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Kukuy EL, Oz MC, Naka Y. Long-Term Mechanical Circulatory Support.
In: Cohn LH, Edmunds LH Jr, eds. Cardiac Surgery in the Adult. New York: McGraw-Hill, 2003:14911506.

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Chapter 62

Long-Term Mechanical Circulatory Support

Eugene L. Kukuy/ Mehmet C. Oz/ Yoshifumi Naka

HISTORY
SYSTEMS
????Implantable Pulsatile Devices
????????HEARTMATE
????????NOVACOR
????Paracorporeal Pulsatile Devices
????????THORATEC
????Rotary Axial Flow Pumps
????????MICROMED-DEBAKEY
????????JARVIK 2000
????????HEARTMATE II
????Totally Implantable Pulsatile Devices
????????ARROW LIONHEART LVD-2000
????Total Artificial Heart
????????CARDIOWEST
????????ABIOCOR
PATIENT AND DEVICE SELECTION
????Patient Selection
????Device Selection
SURGICAL TECHNIQUE
POSTOPERATIVE CARE
COMPLICATIONS
????Bleeding
????Infection
????Thromboembolism
????Mechanical Failure
????Right Heart Failure
????Multiorgan Failure
BRIDGE TO VENTRICULAR RECOVERY/ REMODELING
DESTINATION THERAPY
FUTURE
????HeartSaver LVAD
????Thoratec Intracorporeal VAD
????Novacor II
????Centrifugal Pumps
REFERENCES

?? HISTORY
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Heart failure accounts for approximately 250,000 deaths in America each year.1 Hundreds of thousands of additional patients experience debilitating symptoms despite maximal medical management. About 50% of patients with chronic heart failure will die within 1 year and about 70% within 5 years. Even though heart transplantation has been an effective treatment, the number of donors is limited to about 2300 annually and thousands of people die awaiting heart transplantation.2 Man has long sought to find a mechanical means to support the failing heart, and since the mid-1980s this dream has become a reality. More recently, as the results have improved, the indications for the use of these devices have broadened.

In 1953, Gibbon introduced cardiopulmonary bypass and revolutionized the practice of heart surgery.3 The bypass machine not only started a new era in heart surgery, but also showed that a mechanical device could replace the function of the heart. Spencer in 1959 showed that circulatory support could be used to assist the failing heart.4

DeBakey was the first to successfully use an implantable mechanical assist device in 1963 to aid a failing heart. Cooley followed this in 1969 with the first implantable device used as a bridge to transplantation.5 Subsequently, in the 1970s and early 1980s, further research on these devices was undertaken with the help of government sponsorship, and on several occasions circulatory assist devices were used successfully as a bridge to transplantation.

In 1982, DeVries implanted a total artificial heart (Jarvik-7) into a patient in a much-publicized case. The patient died 112 days after implantation.6 Several subsequent patients in the 1980s received the total artificial heart and many were thus bridged to transplantation. However, these devices were plagued by thromboembolic and infectious complications, and by the end of the 1980s the enthusiasm for the use of a total artificial heart was waning. During the same time, heart transplantation surged with the new use of cyclosporine and focus was turned to devices that could "bridge" the failing heart to transplantation.7,8

The last two decades saw the renaissance of the ventricular assist device as a bridge to transplantation. More recently the use of these devices has been expanded to include bridge to recovery and permanent long-term heart support/replacement. At the same time, the total artificial heart and new smaller devices have emerged as options in the treatment of heart failure.

In this chapter, we will review the major left ventricular assist systems (LVAS) and devices (LVAD) subdivided into categories that include: implantable tethered pulsatile devices, paracorporeal pulsatile devices, rotary axial flow pumps, totally implantable pulsatile devices, centrifugal devices, and the total artificial heart. We will also talk about patient selection, operative technique, postoperative care, and complications. The three end points of treatment will be discussed: bridge to transplantation, bridge to recovery, and destination therapy.


?? SYSTEMS
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Implantable Pulsatile Devices

HEARTMATE

The HeartMate LVAD (Thoratec Corporation, Pleasanton, CA) was designed in 1975 (Fig. 62-1).9 The system was originally a pneumatic vented system that required a large cumbersome console that did not allow patients much mobility outside the hospital. Since 1986, this system has proven to be effective as a long-term support device with the end goal of heart transplantation. The system underwent years of development and in 1991 a clinical trial of an electric vented (VE) model was begun.10 This electric system allowed a greater amount of mobility with portable battery units carried in a holster. Since then, both models have shown a 60% to 70% rate of survival to transplantation.1113 The worldwide average implant duration is 80 to 100 days, and maximum duration on support has exceeded 2 years.13 The probability of device failure has been shown to be 35% at 2 years.14



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FIGURE 62-1 HeartMate left ventricular assist device. (Reproduced with the permission of Thoratec Corp., Pleasanton, CA.)

