Clinical experience with 111 thoratec ventricular assist devices

Weaning from ventricular assist device support after recovery from left ventricular failure with or without secondary right ventricular failure

Although complete myocardial recovery after ventricular assist device (VAD) implantation is rather seldom, systematic search for recovery is worthwhile because for recovered patients weaning from VADs is feasible and can provide survival benefits with long-term freedom from heart failure (HF) recurrence, even if a chronic cardiomyopathy was the primary cause for the drug-refractory HF necessitating left ventricular (LVAD) or biventricular support (as bridge-to-transplantation or definitive therapy) and even if recovery remains incomplete. LVAD patients explanted for myoacardial recovery compared to those transplanted from LVAD support showed similar survival rates and a significant proportion of explanted patients can achieve cardiac and physical functional capacities that are within the normal range of healthy controls. In apparently sufficiently recovered patients, a major challenge remains still the pre-explant prediction of the weaning success which is meanwhile reliably possible for experienced clinicians. In weaning candidates, the combined use of certain echocardiography and right heart catheterization parameters recorded before VAD explantation can predict post-weaning cardiac stability with good accuracy. However, in the absence of standardization or binding recommendations, the protocols for assessment of native cardiac improvement and also the weaning criteria differ widely among centers. Currently there are still only few larger studies on myocardial recovery assessment after VAD implantation. Therefore, the weaning practice relies mostly on small case series, local practice patterns, and case reports, and the existing knowledge, as well as the partially differing recommendations which are based mainly on expert opinions, need to be periodically systematised. Addressing these shortcomings, our review aims to summarize the evidence and expert opinion on the evaluation of cardiac recovery during mechanical ventricular support by paying special attention to the reliability of the methods and parameters used for assessment of myocardial recovery and the challenges met in both evaluation of recovery and weaning decision making.

Recovery of failing hearts by mechanical unloading: Pathophysiologic insights and clinical relevance

By reduction of ventricular wall-tension and improving the blood supply to vital organs, ventricular assist devices (VADs) can eliminate the major pathophysiological stimuli for cardiac remodeling and even induce reverse remodeling occasionally accompanied by clinically relevant reversal of cardiac structural and functional alterations allowing VAD explantation, even if the underlying cause for the heart failure (HF) was dilated cardiomyopathy. Accordingly, a tempting potential indication for VADs in the future might be their elective implantation as a therapeutic strategy to promote cardiac recovery in earlier stages of HF, when the reversibility of morphological and functional alterations is higher. However, the low probability of clinically relevant cardiac improvement after VAD implantation and the lack of criteria which can predict recovery already before VAD implantation do not allow so far VAD implantations primarily designed as a bridge to cardiac recovery. The few investigations regarding myocardial reverse remodeling at cellular and sub-cellular level in recovered patients who underwent VAD explantation, the differences in HF etiology and pre-implant duration of HF in recovered patients and also the differences in medical therapy used by different institutions during VAD support make it currently impossible to understand sufficiently all the biological processes and mechanisms involved in cardiac improvement which allows even VAD explantation in some patients. This article aims to provide an overview of the existing knowledge about VAD-promoted cardiac improvement focusing on the importance of bench-to-bedside research which is mandatory for attaining the future goal to use long-term VADs also as therapy-devices for reversal of chronic HF.

Numerical Simulation and Experimental Validation of Swirling Flow in Spiral Vortex Ventricular Assist Device

Spiral Vortex Ventricular Assist Device (SV-VAD) supports cardiac patients with refractory heart failure. Unfortunately, thrombus formation and risk of stroke due to flow complications may lead to aggravated conditions. The hemodynamics of a continuous flow in the ventricular chamber of a SV-VAD can be analyzed using numerical simulation. Particle image velocimetry and laser Doppler anemometry are utilized for validating the simulated spiral flow in a transparent acrylic SV-VAD replica based on its cross-sectional averaged axial and tangential velocities. After validation, the relationship between swirling flow and blood cell damage is established by evaluating flow effect on thrombosis due to high shear stress. Based on our analysis, stagnancy of the flow within the SV-VAD is insignificant and its low shear stress minimizes hemolysis.

