugal Continuous Flow Left Ventricular Assist Devices

(923) - Differences in Heat Generation Between Axial and Centrifugal Continuous Flow Left Ventricular Assist Devices

(1080) - Correlation of Non-Invasive Flow Estimation of the Axial-Flow Left Ventricular Assist Device with Fick and Thermal Cardiac Output

(1080) - Correlation of Non-Invasive Flow Estimation of the Axial-Flow Left Ventricular Assist Device with Fick and Thermal Cardiac Output

Acoustic Characterization of Axial Flow Left Ventricular Assist Device Operation In Vitro and In Vivo.

The use of left ventricular assist devices (LVADs), implantable pumps used to supplement cardiac output, has become an increasingly common and effective treatment for advanced heart failure. Although modern continuous-flow LVADs improve quality of life and survival more than medical management of heart failure, device malfunction remains a common concern. Improved noninvasive methods for assessment of LVAD function are needed to detect device complications. An electronic stethoscope was used to record sounds from the HeartMate II axial flow pump in vitro and in vivo. The data were then uploaded to a computer and analyzed using two types of acoustic analysis software. Left ventricular assist device acoustics were quantified and were related to pump speed, acoustic environment, and inflow and outflow graft patency. Peak frequency values measured in vivo were found to correlate strongly with both predicted values and in vitro measurements (r > 0.999). Plots of the area under the acoustic spectrum curve, obtained by integrating over 50 Hz increments, showed strong correlations between in vivo and in vitro measurements (r > 0.966). Device thrombosis was found to be associated with reduced LVAD acoustic amplitude in two patients who underwent surgical device exchange.

Acquired von Willebrand Syndrome in Patients With a Centrifugal or Axial Continuous Flow Left Ventricular Assist Device

The aim of this study was to determine whether differences in continuous flow left ventricular assist devices (LVADs) may lead to differences in the von Willebrand profile and the occurrence of bleeding and thromboembolic events. The HeartMate II (Thoratec Corp., Pleasanton, California) and HeartWare Ventricular Assist Device (HVAD) (HeartWare, Inc., Framingham, Massachusetts) systems are the most frequently implanted LVADs worldwide. In all patients with an axial-flow HeartMate II, acquired von Willebrand syndrome (AvWS) due to the loss of large molecular weight multimers was found. The large molecular weight multimers of the von Willebrand factor (vWF) play a key role in primary hemostasis through interactions with platelets. This was a retrospective study of the vWF profile and incidence of bleeding and thromboembolic events in 102 patients receiving the HeartMate II (n= 51) and HVAD (n= 51). Between January 2003 and December 2010, vWF testing was performed in 102 of 175 consecutive patients after LVAD implantation. AvWS was found in all patients, demonstrated by a decrease in the high molecular weight multimers of vWF to 30±14% in HeartMate II patients and 34 ± 13% in patients with an HVAD. Significant predictors of vWF antigen included age (p= 0.011), number of days on the device (p= 0.035), C-reactive protein (p< 0.001), and blood group (p= 0.007). Bleeding and thromboembolic event rates were similar. However, lower fractions of vWF antigen and high molecular weight multimers did not correlate with the rate of bleeding complications or thromboembolic events. AvWS developed in all patients after centrifugal or axial flow pump implantation. Different patterns of AvWS wereseen between the devices as well as individually. However, the complication rates after implantation were similar.

(154) - Systemic Inflammation in End-Stage Heart Failure Patients Undergoing Different Axial-Flow Left Ventricular Assist Devices

(154) - Systemic Inflammation in End-Stage Heart Failure Patients Undergoing Different Axial-Flow Left Ventricular Assist Devices

Mitral Regurgitation and Axial Flow Left Ventricular Assist Device

Good right ventricular function is one of the major determinants of long-term outcomes in patients with implanted left ventricular assist devices (LVADs). In the present study, a computer model was developed to assess the impact of mitral regurgitation on right ventricular workload at different levels of LVAD support. Left ventricular assist device was simulated by a model of HeartMate II. The computer model has shown that the regurgitant volume of the mitral valve falls significantly only after the systolic pressure in the left ventricle decreases, which occurs at higher LVAD revolutions per minute (RPM) when there is no ejection through the aortic valve. However, at low LVAD RPM, the pressures in the left atrium and the pulmonary artery decrease significantly, despite a small decrease in regurgitant volume. According to the computer model, LVAD support decreases mitral regurgitation. Furthermore, regurgitant volume has a smaller impact on the right ventricular afterload when compared with a heart without LVAD support.

Design and Numeric Evaluation of a Novel Axial-Flow Left Ventricular Assist Device

Virtual design characteristics and performance of the first Turkish axial-flow left ventricular assist device (LVAD) are presented, with emphasis on rotor geometry. The patented rotor design includes a central flow channel carved inside the main block, which carries permanent magnets. A concentric rotor-stator gap minimizes the distance between respective magnets, improving electromagnetic efficiency and creating a second blood pathway. Dual sets of three helical blades, placed on the shaft and external surface of the rotor block, ensure unidirectionality. Hemodynamic performance was tested with computational fluid dynamics (CFD); and rotor-blade geometry was optimized, to maximize overall efficiency d and minimize backflow and wall shear stresses. For a shaft radius of 4.5 mm, rotor blade height of 2.5 mm, and blade inlet and exit metal angles of 67° and 32°, pump operation at the nominal head-flow combination (5 L/min and 100.4 mm Hg) was achieved at a rotor speed of 10,313 rpm. At the nominal point, backflow as percent of total flow was 7.29 and 29.87% at rotor inlet and exit, respectively; overall hydraulic efficiency reached 21.59%; and maximum area-averaged shroud shear was 520 Pa. Overall efficiency peaked at 24.07% for a pump flow of 6.90 L/min, and averaged at 22.57% within the flow range of 4-8 L/min. We concluded that the design satisfies initial rotor design criteria, and that continued studies with diffuser optimization and transient flow analysis are warranted.