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The device is made of a titanium alloy external housing with inflow and outflow tracts that utilize porcine xenograft valves (25 mm). The unique characteristic of the device is its internal blood-contacting surface, which is made on one side of textured titanium and on the other of textured polyurethane. This textured surface encourages the deposition of a fibrin-cellular matrix that forms a pseudo-neointima. The formation of this surface greatly reduces the need for anticoagulation because thrombus formation is greatly reduced.13 Patients with these devices take aspirin (primarily as an anti-inflammatory, not as an anticoagulant) as their only anticoagulation with a subsequent low rate of thromboembolic complications (7%).12,13,15 The device has a pumping capacity in excess of 10 L/min and a stroke volume of 83 mL. The pulsatile flow is created using a pusher plate system.13 The device is operated in either a fixed-rate or automatic mode. In automatic mode, the pump senses when the chamber is full and activates the pusher plate. The pump is inserted into the left upper quadrant of the abdomen either pre- or intraperitoneally. The driveline, consisting of an air vent and power cables, is tunneled and brought out of the skin in the right upper quadrant. Small battery units, worn in a harness, are connected to the cables. Battery life is between 4 and 6 hours depending on activity level.13 In case of an emergency, a portable hand pump can be used to activate the device. The patient's body size is an important factor in allowing device placement. The size of the device requires patients to have a body surface area of more than 1.5 m2. This device was used in the Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial to compare medical and circulatory assist device treatments for end-stage heart failure. Patients with this device showed better results than the medically treated group (see later section on destination therapy).

NOVACOR

The Novacor (World Heart Corp., Ottawa, ON, Canada) left ventricular assist system (LVAS) was developed by Peer Portner in collaboration with Stanford University and was first used in 1984 in a successful bridge to transplant application (Fig. 62-2).16 Initially designed as a totally implantable system for long-term support, it has evolved through a console-based controller system to a wearable controller that has been available since 1993. This system has proven to be reliable, with about 60% to 70% of patients surviving to transplantation.1617 The worldwide median time of LVAS support using this system is 100 days with the device lasting as long as 1512 days.16,17 The company currently claims a 3-year pump reliability of greater than 90%.19



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FIGURE 62-2 Novacor left ventricular assist system. (Courtesy of World Heart Corp., Ottawa, ON.)

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The pump works using dual pusher plates that compress a polyurethane sac; 21-mm bioprosthetic valves are used in both inflow and outflow tracts. Stroke volume reaches 70 mL. Similar to the HeartMate device, the pump is placed in the left upper abdominal quadrant, anterior to the posterior rectus sheath. The inflow tract is connected to the left ventricle, and the outflow tract to the ascending aorta. The percutaneous lead is brought out in the right lower quadrant of the abdomen and connected to a controller worn on a belt system. Unlike the HeartMate system, patients require anticoagulation with warfarin to avoid embolic events. Currently the Investigation of Non-Transplant-Eligible Patients Who Are Inotrope Dependent (INTREPID) trial is underway to evaluate the use of this device as a long-term alternative to transplantation.

Paracorporeal Pulsatile Devices

Numerous Pierce-Donachy type pumps are available, such as Thoratec, Medos, German Heart, and Toyobo Heart. We will discuss here the most utilized device, the Thoratec VAD.

THORATEC

The Thoratec VAD (Thoratec Laboratories Corp., Pleasanton, CA) is another reliable and often used system for ventricular support (Fig. 62-3). Unlike the previously mentioned Novacor and HeartMate, Thoratec is a paracorporeal system that can be applied for univentricular or biventricular support. Since the actual pump chamber is outside of the body, this device can be used on patients with small body size who would not meet the size criteria to house a HeartMate or Novacor system. However, a paracorporeal system limits mobility and presents an obstacle for patients in a long-term setting. William Pierce and James Donachy of Pennsylvania State University designed the pump. In 1984 the first Thoratec system was used as a successful bridge to transplantation. The system received FDA approval for bridging to transplantation in 1995 and for postcardiotomy support in 1998.20



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FIGURE 62-3 Thoratec ventricular assist device. (Reproduced with the permission of Thoratec Corp., Pleasanton, CA.)

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The pump consists of a prosthetic ventricle with 65-mL stroke volume and cannulas for ventricular or atrial inflow and arterial outflow. Currently a large pneumatic drive console is available and a smaller briefcase-sized power driver unit is in trial.20 Pneumatic drivers provide alternating air pressure to fill and empty the blood pump. The pump flow rate ranges from 1.3 to 7.2 L/min.20 The smallest patient receiving the device was a 7-year-old child weighing 17 kg with a BSA of 0.7m2. Inflow cannula placement can occur in an atrial or ventricular position. Ventricular cannula placement is better for left side support as it allows for greater flow rates than the atrial cannulation. Anticoagulation is similar to that used for patients with mechanical valves, with warfarin as a typical therapy.20

The device has been used in over 1000 patients for uni- and biventricular support for both bridge to transplantation and postcardiotomy recovery. Survival to transplantation has been in the 60% to 80% range depending on which ventricle was supported.20,21 The great benefit of this system is its versatility. It is easy to place with less surgical dissection, can be used for different sized patients, can be attached to either the atrium or ventricle, and can be used for right and left support. However, its paracorporeal location limits its use as a long-term device.

