Destination therapy: current results and future promise

Hybrid Continuous-Flow Total Artificial Heart

Clinical studies using total artificial hearts (TAHs) have demonstrated that pediatric and adult patients derive quality-of-life benefits from this form of therapy. Two clinically-approved TAHs and other pumps under development, however, have design challenges and limitations, including thromboembolic events, neurologic impairment, infection risk due to large size and percutaneous drivelines, and lack of ambulation, to name a few. To address these limitations, we are developing a hybrid-design, continuous-flow, implantable or extracorporeal, magnetically-levitated TAH for pediatric and adult patients with heart failure. This TAH has only two moving parts: an axial impeller for the pulmonary circulation and a centrifugal impeller for the systemic circulation. This device will utilize the latest generation of magnetic bearing technology. Initial geometries were established using pump design equations, and computational modeling provided insight into pump performance. The designs were the basis for prototype manufacturing and hydraulic testing. The study results demonstrate that the TAH is capable of delivering target blood flow rates of 1-6.5 L/min with pressure rises of 1-92 mm Hg for the pulmonary circulation and 24-150 mm Hg for the systemic circulation at 1500-10 000 rpm. This initial design of the TAH was successful and serves as the foundation to continue its development as a novel, more compact, nonthrombogenic, and effective therapeutic alternative for infants, children, adolescents, and adults with heart failure.

Left ventricular assist device: a bridge to transplant or destination therapy?

Heart failure is a major problem worldwide; it is the leading cause of hospitalisation and is posing a huge financial burden. Advances in healthcare have contributed to increased life expectancy, with a resultant increase in the number of patients with chronic heart failure. For many patients who are still severely symptomatic despite optimal medical therapy and cardiac resynchronisation therapy, cardiac transplantation would be the preferred treatment option. However, hopes are cut short with a limited donor pool of hearts for the increasing number of patients requiring cardiac transplantation. One uprising method to fill this treatment void for patients with advanced end-stage heart failure (ESHF) is the Left Ventricular Assist Device (LVAD). Although traditionally used as a bridge to transplantation, owing to limitation of suitable donors, evidence suggests increasing potential for the use of LVAD as destination therapy (DT), that is, lifelong permanent support. Exploration of DT is a promising avenue to many patients suffering with ESHF who may never be fortunate enough to receive a heart transplant, but not without reservations of its efficacy, safety, effects on quality-adjusted life years and cost-effectiveness, especially in comparison to heart transplantation.

A new Bayesian network-based risk stratification model for prediction of short-term and long-term LVAD mortality

Existing risk assessment tools for patient selection for left ventricular assist devices (LVADs) such as the Destination Therapy Risk Score and HeartMate II Risk Score (HMRS) have limited predictive ability. This study aims to overcome the limitations of traditional statistical methods by performing the first application of Bayesian analysis to the comprehensive Interagency Registry for Mechanically Assisted Circulatory Support dataset and comparing it to HMRS. We retrospectively analyzed 8,050 continuous flow LVAD patients and 226 preimplant variables. We then derived Bayesian models for mortality at each of five time end-points postimplant (30 days, 90 days, 6 month, 1 year, and 2 years), achieving accuracies of 95%, 90%, 90%, 83%, and 78%, Kappa values of 0.43, 0.37, 0.37, 0.45, and 0.43, and area under the receiver operator characteristic (ROC) of 91%, 82%, 82%, 80%, and 81%, respectively. This was in comparison to the HMRS with an ROC of 57% and 60% at 90 days and 1 year, respectively. Preimplant interventions, such as dialysis, ECMO, and ventilators were major contributing risk markers. Bayesian models have the ability to reliably represent the complex causal relations of multiple variables on clinical outcomes. Their potential to develop a reliable risk stratification tool for use in clinical decision making on LVAD patients encourages further investigation.

Ventricular assist devices as destination therapy: psychosocial and ethical implications

One of the candidate evaluation challenges is determining when and how psychosocial domains influence short- and long-term destination therapy ventricular assist device (DT-VAD) outcomes. There are very few DT-VAD studies and no validated instruments to identify psychosocial risk factors. General practice is to borrow from the transplant literature, which may not be applicable to this unique device application. We question the relevance of using transplant psychosocial evaluation for patients who are candidates for DT-VAD only, particularly because these patients require a certain level of cognitive, psychological, and behavioral functioning to ensure proper long-term self-care with the VAD. We may be missing important psychological characteristics in our pre-evaluations by "borrowing" from the transplant literature, thereby underplaying significant factors that are especially relevant for DT-VAD candidates. Conversely, we may be screening out candidates who may benefit greatly from DT-VAD by using transplant criteria as part of the screening process. We use a case study to illustrate some of the challenges of weighing psychosocial risk factors in the DT-VAD population and to emphasize the need for developing distinct psychosocial assessment criteria for DT-VAD patients.

