Ann Thorac Surg 1998;66:519-522
© 1998 The Society of Thoracic Surgeons
Original articles: cardiovascular
Neonatal mechanical bridging to total orthotopic heart transplantation
Michael Weyand, MDa,
Deniz Kececioglu, MDb,
Hans G. Kehl, MDb,
Christof Schmid, MDa,
Heinz M. Loick, MDc,
Johannes Vogt, MDb,
Hans H. Scheld, MDa
a Department of Cardiothoracic Surgery, Westfalian Wilhelms University, Münster, Germany
b Department of Pediatric Cardiology, Westfalian Wilhelms University, Münster, Germany
c Department of Anesthesia and Intensive Care Medicine, Westfalian Wilhelms University, Münster, Germany
Accepted for publication March 13, 1998.
Address reprint requests to Dr Weyand, Department of Cardiothoracic Surgery, Westfalian Wilhelms University, Albert Schweitzer Str 33, 48129 Münster, Germany
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Abstract
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Background. Until recently, newborns with medically intractable cardiac failure caused by congenital malformations were mostly doomed to death because of the severity of the disease, which precludes a palliative operation, or because of fatal deterioration before availability of a suitable donor heart.
Methods. The recently developed paracorporeal pneumatically driven Medos HIA ventricular assist device offers a therapeutic option for these small infants because it is manufactured in various sizes and is even suitable for cardiac assistance in neonates with a body surface area less than 0.3 m2.
Results. We report our initial experience with this device, which we used for univentricular bridging to total orthotopic cardiac transplantation in 3 infants. The device was inserted to support the left ventricle in two instances and to support the right heart in one. Successful bridging to transplantation was achieved in 2 infants for periods of 2 and 7 weeks.
Conclusions. Our experience demonstrates the feasibility of univentricular mechanical support followed by successful cardiac transplantation in infants and newborns.
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Introduction
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The possibility of performing cardiac transplantation in neonates in time, ie, before the development of secondary organ dysfunction or death, is severely hampered by the lack of suitable donor hearts. Waiting periods for newborns with otherwise untreatable congenital cardiac defects in Europe currently exceed 3 months. Whenever possible, it has become our policy to perform corrective or palliative surgical procedures, including the Norwood procedure for hypoplastic left heart syndrome [1, 2]. However, if the underlying defect is too complex or the ventricular function too depressed to allow for palliation or correction, mechanical assistance may be lifesaving in these infants. We report on our successful attempts of mechanical bridging in newborns with a recently developed paracorporeal pneumatic assist system.
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Patients and methods
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Ventricular assist device
The Medos HIA ventricular assist device (VAD) has recently been developed by the Helmholtz Institute in Aachen, Germany (Medos, Stolberg, Germany) [3, 4]. It consists of a paracorporeal diaphragm pump mimicking the human aortic basis, suitable for either right- or left-sided univentricular as well as biventricular support. Filling of the pumping chamber is assisted by light suction caused by negative pressures at the inflow conduit side, whereas blood ejection is achieved by gentle air pressure. The device is able to create a maximal negative pressure of -80 mm Hg at the inflow conduit site. However, to achieve a satisfactory pump filling and thus pump washing, adjusting the negative pressures up to -20 mm Hg resulted in sufficient pump filling. The blood is directed to and from the pump through two polyurethane valves inserted into the conduits close to the pump chamber. The pump is manufactured in various sizes of 10, 25, and 60 mL for left ventricular and 9, 22.5, and 54 mL for right ventricular use. Thus, the device is applicable in a wide range of patients, including neonates with a very small body surface area.
Patients
Three small infants suffering from cardiomyopathy or congenital malformations presented with severe cardiac failure. They did not recover despite mechanical ventilation and intravenous catecholamine and phosphodiesterase inhibitor medication, and finally required cardiopulmonary resuscitation.
