Ventricular assist device

Ventricular assist device
Overview
A ventricular assist device (VAD) is an electromechanical device that provides support for cardiac circulation, which is used either to partially or to completely replace the function of a failing heart. VADs can be used in patients with acute (sudden onset) or chronic (long standing) heart failure, which can occur due to a variety of reasons (e.g. coronary artery disease, atrial fibrillation, valvular disease, and so forth).
Categorization of VADs
VADs may be used to manage a variety of cardiac diseases and can be categorized based on which ventricle the device is assisting, and whether the VAD will be temporary or permanent.
Ventricular Assistance
First, VADs can be categorized based on whether they are designed to assist the right ventricle (RVAD) or the left ventricle (LVAD) or to both ventricles (BiVAD). The type of VAD implanted depends on the type of underlying heart disease (e.g. patients with right ventricular failure from pulmonary arterial hypertension may require an RVAD, versus those with left ventricular failure from a myocardial infarction may require an LVAD). The LVAD is the most common device applied to a defective heart (it is sufficient in most cases; the right side of the heart is then often able to make use of the heavily increased blood flow), but when the pulmonary arterial resistance is high, then an (additional) right ventricular assist device (RVAD) might be necessary to resolve the problem of cardiac circulation. If both an LVAD and an RVAD are needed a BiVAD is normally used, rather than a separate LVAD and RVAD.
Duration
VADs can further be divided by the duration of their use (i.e. temporary versus permanent). Some VADs 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 with advanced heart failure
Temporary use of VADs may vary in scale (e.g. days to months) depending on a patient's condition. Certain types of VADS may be used in patients with signs of acute (sudden onset) heart failure or cardiogenic shock as a result of an infarction, valvular disease, among other causes. In patients with acute signs of heart failure, small percutaneous (introduced to the heart through the skin into a blood vessel rather than through an incision) VADs such as the Impella 5.5, Impella RP, and others can be introduced to either the left or right ventricle (depending on the patient-specific needs) using a wire and that is introduced through the arteries or veins of the neck, axilla, or groin.
Long-term use of VADs may also vary in its scale (i.e. months to permanently). VADs that are intended for long term use are also termed "durable" VADS, due to their design to function for longer periods of time compared to short term VADs (e.g. Impella, etc.). The long-term VADs can be used in a variety of scenarios. First, VADs may be used as bridge to transplantation (BTT) – keeping the patient alive, and in reasonably good condition, and able to await heart transplant outside of the hospital. Other "bridges" include bridge to candidacy (used when a patient has a contraindication to heart transplantation but is expected to improve with the VADs support) , bridge to decision (used to support a patient while their candidacy status is decided), and bridge to recovery (used until patients native heart function improves after which the device would be removed). In some instances, VADs are also used as destination therapy (DT) which indicates that the VAD will remain implanted indefinitely. VADs as destination therapy are used in circumstances where patients are not candidates for transplantation and will thus rely on the VAD for the remainder of their life.
Other Cardiac Support Devices
Some devices are designed to support the heart and its various components/function but are not considered VADs, below are some common examples.
Pacemakers and Internal Cardiac Defibrillators (ICDs) – the function of a VAD differs from that of an artificial cardiac pacemaker in that a VAD pumps blood, whereas a pacemaker delivers electrical impulses to the heart muscle.
Total Artificial Heart – VADs are distinct from artificial hearts, which are designed to assume cardiac function, and generally require the removal of the patient's heart.
Extracorporeal Membrane Oxygenation (ECMO) – is a form of mechanical circulatory support typically used in critically ill patients in cardiogenic shock that is established by introducing cannula into the arteries and or veins of the neck, axilla or groin. Generally, a venous cannula pulls deoxygenated blood from the patient's veins into an oxygenating device at the patient's bedside, after which a motor powered pump moves the oxygenated blood is back to the body (either into a vein or the arterial system, typically the aorta). There are different ECMO configurations (venoarterial ECMO, venovenous ECMO, etc.) the end goal remains the same; to oxygenate blood and return it to the body. In this sense, the ECMO circuit bypasses one or both ventricles and is therefore not in contact with the patient's native ventricle and is generally not considered a type of VAD.