Rotary Axial Flow Pumps

Continuous blood flow in circulatory support is a concept as old as the heart-lung machine of the 1950s. Researchers realized that axial pumps had the advantage of smaller size, less power consumption, minimal moving parts, and no valves. Early research focused on problems of hemolysis and questionable problems with long-term nonpulsatile blood flow. Numerous experiments with different pumps were carried out throughout the 1960s, 1970s, and 1980s. However, it is the MicroMed-DeBakey VAD, the HeartMate II, and the Jarvik 2000 pumps that have lately shown most promise in the clinical setting.22

MICROMED-DEBAKEY

The MicroMed-DeBakey VAD (Houston, TX) was initially developed in the 1980s as a collaboration between Dr. George Noon and Dr. Michael DeBakey of Baylor College of Medicine and engineers from NASA (Fig. 62-4). MicroMed Technology, Inc., received the license for this technology in 1996 and has continued to develop this device for clinical use.23 The first clinical use of the device was in Europe in November of 1998 with subsequent trials starting in United States in June of 2000.23,24



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FIGURE 62-4 MicroMed-DeBakey ventricular assist device. (Courtesy of MicroMed Technology Inc., Houston, TX.)

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The pump unit is 1.2 inches in diameter, 3 inches long, and weighs 95 grams. It is made of titanium casing with an impeller/inducer capable of pumping 10 L/min. The rest of the pump consists of a titanium inflow cannula, a flow meter, a Dacron outflow graft (Sulzer Inc., Austin, TX), and a percutaneous cable connected to a wearable battery/control console.23 The inflow cannula is inserted into the left ventricular apex, the pump is placed into a small abdominal pocket, and the outflow graft is anastomosed to the ascending or descending aorta. Patients are chronically anticoagulated with warfarin.23,25 A pump index of 2.0 to 2.5 L/min/m2 or higher is recommended and the pump is started at 7500 rpm and then adjusted. Average pump flow is 3.9 to 5.4 L/min. The flow is volume and preload related. High rpm with inadequate preload can cause suction and ventricular collapse, but this problem is not typically seen.23,25 The flow is not nonpulsatile but is low pulsatile due to the recovering ventricle and change in ventricular volume. Increase in rpm leads to diminished pulses. No consistent significant clinical hemolysis based on plasma-free hemoglobin has been reported. Lactate dehydrogenase, however, is consistently elevated.24,26

In the clinical trial in Europe, the device was tested as a bridge to cardiac transplantation. The trial lasted from November 1998 to March 2001 with 78 patients enrolling in 12 centers. The U.S. trial was begun in June 2000 with 18 patients implanted as of this writing. The total number of worldwide implants is 140. Average time on pump is 79 days with 11 patients surviving longer than 111 days on pump. Longest duration with the pump has been greater than 1 year.25 The probability of 30-day survival is 81%. Out of the initial 32 patients receiving the device, 11 were transplanted and 10 died on support. Death was the result of multiorgan failure but could not be related to device performance as there was no difference in pump index between survivors and nonsurvivors.23 The major complication was late bleeding and was apparently related to the level of anticoagulation, which has since been decreased to a target International Normalized Ratio (INR) of 2.02.5.23 Follow-up of patients with the device has shown improved exercise tolerance and ability to go home with the device while awaiting transplantation.27

JARVIK 2000

The Jarvik 2000 (Jarvik Heart, Inc., New York, NY) is another extensively developed axial-flow pump initially developed by Dr. Jarvik (Fig. 62-5). The pump underwent animal testing at the Texas Heart Institute and Columbia-Presbyterian Medical Center from 1991 to 1999.28 Clinical patient trials to evaluate the device as a bridge to heart transplantation started in April 2000 at the Texas Heart Institute and shortly thereafter in Oxford, United Kingdom. The Oxford protocol included patients who were not transplant candidates and who received the device as destination therapy.29



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FIGURE 62-5 Jarvik 2000. (Courtesy of Texas Heart Institute.)

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The titanium pump measures 2.5 cm in diameter, displaces 25 mL, and weighs 90 grams. The rotor includes titanium impeller blades and is held in place by two ceramic bearings. The impeller rotates at 8,000 to 12,000 rpm producing a flow rate of 7 L/min. Unlike the DeBakey VAD or the HeartMate II pump, the pump is positioned inside the ventricle with the outflow graft extended to the descending aorta. The pump can operate in fixed rate or variable mode and has a manual rate adjustment capability for times of increased activity. Three different control and energy systems are currently under investigation. A percutaneous model that, like most other LVAD systems, has a power lead that exits the patient's skin; a fully implantable model that uses the transcutaneous energy transfer system (TETS), which is still in development; and a modified percutaneous system that uses a titanium pedestal screwed into the skull with a connector piercing the skin and attaching to the external cable. The fixed skull implantation provides a low level of repeated trauma and minimizes the risk of infection seen with percutaneous systems due to high vascularity of the scalp; however, a risk of subsequent intracranial bleeding exists. Clinical implantations of the skull pedestal are currently used in Britain.29,30 Unlike the other systems, which require a sternotomy, the Jarvik 2000 is implanted through a left thoracotomy incision. Similar to other systems, the pump provides a low pulsatile flow with a narrowing of pulse pressure at higher speeds.29

