Axial Left Ventricular Assist Device Research Articles

Numerical simulation analysis of multi-scale computational fluid dynamics on hemodynamic parameters modulated by pulsatile working modes for the centrifugal and axial left ventricular assist devices

Continuous flow (CF) left ventricular assist devices (LVAD) operate at a constant speed mode, which could result in increased risk of adverse events due to reduced vascular pulsatility. Consequently, pump speed modulation algorithms have been proposed to augment vascular pulsatility. However, the quantitative local hemodynamic effects on the aorta when the pump is operating with speed modulation using different types of CF-LVADs are still under investigation. The computational fluid dynamics (CFD) study was conducted to quantitatively elucidate the hemodynamic effects on a clinical patient-specific aortic model under different speed patterns of CF-LVADs. Pressure distribution, wall shear stress (WSS), time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and velocity were calculated to compare their differences at constant and pulsatile speeds under centrifugal and axial LVAD support. Results showed that pulse pressure on the aorta was significantly larger under pulsatile speed mode than that under constant speed mode for both CF-LVADs, indicating enhanced aorta pulsatility, as well as the higher peak blood flow velocity on some representative slices of aorta. Pulsatile speed modulation enhanced peak WSS compared to constant speed; high TAWSS region appeared near the branch of left common carotid artery and distal aorta regardless of speed modes and CF-LVADs but these regions also had low OSI; RRT was almost the same for all the cases. This study may provide a basis for the scientific and reasonable selection of the pulsatile speed patterns of CF-LVADs for treating heart failure patients.

Abstract 15045: Impact of Left Ventricular Assist Device (LVAD) Type on Arrhythmic Outcomes in Patients With Continuous Flow LVADs

Introduction: Cardiac arrhythmias are common in continuous flow left ventricular assist device (LVAD) recipients. The impact of axial vs. intrapericardial centrifugal LVAD pumps on arrhythmia incidence and associated clinical outcomes is unclear. Hypothesis: This multicenter study evaluated the impact of LVAD type (axial vs. centrifugal) on incidence of atrial and ventricular arrhythmias, ICD shocks and mortality in LVAD patients. Methods: Analysis was done on 536 patients who underwent LVAD implantation at 5 US centers from 2008 to 2016. The groups were divided based on their LVAD type (axial - HeartMate II [HMII, n=433] vs. centrifugal - HeartWare (HW, n=103). Baseline characteristics as well as incidence of post-LVAD atrial arrhythmias (PL-AA), ventricular arrhythmias (PL-VA) and ICD shocks were analyzed in these groups. Multivariable Cox Regression analysis was used to identify predictors of survival. Results: Of 536 patients, 433 had HMII axial LVAD and 103 had HW centrifugal VAD implant. At baseline, HMII group had more males, higher proportion of CRT-D and higher prevalence of AA (Table 1A). Left ventricular dimensions were similar between groups. During a median follow-up of 537 days of LVAD support, incidence of PL-VA and ICD shocks were significantly higher in the HM2 group compared to HW group whereas incidence of PL-AA was not significantly different (Table 1A). In multivariable Cox Regression analysis, LVAD indication was the only variable that predicted survival (Table 1B). Type of LVAD (axial vs. centrifugal) was not associated with survival (HMII vs. HW - HR 1.04, P=0.48). Conclusions: In this multi-center continuous flow LVAD cohort, axial HM2 VAD patients had a higher incidence of PL-VA and ICD shocks. Type of LVAD (axial vs. centrifugal) was not associated with survival.

Carotid artery duplex velocity criteria might be equivocal after left ventricular assist device implantation

