Keywords
INTRODUCTION
Percutaneous closure of a patent ductus arteriosus (PDA) was first described by Porstmann in 1966.1,2 Since that time, different types of coils and occluder devices have been used,3-6 with varying results. Although the use of Cook® detachable coils7,8 has produced satisfactory results in closure of small PDAs (<2 mm), an increased incidence of residual shunt, hemolysis, and embolization have been reported in closure of larger PDAs.9,10 In 1998, Masura et al11 published the first series of cases of percutaneous closure of PDA using the Amplatzer occluder device, which is self-expanding, can be repositioned, and is specially designed for moderate and large PDAs. In recent years, this device has been widely used (more than 1400 published cases as of the publication of this article),12-14 decreasing the incidence of residual short-circuit, embolization and hemolysis, especially in the closure of larger PDAs.
The aim of this study was to evaluate the efficacy and safety of the Amplatzer duct occluder device over the short- and medium-term for the closure of PDAs in children.
PATIENTS AND METHODS
Patients
From October, 1999, to December, 2001, 30 children (9 boys and 21 girls) with a diagnosis of PDA underwent percutaneous closure. An ECG, chest X-ray, and echocardiogram were performed on all patients prior to the procedure, and informed consent was obtained from the children´s parents or guardians. Study inclusion criteria were: body weight of more than 4 kg, pulmonary vascular resistance <8 Wood units/m2, and a PDA size ≥1.8 mm. Patient age varied from 4 months to 14 years (mean, 5±4.02 years), with body weight that varied between 4.5 and 45 kg (mean 20±10.3 kg); 46% of the children in the study having a weight of less than 10 kg.
Associated anomalies seen included: right anomalous subclavian artery (1 patient), moderate to severe aortic insufficiency (1 patient), small muscular interventricular communication (1 patient), and permeable foramen ovale (2 patients). One patient had human immunodeficiency virus (HIV). One of the patients had a residual PDA following surgical ligature.
Device
The Amplatzer (AGA®) duct occluder (Figure 1A) is a self-expanding nitinol stent that is made up of a flat retention flange that is placed on the aortic wall and a tube (which is placed in the PDA itself) that contains thrombogenic material (a polyester patch sewn to the nitinol stent). The diameter of the retention flange is 4 mm larger than the tube sheath, which is in the form of a cone; the pulmonary end of the cone is 2 mm smaller than the end that is attached to the retention flange. The different Amplatzer duct occluder models refer to the size in millimeters of the two ends of the tube: 6/4, 8/6, 10/8, 12/10, 14/12, and 16/14. The total length of the device is 7 mm in the 6/4 and 8/6 models, and 8 mm in the remaining models (Figure 1B). The implantation system consists of a detachable cable that screws into the device, and a large delivery sheath of 5 Fr to 7 Fr (in accordance with the size of the device). Once the device is implanted, it is possible to remove it while it remains screwed in the removable cable.
Fig. 1. A. Amplatzer duct occluder device for PDA. B. Drawing of the dimensions of a 10/8 Amplatzer duct occluder device.
Catheterization
The procedure were performed under sedation. The femoral artery and vein were catheterized in all patients, 30 mg/kg of cephazoline was administered at the start of the catheterization, and 100 UI/kg of sodium heparin was administered after catheterizing the artery. After recording pulmonary and systemic pressures, a lateral projection aortogram was performed to define the morphology and size of the PDA (Figure 2A). The PDA was catheterized in an anterograde manner in 28 patients, and a multipurpose catheter was substituted for the 35-inch guided exchange introductory sheath in 2 patients in whom the PDA could not be catheterized from the pulmonary trunk. In these cases, the PDA was catheterized in a retrograde manner from the aortic side, using an arteriovenous opening to then introduce the sheath in an anterograde manner. A device was selected than was at least 1 to 2 mm larger than the smallest part of the PDA, and the device was introduced screwed onto the end of the removable cable via the sheath, up to the descending aorta. Once this site was reached, the sheath was removed in order to open the retention flange, which was positioned at the aortic end of the ductal ampulla and, while maintaining tension on the cable, the remainder of the sheath was pulled back toward the pulmonary trunk, positioning the tubular portion of the Amplatzer device within the PDA. With the device still attached to the removable cable, an aortogram was performed (Figure 2B) and, once it was determined that the Amplatzer was in a good position, this was detached by turning the cable counterclockwise. Ten minutes after the detachment angiography of the aorta was performed to determine whether or not a residual short-circuit was present (Figure 2C), and pulmonary and systemic pressures were taken again.
Fig. 2. A. Lateral projection baseline angiography (patient number 28). B. Lateral angiography with the device implanted and still attached to the removable cable. C. Lateral angiography after detachment of the device.
During the 24 hours following catheterization, the patients received 3 doses of cephazoline, a chest radiograph, and color echo-Doppler. The device was checked using chest radiograph and echo-Doppler at 1, 4, and 12 months postimplant.
