Dr Jayan Parameshwar, consultant cardiologist at Papworth Hospital's transplant unit, gives an update on heart support devices
Ventricular assist devices (VADs) are mechanical blood pumps that work to augment the output of the native ventricle (lower pumping chambers of the heart). 
A left ventricular assist device (LVAD) draws blood from the left atrium or ventricle and returns it to the aorta while a right ventricular assist device (RVAD) draws blood from the right atrium or ventricle and returns blood to the pulmonary artery. Advanced heart failure due to any cause may be suitable for this form of therapy but most experience is in patients with enlarged ventricles and poor systolic (heart contracting) function.
Bridge to transplantation
Successful cardiac transplantation provided the stimulus for the development of devices that could be used to support sick patients until a suitable donor organ became available. As the availability of donor hearts is unpredictable, a patient who is critically ill needs other methods of circulatory support when drug therapy does not maintain adequate flow to the vital organs. Kidney and liver function improve on mechanical support, and nutrition and muscle strength recover. This reduces the risk to the patient of any subsequent transplantation. All the heart transplant centres in England now have access to some form of mechanical support.
Permanent support
The prevalence of heart failure between the ages of 65 and 75 years is ten to 12 per cent. Between five and ten per cent of these patients are estimated to have severe heart failure. Most of them will not be candidates for heart transplantation by virtue of age and co-morbidity (other co-existing disease). Ventricular assist devices were originally developed as a long-term treatment for heart failure but patients who are not transplant candidates can now be considered for this form of therapy. Survival in this population is improving and some patients have been supported for more than five years. In 2002 the US Food and Drug Administration approved a device for permanent support and several devices have been used in Europe for permanent support. The NHS does not fund LVAD insertion for permanent support although using it as a bridge to transplantation is supported by central government funding.
Bridge to recovery
Patients dying from some forms of acute heart failure can be supported with mechanical circulatory support (MCS) and it is not uncommon to see recovery of myocardial function to the point where the device can be removed. Recovery has also been reported in patients with idiopathic dilated cardiomyopathy. LVADs “rest” the ventricle to a degree that cannot be achieved by drug therapy. There is a considerable body of evidence to show that the heart muscle recovers at the cellular level with MCS. Improvement detectable by echocardiography occurs much less frequently, and clinical recovery to the point where the device can be safely removed is rarer still (less than ten per cent of patients in most studies). There are intriguing reports of higher rates of clinical recovery from a few centres. Studies are ongoing but at present implantation of a device in patients with chronic heart failure must be viewed as a bridge to heart transplantation or as permanent support.
Devices for short term support
Several devices are available for use in patients who need support for days to periods of up to four to six weeks. In some patients a short-term device may be a bridge to a longer-term device or to heart transplantation. Occasionally patients may improve to the point where the device can be removed and the patient stabilised on medical therapy.
Devices for long term support
These devices have been used to support patients for weeks to years. There are now many devices available for clinical use. They are broadly divided into two groups: a) pulsatile devices b) rotary (continuous flow) devices. All the devices currently used have an external power source and therefore need a “drive line” exiting from the body.
Pulsatile devices
Pulsatile devices have been used for over 20 years in several thousand patients. 
They have a chamber that ejects when filled by the left ventricle. The maximum volume of blood ejected per beat varies from 65 to 85ml depending on the device used. One device (the Thoratec) can be used to support either ventricle. All other devices (including the continuous flow devices) are designed for left ventricular support. The pump sits in a pocket in the abdomen and connects with the ventricle and aorta via cannulae (hollow surgical tube) with valves to direct blood flow.
Rotary ventricular assist devices
The pulsatile devices are large and are often not suitable for small adults and children. Rotary devices are smaller. Newer pumps also lack bearings and it is hoped will be more durable. Implantation is generally easier; infections are less common because of a small pump pocket and smaller drive line. Rotary pumps provide continuous flow and are therefore not “physiological”. Patients usually do not have a palpable pulse. Several continuous flow devices have been in use for the last decade. No one device has been universally accepted as superior to others. Clinical trials with the newer devices are ongoing. In the bridge to transplant setting, patient survival has been similar to that with pulsatile devices though quality of life may be better.
Complications
The major complications of this form of treatment include:
♥ Infection of either pump pocket or drive line site in up to a quarter of patients
♥ Formation of blood clots resulting in strokes though most such episodes tend to be transient and reversible. They occur in up to a fifth of patients and vary between different devices.
♥ Haemolysis (destruction of red blood cells) or breakdown of cells in the blood by the device.
♥ Device malfunction (usually a late complication).
Conclusion
The introduction of MCS has revolutionised the treatment of patients with advanced heart failure who become critically ill. Devices that are currently used are very effective in supporting patients until a transplant can be carried out. MCS is also being increasingly used as a treatment for heart failure in patients who would not be eligible for a transplant although there is no funding for this in the NHS at present. Quality of life while being supported with a device is improving but is still not as good as with a successful heart transplant. Technological improvements in the next decade will undoubtedly make this form of treatment appropriate for more people with advanced heart failure.
Dedicated to Damian McLoughlin, who died age 20 of cardiomyopathy. This site is supported by Damian's family and friends.
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