BackgroundAlthough conventional angiography remains the reference standard for the grading of carotid stenosis, carotid duplex ultrasound (CDUS) is the most commonly used modality for determining the degree of carotid stenosis. The validity of CDUS findings for patients after left ventricular assist device (LVAD) implantation is questionable, because the velocities are often altered secondary to the continuous flow nature of the devices. MethodsA retrospective review was performed of all patients who had undergone LVAD implantation from January 2007 to December 2019. All patients who had undergone CDUS before and after LVAD implantation were included. Patients receiving extracorporeal membrane oxygenation, those with unusable carotid imaging studies, and those with internal carotid artery (ICA) occlusion were excluded. The peak systolic velocity (PSV) and end-diastolic velocity (EDV) in the ICA and common carotid artery (CCA) and the ICA/CCA ratios were compared before and after LVAD implantation. ResultsA total of 36 patients (mean age 59 years; 30 men; 6 women) had undergone CDUS both before and after LVAD implantation (mean, 647 days between imaging studies). A total of 61 ICAs had met the criteria for inclusion. Before LVAD, 7 carotid arteries (13%) had had >50% carotid stenosis and 53 (87%) had had 0% to 50% stenosis. The mean changes in the velocities after LVAD were as follows. The ICA PSV had decreased by 6.12 ± 4.34 cm/s, and the ICA EDV had increased by 13.44 ± 4.23 cm/s. The CCA PSV had decreased by 17.22 ± 4.95 cm/s, and the CCA EDV had increased by 10.83 ± 2.59 cm/s. The mean ICA/CCA ratio had increased by 0.18 ± 0.05. All the mean changes in velocity were significant (P < .01), except for the ICA PSV (P = .167). Among four patients with known stenosis of 60% to 69%, the degree of increase in the ICA and CCA EDVs (75.8 and 13.3 cm/s, respectively) was significantly greater than that for patients with <50% or no stenosis. Carotid artery laterality did not significantly affect the differences in mean velocity. Centrifugal LVADs resulted in a significantly larger increase in the ICA EDV compared with axial LVADs (26.0 vs 6.3 cm/s; P < .01). ConclusionsLVADs were associated with significant changes in CCA PSV, ICA and CCA EDV, and ICA/CCA ratios. However, the magnitude of these changes in patients with <50% stenosis was minimal and might not be clinically significant. The LVAD type might only have an effect on EDV measurements in the CCA, and the left and right carotid arteries did not appear to have different degrees of change in velocity. The currently used criteria for determining carotid stenosis might result in an under- or overestimation of carotid stenosis in patients with an LVAD.

HLA Allosensitization in Patients on Continuous Flow LVAD Support: Are Patients at Increased Risk?

Allosensitization poses a challenge in identifying appropriate donors for patients (pts) awaiting cardiac transplantation. Continuous flow left ventricular assist device (LVAD) can induce significant allosensitization to human leucocyte antigens (HLA). With advances in surgical approaches and improved LVAD hemocompatibility, the prevalence of allosensitization is not well studied. We evaluated the development of allosensitization in a contemporary LVAD cohort including centrifugal and axial LVADs. In consecutive pts who underwent LVAD in a single center from 2014 to 2018, we examined HLA immune status prior to LVAD and at time of transplant if less than one year or up to one year of LVAD support. Serum alloantibodies were detected with single-antigen beads using a Luminex platform. HLA allosensitization was defined as having a calculated panel reactive antibody (cPRA) >10%. LVAD-associated allosensitization was defined as having a cPRA >10% and cPRA <10% before LVAD. A total of 50 pts who underwent LVAD implantation as bridge to transplant had available cPRA prior to and after LVAD implantation. Mean follow up was 268±91 days. Mean age was 53±13 years, and 26% were female. 18 pts (36%) had centrifugal LVAD. At 1 year, 28 pts (56%) were transplanted, 18 pts (36%) remained on LVAD support, and 4 pts (8%) expired. Of the 50 patients, 14% (n=7) had PRA over 10%. Though the proportion of patients with allosensitization after LVAD increased to 24%, this was not statistically significant (Fig 1A&B). Eight pts had LVAD-associated allosensitization, and in this group, type of device (centrifugal vs axial) was not associated with allosensitization. In our single-center, contemporary cohort, allosensitization before LVAD was not common. LVAD associated allosensitization occurred in about one-fifth of patients.

Does Diabetes Influence Post-Transplant Survival in CF-axial LVAD BTT Patients?

