*2.2.2 HeartMate 3*

The HeartMate 2 and HeartMate 3 (Abbott, Abbott Park, IL, US) are two devices that are implantable compact continuous-flow VADs designed for use in adults that is being implanted in children [9]. However, the HeartMate 2 is no longer the preferred device in this age group. Some older studies, such as reference [9], authors describe their experience at their institution of developing education and support so that there is comfort and experience in implanting HeartMate 2 devices and allowing pediatric patients to be discharged home and managed as an outpatient. This was a significant improvement from the paracorporeal or centrifugal devices requiring management in the hospital. The MOMENTUM 3 trial released the results for usage of the HeartMate

3 which can provide flows between 2.5 L/min and 10 L/min and alternating rotor speeds every other second [9].

The recall of the other lower profile device, discussed in the subsequent section, has made implementation of HeartMate 3 as the ideal device for smaller patients, with an outer diameter of 50 mm [4]. In [11] the early experience described by the Advanced Cardiac Therapies Improving Outcomes Network (ACTION) published in 2020, 35 patients from 2017 to 2019 at multiple centers had a HeartMate 3 implanted in pediatric and adult patients with congenital heart disease. There were patients as small as 19 kg who were successfully implanted and supported (median age = 15.7) – establishing this device as a feasible option for adolescents [11]. Currently, the consensus for appropriate device usage is for older children or young adults weighing greater than 30 kg, although there is no minimum weight restriction [5]. Research is on-going regarding utilization of preoperative advanced imaging to virtually plan implantation.

#### *2.2.3 HeartWare HVAD*

The HeartWare HVAD (HeartWare, Inc., Framingham, MA, US) is another implantable compact continuous-flow VAD that was designed for adults and was being implanted in older children [9]. As in Ref. [9], as of recently, there were excitement and documented case reports describing successful implantation of this compact option even in a child as small as 13 kg and as young as 4 years old for over 600 days. There were published studies from a multicenter study describing the implantation in small children. They described a 33% rate of pump thrombosis yet at this single center, Burki et al. describe no pump thrombosis out of 19 patients [9]. However, this device was discontinued after the rates of thrombosis were very high. Unfortunately, it is no longer an option. Without this device as an option, it is difficult to know what the smaller threshold would have been to avoid patient-device size mistmatch between very small children and adult-designed VADs [9].

Over 5 years, it appeared that the implantation of HVAD was steadily increasing through 2017. Even worldwide, there was reported success in children in achieving goal to transplant – over 200 patients from 2015 to 2016 [12]. Perhaps, this was from the innovation of implantation techniques, and even reports demonstrating improvement with biventricular support. Unfortunately, despite these successes, in 2021, the Heartware HVAD was withdrawn completely from the market. Overall, this was a huge setback for the field, but since this was one of two smaller profile devices that were most commonly used in pediatrics, there is currently a gap in comparison to experience versus now this device being unavailable for implantation. HeartMate 3 devices may be able to address the gap for patients that are greater than 30 kg with an adequate chest cavity size. However, practically, given the prevalence of the Berlin Heart as being the only other device having available device sizes from 15 to 30 kg, the removal of the HVAD from markets leaves yet another gap for smaller children less than 30 kg. This is not an ideal replacement, since the Berlin Heart currently requires an inpatient admission without the ability for patients to be discharged home [5]. The impact of this recent device disappearing from the already limited toolkit of the pediatric cardiac surgeon is estimated to have a significant clinical impact without an immediate solution.

#### *2.2.4 Other devices*

The Syncardia Total Artificial Heart (Syncardia, Inc., Tuscon, AZ, US) is an option with size constraints to the pumps: a smaller pump 50 mL for the pediatric population which was made available in 2022 and the pre-existing 70 mL pump which is too large for most pediatric patients [9].

Short-term, centrifugal paracorporeal devices using in smaller children such as the PediMag, RotaFlow, or CentriMag (Abbott, Abbott Park, IL, US) are all important as contemporary options for mechanical circulatory support for inpatients who are critically ill [5]. However, the discussion of the usage of these devices compared to implantable durable devices is beyond the scope of this chapter.

#### **2.3 Device development**

Currently, there very few clinical trials with device development geared specifically towards pediatric patients [5]. Unfortunately, progress has been slow and halting. Resources are limited. Reasons studies are lacking and difficulty in making substantial progress with a potentially life-saving device are multifactorial including small consumer numbers, substantial regulatory and administrative burden, and patient variability [9]. One potential solution is to encourage device development for both adults and pediatrics [5]. The MVAD (Heartware, Inc.) is another adult-size continuous-flow compact device undergoing testing with a volume of 20 mL [9]. Despite multiple studies originally being funded, there is only one that is currently on-going specifically for pediatrics [7]. The most well-described, smallest device is the Jarvik Infant 2015 which is a continuous-flow VAD targeted towards children 8 kg to 20 kg; the device length is about equal to a AA-battery [9, 13]. The difficulty in performing research in this specific area has been well-described by the lead investigators at Texas Heart Institute [7, 13]. One of the biggest hurtles in developing this device was addressing hemolysis [9]. Another obstacle is the concern for thrombosis. This comes from the inherent patient-device mismatch from implanting adult devices into pediatric patients [7]. Finally, this long awaited device specifically designed for kids will be ready to enroll patients in the PumpKIN (pumps for kids, infants, and neonates) trial [7, 9, 13]. We eagerly await the results for at least another feasible option in the treatment of young children.
