Effects of a fully magnetically levitated centrifugal-flow or axial-flow left ventricular assist device on von Willebrand factor: A prospective multicenter clinical trial

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Effects of a fully magnetically levitated centrifugal-flow or axial-flow left ventricular assist device on von Willebrand factor: A prospective multicenter clinical trial Aditya Bansal, MD,a Nir Uriel, MD,b Paolo C. Colombo, MD,c Keerthy Narisetty, MD,d James W. Long, MD, PhD,e Arvind Bhimaraj, MD,f Joseph C. Cleveland, Jr, MD,g Daniel J. Goldstein, MD,h John M. Stulak, MD,i Samer S. Najjar, MD,j David E. Lanfear, MD,k Eric D. Adler, MD,l Walter P. Dembitsky, MD,m Sami I. Somo, PhD,n Daniel L. Crandall, PhD,n Dong Chen, MD, PhD,i Jean Marie Connors, MD,o and Mandeep R. Mehra, MDo From the aOchsner Medical Center, New Orleans, Louisiana; bUniversity of Chicago School of Medicine and Medical Center, Chicago, Illinois; cColumbia University Medical Center, New York, New York; dBaptist Health Medical Center, Little Rock, Arkansas; eIntegris Baptist Medical Center, Oklahoma City, Oklahoma; fMethodist Hospital, Houston, Texas; g University of Colorado Hospital, Aurora, Colorado; hMontefiore Einstein Center for Heart and Vascular Care, Bronx, New York; iMayo Clinic, Rochester, Minnesota; jMedstar Washington Hospital Center, Washington, DC; kHenry Ford Hospital, Detroit, Michigan; lUniversity of California San Diego, La Jolla, California; mSharp Memorial Hospital, San Diego, California; nAbbott, Chicago, Illinois; and the oBrigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts.

KEYWORDS: left ventricular assist device; advanced heart failure; bleeding; HeartMate 3; von Willebrand factor

BACKGROUND: Increased shear stress conferred upon the circulation by continuous-flow pumps is associated with hemocompatibility-related adverse events, principally bleeding within the gastrointestinal system, and linked to the degradation of high-molecular-weight multimers (HMWMs) of von Willebrand factor (vWF). We evaluated the structure and functional characteristics of vWF HMWMs in patients with the fully magnetically levitated centrifugal-flow HeartMate 3 (HM3) and the continuous axial-flow HeartMate II (HMII) pump. Findings were correlated with bleeding events. METHODS: In a prospective, multicenter, comparative cohort study, 60 patients from the Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Support Therapy With HeartMate 3 Continued Access Protocol (NCT02892955) with an HM3 pump were compared with 30 randomly selected HMII patients from the PREVENtion of HeartMate II Pump Thrombosis study (NCT02158403) biobank. The primary end point was the difference in the normalized vWF HMWM ratio (ratio of the HMWMs to the intermediate- and low-molecular-weight multimers, normalized to pooled plasma from healthy volunteers) between the HM3 and the HMII pump at 90 days after implantation. Assay tests for vWF activity, vWF antigen, vWF activity to antigen ratio, coagulation factor VIII activity, and ADAMTS13 activity were measured by using standard protocols. Differences in

Reprint requests: Mandeep R. Mehra, MD, MSc, FRCP (London). Brigham and Women’s Hospital Heart and Vascular Center, 75 Francis Street, Boston, MA 02115. Telephone: 617-732-8534. Fax: 617-264-5265. E-mail address: [email protected]

See Related Editorial, page 817

1053-2498/$ - see front matter Ó 2019 The Author(s). Published by Elsevier Inc. on behalf of International Society for Heart and Lung Transplantation. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/) https://doi.org/10.1016/j.healun.2019.05.006

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these markers were compared in the context of clinical characteristics and correlated with adjudicated bleeding events within the HM3 group. RESULTS: Of 51 and 29 evaluable patients in the HM3 and HMII arms, respectively, those implanted with the HM3 pump exhibited greater preservation of the vWF HMWM ratio than those with the HMII pump at 90 days after implantation (54.1% vs 42.4%, p < 0.0001). Laboratory values for all vWF assays (antigen, activity, and coagulation factor VIII activity) remained within the normal functional range with no significant differences observed between the pumps at 90 days after implantation. At baseline, there was a decrease in the structural integrity of vWF HMWMs that correlated with increasing heart failure severity as measured by the Interagency Registry for Mechanically Assisted Circulatory Support profile. Multivariable modeling identified the HM3 pump as the only independent variable that determined post-implantation preservation of the structural integrity of vWF HMWMs. CONCLUSIONS: This prospective, multicenter comparative analysis study demonstrates that the fully magnetically levitated centrifugal-flow HM3 left ventricular assist device is associated with greater preservation of the structure of vWF HMWMs than the HMII mechanical bearing axial-flow pump. J Heart Lung Transplant 2019;38:806−816 Ó 2019 The Author(s). Published by Elsevier Inc. on behalf of International Society for Heart and Lung Transplantation. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/)

