Complications in children with ventricular assist devices: systematic review and meta-analyses

Machine learning based on computational fluid dynamics enables geometric design optimisation of the NeoVAD blades

The NeoVAD is a proposed paediatric axial-flow Left Ventricular Assist Device (LVAD), small enough to be implanted in infants. The design of the impeller and diffuser blades is important for hydrodynamic performance and haemocompatibility of the pump. This study aimed to optimise the blades for pump efficiency using Computational Fluid Dynamics (CFD), machine learning and global optimisation. Meshing of each design typically included 6 million hexahedral elements and a Shear Stress Transport turbulence model was used to close the Reynolds Averaged Navier-Stokes equations. CFD models of 32 base geometries, operating at 8 flow rates between 0.5 and 4 L/min, were created to match experimental studies. These were validated by comparison of the pressure-flow and efficiency-flow curves with those experimentally measured for all base prototype pumps. A surrogate model was required to allow the optimisation routine to conduct an efficient search; a multi-linear regression, Gaussian Process Regression and a Bayesian Regularised Artificial Neural Network predicted the optimisation objective at design points not explicitly simulated. A Genetic Algorithm was used to search for an optimal design. The optimised design offered a 5.51% increase in efficiency at design point (a 20.9% performance increase) as compared to the best performing pump from the 32 base designs. An optimisation method for the blade design of LVADs has been shown to work for a single objective function and future work will consider multi-objective optimisation.

Chest X-ray Interpretation: Detecting Devices and Device-Related Complications

This short review has the aim of helping the radiologist to identify medical devices when interpreting a chest X-ray, as well as looking for their most commonly detectable complications. Nowadays, many different medical devices are used, often together, especially in critical patients. It is important for the radiologist to know what to look for and to remember the technical factors that need to be considered when checking each device's positioning.

Rethinking status 1A criteria in pediatric cardiac transplantation: A case for the prioritization of patients with single ventricle anatomy supported by ventricular assist devices

Over the past 2 years advancements in the techniques and technology of pediatric heart transplantation have exponentially increased. However, even as the number of pediatric donor hearts has grown, demand for this limited resource continues to far outpace supply. Thus, lifesaving support in the form of ventricular assist devices (VAD) has become increasingly utilized in bridging pediatric patients to cardiac transplant. In the current pediatric heart transplant listing criteria, adopted by the United Network for Organ Sharing (UNOS) in 2016, all pediatric patients with a VAD are granted 1A status and assigned top transplant priority regardless of their underlying pathology. However, should this be the case? We suggest that the presence of a VAD alone may not be sufficient for status 1A listing. In doing so, we specifically highlight the heightened acuity, resource utilization, risk profile, and diminished outcomes in patients with single ventricle physiology supported with VAD as compared to patients with structurally normal hearts who would both be listed under 1A status. Given this, from a distributive justice perspective, we further suggest that the lack of granularity in current pediatric cardiac transplant listing categories may inadvertently lead to an inequitable distribution of donor organs and hospital resources especially as it pertains to those with single ventricle anatomy on VAD support. We propose revisiting the current listing priorities in light of improved techniques, technology, and recent data to mitigate this phenomenon. By doing this, pediatric patients with single ventricle disease might be more equitably stratified while awaiting heart transplant.

Perioperative Outcomes in Patients With Failing Single-Ventricle Physiology Undergoing Ventricular Assist Device Placement: A Single Institutional Experience

OBJECTIVE

To address the current lack of specified data existing regarding the perioperative characteristics and outcomes in a novel patient population, which may bridge the current understanding of how patient characteristics and perioperative management may influence the postoperative hospital course before cardiac transplantation.

DESIGN

A retrospective electronic chart review included all patients with failing single- ventricle (SV) physiology receiving ventricular assist device (VAD) support at a high-volume pediatric VAD center between April 5, 2010, and December 1, 2020, using institution-based electronic medical records for retrospective analysis.

SETTING

At a single pediatric hospital.

