Mechanical cardiopulmonary support in children and young adults: extracorporeal membrane oxygenation, ventricular assist devices, and long-term support devices

Integrated long-term multifunctional pediatric mechanical circulatory assist device

There continues to be limited, viable ventricular assist device technology options to support the dysfunctional states of pediatric heart failure. To address this need, we are developing a magnetically suspended, versatile pumping technology that uniquely integrates two blood pumps in a series configuration within a single device housing. This device enables operational switching from the usage of one pump to another as needed for clinical management or to support growth and development of the pediatric patient. Here, we present the initial design where we conducted a virtual fit study, the Taguchi Design Optimization Method, iterative design to develop pump geometries. Computational tools were used to estimate the pressure generation, capacity delivery, hydraulic efficiency, fluid stress levels, exposure time to stresses, blood damage index, and fluid forces on the impellers. Prototypes of the pumps were tested in a flow loop using a water-glycerin solution. Both designs demonstrated the capability to generate target pressures and flows. Blood damage estimations were below threshold levels and achieved design requirements; however, maximum scalar stress levels were above the target limit. Radial and axial forces were less than 1 N and 10 N, respectively. The performance data trends for physical prototypes correlated with theoretical expectations. The centrifugal prototype was able to generate slightly higher pressure rises than numerical predictions. In contrast, the axial prototype outperformed the computational studies. Experimental data were both repeatable and reproducible. The findings from this research are promising, and development will continue.

The Use of Berlin Heart EXCOR VAD in Children Less than 10 kg: A Single Center Experience

Objective: Despite the improvement in ventricular assist device (VAD) therapy in adults and in adolescents, in infant population only Berlin Heart EXCOR (BHE) is licensed as long term VAD to bridge children to Heart Transplantation (HTx). Particularly demanding in terms of morbidity and mortality are smallest patients namely the ones implanted in the first year of life or with a lower body surface area. This work aims at retrospective reviewing a single center experience in using BHE in children with a body weight under 10 kg.

Methods: Data of all pediatric patients under 10 kg undergoing BHE implantation in our institution from March 2002 to March 2016 were retrospectively reviewed.

Results: Of the 30 patients enrolled in the study, 53% were male, 87% were affected by a dilated cardiomyopathy with an average weight and age at the implantation of 6.75 ± 2.16 Kg and 11.57 ± 10.12 months, respectively. Three patients (10%) required a BIVAD implantation. After the implantation, 7 patients (23%) required re-intervention for bleeding and 9 patients (30%) experienced BHE cannulas infection. A total of 56 BHE pump were changed for thrombus formation (1.86 BHE pump for patient). The average duration of VAD support was 132.8 ± 94.4 days. Twenty patients (67%) were successfully transplanted and 10 patients (33%) died: 7 for major neurological complication and 3 for sepsis.

Conclusion: Mechanical support in smaller children with end stage heart failure is an effective strategy for bridging patients to HTx. The need for BIVAD was relegated, in the last years, only to restrictive cardiomiopathy. Further efforts are required in small infants to improve anticoagulation strategy to reduce neurological events and BHE pump changes.

Steady and transient flow analysis of a magnetically levitated pediatric VAD: time varying boundary conditions

A magnetically levitated impeller within a pediatric ventricular assist device operates under highly transient flow conditions. In this study, computational analyses were performed to investigate the hydraulic performance and fluid forces on the impeller under the steady and dynamic flow conditions, including: 1) time-varying boundary conditions (TVBC) considering a pulsed pump flow rate and pulsed left ventricular pressure; 2) transient rotational sliding interfaces (TRSI) to capture virtual blade rotation. Under steady flow conditions, the pressure generation for 0.5-6 l/min over 6000-10000 rpm was 20-140 mmHg; experimental validation agreed to within 6-27%. Under transient flow conditions, the outflow pressure of the pump increased with higher inlet pressure during the TVBC simulation. During TVBC, the pressure rise across the pump decreased as a function of higher flow rates and increased as a function of lower flow rates. The radial fluid forces varied directly with the flow rate by demonstrating larger forces at higher flow rates. For TRSI simulations, pressure fluctuations due the blade passage frequency were found to have 12 peaks per revolution, having magnitude ranges of 
0.7 and 1.0 mmHg for 8 000 and 10 000 rpm, respectively. At 8 000 rpm, the fluid forces ranged from 1.15-1.17 N (axial) and 0.02-0.11 N (radial). Transient simulations model implant scenarios more realistically and provide critical information about the fluid conditions in the pump.

