The total artificial heart

Harnessing developmental cues for cardiomyocyte production

Developmental research has attempted to untangle the exact signals that control heart growth and size, with knockout studies in mice identifying pivotal roles for Wnt and Hippo signaling during embryonic and fetal heart growth. Despite this improved understanding, no clinically relevant therapies are yet available to compensate for the loss of functional adult myocardium and the absence of mature cardiomyocyte renewal that underlies cardiomyopathies of multiple origins. It remains of great interest to understand which mechanisms are responsible for the decline in proliferation in adult hearts and to elucidate new strategies for the stimulation of cardiac regeneration. Multiple signaling pathways have been identified that regulate the proliferation of cardiomyocytes in the embryonic heart and appear to be upregulated in postnatal injured hearts. In this Review, we highlight the interaction of signaling pathways in heart development and discuss how this knowledge has been translated into current technologies for cardiomyocyte production.

It's all relative: analyzing microbiome compositions, its significance, pathogenesis and microbiota derived biofilms: Challenges and opportunities for disease intervention

Concept of microorganisms has largely been perceived from their pathogenic view point. Nevertheless, it is being gradually revisited in terms of its significance to human health and now appears to be the most dominant force that shapes the immune system of the human body and also determines an individual's predisposition to diseases. Human inhabits bacterial diversity (which is predominant among all microbial communities in human body) occupying 0.3% of body mass, known as microbiota. On birth, a part of microbiota that child obtains is essentially a mother's legacy. So, the review was initiated with this critical topic of microbiotal inheritance. Since, each body site has distinct physiological specifications; therefore, they contain discrete microbiome composition that has been separately discussed along with dysbiosis-induced pathologies originating in different body organs. Factors affecting microbiome composition and may cause dysbiosis like antibiotics, delivery, feeding method etc. as well as the strategies that immune system adopts to prevent dysbiosis have been highlighted. We also tried to bring into attention the topic of dysbiosis induced biofilms, that enables cohort to survive stresses, evolve, disseminate and infection resurgence that is still in dormancy. Eventually, we put spotlight on microbiome significance in medical therapeutics. We didn't merely confine article to gut microbiota, that is being studied more extensively. Numerous community forms at diverse body sites are inter-related, and being exposed to awfully variable perturbations appear to be challenging to evaluate perturbation risks holistically. All aspects have been elaborately discussed to achieve a global depiction of human microbiota in order to meet urgent necessity for protocol standardisation. Demonstrates that environmental challenges (antibiotic use, alterations in diet, stress, smoking etc.) might cause dysbiosis i.e. transition of healthy microbiome composition to the one in which pathogenic microorganisms become more abundant, and eventually results in an infected state.

Fluid-structure interaction modelling of a positive-displacement Total Artificial Heart

For those suffering from end-stage biventricular heart failure, and where a heart transplantation is not a viable option, a Total Artificial Heart (TAH) can be used as a bridge to transplant device. The Realheart TAH is a four-chamber artificial heart that uses a positive-displacement pumping technique mimicking the native heart to produce pulsatile flow governed by a pair of bileaflet mechanical heart valves. The aim of this work was to create a method for simulating haemodynamics in positive-displacement blood pumps, using computational fluid dynamics with fluid-structure interaction to eliminate the need for pre-existing in vitro valve motion data, and then use it to investigate the performance of the Realheart TAH across a range of operating conditions. The device was simulated in Ansys Fluent for five cycles at pumping rates of 60, 80, 100 and 120 bpm and at stroke lengths of 19, 21, 23 and 25 mm. The moving components of the device were discretised using an overset meshing approach, a novel blended weak-strong coupling algorithm was used between fluid and structural solvers, and a custom variable time stepping scheme was used to maximise computational efficiency and accuracy. A two-element Windkessel model approximated a physiological pressure response at the outlet. The transient outflow volume flow rate and pressure results were compared against in vitro experiments using a hybrid cardiovascular simulator and showed good agreement, with maximum root mean square errors of 15% and 5% for the flow rates and pressures respectively. Ventricular washout was simulated and showed an increase as cardiac output increased, with a maximum value of 89% after four cycles at 120 bpm 25 mm. Shear stress distribution over time was also measured, showing that no more than [Formula: see text]% of the total volume exceeded 150 Pa at a cardiac output of 7 L/min. This study showed this model to be both accurate and robust across a wide range of operating points, and will enable fast and effective future studies to be undertaken on current and future generations of the Realheart TAH.