Acquired coagulopathy in patients with left ventricular assist devices

Chronic heart failure (HF) is a major emerging healthcare problem, associated with a high morbidity and mortality. Left ventricular assist devices (LVADs) have emerged as a successful treatment option for patients with end-stage HF. Despite its great benefit, the use of LVAD is associated with a high risk of complications. Bleeding, pump thrombosis and thromboembolic events are frequently observed complications, with bleeding complications occurring in over a third of the patients. Although the design of the third-generation LVAD has improved greatly, these hemostatic complications still occur. The introduction of an LVAD into the circulatory system results in an altered hematological balance as a consequence of blood-pump interactions, changes in hemodynamics, the rheology, and the concomitant need for anticoagulation while implanted with an LVAD. The majority, if not all, LVAD patients experience a form of platelet dysfunction and impaired von Willebrand factor activity, leading to acquired coagulopathy disorders. Different diagnostic tools and treatment strategies have been reported; however, they require validation in LVAD patients. The present review focuses on acquired coagulopathies, describing the incidence, impact and underlying mechanism of acquired coagulopathy disorders in patients supported by LVADs. In addition, we will discuss diagnostic and management strategies for these acquired coagulopathies.

Toward the Virtual Benchmarking of Pneumatic Ventricular Assist Devices: Application of a Novel Fluid-Structure Interaction-Based Strategy to the Penn State 12 cc Device

The pediatric use of pneumatic ventricular assist devices (VADs) as a bridge to heart transplant still suffers for short-term major complications such as bleeding and thromboembolism. Although numerical techniques are increasingly exploited to support the process of device optimization, an effective virtual benchmark is still lacking. Focusing on the 12 cc Penn State pneumatic VAD, we developed a novel fluid-structure interaction (FSI) model able to capture the device functioning, reproducing the mechanical interplay between the diaphragm, the blood chamber, and the pneumatic actuation. The FSI model included the diaphragm mechanical response from uniaxial tensile tests, realistic VAD pressure operative conditions from a dedicated mock loop system, and the behavior of VAD valves. Our FSI-based benchmark effectively captured the complexity of the diaphragm dynamics. During diastole, the initial slow diaphragm retraction in the air chamber was followed by a more rapid phase; asymmetries were noticed in the diaphragm configuration during its systolic inflation in the blood chamber. The FSI model also captured the major features of the device fluid dynamics. In particular, during diastole, a rotational wall washing pattern is promoted by the penetrating inlet jet with a low-velocity region located in the center of the device. Our numerical analysis of the 12 cc Penn State VAD points out the potential of the proposed FSI approach well resembling previous experimental evidences; if further tested and validated, it could be exploited as a virtual benchmark to deepen VAD-related complications and to support the ongoing optimization of pediatric devices.

Mechanistic insight of platelet apoptosis leading to non-surgical bleeding among heart failure patients supported by continuous-flow left ventricular assist devices

Non-surgical bleeding (NSB) is the most common clinical complication in heart failure (HF) patients supported by continuous-flow left ventricular assist devices (CF-LVADs). In this study, oxidative stress and alteration of signal pathways leading to platelet apoptosis were investigated. Thirty-one HF patients supported by CF-LVADs were divided into bleeder (n = 12) and non-bleeder (n = 19) groups. Multiple blood samples were collected at pre-implant (baseline) and weekly up to 1-month post-implant. A single blood sample was collected from healthy subjects (reference). Production of reactive oxygen species (ROS) in platelets, total antioxidant capacity (TAC), oxidized low-density lipoproteins (oxLDL), expression of Bcl-2 and Bcl-xL, Bax and release of cytochrome c (Cyt.c), platelet mitochondrial membrane potential (Δψ _m), activation of caspases, gelsolin cleavage and platelet apoptosis were examined. Significantly elevated ROS, oxLDL and depleted TAC were evident in the bleeder group compared to non-bleeder group (p < 0.05). Platelet pro-survival proteins (Bcl-2, Bcl-xL) were significantly reduced in the bleeder group in comparison to the non-bleeder group (p < 0.05). Translocation of Bax into platelet mitochondria membrane and subsequent release of Cyt.c were more prevalent in the bleeder group. Platelet mitochondrial damage, activation of caspases, gelsolin cleavage, and ultimate platelet apoptosis in the bleeder group were observed. Oxidative stress and activation of both intrinsic and extrinsic pathways of platelet apoptosis may be linked to NSB in CF-LVAD patients. Additionally, biomarkers of oxidative stress, examination of pro-survivals and pro-apoptotic proteins in platelets, mitochondrial damage, caspase activation, and platelet apoptosis may be used to help identify HF patients at high risk of NSB post-implant.