Design
Pumps
The pumps used in VADs can be divided into two main categories – pulsatile pumps, which 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 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.
History
The first left ventricular assist device (LVAD) system was created by Domingo Liotta at Baylor College of Medicine in Houston in 1962. The first LVAD was implanted in 1963 by Liotta and E. Stanley Crawford. The first successful implantation of an LVAD was completed in 1966 by Liotta along with Dr. Michael E. DeBakey. The patient was a 37-year-old woman, and a paracorporeal (external) circuit was able to provide mechanical support for 10 days after the surgery. The first successful long-term implantation of an 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 HeartMate, 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, 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.
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 the user will not have a pulse,
or that the pulse intensity will be seriously reduced.
A very different approach in the early stages of development was 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. However, a similar operation (cardiomyoplasty) was tried in the 1990s with disappointing results.
At one time Peter Houghton was the longest surviving recipient of a VAD for permanent use. He received an experimental Jarvik 2000 LVAD in June 2000. Since then, he completed a 91-mile charity walk, published two books, lectured widely, hiked in the Swiss Alps and the American West, flew in an ultra-light aircraft, and traveled extensively around the world. He died of acute kidney injury in 2007 at the age of 69. Since then, patient Lidia Pluhar has exceeded Houghton's longevity on a VAD, having received a HeartMate II in March 2011 at age 75, and currently continues to use the device. In August 2007 the International Consortium of Circulatory Assist Clinicians (ICCAC) was founded by Anthony "Tony" Martin, a nurse practitioner (NP) and clinical manager of the mechanical circulatory support (MCS) program at Newark Beth Israel Medical Center, Newark, N.J. The ICCAC was developed as a 501c3 organization, dedicated to the development of best practices and education related to the care of individuals requiring MCS as a bridge to heart transplantation or as destination therapy in those individuals who don't meet the criteria for heart transplantation.
Studies and outcomes
Recent developments
In August 2007 The International Consortium of Circulatory Assist Clinicians (ICCAC) was founded by Anthony "Tony" Martin. A nurse practitioner (NP) and clinical manager of the mechanical circulatory support (MCS) program at Newark Beth Israel Medical Center, Newark, N.J..
In July 2009 in England, surgeons removed a donor heart that had been implanted in a toddler next to her native heart, after her native heart had recovered. This technique suggests mechanical assist device, such as an LVAD, can take some or all the work away from the native heart and allow it time to heal.
In July 2009, 18-month follow-up results from the HeartMate II Clinical Trial concluded that continuous-flow LVAD provides effective hemodynamic support for at least 18 months in patients awaiting transplantation, with improved functional status and quality of life.
Heidelberg University Hospital reported in July 2009 that the first HeartAssist5, known as the modern version of the DeBakey VAD, was implanted there. The HeartAssist5 weighs 92 grams, is made of titanium and plastic, and serves to pump blood from the left ventricle into the aorta.
A phase 1 clinical trial is underway (as of August 2009), consisting of patients with coronary artery bypass grafting and patients in end-stage heart failure who have a left ventricular assist device. The trial involves testing a patch called Anginera which contains cells that secrete hormone-like growth factors stimulating other cells to grow. The patches are seeded with heart muscle cells and then implanted onto the heart with the goal of getting the muscle cells to start communicating with native tissues in a way that allows for regular contractions.
In September 2009, a New Zealand news outlet, Stuff, reported that in another 18 months to two years, a new wireless device will be ready for clinical trial that will power VADs without direct contact. If successful, this may reduce the chance of infection as a result of the power cable through the skin.
The National Institutes of Health (NIH) awarded a $2.8 million grant to develop a "pulse-less" total artificial heart using two VADs by Micromed, initially created by Michael DeBakey and George Noon. The grant was renewed for a second year of research in August 2009. The total artificial heart was created using two HeartAssist5 VADs, whereby one VAD pumps blood throughout the body and the other circulates blood to and from the lungs.
HeartWare International announced in August 2009 that it had surpassed 50 implants of their HeartWare Ventricular Assist System in their ADVANCE Clinical Trial, an FDA-approved IDE study. The study is to assess the system as bridge-to-transplantation for patients with end-stage heart failure. The study, Evaluation of the HeartWare LVAD System for the Treatment of Advanced Heart Failure, is a multi-center study that started in May 2009.