Differential Response to Afterload in Axial and Centrifugal Continuous Flow Left Ventricular Assist Devices (CV-LVAD)

Purpose CF-LVADs generate a specific flow for a given pressure differential across the pump. Implications of difference between afterload sensitivity of axial and centrifugal pumps has not been previously described. Methods and Materials All CF LVAD at a single center from 5/06 to 10/11, supported >30 days and managed with a standardized blood pressure (BP) protocol with target mean ≤ 80 mmHg. Mean number of data points per patient was 318. Contour mapping compared speed, pressure, and power. Results There were 96 CF-LVADs with mean support of 262 days. Patient demographics: age 55 years, male 80%, white 79%, ischemic 50%, BTT 55%, 61 axial & 35 centrifugal LVAD. Mean BP was near goal and not different between axial and centrifugal devices ( Figure 1a ). No BP meds at end of follow-up: 25 patients, 14 of whom died on device. Of patients on therapy, 38 were managed on 1 medication and 33 on 2+ medications. As expected, for each pump type at the same BP (afterload), power consumption and thus flow, increased with increasing pump speed. However, pump types differed somewhat in their response to increased afterload ( Figure 1b ). For axial pumps, at a given pump speed there was little change in pump power over clinically relevant ranges of afterload. In contrast, centrifugal pumps had more afterload dependence with a decrease in pump power with increasing afterload. Conclusions In the setting of aggressive BP control, axial and centrifugal pumps demonstrated a differential response to increasing afterload, with centrifugal pumps having greater afterload dependence. BP control is important in all patients with CF-LVADs, but poorly controlled BP may impair pump flow to a greater degree in patients with centrifugal devices.

Readmissions After Implantation of Axial Flow Left Ventricular Assist Device

The purpose of this study was to determine the occurrence and causes of readmissions after implantation of axial flow left ventricular assist device (LVAD). Based on the REMATCH (Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure) study experience, readmissions after LVAD implantation are thought to be frequent. We retrospectively analyzed admissions to our facility in a cohort of 115 patients implanted between January 2008 and July 2011 with the HeartMate II axial flow LVAD, of whom 42 were bridged to transplant. To account for repeated events, Andersen-Gill models were used to determine possible predictors. The patients were followed for 1.4 ± 0.9 years. There were 224 readmissions in 83 patients. The overall readmission rate was 1.64 ± 1.97 per patient-year of follow-up. The readmission rate for the first 6 months was 2.0 ± 2.3 and decreased to 1.2 ± 2.1 during subsequent follow-up. Leading causes were bleeding (66 readmissions in 34 patients), mostly gastrointestinal bleed (51 in 27 patients), cardiac (51 in 36 patients, most for HF or arrhythmia), infections (32 in 25 patients) of which 6 were pump related, and thrombosis (20 in 15 patients) including 13 readmissions due to hemolysis. Preoperative variables associated with (fewer) readmissions in a multivariate model include residence within our hospital-extended referral zone of Minnesota and the neighboring states (hazard ratio: 0.66; 95% confidence interval: 0.48 to 0.91; p = 0.011), hemoglobin (hazard ratio: 0.91, 95% confidence interval: 0.84 to 0.99; p = 0.027) and N-terminal pro-B-type natriuretic peptide (hazard ratio: 0.98; 95% confidence interval: 0.96 to 1.0 per 1,000-unit increase, p = 0.022). C-statistic for the model: 0.63. Readmission rates after axial flow LVAD implantation decrease during the first 6 months and then stabilize. The leading causes are bleeding, cardiac (heart failure and arrhythmia), infections, and thrombosis.

Circulation: Cardiovascular Interventions Editors’ Picks

<i>Circulation: Cardiovascular Interventions</i> Editors’ Picks

Response to Letter Regarding Article, “Mechanisms of Bleeding and Approach to Patients With Axial-Flow Left Ventricular Assist Devices”

We appreciate the letter by Dr Jennings regarding our recently published review.1 This letter clarifies the anticoagulation protocol used by the Henry Ford Hospital for patients treated with Heartmate II left ventricular assist device, which we reported incorrectly.1 Our source for the reported international normalized ratio (INR) range of 1.8 to 2.2 was the abstract presented by Henry Ford group at the American Society of Artificial Organs in 2011 …

Letter by Jennings Regarding Article, “Mechanisms of Bleeding and Approach to Patients With Axial-Flow Left Ventricular Assist Devices”

I would like to draw your attention to several errors in the publication by Suarez et al1 entitled “Mechanisms of bleeding and approach to patients with axial-flow left ventricular assist devices.”1 In this article, the authors state that, “For instance, to reduce gastrointestinal tract bleeding risk in these patients, the Henry Ford Hospital (Detroit, Mich) has lowered the anticoagulation target to an INR of 1.8–2.2, with no increase in thromboembolic complications.” First, I believe that the authors have the wrong reference cited for this statement. In the article, this statement is supported by reference 18, which is a cohort of patients …