Required anticoagulation is reported to be minimal with some patients taking warfarin while others showing no clot formation with only aspirin. No significant hemolysis is observed between 8,000 and 12,000 rpm. The small size of the device allows patients with small body surface areas to be treated, and the manual control with the ability to increase the pump rate allows patients to control pump output during exercise as shown in the Oxford experience. Patients receiving destination therapy in the United Kingdom have also been discharged from the hospital on the device.30

HEARTMATE II

The HeartMate II LVAD (Thoratec Corp., Pleasanton, CA), like the two previously mentioned pumps, is an axial flow pump that had its origin in the early 1990s with a collaboration between Nimbus Company and the University of Pittsburgh (Fig. 62-6). After many years of animal experiments and development, the device was first implanted in July 2000 in a patient in Israel. Six other patients have received the device in Europe and the company is currently starting a European and U.S. study involving 20 patients in multiple centers.31



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FIGURE 62-6 HeartMate II left ventricular assist device. (Reproduced with the permission of Thoratec Corp., Pleasanton, CA.)

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Similar to the other pumps, this is an axial-flow rotary LVAD made of titanium with a rotor capable of producing flow rates greater than 10 L/min at rpms greater than 10,000. Like the DeBakey VAD, the inflow cannula is joined to the apex of the left ventricle, with the outflow graft connected to the ascending aorta. Like the other axial-flow pumps, there is a risk of generating negative intraventricular pressure and collapsing the ventricle. As a result, inflow cannula positioning and ventricular preload are important. The intraventricular portion of the inflow tract has been elongated and as a result tends to stent open the middle of the ventricle, thus improving reliability of continuous flow throughout the cardiac cycle.31 Anticoagulation is at present required to keep INR between 1.5 and 2.5. The pump is small (124 mL) and is inserted preperitoneally or within the abdominal musculature. Power and control are supplied by a percutaneous lead that is attached to a system driver that can be connected to a power base unit or to rechargeable batteries and worn in a manner similar to the pulsatile HeartMate LVAD. The system can be operated in manual or auto mode with the auto mode preferred for everyday use.31 Currently research is underway to develop and test a totally implantable system using TETS coil to deliver power to the system.32 This pump is a promising system and with the upcoming trials more results are expected in the near future.

Totally Implantable Pulsatile Devices

As our experience with long-term devices improves and the future of destination therapy draws near, completely implantable devices become increasingly important. Two design issues with total implantable systems involve energy transfer and volume displacement. Several models are currently under investigation, including the current Arrow LionHeart LVD-2000 designed with collaboration between Pennsylvania State University and Arrow International (Reading, PA).

ARROW LIONHEART LVD-2000

The Arrow LionHeart LVD-2000 is the first system designed specifically with destination support in mind. It is a completely implantable system with a transcutaneous energy transmission system (TETS) and a compliance chamber, which allows for complete implantation with no percutaneous lines or connections. The pump is made of a titanium casing with pumping activated by a pusher plate. Unidirectional blood flow is maintained via two Delrin disk monostrut valves (27-mm inlet; 25-mm outlet). The inflow and outflow tracts are positioned in the ventricular apex and aorta respectively. Maximum pump flow is 8 L/min with stroke volume of 64 mL.33 The controller is housed in a titanium casing that also houses rechargeable batteries. The control system is dependent on continual monitoring of end-diastolic volume, and thus the patient's physiologic demands control the filling volume of the pump.33 The compliance chamber consists of a circular polymer sac and an attached subcutaneous port infusion system. This compliance chamber loses gas through the polymer and requires replenishment of gas once a month.34 Recharging of the battery is accomplished through a transcutaneous system with a wand overlying the skin over the recharging coil. The patient may be completely disconnected from the external power supply for a short period of time and rely on internal back-up batteries. The internal coil must be positioned under the skin so as to allow no more than 1 cm of tissue thickness between the coil and skin surface.33,34

The LionHeart underwent initial studies in Europe using 5 centers with 20 patients receiving the device. A U.S. clinical trial has begun with FDA approval for a phase I clinical human trial.34

Total Artificial Heart

CARDIOWEST

Mechanical left ventricular support is adequate for the majority of heart failure patients. However, a subgroup of patients requires biventricular support and complete replacement of native heart function. The total artificial heart (TAH) has been under development for decades. In 1982 a Jarvik-7 TAH was used in a much publicized case.6 The CardioWest Total Artificial Heart (CardioWest Technologies, Inc., Tucson, AZ) is a device derived from the Jarvik pump and subsequently modified into the Symbion Jarvik-70 TAH and finally the CardioWest C-70 TAH. Since its inception, the device has been implanted in over 300 people worldwide, and since an FDA-approved study was begun in 1993, the device has been successfully used in over 150 patients as a bridge to transplantation.35 The pneumatic device is implanted into the chest cavity of critically ill patients with a minimal body surface area of 1.7 m2. The prosthetic ventricles of the device replace the patient's native ventricles and connections are made to the patient's great vessels and atrial cuffs. The patients require chronic anticoagulation. Those who are eligible to receive the device must have large chests with 10-cm anteroposterior diameter at T10. The overall survival of patients on the device has been as high as 83% with a low postoperative stroke rate of 0.6 events/patient-year. Serious infection has occurred in approximately 20% of patients, and the mean duration of device support until transplantation has been 84 days. The CardioWest pump should be considered in a patient with biventricular failure and a large chest cavity. The lack of a small portable controller does limit ambulation on this device.35,36

ABIOCOR

Another device showing much promise is the AbioCor (ABIOMED Inc, Danvers, MA) totally implantable artificial heart (Fig. 62-7). The pump is an electrohydraulically actuated device implanted in the pericardial space after excision of the native heart. The pump chambers are sutured to atrial tissue and great vessels by textured Dacron atrial cuffs and grafts. Two polyurethane blood pump chambers with a 60-mL stroke volume produce 8 L/min of flow. The pump is connected to internal components including controller, battery, and transcutaneous energy transfer (TET) coil.37 The patients require chronic anticoagulation after implantation to prevent thromboembolic events.



