A Ventricular assist device, or VAD, is mechanical device that is used to partially or completely replace the function of a failing heart. The devices are generally designed to replace or assist cardiac function temporarily, but recently devices are becoming available that can be implanted permanently for so called "destination therapy." Most patients using the devices, however, are awaiting heart transplant. In at least one case the patient's heart has recovered during this waiting period sufficiently to enable the VAD to be removed and the transplant to be unnecessary^[1] . Wind turbines The scientific definition of a machine is any device that transmits or modifies energy. ... The heart and lungs, from an older edition of Grays Anatomy. ... An implant is an artificial device made to replace and act as a missing biological structure. ...

VADs are designed to assist either the right (RVAD) or left (LVAD) ventricle, or both at once. The choice of device depends on the underlying heart disease and the pulmonary arterial resistance which determines the load on the right ventricle. Generally when pulmonary arterial resistance is high, right ventricular assist becomes necessary. Because the devices generally result in blood flowing over a non biologic surface, predisposing the blood to clotting, there is need for anticoagulation. There is one device, the Heartmate, which provides a biologic surface derived from fibrin and does not require long term anticoagulation; unfortunately, this biologic surface may predispose to infection. In the heart, a ventricle is a heart chamber which collects blood from an atrium (another heart chamber that is smaller than a ventricle) and pumps it out of the heart. ... Heart disease is an umbrella term for a number of different diseases which affect the heart and is the leading cause of death in the United States as of 2007. ... Coagulation is a complex process by which blood forms solid clots. ... An anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting. ... Fibrin is a protein involved in the clotting of blood. ...

VADs need to be clearly distinguished from artificial hearts, which are designed to completely take over cardiac function and generally require the removal of the patient's heart. An artificial heart is a device that is implanted into the body to replace the original biological heart. ...

Outcomes

A test carried out in 2001 by Dr Eric Rose and the REMATCH study group using patients with Congestive Heart Failure and were ineligible for a transplant showed a survival at two years of 23% for those implanted with an LVAD compared with 8% for those who were given drug treatment. The two major complications of VAD implantation were infection and mechanical failure.

The CE Mark bridge to transplant clinical trials for the VentrAssist device showed that after 154 days 40 per cent of patients had received transplants and 43 per cent were still alive and transplant eligible, giving a success rate for the trial of 83 per cent ^[2].

New VAD designs which are now approved for use in the European Community and are undergoing trials for FDA approval have all but eliminated mechanical failure.

VAD-related infection can be caused by a large number of different organisms:^[3] An infection is the detrimental colonization of a host organism by a foreign species. ...

• Gram positive bacteria (Staphylococci especially Staph. aureus, Enterococci)
• Gram negative bacteria (Pseudomonas aeruginosa, Enterobacter species, Klebsiella species)
• Fungi especially Candida sp.

Treatment of VAD-related infection is exceedingly difficult and many patients die of infection despite optimal treatment. Initial treatment should be with broad spectrum antibiotics, but every effort must be made to obtain appropriate samples for culture. A final decision regarding antibiotic therapy must be based on the results of microbiogical cultures. Binomial name Rosenbach 1884 Staphylococcus aureus , (literally Golden Cluster Seed) the most common cause of staph infections, is a spherical bacterium, frequently living on the skin or in the nose of a person, that can cause a range of illnesses from minor skin infections (such as pimples, boils, and cellulitis... Species Enterococcus is a genus of bacteria of the phylum Firmicutes. ... Binomial name Pseudomonas aeruginosa (Schroeter 1872) Migula 1900 Synonyms Bacterium aeruginosum Schroeter 1872 Bacterium aeruginosum Cohn 1872 Micrococcus pyocyaneus Zopf 1884 Bacillus aeruginosus (Schroeter 1872) Trevisan 1885 Bacillus pyocyaneus (Zopf 1884) Flügge 1886 Pseudomonas pyocyanea (Zopf 1884) Migula 1895 Bacterium pyocyaneum (Zopf 1884) Lehmann and Neumann 1896 Pseudomonas polycolor... Klebsiella pneumoniae is a gram-negative rod-shaped bacteria, and clinically the most important member of the Klebsiella genus of Enterobacteriaceae. ...

Other problems include immunosuppression, clotting with resultant stroke, and bleeding secondary to anticoagulation. It is interesting to note that some of the polyurethane components used in the devices cause the deletion of a subset of immune cells when blood comes in contact with them. This predisposes the patient to fungal and some viral infections necessitating appropriate prophylactic therapy. Immunosuppression is the medical suppression of the immune system. ... Stroke (or cerebrovascular accident or CVA) is the clinical designation for a rapidly developing loss of brain function due to an interruption in the blood supply to all or part of the brain. ... Blood from a finger Bleeding is the loss of blood from the body. ... A polyurethane is any polymer consisting of a chain of organic units joined by urethane links. ... A scanning electron microscope image of normal circulating human blood. ... For the fictional character, see Fungus the Bogeyman. ... Groups I: dsDNA viruses II: ssDNA viruses III: dsRNA viruses IV: (+)ssRNA viruses V: (-)ssRNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses A virus (from the Latin noun virus, meaning toxin or poison) is a microscopic particle (ranging in size from 20 - 300 nm) that can infect the... Prophylaxis refers to any medical or public health procedure whose purpose is to prevent, rather than treat or cure, disease. ...

