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In this report, we describe stenting of the ductus arteriosus to maintain its patency as a bridge procedure to heart transplantation in five infants with the hypoplastic left-heart syndrome. All the stenting procedures were successful and provided hemodynamic stability. Four of the five infants subsequently underwent successful orthotopic cardiac transplantation. The other infant had a cardiac arrest 24 hours after the procedure -- during placement of a subclavian catheter -- and died. This preliminary experience suggests that it may be possible to prolong the period of search for a donor heart for such critically ill infants.
Methods
This study, performed from April 1991 through March 1992, was carried out under the Food and Drug Administration Investigational Device Exemption after approval was obtained from the institutional review board of Loma Linda University Medical Center. Five patients with the hypoplastic left-heart syndrome were included. Informed consent was obtained from the parents in each case.
Hemodynamic instability with congestive heart failure despite high doses of alprostadil, dopamine, and dobutamine by infusion was observed in all five patients before placement of the stent. All the infants underwent endotracheal intubation and mechanical ventilation during the procedure. Oral dipyridamole was started on the day of the procedure and continued thereafter. Prophylactic antibiotics were also given. Alprostadil was continued throughout the procedure and reduced to a low dose thereafter.
After a 6-French sheath (1 French unit = 0.33 mm) was placed in the femoral vein, heparin was given intravenously in a dose of 100 units per kilogram of body weight. A 5-French angiographic Berman catheter (Arrow International, Reading, Pa.) was then placed into the main pulmonary artery and from there into the ductus arteriosus, and angiograms were obtained in anteroposterior and lateral projections. The diameter of the ductus was measured with use of calibration grids. A 7-French multipurpose sheath (Cordis, Miami), 45 cm in length, was then introduced over a 0.89-mm (0.035 inch) guide wire previously placed across the ductus and into the descending aorta. A Palmaz-Schatz balloon-expandable articulated stent (Johnson & Johnson Interventional Systems, Warren, N.J.) with a nominal unexpanded outside diameter of 2.5 mm and a length of 2 cm was mounted by hand on a 5-French Medi-tech PE-MT balloon-angioplasty catheter (Boston Scientific, Watertown, Mass.). With the sheath and wire held in place, the balloon catheter with the stent mounted around it was advanced and positioned in the stenotic ductus arteriosus. The sheath was then pulled back, the balloon was inflated, and the stent was deployed. Angiograms and pull-back pressure tracings across the ductus arteriosus were then obtained.
Results
The clinical data on the five infants are summarized in Table 1. Highlights of the individual cases are described below.
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Patient 3 was a baby boy in whom severe metabolic acidosis and hypotension developed shortly after birth. Clinical improvement followed the administration of dopamine, dobutamine, and alprostadil in conjunction with emergency atrial septal angioplasty. Hemodynamic instability with severe progressive metabolic acidosis recurred at 28 days, however, because of narrowing of the ductal lumen, documented by Doppler echocardiography. The stenting procedure was uneventful. Successful cardiac transplantation was accomplished 50 days later. Histopathological examination demonstrated a completely endothelialized stent in the ductus, with no clots.
Patient 4 was a baby boy in whom congestive heart failure with hemodynamic instability developed at 57 days of age. Narrowing of the ductal lumen was documented by Doppler echocardiography. Staphylococcus epidermidis sepsis was documented before the procedure. The stent was first deployed with an 8-mm balloon catheter; however, cineangiography demonstrated that the stent was mobile within the ductus. A 9-mm balloon catheter was then introduced in an attempt to anchor the stent correctly. The stent was fully expanded but was noted, after deflation of the balloon, to be still moving inside the ductus and protruding into the pulmonary artery. Despite further manipulations, we were unable to secure the stent adequately. In view of a final large ductal patency, we elected to terminate the procedure. The patient was returned to the neonatal intensive care unit in a stable condition. Twenty-four hours later, the patient had a cardiac arrest during placement of a right subclavian catheter. An autopsy revealed a large right hemothorax. The stent, which was found between the pulmonary artery and the ductus, was patent without evidence of thrombus. No perforation or tear was noted in the ductus or in the pulmonary artery.
Patient 5 was a baby girl who had tachypnea soon after birth. Because of a restrictive atrial septal defect, the patient underwent balloon atrial septostomy. During the same procedure, the ductus arteriosus was found to be constricted, with a diameter of only 4 mm. Ductal stenting was successful. Successful heart transplantation was performed eight days later. The stent, which was retrieved at that time, was patent without clots.
(Since this article was written, successful ductal stenting was performed in a sixth patient with the hypoplastic left-heart syndrome on October 16, 1992. This baby girl underwent successful cardiac transplantation 157 days after the stenting procedure. She was in stable condition at the most recent follow-up visit).
Discussion
A policy of conservative treatment of patients with the hypoplastic left-heart syndrome has been modified during the past decade after the development of improved palliative surgical procedures3,6,7,8,9,10,11 and the introduction of neonatal heart transplantation3,12,13,14. At Loma Linda University Medical Center, the focus has been on neonatal cardiac allotransplantation as an option in treating this complex cardiac anomaly.