A Comprehensive Review of Mechanical Circulatory Support Devices

Treatment strategies to combat cardiogenic shock (CS) have remained stagnant over the past decade. Mortality rates among patients who suffer CS after acute myocardial infarction (AMI) remain high at 50%. Mechanical circulatory support (MCS) devices have evolved as novel treatment strategies to restore systemic perfusion to allow cardiac recovery in the short term, or as durable support devices in refractory heart failure in the long term. Haemodynamic parameters derived from right heart catheterization assist in the selection of an appropriate MCS device and escalation of mechanical support where needed. Evidence favouring the use of one MCS device over another is scant. An intra-aortic balloon pump is the most commonly used short-term MCS device, despite providing only modest haemodynamic support. Impella CP® has been increasingly used for CS in recent times and remains an important focus of research for patients with AMI-CS. Among durable devices, Heartmate® 3 is the most widely used in the USA. Adequately powered randomized controlled trials are needed to compare these MCS devices and to guide the operator for their use in CS. This article provides a brief overview of the types of currently available MCS devices and the indications for their use.

IGF1-PI3K-induced physiological cardiac hypertrophy: Implications for new heart failure therapies, biomarkers, and predicting cardiotoxicity

Heart failure represents the end point of a variety of cardiovascular diseases. It is a growing health burden and a leading cause of death worldwide. To date, limited treatment options exist for the treatment of heart failure, but exercise has been well-established as one of the few safe and effective interventions, leading to improved outcomes in patients. However, a lack of patient adherence remains a significant barrier in the implementation of exercise-based therapy for the treatment of heart failure. The insulin-like growth factor 1 (IGF1)-phosphoinositide 3-kinase (PI3K) pathway has been recognized as perhaps the most critical pathway for mediating exercised-induced heart growth and protection. Here, we discuss how modulating activity of the IGF1-PI3K pathway may be a valuable approach for the development of therapies that mimic the protective effects of exercise on the heart. We outline some of the promising approaches being investigated that utilize PI3K-based therapy for the treatment of heart failure. We discuss the implications for cardiac pathology and cardiotoxicity that arise in a setting of reduced PI3K activity. Finally, we discuss the use of animal models of cardiac health and disease, and genetic mice with increased or decreased cardiac PI3K activity for the discovery of novel drug targets and biomarkers of cardiovascular disease.

Hybrid membranes for the production of blood contacting surfaces: physicochemical, structural and biomechanical characterization

Background

Due to the shortage of organs’ donors that limits biological heart transplantations, mechanical circulatory supports can be implanted in case of refractory end-stage heart failure to replace partially (Ventricular Assist Device, VAD) or completely (Total Artificial Heart, TAH) the cardiac function. The hemocompatibility of mechanical circulatory supports is a fundamental issue that has not yet been fully matched; it mostly depends on the nature of blood-contacting surfaces.

Methods

In order to obtain hemocompatible materials, a pool of hybrid membranes was fabricated by coupling a synthetic polymer (polycarbonate urethane, commercially available in two formulations) with a decellularized biological tissue (porcine pericardium). To test their potential suitability as candidate materials for realizing the blood-contacting surfaces of a novel artificial heart, hybrid membranes have been preliminarily characterized in terms of physicochemical, structural and mechanical properties.

Results

Our results ascertained that the hybrid membranes are properly stratified, thus allowing to expose their biological side to blood and their polymeric surface to the actuation system of the intended device. From the biomechanical point of view, the hybrid membranes can withstand deformations up to more than 70 % and stresses up to around 8 MPa.

