YF Cheung, MP Leung, kT Chau

Abstract

This retrospective review aimed to compare the efficacy and safety of occlusion of native and residual arterial ducts by detachable and non-detachable coils. Sixty-two patients underwent transcatheter coil occlusion, of which 42 had native and 20 had residual arterial ducts. The mean age and weight were 5.2±3.3 years and 17.2±7.5 kg, respectively. All the procedures were performed under general anaesthesia. The procedural and screening times were 107.6±45.4 minutes and 33.9±31.4 minutes, respectively. The ductal size measured 2.3±0.9 mm. Coil occlusion was feasible in 92% (57/62) of patients. Detachable coils were employed in 24 patients, non-detachable coils in 31, and combinations in 2. A single coil was implanted in 34 patients, 2 coils in 22 and 3 coils in 1. The prevalence of residual leak at 24 hours, 3 and 6 months were respectively 40%, 24% and 20% for native ducts and 48%, 25% and 19% for residual ducts (p=0.86). Coil embolization occurred in 2/62 (3.2%) of procedures, while intravascular haemolysis occurred in 2/57 (3.5%) of patients. There was no significant relation between the coil type and the risk of embolization. The only risk factor for persistent residual leak was ductal size. We concluded that transcatheter coil implantation is equally effective and safe in occluding both native and residual arterial ducts.

Introduction

Percutaneous transcatheter occlusion has gained wide acceptance as the method of choice for the closure of persistent arterial ducts.^1-2 The procedure obviates the need for surgery and its ensuing complications. The widely used Rashkind umbrella has decreased in popularity in view of the requirement of a large transvenous delivery sheath (8 F and 11 F for sizes 12 mm- and 17 mm-umbrella respectively), the expensive cost and disapproval due to regulatory issues in United States.^3-4 Sideris buttoned device has never gained universal acceptance for occluding arterial ducts.⁵ In the recent few years, coils have been increasingly utilized as the device for occlusion of both small and moderate size persistent arterial ducts. Different types of coils were employed, including simple non-detachable embolization coils and detachable ones.^6-10 Majority of the reports have been focussing on the use of a single type of coil for occlusion of native arterial ducts, with good results reported. There are, however, limited studies to evaluate the use of different types of coils in native and residual arterial ducts.

This study aimed to compare the efficacy and safety of coils for the occlusion of native and residual arterial ducts. Both non-detachable and detachable coils had been used in the study period and the experience with these 2 coil types would be discussed.

Patients and method

Patients

From April 1995 to November 1997, 62 consecutive patients underwent transcatheter coil occlusion of persistent arterial ducts. Coil occlusion was the treatment of choice in the study period, other types of occluding devices as alternatives should coil occlusion failed. Surgical ligation was limited to large ducts (>=7 mm), small infants weighing less than 7 kg with haemodynamically significant arterial ducts, and tackling of transcatheter-related complications. The mean age and weight were 5.2±3.3 years and 17.2±7.5 kg, respectively. Forty-two patients had native arterial ducts while 20 had residual ducts despite previous attempts of transcatheter occlusion or surgical ligation; of which 13 were after previous Rashkind umbrella implantation, 5 after Sideris buttoned device placement and 2 after surgical ligation. The demographic data of the patients with native and residual arterial ducts was shown in Table. Associated cardiac lesions included small ventricular septal defect in 5 patients and one each of mild valvar pulmonary stenosis and mild subaortic stenosis due to subaortic membrane.

Coil selection and implantation procedure

Two types of coils were used for occluding the persistent arterial ducts, namely detachable and non-detachable ones. Detachable coils (Ductocclud devices and Cook detachable embolization coils) were mounted onto the delivery system and being fully retrievable up to the point of release, while simple non-detachable coils (Gianturco embolization coils) were deployed by pushing the straightened coil through an end-hole catheter with a straight 0.035 inch guidewire. The type of coil selected for the occlusion of native ducts was dependent mainly on the availability of the device at the time of occlusion. The choice was not affected by the ductal dimension nor the ductal morphology. For occlusion of residual ducts, simple Gianturco embolization coil was usually the first choice as coil positioning was thought to be easier with the existing occluding device serving as the landmark and framework for securing the coil. The diameters of the Gianturco and detachable embolization coils chosen were at least twice the narrowest internal ductal dimension, while the length sufficient to produce at least 3 loops, allowing placement of 2 or more loops in the aortic end and 1 loop in the pulmonary end. For Ductocclud coils, the distal diameter of the coil was 1 to 2 mm larger than the mid diameter of the ampulla.⁷

All the occlusions were performed under general anaesthesia. The procedural and screening times were 107.6±45.4 minutes and 33.9±31.4 minutes, respectively. A 4 or 5F pigtail catheter was advanced through the arterial sheath for performing descending aortography. The minimum internal ductal dimension was measured using the pigtail catheter as magnification correction factor and the site of leakage in the residual duct was ascertained. Aortography was performed before attempts to cross the arterial duct by the transvenous end-hole catheter to avoid ductal spasm and hence underestimation of the ductal size.

