**Abstract**

In the past 2 decades, pediatric mechanical circulatory support (MCS) strategies have improved. Focus on ventricular assist devices (VAD) is an important topic for pediatric heart failure patients and single ventricle palliation. Application of VADs continues to evolve, including implanting compact adult continuous-flow devices to larger children (HeartMate 3) along with the recent discontinuation of the HeartWare. The Berlin Heart ExCOR has received improved outcomes with adjustments to anticoagulation. Syncardia Total Artificial Heart has also released a smaller version which has been implanted in adolescents. Advanced cross-sectional imaging can now be used for pre-operative planning of device placement. Finally, special consideration is required for usage of these devices in a failing Fontan circulation (univentricular physiology) with some lab studies and small cases highlighting the unique challenges. The potential options for VAD as a bridge to transplant, destination therapy, or recovery continue to expand the crucial role of MCS in congenital heart disease. Smaller patient size, limited availability of organs for heart transplant, and longer survival of pediatric congenital patients continues to make innovation in MCS necessary.

**Keywords:** children heart failure, mechanical circulatory support, congenital, single ventricle, ventricular assist devices, anticoagulation

### **1. Introduction**

For patients with severe end-stage heart failure, there are limited therapeutic options past medical goal-directed therapy. The surgical options for treatment of pediatric congenital patients who require mechanical circulatory support (MCS) is gradually increasing with many opportunities for ongoing research, clinical studies, and device innovation. This chapter will focus specifically on ventricular assist devices (VAD) in a pediatric population. Subtopics will include research within the past few decades, size and availability of pediatric devices, anticoagulation, and special anatomic considerations in congenital heart disease (CHD).

### **2. Sizing and device selection**

One of the biggest challenges in utilizing MCS devices in young children is the limited availability of products for a range of patients that are not yet adult-sized. There are several ways to combat this in order to find the optimal available device. One is to identify the currently available range of devices for use in pediatrics. With technological advances in imaging, pre-operative digital modeling can help with preoperative planning. And, lastly, there are currently trials for more products that will hopefully become available for use in children to increase the availability of MCS devices.

#### **2.1 Preoperative advanced imaging and three-dimensional printing**

One of the advantages of utilization advanced imaging and customizable technology in congenital heart disease patients is the ability to adapt to variable anatomy. Surgical aspects of implanting a device may benefit from newer technologies such as preoperative computed tomography (CT) or three-dimensional (3D) printing. A few examples include cannula placement and device location in adults with congenital heart disease and heart failure.

Recent usage of this technology over the past two decades requires specific resources including excellent dataset image acquisition, image processing software, a variety of printing materials, and a 3D printer [1]. In Ref. [1], usage in various adult cardiac and congenital heart patients is explored demonstrating interest with multiple clinically useful applications including patient/family education, training, and operative planning. Some interesting case examples include VAD implantation in a failing systemic right ventricle or after Fontan palliation [2]. In Ref. [3], multiple 3D printed models are shown including color cardiac models and a whole-chest with sternum/ ribs along with other soft tissue to simulate the ideal location of a VAD device for a congenital heart patient. The future of 3D printing and MCS offers a unique ability to personalize each patient's anatomy. Although an exciting new tool, the barriers to increased adoption of this technology include cost, inability to print certain valve structures, access to software, image datasets acquisition expertise, printing materials that closely replicate living tissue, personnel, and 3D printers [1, 2].

In terms of precise preoperative management and placement of VADs, the ability to acquire and measure using CT imaging offers an advantage, especially when assessing children who may be borderline candidates due to smaller thoracic cavity size. Some anthropometric measures include chest cavity dimensions (i.e. internal transverse diameter at different levels, etc.). Patients as young as 8 years-old have been described as receiving implantation, with others from 9 to 11 years of age undergoing preoperative CT imaging and successful implantation. One of the major obstacles to placing a sparse selection of VAD device sizes is compromising the position of the pump after closing the chest. Due to patient size variability, CT imaging offers an objective measure to determine feasibility and evaluate technical implantation preoperatively [4].

#### **2.2 Available implantable devices**

Currently, out of over 200 annual pediatric device implantations worldwide, there are only a few types of devices that are available for use in pediatric patients [5]. Another additive factor includes an increase in heart failure hospitalizations in the pediatric population requiring increased usage of these devices, specifically for CHD [5, 6]. There are two broad categories of VAD implantable devices: continuous-flow and pulsatile. The majority of devices being implanted since 2014 are continuous-flow due to the miniaturization and availability of these adult intracorporeal devices to be placed into adolescents [7]. One of the devices which was available for implantation was recently recalled due to thrombosis risk: Heartware (Medtronic, MN, US) [4]. In a 2019 published article [8], the database of the Pediatric Interagency Registry for

#### *Pediatric Ventricular Assist Devices DOI: http://dx.doi.org/10.5772/intechopen.113970*

Mechanical Circulatory Support (Pedimacs), reviewed recent outcomes for children with VADs. There were 108 CHD patients over about 5-year span and these were compared to non-CHD patients; CHD patients tended to be younger and smaller (average age 5.7 years with BSA 0.8 m^2) [8]. This study found that CHD was associated with an increased mortality and decreased transplant rates; however, the subgroup who received implantable devices at high volume centers had higher survival rates [8]. There is a consistent trend with increased numbers of children being implanted with these devices within the last decade [5]. Although limited, clinical trials are on-going to make smaller and improved devices for use in pediatrics.

#### *2.2.1 Berlin Heart EXCOR*

A pulsatile, paracorporeal ventricular assist device currently approved for pediatric use is the Berlin Heart EXCOR (Berlin Heart, Inc., The Woodlands, TX, US) [9]. Since the first implantation in 1990s, this device offers multiple pump sizes ranging from 10 to 80 mL stroke volume to be assigned based on the patient's body surface area (BSA) [10]. In Ref. [10], comparison of 80 patients divided into three groups with an optimally sized pump matching stroke volume to BSA, it appeared that thrombotic events were more frequent statistically significantly in children who had a larger pump placed in comparison to BSA. Also, in a much smaller patient (i.e. <3 kg), the smallest pump (10 mL) may need to be run at a rate that is much lower than the optimal heart rate resulting in lower flow and potentially a risk for thrombosis [9]. One potential solution is to insert an assist device on the right and left ventricular in order to maintain a high enough output [9]. There are studies showing some decrease in survival with biventricular support; however, this may be due to the advanced stages of heart failure, which may be alleviated with earlier implementation of univentricular support [10]. Also, patients less than 5 kg were disproportionately at risk for death, possibly due to size mismatch of the device compared to intrinsic native cardiac output in small infants [9]. There are good results for ultimate transplantation or even recovery; however, there is also noted a high incidence of bleeding and thrombosis. Reference [10] studied a total of 80 children who underwent Berlin Heart implantation. They found that 25 children died (mortality rate of 31.6%); 49% of patients were successfully transplanted and 19% of devices explanted. BSA, young age, or having biventricular support did not appear to be associated with increased mortality – potentially attributable to increased experience. Other technical aspects such as site of cannulation or coated cannulas may also lead to improved results [10]. Another limitation of this device is training of hospital personnel and requirements of staying inpatient for device monitoring.
