Ventricular Assist Device in Children with Cardiac Graft Failure

Clinical approach to mechanical circulatory support in the transplant patient from the Pediatric Heart Transplant Society

The use of mechanical circulatory support (MCS) for pediatric patients who have undergone heart transplant has grown rapidly in the past decade. This includes support in the immediate post-transplant period and "rescue" therapy for patient later in their transplant course. Extracorporeal membrane oxygenation (ECMO) remains a standard modality of support for intraoperative concerns and for acute decompensation in the immediate post-transplant period. However, both pulsatile and continuous flow ventricular assist devices (VADs) have been used with increasing success in transplant patients for longer durations of support. Centers participating in the Pediatric Heart Transplant Society (PHTS) were queried to provide their internal protocols and rationale for mechanical circulatory support following heart transplant. These protocols coupled with evidence-based literature were used to provide the following description of clinical approaches to MCS in the transplant patient highlighting areas of both broad consensus and significant practice variation.

Ventricular assist device support following pediatric heart transplantation

BACKGROUND

VAD support for early graft failure after HTx is a rare event in pediatrics.

METHODS

We retrospectively describe our single-center experience with post-HTx VAD support in a cohort of patients transplanted between 01/05 and 12/20.

RESULTS

Nine patients underwent VAD insertion in the early post-HTx period [median age 6.1 years (Range 0.3-20.3), median weight 17.6 kg (Range 3.5-65.0), and congenital heart disease (67%)]. Of the nine patients with early graft failure, almost half (44%) were implanted after 2015 and all of these patients had a pre-HTx plan for possible post-transplant VAD insertion. Time to VAD implant was a median of 0 day (Range 0-11). Total time on VAD support was a median of 12 days (Range 3.0-478.0). Two-thirds (n = 6; 67%) of the patients were weaned from support, retransplanted (11%) and two patients died (22%). In all of the patients where post-HTx VAD was anticipated there was 100% survival.

CONCLUSIONS

In this small patient series, post-HTx VAD was a useful measure in selected patients especially with pre-HTx planning. However, more shared experiences to verify these findings are needed.

Moderate-severe primary graft dysfunction after pediatric heart transplantation

BACKGROUND

PGD is a complication after heart transplantation (OHT) and a significant cause of mortality, particularly in infant recipients. Lack of standardized definition of PGD in the pediatric population makes the prevalence and magnitude of impact unclear.

METHODS

ISHLT PGD consensus guidelines, which include inotrope scores and need for MCS, were applied retrospectively to 208 pediatric OHT recipients from a single institution from 1/2005-5/2016. PGD was defined as: moderate PGD-inotrope score >10 on postoperative day 1 (24-48 hours), and severe PGD-MCS within 24 hours (in the absence of detectable rejection).

RESULTS

PGD occurred in 34 patients (16.3%); 14 of which had severe PGD (6.7%). Multivariate risk factors for PGD included CPB time (OR 10.3/10 min, 95% 10.05, 10.2, P = 0.03), Fontan palliation (OR 1.9, 95% 1.2, 3.97), and PCM (OR 5.65, 95% 1.52, 22.4); but not age, weight, ischemic time, or donor characteristics. Upon sub-analysis excluding patients with PCM, increased CPB was a significant multivariate risk factor (OR 10.09, 95% 9.89, 10.12, P = 0.003). Patients with PGD had decreased discharge survival compared to those without PGD (85% vs 96%, P < 0.01). Severe PGD was associated with the poorest 1-year survival (57% vs 91% without PGD, P = 0.04).

CONCLUSION

Patients with prolonged CPB are potentially at risk for developing PGD. Neither infant recipients nor donor characteristics were associated with an increased risk of PGD in the current era.

Pediatric ventricular assist devices: current challenges and future prospects

The field of mechanical circulatory support has made great strides in the preceding 2 decades. Although pediatric mechanical circulatory support has lagged behind that of adults, the gap between them is expected to close soon. The only device currently approved by the US Food and Drug Administration for use in children is the Berlin Heart EXCOR ventricular assist device (VAD). The prospective Berlin Heart Investigational Device Exemption Trial demonstrated good outcomes, such as bridge to transplantation or recovery, in ~90% of children supported with this device. However, a high incidence of hemorrhagic and thrombotic complications was also noted. As a result, pediatric centers have just started implanting adult intracorporeal continuous-flow devices in children. This paradigm shift has opened a new era in pediatric mechanical circulatory support. Whereas children on VAD were previously managed exclusively in hospital, therapeutic options such as outpatient management and even destination therapy have been becoming a reality. With continued miniaturization and technological refinements, devices currently in development will broaden the range of options available to children. The HeartMate 3 and HeartWare MVAD are two such compact VADs, which are anticipated to have great potential for pediatric use. Additionally, a pediatric-specific continuous-flow VAD, the newly redesigned Jarvik Infant 2015, is currently undergoing preclinical testing and is expected to undergo a randomized clinical trial in the near future. This review aims to discuss the challenges posed by the use of intracorporeal adult continuous-flow devices in children, as well as to provide our perspective on the future prospects of the field of pediatric VADs.

Pediatric ventricular assist devices

The domain of pediatric ventricular assist device (VAD) has recently gained considerable attention. Despite the fact that, historically, the practice of pediatric mechanical circulatory support (MCS) has lagged behind that of adult patients, this gap between the two groups is narrowing. Currently, the Berlin EXCOR VAD is the only pediatric-specific durable VAD approved by the U.S Food and Drug Administration (FDA). The prospective Berlin Heart trial demonstrated a successful outcome, either bridge to transplantation (BTT), or in rare instances, bridge to recovery, in approximately 90% of children. Also noted during the trial was, however, a high incidence of adverse events such as embolic stroke, bleeding and infection. This has incentivized some pediatric centers to utilize adult implantable continuous-flow devices, for instance the HeartMate II and HeartWare HVAD, in children. As a result of this paradigm shift, the outlook of pediatric VAD support has dramatically changed: Treatment options previously unavailable to children, including outpatient management and even destination therapy, have now been becoming a reality. The sustained demand for continued device miniaturization and technological refinements is anticipated to extend the range of options available to children-HeartMate 3 and HeartWare MVAD are two examples of next generation VADs with potential pediatric application, both of which are presently undergoing clinical trials. A pediatric-specific continuous-flow device is also on the horizon: the redesigned Infant Jarvik VAD (Jarvik 2015) is undergoing pre-clinical testing, with a randomized clinical trial anticipated to follow thereafter. The era of pediatric VADs has begun. In this article, we discuss several important aspects of contemporary VAD therapy, with a particular focus on challenges unique to the pediatric population.