Patient 1
In the first infant, congenital cardiomyopathy was diagnosed at the age of 2 months. The dystrophic neonate could be stabilized medically for 2 months, at which point cardiovascular deterioration occurred, as indicated by a loss in urine production and a drop in blood oxygen saturation. At that time, length was 54 cm, body weight 3,400 g, and resulting body surface area calculated as 0.24 m2, similar to a newborn. The VAD was implanted to support the left heart only [5].
Patient 2
The second infant deteriorated right after delivery. Echocardiography demonstrated severe endocardial fibroelastosis and congenital aortic stenosis with heavily thickened valve leaflets in a small annulus (Fig 1). As surgical correction was deemed impossible and the child’s condition failed to respond to medical treatment, the left VAD was inserted on day 10 of life. The child was 51 cm with a body weight of 3,300 g and a body surface area of 0.23 m2.
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Fig 1. Explanted heart of patient 2 with severe endocardial fibroelastosis and aortic stenosis. Note the anastomosis between the outflow conduit and the ascending aorta.
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Patient 3
In the third newborn, perinatal echocardiography revealed a severely enlarged heart, approaching the chest wall bilaterally. This finding was confirmed by conventional chest radiography (Fig 2). Echocardiography revealed type D Ebstein’s malformation of the tricuspid valve, according to the classification of Carpentier and colleagues [6], as the underlying cause. Cardiac catheterization further demonstrated a considerably underdeveloped pulmonary vascular bed rendering immediate cardiac transplantation a high-risk procedure. Because left ventricular function was appropriate, a 9-mL artificial ventricle was implanted to support the right heart.
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Fig 2. Digitized reproduction from the preoperative angiography of patient 3, demonstrating severe bilateral enlargement of the heart caused by tricuspid insufficiency and right ventricular failure.
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Surgical procedure
Insertion of the pump followed an identical scheme in all 3 patients. After midline sternotomy the thymus was fully excised. The pericardium was opened and the infants placed on normothermic cardiopulmonary bypass with a 7F aortic cannula (Stöckert, Munich, Germany) accessing the proximal aorta close to the origin of the truncus to gain enough space for an anastomosis with the outflow graft of the pump system. Venous cannulation (Stöckert) was achieved with a single right-angled 18F cannula (Jostra, Hirrlingen, Germany) in the right atrium in patients 1 and 3. Bicaval cannulation using two 8F cannulas (Jostra) was used in patient 2, as concomitant closure of an atrial septal defect had to be performed. After emptying the enlarged hearts, sufficient right-sided access to the left atrium was achieved. With the ventilation stopped, but the heart beating, left (or right in patient 3) atrial cannulation was performed first [7]. Two 6-0 Prolene (Ethicon, Somerville, NJ) pursestring sutures were placed in the atrial groove and a right-angled 18F cannula was inserted (Fig 3). The distal end of the cannula was placed to exit the body below the right lower rib cage. The 4-mm polytetrafluoroethylene end of the outflow conduit (Jostra) was anastomosed to the ascending aorta with a continuous running 6-0 Prolene suture. The intrathoracic part of the cannula was covered with a shielded 8-mm Dacron (Vaskutek Ltd, Rewshire, Scotland) prosthesis, which was also sewn to the ascending aorta encircling the primary anastomosis. The outflow cannula was guided outside below the left rib cage. Ventilation was restarted and circulating volume increased. The pump chamber was carefully primed with warm Ringer’s lactate solution and, after meticulous removal of air, was connected to the conduits. The pump was placed on the abdomen of the patient, with its air chamber on top to easily enable visual control of the diaphragm (Fig 4). In all patients, pump action was started in a fixed rate mode at a frequency of 80 beats per minute corresponding to a cardiac output of up to 0.8 L/min and a cardiac index more than 3 L · min-1 · m-2. Extracorporeal circulation was stopped immediately and the remaining pump volume reinfused through the aortic cannula. Heparinization was fully reversed by protamine infusion, two chest tubes were placed, and the chest was directly closed. Anticoagulation with intravenous heparin aiming at activated clotting times of 160 to 200 seconds was started 4 to 12 hours after the operation when drainage was minimal.