Right Ventricular Function in Patients With Left Ventricular Assist Device Support by Pulsatile Polvad MEV and Continuous-Flow Pumps Heartware and Heartmate II

BACKGROUND

Left ventricular assist device (LVAD) support is increasingly used in patients with heart failure. The right ventricle (RV) plays a main role in LVAD support. Little is known about the effects of pulsatile Polvad MEV devices or continuouseconds flow pumps on RV function. We compared hemodynamic parameters of RV in patients after implantation of Polvad MEV (PM) and Heartware (HW) or Heartmate II (HMII) LVADs.

METHODS

Forty-four patients were retrospectively reviewed after implantation of PM (group P; n = 24 [21 M, 3 F]) or HW or HMII (group C; n = 20 [20 M, 0 F]) LVADs from April 2007 to February 2014. Hemodynamic data-mean pulmonary pressure (mPAP), central venous pressure (CVP), cardiac output (CO), and cardiac index (CI)-were collected before surgery, after surgery, and every 2 hours in the intensive care unit, with the time points numbered from 1 to 120. Right ventricular work (RVW) was calculated according to the equation: RCW = CO × (mPAP - CVP) × 0.0144 (g·m).

RESULTS

Baseline characteristic of the patients were similar. mPAP values were similar between groups. CVP values were higher in group P, significantly at time points 5 and 7-33. CO values were higher in group C, significantly from point 3 and almost all the time to point 43. CI reached significance at point 9, 12-14, 16-19, and 30-41. RCW was higher in group P before implantation. Post-implantation RCW values were higher in group C, significantly at time points 19, 20, 32-34, 51-53, and 55-57.

CONCLUSIONS

Continuous-flow pumps more effectively optimize RV function than pulsatile LVADs, which can result in more effective prevention of RV failure or insuffiency in that group.

Biventricular mechanical support devices--clinical perspectives

Cardiac transplantation remains the optimal treatment for end stage heart failure in selected patients. However, the shortage of donor hearts, rigorous eligibility criteria and long waiting lists have increased the demand for alternative treatment strategies such as mechanical circulatory support. While many patients are adequately supported with left ventricular assist devices, frequently there is right heart failure or involvement of the right ventricle, requiring biventricular support. Pulsatile flow biventricular devices and total artificial hearts approved for temporary biventricular support have limitations including size, high rates of adverse events and restricted mobility which makes them unsuitable for long term support. A number of centres have reported dual continuous flow left ventricular assist devices as a means of supporting the left and right heart. This review will summarise the literature on the outcomes and complications from current biventricular support devices and assess the role of dual continuous flow VAD therapy, and the new continuous flow total heart replacement devices.

Surgical therapy for heart failure

Today's healthcare delivery system is challenged with an escalating number of heart failure patients who have exhausted medical therapy and overwhelmed the limits of organ transplantation. Scientific and technological advances over the last 20 years have now brought new surgical options to this vast patient population, ranging from ventricular restoration surgery to surgical gene therapy and beyond. This article reviews the myriad of surgical options that are available to these patients, their benefits and shortcomings, as well as potential future directions.

Currently available ventricular-assist devices: capabilities, limitations and future perspectives

The continuous progress in ventricular-assist device (VAD) technology and the management of patients with VADs has broadened the treatment options for end-stage heart failure patients. The available line-up of clinical devices provides the current optimal therapies to meet the specific needs of each patient. The extended durability, safety, efficacy and improved quality of life of the patients provides sufficient proof for the VAD to be a likely alternative therapy to heart transplantation. The sequential progress from the first-, to the second- and to the third-generation VAD technology is expected to bring increasing benefits to clinical outcomes. This article reviews the current status, capabilities, limitations and future perspectives of currently available VADs by generally classifying them via support duration, alignment of pump devices and via pulsatile or nonpulsatile mode of perfusion. Furthermore, the future direction of research and development for next-generation VADs is presented based on the lessons learned from currently available VADs.

Ventricular Assist Devices - Evolution of Surgical Heart Failure Treatment

End-stage heart failure represents a substantial worldwide problem for the healthcare system. Despite significant improvements (medical heart failure treatment, implantable cardioverters, cardiac resyschronisation devices), long-term survival and quality of life of these patients remains poor. Heart transplantation has been an effective therapy for terminal heart failure, but it remains limited by an increasing shortage of available donor organs along with strict criteria defining acceptable recipients. For the last 50 years, mechanical alternatives to support the circulation have been investigated; however, during the early years device development has been marked in general by slow progress. However, in the past two decades, the technology has evolved dramatically. The purpose of this review is to give a short summary on the evolution of ventricular assist device (VAD) therapy and to give perspectives for future treatment of heart failure.