The advent of left ventricular assist devices (LVADs) for advanced heart failure was envisaged to provide pulsatile support to mimic human physiology. Such large profile devices possessed displacement chambers with valves to maintain pulsatile flow, which limited durability because of degeneration of the multiple moving parts.1 The introduction of smaller profile continuous-flow pumps with fewer moving parts conferred durability and greatly improved survival and quality of life, ensuring adoption into our clinical armamentarium.1 The paradigm shift of continuous flow was associated with an increase in shear stress upon circulating blood elements, a factor that marshaled emergence of hemocompatibility-related adverse events, principally signaled by the unique propensity for mucosal bleeding, particularly in the gastrointestinal (GI) system.2 Similar to the Heyde syndrome observed in aortic stenosis, a spate of GI bleeding associated with arteriovenous malformations ensued, and early investigations established a link between degradation of high-molecular-weight multimers (HMWMs) of von Willebrand factor (vWF) and the occurrence of low-grade hemolysis, markers that were correlated with bleeding and de novo pump thrombosis.3−5 Subsequent heart transplantation restored a physiological pulsatile circulatory state and also normalized the acquired von Willebrand syndrome (AvWS).4 Curiously, studies were unable to consistently connect the structural loss of vWF HMWMs with downstream functional abnormalities in standard quantitative ex vivo assessments of vWF activity. More recent studies have established the sheer complexity of the genesis of arteriovenous mucosal bleeding with the discovery of diverse pathways implicated in its development.6 The pattern of change in vWF HMWMs remains an important biomarker to arbitrate differences in rheology and hemocompatibility of distinctly engineered pumps. The HeartMate 3 (HM3; Abbott, Chicago, IL) centrifugal-flow LVAD has been developed to be a more hemocompatible pump that uses a frictionless magnetically levitated rotor programmed to create an intrinsic fixed pulse (to prevent blood stasis), all while housed in a low-profile intrathoracic frame that permits wide blood flow

pathways.7,8 These unique hybrid engineering characteristics were tested in the Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Support Therapy With HeartMate 3 (MOMENTUM 3) randomized study that compared the HM3 pump with the HeartMate II (HMII; Abbott) device, a continuous axialflow pump.9,10 The final results of this trial established a favorable hemocompatible profile for this pump by demonstrating near-elimination of pump thrombosis; a marked reduction in stroke of any type and severity; and a reduction in bleeding from any cause, including GI bleeding.11 An early single-center experience evaluating vWF HMWMs suggested greater preservation of vWF HMWMs with the HM3 pump than the HMII pump, but did not demonstrate a difference in functional attributes.12 Another investigation that compared the HM3 with the HVAD (Medtronic, Minneapolis, MN) centrifugal-flow pump also illustrated a greater preservation of the structural integrity of vWF in HM3 patients.13 Although important, these studies included selected patients at single centers and were not designed to evaluate clinical outcomes from bleeding. This investigation was undertaken with the following principal objectives: 1. To evaluate the preservation of the vWF HMWMs between the HM3 and HMII pumps at 90 days of pump support; 2. To assess the characteristics of vWF including antigen, functional activity, and coagulation factor VIII (FVIII) (which vWF carries and protects from rapid degradation in the circulation), between the HM3 and HMII pumps; and 3. To correlate clinical characteristics with changes in the vWF HMWMs and their association with outcomes related to bleeding complications.

Methods The completion of enrollment in the randomized phase of the MOMENTUM 3 study was followed by the Continued Access

