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Ann Thorac Surg 1999;68:684-687
© 1999 The Society of Thoracic Surgeons
a Section of Cardiothoracic and Vascular Surgery, Department of Surgery, The Milton S. Hershey Medical Center, The Penn State Geisinger Health System, Hershey, Pennsylvania, USA
Address reprint requests to Dr Pae, Section of Cardiothoracic and Vascular Surgery, Department of Surgery, The Milton S. Hershey Medical Center, The Penn State Geisinger Health System, PO Box 850, MC H165, Hershey, PA 17033-0850
Presented at the Fourth International Conference on Circulatory Support Devices for Severe Cardiac Failure, Houston, TX, Oct 3–5, 1997.
Abstract
Background. During the past decade, ventricular assist devices as a bridge to transplantation have moved from the experimental arena to accepted therapy. Our institution has been at the forefront of the development of this technology and consequently has had extensive experience with the devices that are currently approved by the Food and Drug Administration for use as a bridge to heart transplantation.
Methods. The successful management of patients with assist devices hinges on patient and device selection as well as perioperative management strategies. The routine use of agents such as aprotinin, vasopressin, milrinone, and inhaled nitric oxide has contributed to successful management of these patients. We present our perspectives on the advantages and disadvantages of the Thermo-Cardiosystems HeartMate 1000 IP device and the Thoratec (Pierce-Donachy) system. We also discuss our protocols and methods for patient selection, preoperative preparation, intraoperative strategy, and postoperative management that have resulted in improved patient outcomes.
Results. More than 60 device implantation procedures have been performed since the inception of our bridge to transplantation program. During this time, two thirds of our patients were successfully bridged to transplantation. Of these patients, 92% were alive at 1 month after transplantation, and 83% were alive at 1 year after transplantation.
Conclusions. Both support systems are effective in supporting patients to heart transplantation. We have developed a preference for the Thermo-Cardiosystems HeartMate 1000 IP device because of its portability and associated better quality of life. However, the Thoratec device is the more versatile device, and circumstances exist when its use is clearly advantageous. In our institutional experience, outcome for bridging to transplantation has not been device dependent.
For more than a decade, we have relied on ventricular assist devices as a bridge to transplantation. The use of these devices remains an important therapeutic adjunct and a clinical proving ground for refining surgical techniques, patient selection, postoperative management, timing for device insertion, and the development of devices for destination therapy. During the first 10 years of use, we relied exclusively on the Pierce-Donachy pneumatic system (Thoratec) (Thoratec Laboratories Corporation, Berkeley, CA), which has been well described in multiple reports [1, 2]. Since 1995, we have also used the Thermo-Cardiosystems HeartMate 1000 IP device (Thermo-Cardiosystems Inc [TCI], Woburn, MA), thus providing a choice of devices, each with unique advantages and disadvantages with regard to clinical applications. The following is an overview of our clinical experience, with special attention to our protocols, techniques, and practices based on more than 60 implantation procedures with the only two systems currently approved by the Food and Drug Administration for bridge to transplantation. Our recent preference for the TCI device is based on increased patient mobility, improvement in patient quality of life, and economic concerns. At present, patients in our institution can be transferred to an assisted-living environment, so that costs are reduced from nearly $1,000/day while in the hospital to $250/day in the assisted-living environment.
Material and methods
Overview of devices: advantages and disadvantages
Thoratec system
The Thoratec system is composed of a smooth, segmented polyurethane inner sac enclosed in a rigid plastic case. The device is pneumatically actuated, and unidirectional forward flow is provided by tilting disc mechanical valves attached at both the inlet and outlet arms of the device. The device is paracorporeal, lying on the abdominal wall with the inflow and outflow cannulas crossing the skin. Stroke volume is 65 mL when running in fill-to-empty mode (volume mode). The Thoratec device offers several advantages. It is the only device that can be used for biventricular support, with the option of right atrial, left atrial, or left ventricular inlet cannulation, thereby offering a wide array of configurations. Because the left atrium may be used for inflow, the device can be inserted either during or after cardiopulmonary bypass. The device is paracorporeal and does not require internalization; it can therefore be used in smaller patients, including those with a body surface area as small as 0.8 m2. In our experience, insertion and removal are easier and less complicated than with the TCI device. The Thoratec device is a left ventricular assist device and offers an initial economic advantage over the TCI unit, which has a higher initial cost. The main disadvantage of the Thoratec is its large, bulky drive unit, which limits patient mobility and portability. It is therefore not as conducive for use in an outpatient setting. This lack of portability affects not only quality of life issues, but overall cost issues as well. The other disadvantage of the Thoratec device is the need for intense anticoagulation. Future directions for this system include internalization of the pump and development of a compact and portable drive unit to facilitate outpatient management. These modifications should improve quality of life, increase patient mobility, and potentially reduce overall costs.