Mechanical circulatory support: devices, outcomes and complications

Systolic heart failure is a problem of substantial magnitude worldwide. Over the last 25 years great progress has been made in the medical management of heart failure with the recognition of the benefits of beta-adrenergic blockade, modulation of the renin-angiotensin and mineralocorticoid axes and judicious diuretic therapy. In addition, cardiac resynchronization therapy and prophylactic implantation of cardiac defibrillators have been responsible for measurable benefits in terms of functional status and dysrhythmia-related mortality, respectively. Unfortunately, progressive cardiac dysfunction often results in activity limitation, symptoms at rest, hospital admission, end-organ dysfunction and death despite maximal implementation of standard therapies. Heart transplantation has been a dramatic and effective therapy for end-stage heart failure, but it remains limited by a shortage of donor organs, strict criteria defining acceptable recipients and often unsatisfactory long-term success. Mechanical alternatives to support the failing circulation have been sought for the last 50 years. The history of device development has been marked in general by the slow progress achieved by a few dedicated and persevering pioneers. In the past decade, however, evolving technology has dramatically changed the field and broadened the options for the treatment of advanced heart failure. This review will detail the important milestones and the current state of the art, with an emphasis on implantable devices for intermediate to long term support.

Left ventricular assist devices: from the bench to the clinic

The development of ventricular assist devices (VADs) over the past 5 decades as therapy for advanced heart failure (HF) has been extraordinary. Since the original VAD design by Michael DeBakey in the early 1960s, numerous devices for mechanical circulatory support have been engineered, assessed in preclinical studies, applied to human patients in large multicenter clinical trials, and now, select devices are Food and Drug Administration-approved therapy for advanced HF patients. This review highlights select examples of durable VADs from the engineering aspect of design and conception to experimental studies and clinical application underscoring the remarkable progression of such technology to now becoming the standard of care for many advanced HF patients.

Temporary percutaneous right ventricular support using a centrifugal pump in patients with postoperative acute refractory right ventricular failure after left ventricular assist device implantation

OBJECTIVE

Acute right ventricular (RV) failure is a life-threatening condition with a poor prognosis, and sometimes the use of mechanical circulatory support is inevitable. In this article, we describe our experience using a centrifugal pump as a temporary percutaneous right ventricular assist device (RVAD) in patients with postoperative acute refractory RV failure after left ventricular assist device (LVAD) implantation.

METHODS

We retrospectively reviewed eight consecutive patients with acute RV failure who underwent temporary percutaneous RVAD implantation using a centrifugal pump after LVAD implantation between April 2008 and February 2011. A Dacron graft was attached to the main pulmonary artery and passed through a subxiphoid exit, where the outflow cannula was inserted. The inflow cannula was percutaneously cannulated using Seldinger's technique in the femoral vein. The chest was definitely closed. The technique allowed bedside removal, avoiding chest re-opening.

RESULTS

The median patient age was 52 years (range: 41-58). The median duration of support was 14 days (range: 12-14). RV systolic function improved; central venous pressure and mean pulmonary artery pressure decreased significantly after RVAD support. In three patients, an oxygenator was integrated into the RVAD due to impaired pulmonary function. Six patients were successfully weaned. Five patients survived to hospital discharge. Technical problems or serious complications concerning decannulation were not observed.

CONCLUSION

This report suggests that implantation of temporary percutaneous RVAD using a centrifugal pump is a safe alternative in the treatment of postoperative acute refractory RV failure. Ease of device implantation, weaning, explantation, and limited number of complications justify a liberal use.