All the coils were deployed via the antegrade transvenous route. For the delivery of a single coil, a 4 or 5F catheter was passed across the duct into the descending aorta. The distal 2 to 3 loops were extruded into the descending aorta and the catheter with the extruded loops were then pulled into the aortic ampulla. When optimal positioning was obtained, the delivery catheter was pulled back into the main pulmonary artery with the aim of leaving only one proximal loop of coil in the pulmonary end (Fig. 1). The release mechanism of the detachable coils was then triggered to complete the procedure. When two coils were deemed necessary as for ducts over 2 mm in diameter, two end-hole catheters would be placed across the duct simultaneously (Fig. 2). The distal windings were extruded and allowed to entangle in the descending aorta before pulling into the aortic ampulla. Repeated aortogram was performed 10 minutes after deployment of the coils. If significant residual leakage was present, the site of residual leak would be probed using a guidewire or an end-hole catheter and additional coils would be placed accordingly.

Fig. 1 Complete occlusion of a small native arterial duct by a single non-detachable coil. (a) Descending aortogram showing a small persistent arterial duct (arrow). (b) There is complete occlusion of the duct. The two distal windings of the coil are well-seated in the aortic ampulla, while the closely apposed proximal winding in the pulmonary end would not be expected to cause significant pulmonary arterial stenosss.

Fig. 2 Occlusion of moderate-size native arterial duct by 2 detachable coils. (a) Two end-hole delivery catheters were emp1oyed simultaneously for the deployment, the distal windings of the 2 coils are positioned in the aortic end; one coil was completely released (thin arrow), while the proximal end of the other coil is still inside the delivery catheter (bold arrow). (b) Repeated aortogram after coil release reveals almost complete ductal occlusion.

Follow-up

Echocardiographic assessment by colour flow mapping and chest X-ray were performed within 24 hours of occlusion. Outpatient follow-ups were at intervals of 2 weeks, 1 month and thereafter 3 to 4 monthly until complete closure was documented by colour Doppler study. Subsequent followed-ups were on a 6 to 12 monthly basis. Serial Doppler studies to assess for potential left pulmonary arterial stenosis and turbulent flow in the descending aorta would be performed.

Statistics

Results were expressed as mean±standard deviation, unless otherwise stated. Comparisons of the means of clinical parameters between patient groups were performed using the Student's t test. The type of coils selected in relation to the nature of the duct occluded and the risk of embolization was examined by Fisher's exact test. The decrease in the prevalence of residual shunting with time was analyzed by the Kaplan-Meier survival analysis and log rank test was used for evaluating the equality of survival functions between those with native and residual ducts. Logistic regression was used to assess the risk factors for persistent residual leak. Variables that were entered into analysis included age, sex, weight, ductal dimension, Q_p:Q_s ratio, types and number of coils used and systolic pulmonary arterial pressure as a ratio of the systemic systolic pressure. A p-value of 0.05 was regarded as statistically significant.

Results

The narrowest ductal diameter measured angiographically was 2.3±0.9 mm. Coil occlusion was feasible in 92% (57/62) of the patients. There was pull through of the detachable coils in 4 patients. In one patient, the Gianturco coil embolized to the right pulmonary upon deployment, but could successfully be retrieved. Rashkind umbrellas were then implanted in these 5 patients, all of which had native arterial ducts. Detachable coils were employed in 24 patients, and non-detachable coils in 31 patients. Two patients had combinations of different devices implanted; one with a Rashkind umbrella and a Gianturco coil simultaneously placed, the other with one each of detachable and simple embolization coil.

Native arterial ducts

Thirty-seven patients had coil occlusion of the native arterial ducts. The narrowest ductal dimension was 2.0±0.8 mm. One coil was placed in 25 patients and 2 coils in 12 patients. Of a total of 49 coils, 19 were simple embolization coils, and 30 were detachable coils. The prevalence of residual leakage was 40% at 24 hours of placement, 24% at 3 months and 20% at 6 months and after (Fig 3).