Thermo-cardiosystems heartmate 1000 IP
The TCI HeartMate 1000 IP is an implantable pneumatic device with a percutaneous driveline. The outer housing is composed of titanium, and the internal blood-contacting surface of the titanium shell is lined with sintered titanium microspheres. There is a textured polyurethane diaphragm attached to a pneumatic pusher plate. Forward flow is maintained by 25-mm porcine valves attached at both the inlet and outlet arms of the device. The blood–surface interactions are designed to promote the development of a pseudointimal lining [3, 4] that obviates the need for device-mandated anticoagulation. The pump is designed to be placed either intraperitoneally or preperitoneally in the left upper quadrant, although we have exclusively used the preperitoneal approach [5]. Inflow options are limited to the left ventricular apex. Outflow is by prosthetic graft attached to the ascending aorta, similar to the Thoratec device. There is a percutaneous driveline that is tunneled and exits the skin in the left lower quadrant. Stroke volume can be up to 85 mL.
Because of its smaller and simpler drive unit, the main advantage of the TCI device is its portability and mobility. Not only is quality of life improved for as long as the device remains in the patients, but patients also can be managed in an assisted-living environment, which results in an overall cost reduction. Also, use of this device does not mandate anticoagulation. The need for anticoagulation is determined by other patient-specific factors rather than device-related factors. Generally only aspirin is administered for reasons related to antibody formation and not necessarily its antiplatelet activity.
The main disadvantages of the TCI device include its limitation to univentricular support only and that the left ventricular apex is the only inflow option. Cardiopulmonary bypass is therefore always required for implantation. The actual size and flow requirements of the device make it unsuitable for implantation in patients with a small body habitus (body surface area < 1.5 m2), thereby further limiting its application. The initial cost of the TCI device is more than that for the Thoratec device; however, the cost differential is negated by early discharge to an assisted-living environment. The future directions for the TCI device include plans for a more portable pneumatic driver, which would facilitate outpatient use, thus decreasing overall costs and improving patient quality of life.
Key for success: timing, patient selection, and preoperative evaluation
Regardless of the choice of device, we believe that the key to success is primarily patient selection combined with early implantation. Patients who are being evaluated for ventricular assistance usually have complications, with several significant comorbid conditions, making postoperative management challenging. Common comorbid conditions potentially affecting outcome in patients undergoing bridge to transplantation are the following:
The initial hurdle is to determine whether the patient is a candidate for heart transplantation. Patients who are selected for left ventricular assist device implantation are usually those with chronic heart failure who are receiving high-dose combination inotropes and are experiencing failing medical management. They may also have come to require intraaortic balloon pump placement. Such patients usually have some degree of reversible end-organ failure manifested by neurologic, renal, or hepatic symptoms. The clinical course of these patients is characterized by deterioration, with their demise often precipitated by arrhythmias. The challenge for the surgeon and cardiologist is to identify these patients early, maximize hemodynamic variables, and then place the device as a semielective measure rather than a resuscitative one.