Neurosurgical complications of left ventricular assist devices in children

OBJECT

Left ventricular assist devices (LVADs) are continuous or pulsatile flow devices that could potentially be life-saving measures for patients with end-stage heart failure. These devices have clear advantages over extracorporeal membrane oxygenation (ECMO) and are often used in adults. They are only recently being commonly used in the pediatric age group. As the use of LVADs becomes more mainstream in children, it is important to determine the complication profile associated with these devices. Furthermore, with the increasing application of LVADs in children, pediatric neurosurgeons are seeing a correlative increase in associated neurological complications. In this study, the authors reviewed the incidence of neurological complications due to LVAD use in the pediatric age group and the role of neurosurgery in treatment.

METHODS

The authors examined data regarding patients with LVADs from the Texas Children's Hospital Heart Center database (July 01, 2007, to June 30, 2011) and recorded neurological complications requiring neurosurgical consultation. They identified 2 children who underwent craniotomies during LVAD treatment.

RESULTS

Intracranial hemorrhage occurred in 3 (6.5%) of the 46 patients treated with an LVAD at the authors' institution. Of these patients, 2 were treated with craniotomies for life-threatening intracranial hemorrhages. The 3 patients in the neurosurgical cohort presented with cerebral infarction, decreased level of consciousness, and/or seizure. At the last follow-up (286, 503, and 550 days), 1 patient (case 2) had no decline in neurological status, underwent a successful heart transplant, and was discharged home; 1 patient (case 1) died of refractory cardiac failure; and 1 patient (case 3) was on an LVAD for destination therapy (that is, the LVAD is not a bridge to transplantation but rather the final treatment). This patient was discharged from the hospital, but he died of overwhelming fungemia at 286 days while on VAD support.

CONCLUSIONS

Intracranial hemorrhage is a serious and feared complication of LVAD treatment. While the surgical risk is substantial due to systemic anticoagulation and significant medical comorbidities, neurosurgical evacuation of hemorrhage plays an important life-saving role that can yield successful and acceptable outcomes.

Single-center experience with levosimendan in children undergoing cardiac surgery and in children with decompensated heart failure

Background

Levosimendan has pharmacologic and hemodynamic advantages over conventional intravenous inotropic agents. It has been used mainly as a rescue drug in the pediatric intensive care unit or in the operating room. We present the largest single-center experience of levosimendan in children.

Methods

Retrospective analysis of all children who received levosimendan infusions between July 5, 2001 and July 4, 2010 in a pediatric intensive care unit. The results of a questionnaire for physicians (anesthesiologist/intensivists, cardiologists and cardiac surgeons) concerning their clinical perceptions of levosimendan are evaluated

Results

During the study period a total of 484 infusions were delivered to 293 patients 53% of whom were male. The median age of the patients was 0.4 years (4 hours-21.1 years) at the time of levosimendan administration. A majority of levosimendan infusions were administered to children who were undergoing cardiac surgery (72%), 14% to children with cardiomyopathy and 14% to children with cardiac failure. Eighty-nine out of the 293 patients (30.4%) received repeated doses of levosimendan (up to 11 infusions). The most common indication for the use of levosimendan (94%) was when the other inotropic agents were insufficient to maintain stable hemodynamics. Levosimendan was especially used in children with cardiomyopathy (100%) or with low cardiac output syndrome (94%). A majority (89%) of the respondents believed that levosimendan administration postponed the need for mechanical assist devices in some children with cardiomyopathy. Moreover, 44% of respondents thought that the mechanical support was totally avoided in some patients undergoing cardiac surgery after receiving levosimendan.