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Protocol (CAP), a single arm, multicenter, prospective study conducted at 68 sites in the United States. Of all sites open to enrollment in the MOMENTUM 3 CAP study, 5 sites were selected to participate in the AvWS sub-study. Prospectively, 60 patients were entered into the sub-study for analysis of AvWS (the HM3 arm). Citrated plasma samples were collected at baseline (within 14 days before LVAD implantation) and at 90 days after implantation. To compare the HM3 with the HMII pump, we used a biobank from the PREVENtion of HeartMate II Pump Thrombosis (PREVENT) study, which was a prospective, multicenter trial that enrolled 300 patients from 23 centers and evaluated the adoption of practices aimed at reducing pump thrombosis by standardizing the surgical implant technique, maintaining controlled LVAD speeds and anti-coagulation.14 To develop the comparison HMII arm, patients were enrolled from within the PREVENT study among those with 3 citrate samples available in the biobank at baseline (taken 7 days before implantation) and at 90 days after implantation. These patients were ordered by ascending study identifier and random numbers from 1 to 174 were generated until 30 unique patients had been selected. The list of centers that participated in the study are included in the Appendix (available online at www.jhltonline.org). Both the MOMENTUM 3 CAP and PREVENT studies excluded patients with ongoing mechanical circulatory support (except the use of an intra-aortic balloon pump) at baseline. Institutional Review Board approval was obtained for all centers, and informed consent was obtained from all patients before device implantation for both the MOMENTUM 3 CAP study (NCT 02892955) and the PREVENT study (NCT 02158403). The prospectively established primary end point for the study was a comparison of the differences in the normalized vWF HMWM ratio (ratio of the HMWMs to the intermediateand low-molecular-weight multimers, normalized to pooled plasma from healthy volunteers) between the HM3 and the HMII pump at 90 days after implantation. The secondary end points included characterization of the quantitative vWF properties (described subsequently) over time and the relationship to clinical outcomes and adverse events. Adverse event data (definitions available in the Supplementary Material online) in the MOMENTUM 3 CAP study were collected through an electronic data capture system and adjudicated by an independent clinical events committee. To analyze bleeding, HM3 patients were categorized based on incidence of major bleeding of any type, GI bleed, or a non-surgical major bleed. Surgical bleeds were defined as bleeds adjudicated as perioperative or post-procedural bleeding, mediastinal bleeds, or bleeding relating to the surgical site. Multimer and vWF properties were assessed, as detailed subsequently, for each group of patients and compared with patients who were free of any type of major bleeding event.

Plasma vWF multimer analysis Plasma vWF multimers were analyzed by using an intermediate resolution discontinuous electrophoretic agarose gel system with in-gel immunostaining, and near-infrared fluorescent images were acquired and processed by using an Odyssey imaging system (LICOR Biosciences, Lincoln, NE). Quantification of loss of HMWMs involved scanning of the raw fluorescent intensity of patients’ gels by using an Odyssey Infrared Imager version 2.0 (LI-COR Biosciences). Bands 2−15 were defined as low- and intermediatemolecular-weight multimers, and HMWM bands were defined as band 16 and above, as previously described. The first band was not included in the analysis because of potential artifact distortion. The ratio of HMWMs to intermediate- and low-molecular-weight multimers was recorded as a continuous variable for the sample and

control plasma within the same gel. The normalized vWF HMWM ratio was obtained by using the ratio of the HMWMs in the patient sample to the control plasma (Figure 1).15,16

vWF quantitative analysis HemosIL latex immunoassays (LIAs) (Instrumentation Laboratory, Lexington, MA) with 2 ACL TOP coagulation system analyzer kits (Beckman Coulter, Brae, CA) were used to measure plasma vWF antigen (vWF:Ag) and plasma vWF activity (vWF: Act LIA), following manufacturer’s instructions. vWF:Ag measures the protein level of vWF in plasma, whereas the vWF:Act LIA measures the ability to bind platelet glycoprotein Ib utilizing an automated latex particle-enhanced immunoturbidimetric assay. The normal range for vWF:Ag and vWF:Act LIA is 55%−200%. The ratio of vWF activity to the antigen is a comparison of the platelet binding activity with the protein concentration, most frequently used to characterize congenital forms of von Willebrand disease. Values <0.7 are indicative of decreased functional activity compared with antigen concentration. FVIII activity was measured by a one-stage clot-based assay using the ACL TOP 500 (Instrumentation Laboratory). FVIII is an intrinsic pathway of coagulation factor. The circulating half-life is increased from 24 minutes to 24 hours by binding to vWF. FVIII levels are reduced in patients with no or decreased levels of vWF antigen or with defects in the vWF FVIII binding site. ADAMTS13 activity was measured by using a LIFECODES ATS-13 Activity Assay Kit (Immucor, Peachtree Corners, GA) on a Biomek analyzer (Beckman Coulter) and read by a Paradigm Microplate Reader (Molecular Devices, San Jose, CA). ADAMTS13 cleaves vWF that has been unfolded because of shear stress, which exposes the ADAMTS13 cleavage site. Higher-molecular-weight multimeric chains of vWF are more biologically active with regard to vWF-mediated platelet adhesion and aggregation.17