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FIGURE 62-7 AbioCor totally implantable artificial heart. (Courtesy of ABIOMED Inc., Danvers, MA.)

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After extensive animal testing starting in 1998 at the University of Louisville and the Texas Heart Institute, the device received FDA approval for a multicenter limited human testing trial involving patients requiring total heart support who did not qualify for heart transplantation. The first patient received the heart on July 2, 2001, and was kept alive for almost 5 months on the device. His death was a result of anticoagulation complications and was not device related.38 This early experience will heighten awareness of the significance of right heart failure during left ventricular support.


?? PATIENT AND DEVICE SELECTION
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As LVAD technology improves so does the desire to apply this technology to an ever growing population. However, patients receiving this therapy still experience a large risk of morbidity and mortality. In order to minimize this risk, both the technology and the patient selection need to improve.

Patient Selection

The HeartMate and the Novacor LVAD systems have been tested for years and have a greater than 70% rate of survival to transplantation.11131618 One of the most important aspects of device implantation is patient selection. Heart failure in some form (chronic congestive, idiopathic dilated, acute postcardiotomy, or other) must be present. Signs of failure such as pulmonary capillary wedge pressure higher than 20 mm Hg, cardiac index less than 2.0 L/min/m2, or systolic blood pressure below 80 mm Hg despite best medical management should be present.11 Columbia University and the Cleveland Clinic Foundation devised a scoring system in 1995 to predict which patients would have a successful outcome after LVAD implantation.39 However, as the technology evolved, it widened and extended the use of these devices and the Columbia score was revised to better reflect the current LVAD-eligible population.40 The previous score utilized 10 factors found to be significant for mortality using univariate analysis with a score higher than 5 corresponding to more than a 33% risk of postimplantation death.39 The revised score was based on 130 patients receiving vented electric HeartMate devices from 1996 to 2001 (Table 62-1). Univariate and multivariate analyses were performed to determine operative mortality.


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TABLE 62-1 Scoring systems for prediction of successful outcome after LVAD implantation

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The new preoperative risk factors predicting mortality by univariate analysis are: previous LVAD/RVAD, acute MI, postcardiotomy, central venous pressure (CVP) greater than 16 mm Hg, prothrombin time (PT) greater than 16 seconds, preoperative ventilation, redo surgery, coronary artery disease, and dilated cardiomyopathy. Interestingly, preoperative renal insufficiency was not found to impact survival in the new scoring system, unlike the old system. This is likely due to aggressive treatment of renal insufficiency with ultrafiltration and hemodialysis. A stepwise linear regression model identified a ventilated patient and a previous LVAD as independent predictors of mortality following device insertion.42 After multivariate analysis the 5 new factors included in the scoring system were: ventilated patients (score of 4), redo surgery (score of 2), previous LVAD inserted (score of 2), CVP higher than 16 mm Hg (score of 1), and PT higher than 16 seconds (score of 1). A score higher than 5 corresponds with a 47% mortality, compared with 9% mortality for a score lower than 5. The positive and negative predictive value of this scoring system is 79% and 70% respectively.40

The urgency of device placement has also been shown to play a factor in survival. In a study by Deng et al, patients receiving emergent LVADs had a lower survival to transplantation rate than those receiving devices urgently or those who did not need devices. However, electively implanted LVAD patients with no subsequent transplantation had better survival than medically treated heart failure patients who also did not get transplanted. This occurred despite the fact that the LVAD recipients were a sicker group of patients.41

Device Selection

Once we decide that the patient will receive an assist device, the next step is to select the right device for the patient. As mentioned previously, numerous reliable devices are available, and many more will be available in the near future. However, not all of the devices are ideal for every situation. First, the decision needs to be made about the goals for the patient. Will it be short-term or long-term heart recovery? Is it bridge to transplantation or destination therapy? What is the size of the patient, and what size device will they tolerate? Does the patient need biventricular or only left-sided support? A paracorporeal system such as the Thoratec system can be used for short- and medium-term support of less than 6 months as well as for right-sided support. The implantable systems such as the Novacor and Thoratec VADs can be used for medium-term, long-term, and destination therapy and have become the workhorses in this field. However, these devices support only the left side and require a minimum body size greater than 1.5 m2. For smaller patients an axial-flow pump such as the DeBakey VAD, Jarvik 2000, or HeartMate II would be ideal; however, a Thoratec system can also be used until the other devices become fully approved. For destination therapy and biventricular support, the AbioCor TAH may become the system of choice. Biventricular support can be considered in patients with high central venous pressures (CVP), increased pulmonary vascular resistance, multiple organ dysfunction, or severe malignant arrhythmias refractory to medical therapy.42 It is important to tailor the device to the patient and not the patient to the device.