Diabetes is an important factor in post-transplant survival. However its impact on post-transplant survival of Continuous Flow (CF) axial left ventricular assist device (LVAD) i.e. Heartmate II (HM II) bridge to transplant (BTT) population has not been studied. This study addresses the influence of Diabetes type II (DM type II) in this population. The study consisted of two cohorts derived from the UNOS database (2005-2015). Cohort 1 consisted of Type II Diabetes patients with HM II (n=1172) and without HM II (n=1097). Cohort 2 consisted of HM II patients with DM type II (n=1172) and without DM type II (n=1171). Cox's proportional hazards regression was used to investigate the effect of diabetes on post-transplant survival in this population. Hazard ratio (OR) and the 95% confidence interval (CI) were calculated with statistical significance set at p< 0.05. Propensity score matching was done to match HMII recipients with Type II diabetes and without diabetes. Analyses were done using IBM SPSS software by logistic regression on the group indicator which then uses the propensity score obtained to select matched cohorts. Kaplan Meir survival curves were generated for 2-year post-transplant survival RESULTS: The Kaplan Meir survival curve for cohort 1 showed that DM type II patients had better survival when they were bridged to transplant with HM II. The Hazard ratio (OR) for Cohort 1 was 0.717(p=0.00514)). In cohort 2 the Kaplan Meir survival curve showed that HMII without DM type II had better survival than those with type II DM. The hazard ratio (OR) for Cohort 2 was 1.31 (p=0.0209). The cohorts were propensity-matched. This study shows for the first time that HM II implantation in DM type II patients have a better 2 year post-transplant survival as opposed to those without the device. This effect is probably best explained by improved hemodynamics on the endothelium in CF axial LVAD patients.

Quantification of Pulsed Operation of Rotary Left Ventricular Assist Devices with Wave Intensity Analysis.

The current generation of left ventricular assist devices (LVADs) provides continuous flow and has the capacity to reduce aortic pulsatility, which may be related to a range of complications associated with these devices. Pulsed LVAD operation using speed modulation presents a mechanism to restore aortic pulsatility and potentially mitigate complications. We sought to investigate the interaction of axial and centrifugal LVADs with the LV and quantify the effects of continuous and pulsed LVAD operations on LV generated wave patterns under different physiologic conditions using wave intensity analysis (WIA) method. The axial LVAD created greater wave intensity associated with LV relaxation. In both LVADs, there were only minor and variable differences between the continuous and pulsed operations. The response to physiologic stress was preserved with LVAD implantation as wave intensity increased marginally with volume loading and significantly with infusion of norepinephrine. Our findings and a new approach of investigating aortic wave patterns based on WIA are expected to provide useful clinical insights to determine the ideal operation of LVADs.

Abstract 21156: Abo Status and Stroke Free Survival in Lvad Patients

Introduction: Left Ventricular Assist Devices (LVAD) improve survival in selected patients. Complications include thromboembolism and bleeding. Alterations in von Willebrand factor (vWF) multimers may play a role, especially with continuous flow LVADs. AbO antigens are expressed on vWF where these antigens influence its processing into subunits. There are reports of higher bleeding rates in O patients and higher thrombosis rates in non-O patients. Hypothesis: ABO status is routinely determined prior to LVAD implantation and we correlated ABO status with outcomes. It may allow adjustment of anticoagulation to minimize adverse events. Methods: We studied adults with first implant of continuous axial LVAD entered into the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS). The implant operations occurred between the second quarters of 2012-2016. A total pf 6,462 patients were studied. A Cox proportional hazards model was analyzed using gender, age category, BMI, white race and blood type to predict the hazard rate of stroke or death after implant. Follow up was from time of implant until death, transplant, exchange, recovery, stroke or end of data set. Results: Increases in the hazard rate was seen in females (HR 1,26, 95% CI: 1.13-1.41; p&lt;0.0001); age &gt;50 (HR 1.62; 95% CI 1.42- 1.84; p&lt;0.0001), and white race (HR 1.18; 95% CI: 1.06-1.31; p=0.002). Blood group O decreased the hazard rate compared to patients with non-O blood group (HR 0.92; 95% CI: 0.83-1.00; p=0.06). Conclusions: O blood group was associated with improved stroke free survival in multivariate analysis including gender, age category, BMI and race. This effect could be due to the lower levels of vWF in O blood group patients. Further work is being done to assess the effect of ABO blood group status on other thromboembolic events as well as bleeding outcomes. The impact of antiplatelet agents and anticoagulants on these outcomes will also need to be evaluated.

