Mechanical Circulatory Support in Congenital Heart Disease

Improved surgical survival for those with congenital heart disease (CHD) and better recognition and management of pediatric patients with CHD has vastly increased the population of pediatric patients with impaired ventricular function. As a result, it is estimated that there are nearly 15,000 admissions for pediatric heart failure (HF) each year. Whether acute or chronic, these patients present with low cardiac output and threatened end organ function. These admissions carry a mortality of approximately 10% and 10-15% result in mechanical circulatory support.1,2

The first ventricular assist device (VAD) was developed in Houston in the early 1960s. Liotta, Crawford, and Hall implanted a tubular left ventricular assist device (LVAD) between the left atrium and the descending thoracic aorta.3 The first clinical success came in1967 with the implantation by DeBakey of a LVAD with inflow from the left atrium and outflow to the right subclavian artery.4 This patient survived to discharge. Cooley implanted the first total artificial heart in 1969 as a bridge to transplant.5 The recipient was supported for 64 hours prior to heart transplantation.

The prevalence of HF is significantly greater in the adult population compared to pediatrics. As such, the development of devices for adults with end stage HF has grown and matured at a faster pace. The use of VADs in pediatric patients began with the application of adult devices in adolescents. These devices present significant size mismatch issues in the cohort of smaller pediatric patients. A study from the Pediatric Heart Transplant Study database in 2006 examined the outcome of pediatric patients (n = 99) supported with adult VADs and revealed very poor outcomes in smaller patients.6 Children above age 14 had a six-month survival of 90%, but those younger than age 10 years had only a 38% six-month survival. The Berlin Heart EXCOR (Berlin Heart AG, Berlin, Germany) is the device that has been used most extensively in pediatric patients. It was introduced in Germany in 1991 and approved for use in Europe in 1996. It was first used in the United States in 2000 under a compassionate exemption, and was finally approved by the United States Food and Drug Administration (FDA) in 2011. The EXCOR is a paracorporeal device and in its Investigational Device Exemption trial the rate of complications including bleeding, infection and stroke were not trivial.7 Also, the later generation adult devices have become miniaturized with some allowing intrapericardial placement, improved ambulation and hospital discharge. These forces led the United States National Heart, Lung, and Blood Institute (NHLBI) to develop a Pediatric Circulatory Support Program in 2004. In 2010, this matured into the Pumps for Kids, Infants, and Neonates Program (PumpKIN). After originally starting with five potential devices, only the Child/Infant Jarvik 2000 (Jarvik Heart, New York, NY) will be compared to the Berlin Heart EXCOR in a prospective, randomized trial set to begin soon at 22 centers. The Berlin Heart EXCOR will be described below. The Child and Infant Jarvik 2000 are the smallest assist devices in the Jarvik line of axial flow devices. The Jarvik devices are uniquely designed for intraventricular positioning. Compared to the Heartmate II, the adult Jarvik 2000 has demonstrated a greater ability to be inserted off pump, fewer intraoperative packed red blood cell transfusions, a faster time to extubation, and the ability to be inserted via left thoracotomy. This has led to enthusiasm about the possibilities with the child and infant versions.8 The primary endpoint of the trial is survival at 180 days without new severe neurologic injury.

In general, the use of mechanical circulatory support in pediatric patients with acute or chronic end stage HF is indicated when conventional medical therapy has failed. Although listing for heart transplantation is often done, the scarcity of organs usually prompts the consideration of mechanical support. Pediatric VADs are used almost exclusively as either bridge to transplant or bridge to recovery. Unlike the adult population, destination therapy is not a primary option in the pediatric population, but it has been reported in patients with Duchenne muscular dystrophy.9

Contraindications to the use of VADs in pediatric patients include irreversible end-organ dysfunction and active infection. Also, extreme prematurity, very low birth weight and certain chromosomal defects are considered contraindications.10 It is important and often challenging to avoid initiating mechanical support too late. Moderate end organ dysfunction often improves with mechanical circulatory support, especially renal and hepatic dysfunction.10,11,12 Other considerations include thickness of the ventricles, semilunar valve regurgitation and intracardiac shunts. Thick ventricles (such as those in hypertrophic cardiomyopathy) can prevent proper filling of the VAD and these patients are considered on a case-by-case basis.13 In some patients with thick ventricles, atrial cannulation will permit proper filling of the device. In those with a small atrium, this may not be possible. Significant aortic insufficiency (and/or pulmonary insufficiency) will not permit adequate emptying of the ventricle and often necessitates closure of the aortic valve at the time of VAD implantation.14 Closure of intracardiac defects will prevent embolization of thrombus and/or air.