?? SURGICAL TECHNIQUE
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The techniques for implantation of these multiple devices are varied. We will briefly describe the placement of the HeartMate LVAD. The patient is prepared for open heart cardiopulmonary bypass surgery as usual. The sternum is opened and prior to heparinization a pre-peritoneal LVAD pocket is created in the abdominal left upper quadrant through an extension of the midline sternotomy incision. Once the pocket is created, the heart is cannulated for bypass. The device is primed and brought into the field. The LVAD driveline is passed through its tract and out of the skin in the right upper quadrant of the abdomen. If the patient's hemodynamic status allows, we prefer to do off-pump aortic anastomosis first with the use of a side-biting clamp to minimize bypass time. After full heparinization, we measure the length of the graft. Once the graft is measured and trimmed, a side-biting aortic clamp is applied and an elipticolongitudinal aortotomy is created. The graft is sewn into place using 4-0 Prolene sutures. To prevent bleeding, BioGlue (CryoLife Inc., Kennesaw, GA) is generously applied over the entire anastomosis line. Bypass is instituted and aortic pressure is lowered prior to releasing the aortic side clamp to minimize the bleeding associated with high pressure. Hemostasis is confirmed immediately after releasing the clamp. A circular core bored out of the apex of the left ventricle allows for placement of the inflow cannula. Sutures are placed circumferentially around the cored opening and passed through the inflow cannula Teflon ring. Once all the sutures are placed, the cannula is brought down to the ventricle and all the sutures are tied. The inflow cannula is secured to the LVAD body and additional BioGlue is used to reinforce the anastomosis. The pump is manually primed and vented through the outflow tract as the patient is weaned from bypass with the pump on. Chest tubes are placed in the pleural cavities and drains are placed in the mediastinum and in the LVAD pocket. After hemostasis is achieved, the chest and upper abdomen are closed in the standard fashion.


?? POSTOPERATIVE CARE
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After LVAD implantation patients are moved to the intensive care unit on a ventilator. Extra care needs to be taken to ensure that the right heart is well supported, and as a result milrinone and inhaled nitric oxide (iNO) therapy are now routinely used in the immediate postoperative period.12 If excessive bleeding is encountered in the operating room, the chest may be packed and left open upon transfer to the intensive care unit. The patient is then brought back to the operating room after the coagulopathy is corrected for irrigation and chest closure. In the intensive care unit, the patient is weaned from NO and extubated once pulmonary artery pressures are in the normal range. With no further sign of active bleeding, the drains and chest tubes are removed. Anticoagulation with aspirin is used for patients with all devices. Additional anticoagulation with warfarin is used for patients receiving the Thoratec and Novacor, as well as the axial-flow devices. Physical therapy and nutrition are addressed early. The LVAD recipient discharge program was instituted in 1993 by the FDA. Since then, numerous centers have reported selective patients who are sent home to live with their devices while awaiting transplantation or as destination therapy. The FDA program created numerous functional and clinical discharge criteria. General criteria include physical rehabilitation, echocardiographic evidence of marginal heart function (to keep the patient alive until manual pumping can be instituted in case the device fails), and a training course in use and care of the device. Once these criteria are met, patients undergo a gradual program with longer trips outside the hospital and finally discharge with weekly returns.11,43


?? COMPLICATIONS
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Six common complications occur after VAD implantation. We will review these in context of the three most common pumps used: Thoratec, HeartMate, and Novacor.

Bleeding

Postoperative bleeding occurs frequently after device placement. Normal postoperative bleeding is made excessive by preoperative heart failure leading to hepatic dysfunction, need for anticoagulation, coagulopathy caused by human-device interaction, extensive surgical dissection, and prolonged cardiopulmonary bypass time. Excessive perioperative bleeding occurs between 20% and 50% of the time in all three devices. This rate, however, has decreased as the experience with the devices has grown.42,44 Coagulation parameters as well as complete blood count must be monitored closely and products replaced as necessary. Death due to bleeding has been reported in the range of 0% to 15% for the three devices.16,44 Reexploration for bleeding is also common and at times can be planned. If excessive bleeding is noted at the time of chest closure, the chest can be left open, packed, and the patient taken to the ICU for resuscitation. The chest is closed once coagulation is normalized.