Peripheral Vascular Pulsatility in Heart Failure Patients with Continuous Flow Centrifuge and Axial Left Ventricular Assist Devices

Current continuous flow left ventricular assist devices (LVAD) decrease peripheral vascular pulsatility, which may contribute to side effects such as bleeding, thrombotic events and orthostatic intolerance. PURPOSE: To investigate the impact of manipulating LVAD pump speed, documented as revolutions per minute (RPM), on peripheral (brachial artery) pulsatility index (PI) in 20 heart failure patients implanted with a HeartWare (HVAD, n = 10) or HeartMateII (HMII, n = 10) LVAD. METHODS: Doppler ultrasound blood velocity in the brachial artery was recorded at baseline and 3 minutes after altering RPM, at three different RPM settings above and below baseline (60 RPM increments for HVAD and 200 for HMII). Brachial PI was calculated for each cardiac cycle by dividing the difference between minimum and maximum blood velocity by the time averaged mean blood velocity. LVAD device pulsatility indices that are used clinically were also recorded: maximal blood velocity (HVADVmax) and minimum blood velocity (HVADVmin) (HVAD) and HMIIPI (HMII). Relationships were evaluated using multilevel linear modeling with random intercepts and data are reported as mean±SE. RESULTS: Baseline RPMs were 2509±44 (HVAD) and 9220±75 (HMII). Brachial PI changed significantly across the range of LVAD RPM speeds tested (HVAD: 360; HMII: 1200), from 2.3±0.6 to 4.1±0.9 with the HVAD and from 1.8±0.6 to 3.6±1.0 with the HMII, with no differences in brachial PI between device across relative pump speed stages. Specifically, a 180 RPM decrease of the HVAD resulted in a 0.9±0.1 (37±4%) increase in brachial PI and a 600 RPM decrease in the HMII resulted in a 0.8±0.1 (38±3%) increase. These reductions in pump speed resulted in an ~20.0% fall in LVAD power consumption and a reduction in device reported blood flow of ~9%. Brachial PI correlated with HVAD HWVmax and HWVmin (r = 0.45 and r = -0.31, respectively), and HMII device HMIIPI (r = 0.73), suggesting device derived indices of PI provide a fair to good linear prediction of peripheral vascular pulsatility. CONCLUSION: Reducing HVAD or HMII LVAD pump speed within a clinically acceptable outpatient range yields a measurable and potentially clinically and physiologically meaningful change in peripheral vascular pulsatility, accompanied by substantial power savings.

Levitronix CentriMag Third-Generation Magnetically Levitated Continuous Flow Pump as Bridge to Solution

The Levitronix CentriMag (Levitronix LLC, Waltham, MA) ventricular assist device (VAD) is a magnetically levitated rotary pump designed for temporary extracorporeal support. Between February 2004 and May 2010, 42 consecutive adult patients were supported with Levitronix at our institution (32 men; age 62.3 ± 10.5 years, range: 31-76 years). Indications for support were (group A, n = 37) failure to wean from the cardiopulmonary bypass in the setting of postcardiotomy (n = 23), primary donor graft failure (n = 4), or right ventricular failure after axial left VAD (LVAD) placement (n = 10) and (group B, n = 5) refractory heart failure after acute myocardial infarction. The mean support time was 11.2 ± 6.8 days (range: 3-43 days) in group A and 8.6 ± 4.3 days (range: 5-11 days) in group B. In the postcardiotomy cohort (group A), 11 (47.8%) patients were weaned from support as all were supported graft failure patients. Eight patients of axial LVAD cohort were weaned from right VAD (RVAD). One patient was bridged to heart transplantation (Htx). Thirteen (35.1%) patients died on support in group A. In group B, one patient was bridged to Htx and four died on support. In overall population, bleeding requiring reoperation occurred in 15 (35.7%) cases and cerebral major events in four (9.5%). There were no device failures. Of the 23 (54.7%) patients who recovered and were discharged home, 20 (47.6%) are presently alive, and additionally, two patients of both groups who were bridged to Htx (overall n = 22, 52.3%). The Levitronix proved to be useful in patients previously considered nonsuitable for transplantation or long-term assist device. The device was technically easy to manage, and the results were encouraging.

Focused Review on Transthoracic Echocardiographic Assessment of Patients with Continuous Axial Left Ventricular Assist Devices

Left ventricular assist devices (LVADs) are systems for mechanical support for patients with end-stage heart failure. Preoperative, postoperative and comprehensive followup with transthoracic echocardiography has a major role in LVAD patient management. In this paper, we will present briefly the hemodynamics of axial-flow LVAD, the rationale, and available data for a complete and organized echocardiographic assessment in these patients including preoperative assessment, postoperative and long-term evaluation.