Initial preoperative workup begins with gathering and reviewing all pertinent data. All previous operative notes must be reviewed if this is to be a reoperative procedure. Recent angiographic data should be reviewed with attention to previous graft patency, as well as any right coronary system lesions that may benefit from concomitant right coronary artery bypass grafting. Right heart catheterization data should also be reviewed to determine the degree of right heart failure and fixed pulmonary hypertension. Right heart dysfunction may therefore need to be addressed, and right ventricular support may be indicated if inadequate left-sided flows are obtained after left ventricular assist device placement. Echocardiographic data should be obtained and reviewed, with particular attention to any aortic insufficiency, tricuspid regurgitation, patent foramen ovale, apical thrombus, and left and right ventricular size and contractility. Patient size may ultimately determine which device is utilized. The blood group, percent reactive antibody, and size (extremes of the spectrum) of the patient are also factors that need to be taken into account and may lead to earlier implantation if a long wait to transplantation is expected.
Preoperative preparation
Our initial preoperative preparation includes stopping warfarin sodium therapy and giving the patient preoperative vitamin K as well as a preoperative fresh-frozen plasma bolus and continuous fresh-frozen plasma infusion before operation. These patients are often receiving anticoagulation but can also have poor hepatic synthetic capacity secondary to right heart failure and hepatic congestion. Blood products that may be required are all given as leuko-depleted products to prevent antibody sensitization. A circuit for inhaled nitric oxide is made available for use in the operating room. Inhaled nitric oxide is a direct-acting vasodilator that results in a drastic decrease in pulmonary vascular resistance and has become indispensable in the management of right heart failure, often obviating the need for a right heart device. Our preoperative antibiotic regimen is broad spectrum and currently consists of vancomycin, aztreonam, and fluconazole.
Operative strategy
The initial strategy in the operating room includes minimizing traffic for infectious considerations. Transesophageal echocardiography is indispensable and yields data regarding ventricular apical clot, patent foramen ovale, tricuspid regurgitation, and aortic insufficiency, as well as left ventricular decompression and cannula position after implantation. External defibrillator pads are placed for all reoperations, as is a femoral artery catheter if an intraaortic balloon pump is not already in place. Aprotinin (Miles Incorporated, West Haven, CT) is used in all our implantation procedures because bleeding and subsequent transfusion can be a catastrophic complication, leading to exacerbation of right heart failure, immune sensitization, and disease transmission [6, 7]. All dissection is carried out carefully so as to maximize hemostasis. Meticulous attention is paid to device setup, removal of air, and graft preparation.
Operation begins with a median sternotomy with adequate dissection to achieve cannulation for bypass. Preperitoneal dissection for device pocket formation is carried out in the absence of heparinization (TCI device). Heparin is administered, and cardiopulmonary bypass is instituted. Bypass strategy includes normothermic bypass with active warming and aggressive hemoconcentration. We do not routinely cross-clamp to perform apical cannulation of the left ventricle. In our experience, apical ventricular cannulation is optimal because it yields the best flows with complete ventricular decompression and unloading of the heart. The improved flows and left ventricular decompression achieved from ventricular cannulation also result in lower thromboembolic rates than those seen with atrial cannulation. When implanting the Thoratec device, all skin tunnels are kept well away from the costal margins while maintaining the external cannula lengths as short as possible to prevent kinking. The aortic anastomosis is performed using a partial occluding clamp, keeping the anastomosis low and along the greater curvature of the aorta. The inlet to the device is connected; we then perform air removal and connect the outlet cannula. Associated procedures such as patent foramen ovale closure (patent foramen ovale may only now be apparent with the left side decompressed) and right coronary artery grafting are carried out with the heart beating under local stabilization [8].
Access of the left ventricular apex warrants special attention. Exposure of the apex is obtained by placing two to three laparotomy pads under and lateral to the apex, both bringing the heart medially and elevating it as well. Buttressed sutures are placed circumferentially around the apical dimple. The patient is placed in the Trendelenburg position, and a stab incision is made in the center of the circle created by the suture placement. A 20F Foley catheter, with a 30 mL balloon is passed through the lumen of a sharpened cork borer, and the Foley catheter is inserted into the stab incision and inflated (with saline only because air can be ejected). The sharpened cork borer is lowered into position. The Foley balloon is used as an anvil, and a core of myocardial apex is excised. A weighted pump sucker is placed into the apex, and the blood level should be kept above the level of the mitral valve to prevent air from being trapped in the left atrium.
