Current status of mechanical circulatory support: a systematic review

Evaluation of aspirin platelet inhibition in left ventricular assist device population

INTRODUCTION

Aspirin therapy is recommended in durable left ventricular assist device (LVAD) patients to prevent thromboembolic complications. Up to 30% of patients treated with aspirin may demonstrate aspirin resistance, which has been related to thrombotic complications. However, it is unknown whether individual patients exhibit temporal alterations in aspirin sensitivity during LVAD support. We hypothesized that aspirin platelet inhibition would wane after the initial postimplant period.

METHODS

This was a retrospective, observational, single center study conducted at an academic medical center. This study evaluated changes in aspirin platelet inhibition over the first 6 months of LVAD support. Patients who underwent placement of centrifugal LVAD with aspirin platelet sensitivity assays were included for analysis. Aspirin responsiveness was assessed postimplant after 5 days, 3 months, and 6 months.

RESULTS

A total of 28 patients were included for analysis of which 7% of patients were aspirin resistant initially. At 3 months, 32% (odds ratio [OR], 6.1, p = .03) of patients were aspirin resistant and 28% (OR, 4.1, p = .1) at 6 months. Over the first 3 months postimplant, the odds of aspirin resistance increased sixfold and remained relatively constant at 6 months. Patients who were aspirin resistant and received an increase in aspirin dose at 3 months subsequently had a sensitive ARU at 6 months.

CONCLUSION

Aspirin responsiveness not only varies between patients but can significantly wane within individual LVAD patients over time. Additional study is needed to determine if monitoring aspirin resistance may prevent thrombotic complications after LVAD implantation.

The evolution of long-term pediatric ventricular assistance devices: a critical review

Introduction: The gap between the number of heart failure patients and the number of potential heart donors has never been larger than today, especially among the pediatric population. The use of mechanical circulatory support is seen as a potential alternative for clinicians to treat more patients. This treatment has proven its efficiency on short-term use. However, in order to replace heart transplant, the techniques should be used over longer periods of time.Areas covered: This review aims at furnishing an engineering vision of the evolution of ventricular assistance devices used in pediatrics. A critical analysis of the clinical complications related to devices generation is made to give an overview of the design improvements made since their inception.Expert opinion: The long-term use of a foreign device in the body is not without consequences, especially among fragile pediatric patients. Moreover, the size of their body parts increases the technical difficulties of such procedure. The balance between the living cells of the body is disturbed by the devices, mostly by the shear stress generated. To provide a safe mechanical circulatory support for long-term use, the devices should be more hemocompatible, preserving blood cells, adapted to the patient's systemic grid and miniaturized for pediatric use.

Investigation of the inherent left-right flow balancing of rotary total artificial hearts by means of a resistance box

With the incidence of end-stage heart failure steadily increasing, the need for a practical total artificial heart (TAH) has never been greater. Continuous flow TAHs (CFTAH) are being developed using rotary blood pumps (RBPs), leveraging their small size, mechanical simplicity, and excellent durability. To completely replace the heart with currently available RBPs, two are required; one for providing pulmonary flow and one for providing systemic flow. To prevent hazardous states, it is essential to maintain balance between the pulmonary and systemic circulation at a wide variety of physiologic states. In this study, we investigated factors determining a CFTAH's inherent ability to balance systemic and pulmonary flow passively, without active management of pump rotational speed. Four different RBPs (ReliantHeart HA5, Thoratec HMII, HeartWare HVAD, and Ventracor VentrAssist) were used in various combinations to construct CFTAHs. Each CFTAH's ability to autonomously maintain pressures and flows within defined ranges was evaluated in a hybrid mock loop as systemic and pulmonary vascular resistance (PVR) were changed. The resistance box, a method to quantify the range of vascular resistances that can be safely supported by a CFTAH, was used to compare different CFTAH configurations in an efficient and predictive way. To reduce the need for future in vitro tests and to aid in their analysis, a novel analytical evaluation to predict the resistance box of various CFTAH configurations was also performed. None of the investigated CFTAH configurations fully satisfied the predefined benchmarks for inherent flow balancing, with the VentrAssist (left) and HeartAssist 5 (right) offering the best combination. The extent to which each CFTAH was able to autonomously maintain balance was determined by the pressure sensitivity of each RPB: the sensitivity of outflow to changes in the pressure head. The analytical model showed that by matching left and right pressure sensitivity the inherent balancing performance can be improved. These findings may ultimately lead to a reduced need for manual speed changes or active control systems.

