Intravascular stent implantation for the management of pulmonary artery stenosis

REVIEW

Review

Intravascular stent implantation for the management of pulmonary artery stenosis Charles Krisnanda, BMedSci a,b , Samuel Menahem, MD, FRACP, FACC, FCSANZ a,c,d,∗ and Geoffrey K. Lane, MB, FRACP, FACC, FCSANZ e a

Faculty of Medicine, Dentistry, and Health Sciences, University of Melbourne, Melbourne, Australia b Faculty of Medicine, University of Indonesia, Jakarta, Indonesia c Monash Heart, Monash Medical Centre, Clayton, Australia d Monash University, Monash Medical Centre, Clayton, Australia e Cardiology Department, The Royal Children’s Hospital, Melbourne, Australia

Pulmonary artery stenosis is a challenging problem in the management of congenital heart disease. Untreated pulmonary artery stenosis may contribute to increased mortality and morbidity, and lead to suboptimal results following surgical repair of congenital heart disease. Intravascular stent implantation has emerged as one of the preferred treatment options for pulmonary artery stenosis. However, issues regarding the effectiveness and complications of stent implantation for pulmonary artery stenosis need to be identified. In addition, difficulties of stent implantation in the paediatric setting, as a consequence of small vessel size and subsequent vessel growth, are also important considerations. This review will evaluate the short and long-term effectiveness, the outcomes and complications, and discuss the potential problems of stent implantation for pulmonary artery stenosis. (Heart, Lung and Circulation 2013;22:56–70) © 2012 Australian and New Zealand Society of Cardiac and Thoracic Surgeons (ANZSCTS) and the Cardiac Society of Australia and New Zealand (CSANZ). Published by Elsevier Inc. All rights reserved. Keywords. Pulmonary artery stenosis; Stents; Intravascular procedures; Interventional cardiology

Introduction

P

ulmonary artery stenosis, particularly branch pulmonary artery stenosis, is one of the most common forms of vascular stenosis associated with congenital heart disease [1,2]. Untreated pulmonary artery stenosis may contribute to an increased mortality and morbidity, and lead to suboptimal results following congenital heart disease surgical repair [3,4]. Correction of pulmonary artery stenosis through conventional surgical repair is frequently less than ideal as pulmonary artery stenosis may not be surgically accessible [5–7]. Although percutaneous balloon angioplasty of a stenotic vessel is effective in many cases, sustained relief of obstructions is only achieved in approximately 60% of cases [8–11]. Restenosis often occurs from the natural recoil of vascular tissue and scarring at the lesion site. Technical advances using balloons with bonded microtome blades, so called cutting balloons, may relieve vessel stenosis resistant to simple angioplasty [12]. A recent review [13] suggested that cutting balloon Received 14 November 2011; received in revised form 18 July 2012; accepted 13 August 2012; available online 25 September 2012 ∗

Corresponding author at: Department of Paediatrics, Monash University, Monash Medical Centre, 246 Clayton Road, Clayton, VIC 3168, Australia. Tel.: +61 3 95946666; fax: +61 3 95761352. E-mail address: [email protected] (S. Menahem).

angioplasties in those not responding to low pressure angioplasty (8 atmosphere of pressure) was more effective therapy compared to high pressure balloon angioplasty with a similar safety profile (26 out of 47 vessels initially treated by high pressure balloon angioplasty resulting in an almost half further increase in vessel diameter). Nonetheless, despite the use of cutting balloons, vessels have the same rate of restenosis as conventional balloon angioplasty [14] and may lead to vessel perforation and/or rupture due to repeated intravascular trauma [15]. Intravascular stent implantation, therefore, emerges as an important adjunct in the management of pulmonary artery stenosis. Reports over the last two decades have shown good outcomes in terms of increasing vessel diameter and decreasing pressure gradients across the stenosis of stent implantation for pulmonary artery stenosis [16–21]. However, several authors have raised questions regarding the effectiveness of stent implantation in the management of pulmonary artery stenosis. van Gameren et al. [22], in a multicentre study conducted in Europe, concluded that complications both minor and major following stent implantation for pulmonary artery stenosis are common (17%). Difficulties of stent implantation in the paediatric setting arise as a consequence of the small vessels that need stenting together with the issues of the subsequent need for growth

© 2012 Australian and New Zealand Society of Cardiac and Thoracic Surgeons (ANZSCTS) and the Cardiac Society of Australia and New Zealand (CSANZ). Published by Elsevier Inc. All rights reserved.

1443-9506/04/$36.00 http://dx.doi.org/10.1016/j.hlc.2012.08.008

of the vessel with the growth of the infant and child [23,24]. In light of these considerations, there is a need to evaluate the use of intravascular stent implantation for pulmonary artery stenosis. This review will focus on key questions regarding the short and long-term effectiveness, including the outcomes and complications, and the potential problems of stent implantation for pulmonary artery stenosis.

Implantation of Intravascular Stents The purpose of stent implantation is to provide a framework to support a stenosed vessel in order to prevent elastic recoil and overcome external compressive forces [20]. Stent implantation was introduced to congenital heart disease patients in late 1989 by O’Laughlin et al. [25]. Thereafter, the use of stent implantation to treat a variety of congenital heart diseases, including pulmonary artery stenosis, has become widespread [18,19,26].