Fig. 3 Kaplan-Meier analysis of residual shunting after coil occlusion of native (dashed line) and residual arterial ducts (solid line). There was no statistically significant difference between the two groups (p=0.86).

Residual arterial ducts

Twenty patients underwent coil occlusion for residual ducts. Clinically, 12 had a continuous ductal murmur, 5 with a systolic murmur and 2 silent ducts; 1 had an ejection systolic murmur related to the subaortic membrane. The main leakage site was across usually at the superior border after previous Rashkind umbrella placement (Fig. 4). Multiple jets of leak was evident in 4 patients, 2 each after previous occlusions by Rashkind umbrellas and buttoned devices. The predominant jet of residual leak measured 2.4±0.8 mm. There was no significant difference when compared with the dimension of native ducts (Table). One coil was placed in 9 patients, two coils in 10, and three coils in 1 patient. Thirty non-detachable Gianturco coils were used, as contrast to only 2 detachable coils being employed. As explained, there was a preferential choice of non-detachable Gianturco embolization coils in occluding residual arterial ducts (p<0.001). The prevalence of residual leak was 48% at 24 hours of placement, 25% at 3 months and 19% at 6 months and after. There was no significance difference in prevalence of residual leak as compared to that after native ductal occlusion (p= 0.86) (Fig 3).

Fig. 4 Coil occlusion of residual duct. (a) Residual ductal leak across the superior aspect of the previously placed Rashkind umbrella (arrows). (b) There was complete occlusion after placement of a single non-detachable coil.

Complications

Embolization of coils to the pulmonary artery occurred in 3.2% (2/62) of the procedures, both of which had native ducts. In the first as mentioned, the Gianturco coil embolized to the right pulmonary artery immediately after release. In the second, minimal contrast leak was documented by aortography 10 minutes after deployment of 2 Cook detachable coils. A loud, continuous ductal murmur was audible five hours after the procedure and chest X-ray confirmed embolization of the 2 coils enmasse to the left pulmonary artery. The actual ductal size was probably underestimated in the first instance due to overlapping of the ductal image with that of the pulmonary artery. In both patients, the embolized coils were successfully retrieved by a snare (Microvena) and ductal occlusions were accomplished by Rashkind umbrellas. Considering native ducts in isolation, the incidence of embolization was 4.8% (2/42).

The incidence of intravascular haemolysis after coil placement was 3.5% (2/57 patients). Haemoglobinuria was evident within 12 hours of transcatheter ductal occlusion. One patient who had severe intravascular haemolysis after simultaneous placement of a Rashkind umbrella and a Gianturco coil was the subject of a previous case report.¹¹ The intravascular haemolysis was successfully abolished after placement of 3 more Gianturco embolization coils. In the second patient, a simple embolization coil was again utilized for the occlusion of a residual duct after previous Rashkind umbrella occlusion. Despite deployment of 5 additional Gianturco coils, haemolysis continued and surgical ligation without removal of the occluding devices was required to abolish the residual shunting and haemolysis.

Follow-up

The follow-up duration was 12.6±9.3 months. All patients were asymptomatic clinically. There were no episodes of infective endocarditis in patients with persistent ductal shunting. No significant left pulmonary arterial stenosis or turbulent descending aortic flow were documented by serial Doppler studies.

Risk factors for persistent residual leak

Ductal dimension and body weight were significant factors related to persistent ductal leak. The size of the arterial duct had a significant negative partial correlation (p=0.028), while the body weight had a significant positive partial correlation (p=0.02) with complete occlusion of the arterial duct. For arterial ducts of <=3 mm the incidence of residual leak at 4 months and beyond was 17.6%, in contrast to the 34.4% incidence after occlusion of duct > 3 mm (p=0.034).

Discussion

Transcatheter coil occlusion offers a simple methodology for closure of small ducts by virtue of the need to pass only a 4 or 5 F catheter via the antegrade transvenous or the retrograde transarterial route. Although there is no consensus for the occlusion of clinically 'silent' ducts, endocarditis associated with a silent duct has been reported.¹² Currently we occlude these tiny arterial ducts in view of the low morbidity and excellent success rate, unless unequivocal evidence to the contrary is demonstrated. The passage of large transvenous sheath for delivery of Rashkind umbrella through small native ducts and tiny residual ducts has been difficult, requiring balloon predilatation of the duct in some occasions.¹³ Recently, successful attempts of coil occlusion of moderate to large persistent arterial ducts has been reported.⁹