A critical decision when considering mechanical support is the use of a systemic VAD only or biventricular VAD (BiVAD) support. For a systemic VAD to function properly, it has to be adequately filled from the pulmonary ventricle. Biventricular dysfunction and elevated pulmonary vascular resistance frequently accompanies pediatric heart failure.15 There are data to suggest that BiVAD support is more common in pediatric patients when compared to adult patients.7,16

Three factors drive device selection – type of support (cardiopulmonary or cardiac); planned duration of support and body surface area. Extracorporeal membrane oxygenation (ECMO), successfully clinically used since the mid-1970s, is the only temporary device that is widely available for biventricular cardiopulmonary support. It is most commonly employed for failure to wean from cardiopulmonary bypass, emergent support after cardiac arrest and failure of medical resuscitation, and early graft failure after cardiac transplantation. Biventricular support with ECMO requires either an opening in the atrial septum or an additional cannula placed in the left heart (pulmonary vein, left atrial appendage or left atrium). Many centers have a long ECMO experience, the hardware is stocked in most major children's hospitals, and it is rapidly deployed by a multidisciplinary team of professionals. If necessary, a patient on ECMO can be transported by air or ground to centers that offer heart transplant and assist devices. It is important to note that after approximately 2 weeks the risk of bleeding, thromboembolism, stocking and glove ischemia and other major complications are common.

ECMO is a very short-term device until one of three outcomes occur: pulmonary recovery leads to insertion of longer-term cardiac support, cardiopulmonary recovery results in decannulation or no recovery of either organ system leads to withdrawal of support. Those patients requiring cardiac support only are divided into short-term and long-term groups. Short-term support (less than 14 days) is used for acute myocarditis, graft dysfunction after cardiac transplant and patients with unknown diagnoses or unknown neurological status. It is also described for failure to wean from cardiopulmonary bypass. Long-term support (greater than 14 days) is often used in patients with known cardiomyopathy and failure to improve and in some with refractory congenital heart disease, such as a Fontan patient that has exhausted medical therapy and has no other surgical options. There are three short-term and five long-term devices that will be reviewed.

Short-term Devices

  1. The RotaFlow (Maquet Cardiovascular, Wayne, NJ) is an extracorporeal, centrifugal, continuous flow device that can be used in patients of all sizes (from neonates to adults; no minimum body surface area [BSA]) and can flow up to 10L/min. It has a small priming volume (32mL) and can be used along with a membrane oxygenator as an ECMO circuit. An electromagnetic mechanism powers the device, and the circuit is levitated. The levitation is designed to decrease wear and hemolysis.10 It is approved by the Food and Drug Administration (FDA) for up to 6 hours of use.
  2. The PediMag (Thoratec, Pleasanton, CA) is the pediatric version of the CentriMag (Thoratec, Pleasanton, CA). It is an extracorporeal, centrifugal, continuous flow device for those <20kg. It has a priming volume of only 14mL and can provide up to 1.5L/min flow. The device has a bearingless, magnetically levitated technology with no points of contact. The PediMag is approved by the FDA for up to 6 hours of support. It is commonly used as part of an ECMO circuit.
  3. The TandemHeart (CardiacAssist, Pittsburgh, PA) is an extracorporeal, centrifugal continuous flow device with a small priming volume (10mL) designed for percutaneous placement. It can provide up to 5L/min flow. The transseptal cannula is placed into the left atrium via the femoral vein. The outflow is into the femoral artery. It is FDA approved for up to 6 hours of support and is for larger pediatric patients (BSA > 1.3m2).