Comparative efficacy of in vitro and in vivo metabolized aspirin in the DeBakey ventricular assist device

Ventricular assist devices (VADs) are implanted in patients with end-stage heart failure to provide both short- and long-term hemodynamic support. Unfortunately, bleeding and thromboembolic complications due to the severely disturbed, dynamic flow conditions generated within these devices require complex, long-term antiplatelet and anticoagulant therapy. While several studies have examined the effectiveness of one such agent, aspirin, under flow conditions, data comparing the efficacy of in vitro and in vivo metabolized aspirin is lacking. Two sets of studies were conducted in vitro with purified human platelets circulating for 30 min in a flow loop containing the DeBakey VAD (MicroMed Cardiovascular, Houston, TX, USA): (a) 20 μM aspirin was added exogenously in vitro to platelets isolated from aspirin-free subjects, and (b) platelets were obtained from donors 2 h (n = 14) and 20 h (n = 13) after ingestion of 1,000 mg aspirin. Near real-time platelet activation state (PAS) was measured with a modified prothrombinase-based assay. Platelets exposed to aspirin in vitro and in vivo (metabolized) showed 28.2 and 25.3 % reduction in platelet activation rate, respectively, compared to untreated controls. Our results demonstrate that in vitro treatment with antiplatelet drugs such as aspirin is as effective as in vivo metabolized aspirin in testing the effect of reducing shear-induced platelet activation in the VAD. Using the PAS assay provides a practical in vitro alternative to in vivo testing of antiplatelet efficacy, as well as for testing the thrombogenic performance of devices during their research and development.

Cardiac Health Risk Stratification System (CHRiSS): a Bayesian-based decision support system for left ventricular assist device (LVAD) therapy

This study investigated the use of Bayesian Networks (BNs) for left ventricular assist device (LVAD) therapy; a treatment for end-stage heart failure that has been steadily growing in popularity over the past decade. Despite this growth, the number of LVAD implants performed annually remains a small fraction of the estimated population of patients who might benefit from this treatment. We believe that this demonstrates a need for an accurate stratification tool that can help identify LVAD candidates at the most appropriate point in the course of their disease. We derived BNs to predict mortality at five endpoints utilizing the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) database: containing over 12,000 total enrolled patients from 153 hospital sites, collected since 2006 to the present day, and consisting of approximately 230 pre-implant clinical variables. Synthetic minority oversampling technique (SMOTE) was employed to address the uneven proportion of patients with negative outcomes and to improve the performance of the models. The resulting accuracy and area under the ROC curve (%) for predicted mortality were 30 day: 94.9 and 92.5; 90 day: 84.2 and 73.9; 6 month: 78.2 and 70.6; 1 year: 73.1 and 70.6; and 2 years: 71.4 and 70.8. To foster the translation of these models to clinical practice, they have been incorporated into a web-based application, the Cardiac Health Risk Stratification System (CHRiSS). As clinical experience with LVAD therapy continues to grow, and additional data is collected, we aim to continually update these BN models to improve their accuracy and maintain their relevance. Ongoing work also aims to extend the BN models to predict the risk of adverse events post-LVAD implant as additional factors for consideration in decision making.

Tissue-engineered endothelial cell layers on surface-modified Ti for inhibiting in vitro platelet adhesion

A tissue-engineered endothelial layer was prepared by culturing endothelial cells on a fibroblast growth factor-2 (FGF-2)-l-ascorbic acid phosphate magnesium salt n-hydrate (AsMg)-apatite (Ap) coated titanium plate. The FGF-2-AsMg-Ap coated Ti plate was prepared by immersing a Ti plate in supersaturated calcium phosphate solutions supplemented with FGF-2 and AsMg. The FGF-2-AsMg-Ap layer on the Ti plate accelerated proliferation of human umbilical vein endothelial cells (HUVECs), and showed slightly higher, but not statistically significant, nitric oxide release from HUVECs than on as-prepared Ti. The endothelial layer maintained proper function of the endothelial cells and markedly inhibited in vitro platelet adhesion. The tissue-engineered endothelial layer formed on the FGF-2-AsMg-Ap layer is promising for ameliorating platelet activation and thrombus formation on cardiovascular implants.

Novel nonsurgical left ventricular assist device and system

Treatment options for advanced stages of congestive heart failure remain limited. Left ventricular assist devices (LVADs) have emerged as a means to support failing circulation. However, these devices are not without significant risk such as major open chest surgery. We utilized a novel approach for device placement at the aorto-left atria continuity as a site to create a conduit capable of accommodating a percutaneous LVAD system. We designed and developed an expandable nitinol based device for placement at this site to create a shunt between the LA and aorta. Our experiments support this anatomic location as an accessible and feasible site for accommodation of an entirely percutaneous LVAD. The novelty of this approach would bypass the left ventricle, and thereby minimize complications and morbidities associated with current LVAD placement.