Mechanical circulatory support of the critically ill child awaiting heart transplantation

The majority of children awaiting heart transplantation require inotropic support, mechanical ventilation, and/or extracorporeal membrane oxygenation (ECMO) support. Unfortunately, due to the limited pool of organs, many of these children do not survive to transplant. Mechanical circulatory support of the failing heart in pediatrics is a new and rapidly developing field world-wide. It is utilized in children with acute congestive heart failure associated with congenital heart disease, cardiomyopathy, and myocarditis, both as a bridge to transplantation and as a bridge to myocardial recovery. The current arsenal of mechanical assist devices available for children is limited to ECMO, intra-aortic balloon counterpulsation, centrifugal pump ventricular assist devices, the DeBakey ventricular assist device Child; the Thoratec ventricular assist device; and the Berlin Heart. In the spring of 2004, five contracts were awarded by the National Heart, Lung and Blood Institute to support preclinical development for a range of pediatric ventricular assist devices and similar circulatory support systems. The support of early development efforts provided by this program is expected to yield several devices that will be ready for clinical trials within the next few years. Our work reviews the current international experience with mechanical circulatory support in children and summarizes our own experience since 2005 with the Berlin Heart, comparing the indications for use, length of support, and outcome between these modalities.

Age and preoperative total bilirubin level can stratify prognosis after extracorporeal pulsatile left ventricular assist device implantation

BACKGROUND

In Japan, the TOYOBO left ventricular assist device (LVAD) has been commercially available for heart failure patients as of 2010, but clinical risk stratification before implantation has not been widely performed.

METHODS AND RESULTS

In the present study data from 47 patients (age 38.6 ± 14.6 [SD] years, male 74.5%, non-ischemic 74.5%) implanted with a TOYOBO LVAD between November 2002 and February 2010 were analyzed. Kaplan-Meier survival analysis showed significantly higher mortality in the patients who had cardiogenic shock preoperatively (P = 0.031). Multivariate analysis revealed that the preoperative total bilirubin level (odds ratio [OR] 1.312, P < 0.001) and age (OR 1.076, P = 0.013) were independent risk factors for death. Perioperative necessity of a right ventricular assist device was also an independent risk factor for poor prognosis.

CONCLUSIONS

LVAD implantation is preferable before the patient experiences hemodynamic collapse. The preoperative total bilirubin level can be used to predict prognosis after device implantation in end-stage heart failure patients.

Simple surface modification of a titanium alloy with silanated zwitterionic phosphorylcholine or sulfobetaine modifiers to reduce thrombogenicity

Thrombosis and thromboembolism remain problematic for a large number of blood contacting medical devices and limit broader application of some technologies due to this surface bioincompatibility. In this study we focused on the covalent attachment of zwitterionic phosphorylcholine (PC) or sulfobetaine (SB) moieties onto a TiAl(6)V(4) surface with a single step modification method to obtain a stable blood compatible interface. Silanated PC or SB modifiers (PCSi or SBSi) which contain an alkoxy silane group and either PC or SB groups were prepared respectively from trimethoxysilane and 2-methacryloyloxyethyl phosphorylcholine (MPC) or N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylammonium betaine (SMDAB) monomers by a hydrosilylation reaction. A cleaned and oxidized TiAl(6)V(4) surface was then modified with the PCSi or SBSi modifiers by a simple surface silanization reaction. The surface was assessed with X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and contact angle goniometry. Platelet deposition and bulk phase activation were evaluated following contact with anticoagulated ovine blood. XPS results verified successful modification of the PCSi or SBSi modifiers onto TiAl(6)V(4) based on increases in surface phosphorous or sulfur respectively. Surface contact angles in water decreased with the addition of hydrophilic PC or SB moieties. Both the PCSi and SBSi modified TiAl(6)V(4) surfaces showed decreased platelet deposition and bulk phase platelet activation compared to unmodified TiAl(6)V(4) and control surfaces. This single step modification with PCSi or SBSi modifiers offers promise for improving the surface hemocompatibility of TiAl(6)V(4) and is attractive for its ease of application to geometrically complex metallic blood contacting devices.

Review: The New Concept of ‘‘Interventional Heart Failure Therapy’’: Part 2—Inotropes, Valvular Disease, Pumps, and Transplantation

Recent advances in heart failure therapy include a variety of mechanical and device-based technologies that target structural aspects of heart failure that cannot be treated with drug therapy alone; these newer therapies can collectively be described as interventional heart failure therapy. This article is the second in a 2-part series reviewing interventional heart failure therapy. Interventions included in this discussion include those indicated for the treatment of end-stage refractory heart failure, including interventional medical therapy, interventional treatment of valvular disease, mechanical assist devices, and heart transplantation. Also included is a review of the currently available catheter-based pumps, which are intended to provide temporary support in patients with acute hemodynamic compromise. The use of cellular or stem cell therapy for the treatment of heart failure is an emerging interventional therapy and data supporting its use for the treatment heart failure will also be presented, as will a discussion of the role of palliative care and self-care in heart failure therapy.

