**1. Introduction**

Hospitalization among children suffering from end-stage heart failure (HF) is increasing [1]. If not otherwise correctable and in the absent of contraindications, heart transplantation

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

(HTx) remains the treatment of choice. Pediatric HTx (pHTx) represents a small but very special part in the field of cardiac transplantation. Children remain at an increased risk of death on the waiting list for HTx [2]; especially infant heart transplant recipients are at a greater risk of death compared to older children. The main reason is the search for an appropriately sized organ donor [2–4]. The limited numbers of available pediatric donor heart organs led to an increased mean waiting time in most Western countries [4]. Tapping all potential brain-dead donors and expanding the recipient pool on an international level is thus of vital importance especially for smaller countries in Europe. Therefore, international organ exchange among organ procurement organizations seems to be essential and has a direct positive impact on the chances of patients to get a timely, often life-saving transplantation [5]. All these efforts have, however, not resulted in a decreasing waiting time on the waiting list.

All these considerations come with the need for care providers specialized in this field to determine optimal patient and device selection and to improve outcomes and decrease complication rates for new innovative strategies. This chapter focuses on durable VADs as BTT or

Mechanical Circulatory Support as Bridge to Pediatric Heart Transplantation

http://dx.doi.org/10.5772/intechopen.76144

95

In the 1970s, modifications of the original "heart-lung machine" like ECMO or extracorporeal centrifugal pumps [17] have been the principal art of cardiac support. With the need for real long-term support, the need for durable VADs became evident. In 1989, Frazier implanted a mechanical assist device in a 9-year-old boy who was successfully bridged to heart transplantation with a Biomedicus (Medtronic, Eden Prairie, MN) centrifugal pump; the supporting time was 12 h. In 1990, the first Berlin Heart EXCOR, in adult size 50-mL pump, was implanted in a 9-year-old child for 1 week with an uneventful postoperative time after heart transplantation [18]. Two years later, in 1992, pumps in sizes of 10, 25, and 30-mL have been devised, and the 10-mL pump was implanted in a 12-month-old child [19]. Two years later, the first Medos VAD (Medos Medizintechnik GmbH, Stolberg, Germany) was implanted successfully as bridge to transplantation [20]. In the last years, there has been an increase in the use of MCS in the pediatric population mainly driven by the development of smaller VADs,

Patient selection and timing remain crucial factors for improving outcomes in VAD recipients. In children with critical peripheral perfusion (i.e., metabolic acidosis; cardiac index of <2.0 l/

Selection differs significantly within the pediatric group by structural normal hearts or patients with CHD as well as the age and weight/size of the patient [15, 22, 23]. Some VADs are specified for its use in adults or pediatrics; some are licensed according to a specific body surface area (BsA) and/or some for specific weight/size. Contrarily to adults, where intracorporeal left ventricular assist device (LVAD) has become a routine treatment with subsequent discharge home, options for small children are still limited. A large variety of adult-sized ventricular assist devices (VADs) has proven to be safe for long-term support [10] but only a small number of VADs are available for patients with a body surface area (BSA) of less

Berlin Heart EXCOR are the only two devices currently designed for children with a body

or weight less than 20 kg [12]. The Medos HIS (no longer on the market) and the

/min, mixed venous oxygen saturation of <40%) despite inotropic support, early signs of renal, hepatic, or multiorgan failure without surgical options to correct any residual structural lesions should be considered for MCS. There are only a few contraindications for MCS like malignant neoplastic diseases with a very limited life expectancy, advanced multiorgan failure, complex congenital heart lesions involving intracardiac shunts or irreversible pulmonary failure and severe extracardiac malformations such as chromosomal and genetic syndromes

candidacy in pediatrics.

namely continuous flow (cf)-VADs.

**2.1. Indication and device selection**

with poor quality of life prognosis [21].

m2

than 1.2 m2

**2. Durable VAD support in children as BTT**

Fueled by the uncertainty and the time required to get a donor heart, mechanical circulatory support (MCS) as a bridge to transplantation (BTT) became mandatory to overcome death on the waiting list. Historically, MCS was developed if weaning from cardiopulmonary bypass (CPB) was not possible to allow for a recovery. Therefore, all centers performing congenital heart surgery have experience with extracorporeal membrane oxygenation (ECMO). Its use, however, is timely limited (days to weeks) before serious complications like bleeding occur [6]. Further, ECMO application is limited to short-term support due to immobilization of the patient and the patient must remain on the intensive care unit (ICU). Ventricular assist device (VAD) was shown to be superior to ECMO support, considering the increased risk of 1-year mortality associated with EMCO support [6, 7].

While VAD use in children is gaining more attention, there are several challenges to consider. On anatomical and physiological grounds, three different groups can be distinguished: adult patients with anatomic normal heart, pediatric patients with anatomic normal hearts, and patients with congenital heart disease (CHD) irrespective of age. There are clear differences in the pathophysiology of HF compared between adults, children, and CHD patients. Hospitalization of children suffering from HF due to CHD is increasing [1], while reported survival of children on VAD support suffering from CHD is still low [8, 9].

In adults with structural normal hearts, there is a large variety of different VADs which have proven to be safe for long-term support [10] and have developed as a standard treatment option [11]. For pediatrics, only a few VADs are available for patients with a body surface area (BSA) of less than 1.2 m2 or weight less than 20 kg [12]. Furthermore, limited data are available as children are excluded in major VAD trials. Only one prospective trail is reported by Fraser et al. using the Berlin Heart EXCOR®. Currently, there are only two VADs designed for children with a body surface area below 1.2 m2 : the Medos HIS and the Berlin Heart EXCOR. Finally, in adult patients, the numbers of BiVAD implantations are declining [13, 14]; the incidence of biventricular failure among children remains high, with over 15% requiring BiVAD or total artificial heart support [15] and results seem to be inferior to LVAD only [16].

Finally, if a contraindication for HTx like pulmonary hypertension or malignancy is diagnosed, a concept known as bridge to transplantability may be considered.

All these considerations come with the need for care providers specialized in this field to determine optimal patient and device selection and to improve outcomes and decrease complication rates for new innovative strategies. This chapter focuses on durable VADs as BTT or candidacy in pediatrics.