Statistical analysis Statistical analyses were performed by using SAS software, version 9.4 (SAS Institute, Cary, NC) or SigmaPlot, version 12.5 (Systat Software Inc, San Jose, CA). The primary end point was assessed by a single-tailed Wilcoxon rank-sum test with p < 0.025 considered statistically significant between the HM3 and HMII arm at 90 days after implantation. For baseline characteristics, categorical variables are reported as proportions and were compared between groups with Fisher’s exact test or chi-square test, whereas continuous data are reported as mean § standard deviation or median (quartile 1 [Q1]−quartile 3 [Q3]) and compared between groups with the Student t-test or Wilcoxon rank-sum test, as appropriate. Differences were considered statistically significant at p < 0.05. The boxes of the box and whisker plots represent Q1 and Q3, the 75th and the 25th percentiles, respectively. The median is given as lines, and the whiskers illustrate the 5th−95th percentile. Multivariable linear regression models, using results from univariable linear regression as entry criteria (any factor on univariate analysis at p ≤ 0.10 was entered into the multiple regression model) of the effect of baseline demographics and clinical characteristics on vWF HMWMs prediction at baseline and, separately, at 90 days, were generated. The variables entered into the baseline univariable regression model included the following: age, sex, race, Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) profile, intended goal of treatment, ischemic etiology, body surface area, variables indicative of liver and

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Figure 1 Analysis of multimeric content via gel electrophoresis. Bands 2−15 were classified as low- and intermediate-molecular-weight multimers, and those >15 as HMWMs. The vWF HMWM ratio was calculated for an individual band as the ratio of the fluorescent intensity of HMWMs to the low and intermediate multimers. To account for variability between gels, the normalized vWF HMWM ratio was calculated as the ratio of the patient vWF HMWM ratio and normal pooled plasma vWF HMWM ratio. HMWM, high-molecular-weight multimer; vWF, von Willebrand factor. kidney function (blood urea nitrogen, creatinine, estimated glomerular filtration rate [eGFR], ALT, AST, and total bilirubin), history of disease and surgical procedures, arterial blood pressures (systolic, diastolic, and mean arterial pressure), and laboratory values (platelets, hemoglobin, and lactate dehydrogenase). All variables entered in the baseline model were included in a separate model evaluating effects on vWF HMWMs at 90 days after implantation, with an additional factor of treatment by pump type (HM3 vs HMII). Based on the results of the univariable analysis, the following variables were entered into the baseline multivariable model: age, INTERMACS profile, mean arterial pressure, eGFR, and platelets; and the following were entered into the 90day model: pump type, age, AST, creatinine, blood urea nitrogen, diastolic pressure, body surface area, and prevalence of diabetes.

Results Patients Of the 60 patients enrolled in the HM3 arm, 51 patients had vWF data at baseline and 90 days after implantation. For the HMII arm, of 30 patients, 29 had multimer data at both time points. A consort diagram is provided in Figure 2. A comparison of baseline demographics and clinical characteristics of patients implanted with HM3 or HMII is shown in Table 1. There were no women within the HMII group in this analysis, a result

of the random sampling from the biorepository, whereas 20% of the HM3 arm were women.

Primary end point: vWF HMWMs analysis Assessment of vWF HMWMs degradation is shown in Figure 3. In the primary end point analysis, patients with HM3 demonstrated better preservation of vWF HMWMs, with 30% more vWF HMWMs at 90 days than those with HMII (median [Q1−Q3]; 54.1% [48.0%−60.8%] vs 42.4% [36.5%−46.0%], p < 0.0001). There was no difference in vWF HMWMs between patients with HM3 and HMII at baseline (82.4% [72.4%−91.8%] vs 84.9% [75.8%−94.8%], p = 0.40). Both pumps exhibited degradation of vWF HMWMs from baseline at 90 days. Patients with HM3 had a decrease in vWF HMWMs of 28.3% after 90 days of LVAD support (from 82.4% [72.4%−91.8%] to 54.1% [48.0%−60.8%], p < 0.0001), compared with a 42.5% decrease in vWF HMWMs (from 84.9% [75.8%−94.8%] to 42.4% [36.5%−46.0%], p < 0.0001) in patients with HMII.

Assay results The vWF:Ag, vWF:Act LIA, and ratio of activity to antigen are depicted in Figure 4. Patients with the HMII and patients with the HM3 both had vWF:Ag and vWF:Act LIA

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Figure 2 An overview of patient enrollment and follow-up in the MOMENTUM 3 CAP sub-study and evaluations from the PREVENT biobank. Evaluable population consisted of patients with vWF HMWMs data analyzed at baseline and 90 days after implantation. CAP, Continued Access Protocol; HMWM, high-molecular-weight multimer; MOMENTUM 3, Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Support Therapy With HeartMate 3; PREVENT, PREVENtion of HeartMate II Pump Thrombosis; vWF, von Willebrand factor.