As at July 2007, 69 year old Peter Houghton was the longest surviving recipient of a VAD for permanent use. He received an experimental Jarvik 2000 LVAD in June 2000 ^[4].

VADs not only extend the quantity of life, but also the quality of life. People who have had VADs implanted have had lower rates of depression than those people suffering from cardiac disease that have not undergone implantation surgery. For instance since receiving his LVAD Peter Haughton has completed a 91 mile charity walk,published two books, lectured widely, hiked in the Swiss Alps and the American West, flown in an ultra-light aircraft, and traveled extensively around the world ^[5].

The majority of VADs on the market today are somewhat bulky, however one of the smallest devices available weighs only 20g.

One type of VAD which has CE Mark approval for use in the EU and is present in clinical trials in the US (VentrAssist), relies on a varying current in electrical coils in the pump's housing to drive the rotor within the pump and on hydrodynamic forces to levitate the rotor. This results in a pump with only one moving part and with no contact between moving parts thus minimising wear. As at June 2007 these pumps had been implanted in over 100 patients including a 10 year old girl. In one case the original heart recovered after the device had been implanted for a year and the device was able to be removed.

Another type of VAD currently being developed relies on magnetic levitation to drive the rotor within the pump, thereby minimizing the wear and reducing the size of the pump substantially. The first magnetically levitating pump has recently been implanted for clinical trials in Greece and is expected to begin US Clinical Trials in 2007. Magnetic levitation technologies are expected to result in small pediatric VADs within the next four years.

History

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, which was approved for use in the US by the FDA in October 1994. These devices are commonly referred to as first generation VADs

More recent work has concentrated on continuous flow pumps, which can be roughly categorized as either centrifugal pumps or axial flow impeller driven pumps. These pumps have the advantage of greater simplicity resulting in smaller size and greater reliability. These devices are referred to as second generation VADs. A side effect is that their users need to carry documentation saying that the lack of a pulse does not mean that they are dead.

Third generation VADs suspend the impeller in the pump using either hydrodynamic or electromagnetic suspension, thus removing the need for bearings and reducing the number of moving parts to one.

Another technology undergoing clinical trials is the use of trans cutaneous induction to power and control the device rather than using percutaneous cables. Apart from the obvious cosmetic advantage this reduces the risk of infection and the consequent need to take preventative action. A pulsatile pump using this technology has CE Mark approval and is in clinical trials for US FDA approval.

A very different approach in the early stages of development is the use of an inflatable cuff around the aorta. Inflating the cuff contracts the aorta and deflating the cuff allows the aorta to expand - in effect the aorta becomes a second left ventricle. A proposed refinement is to use the patient's skeletal muscle, driven by a pacemaker, to power this device which would make it truly self contained. In any case it has substantial potential advantages in avoiding the need to operate on the heart itself and in avoiding any contact between blood and the device. Interestingly this approach involves a return to a pulsatile flow.

List of implantable VAD devices

This is a partial list and may never be complete
Referenced additions are welcome

MiTiHeart Corporation is a product technology company specializing in ventricular assist devices for patients suffering from congestive heart failure. ...

In popular culture

• In ABC's television series Grey's Anatomy, an LVAD device was central to the storyline of Denny Duquette, a heart transplant patient who eventually died of complications related to his heart transplant. His intern doctor who was romantically involved with him, Dr. Izzie Stevens, cut his LVAD wires to worsen his condition and put him up higher on the transplant list.

The American Broadcasting Company ( oftenly known as ABC) operates television and radio networks in the United States and is also shown on basic cable in Canada. ... This article is about the television series. ... Dr. Isobel Stevens is the name of a fictional character on the ABC television series Grey’s Anatomy. ...

References

1. ^ First VentrAssist Heart Recovery Featured on National TV
2. ^ CE Mark Clinical Trial Results
3. ^ Gordon RJ, Quagliarello B, Lowy FD (2006). "Ventricular assist device-related infections". Lancet Infect Dis 6 (7): 426–37. 
4. ^ Patient Sets World Record for Living with Heart Assist Device
5. ^ The First Lifetime-Use Patient

UPMC's dolphin, formerly on ECMO, now has a thoratec LVAD.

External links

• Long-Term Mechanical Circulatory Support
• Health Center Online VAD
• Mayo Clinic VAD
• FDA VAD
• Life without a pulse — news story about Canadian man with VAD
• Heart Pump Design Could Give Patients New Hope — A new counter-flow heart pump developed by Queensland University of Technology