On 27 June 2014 Hannover Medical School in Hannover, Germany performed the first human implant of HeartMate III under the direction of Professor Axel Haverich M.D., chief of the Cardiothoracic, Transplantation and Vascular Surgery Department and surgeon Jan Schmitto, M.D., PhD
On 21 January 2015 a study was published in Journal of American College of Cardiology suggesting that long-term use of LVAD may induce heart regeneration.
Hall-of-Fame Baseball Player Rod Carew had congestive heart failure and was fitted with a HeartMate II. He struggled with wearing the equipment, so he joined efforts to help supply the most helpful wear to assist the HeartMate II and HeartMate III.
In December 2018, two clinical cases were performed in Kazakhstan and a fully wireless LVAD system of Jarvik 2000 combine with Leviticus Cardio FiVAD (Fully Implantable Ventricular Assist Device) were implanted in humans. The Wireless power transfer technology based on technique called Coplanar Energy Transfer (CET) which is capable of transferring energy from an external transmitting coil to a small receiving coil that is implanted in the human body. In the early postoperative phase, CET operation was accomplished as expected in both patients, which powered the pump and maintained the battery charged to allow medical and nursing procedures. The Leviticus Cardio FiVAD System with wireless, coplanar energy transfer technology which ameliorates infection risk by driveline elimination while providing successful energy transmission allowing for a substantial (approximately 6 hours) unholstered support of the LVAD.
On June 3, 2021, Medtronic issued an urgent medical device notice stating that their HVAD devices should no longer be implanted due to higher rates of neurological events and mortality with the HVAD vs. other available devices
The majority of VADs on the market today are somewhat bulky. The smallest device approved by the FDA, the HeartMate II, weighs about and measures . This has proven particularly important for women and children, for whom alternatives would have been too large. As of 2017, HeartMate III has been approved by the FDA. It is smaller than its predecessor HeartMate II and uses a full maglev impeller instead of the cup-and-ball bearing system found in HeartMate II.
The HeartWare HVAD works similarly to the VentrAssist—albeit much smaller and not requiring an abdominal pocket to be implanted into. The device has obtained CE Mark in Europe, and FDA approval in the U.S. The HeartWare HVAD could be implanted through limited access without sternotomy, however in 2021 Medtronic discontinued the device.
In a small number of cases left ventricular assist devices, combined with drug therapy, have enabled the heart to recover sufficiently for the device to be able to be removed (explanted). Several surgical approaches, including interventional decommissioning, off-pump explantation using a custom-made plug and complete LVAD removal through redo sternotomy, have been described with a 5-year survival of up to 80%.
HeartMate II LVAD pivotal study
A series of studies involving the use of the HeartMate II LVAD have proven useful in establishing the viability and risks of using LVADs for bridge-to-transplantation and destination therapy.
The HeartMate II pivotal trial began in 2005 and included the evaluation of HeartMate II for two indications: Bridge to transplantation (BTT) and destination therapy (DT), or long-term, permanent support. Thoratec Corp. announced that this was the first time the FDA had approved a clinical trial to include both indications in one protocol.
A multicenter study in the United States from 2005 to 2007 with 113 patients (of which 100 reported principal outcomes) showed that significant improvements in function were prevalent after three months, and a survival rate of 68% after twelve months.
Based on one-year follow up data from the first 194 patients enrolled in the trial, the FDA approved HeartMate II for bridge-to-transplantation. The trial provided clinical evidence of improved survival rates and quality of life for a broad range of patients.
Eighteen-month follow up data on 281 patients who had either reached the study end-point or completed 18 months of post-operative follow-up showed improved survival, less frequent adverse events and greater reliability with continuous flow LVADS compared to pulsatile flow devices. Of the 281 patients, 157 patients had undergone transplant, 58 patients were continuing with LVADs in their body and seven patients had the LVAD removed because their heart recovered; the remaining 56 had died. The results showed that the patients' NYHA Class of heart failure had significantly improved after six months of LVAD support compared to the pre-LVAD baseline. Although this trial involved bridge-to-transplant indication, the results provide early evidence that continuous flow LVADs have advantages in terms of durability and reliability for patients receiving mechanical support for destination therapy.
