Chapter 36: Mechanical Circulatory Support

INDICATIONS FOR MECHANICAL CIRCULATORY SUPPORT

Children with severe cardiac or respiratory failure that is refractory to medical management may require mechanical cardiorespiratory support. Transient respiratory and/or circulatory support can be accomplished using extracorporeal membrane oxygenation (ECMO) (see Chapter 25), but prolonged use of ECMO is associated with increased morbidity and mortality due to the inflammation, thromboembolic complications, and issues with durability related to the oxygenator. Longer-term circulatory support without an oxygenator can be accomplished using a ventricular assist device (VAD) in patients with adequate pulmonary status. Currently, only the Berlin EXCOR is approved by the Food and Drug Administration (FDA) for pediatric use, but a number of adult VADs are being used in older children and adolescents.

CHOOSING A DEVICE

The type of device used depends on expected duration of therapy, patient size, and hemodynamic considerations (see Table 36-1 and Figure 36-1).

• Duration of Therapy: The anticipated duration of therapy is an important component of device selection.

  • Short-Term Therapy (CentriMag/PediMag, RotaFlow, Impella, TandemHeart):

    • Patients experiencing an acute process (classically myocarditis) with hope of possible recovery may benefit from a short-term device that is easier to explant.

    • These devices typically last 2 to 4 weeks (similar duration to ECMO without the sequelae of the oxygenator).

    • These devices can be used while the medical team weighs options (“bridge to decision”) or as a pathway to eventual device explant (“bridge to recovery”) or conversion to a long-term VAD (“bridge to bridge”). On some occasions a donor heart may become available fast enough for the device to serve as a “bridge to transplant.”

  • Long-Term or Destination Therapy:

    • Patients requiring long-term support as a bridge to transplant will be candidates for a different set of devices.

    • Currently, the devices routinely available for pediatric long-term use are the Berlin EXCOR, HeartWare VAD, HeartMate II, and the SynCardia Total Artificial Heart (TAH).

    • Some centers are also beginning to offer VAD placement as destination therapy in those who are not candidates for transplant (ex: Duchenne's muscular dystrophy).

• Type of Flow: There are two types of flow patterns: pulsatile and centrifugal. Whereas pulsatile flow more closely mimics the normal heart function, continuous-flow devices are smaller and more durable.

  • Pulsatile Pumps

    • Berlin EXCOR: Only available device for infants and young children

      • Pump system sits outside the body (paracorporeal).

      • The pump is composed of a blood chamber and an air chamber, which are separated by a diaphragm. A driving unit forces air into and out of the chamber, which moves the diaphragm. The diaphragm's movement draws blood into the chamber via the inflow cannula and then pushes it out to the body via the outflow cannula.

      • Each pump has valves to ensure that blood can only flow forward.

      • The inflow cannula typically drains the patient's atrium. The outflow cannula pumps blood back into one of the great vessels (RA, PA for RVAD vs. LA, Ao for LVAD).

    • Syncardia ...