in the normal range at baseline and at 90 days. Although patients with HMII had similar values of vWF:Ag at baseline and 90 days (median [Q1−Q3]; 211% [185%−296%] vs 213% [140%−253%], p = 0.36), patients with HM3 were noted to have a decrease in vWF:Ag from baseline to 90 days (211% [175%−287%] vs 185% [165%−224%], p = 0.006). Although values remained in the high end of the normal range for patients with HM3, this decrease could indicate a decrease in inflammatory status, as vWF levels increase with inflammation and stress (Figure 4a). vWF:Act LIA decreased from baseline to 90 days with both pumps (HM3: 180% [146%−236%] vs 138% [118%−162%], p < 0.0001; HMII: 206% [158%−250%] vs 164% [103% −193%], p = 0.009) to, generally, within upper end of the normal range (55%-200%) (Figure 4b). Similar trends were observed for the activity to antigen ratio from baseline to 90 days after implantation (HM3: 0.83 [0.76−0.89] vs 0.74 [0.70−0.81], p < 0.0001; HMII: 0.91 [0.84−0.94] vs 0.76 [0.72−0.80], p < 0.0001) (Figure 4c). Comparison of 90-day

post-implantation vWF antigen, vWF activity, and ratio of activity to antigen between HM3 and HMII did not yield any statistical difference. FVIII for HM3 and HMII is illustrated in Figure 5. There was a decrease in FVIII from baseline to 90 days after implantation for both pumps (HM3: 203% [155%−263%] vs 169% [140%−204%], p = 0.009; HMII: 194% [158% −278%] vs 173% [122%−210%], p = 0.03). However, by 90 days, the values for FVIII were maintained within or above the normal functional range. There was an increasing trend in the proportion of patients with normal ADAMTS13 activity (≥70%) from baseline to 90 days after implantation for both pumps (HM3: n = 42/51 (82.4%) vs n = 49/51 (96%), p = 0.05; HMII: n = 21/29 (72.4%) vs n = 27/29 (93.1%), p = 0.08) (Supplementary Table S1 online). Therefore, ADAMTS13 activity did not appear to be responsible for differences in the observed preservation of the HMWMs with the HM3 pump.

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Baseline Characteristics of the HM3 and HMII Groups

Age, years Male, % (no.) Race or ethnic group, % (no.) White Black Asian Other Destination therapy, % (no.) INTERMACS profile, % (no.) INTERMACS - Profile 1−2 INTERMACS - Profile 3−4 Body surface area, m2 Ischemic etiology, % (no.) History of atrial fibrillation, % (no.) History of Stroke, % (no.) Diabetes, % (no.) History of valve replacement or repair, % (no.) Left ventricular ejection fraction, % Arterial blood pressure, mm Hg Systolic Diastolic Mean arterial pressure BUN, mg/dl Creatinine, mg/dl eGFR, ml/min/1.73 m2 Platelets, 103/ml Hemoglobin, g/dl ALT, U/liter AST, U/liter Total bilirubin, mmol/liter LDH, U/liter

HM3(n = 51)

HMII(n = 29)

p-valuea

60.5 § 11.9 80.4% (41/51)

57.2 § 15.9 100.0% (29/29)

0.55 0.01

66.7% (34/51) 27.5% (14/51) 2.0% (1/51) 3.9% (2/51) 86.3% (44/51)

65.5% (19/29) 27.6% (8/29) 3.4% (1/29) 3.4% (1/29) 75.9% (22/29)

1.0

43.1% (22/51) 56.9% (29/51) 2.04 § 0.24 45.1% (23/51) 37.3% (19/51) 7.8% (4/51) 35.3% (18/51) 3.9% (2/51) 16.4 § 5.3

24.1% (7/29) 75.9% (22/29) 2.20 § 0.24 48.3% (14/29) 31.0% (9/29) 10.3% (3/29) 55.2% (16/29) 6.9% (2/29) 19.2 § 9.0

0.006 0.78 0.58 0.70 0.08 0.62 0.29

111.8 § 15.1 68.0 § 10.5 83.5 § 10.6 26.2 § 11.1 1.36 § 0.31 57.8 § 19.3 197.5 § 60.8 11.5 § 1.9 41.5 § 73.6 31.7 § 30.8 1.01 § 0.51 281.7 § 107.8 (n = 47)

108.8 § 16.3 63.7 § 9.1 82.8 § 9.5 33.8 § 16.6 1.47 § 0.51 60.1 § 22.1 210.3 § 63.3 11.1 § 2.8 68.6 § 175.3 52.1 § 97.9 1.13 § 0.69 351.3 § 365.9 (n = 26)

0.42 0.06 0.76 0.06 0.62 0.64 0.38 0.51 0.43 0.29 0.54 0.79

0.24 0.09

Abbreviations: ALT, Alanine Aminotransferase; AST, Aspartate Aminotransferase; BUN, blood urea nitrogen; eGFR, estimated glomerular filtration rate; HM3, HeartMate 3; HMII, HeartMate II; INTERMACS, Interagency Registry for Mechanically Assisted Circulatory Support; LDH, lactate dehydrogenase Data are reported as mean § standard deviation, unless otherwise noted. a Data were compared between groups by using t-test, Wilcoxon rank-sum test, or Fisher’s exact test/chi-square test, as appropriate

