Cardiac assist devices are circulatory (heart lung) support machines that mimic the heart function by using a machine that acts as a mechanical pump to improve blood delivery to the body and decrease symptoms of severe heart failure. Patients are able to breathe easier and experience less fatigue. They usually have improved heart rate, blood pressure and are more stable. It also allows other organs to recover from the stress of heart failure, in particular kidneys, liver and gut.
Cardiac assist devices are used only when all other therapies have been exhausted and heart failure is severe. These devices are typically used as a bridge-to-heart transplant; they can help sustain a failing heart for several months until a suitable donor heart can be found. In some cases a device is used as a bridge-to-recovery, such as in the case of severe myocarditis or transplant rejection. They are used to help the damaged heart recover until it can function on its own.
Several types of mechanical circulatory support are available in the form of ventricular assist devices (VADs) and extracorporeal membrane oxygenation (ECMO). Device selection is critically important in achieving the best outcome. The appropriate type depends on the child’s body size, cause of heart failure, anticipated duration of support, type of assistance needed and the availability of devices. Potential complications of cardiac assist devices include bleeding, infection, blood clots which can lead to stroke and problems with the devices themselves.
Ventricular Assist Devices
Ventricular Assist Devices (VADs) are designed to improve circulation and reverse end-organ dysfunction while allowing physical rehabilitation to improve a patient’s overall condition and likelihood for a successful heart transplant. VADs can be used either for short-term support or long-term support. The cause of heart failure and the likelihood of heart recovery will determine whether a VAD should be used as a bridge-to-recovery or a bridge-to-transplant. Patients may be transitioned from ECMO to a VAD.
The pumps used in VADs can be divided into two main groups according to the method of blood flow: nonpulsatile or pulsatile pumps. Nonpulsatile pumps produce continuous blood flow in which there is no pulse pressure. These continuous pumps can be further subdivided into centrifugal or axial pumps. Pulsatile pumps mimic the natural pulsing action of the heart and are more widely used as a bridge to cardiac transplantation.
Depending on the type of VAD selected, the location of the pumping device can be surgically implanted in the chest (intracorporeal) or placed outside the body (extracorporeal or paracorporeal). Type of support include left ventricular assist devices (LVADs) that take over the function of the lower left heart chambers while biventricular assist devices (BIVADs) support both lower right and left heart chambers and are used in more extreme situations.
Older children who receive VADs may be discharged from the hospital to wait for a heart transplant at home. Children, who are allowed to go home, will be mobile and can resume most of their daily activities with certain precautions.
Extracorporeal Membrane Oxygenation (ECMO)
Extracorporeal member oxygenation (ECMO) is an emergency rescue system that mechanically pumps oxygen into the blood and helps circulate blood through the body. It can provide both cardiac circulatory support and respiratory support to maintain overall circulation. It may be used in critically ill children waiting for a donor heart, especially younger children whose anatomy will not permit other ventricular assist devices. In the event of both heart and lung failure, ECMO frequently is recommended because ventricular assist devices cannot be considered when lung function is inadequate.
The child will be monitored in intensive care while on ECMO. The child may be sedated or conscious but a tube is inserted into their windpipe (intubated), which will restrict their movement and ability to get out of bed.
ECMO can only be used short term because serious complications can develop with extended use, such as bleeding, infection, clotting leading to stroke. At some pediatric heart centers, children can be placed on ECMO while they are receiving cardiopulmonary resuscitation (CPR), with acceptable survival to successful heart transplantation.