Conclusion

Levosimendan is widely used in our institution and many physicians believe that its use could decrease the need for mechanical support in children undergoing cardiac surgery or in children with decompensated heart failure. However, there is a lack of good empirical evidence in children to support this perception.

Clinical experience with Berlin Heart Excor in pediatric patients in Argentina: 1373 days of cardiac support

The objective of this study was to describe our experience (1373 days of support) with the Berlin Heart Excor (BH) ventricular-assist device (VAD) as bridging to cardiac transplantation in pediatric patients with end-stage cardiomyopathy. This study involved a retrospective observational cohort. Records of patients supported with the BH VAD were reviewed. Data regarding age, sex, weight, diagnosis, preoperative condition, single versus biventricular support, morbidity, and mortality were collected. Criteria for single versus biventricular support and intensive care unit management were registered. The procedure was approved by our Institutional Ethics Committee, and informed consent was obtained. Between March 2006 and March 2010, 12 patients with diagnosis of dilated (n = 10) and restrictive (n = 2) cardiomyopathy were supported. Median age was 56.6 months (range 20.1-165.9); mean weight was 18.3 kg (range 8.5-45); and nine patients were female. Every patient presented with severe heart failure refractory to pharmacological therapy. Biventricular support was necessary in four patients. Nine patients underwent heart transplantation. No child was weaned off the BH VAD because of myocardial recovery. Mean length of support was 73 days (range 3-331), and the total number of days of support was 1373. Three patients had fatal complications: 2 had thrombo-hemorrhagic stroke leading to brain death, and one had refractory vasoplegic shock. The BH VAD is a useful and reasonable safe device for cardiac transplantation bridging in children with end-stage heart failure. Team experience resulted in less morbidity and mortality, and time for implantation, surgical procedure, anticoagulation monitoring, and patient care improved.

Extracorporeal life support for treatment of children with enterovirus 71 infection-related cardiopulmonary failure

PURPOSE

Enterovirus 71 (EV71) infection leading to cardiopulmonary failure (CPF) is rare, but usually fatal. In such cases, intensive cardiorespiratory support is essential for survival. In this study, we report our experience in the treatment of EV71-related CPF with extracorporeal life support (ECLS).

METHODS

This was a retrospective study of a total of 13 children, aged 16 +/- 10 months, with EV71-related hemodynamically unstable CPF, which was refractory to conventional treatments, who were rescued by transsternal ECLS from 2000 to 2008. The clinical manifestations and outcomes of the 13 children (present cohort) were compared with those of 10 children (past cohort) who had EV71-related CPF without ECLS between 1998 and 2000.

RESULTS

Among these 13 patients, 10 were successfully weaned off ECLS and survived. The myocardial recovery time was 71 +/- 28 (median, 69) h, and the ECLS duration was 93 +/- 33 (median, 93) h. Six surviving patients had a good neurological outcome at hospital discharge. All surviving patients had some neurological sequelae but showed improvement at follow-up, including dysphagia in nine, central hypoventilation in seven, limb weakness in six and seizure in three. The present cohort had better neurological outcomes (46 vs. 0%, P = 0.005) and a higher survival rate (77 vs. 30%, P = 0.024) than the past cohort, respectively.

CONCLUSIONS

Patients with EV71-related CPF supported by ECLS had a higher survival rate and fewer neurological sequelae than those who only received conventional treatments. ECLS is an effective alternative method for treatment of children with refractory EV71-related CPF.

Extra-corporeal life support following cardiac surgery in children: analysis of risk factors and survival in a single institution

OBJECTIVE

Application of extra-corporeal life support (ECLS) following pediatric cardiac surgery varies between different institutions based on manpower availability and philosophy towards ECLS utilization. We examined a large single institution experience with postoperative ECLS in children aiming to identify outcome predictors.

METHODS

Hospital records of all children who required postoperative ECLS at our institution were reviewed. Patients' demographics, cardiac anatomy, surgical and ECLS support details were entered into a multivariable regression analysis to determine factors associated with survival.