Update on ventricular assist devices

PURPOSE OF REVIEW

Over the past two decades, medicine has seen a robust increase in the use of ventricular assist devices. The purpose of this review is to update the information concerning these devices, their advantages and disadvantages as well as their complications. This is essential, as the demand for these devices is increasing due to the increasing number of patients with end-stage heart failure and limited number of donor hearts available for transplantation.

RECENT FINDINGS

First-generation devices consisted of large, cumbersome consoles requiring patient immobilization and often times hospitalization in an ICU setting. Second-generation models focused on patient mobility and discharge from hospital with an improvement in infection rates as well as 1 and 2-year survival rates. Designs for newer devices are focusing on full implantation without percutaneous lines, axial flow mechanisms and patient comfort. Additionally, total artificial hearts are being designed for the treatment of biventricular failure. The indications for ventricular assist devices are also being expanded to include destination therapy and alternatives to cardiac transplantation, as the supply of organs continues to be limiting.

SUMMARY

This paper reviews the characteristics, outcomes and design of ventricular assist devices.

Increased incidence of gastrointestinal bleeding following implantation of the HeartMate II LVAD

BACKGROUND

The HeartMate II (HMII) Left Ventricular Assist System (Thoratec Corporation, Pleasanton, CA, USA), an axial continuous-flow left ventricular assist device (LVAD), has been approved for use in bridge-to-transplant patients and is under investigation for destination therapy. To avoid device-related thromboembolic complications, antiplatelet, and anticoagulation therapy are routinely administered. A worrisome frequency of gastrointestinal (GI) bleeding events has been observed.

METHODS

A retrospective review of all 33 patients undergoing long-term LVAD implantation between June 1, 2006 and July 31, 2008 at our institution for any indication was conducted. Anticoagulation consisted of heparin (intravenous or subcutaneous) followed by transition to Coumadin therapy to a target INR of two to three. Antiplatelet therapy consisted of low-dose aspirin and dipyridamole.

RESULTS

Twenty patients received the HMII and 13 patients received other devices. Eight (40%) HMII recipients suffered at least one episode of GI bleeding while no GI bleeding occurred in recipients of other devices (p = 0.012). Of 17 total bleeding episodes, no definitive source could be identified in 11 instances (65%).

CONCLUSIONS

Although definitive source identification remains elusive, we believe that the majority of bleeding arises in the small bowel, possibly due to angiodysplasias, similar to the pathophysiology encountered in patients with aortic stenosis and GI bleeding. As we move toward wider use of the HMII and other axial continuous-flow devices in both bridge-to-transplant patients and for destination therapy, more studies will be necessary to understand the mechanisms of this obscure GI bleeding and develop treatment strategies to minimize its development.

Surface modification of a titanium alloy with a phospholipid polymer prepared by a plasma-induced grafting technique to improve surface thromboresistance

To improve the thromboresistance of a titanium alloy (TiAl(6)V(4)) surface which is currently utilized in several ventricular assist devices (VADs), a plasma-induced graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) was carried out and poly(MPC) (PMPC) chains were covalently attached onto a TiAl(6)V(4) surface by a plasma induced technique. Cleaned TiAl(6)V(4) surfaces were pretreated with H(2)O-vapor-plasma and silanated with 3-methacryloylpropyltrimethoxysilane (MPS). Next, a plasma-induced graft polymerization with MPC was performed after the surfaces were pretreated with Ar plasma. Surface compositions were verified by X-ray photoelectron spectroscopy (XPS). In vitro blood biocompatibility was evaluated by contacting the modified surfaces with ovine blood under continuous mixing. Bulk phase platelet activation was quantified by flow cytometric analysis, and surfaces were observed with scanning electron microscopy after blood contact. XPS data demonstrated successful modification of the TiAl(6)V(4) surfaces with PMPC as evidenced by increased N and P on modified surfaces. Platelet deposition was markedly reduced on the PMPC grafted surfaces and platelet activation in blood that contacted the PMPC-grafted samples was significantly reduced relative to the unmodified TiAl(6)V(4) and polystyrene control surfaces. Durability studies under continuously mixed water suggested no change in surface modification over a 1-month period. This modification strategy shows promise for further investigation as a means to reduce the thromboembolic risk associated with the metallic blood-contacting surfaces of VADs and other cardiovascular devices under development.