After removal of air from the device, attention is then directed toward weaning the patient from cardiopulmonary bypass. The main concerns at this point are pulmonary hypertension and residual right ventricular dysfunction resulting from the loss of the septal component to right heart contractility. Hyperventilation and maintaining adequate arterial oxygenation, acid base status, calcium, potassium, and hematocrit levels therefore initially facilitate weaning from bypass. Renal dose dopamine and the addition of preoperative inotropes are very helpful. Our threshold for instituting inhaled nitric oxide is very low and is often based in part on preoperative right heart concerns. This threshold is usually at 20 to 60 ppm. Intraoperative transesophageal echocardiography is of immeasurable assistance in evaluating air status and appropriate functioning of the device, which is implied by a decompressed left ventricle. A patent foramen ovale may only now be apparent because the left side of the heart is now decompressed. Patience and slow weaning are key. No vacuum is added to the Thoratec device until acceptable left atrial and central venous pressures are obtained. Central venous pressure is kept as low as possible while good flow is maintained. Meticulous attention to hemostasis cannot be stressed enough; blood products can exacerbate right heart failure and sensitize the patients. Low-dose arginine vasopressin (0.04 to 0.08 units/min) effectively treats low systemic vascular resistance, particularly in patients with catecholamine-resistant vasodilatory hypotension [9]. Cathecholamine-resistant vasodilatory hypotension is often a problem in these patients, particularly with the institution of milrinone and dobutamine. Low left-sided flows with transesophageal echocardiographic evidence of left ventricular decompression and high right-sided pressures are a strong indication of right heart failure. Although most patients have some degree of right heart failure, they can usually be managed medically with use of the previously discussed measures. Nevertheless, there will be a subset of these patients who will continue to exhibit poor left-sided flows despite these measures. It is in these patients that a right ventricular assist device is indicated and should not be delayed.
Results
We have performed more than 60 device implantation procedures since the inception of our bridge to transplantation program. During this time, two thirds of our patients were successfully bridged to transplantation. Our survival rates are 92% at 1 month after transplantation and 83% at 1 year after transplantation.
Comment
Mechanical circulatory support has a long history at our institution, as does heart transplantation. Our long experience with these devices has afforded us the opportunity to evolve our management of these patients into the protocols we have described. The advent of newer drugs, such as vasopressin, aprotinin, and nitric oxide, have drastically changed the management of these patients. We have developed a preference for the TCI device for the reasons indicated. However, the Thoratec device is the more versatile device, and there still exist circumstances when its use is clearly advantageous. In our institutional experience, outcome for bridging to transplantation has not been device dependent. The selection criteria, operative strategies, and management protocols discussed have proved very successful for our patients. Future adherence to them should allow avoidance of the pitfalls that may be encountered in the management of these complex patients. Successful outcomes will allow expansion of our knowledge base and success in future clinical trials for use of devices as destination therapy.
References
This article has been cited by other articles:
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  M. C. Smith, F. A. Arabia, P. H. Tsau, R. G. Smith, R. K. Bose, D. S. Woolley, B. E. Rhenman, G. K. Sethi, and J. G. Copeland CardioWest Total Artificial Heart in a Moribund Adolescent With Left Ventricular Thrombi Ann. Thorac. Surg., October 1, 2005; 80(4): 1490 - 1492. [Abstract] [Full Text] [PDF]
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 J. A. Morgan, R. John, V. Rao, A. D. Weinberg, B. J. Lee, P. A. Mazzeo, M. R. Flannery, J. M. Chen, M. C. Oz, and Y. Naka Bridging to transplant with the HeartMate left ventricular assist device: The Columbia Presbyterian 12-year experience J. Thorac. Cardiovasc. Surg., May 1, 2004; 127(5): 1309 - 1316. [Abstract] [Full Text] [PDF]
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R. J. Kaplon, X.-s. Qi, F. M. Andreopoulos, M. B. Anderson, E. Bauerlein, A. Nejman, and S. M. Pham Tricuspid valvectomy for right ventricular outflow cannula occlusion with the thoratec ventricular assist device J. Thorac. Cardiovasc. Surg., April 1, 2001; 121(4): 812 - 813. [Full Text] [PDF]
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