Clinical outcomes in the HM3 arm All patients (n = 60) in the HM3 arm were followed for at least 365 days or until outcome (death, n = 3; transplant, n = 4). Three patients expired on day 19, 46, and 239 after implantation because of right heart failure, hemorrhagic stroke, and cancer, respectively. Bleeding of any type occurred in 43% (n = 26, 68 events) of patients, of which 54% (n = 14, 33 events) were GI bleeding; 8 patients experienced surgical bleeding. Baseline demographics and clinical characteristics of patients with bleeding of any type, GI bleed, and nonsurgical bleed compared with those who did not bleed are shown in Supplementary Table S2 online. The no bleeding group had a lower prevalence of diabetes than the bleeding groups. Kidney function was reduced in patients with any bleeding event (mean § standard deviation; creatinine: 1.26 § 0.3 vs 1.47 § 0.29, p = 0.01; eGFR: 64.0 § 20.3 vs 50.8 § 15.7, p = 0.003) and patients with non-surgical bleeding events (creatinine: 1.26 § 0.3 vs 1.46 § 0.30, p = 0.02; eGFR: 64.0 §

20.3 vs 51.8 § 16.5, p = 0.007), but not in patients with GI bleeding events (creatinine: 1.26 § 0.3 vs 1.40 § 0.32, p = 0.20; eGFR: 64.0 § 20.3 vs 57.7 § 18.1, p = 0.18). Preservation of vWF HMWMs was not associated with decreased pump speeds (Supplementary Figure S1 online), lactate dehydrogenase elevation (Supplementary Figure S2 online), or medical management with angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers (Supplementary Figure S3 online).

Biomarker findings and bleeding in the HM3 arm Baseline differences in the vWF HMWM ratio were noted between those that developed any bleeding event, GI bleeding, or non-surgical bleeding episodes (Figure 6a). Similarly, significant differences were observed at 90 days after implantation in the vWF HMWM ratio between those without bleeding and those that suffered bleeding episodes of any type or non-surgical bleeding (Figure 6b). Significance

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Figure 3 Preservation of vWF HMWMs expressed as a percentage of normalized vWF HMWM ratio in the primary end point analysis (at 90 days after implantation) and longitudinal assessments between pumps. The HM3 pump preserves vWF HMWMs compared with the HMII. HM3, HeartMate 3; HMII, HeartMate II; HMWM, high-molecular-weight multimer; vWF, von Willebrand factor.

for GI bleeding alone was not achieved at the 90-day point because of the presence of a beta error (Type II). Importantly, no differences in quantitative vWF values—vWF: Ag, vWF:Act LIA, or vWF:Act LIA/vWF:Ag—were noted between the stratified bleeding groups at baseline or 90 days after implantation (Supplementary Table S3 online).

90 days after implantation The results of the univariable modeling to predict vWF HMWMs at 90 days after implantation is shown in Supplementary Table S6 online. The multivariable analysis confirmed that the preservation of vWF HMWM ratio is driven by the selection of the HM3 pump (p = 0.001, Table 2). The overall model significance was p < 0.001.

Multivariate model: Baseline and 90-days analysis Baseline Exploratory univariable modeling of clinical demographic and characteristic effects on baseline vWF HMWM structure in the combined HM3 and HMII groups is shown in Supplementary Table S4 online. The results of the multivariable model (Supplementary Table S5 online) shows that INTERMACS profile 1−2 was negatively correlated with the baseline vWF HMWM ratio. Specifically, INTERMACS 1−2 patients had reduced baseline vWF HMWMs compared with INTERMACS profile 3−4 patients (p = 0.04; overall model significance: p = 0.001). No other variables were significantly correlated with baseline vWF HMWMs profiles. Importantly, a comparison of baseline vWF HMWMs between patients with existence of an intra-aortic balloon counterpulsation pump (15/51 in the HM3 group and 4/29 in the HMII group) and those without did not yield any significant differences (median, Q1−Q3; HM3: 78.6 [68.1−96.2] [n = 15] vs 84.9 [72.6−91.5] [n = 36], p = 0.64; HMII: 88.5 [76.4−98.4] [n = 4] vs 84.9 [75.8−94.8] [n = 25], p = 0.68).