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Results
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All 3 children had an uneventful initial postoperative course with sufficient urine output and good oxygen saturation. Pump function was regular and the pump rate could be increased up to 90 beats per minute within the first week in all patients. However, reexploration for evacuation of mediastinal clots was necessary in 2 children at days 4 and 10. During these surgical procedures, optimal hemostasis was difficult to achieve and clot formation developed in the inflow bulbs as well as in the pump chamber of the 2 patients, necessitating pump exchange at days 5, 8, and 14. The exchange was performed at the intensive care unit without complications by simply halting the VAD, disconnecting the old pump, and reconnecting the new device.
Clinically evident thromboembolic complications occurred in patients 1 and 2. In the first infant, left-sided cerebral infarction developed after displacement of an embolus from the native left ventricle as evidenced by serial echocardiographic studies. Fortunately, hemiplegia was fully reversible. In patient 3, a large clot formed within the inflow conduit. As it moved and almost totally occluded the right main pulmonary artery, local thrombolysis with recombinant tissue plasminogen activator allowed continued mechanical support.
Two of the 3 infants underwent successful cardiac transplantation after a period of 14 and 49 days of mechanical support (Table 1). Using cardiopulmonary bypass with moderate hypothermia, total orthotopic heart transplantation with direct anastomosis of the right- and left-sided pulmonary vein pedicles and both caval veins was carried out. The operative course was uneventful in both patients. The third infant is still undergoing mechanical support, now for 83 days. The child is fed orally and has been extubated for feeding (Fig 4). Secondary organ function is excellent and infectious signs are absent.
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Table 1. Epidemiologic Data of Newborns Who Underwent Mechanical Bridge to Total Orthotopic Heart Transplantation
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Comment
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As opposed to the United States, cardiac transplantation in neonates in Europe has a waiting period of more than 2 months. Mechanical support for deteriorating infants, aside from extracorporeal membrane oxygenation and the use of a centrifugal pump, has not been available until recently. In addition our limited experience with prolonged extracorporeal membrane oxygenation support, inserted for cardiac failure and intended to bridge to cardiac transplantation, has been catastrophic.
The Medos HIA VAD was originally developed for postcardiotomy support [3, 4]. Therefore, its design consists of atrial cannulation instead of ventricular, similar to systems meant for long-term support. The second special feature is the smoothness of the three-leaflet polyurethane valves. Preclinical testing revealed reliability of these valves for periods up to 40 days; thereafter, exchange becomes necessary for safety purposes. However, we decided to change the pumps much earlier, as clot formation was visible in the inflow bulbs and on the border of the pump diaphragms. These formations occurred despite anticoagulation with intravenous heparin within the recommended range, but may be related to the secondary surgical procedures. Thereafter, we were repeatedly able to demonstrate minor clots that resolved within 1 day without specific treatment and without causing emboli. In contrast to the group from the University of Caen [8], we believe that the artificial surfaces of the HIA VAD stimulate the coagulation system. However, because we aimed for a short period of mechanical support, we decided against the additional use of antithrombotic agents commonly used in adults undergoing long-term support with various devices [9, 10]. Furthermore, it may well be that fluid loss of the children after restoration of kidney function with a concomitant increase of hematocrit and blood viscosity contributed to clot formation, as we clearly observed more and larger clots in various parts of the system during the first week, as opposed to the period thereafter.
Aside from the tendency to form clots, the system provides a good choice of treatment of end-stage cardiac failure in small children and neonates. Pump action is easy to control and stable throughout the course of support. Because the pump creates a slight negative pressure on the inflow side, filling of the pump is maintained despite variations in fluid homeostasis of the body. Moreover, suction from the left atrium can be varied to achieve an optimal filling of the pump chamber, as clinical situation dictates. In the clinical setting negative pressures at the inflow side never had to be increased above -20 mm Hg. During initial insertion sufficient instantaneous pump action was achieved by using a fixed rate of 80 pump cycles per minute with the inflow suction set at -18 mm Hg. Because the patient’s heart and circulatory system were preloaded through the extracorporeal circuit, the extracorporeal circulation stopped, and device action started immediately thereafter, suction of air was avoided.