PARTICIPANTS

Fourteen pediatric patients with failing SV physiology receiving ventricular assist device therapy (SVAD).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Preoperative, intraoperative, and postoperative patient demographic and medical data were obtained from prior inpatient progress notes, laboratory values, anesthetic records, cardiac catheterization reports, echocardiography reports, and postoperative surgical notes entered during inpatient encounters at the time of SVAD placement. Between April 5, 2010, and December 1, 2020, 16 VAD device implants supported 14 pediatric patients with failing SV physiology. Most patients presented with a preoperative diagnosis of hypoplastic left heart syndrome (N = 9, 64.3%). A total of 6 patients expired on VAD therapy (43%), 7 (50%) survived to receive a cardiac transplant, and 1 patient currently remains on device therapy.

CONCLUSION

Although our institutional approach represents a single perspective, we anticipate that our experience institutional experience may prove helpful to others caring for peditric patients with single ventricle physiology undergoing ventricular assist device placement and promote collaborative efforts to improve their care.

Bivalirudin or Unfractionated Heparin for Anticoagulation in Pediatric Patients on Continuous Flow Ventricular Assist Device Support: Single-Center Retrospective Cohort Study

OBJECTIVES

Bivalirudin is a direct thrombin inhibitor that is being increasingly used for anticoagulation in children after ventricular assist device (VAD) implantation. While the data on bivalirudin use in pulsatile flow VADs are growing, reports on its use in patients on continuous flow (CF) VAD as well as comparisons of associated outcomes with unfractionated heparin (UFH) remain limited.

DESIGN

Retrospective cohort study.

SETTING

Single tertiary-quaternary referral center.

PATIENTS

All patients less than 21 years old on CF-VAD support who received bivalirudin or UFH for anticoagulation between the years 2016 and 2020.

INTERVENTIONS

Not applicable.

MEASUREMENTS AND MAIN RESULTS

Clinical characteristics compared between the cohorts included time to target range of anticoagulation, markers of hemolysis, and prevalence of hemocompatibility-related adverse events such as major hemorrhagic complications, ischemic stroke, and pump thrombosis. In 42 unique patients (41 HeartWare HVAD [Medtronic, Minneapolis, MN], one HeartMate 3 LVAD [Abbott Laboratories, Abbott Park, IL]) during the study period, a total of 67 encounters of IV anticoagulation infusions (29 UFH and 38 bivalirudin) were retrospectively reviewed. In comparison with use of UFH, bivalirudin was associated with lesser odds of major bleeding complications (odds ratio [OR], 0.29; 95% CI, 0.09-0.97; p = 0.038). We failed to identify any difference in odds of major thrombotic complications (OR, 2.53; 95% CI, 0.47-13.59; p = 0.450). Eight of the patients (28%) on UFH were switched to bivalirudin due to hemorrhagic or thrombotic complications or inability to achieve therapeutic anticoagulation, while two of the patients (5%) on bivalirudin were switched to UFH due to hemorrhagic complications. Bivalirudin was used for a "washout" in eight cases with concern for pump thrombosis-six had resolution of the pump thrombosis, while two needed pump exchange.

CONCLUSIONS

Use of bivalirudin for anticoagulation in patients on CF-VAD support was associated with lesser odds of hemorrhagic complications compared with use of UFH. Bivalirudin "washout" was successful in medical management of six of eight cases of possible pump thrombosis.

Computational Evaluation of Cardiac Function in Children Supported with Heartware VAD, HeartMate 2 and HeartMate 3 Left Ventricular Assist Devices