RESULTS

Between 1990 and 2007, 180 consecutive children, median age 109 days (range: 1 day-16.9 years), required postoperative ECLS. Sixty-nine children (38%) had undergone palliative treatment for single ventricle pathology. ECLS support was required for failure to separate from cardiopulmonary bypass (n=83) or for postoperative low cardiac output state (n=97). Forty-eight patients (27%) received rescue extra-corporeal membrane oxygenation (ECMO) support during active chest compression for refractory cardiac arrest. Under ECLS support, 37 patients required surgical revision and 20 received orthotopic heart transplantation. One hundred and nine patients (61%) survived >24h following ECLS discontinuation and 68 (38%) were discharged alive. Hospital survivors required shorter ECLS support duration compared to non-survivors (median 3 vs 5 days, respectively, p=0.05) however survival occurred after up to 16 days of ECLS support. ECLS indication (OR: 0.85 for failure to separate from bypass vs postoperative low cardiac output 95% CI (0.47-1.56), p=0.62) and rescue ECMO (OR: 0.63 for rescue ECMO vs not 95%CI (0.32-1.24), p=0.18) were not associated with risk of mortality. In a multivariable logistic regression model, neurological complications (p=0.0007), prolonged ECLS duration (p=0.003), repeat ECLS requirement (p=0.02), renal dysfunction (p=0.04) and not performing heart transplantation (p=0.04) were significant factors for hospital death.

CONCLUSION

ECLS plays a valuable role in children with low cardiac output state following cardiac surgery. More than one third of those patients, including young neonates, older children, patients with single ventricle, or those requiring rescue ECMO can be salvaged. Although prognosis worsens with prolonged ECLS duration, survival can be noted up to 16 days of support. Heart transplantation is often an important ECLS exit strategy and should be considered early in selected children. Patients' survival could improve if renal and neurological complications are avoided.

Mechanical cavopulmonary assist maintains pulmonary and cerebral blood flow in a piglet model of a bidirectional cavopulmonary shunt with high pulmonary vascular resistance

OBJECTIVES

We tested mechanical cavopulmonary blood flow assist by incorporating a novel miniature centrifugal pump into a 1(1/2)-ventricle type cavopulmonary connection in neonatal pigs.

METHODS

Nine 3-week-old piglets (mean body weight, 10.2 kg) were used: mechanical cavopulmonary assist (n = 6) and controls (n = 3). A bidirectional cavopulmonary connection between the superior vena cava and the main pulmonary artery was created. The superior vena cava and pulmonary artery were also connected by cannulas with an interposed centrifugal pump. The cavoarterial mechanical cavopulmonary assist was performed at pump speeds of 1500, 2000, 2500, and 3000 rpm. Retrograde superior vena caval flow was limited by a band on the superior vena cava. A bidirectional cavopulmonary connection was created in the control animals, which then had a pure 1(1/2)-ventricle repair physiology without mechanical support. Hemodynamics, blood gas, and cerebral blood flow measured by ultrasound were analyzed. Catheter-based dilatation of the surgically created superior vena cava obstruction was tested.

RESULTS

Incremental increases in pump speed augmented bidirectional cavopulmonary shunt blood flow (P =.03) and diminished superior vena caval pressure (P =.03), thereby improving cerebral perfusion pressure. Pump flow of 3000 rpm was equivalent to baseline superior vena caval flow (before caval flow, 392 +/- 48 mL/min vs MCPA, 371 +/- 120 mL/min; mean +/- SD; P = not significant). The mechanical cavopulmonary assist group had higher Doppler velocities of the middle cerebral artery and higher transcerebral oxygen difference(P < .05) than controls. Balloon dilatation of the superior vena cava band was successful.

CONCLUSIONS

Mechanical cavopulmonary assist maintained bidirectional cavopulmonary shunt flow, thereby sustaining primary bilateral cavopulmonary shunt physiology in a neonatal pig model of high pulmonary vascular resistance. The mechanical cavopulmonary assist maintained cerebral blood flow and metabolism with an adequate transcerebral pressure gradient.