Covalent surface modification of a titanium alloy with a phosphorylcholine-containing copolymer for reduced thrombogenicity in cardiovascular devices

Our objective was to develop a surface modification strategy for a titanium alloy (TiAl6V4) to provide thromboresistance for surfaces in rigorous blood-contacting cardiovascular applications, such as that found in ventricular assist devices. We hypothesized that this could be accomplished by the covalent attachment of a phospholipid polymer, poly(2-methacryloyloxyethylphosphorylcholine (MPC)-co-methacryl acid) (PMA). TiAl6V4 was H2O plasma treated by radio frequency glow discharge, silanated with 3-aminopropyltriethoxysilane (APS), and ammonia plasma treated to increase surface reactivity. The TiAl6V4 surface was then modified with PMA via a condensation reaction between the amino groups on the TiAl6V4 surface and the carboxyl groups on PMA. The surface composition was verified by X-ray photoelectron spectroscopy, confirming successful modification of the TiAl6V4 surfaces with APS and PMA as evidenced by increased Si and P. Plasma treatments with H2O and ammonia were effective at further increasing the surface reactivity of TiAl6V4 as evidenced by increased surface PMA. The adsorption of ovine fibrinogen onto PMA-modified surfaces was reduced relative to unmodified surfaces, and in vitro ovine blood contact through a rocking test revealed marked reductions in platelet deposition and bulk phase platelet activation relative to unmodified TiAl6V4 and polystyrene controls. The results indicate that the PMA-modification scheme for TiAl6V4 surfaces offers a potential pathway to improve the thromboresistance of the blood-contacting surfaces of cardiovascular devices.

Contributions of contact activation pathways of coagulation factor XII in plasma

Activation of human blood plasma coagulation by contact with hydrophilic or hydrophobic surfaces (procoagulants) is dominated by kallikrein (Kal)-mediated activation of the blood zymogen FXII (Hageman Factor). Mathematical modeling of prekallikrein (PK)-deficient platelet-poor plasma (d(PK)PPP) and PK-reconstituted d(PK)PPP (Rd(PK)PPP) coagulation shows that autoactivation of FXII (FXII-->[surface]FXII) produces no more than about 25% of the total FXIIa produced by the intrinsic pathway. Autoactivation and reciprocal-activation increase in the same proportion with procoagulant surface energy (water-wettability), whereas total amount of FXIIa produced per-unit-area procoagulant remains roughly constant for any particular procoagulant. These results suggest that procoagulant surfaces initiate the intrinsic cascade by producing a bolus of FXIIa in proportion to surface energy or surface area but play no additional role in subsequent molecular events in the cascade. Results further suggest that reciprocal-activation occurs in proportion to the amount of FXIIa produced by the initiating autoactivation step.

Temporary Right Ventricular Support with Impella Recover RD Axial Flow Pump

Post-cardiotomyright ventricular failure is a serious complication that frequently results in adverse outcomes. We reviewed our experience with the Impella Recover RD (Impella Cardiosystems GMbH, Aachen, Germany). From January 2007 to December 2007, 7 patients (5 males, 54 + 7 years old) had this device implanted for temporary support after heart transplantation in 4, after repeat mitral valve replacement in 2, and with a left ventricular assist device in 1. Devices were implanted during initial operation ( n = 5) or shortly thereafter ( n = 2). Six patients underwent implantation without cardiopulmonary bypass. Effective support with pump flows of 4.0-4.5 L · min−1 and adequate unloading (central venous pressure decreased from 15.3 ± 1.4 to 9.4 ± 1.2 mm Hg) was achieved in all patients. Patients were assisted for a mean duration of 4.9 ± 4.5 days. Three patients could be weaned after 7.0 ± 5.6 days of support and underwent device explantation without cardiopulmonary bypass. One of these patients died of recurrent right ventricular failure, 2 remained stable but died later of sepsis. The patient with a left ventricular assist device was switched to an alternative device for prolonged support. Two patients experienced pump dysfunction. Our preliminary experience shows that the Impella Recover RD is an effective device that can be easily implanted and explanted. However, its mechanical reliability needs to be improved.