Heart failure is one of the principal causes of morbidity and mortality in children. Treatment techniques may not work, and heart transplantation may be required as a result. The current state of donor-organ supply means that many patients cannot undergo transplantation. In these patients, ventricular assist devices (VADs) may be used to bridge the time until the transplantation. Continuous-flow VADs are increasingly being implanted to paediatric patients. The aim of this study was to evaluate cardiac function in children supported with Heartware HVAD, HeartMate2 and HeartMate3 devices using computational simulations. A lumped-parameter model simulating cardiac function in children around 12 years of age was used to simulate dilated cardiomyopathy and heart-pump support. The operating speeds in HVAD, HeartMate2 and HeartMate3 were selected as 2600 rpm, 8700 rpm and 5200 rpm constant speed, respectively, while the Lavare cycle and artificial-pulse modes were used to generate mean pump outputs at around 4.40 L/min and mean arterial pressures at around 82 mmHg in each device. Aortic pulse pressure was 11 mmHg, 14 mmHg and 6 mmHg under HVAD, HeartMate2 and HeartMate3 support, respectively. HVAD’s Lavare cycle and HeartMate3’s artificial pulse increased aortic pulse pressure to 15 mmHg and 20 mmHg. HeartMate3 with artificial-pulse mode may be more beneficial in reducing arterial-pulsatility-associated problems.

Patient-Specific Modelling and Parameter Optimisation to Simulate Dilated Cardiomyopathy in Children

PURPOSE

Lumped parameter modelling has been widely used to simulate cardiac function and physiological scenarios in cardiovascular research. Whereas several patient-specific lumped parameter models have been reported for adults, there is a limited number of studies aiming to simulate cardiac function in children. The aim of this study is to simulate patient-specific cardiovascular dynamics in children diagnosed with dilated cardiomyopathy, using a lumped parameter model.

METHODS

Patient data including age, gender, heart rate, left and right ventricular end-systolic and end-diastolic volumes, cardiac output, systolic and diastolic aortic pressures were collected from 3 patients at Great Ormond Street Hospital for Children, London, UK. Ventricular geometrical data were additionally retrieved from cardiovascular magnetic resonance images. 23 parameters in the lumped parameter model were optimised to simulate systolic and diastolic pressures, end-systolic and end-diastolic volumes, cardiac output and left and right ventricular diameters in the patients using a direct search optimisation method.

RESULTS

Difference between the haemodynamic parameters in the optimised cardiovascular system models and clinical data was less than 10%.

CONCLUSION

The simulation results show the potential of patient-specific lumped parameter modelling to simulate clinical cases. Modelling patient specific cardiac function and blood flow in the paediatric patients would allow us to evaluate a variety of physiological scenarios and treatment options.

Ethical and practical dilemmas in cardiac transplantation in infants: a literature review

The waiting time in infants for a cardiac transplant remains high, due to the scarcity of donors. Consequently, waiting list morbidity and mortality are higher than those in other age groups. Therefore, the decision to list a small infant for cardiac transplantation is seen as an ethical dilemma by most physicians. This review aims to describe outcomes, limitations, and ethical considerations in infant heart transplantation. We used Medline and Embase as data sources. We searched for publications on infant (< 1 year) heart transplantation, bridge-to-transplant and long-term outcomes, and waiting list characteristics from January 2009 to March 2021. Outcome after cardiac transplant in infants is better than that in older children (1-year survival 88%), and complications are less frequent (25% CAV, 10% PTLD). The bridge-to-transplant period in infants is associated with increased mortality (32%) and decreased transplantation rate (43%). This is mainly due to MCS complications or the limited MCS options (with 51% mortality in infancy). Outcomes are worse for infants with CHD or in need of ECMO-support.Conclusion: Infants listed for cardiac transplantation have a high morbidity and mortality, especially in the period between diagnosis and transplantation. For those who receive cardiac transplant, the outlook is encouraging. Unfortunately, despite growing experience in VAD, mortality in children < 10 kg and children with CHD remains high. After transplantation, patients carry a psychological burden and there is a probability of re-transplantation later in life, with decreased outcomes compared to primary transplantation. These considerations are seen as an important ethical dilemma in many centers, when considering cardiac transplantation in infants (< 1 year). What is Known: • For infants, waitlist mortality remains high. In the pediatric population, MCS reduces the waiting list mortality. What is New: • Outcomes after infant cardiac transplantation are better than other age groups; however, MCS options remain limited, with persistently high waiting list mortality. • Future developments in MCS and alternative options to reduce waiting list mortality such as ABO-incompatible transplantation and pulmonary artery banding are encouraging and will improve ethical decision-making when an infant is in need of a cardiac transplant.