RESULTS
The device was successfully implanted in all patients. Patient clinical data is shown in Table 1. The smallest PDA diameter ranged from 1.8 to 8.0 mm (mean, 4.4±1.8 mm), and the largest diameter from 21.0 to 5.2 mm (mean, 8.8±4.1 mm). According to the classification of Krichenko et al,15 there were 22 type A PDAs, 2 type B PDAs, 1 type D PDA, and 5 type E PDAs. Ten of the 30 patients (33.3%) had pulmonary hypertension, with a pulmonary:systemic pressure >35%, which decreased or normalized following PDA closure. The size of the implanted device was 6/4 in 19 patients, 8/6 in 8 patients, and 10/8 in 3 patients (Table 1). In 2 patients, the first implanted device had to be removed (before it was detached from the cable) in order to implant another that was larger. Immediate complete occlusion of the PDA was achieved in 28 of the 30 cases (93.3%) (Figure 3), and in 100% of cases upon check by echography performed 24 hours postimplant. None of the patients had a gradient through the aortic arch on post-implant hemodynamic evaluation.
Fig. 3. Lateral projection angiography corresponding to patient number 17 in the series. A. Baseline angiography. B. Post-implant aortogram and detachment of the device.
There were no cases of embolization of the device or hemolysis. One 8-month-old patient required a blood transfusion because of anemia in the hours following the catheterization, and another required 20 hours of heparin perfusion because of a decrease in the pedal pulse. All patients were discharged 24 hours after the procedure.
Twenty-eight of the 30 patients (93.3%) came in for clinical follow-up, and also underwent ECG, chest radiograph, and echo-Doppler. Follow-up periods ranged from 1 month to 25 months (mean 13±7.6 months). All patients were asymptomatic and none of them showed breakage or later displacement of the device. There was no flow acceleration in the left pulmonary artery noted that was more than 1.5 m/second. One 19-month, 7 kg girl, who had undergone PDA closure with a 6/4 Amplatzer device and who had no evidence of postimplant aortic occlusion on hemodynamic evaluation, progressively during the 5 months post PDA closure developed a gradient at the level of the aortic isthmus both clinically (decrease of femoral pulses) and on echographic evaluation (acceleration of flow velocity in the descending aorta up to 3.7 m/second with diastolic flow prolongation). At the 5th month postimplant, the patient was catheterized again, and a baseline peak systolic gradient of 20 mm Hg and 34 mm Hg postangiography was confirmed at the level of the isthmus, with a significant reduction in aortic size at this level, but without evidence of displacement of the Amplatzer device. Percutaneous balloon angioplasty was performed, producing a reduction of the postangiographic gradient to 24 mm Hg and the disappearance of the diastolic flow prolongation on postangioplasty echography.
DISCUSSION
The percutaneous closure of a PDA is a well-established technique that has a low incidence of complications. Nevertheless, and in spite of the different devices that have been used up until this point16,17 (such as double umbrella, controlled removable coils, etc), the closure of medium or large PDAs and treatment of PDA in lower-weight infants presented some difficulties since this type of patient has a greater incidence of complications (residual short-circuit, embolization of the device) and the need to implant a device more often, which lengthens scope times and increases the risk of embolization -- surgery is frequently the only therapeutic option in low weight patients with large PDAs.
The Amplatzer duct occluder provides several improvements over the devices used until recently. Closure of the PDA is achieved by a mechanical barrier that the prosthesis creates that, in addition to the thrombogenic effect of the polyester patches inside it, decreases the incidence of residual short-circuit and allows repositioning and removal of the device while it remains attached to the removable cable, diminishing the risk of embolization. The implantation is performed using low profile (5 Fr to 7 Fr) sheaths, which facilitates their use in low-weight infants.
The results of our study of percutaneous PDA closure with the Amplatzer duct occluder, with an occlusion rate of 100% at 24 hours, concurs with results reported in other studies,12,18 thus confirming the increased efficacy of the Amplatzer device in the closure of medium and large PDAs. Similarly and in accordance with other authors,19 the results were equally efficacious for smaller PDAs (<2.5 mm), in which, if the PDA anatomy is favorable and a smaller diameter device is used that allows for passage of a 5 Fr sheath, Amplatzer device implantation which may be an alternative to using coils.
On followup we did not observe any significant stenosis of the left pulmonary artery, possibly due to the low profile of the pulmonary end of the prosthesis. The only significant complication encountered in our series was the development of an aortic occlusion in 1 of our patients. This is one of the principal problems this device can cause in lower-weight children and, although it is not a frequent complication, it has also been described by other authors.12,20 The low patient weight (smaller aortic lumen size in the isthmus area), the larger device size at its aortic end (retention flange), and the anatomy of the PDA (size, length, and angle between the PDA and the aortic arch) are some of the factors that may influence the development of this complication. It is possible that the Amplatzer duct occluder, still in experimental testing,21 in which the retention flange forms a 32° angle with the cylindrical body of the device (to adapt to the curvature of the thoracic aorta), may eliminate protrusion of the retention flange into the descending aorta. In any case, and although successful closure with the Amplatzer device has been reported in children weighing <4 kg,14,22 greater difficulty with the implantation22 and an increased risk of complications frequently occur.
CONCLUSIONS
Percutaneous PDA closure with the Amplatzer duct occluder device is an effective method for the treatment of PDA.
The low incidence of complications and of residual shunts makes this device ideal for the percutaneous closure of medium or large PDAs, and its elective use for small PDAs.
Studies of larger patient populations and with longer follow-up periods are necessary to determine the safety of this device for lower-weight children.
Correspondence: Dra. A. Fernández Ruiz.
Servicio de Cardiología Pediátrica.
Hospital Infantil La Paz.
Paseo de la Castellana, 261. 28046 Madrid. España.
E-mail: afernandez@hulp.insalud.es