**2. Ventricular assist devices**

Mechanical circulatory support has become increasingly common in the management of heart failure. The initial objective of VAD therapy was a temporary form of mechanical circulatory support as a bridge to cardiac transplantation. Improved survival with VADs and deficient donor organ supply has since resulted in increased use as destination therapy. In modern practice, VADs are often used as chronic therapy or permanent circulatory support.

Device selection and timing of initiating VAD support are vital in optimizing cardiac function recovery and chance for survival. Anatomic variations secondary to congenital heart disease or surgical interventions pose technical challenges to VAD implantation [12]. Other factors including severe neurologic impairment, chromosomal or congenital anomalies with anticipated poor outcome and significant prematurity or low body weight should be taken into consideration prior to VAD implantation. Patient size, anticipated duration, type of support, and ultimate goal of therapy are important elements in device selection.

The EXCOR © (Berlin Heart) is specifically designed for infants and children, providing mechanical circulatory support via pulsatile membrane pumps. The system offers multiple pump and cannula sizes to accommodate different patient sizes. It is important to avoid mismatch between patient and device size as mismatch has been associated with poor outcome [12]. Unfortunately, early generation VADs utilizing pulsatile flow were characterized by high rates of complications including high incidence of device failure and poor survival. These early devices were preloaddependent and sensitive to changes in cardiac output including those related to arrhythmia. There has been notable improvement in patient survival and reduction in complications with transition to continuous flow VADs [8].

There are two subclassifications of continuous flow VAD design – axial and centrifugal. In general, axial flow is generated by a propeller in a pipe with filling completed by use of negative pressure while a bladed disk spinning in a cavity generates centrifugal flow [13]. The second-generation VAD HeartMate II © (Abbott) provides

#### *Arrhythmia Management in Pediatric Patients with Ventricular Assist Devices DOI: http://dx.doi.org/10.5772/intechopen.107061*

short or long-term circulatory support for heart failure patients as a continuous flow system that funds via axial flow generated with mechanical bearings. It has a lower incidence of thromboembolic events compared to the first-generation VADs [12, 13]. The HVAD pump (HeartWare Inc) is a continuous-flow device with a centrifugal pump that is attached directly to the inflow cannula. It is smaller than the HeartMate II and, with adjustment in the implantation technique, has demonstrated utility in the pediatric heart failure population [14]. While output from continuous flow VADs is not immediately affected by arrhythmias, there may still be hemodynamic instability from deficient right ventricular support. Third generation VADs, HeartMate 3© (Abbott), generate continuous flow via a centrifugal flow pump utilizing a magnetically levitated rotor. The CentriMag/PediMag© (Abbott) is a centrifugal pump that is used for temporary support. The presence of arrhythmia may lead to a reduction in preload and subsequent decrease in device flow [15].

In select patients with severe biventricular systolic dysfunction, complete replacement of the ventricles may be warranted. This is achieved with temporary total artificial hearts (TAH, Syncardia). These devices provide global circulatory support through a pneumatic pulsatile pump with an external portable drive. The temporary total artificial heart is traditionally utilized as a bridge to transplantation.

The use of VADs in pediatric heart failure patients has increased in the past decade [7, 9, 16]. While the use of pulsatile-flow and continuous flow devices in pediatric patients have each increased over time, pulsatile-flow devices were more frequently utilized in younger, smaller patients and those with congenital heart disease [16]. In this population, the majority of VADs were implanted as bridge to transplant.