Similar to adult left ventricular support, drainage of the left ventricular apex as opposed to the left atrium would most likely result in better pump performance and the ability to decrease the negative inflow pressures. However, the respective apical cannulas are not available, although several designs are under consideration by the manufacturer.
We have recently demonstrated that successful mechanical bridging to cardiac transplantation in very small infants is possible [5]. The current report demonstrates that mechanical bridging in newborns is possible, and recovery of secondary organ dysfunction, especially liver, kidney, and lungs, occurs in children similarly as in adults [9–11]. It is noteworthy that in the third patient, in whom the underdevelopment of the pulmonary tree precluded successful tricuspid valve repair and cardiac transplantation, the assist device was placed not only for right ventricular failure but also to induce growth of the pulmonary vessels. Two months after right VAD insertion, angiography confirmed adequate growth of the pulmonary vessels, and the infant is now scheduled for transplantation. The concomitant clinical improvement even allowed the child to be extubated. However, clot formation with the resulting necessity to exchange the pump restricted this period to 3 days.
In summary, the Medos HIA VAD used offers a reliable option for infants and newborns with end-stage cardiac failure. However, because mechanical support is restricted to weeks or a few months only, its use should be considered only in institutions in which the final therapy of cardiac transplantation is also offered.
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Addendum
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Unfortunately the satisfactory clinical course of the third patient has altered after submission of the manuscript. Fever unresponsive to antibiotic treatment developed in the infant. Blood cultures were positive for staphylococci; the same species were grown from the tip of an indwelling catheter. Eventually the child died of septic multiorgan failure on day 98 of mechanical support. This is also by far the most common cause of death in our adult patient cohort undergoing mechanical bridging to transplantation.
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References
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- Allan L.D., Sharland G., Tynan M.J. The natural history of hypoplastic left heart syndrome. Int J Cardiol 1989;25:341-343.[Medline]
- Norwood W.I., Lang P., Hansen D.D. Physiologic repair of aortic atresia—hypoplastic left heart syndrome. N Engl J Med 1983;308:23-26.[Medline]
- Rakhorst G., Hensens A.G., Verkerke G.J., et al. In-vivo evaluation of the HIA-VAD: a new German ventricular assist device. Thorac Cardiovasc Surg 1994;42:136-140.[Medline]
- Eilers R., Harbott P., Reul H., Rakhorst G., Rau G. Design improvements of the HIA-VAD based on animal experiments. Artif Organs 1994;18:473-478.[Medline]
- Weyand M., Schmid C., Kececioglu D., et al. Successful bridging to cardiac transplantation in a dystrophic infant using a new paracorporeal diaphragm pump. J Thorac Cardiovasc Surg 1997;114:505-507.[Free Full Text]
- Carpentier A., Chauvaud S., Mace L. A new reconstructive operation for Ebstein’s anomaly of the tricuspid valve. J Thorac Cardiovasc Surg 1988;96:92-101.[Abstract]
- Scheld H.H., Hammel D., Schmid C., et al. Beating heart implantation of a wearable Novacor left-ventricular assist device. Thorac Cardiovasc Surg 1996;44:62-66.[Medline]
- Babatasi G., Masseti M., Bhoyroo S., Khayat A. Clinical experience with the Medos assist device. Cardiovasc Eng 1997;2:16-18.
- Kormos R.L., Borovetz H.S., Gasior T., et al. Experience with univentricular support in mortally ill cardiac transplant candidates. Ann Thorac Surg 1990;49:261-272.[Abstract/Free Full Text]
- Weyand M., Hammel D., Hoffmeier A., et al. Erfahrungen mit dem tragbaren Links-Herz-Unterstützungssystem NOVACOR N 100. Transplantationsmedizin 1994;6:245-252.
- Frazier O.H., Duncan J.M., Radovancevic B., et al. Successful bridge to heart transplantation with a new left ventricular assist device. J Heart Lung Transplant 1992;11:530-537.[Medline]
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Abstract
Introduction