Discussion In this prospective, multicenter, comparative cohort clinical trial we assessed the differences in the normalized vWF HMWM ratio, vWF activity, vWF antigen, vWF activity to antigen ratio, FVIII, and ADAMTS13 between HM3 and HMII pumps and studied these changes in the context of clinical outcome. Our study reveals several principal findings. First, with respect to the primary end point of the trial at 90 days, we found that the HM3 pump is associated with a significantly greater preservation in the structure of vWF HMWMs than is the HMII device. Second, we demonstrated that patients with advanced heart failure at baseline exhibit degradation in the structure of vWF HMWMs, a finding related to the severity of pre-implant heart failure, which is not affected by the presence of an intra-aortic balloon counterpulsation device. Third, we determined that quantitative values for vWF antigen and activity decrease from baseline to 90 days but exhibit no significant differences between the 2 device groups, and generally remain within ranges considered functionally normal. This is true for the protein level of vWF (vWF:Ag) in plasma as well as the binding capacity of the vWF−platelet glycoprotein Ib

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Figure 4 Plasma concentrations of (A) vWF:Ag, (B) vWF:Act LIA, and (C) vWF:Act LIA/vWF:Ag ratio. Reduction is observed for all functional assays from baseline to 90 days after implantation. Act, activity; Ag, antigen; LIA, latex immunoassay; vWF, von Willebrand factor.

binding domain, which is measured by vWF:Act LIA. Furthermore, FVIII, which is carried to its effector site by vWF, also remains within the functionally normal range. Finally, despite the absence of functional differences, structural alterations in vWF (encountered at the pre-implantation phase as well as at 90 days after implantation) are closely correlated with episodes of any bleeding and nonsurgical bleeding. The state of advanced heart failure is associated with a low pulse pressure and a circulation characterized by an increase in shear stress and systemic inflammation.18 Our study demonstrates a loss in vWF HMWMs early in the pre-implantation phase when compared with the normal state, and this finding is correlated with increasing severity of heart failure (worse in those with unstable heart failure: INTERMACS 1−2 profile). Because the inclusion criteria did not allow the use of temporary mechanical support devices other than support with an intra-aortic balloon counterpulsation pump (the use of which did not alter the baseline vWF HMWM ratio), these changes reflect the

abnormal pathophysiology of heart failure. In an intriguing study, Patel and colleagues19 demonstrated that patients with heart failure with reduced systolic function and those implanted with continuous-flow pumps exhibited a high prevalence of hypervascularity of the nasal mucosa (a surrogate for arteriovenous malformations in mucosal sites) and differed only in their severity grade (higher in the LVAD group). This finding supports the contention that the substrate for subsequent mucosal bleeding is present at the time of pump implantation in many patients and is likely compounded by the introduction of the altered circulatory physiology conferred by the LVAD. Our study then further suggests that the HM3 pump is more forgiving than the HMII pump on destruction of vWF structure, a biomarker difference that supports the observed improvement in hemocompatibility-related adverse events in clinical experience. Despite an improvement in bleeding complications with the HM3 pump, the rates of such complication remain elevated, and there is a need to continually focus on efforts to address the proclivity for these complications. Efforts to

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Figure 5 FVIII for the HM3 and HMII pumps. FVIII reduced from baseline to 90 days after implantation for both pumps; values were within normal range. Samples’ specific interference data points were excluded from the analysis. FVIII, coagulation factor VIII; HM3, HeartMate 3; HMII, HeartMate II.

Figure 6 vWF HMWMs in stratified bleeding groups at (A) baseline and (B) 90 days after implantation. Statistical differences were observed between the no bleeding and bleeding groups at baseline and 90 days post-implantation. HMWM, high-molecular-weight multimer; vWF, von Willebrand factor.

address lower intensity anti-coagulation or to carefully evaluate the need for anti-platelet agents with the HM3 pump will be needed.20,21 The dissonance between structural alterations, which show convincing differences between the distinctly engineered pumps, and preservation of functional characteristics in the vWF pathway warrants further discussion. Although the vWF HMWMs are degraded differentially, it is possible that the remaining multimers and those in the intermediate and low category are sufficient to maintain the normal functional characteristics of the molecule, at least in

the context of the ex vivo assays utilized in this study. Similarly, despite the decrease in the vWF HMWMs, there appears to be sufficient carrying capacity retained for FVIII. It is also possible that the maintenance of functional characteristics in the normal range may reflect inflammation that accompanies implantation of the pump, and although we cannot be certain of its implications, it is more likely that the discrepant effects simply reflect the fact that the structural alteration in vWF may represent a marker of risk rather than a factor with direct causative inference for bleeding events. Evidence for this contention comes from

Bansal et al.

vWF degradation in centrifugal-flow or axial-flow LVADs

Table 2 Multivariable Analysis of vWF HMWMs 90 Days after Implantation Covariate

Coefficient

vWF HMWM

p-valuea

Pump (HM3 vs HMII) AST Creatinine BUN Diastolic pressure Body surface area Age Diabetes