Conclusions

The hybrid membranes are suitable for the construction of the ventricular chambers of innovative mechanical circulatory support devices.

3D Tissue and Organ Printing-Hope and Reality

Three-dimensional (3D) bioprinting is an emerging, groundbreaking strategy in tissue engineering, allowing the fabrication of living constructs with an unprecedented degree of complexity and accuracy. While this technique greatly facilitates the structuring of native tissue-like architectures, many challenges still remain to be faced. In this review, the fruits of recent research that demonstrate how advanced bioprinting technologies, together with inspiring creativity, can be used to address these challenges are presented and discussed. Next, the future of the field is discussed, in terms of expected developments, as well as possible directions toward the realization of the vision of fully functional, engineered tissues, and organs. Last, a few hypothetical scenarios for the role 3D bioprinting may play in future tissue engineering are depicted, with an emphasis on its impact on tomorrow's regenerative medicine.

Designing Biomaterial Platforms for Cardiac Tissue and Disease Modeling

Heart disease is one of the leading causes of death in the world. There is a growing demand for in vitro cardiac models that can recapitulate the complex physiology of the cardiac tissue. These cardiac models can provide a platform to better understand the underlying mechanisms of cardiac development and disease and aid in developing novel treatment alternatives and platforms towards personalized medicine. In this review, a summary of engineered cardiac platforms is presented. Basic design considerations for replicating the heart's microenvironment are discussed considering the anatomy of the heart. This is followed by a detailed summary of the currently available biomaterial platforms for modeling the heart tissue in vitro. These in vitro models include 2D surface modified structures, 3D molded structures, porous scaffolds, electrospun scaffolds, bioprinted structures, and heart-on-a-chip devices. The challenges faced by current models and the future directions of in vitro cardiac models are also discussed. Engineered in vitro tissue models utilizing patients' own cells could potentially revolutionize the way we develop treatment and diagnostic alternatives.

Exercise training with cycle ergometry in the intensive care unit after total artificial heart implantation

A 53-year-old male mountain biker received a total artificial heart and remained in the cardiovascular intensive care unit for 56 days. To reduce functional decline caused by inactivity, he performed a six-session cycle ergometer exercise program in his hospital room. Traditional cardiac responses for exercise prescription were not applicable; therefore, a symptom-limited, monitored progression scheme in conjunction with recommendations for the artificial heart was implemented to modify duration and intensity. Over the six sessions, the patient improved his distance pedaled by 320% and functional capacity by 1 metabolic equivalent. He was subsequently discharged from the hospital and later successfully transplanted without readmission.

Chronic Kidney Disease and Acute Kidney Injury Outcomes Post Left Ventricular Assist Device Implant

Introduction

Left ventricular assist devices (LVAD) are used as a bridge to heart transplant or destination therapy for patients with the New York Heart Association (NYHA) class 3 or 4 heart failure. Acute kidney injury (AKI) or need for renal replacement therapy (RRT) post-LVAD implant can lead to poor outcomes. Identifying risk factors of AKI post-LVAD implant can help stratify potential LVAD candidates.

Methods

This is a retrospective study of all patients who received continuous-flow LVAD at our institution from January 2015 until August 2017. We calculated the incidence of AKI and the need for RRT post-LVAD implant, as well as the rate of renal recovery and survival rates at 30 days and 1-year post-LVAD implant. The presence of chronic kidney disease (CKD) and proteinuria was assessed, and kidney ultrasound results were reviewed on all patients, if available. CKD was present if estimated glomerular filtration rate (eGFR) was <60 mL/min per 1.73m² for ≥3 months preceding LVAD implant and/or presence of proteinuria ≥ 20 mg/dL on two or more urine samples prior to LVAD implant and/or an abnormal kidney ultrasound with increased echogenicity, small size <9 cm or scarring. AKI was defined as per the current Kidney Disease Initiative Global Outcomes (KDIGO) guidelines.