Long-term Devices

  1. At this time, the Berlin Heart EXCOR (Berlin Heart, Berlin, Germany) is the most popular pediatric long-term support device. It has a variety of pump sizes up to 60mL and can be used in almost all pediatric patients, including adult-size patients with BSA >1.3m2. The pneumatic IKUS driver powers the EXCOR, but a newer generation driver is under development that will permit discharge from the hospital.10 It is the only FDA approved long-term device for neonates and infants. It is a pulsatile device and is positioned in a paracorporeal location. It can be used as a LVAD, right ventricular assist device (RVAD) or biventricular assist device (BiVAD). It is also possible to add an oxygenator to the right assist device, creating a modified ECMO circuit. Cannulation for LVAD use can be done via the left atrium or the apex of the left ventricle. There is anecdotal evidence that ventricular apical cannulation is associated with fewer thrombotic complications.18 The cannulas exit the skin to the paracorporeal location through the upper abdominal wall. One advantage to the external location is the ability to simply change the device if thrombus formation is identified in the device.
  2. The Thoratec VAD (Thoratec, Pleasanton, CA), like the Berlin Heart, is a pneumatically driven, pulsatile pump capable of delivering up to 7 L/min flow. The iVAD is implantable and is slightly smaller than the paracorporeal pVAD. It can be used in the LVAD, RVAD, or BiVAD configurations. There are 30 years of experience with this first generation device and it is for larger pediatric patients. It is FDA approved for bridge to transplant.
  3. The HeartMate II (Thoratec, Pleasanton, CA) is an implantable, axial continuous flow device that has been used in over 10,000 adults. It is capable of providing greater than 2.5L/min of flow, and it is FDA approved for bridge to transplant and destination therapy. In the pediatric population, this device is commonly used in adolescent patients with a BSA >1.4 m2. The device is placed in a pocket that is developed by dissecting the diaphragm away from the abdominal wall. In a trial that compared it to other types of VADs for bridge-to-transplant, The HeartMate II had similar or decreased rates of adverse events and a much lower mortality rate (4% compared to 11% for other VADs).19 In a study that compared older pediatric patients to young adult patients receiving the HeartMate II, 6-month survival was comparable between the two groups (95% vs. 96%, p = 0.341).20 The HeartMate 3 (Abbott) is an implantable, centrifugal continuous flow device that is designed for intrapericardial placement. No VAD pocket is required and the driveline exits the skin. It can provide up to 10 L/min flow.
  4. The HeartWare (HeartWare, HeartWare Systems, Framingham, MA) device is a centrifugal continuous flow device for patients with BSA >1.0m2 that can provide up to 10 L/min flow. It is very small, sits in the pericardial space, requires no VAD pocket, and only the driveline exits the skin. It is FDA approved for bridge-to-transplant and it is anticipated that it will be approved soon for destination therapy. The ADVANCE (Evaluation of the HeartWare Left Ventricular Assist Device for the Treatment of Advanced Heart Failure) trial is the study that provided data for FDA approval.21 In this trial, 140 patients receiving HeartWare were compared to a control group (n = 499) from the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) database. Most of the control group had received the HeartMate II device. There was less bleeding and infection in the HeartWare cohort and similar 180-day survival. Proper fit and function of the device often requires creative cannulation strategies and other operative techniques due to the small size and varying anatomy of children with circulatory failure. A novel cannulation strategy that is applicable in select patients is right atrial cannulation. This location can be utilized in both univentricular and biventricular hearts. Also, excision of the systemic atrioventricular (AV) valve, including the subvalvar apparatus, is one strategy to prevent inflow obstruction to the ventricular assist device in smaller sized hearts. This technique is applicable with either apical or atrial cannulation and in both univentricular and biventricular hearts.
  5. The SynCardia Total Artificial Heart (SynCardia Systems, Tucson, AZ) is an implantable biventricular device that provides up to 9.5 L/min of pulsatile flow. Each pump is 70 mL and a 50 mL version is also available. It is FDA approved for bridge to transplant. Patients need a BSA greater than 1.7m2 (1.2-1.7m2 for the 50mL pump) and there is a rule of thumb that patients need 10cm of anterior posterior diameter at T10 to determine if the device will fit.10 This can be determined through computed tomography of the chest. There have been over 1200 implants worldwide and it immediately eliminates concern over right heart failure, atrioventricular valve issues, dysrhythmias, left ventricular clot and intracardiac shunts.10 A recent review of the SynCardia database showed that the total artificial heart was used in 24 patients with congenital heart disease (2.2% of total implants).22 Six of the 24 were adolescents (age 12-18), and this subgroup had 100% survival. For the entire congenital heart disease cohort, survival was 62%. At two months after implantation, 34% were still on the total artificial heart, 33% had been transplanted and 33% died.

Mechanical circulatory support is being used in the single ventricle patient population. However, there is not much data available at this time and what are available are case reports.26 There are no straightforward mechanical support options for these patients. Mechanical support has been reported after all stages of single ventricle palliation (systemic to pulmonary shunt or pulmonary artery banding; superior cavopulmonary anastomosis; Fontan completion). Mortality in this cohort is very high at nearly 40%.26 Because a majority of patients with palliative cavopulmonary connection (both superior cavopulmonary connection and total cavopulmonary connection) will develop HF, and due to the lack of experience of mechanical support in the single ventricle population at even the busiest centers, a registry has been developed.27 The purpose of the Mechanical Support as Failure Intervention in Patients with Cavopulmonary Shunts (MFICS) registry is to improve the quality of care in those single ventricle patients receiving mechanical support.

Improved survival, recognition and management of patients with CHD have increased the number of pediatric patients with ventricular dysfunction. Many of these patients require mechanical support to bridge to transplant or recovery. Development of pediatric VADs has lagged behind adult devices. Until recently, adult devices were used in pediatric patients with suboptimal results in the smaller patient population. ECMO can be lifesaving, but is a poor choice for long-term support. The Berlin Heart EXCOR is a paracorporeal device with a variety of pumps for patients of all sizes. The PumpKIN Trial will compare this device to the Infant Jarvik 2000 in a prospective, randomized study. The single ventricle population presents unique challenges to placement and proper functioning of assist devices. Data is anecdotal and mortality is high. A registry has been developed to assist in caring for this challenging population.


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Keywords: Thoracic Surgery, Infant, Newborn, Infant, Infant, Low Birth Weight, Adolescent, Heart-Assist Devices, Extracorporeal Membrane Oxygenation, Cucurbita, Body Surface Area, Cardiac Output, Low, Atrial Septum, Aortic Valve, Aorta, Thoracic, Pulmonary Veins, Cardiopulmonary Bypass, Catheters, Walking, Factor VII, Prevalence, Thoracotomy, Muscular Dystrophy, Duchenne, Subclavian Artery, Airway Extubation, Erythrocyte Transfusion, Prospective Studies, Atrial Appendage, Atrial Fibrillation, Heart Transplantation, Heart Failure, Ventricular Function, Thrombosis, Thromboembolism, Cardiomyopathy, Hypertrophic, Stroke, Heart Arrest, Vascular Resistance, Catheterization, Patient Care Team, Cohort Studies

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