0.0873 ¡ ¡ ¡ ¡ ¡ ¡ ¡

"(Preserves) ¡ ¡ ¡ ¡ ¡ ¡ ¡

0.001 0.37 0.31 0.79 0.18 0.28 0.13 0.37

Abbreviations: AST, aspartate transaminase; BUN, blood urea nitrogen; HM3, HeartMate 3; HMII, HeartMate II; HMWM, high-molecularweight multimer; vWF, von Willebrand factor a Model p-value < 0.001

several sources, including the findings of pre-existing arteriovenous malformations at the time of implantation, as described earlier, and pathways in angiogenesis that are upregulated independent of the vWF system after implantation with continuous-flow LVADs. Tabit and colleagues6 have pointed to deregulation of an angiogenic factor, angiopoietin-2, which in turn is associated with increased angiogenesis and higher non-surgical bleeding rates in patients supported with continuous-flow devices. Other studies have suggested a modulatory effect of exposure to anti-cytokine −based therapy; anti-inflammatory agents such as fish oil; pharmacological modulators of the renin-angiotensin-aldosterone axis; and even old drugs such as digoxin, an inhibitor of hypoxia inducing factor-1a synthesis, on the angiogenesis pathway.22−27 We were unable to confirm a direct link between preservation of vWF HMWMs and use of anti-hypertensive therapy with either angiotensin-converting enzyme inhibitors or angiotensin receptor blockers in this analysis. Although these lines of evidence remain anecdotal, they do emphasize the complexity in the emergence of mucosal bleeding complications that are not solely determined through singular pathways such as vWF. Nevertheless, we now add to the literature confirming the utility of vWF as a sensitive marker for the change in circulatory physiology with different LVADs. This study is not randomized and enrolled patients from 2 separate, but contemporaneous, studies that resulted in baseline imbalances, particularly in gender. We do not believe that these distinctions reduce the validity of our findings for several reasons. The PREVENT study was performed to establish practices that resulted in the lowest rates of complications with the HMII pump because close attention to pump speeds, surgical technique for pump placement, and strict attention to anti-coagulation was maintained. Thus, we compared the outcomes of the HM3 pump arm to a homogenous group of well-treated patients with the HMII pump who were less ill than the HM3 cohort. Next, we controlled for any differences in baseline factors by developing a multivariable model that independently confirmed the findings of the greater preservation of vWF HMWMs with the HM3 pump after controlling for age,

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gender, severity of illness at baseline, and other demographic differences. Furthermore, in comparison with prior studies, this represents 2 prospective multicenter trials, MOMENTUM 3 and PREVENT, and the analyses were performed independently and in a manner blinded to the patient characteristics with clinical events (in the HM3 arm) that were independently adjudicated.

Conclusions This prospective, multicenter comparative cohort study demonstrates that the fully magnetically levitated centrifugal-flow HM3 LVAD is associated with a greater preservation of vWF HMWMs than the HMII, a mechanical bearing continuous axial-flow pump. We also find that the state of advanced heart failure at baseline establishes the conditions for alterations in the structure of vWF, which are then further compounded following implantation of LVADs, likely contributing to bleeding complications. We confirm that changes in vWF may serve as a biomarker for the alterations observed in the circulatory (patho)physiology with continuous-flow LVADs and subsequent bleeding.

Disclosure statement AB is a consultant and recipient of research grants from Abbott and TandemLife and on the Advisory board for TandemLife. NU is a consultant and received research grants from Abbott and Medtronic. PCC is a consultant (without honoraria) and received research grants from Abbott. KN has no conflicts to disclose. JWL is an educator for Abbott. AB is a consultant for Abbott. JCC received institutional research grants from Abbott. DJG is a proctor and educator for Abbott; has received travel from support Abbott; and is a consultant for Terumo Inc. JS has no conflicts to disclose. SSN is a consultant and recipient of research grants from Abbott and Medtronic. DEL is a consultant for Abbott Diagnostics (Clinical events committee for biomarker trial) Abiomed, Amgen (trial steering committee), and DCRI (Novartis) and has research grants from Amgen, Bayer, and Novartis. EDA is a consultant for Medtronic and a speaker for Abbott. WD received research support from Abbott. SIS and DLC are employees of Abbott. DC received grants from Abbott. JMC is a consultant for Abbott. MRM is a consultant for Abbott (fees paid to Brigham and Women’s Hospital), Portola, Bayer, and Xogenex; a trial steering committee member for Medtronic and Janssen; a scientific advisory board member for NupulseCV and FineHeart; and a DSMB member for Mesoblast. Dr. Mehra also reports that he is editor-in-chief of the Journal of Heart and Lung Transplantation and these findings must not be considered to represent the official stance of the journal nor the society that it represents, the ISHLT. This study was funded by Abbott, USA.

Supplementary data Supplementary data associated with this article can be found in the online version at www.jhltonline.org/.

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Supplementary materials Supplementary material associated with this article can be found in the online version at https://doi:10.1016/j.hea lun.2019.05.006.

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