Ventricular assist device | |
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MedlinePlus | 007268 |
A ventricular assist device (VAD) is an electromechanical device that provides support for cardiac pump function, 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 coronary artery disease, atrial fibrillation, valvular disease, and other conditions. [1] [2]
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.[ citation needed ]
Duration
VADs can further be divided by the duration of their use (i.e. temporary versus permanent). Some VADs are for short-term use, [3] 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 [ citation needed ]
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. [4] 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. [5]
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 a patient’s native heart function improves after which the device would be removed). [6] 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. [7] [8]
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. [9]
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. [10] 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.
The pumps used in VADs can be divided into two main categories – pulsatile pumps, [11] which mimic the natural pulsing action of the heart, and continuous-flow pumps. [12] Pulsatile VADs use positive displacement pumps. [13] [14] [15] In some pulsatile pumps (that use compressed air as an energy source [16] ), 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. [17] 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. [18]
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") [19] [20] [21] or hydrodynamic suspension.
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. [23] 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. [24] 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. [25]
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, [26] or that the pulse intensity will be seriously reduced. [27]
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.[ citation needed ]
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. [28] [29] 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. [30]
The majority of VADs on the market today are somewhat bulky. The smallest device approved by the FDA, the HeartMate II, weighs about 1 pound (0.45 kg) and measures 3 inches (7.6 cm). This has proven particularly important for women and children, for whom alternatives would have been too large. [45] 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. [46]
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. [47] [44]
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). [7] [8] 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%. [48]
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 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. [57]
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. [58]
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. [59]
There are a number of potential risks associated with VADs. The most common of these are bleeding events, stroke, pump thrombosis, and infections. [60]
Bleeding
Because the VADs generally result in blood flowing over a non-biologic surface (e.g. metal, synthetic polymers, etc.) this can result in formation of blood clots, also referred to as thrombosis. Due to these clotting abnormalities, anticoagulation medications are used to decrease the risk of thrombosis. 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, however this device was phased out of use starting in 2009 in favor of newer devices. [61] [62]
Due to the use of anticoagulation, bleeding is the most common postoperative early complication after implantation or explantation of VADs, necessitating reoperation in up to 60% of recipients. [63] [64] Most commonly bleeding occurs in the gastrointestinal tract resulting in dark or bright red stools, [65] however if trauma to the head occurs, intracranial bleeding may also occur. [66] Bleeding events may require massive blood transfusions and incur certain risks including infection, pulmonary insufficiency, increased costs, right heart failure, allosensitization, and viral transmission, which can prove fatal or preclude transplantation. [64] When bleeding occurs, it impacts the one year Kaplan-Meier mortality. [63] 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. [67]
Ischemic Stroke and Pump Thrombosis
In patients with VADs, ischemic strokes and pump thrombosis occur when there is inadequate anticoagulation to counter act the blood's tendency to form blood clots when exposed to the foreign materials in a VAD. Stroke risk varies based on the type of VAD in place and other risk factors. [60] Both atrial fibriliation and high blood pressure may increase risk of stroke and high blood pressure can increase a patient's risk of stroke in the setting of VAD use. [68] However, 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. [69]
Infections
Infections in VAD patients occur because the artificial surfaces of the devices serve as a surface for bacterial and or fungal growth. [70] Most infections are classified as driveline infections, which are infections that occur where the device's power cord enters the skin (usually in the upper abdomen) [70]
VAD-related infection can be caused by a large number of different organisms: [71] [70]
Other immune system related problems include immunosuppression. 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. [72]
Considering the multitude of risks and lifestyle modifications associated with ventricular assist device implants, [73] it is important for prospective patients to be informed prior to decision making. [74] In addition to physician consult, various Internet-based patient directed resources are available to assist in patient education. [75] [76]
This section needs to be updated.(April 2015) |
This is a partial list and may never be complete
Referenced additions are welcome
Device | Manufacturer | Type | Approval Status as of July 2010 |