Following the FDA approval of HeartMate II LVAD for bridge-to-transplantation purposes, a post-approval ("registry") study was undertaken to assess the efficacy of the device in a commercial setting. The study found that the device improved outcomes, both compared to other LVAD treatments and baseline patients. Specifically, HeartMate II patients showed lower creatinine levels, 30-day survival rates were considerably higher at 96%, and 93% reached successful outcomes (transplant, cardiac recovery, or long-term LVAD).
HARPS
The Harefield Recovery Protocol Study (HARPS) is a clinical trial to evaluate whether advanced heart failure patients requiring VAD support can recover sufficient myocardial function to allow device removal (known as explantation). HARPS combines an LVAD (the HeartMate XVE) with conventional oral heart failure medications, followed by the novel β2 agonist clenbuterol. This opens the possibility that some advanced heart failure patients may forgo heart transplantation.
REMATCH
The REMATCH (Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure) clinical trial began in May 1998 and ran through July 2001 in 20 cardiac transplant centers around the USA. The trial was designed to compare long-term implantation of left ventricular assist devices with optimal medical management for patients with end-stage heart failure who require, but do not qualify to receive cardiac transplantation. As a result of the clinical outcomes, the device received FDA approval for both indications, in 2001 and 2003, respectively.
According to a retrospective cohort study comparing patients treated with a left ventricular assist device versus inotrope therapy while awaiting heart transplantation, the group treated with LVAD had improved clinical and metabolic function at the time of transplant with better blood pressure, sodium, blood urea nitrogen, and creatinine. After transplant, 57.7% of the inotrope group had kidney failure versus 16.6% in the LVAD group; 31.6% of the inotrope group had right heart failure versus 5.6% in the LVAD group; and event-free survival was 15.8% in the inotrope group versus 55.6% in the LVAD group.
Complications and side effects
Bleeding is the most common postoperative early complication after implantation or explantation of LVADs, necessitating reoperation in up to 60% of recipients. The implications of massive blood transfusions are great and include infection, pulmonary insufficiency, increased costs, right heart failure, allosensitization, and viral transmission, some of which can prove fatal or preclude transplantation. When bleeding occurs, it impacts the one year Kaplan-Meier mortality. In addition to complexity of the patient population and the complexity of these procedures contributing to bleeding, the devices themselves may contribute to the severe coagulopathy that can ensue when these devices are implanted.
Because the devices generally result in blood flowing over a non-biologic surface, predisposing the blood to clotting, there is need for anticoagulation measures. One device, the HeartMate XVE, is designed with a biologic surface derived from fibrin and does not require long term anticoagulation (except aspirin); unfortunately, this biologic surface may also predispose the patient to infection through selective reduction of certain types of leukocytes.
It is difficult to measure blood pressure in LVAD patients using standard blood pressure monitoring and the current practice is to measure by Doppler ultrasonography in outpatients and invasive arterial blood pressure monitoring in inpatients.
VAD-related infection can be caused by a large number of different organisms:
Gram positive bacteria (Staphylococci, especially Staph. aureus, Enterococci)
Gram negative bacteria (Pseudomonas aeruginosa, Enterobacter species, Klebsiella species)
Fungi, especially Candida species
Other problems include immunosuppression, clotting with resultant stroke, and bleeding secondary to anticoagulation. 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.
Considering the multitude of risks and lifestyle modifications associated with ventricular assist device implants, it is important for prospective patients to be informed prior to decision making. In addition to physician consult, various Internet-based patient directed resources are available to assist in patient education.
List of implantable VAD devices
This is a partial list and may never be complete
Referenced additions are welcome
See also
Intra-aortic balloon pump
Pump thrombosis
References
External links
MyLVAD.com—Non-branded site with information on various LVADs
DECIDE-LVAD Patient Decision Aid - Non-branded site with information on decision making for LVAD
Implants (medicine)
Cardiology
Prosthetics
Interventional cardiology
Medical devices