Evolving understanding of total artificial heart support of young infants and children

SMC5 Plays Independent Roles in Congenital Heart Disease and Neurodevelopmental Disability

Up to 50% of patients with severe congenital heart disease (CHD) develop life-altering neurodevelopmental disability (NDD). It has been presumed that NDD arises in CHD cases because of hypoxia before, during, or after cardiac surgery. Recent studies detected an enrichment in de novo mutations in CHD and NDD, as well as significant overlap between CHD and NDD candidate genes. However, there is limited evidence demonstrating that genes causing CHD can produce NDD independent of hypoxia. A patient with hypoplastic left heart syndrome and gross motor delay presented with a de novo mutation in SMC5. Modeling mutation of smc5 in Xenopus tropicalis embryos resulted in reduced heart size, decreased brain length, and disrupted pax6 patterning. To evaluate the cardiac development, we induced the conditional knockout (cKO) of Smc5 in mouse cardiomyocytes, which led to the depletion of mature cardiomyocytes and abnormal contractility. To test a role for Smc5 specifically in the brain, we induced cKO in the mouse central nervous system, which resulted in decreased brain volume, and diminished connectivity between areas related to motor function but did not affect vascular or brain ventricular volume. We propose that genetic factors, rather than hypoxia alone, can contribute when NDD and CHD cases occur concurrently.

Pediatric mechanical circulatory support - a review

The history of mechanical circulatory support began in 1953, as the first heart-lung machine enabled surgeons to perform complex open heart surgery. Heart failure is more prevalent in adults than pediatric patients which has led to the development of devices for adults with end-stage heart failure at a faster pace. Pediatric mechanical circulatory support has been derived from adult durable devices and subsequently applied in the adolescent population. The application of adult devices in children is inherently problematic due to size mismatch, especially in smaller patients. There has been an increasing interest in developing durable pumps that are appropriate for children for several reasons, with the primary factor being the number of children with end-stage heart failure far exceeding the number of potential donors. Mechanical circulatory support (MCS) for children can be divided into short-term temporary support and long-term durable support. The goal of this review is to discuss the devices available for the pediatric population and review the options for support in complex patients including single-ventricle anatomy, biventricular support, and total artificial heart options. We will also briefly discuss the Pumps for Kids, Infants, and Neonates (PumpKIN) Trial and MCS registries, including the Advanced Cardiac Therapies Improving Outcomes Network (ACTION).

Patient and Device Selection in Pediatric MCS: A Review of Current Consensus and Unsettled Questions

The field of pediatric ventricular assist device (VAD) support has expanded significantly over the past 20 years, with one third of pediatric heart transplant recipients currently being bridged to transplant with a VAD. Despite increased pediatric VAD utilization, however, there remains little formalized guidance for patient or device selection. The population of children with advanced heart failure is quite heterogeneous, and the available data suggest that VAD outcomes vary significantly based upon patient size, anatomy, level of illness, and type of device implanted. In an effort to better understand current practice patterns and identify populations for whom there does not appear to be a consensus approach to achieving optimal VAD outcomes, the Advanced Cardiac Therapies Improving Outcomes Network (ACTION) has surveyed clinical decision-making among member sites and conducted a review of the available literature regarding patient population-specific VAD outcomes and center-specific practices related to patient and device selection. Rather than aiming to provide clinical guidelines, this document offers an overview of contemporary approaches to patient and device selection, highlighting specific populations for whom there is not a consensus approach to achieving reliably good VAD outcomes, as these populations may benefit most from future research and quality improvement efforts directed toward identifying best practice.

Mechanical Support for The Failing Single Ventricle at Pre-Fontan Stage: Current State of The Field and Future Directions

With the substantial growth of pediatric ventricular assist device (VAD) support, there has been an expansion of the target population towards more complex patients, including congenital heart disease (CHD) with single ventricle (SV) physiology. The outcomes of Stage I and Stage II SV-CHD patients on VAD support from the Pedimacs database are poor, with less than 50% survival on VAD by the 3-month mark in both. The primary objective of this article is to describe the current state of VAD support for the failing Stage I and II SV-CHD circulation, to provide insight into potential areas of outcome improvement. We reviewed the published literature in the form of database and registry reports as well as single-center studies to discuss the outcomes of Stage I and Stage II SV-CHD patients on VAD support. Registry-based studies suggest that VAD support for the failing Stage I and Stage II SV-CHD circulations is challenging. However, the more promising outcomes in several single-institutional reports for both Stage I and Stage II SV-VAD indicate that the grim picture from the databases does not reflect the best outcomes that are possible to be achieved, potentially at experienced centers with higher volumes. Areas of future study and potential improvement including timely initiation of VAD support in the cohort of patients expected to not be a candidate for standard SV palliations, pump selection and the benefits of continuous-flow devices, and the decision-making for setting up the optimum circulation for VAD support, be it Fontan completion if feasible or takedown to shunt physiology.

The total artificial heart in patients with congenital heart disease

Background

While ventricular assist devices (VADs) remain the cornerstone of mechanical circulatory support (MCS), the total artificial heart (TAH-t) has gained popularity for certain patients in whom VAD support is not ideal. Congenital heart disease (CHD) patients often have barriers to VAD placement due to anatomic and physiological variation and thus can benefit from the TAH-t. The purpose of this study is to analyze the differences in TAH application and outcomes in patients with and without CHD.

Methods

The SynCardia Department of Clinical Research provided data upon request for all TAH-t implantations worldwide from December 1985 to October 2019. These patients were divided into two groups by pre-implantation diagnosis of CHD and non-CHD.

Results

A total of 1,876 patients were identified. Eighty (4%) of these patients also carried a diagnosis of CHD. There was a higher proportion of children in the CHD cohort (16.3% vs. 2.1%, P<0.001) and this translated into a lower average age amongst the two groups (34±13 vs. 49±13 years, P<0.001). There were also significantly more females in the CHD group (22.8% vs. 12.8%, P=0.010). CHD patients were more likely to be supported with a 50 cc TAH-t (11.3% vs. 4.5%, P=0.005) while all other support characteristics, including duration of support, were similar between the groups. All measured outcomes were similar between CHD and non-CHD patients including positive outcome (alive on device or transplanted), 1-month conditional survival, and rate of Freedom Driver use.

Conclusions

TAH-t is an effective means to support patients with CHD. Patients with CHD had similar survival, support characteristics, and frequency of discharge compared to patients without CHD. As MCS continues to grow, its indications broadened, and its contraindications narrowed, more patient populations will see the benefit of the TAH's continuously developing technology.