Quality of life with an LVAD: A misunderstood concept

The present study aims to synthesize current evidence on the impact of LVAD implantation on quality of life. Current evidence was systematically reviewed to obtain relevant quantitative and qualitative articles published after 2007. Sandelowski's recommended steps for meta-summary were used to analyze the 19 studies that met the inclusion criteria. LVADs can improve HF symptoms and some aspects of QoL. Emotional and physical adaptation involves many changes and learning to manage the device takes time. Functional limitations still exist and patients still lack independence. LVAD-related complications significantly impact QoL. Psychological distress remains high after implantation. LVADs significantly impact the caregiver as well and their perspective is not well heard in the existing evidence. It is important for providers to have ongoing, in-depth discussions with patients and their caregivers regarding treatment options, goals of care, anticipated end-of-life trajectories with an LVAD, possible LVAD-complications, and the caregiver burden associated with an LVAD.

Assessing Consequences of Intraaortic Balloon Counterpulsation Versus Left Ventricular Assist Devices at the Time of Heart Transplantation

The proportion of heart transplant recipients bridged with durable, intracorporeal left ventricular assist devices (dLVADs) has dramatically increased; however, concern exists regarding obligate repeat sternotomy, increased bleeding risk because of anticoagulation and acquired von Willebrand disease, and increased rates of allosensitization. Whether dLVAD patients have impaired posttransplant outcomes compared with equivalent patients with less invasive intraaortic balloon pump counterpulsation (IABP) at the time of transplant is unknown. Therefore, we analyzed adult, first time, heart-only transplant procedures with dLVAD (n = 2,636) compared with IABP (n = 571) at the time of transplant based on data from the United Network for Organ Sharing (UNOS) July 2004 to December 2011. There was clear geographic variation in IABP and dLVAD at transplant. Multivariable analysis demonstrated equivalent cumulative risk of death (adjusted Cox proportional hazard ratio, 1.08; 95% confidence interval, 0.87-1.33; p = 0.51). There was no significant difference in adjusted comparison of perioperative morality, length of stay, postoperative renal failure requiring dialysis, or early acute rejection (p ≥ 0.14 for all). Therefore, data from UNOS suggest that the presence of dLVAD at the time of heart transplantation does not have a detrimental effect on postoperative outcomes compared with IABP, which must be considered in the context of pretransplant mortality and locoregional organ availability.

Rotary mechanical circulatory support systems

A detailed survey of the current trends and recent advances in rotary mechanical circulatory support systems is presented in this paper. Rather than clinical reports, the focus is on technological aspects of these rehabilitating devices as a reference for engineers and biomedical researchers. Existing trends in flow regimes, flow control, and bearing mechanisms are summarized. System specifications and applications of the most prominent continuous-flow ventricular assistive devices are provided. Based on the flow regime, pumps are categorized as axial flow, centrifugal flow, and mixed flow. Unique characteristics of each system are unveiled through an examination of the structure, bearing mechanism, impeller design, flow rate, and biocompatibility. A discussion on the current limitations is provided to invite more studies and further improvements.

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and trade one defect for another. Tissue engineering holds the promise to address this increasing demand. However, most tissue engineering strategies fail to generate stable and functional tissue substitutes because of poor vascularization. This paper focuses on an in vivo tissue engineering chamber model of intrinsic vascularization where a perfused artery and a vein either as an arteriovenous loop or a flow-through pedicle configuration is directed inside a protected hollow chamber. In this chamber-based system angiogenic sprouting occurs from the arteriovenous vessels and this system attracts ischemic and inflammatory driven endogenous cell migration which gradually fills the chamber space with fibro-vascular tissue. Exogenous cell/matrix implantation at the time of chamber construction enhances cell survival and determines specificity of the engineered tissues which develop. Our studies have shown that this chamber model can successfully generate different tissues such as fat, cardiac muscle, liver and others. However, modifications and refinements are required to ensure target tissue formation is consistent and reproducible. This article describes a standardized protocol for the fabrication of two different vascularized tissue engineering chamber models in vivo.

An insight into short- and long-term mechanical circulatory support systems

Cardiogenic shock due to acute myocardial infarction, postcardiotomy syndrome following cardiac surgery, or manifestation of heart failure remains a clinical challenge with high mortality rates, despite ongoing advances in surgical techniques, widespread use of primary percutaneous interventions, and medical treatment. Clinicians have, therefore, turned to mechanical means of circulatory support. At present, a broad range of devices are available, which may be extracorporeal, implantable, or percutaneous; temporary or long term. Although counter pulsation provided by intra-aortic balloon pump (IABP) and comprehensive mechanical support for both the systemic and the pulmonary circulation through extracorporeal membrane oxygenation (ECMO) remain a major tool of acute care in patients with cardiogenic shock, both before and after surgical or percutaneous intervention, the development of devices such as the Impella or the Tandemheart allows less invasive forms of temporary support. On the other hand, concerning mid-, or long-term support, left ventricular assist devices have evolved from a last resort life-saving therapy to a well-established viable alternative for thousands of heart failure patients caused by the shortage of donor organs available for transplantation. The optimal selection of the assist device is based on the initial consideration according to hemodynamic situation, comorbidities, intended time of use and therapeutic options. The present article offers an update on currently available mechanical circulatory support systems (MCSS) for short and long-term use as well as an insight into future perspectives.