Mechanical support availability in pediatric cardiac surgery: program size should not matter

Intractable heart failure may require Extracorporeal Life Support (ECLS) techniques for rescue therapy. Nevertheless, in many small to middle-sized centers in Europe, this valuable resource is not available. In our University pediatric intensive care unit 0.9% of 1360 open-heart surgical patients required mechanical assistance over the latest 9 years with a survival rate of 69.2% and low residual morbidity. This favorable overall outcome suggests that regardless of the program size, it is possible to ensure the availability of efficient mechanical assistance that appears to be fundamental in a center performing surgery for complex congenital or acquired cardiac diseases.

CFD analysis of a Mag-Lev ventricular assist device for infants and children: fourth generation design

Thousands of pediatric patients suffering from heart failure would benefit from longer-term mechanical circulatory support. There are, however, few support systems available in the United States as viable mechanical assist alternatives for these patients. Therefore, we have designed and developed an axial flow pediatric ventricular assist device (PVAD) with an impeller that is fully suspended by magnetic bearings. This blood pump is designed to generate 0.5-4 L/min for pressure rises of 50-95 mm Hg over 6,000-9,000 rpm. We have performed four major design iterations. Building upon the third design phase, we made improvements to create the PVAD4 model. Numerical simulations of the PVAD4 under steady flow simulations were performed to compare the predictions of the latest PVAD4 model to the earlier PVAD3 design. The PVAD4 design resulted in lower fluid stress levels and an increase in pressure generation. A blood damage analysis was also completed. As compared with the earlier PVAD3 design, the damage analysis of the PVAD4 indicated a reduction in the mean and maximum damage index for the new design. All of these numerical findings are encouraging and demonstrate progress toward achieving a superior pump design.

Serial plasma BNP levels in assessing inadequate left ventricular decompression on ECMO

We describe a female infant with complex single ventricle physiology who had undergone median sternotomy for placement of a right-sided systemic-to-pulmonary artery shunt, division of a patent ductus arteriosus, and left pulmonary artery augmentation. Her early postoperative course was complicated by cardiac arrest requiring institution of extracorporeal membrane oxygenation (ECMO) support. The brain natriuretic peptide (BNP) levels acutely improved after left ventricular decompression by insertion of a left atrial cannula. In this setting BNP levels may be an indicator of left ventricular stretch and are potentially a useful index to monitor left ventricular distension.

Numerical design and experimental hydraulic testing of an axial flow ventricular assist device for infants and children

Mechanical circulatory support options for infants and children are very limited in the United States. Existing circulatory support systems have proven successful for short-term pediatric assist, but are not completely successful as a bridge-to-transplant or bridge-to-recovery. To address this substantial need for alternative pediatric mechanical assist, we are developing a novel, magnetically levitated, axial flow pediatric ventricular assist device (PVAD) intended for longer-term ventricular support. Three major numerical design and optimization phases have been completed. A prototype was built based on the latest numerical design (PVAD3) and hydraulically tested in a flow loop. The plastic PVAD prototype delivered 0.5-4 lpm, generating pressure rises of 50-115 mm Hg for operating speeds of 6,000-9,000 rpm. The experimental testing data and the numerical predictions correlated well. The error between these sets of data was found to be generally 7.8% with a maximum deviation of 24% at higher flow rates. The axial fluid forces for the numerical simulations ranged from 0.5 to 1 N and deviated from the experimental results by generally 8.5% with a maximum deviation of 12% at higher flow rates. These hydraulic results demonstrate the excellent performance of the PVAD3 and illustrate the achievement of the design objectives.

Perioperative management of ventricular assist devices in children and adolescents

Ventricular assist devices are an integral part of therapy for patients with end-stage heart failure. Devices can either bridge to recovery or to transplantation. Options for ventricular assist devices include those that are centrifugal, pulsatile, and new rotary/axial devices. Care of the patient on a ventricular assist device is multifaceted, involving pharmacologic or mechanical support of the right ventricle, management of systemic vascular resistance, and manipulation of the hematologic system to avoid bleeding or thrombosis. In addition, care of these patients involves support of all end organs and avoidance of infectious complications. Care of these patients is complex, requiring a highly integrated team for optimal outcome.