This study demonstrates comparable efficacy of occluding both native and residual ducts by coils. The decrease in prevalence of residual leak is similar in the two groups, which is in agreement with the finding of Tometzki et al.⁶ The prevalence of persistent residual leak at and beyond six months was 20% and 19% for occlusion of native and residual ducts, respectively. This is similar to the result of actuarial analysis of early prevalence of residual shunting by Shim et al.¹⁴ The majority, however, report a prevalence of less than 10% by 6 months after initial coil placement.^6,8-10 One possible reason for the observed discrepancy is that we are looking at different groups of patients with different ductal size and hence with varying prevalence of residual shunting. Apart from the limited number of patients with large arterial ducts of 4 mm being satisfactorily occluded with a median of 4 coils by Hijazi et al,⁹ majority of the reports are focussing on the occlusion of small ducts, with a mean of 1.6 to 1.7 mm in diameter.^8,14,15 The other factor may be related to our approach of allowing trace to mild residual leakage and avoiding placement of multiple coils that might cause significant left pulmonary arterial stenosis.¹⁶ Recent reports, however, suggest that implantation of 3 or more coils is possible without causing significant gradients in the aorta or the pulmonary artery.^9,10 The long term potential complications, however, has yet to be seen. This is an important consideration in neonates and small infants, therefore our current practice is to avoid transcatheter occlusion in those weighing less than 7 kg. Another point worth noting is that multiple jets of residual leak are possible after previous occlusion by Rashkind umbrella and Sideris buttoned devices; the main leakage site being usually at the superior aspect of the previously implanted Rashkind umbrella. It is important to look for other sites of significant residual leakage after initial coil occlusion of the main site for residual ducts.

The incidence of immediate embolization of detachable and non-detachable coils in our series was 0% and 3.2%, respectively, which compares favourably with the others. The reported incidence for detachable coils ranges from 1.4% to 5.8%,^6,7 while that of non-detachable coils is higher, with incidence between 3.3% and 16% reported.^8-9 Detachable coils have the theoretical advantage of better control of the release after attaining the optimal position. Though diminishing the risk of immediate embolization, delayed migration has been reported with detachable coils.⁷ The use of detachable coils to occlude native ducts might, therefore, be a good start when first initiating a programme of transcatheter coil occlusion, though at the expense of cost and a slightly complicated delivery mechanism. With increasing experience with non-detachable coils, the immediate embolization incidence is expected to decrease.

We initially speculated a lower risk of embolization in residual ducts in view of the pre-existing occluding device offering a clear landmark for deployment of the coil and providing a framework for the coils to clench upon. We, therefore, used the non-detachable coils Gianturco coils to work on the residual ducts in the early phase of the learning curve. With the cumulative experience, the use of non-detachable coils was extended to the small and moderate size native ducts. Indeed there was no documented immediate or delayed embolization after occlusion of residual ducts, as contrast to the 4.8% incidence of coil embolization after native ductal occlusion. No statistically significant difference is, however, demonstrable (p=0.54).

Correct estimation of the size of the persistent arterial duct is important as to reduce the risk of pulling through the detachable coils and coil embolization after deployment. Underestimation of the ductal size may be due to spasm of the ductal tissue during catheter manipulation or overlapping of the angiographic image with the pulmonary arterial shadow. Angiogram should preferably be performed without traversing any catheter across the arterial duct. A slight left anterior oblique angled-view might be required to profile the duct clearly in some patients.

The other major complication after coil deployment in our patients is intravascular haemolysis, with an incidence of 3.5%. The incidence after Rashkind umbrella occlusion is 0.5%,¹⁷ while occurrence after coil occlusion has not been reported in literature previously. The exact mechanism is unknown, but probably related to the high velocity jet passing through the occluding devices and causing cellular destruction.¹¹ We have reported on a novel method of completely abolishing the haemolysis by antegrade placement of additional coils.¹¹ The examination of urine for evidence of intravascular haemolysis is important in the first 24 hours after ductal occlusion by coils.

In conclusion, transcatheter coil implantation is effective and safe in occluding both native and residual arterial ducts. Detachable coils may be a good choice in the initial learning phase, though simpler non-detachable coils be equally effective as one gains confidence in coil manipulation with the accumulating experience. It might be advisable to aim at complete occlusion as documented by angiography before leaving the catheterization laboratory in order to reduce the high prevalence of residual shunting for moderate and large size arterial ducts, by implanting up to 3 to 4 coils if necessary. One has to bear in mind, however, the possibility of potential long term complications of pulmonary arterial stenosis and disturbance of descending aortic flow.

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