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Long Term Ventricular Assist Devices

13/09/2005

There are three Thoratec long-term Ventricular Assist Devices (VADs) currently in use at Papworth: PVAD, IVAD and Heartmate 1 XVE LVAS.

This treatment is generally in the form of bridge to transplant, i.e. placing the patient on mechanical circulatory support until a suitable donor heart becomes available. In addition to "buying time", this also enables improvement of the patientís overall fitness and organ function in preparation for a transplant.

For the group of patients with severe heart failure unresponsive to inotropic support, this treatment may be the only means of preserving life until organs become available.

The Thoratec PVAD is a pneumatic paracorporeal pump that can be used to treat patients with severe heart failure by providing either uni or bi-ventricular support.

The cutaway view shows the internal components of the VAD. Blood passes from a percutaneous inflow cannula, through a mechanical tilting disc valve that maintains uni-directional flow, and into the blood sac. On exertion of drive pressure, blood is forced out of the VAD through another mechanical valve and into the outflow cannula, to return to the patient.

The Thoratec VAD is a versatile pump that can be used as either an LVAD, RVAD or BIVAD.

For an LVAD a percutaneous inflow cannula drains blood from either the left atrium or the left ventricular apex into the pump. The blood is then returned via a percutaneous outflow cannula to the ascending aorta.

An RVAD drains from either the right atrium or right ventricle, and the RVAD flow would then return to the pulmonary trunk.

The Thoratec IVAD is essentially the same as the PVAD but housed in a smooth titanium casing, which facilitates internal placement just below the diaphragm, with a driveline extending out through the skin. The internal components and cannulation options are the same, therefore it can also be used for either uni or bi-ventricular support.

The Dual Drive Console is the main control unit for the Thoratec PVAD and IVAD, and allows adjustment of various settings:

Mode of operation - either "fixed rate" or "fill to empty". The main advantage of "fill to empty" being the ability of the pumps to respond to the patientís increased demands during exercise, as the rate depends on how quickly the chamber fills.
Set the drive pressure required to empty the VADs.

Adjust the systolic time and vacuum levels to optimise flows.

Alternatively, the PVAD and IVAD can be run from a portable unit which allows the patient to be much more mobile and independent. The patient and their family are trained in all aspects of operating and maintaining their portable unit, allowing them the freedom and independence to leave the hospital and return to a normal life.

The Thoratec Heartmate 1 XVE LVAS is an LVAD that can be either electrically or pneumatically driven. It is similar to the PVAD and IVAD in its function. It has inflow and outflow valves to maintain unidirectional flow and the cannulation options are left ventricular apex to ascending aorta.

It can only be used in an LVAD position, thus can only provide uni-ventricular support. Despite this, with its greater stroke volume, it can be very beneficial in supporting larger patients.

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QAIC/UK/1814