Despite all efforts, about 20 percent of neonates registered for heart transplantation still die before a matched donor organ can be found14. Death is usually due to closing of the ductus arteriosus and the resultant decrease in systemic perfusion7. Alprostadil is effective in maintaining ductal patency in most patients, but its long-term use has practical limitations and there is a substantial incidence of side effects (e.g., fever, hypotension, hyperostosis, or increased fragility of the vascular tissue)15,16,17. Thus, the idea of maintaining ductal patency mechanically by a percutaneous approach is attractive, since it would obviate the need for palliative surgery and reduce the need for drugs and central venous access.
Stents have been shown to be a safe and effective nonsurgical method of treating vascular and biliary-duct stenosis18,19,20. Similarly, stenting of the ductus arteriosus has proved feasible in several studies that were conducted in animals21,22,23. We report evidence of the feasibility of this procedure in humans. Stenting was attempted in five patients and was technically successful in all of them. Successful orthotopic cardiac transplantation was subsequently performed in four of the patients 1, 8, 15, and 50 days after placement of the stent.
Despite the administration of alprostadil, dopamine, and dobutamine, all five patients were hemodynamically unstable before the procedure, and it is highly unlikely that any of these infants would have survived to heart transplantation without ductal stenting. Hemodynamic stability is of great importance in such patients because it allows time for better matching of the transplant recipient with a donor. In fact, on the basis of our experience, we believe that all patients with hypoplastic left-heart syndrome could eventually receive transplants if they remained hemodynamically stable. The waiting period for an appropriate donor is unpredictable, however, and can be lengthy. The delay raises the issue of balloon dilation alone, which may result in a satisfactory immediate result but carries the risk of early reclosure; redilation may also be limited by venous access. In a recent study Rosenthal et al.21 clearly demonstrated the superior hemodynamic and angiographic results achieved after ductal stenting as compared with balloon dilation alone.
During implantation, considerable care must be taken to avoid misplacement or migration of the stent. In fact, migration of the stent occurred in one of our patients (Patient 4), and we were unable to explain it adequately. Perhaps migration was related to hyporeactivity of the ductus, which failed to constrict around the stent to keep it in place. Such ductal hyporeactivity might have been due to balloon distention or possibly to the history of sepsis in this patient. When the ductus was examined at autopsy, there was no evidence of disruption of the media or rupture of the ductus.
Protrusion of the stent into the pulmonary artery or the descending aorta should also be prevented because there is a theoretical risk of thrombus formation and vessel injury. In addition, protrusion of the device into the aortic isthmus can compromise the blood flow to the great vessels. In none of these five patients was the stent placed distally into the descending aorta. Color Doppler assessment of the blood flow did not show any evidence of obstructed flow in the ascending or descending aorta. Furthermore, there was no gradient between the systolic pulmonary-artery pressure and the systolic blood pressure in the arm after the procedure or at follow-up in any of these patients.
Thrombosis in the stent did not seem to be a problem in this preliminary study. This fact is probably explained by the large diameter of the stented ductus and the resulting vigorous flow, which lessens the likelihood of clot formation inside the ductus. Also, endothelialization, which occurred sooner than expected (it occurred within 15 days after the stenting procedure in Patient 1) might have contributed to a diminished risk of late thrombosis.
Although alprostadil should no longer be necessary after the stenting procedure, it was deliberately maintained at a low dose in our first four patients, since we were in the early stage of this experimental study and in need of data before making the decision to stop alprostadil after stenting. In fact, we were able to discontinue alprostadil in our fifth patient 48 hours after the procedure with no clinical consequences.
Clinical indications for ductal stenting in patients with the hypoplastic left-heart syndrome will certainly be revised as we learn more about the procedure. On the basis of this preliminary study, however, we believe that this procedure should be considered for infants who have evidence of ductal stenosis despite the administration of alprostadil or who have serious side effects or are unresponsive to a high dose of this drug. In patients who require intervention for a restrictive atrial septal defect, even in the absence of clinically important narrowing of the ductus, ductal stenting might be performed at the same time, since subsequent access to the femoral vein may be limited.
In summary, the encouraging results of this pilot study document the feasibility, safety, and efficacy of stenting in maintaining ductal patency and producing hemodynamic stability in patients with the hypoplastic left-heart syndrome who are waiting for heart transplants. Studies of larger numbers of patients with longer follow-up are required to assess the real effect of this procedure on the outcome of patients with this otherwise fatal disorder.
We are indebted to Professor Michael Tynan, M.D., and Peter Whittaker, Ph.D., for their review of the manuscript; to Grace June Marshall, Ph.D. (who died on September 24, 1992), for her assistance in the scanning electron-microscopical study; and to Charles E. Mullins, M.D., for technical assistance.
Source Information
From the Section of Pediatric Cardiology, Rm. 4433, Loma Linda University Medical Center, 11234 Anderson St., P.O. Box 2000, Loma Linda, CA 92354-0200, where reprint requests should be addressed to Dr. Ruiz.
References
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