Ventricular assist device

A ventricular assist device (VAD) is an electromechanical device for assisting cardiac circulation, which is used either to partially or to completely replace the function of a failing heart. The function of VADs is different from that of artificial cardiac pacemakers; some are for short-term use, typically for patients recovering from myocardial infarction (heart attack) and for patients recovering from cardiac surgery; some are for long-term use (months to years to perpetuity), typically for patients suffering from advanced heart failure. VADs are designed to assist either the right ventricle (RVAD) or the left ventricle (LVAD), or to assist both ventricles (BiVAD). The type of ventricular assistance device applied depends upon the type of underlying heart disease, and upon the pulmonary arterial-resistance, which determines the workload of the right ventricle. The left-ventricle assistance device (LVAD) is the most common device applied to a defective heart (as it is sufficient in most cases -the right side of the heart is then often already able to make use of the heavily increased blood flow-), but when the pulmonary arterial-resistance is high, then an (additional) right-ventricle assistance device (RVAD) might be necessary to resolve the problem of cardiac circulation. If both a LVAD and a RVAD is needed a BiVAD is normally used, rather than a separate LVAD and an RVAD. Normally, the long-term VAD is used as a bridge to transplantation (BTT)—keeping the patient alive, and in reasonably good condition, and able to await the heart transplant outside of the hospital.Other 'bridges' include bridge to candidacy, bridge to decision, and bridge to recovery. In some instances VAD's are also used as destination therapy (DT). In this instance, the patient shall not undergo a heart transplantion and the VAD is what the patient will use for the remainder of their life. VADs are distinct from artificial hearts, which are designed to assume cardiac function, and generally require the removal of the patient's heart. The pumps used in VADs can be divided into two main categories—pulsatile pumps, that mimic the natural pulsing action of the heart, and continuous flow pumps. Pulsatile VADs use positive displacement pumps. In some pulsatile pumps (that use compressed air as the/an energy source), the volume occupied by blood varies during the pumping cycle. If the pump is contained inside the body then a vent tube to the outside air is required. Continuous-flow VADs are smaller and have proven to be more durable than pulsatile VADs. They normally use either a centrifugal pump or an axial flow pump. Both types have a central rotor containing permanent magnets. Controlled electric currents running through coils contained in the pump housing apply forces to the magnets, which in turn cause the rotors to spin. In the centrifugal pumps, the rotors are shaped to accelerate the blood circumferentially and thereby cause it to move toward the outer rim of the pump, whereas in the axial flow pumps the rotors are more or less cylindrical with blades that are helical, causing the blood to be accelerated in the direction of the rotor's axis. An important issue with continuous flow pumps is the method used to suspend the rotor. Early versions used solid bearings; however, newer pumps, some of which are approved for use in the EU, use either magnetic levitation ('maglev') or hydrodynamic suspension. These pumps contain only one moving part (the rotor). The first successful implantation of a left ventricular assist device was completed in 1966 by Dr. Michael E. DeBakey to a 37-year-old woman. A paracorporeal (external) circuit was able to provide mechanical support for 10 days after the surgery. The first successful long-term implantation of an artificial LVAD was conducted in 1988 by Dr. William F. Bernhard of Boston Children's Hospital Medical Center and Thermedics, Inc of Woburn, MA under a National Institutes of Health (NIH) research contract which developed Heart-mate, an electronically controlled assist device. This was funded by a three-year $6.2 million contract to Thermedics and Children's Hospital, Boston MA from the National Heart and Lung and Blood Institute, a program of the NIH. The early VADs emulated the heart by using a 'pulsatile' action where blood is alternately sucked into the pump from the left ventricle then forced out into the aorta. Devices of this kind include the HeartMate IP LVAS, which was approved for use in the US by the Food and Drug Administration (FDA) in October 1994. These devices began to gain acceptance in the late 1990s as heart surgeons including Eric Rose, O. H. Frazier and Mehmet Oz began popularizing the concept that patients could live outside the hospital. Media coverage of outpatients with VADs underscored these arguments.