Rotary blood pumps as definitive treatment for severe heart failure

Rotary blood pumps are increasingly recognized as mainstream therapy for severely symptomatic heart failure. Carefully targeted refinements in patient selection and postoperative care have substantially reduced the adverse event burden. These improvements translate into better survival and quality of life in comparison with medical management. Medium-term outcomes now compete favorably with cardiac transplantation, although evidence-based outcome data indicate that transplant and ‘lifetime’ left ventricular-assist device (LVAD) candidates are fundamentally different. Significant challenges remain in relation to neurological injury and right heart failure, which may continue to limit exercise capacity. In the meantime, both physician awareness and patient access to LVAD technology remain limited. The debate is rarely between cardiac transplant or lifetime LVAD. It should focus on the choice between pump versus palliative care for the thousands of patients of all age groups who are judged ineligible for transplantation. Comprehensive healthcare systems must consider contemporary evidence and provide the most symptomatic of heart failure patients with effective care. Cardiac resynchronization therapy is no longer the ceiling for this.

A Classification Approach for Risk Prognosis of Patients on Mechanical Ventricular Assistance

The identification of optimal candidates for ventricular assist device (VAD) therapy is of great importance for future widespread application of this life-saving technology. During recent years, numerous traditional statistical models have been developed for this task. In this study, we compared three different supervised machine learning techniques for risk prognosis of patients on VAD: Decision Tree, Support Vector Machine (SVM) and Bayesian Tree-Augmented Network, to facilitate the candidate identification. A predictive (C4.5) decision tree model was ultimately developed based on 6 features identified by SVM with assistance of recursive feature elimination. This model performed better compared to the popular risk score of Lietz et al. with respect to identification of high-risk patients and earlier survival differentiation between high- and low- risk candidates.

The biocompatibility of titanium cardiovascular devices seeded with autologous blood-derived endothelial progenitor cells: EPC-seeded antithrombotic Ti implants

Implantable and extracorporeal cardiovascular devices are commonly made from titanium (Ti) (e.g. Ti-coated Nitinol stents and mechanical circulatory assist devices). Endothelializing the blood-contacting Ti surfaces of these devices would provide them with an antithrombogenic coating that mimics the native lining of blood vessels and the heart. We evaluated the viability and adherence of peripheral blood-derived porcine endothelial progenitor cells (EPCs), seeded onto thin Ti layers on glass slides under static conditions and after exposure to fluid shear stresses. EPCs attached and grew to confluence on Ti in serum-free medium, without preadsorption of proteins. After attachment to Ti for 15 min, less than 5% of the cells detached at a shear stress of 100 dyne / cm(2). Confluent monolayers of EPCs on smooth Ti surfaces (Rq of 10 nm), exposed to 15 or 100 dyne/cm(2) for 48 h, aligned and elongated in the direction of flow and produced nitric oxide dependent on the level of shear stress. EPC-coated Ti surfaces had dramatically reduced platelet adhesion when compared to uncoated Ti surfaces. These results indicate that peripheral blood-derived EPCs adhere and function normally on Ti surfaces. Therefore EPCs may be used to seed cardiovascular devices prior to implantation to ameliorate platelet activation and thrombus formation.

General overview of the Sixth International Symposium on Stem Cell Therapy and Cardiovascular Innovations

Being one of the main stem cell therapy meetings of the year, the Sixth International Symposium on Stem Cell Therapy and Cardiovascular Innovations was held on April 23rd-24th, 2009, at the Auditorium of the High Council of Scientific Research of Spain (CSIC) in Madrid. Gathering the most prestigious basic researchers and clinical experts in the field of cardiovascular regenerative medicine, the aim of the meeting was to discuss the available evidence and the recent contributions from preclinical investigators, cardiologists, and cardiac surgeons in a participative translational fashion. The role of young "clinician scientists" was reinforced with a special poster session and three awards. The main conclusions of the symposium were (1) that standardization, larger clinical trials, and true translational research are needed, and (2) that new-allogeneic-stem cell products, biotechnological devices, and cell-based bioartificial organs are potentially exciting options for the future.

Mechanical circulatory support in the ICCU

The mortality of acute heart failure (AHF) remains high despite advances in treatment. Mechanical circulatory support (MCS) can be applied in AHF, refractory to conventional measures, to improve outcomes. This article aims to describe the current and the prospective role of MCS in the treatment of AHF. The support strategies and the indications of MCS are continuously evolving, including situations considered as contraindications in the past. Appropriate patient selection, advanced device technology and improved patient management have contributed to the substantially improved results. Evolution in device technology results in evolution of the clinical applications of MCS. Earlier application of MCS, with novel, flexible and individualized support strategies is now feasible. Bridging to recovery is the most intriguing support strategy and bridging to future treatments is feasible with long-term support. The progressively expanding role of MCS in the treatment of heart failure is not reflected in the existing guidelines. Being reserved for refractory heart failure, MCS has been applied to the sickest patients who were less amenable to randomization. This explains the lack of robust evidence, but also highlights the value of the progressively improving results. The anticipated wider application of MCS should be better defined, systematically recorded, and guided.