Results

A total of 137 patients received LVAD during this time period. There were 112 males and 25 females with a mean age of 59.2 years. Incidence of AKI and the need for RRT post-LVAD implant were 64% and 19.7%, respectively. Sub-group analysis was performed based on the presence of CKD, advanced CKD stage (Stage 1-2 vs 3-5), proteinuria and abnormal kidney ultrasound. The incidence of AKI post-LVAD implant was significantly higher if baseline CKD was present (P = 0.028), and patient had an advanced CKD stage (P = 0.008). The need for RRT post-LVAD implant was significantly higher if baseline CKD was present (P = 0.015), and the patient had an abnormal kidney ultrasound (P = 0.04). Thirty-day and one-year mortality rates post-LVAD implants were 4.3% and 21.1%, respectively for the entire cohort. Out of the 27 patients requiring RRT, nine (33.3%) came off RRT before one year. Compared to the eGFR on the day of LVAD implant, eGFR at 30 days post-LVAD implant was higher in 57% and lower in 42% patients. At one year, this eGFR improvement reversed and eGFR was lower in 67% and higher in 32% patients.

Conclusion

The incidence of AKI and need for RRT post-LVAD implant are very high. The presence of CKD, advanced CKD stage, and an abnormal kidney ultrasound are statistically significant risk factors of AKI post-LVAD implant and/or need for RRT. Identifying these renal risk factors can help stratify the potential LVAD candidates. Only one out of three patients requiring RRT achieved dialysis independence by one-year post-LVAD implant.

Cardiac Assist Devices: Early Concepts, Current Technologies, and Future Innovations

Congestive heart failure (CHF) is a debilitating condition that afflicts tens of millions of people worldwide and is responsible for more deaths each year than all cancers combined. Because donor hearts for transplantation are in short supply, a safe and durable means of mechanical circulatory support could extend the lives and reduce the suffering of millions. But while the profusion of blood pumps available to clinicians in 2019 tend to work extremely well in the short term (hours to weeks/months), every long-term cardiac assist device on the market today is limited by the same two problems: infections caused by percutaneous drivelines and thrombotic events associated with the use of blood-contacting surfaces. A fundamental change in device design is needed to address both these problems and ultimately make a device that can support the heart indefinitely. Toward that end, several groups are currently developing devices without blood-contacting surfaces and/or extracorporeal power sources with the aim of providing a safe, tether-free means to support the failing heart over extended periods of time.

How New Support Devices Change Critical Care Delivery

Mechanical support devices are used to support failing cardiac, respiratory, or both systems. Since Gibbon developed the cardiopulmonary bypass in 1953, collaborative efforts by medical centers, bioengineers, industry, and the National Institutes of Health have led to development of mechanical devices to support heart, lung, or both. These devices are used as a temporary or long-term measures for acute collapse of circulatory system and/or respiratory failure. Patients are managed on these support devices as a bridge to recovery, bridge to long term devices, or bridge to transplant. The progress in development of these devices has improved mortality and quality of life in select groups of patients. Care of these patients requires a multidisciplinary team approach, which includes cardiac surgeons, critical care physicians, cardiologists, pulmonologists, nursing staff, and perfusionists. Using a team approach improves outcomes in these patients.

Death, Devices, and Double Effect

Along with the growing utilization of the total artificial heart (TAH) comes a new set of ethical issues that have, surprisingly, received little attention in the literature: (1) How does one apply the criteria of irreversible cessation of circulatory function (a core concept in the Uniformed Determination of Death Act) given that a TAH rarely stops functioning on its own? (2) Can one appeal to the doctrine of double effect as an ethical rationale for turning off a TAH given that this action directly results in death? And, (3) On what ethical grounds can a physician turn off a TAH in view of the fact that either the intent of such an action or the outcome is always, and necessarily, death? The aim of this article is not to answer these questions but to highlight why these questions must be explored in some depth given the growing use of TAH technology.