Infection

Infection is another serious complication affecting long-term mechanical circulatory support patients. There is some controversy and lack of definitions regarding what constitutes the various subgroups of device infection. LVAD infection can manifest as driveline, pocket, blood, or device endocarditis. At times it can be difficult to decide if a pocket infection is present or exactly where the offending organism is harbored in an LVAD-supported patient with positive blood cultures and multiple catheters and intravenous lines. In addition to device infections, the patients are susceptible to the standard common infections seen in critically ill patients such as pneumonia, line sepsis, and urinary tract infections. The reported infection rates in these patients range from 12% to 55%.42,45 Pocket infection rates have been reported to be 11% to 24% for the HeartMate and Novacor systems with the driveline infection rates even higher and in the range of 18% to 30% for the two devices.42,44 There is much variability in this data since definitions for these infections have not been standardized and in many cases clinical presentation is not clear cut. Sepsis accounts for 21% to 25% of LVAD deaths and occurs in 11% to 26% of patients.14,16,42,44 Infection, however, is not a contraindication to transplantation in this population and transplantation can successfully be accomplished.46

The interaction between device and human that occurs after VAD implantation is a topic of much interest. It is well established that B-cell hyperreactivity in LVAD patients leads to the development of antibodies to HLA class I or II antigens with subsequent high panel reactive antibody (PRA) results. Several studies from Columbia University have also pointed to immune system activation with T-cell dysfunction, apoptosis, and elevation in CD-95 levels in patients after LVAD implantation. In comparison to medically managed patients, LVAD patients were also found to have lower T-cell proliferative responses after activation.47,48 This immunologic dysfunction may play a key role in the high infection rates seen in patients with long-term circulatory assist devices. More work is needed in this area to further define the causes of this phenomenon.

Thromboembolism

Thromboembolism is a major concern in any patient with mechanical circulatory support due to blood-device interface. The prevalence of embolism varies depending on the system used and varies from 7% to 47%, with the majority occurring in cerebral distribution in the 25% range.42,44 The HeartMate device has the lowest thromboembolic rate, reported to be as low as 7.4%.42 This is likely due to its unique textured blood-interface surface, which promotes a formation of neointima with subsequent low thrombus formation despite minimal anticoagulation with aspirin. All other pumps require warfarin as well as antiplatelet agents for anticoagulation to prevent this complication. In addition to device-surface interaction, thrombus formation can occur due to turbulent flow in any one of the conduits or in the device itself.

Mechanical Failure

Mechanical failure is a complication on the decline. Constant modifications of pump design result in more reliable systems. The failure can occur in multiple places in the device itself or in the controller. The rate of failure is 10% or less including the long-term studies with device duration longer than 1 year.14,44 Device failure, however, does not always result in patient death. In many cases ample time or reserve is available to replace the device or the controller.

Right Heart Failure

Patients must be observed for signs of right ventricular failure from the time before device implantation until the early postoperative period. The clinician must keep right heart function in mind when evaluating a patient for LVAD placement. In most cases, the unloading and support of the left ventricle will help the right side. However, a rise in central venous pressure with a decrease in device flow and an empty left ventricle signals right ventricular failure. Inhaled nitric oxide is useful in this situation; however, at times an RVAD needs to be implanted. The incidence of right heart failure is above 10%, and 20% of patients are on prolonged inotropic support due to right heart failure. Right heart failure is also associated with high transfusion rate and increased rate of end-organ failure. The number of days in the intensive care unit and the mortality rate are also increased in the right heart failure patients.49

Multiorgan Failure

Multiorgan failure is another frequent complication in this population. Due to a significant amount of preoperative end-organ dysfunction and comorbid conditions, some of these patients do not fully recover after device implantation. In many situations multiorgan failure is the end result of a long cascade of complications including sepsis, bleeding, and other events. At other times it may be the result of significant preoperative multiorgan dysfunction that gets worse after the insult of surgery. In all these scenarios it can account for 11% to 29% of deaths with the device.44


?? BRIDGE TO VENTRICULAR RECOVERY/ REMODELING
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There is increasing evidence that hemodynamic unloading of the ventricle can reverse and in some cases normalize several aspects of a failing heart's structure and function. Consistent data show that LVAD support provides both pressure and volume unloading of the left ventricle.50,51 LVADs have been shown to cause a reversal of ventricular chamber enlargement, reduction of left ventricular mass, regression of myocyte hypertrophy, increased contractile properties of myocytes, and normalization of gene expression encoding for proteins involved in calcium metabolism in the failing heart.50,52 Clinical experience has shown that in some patients LVAD support may lead to improvement of pump function of sufficient magnitude to allow explantation of the device without transplantation.51,53,54 These findings have led to the idea of using LVADs as a bridge to recovery. Reports of heart failure recovery leading to explantation of the device date back to 1991.55 Since the mid-1990s an increasing amount of work has been done in this field. Some of the studies were done using the HeartMate LVAD system in which a flow limiter was used to decrease LVAD flow and assess potential candidates for device explantation, using exercise testing, echocardiography, and max Vo2. Other centers have used rate weaning and dobutamine stress studies in combination with cardiac echocardiography to select patients who may tolerate the removal of device. As of now, this "recovery" has been shown to occur in a limited number of patients. Additional work is currently being done in this area under the LVAD Working Group (LWG) multicenter study in an attempt to better classify who will benefit from this form of therapy and what parameters are to be used to wean the patient off the LVAD.56 Specific and unique pharmacotherapy may also prove to be beneficial in this patient population with the resulting treatment formula being a combination of device implantation and pharmacologic manipulation. Yacoub has previously published work showing the benefit of this combined treatment with medications such as clenbuterol.57 At present this form of therapy is not the standard of care.