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HeartAssist5 | ReliantHeart | Continuous flow driven by an axial flow rotor. | Approved for use in the European Union. The child version is approved by the FDA for use in children in USA. Undergoing clinical trials in USA for FDA approval. |
Novacor | World Heart | Pulsatile. | Was approved for use in North America, European Union and Japan. Now defunct and no longer supported by the manufacturer. (HeartWare completed acquisition August 2012) |
HeartMate XVE | Thoratec | Pulsatile | FDA approval for BTT in 2001 and DT in 2003. CE Mark Authorized. Rarely used anymore due to reliability concerns. |
HeartMate II | Thoratec | Rotor driven continuous axial flow, ball and cup bearings. | Approved for use in North America and EU. CE Mark Authorized. FDA approval for BTT in April 2008. Recently approved by FDA in the US for Destination Therapy (as at January 2010). |
HeartMate III | Thoratec | Continuous flow driven by a magnetically suspended axial flow rotor. | Pivotal trials for HeartMate III started in 2014 and supported with CarewMedicalWear. FDA approval for BTT in 2017 |
Incor | Berlin Heart | Continuous flow driven by a magnetically suspended axial flow rotor. | Approved for use in European Union. Used on humanitarian approvals on a case-by-case basis in the US. Entered clinical trials in the US in 2009. |
Excor Pediatric | Berlin Heart | External membrane pump device designed for children. | Approved for use in European Union. FDA granted Humanitarian Device Exemption for US in December 2011. |
Jarvik 2000 | Jarvik Heart | Continuous flow, axial rotor supported by ceramic bearings. | Currently used in the United States as a bridge to heart transplant under an FDA-approved clinical investigation. In Europe, the Jarvik 2000 has earned CE Mark certification for both bridge-to-transplant and lifetime use. Child version currently being developed. |
MicroMed DeBakey VAD | MicroMed | Continuous flow driven by axial rotor supported by ceramic bearings. | Approved for use in the European Union. The child version is approved by the FDA for use in children in USA. Undergoing clinical trials in USA for FDA approval. |
VentrAssist | Ventracor [77] | Continuous flow driven by a hydrodynamically suspended centrifugal rotor. | Approved for use in European Union and Australia. Company declared bankrupt while clinical trials for FDA approval were underway in 2009. Company now dissolved and intellectual property sold to Thoratec. |
MTIHeartLVAD | www.mitiheart.com | Continuous flow driven by a magnetically suspended centrifugal rotor. | Currently in animal testing, recently completed successful 60-day calf implant. |
C-Pulse (Now "Aquadex") | Sunshine Heart (Now "CHF Solutions") | Pulsatile, driven by an inflatable cuff around the aorta. | Currently available commercially |
HVAD | HeartWare (now Medtronic) | Miniature "third generation" device with centrifugal blood path and hydromagnetically suspended rotor that may be placed in the pericardial space. | Obtained CE Mark for distribution in Europe, January 2009. Obtained FDA approval in the U.S., November 2012. Initiated US BTT trial in October 2008 (completed February 2010) and US DT trial in August 2010 (enrollment completed May 2012). FDA approval for BTT in 2012 and DT in 2017. Withdrawn from market in June 2021 [78] |
MVAD | HeartWare | HeartWare's MVAD Pump is a development-stage miniature ventricular assist device, approximately one-third the size of HeartWare's HVAD pump. | HeartWare Completed GLP Studies (September 2011). |
DuraHeart | Terumo | Magnetically levitated centrifugal pump. | CE approved, US FDA trials underway as at January 2010. |
Thoratec PVAD (Paracorporeal Ventricular Assist Device) | Thoratec | Pulsatile system includes three major components: Blood pump, cannulae and pneumatic driver (dual drive console or portable VAD driver). | CE Mark Authorized. Received FDA approval for BTT in 1995 and for post-cardiotomy recovery (open heart surgery) in 1998. |
IVAD—Implantable Ventricular Assist Device | Thoratec | Pulsatile system includes three major components: Blood pump, cannulae and pneumatic driver (dual drive console or portable VAD driver). | CE Mark Authorized. Received FDA approval for BTT in 2004. Authorized only for internal implant, not for paracorporeal implant due to reliability issues. |
FiVAD | Leviticus Cardio | Versatile wireless system for LVAD. Allow 6-hour of freedom to the patients | Investigation device, 2 patients trial conduct in Dec 2018 with Jarvik 2000 LVAD in Astana by prof Pya. [43] |
An artificial heart is an artificial organ device that replaces the heart. Artificial hearts are typically used to bridge the time to complete heart transplantation surgery, but research is ongoing to develop a device that could permanently replace the heart in the case that a heart transplant is unavailable or not viable. As of December 2023, there are two commercially available full artificial heart devices; in both cases, they are for temporary use, of less than a year, for total heart failure patients awaiting a human heart to be transplanted into their bodies.
Diastole is the relaxed phase of the cardiac cycle when the chambers of the heart are refilling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventricular diastole the relaxing of the ventricles.
Cardiogenic shock is a medical emergency resulting from inadequate blood flow to the body's organs due to the dysfunction of the heart. Signs of inadequate blood flow include low urine production, cool arms and legs, and decreased level of consciousness. People may also have a severely low blood pressure and heart rate.
O. H. "Bud" Frazier is a heart surgeon and director of cardiovascular surgery research at the Texas Heart Institute (THI), best known for his work in mechanical circulatory support (MCS) of failing hearts using left ventricular assist devices (LVAD) and total artificial hearts (TAH).