Whole blood hypercoagulability despite anticoagulation during mechanical cardiac assist

We report hypercoagulability despite activated partial thromboplastin time (APTT)-guided heparin treatment during Berlin Heart®-supported circulation in a 38-year-old man with heart failure for 19 days. The patient was anticoagulated using unfractionated heparin, acetylsalicylic acid and dipyridamole. Contact and tissue factor-activated thromboelastometry revealed increased clot firmness, although anticoagulation assessed by APTT was in accordance with the treatment protocol. Strength of polymerized fibrin was also increased. We saw no clinical signs of thrombosis. Thromboelastometry normalized after heart transplantation. Our results suggest that hypercoagulability is due to excess fibrin formation. Monitoring anticoagulation using APTT may, therefore, be misleading during mechanical cardiac assist.

Results of a multicenter clinical trial with the Thoratec Implantable Ventricular Assist Device⁎⁎Thoratec Corporation, Pleasanton, Calif

OBJECTIVE

The Thoratec Implantable Ventricular Assist Device (Thoratec Corporation, Pleasanton, Calif) can be used for univentricular or biventricular support in patients with a body surface area as low as 1.3 m(2). Results of the multicenter clinical trial are reviewed.

METHODS

Between October 2001 and June 2004, a total of 39 patients at 12 institutions were supported with the Thoratec Implantable Ventricular Assist Device. Twenty-four patients (62%) received left ventricular assist devices and 15 (38%) received biventricular assist devices. Indications included bridge to transplantation (n = 30) and postcardiotomy failure (n = 9). The control group included 100 patients from the Food and Drug Administration approval submissions for the paracorporeal version of the ventricular assist device.

RESULTS

Twenty-eight male and 11 female patients, with mean age of 48 years (16-71 years) and body surface area of 1.9 m(2) (1.3-2.4 m2) were supported for 3938 patient-days (10.8 patient-years). Mean left ventricular assist device flow index on the first postoperative day was 2.5 +/- 0.5 L/(min x m2). Mean duration of support was 101 days (9-597 days). Eighteen patients were discharged after a mean duration of 96 days. There were no ventricular assist device failures. Complications included 13 cases of bleeding requiring reexploration (33.3%), 1 embolic and 2 hemorrhagic strokes (7.7%), 5 driveline infections (12.8%), and 2 pocket infections (5%). Support to successful outcomes was 70% for bridge to transplantation and 67% for postcardiotomy recovery, versus historical results for the paracorporeal ventricular assist device of 69% for bridge to transplantation and 48% for postcardiotomy recovery.

CONCLUSION

The Thoratec Implantable Ventricular Assist Device is a new implantable pulsatile ventricular assist device that allows hospital discharge for patients as a bridge to transplantation or for postcardiotomy failure. It is the first Food and Drug Administration-approved implantable ventricular assist device with biventricular capability.

Ventricular assist devices in children: current achievements and future perspectives

Mechanical circulatory support systems for the treatment of acute and chronic heart failure are now available for use in several clinical situations and are designed for different indications and support times. In children, particularly in small infants, extracorporeal membrane oxygenation and centrifugal pumps have been most widely used in the past. These systems are preferred for support after cardiac operations and for use in patients who have concomitant respiratory failure, but they are suitable for short-term application only and intensive care is obligatory. VADs are designed for long-term application and allow patients to be discharged home. Pneumatic pulsatile VADs have been available in pediatric sizes since 1992. Currently at our institution, 74 children have been supported with pediatric extracorporeal VADs for up to 14 months. In the past five yr, a notable rise in survival has been achieved by improvements in pump design and pre- and post-operative management. We have been able to discharge 78% of the infants under one yr old. In this review, our current VAD experience in children will be presented in the light of improvements in decision-making, device technology, and implantation techniques, and in coagulation monitoring and anticoagulation. Additionally, new developments in the field of pediatric assist devices will be presented.

Pediatric ventricular assist devices

Ventricular assist device therapy is continuing to evolve in the practice of pediatric cardiac surgery. Although ECMO is still the most often applied mechanical support for infants and young children, a broader range of pulsatile, paracorporeal, as well as implantable ventricular assist devices are now available for pediatric application. A number of these innovative devices have been developed specifically for pediatric use with miniaturized pumps and optimized cannulas suitable for the entire age range of pediatric patients including neonates. Unlike ECMO, these devices can offer medium- to long-term support and have been successfully utilized as a bridge to transplant as well as a bridge to recovery. This review examines the different types of devices currently available, their clinical indications for use, future devices, and the current results of pediatric ventricular assist device therapy in the treatment of heart failure in the pediatric population.