?? DESTINATION THERAPY
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Due to the constant shortage of available donor organs, the large group of patients who would benefit from circulatory assistance, and the positive results from the use of current LVADs as long-term support, a multicenter trial was conducted to evaluate the use of a LVAD as a permanent device in the treatment of heart failure. The REMATCH Study was undertaken in 1998 and included 129 patients in 20 centers. The Thoratec HeartMate vented electrical LVAD was used as the tested device. Eligible patients were adults with end-stage heart failure and contraindications for transplantation. The patients in the study were randomly assigned to receive either an LVAD or optimal medical therapy. The study used death as the primary end point and included a number of secondary end points to assess quality of life, complications, and hospitalizations. The study ended in July 2001 once a predetermined number of deaths occurred. Sixty-eight percent of patients received LVADs and 61% received only medical management. The two groups were similar in baseline characteristics. There was a reduction of 48% in the risk of death in the group treated with LVADs as compared to the medically treated group. Quality of life measurements were also better in the LVAD-treated groups. In the adverse events category, patients with devices were more than twice as likely to have an adverse event. Patients with LVADs had a higher median number of days spent in and out of the hospital.14

The INTREPID trial is another similar study currently under way and near completion. This study involves the Novacor LVAS, which has been shown to work without failure an average of 4 years in 12 patients.58 The results of this study may further reconfirm the LVAD as an alternative to transplantation and a good tool in the fight against heart failure.


?? FUTURE
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Long-term mechanical circulatory support is at a point of intense research and development. The potential of these devices not only as a bridge to transplantation but also as destination therapy is being shown in clinical trials. A number of devices are currently under development and will soon reach clinical application.

HeartSaver LVAD

The HeartSaver LVAD (World Heart Corporation, Ottawa, ON, Canada) is designed as a totally implantable LVAD system using TET coil for transcutaneous energy transfer. Similar to other LVADs, the inflow cannula is inserted into the apex of the left ventricle with the outflow going to the ascending aorta. The pump has an attached volume displacement chamber and as an entire unit is implanted into the left thoracic cavity. The preclinical work with the device is being done at the University of Ottawa Heart Institute and numerous animal studies have shown promise.59

Thoratec Intracorporeal VAD

The Thoratec Intracorporeal VAD (Thoratec Laboratories Corp., Pleasanton, CA) is being designed by the same firm that developed the paracorporeal device. The intracorporeal system is the same size as the external system but is cased in a titanium alloy housing and will be implantable. The advantages of this system will be its use as implantable right ventricular support, and its small size, reliability, and proven and extensively tested technology based on the currently used Thoratec system. It will be targeted toward patients who would benefit from long-term support and the benefits of an implanted device.60

Novacor II

Novacor II (World Heart Corp., Ottawa, ON, Canada) is a concept heart created by a company with extensive LVAD experience. It will be a totally implantable pump for definitive treatment of heart failure. Its unique dual-chamber, four-valve pump requires no volume compensator. The pusher plate is suspended and magnetically driven thus providing for a system with few moving parts. The two chambers fill alternately creating pulsatile flow. The system also uses transcutaneous energy transfer technology to supply power. It is currently in preclinical testing.18

Centrifugal Pumps

Years after the invention of centrifugal pumps, researchers in several centers are looking into these pumps as next-generation implantable circulatory assist devices. The HeartQuest System (MedQuest Products Inc., Salt Lake City, UT) is one such pump built on the maglev (magnetic levitation) concept, which allows for frictionless pumping, low thrombogenicity, minimal noise and vibration, and durability due to lack of metal to metal contact. These pumps have been tested in animals with promising results.61 The VentrAssist (Micromedical Industries, Ltd., Chatswood, NSW, Australia) is another promising centrifugal pump currently undergoing animal testing. It has been implanted in animals without cardiopulmonary bypass. The centrifugal pump is hydrodynamically suspended resulting in no wear, no hemolysis, and no need for anticoagulation.62 Another centrifugal pump in the making is the HeartMate III from the Thoratec Corporation, which created the HeartMate I and II. This pump is their third-generation pump powered by a magnetically levitated centrifugal impeller. It is about one third the size of the HeartMate I pump and is about 3 times the volume of HeartMate II.63,64 Another unique pump, the Terumo DuraHeart LVAS (Terumo Cardiovascular Systems, Ann Arbor, MI) incorporates a unique centrifugal pump with a magnetically levitated impeller. The pump provides contact-free rotation of the impeller without material wear and tear and therefore is one of the most durable blood pumps. More than 50 animal experiments have been conducted with the longest thrombus-free operation up to 864 days. The first human clinical study is expected to begin in 2002. The Kriton VAD (Kriton Medical Inc., Miramar, FL) is also a small centrifugal pulsatile pump now in long-term animal studies. The pump's displaced volume is 48 and the pump is capable of pumping 15 L/min in a pulsatile fashion. Since the pump's bearings are magnetically suspended, the pump should last for years with minimal wear.65 All of these centrifugal pumps share the common advantage of ease of operation and dependability with few moving parts. Within the next few years we will see further advancement of mechanical circulatory support as these next devices come into clinical use.

Long-term mechanical circulatory support has become a tool for the treatment of congestive heart failure. In the years to come, further understanding of heart failure, myocardial recovery, and immunology and further device modifications will lead to improved outcomes and greater utilization of this treatment option. FDA approval of this new technology as treatment for heart failure is a critical step in the future of this field.


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