Peer Michael Portner was a heart researcher whose work led to the development of the ventricular assist device, an electrical pump that permits patients in heart failure to survive until a heart transplant could be performed.
Cardiac resynchronisation therapy is the insertion of electrodes in the left and right ventricles of the heart, as well as on occasion the right atrium, to treat heart failure by coordinating the function of the left and right ventricles via a pacemaker, a small device inserted into the anterior chest wall.
Management of heart failure requires a multimodal approach. It involves a combination of lifestyle modifications, medications, and possibly the use of devices or surgery.
A wearable cardioverter defibrillator (WCD) is a non-invasive, external device for patients at risk of sudden cardiac arrest (SCA). It allows physicians time to assess their patient's arrhythmic risk and see if their ejection fraction improves before determining the next steps in patient care. It is a leased device. A summary of the device, its technology and indications was published in 2017 and reviewed by the EHRA Scientific Documents Committee.
Destination therapy is a therapy that is final rather than being a transitional stage until another therapy—thus, in transportation metaphor, a destination in itself rather than merely a bridge or road to the destination. The term usually refers to ventricular assist devices or mechanical circulatory support to keep the existing heart going, not just until a heart transplant can occur, but for the rest of the patient's life expectancy. It is thus a course of treatment for severe heart failure patients who are not likely candidates for transplant. In contrast, bridge-to-transplant therapy is a way to stay alive long enough, and stay healthy enough, to await transplant while maintaining eligibility for transplant.
Thoratec Corporation is a United States-based company that develops, manufactures, and markets proprietary medical devices used for mechanical circulatory support for the treatment of heart-failure patients worldwide. It is a global leader in mechanical circulatory support devices, particularly in ventricular assist devices (VADs).
Impella is a family of medical devices used for temporary ventricular support in patients with depressed heart function. Some versions of the device can provide left heart support during other forms of mechanical circulatory support including ECMO and Centrimag.
Cardiac contractility modulation is a therapy which is intended for the treatment of patients with moderate to severe heart failure with symptoms despite optimal medical therapy who can benefit from an improvement in cardiac output. The short- and long-term use of this therapy enhances the strength of ventricular contraction and therefore the heart's pumping capacity by modulating (adjusting) the myocardial contractility. This is provided by a pacemaker-like device that applies non-excitatory electrical signals adjusted to and synchronized with the electrical action in the cardiac cycle.
William F. Bernhard was an American cardiovascular surgeon, Emeritus Professor of Surgery at Harvard Medical School, and cardiovascular surgical pioneer.
Sharon Ann Hunt is a cardiology professor and Director of the Post Heart Transplant Programme in Palo Alto, California and is affiliated with Stanford University Medical Center, professionally known for her work in the care of patients after heart transplantation.
ReliantHeart, Inc. is a privately held American company headquartered in Houston, Texas that designs, manufactures, and provides remote monitoring capabilities for its left ventricular assist devices which are used to assist circulation for failing hearts.
Berlin Heart GmbH is a German company that develops, produces and markets ventricular assist devices (VADs). The devices mechanically support the hearts of patients with end-stage heart failure. Berlin Heart's products include the implantable INCOR VAD and the paracorporeal EXCOR VAD. To date, Berlin Heart produces the only device of its kind available for babies and children with severe heart failure.
Pump thrombosis (PT) is considered a specific case of a major device malfunction, and is classified as either suspected or confirmed pump thrombus. Typically, the device is an implanted blood pump such as a left ventricular assist device. The malfunction is a blockage in the flow of blood anywhere along a vessel and it is mainly due to the bio-incompatible presence of a fairly complex mechanical apparatus. Pump thrombus is dreaded complication of CF LVAD technology that can require repeat surgery to replace the pump or lead to death.
Bridge therapy is therapy intended, in transportation metaphor, to serve as a figurative bridge to another stage of therapy or health, helping a patient past a challenging period caused by particular severe illness. There are various types of bridge therapy, such as bridge to transplant, bridge to candidacy, bridge to decision, bridge to recovery, and anticoagulation bridge. Bridge therapy exists in contrast to destination therapy, which is the figurative destination rather than a bridge to something else.
Jack Greene Copeland is an American cardiothoracic surgeon, who has established procedures in heart transplantation including repeat heart transplantation, the implantation of total artificial hearts (TAH) to bridge the time to heart transplant, innovations in left ventricular assist devices (LVAD) and the technique of "piggybacking" a second heart in a person, while leaving them the original.
Eric A. Rose is an American cardiothoracic surgeon, scientist, entrepreneur and professor and Chairman of the Department of Population Health Science & Policy, and Associate Director for Clinical Outcomes at Mount Sinai Heart. He is best known for performing the first successful paediatric heart transplant, in 1984 while at NewYork–Presbyterian Hospital (NYP).
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