Indications Stent implantation is rarely performed for native branch pulmonary stenosis as the stenosis is often mild and may improve with age [27] though it may be indicated if the stenosis is more severe. Indications for stent implantation in pulmonary artery stenosis frequently encompass lesions, which are unresponsive to conventional balloon angioplasty [28]. These lesions include pulmonary artery stenosis attributable to (1) kinking or tension, (2) external compression, (3) intimal flaps, (4) stenoses presenting in the postoperative period, and (5) relatively mild stenosis and restenosis following successful balloon angioplasty [28].

Implantation Technique Stent implantation is normally performed under general anaesthesia. Following haemodynamic and angiographic assessment, a catheter is placed across the lesion of interest. Once the catheter is well-positioned, an extra-stiff guide wire is advanced so that the tip of the wire is situated in a distal branch of the vessel undergoing intervention. The catheter is then withdrawn and a long sheath is loaded over an introducer passing across the stenotic area. Thereafter, the introducer is removed, leaving the extra-stiff wire and the sheath through the stenotic region. The stent is typically back loaded on the balloon secured by hand crimping and advanced through a long sheath over the wire. Some operators prefer to use a protective short sheath when the stent is advanced through the haemostatic valve. The stent position is checked by angiographic injection, either through the long sheath or via a separate angiographic catheter. The stent is then fully uncovered by withdrawal of the long sheath followed by the balloon inflation resulting in the expansion of the stent to the diameter of the balloon. The balloon is subsequently deflated and withdrawn leaving the expanded stent opposed to the wall of the vessel. Further haemodynamic and angiogram measurements are obtained and on occasion, further balloon angioplasty is

Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

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performed if required. Once the operator is satisfied with the result, the wire and the sheath are withdrawn.

Type of Stents The most extensively used stents have been the balloon expandable Palmaz stents (Johnson & Johnson Interventional, Warren, NJ, USA). The unexpanded diameter of hepatobiliary/renal stents (medium sized stents) and iliac stents (large sized stents) are 2.5 mm and 3.4 mm, respectively. Medium sized stents come in lengths of 10, 15, and 20 mm, while large sized stents are 12, 18, and 30 mm. The recommended expansion range is 4–9 mm for medium sized stents and 8–12 mm for large sized stents. There is evidence that the large sized stent can be expanded to 18 mm [18,29], which allows for redilation to an adult sized pulmonary artery with a diameter of approximately 18–22 mm [30]. Other types of balloon expandable stents and self-expanding stents have also been used and is tabulated by Peters et al. [24], see Tables 1a and 1b, which also addresses the issues of stent redilatation for the commonly used stents. For example the Genesis medium sized stents can be dilated to 5–8 mm but overdilatation to 12 mm is possible, while the Genesis large maybe dilated to 12–15 mm, Genesis XD up to 18 mm.

Effectiveness of Intravascular Stent Implantation Short Term Effectiveness SHORT TERM CLINICAL OUTCOMES. Stent implantation has been shown to significantly increase vessel diameter across the stenotic segment of the pulmonary artery (Table 2). A resultant decrease in the systolic pressure gradient across the stenosis along with a decrease in the right ventricle to systemic blood pressure ratio has also been reported (Table 2). Several studies investigating pulmonary perfusion following stent implantation in unilateral branch pulmonary artery stenosis further demonstrated a significant improvement in the perfusion of the affected lung [19,25,29,31–33]. However, successful implantation may lead to pulmonary oedema in the affected pulmonary segment as a result of increased blood flow or pressure. As a consequence, careful monitoring of the patient is required for the first 24 h post-implantation. EARLY COMPLICATIONS. Potential complications arising from stent implantation include stent migration, stent malpositioning, stent embolisation, balloon rupture, vessel dissection, pulmonary oedema, arrhythmia, or in situ thrombosis (Table 2). The first five complications account for more than 50% of the reported early complications in the majority of studies. The rate of total complications in stent implantation for pulmonary artery stenosis varies from 0% to 40% (see Table 3). Major complications are relatively uncommon (<10%) in most studies, except for two [33,34] which reported moderate rates of 14% and 23%. In the former stenting was done with very small stents 3–4 mm, while the latter study involved intra-operative stenting. Mortality is rare (<5%) in most reports. Nevertheless, Pass et al. [35] reported a mortality rate of one in ten small children

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Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

Heart, Lung and Circulation 2013;22:56–70

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Table 1a. Commonly used Balloon Expandable Stents for Congenital Heart Disease.* Stent

Open cell

Closed cell

Range of diameter (mm)

Range of length (mm)

Medium stents •

Palmaz 4 series

2–4 (−11)

10–15

•

4–8 (−12)

12–24

Genesis large

•

5–10 (−12)

29–79

NIR stent

•

4–8 (−10)

14–17

Jostent peripheral (large)*

•

6–12 (−16)

12–58

Genesis

medium*

Bridge X3

•

5–7 (−14)

10–28

Guidant Omnilink*

•

5–10 (−12)

12–18

Guidant Herculink

•

5–10 (−12)

12–18

Jostent Wavemax

•

4–12 (−14)

12–58

Large stents Pamlaz 8 series

•

4–8 (−20)

10–30

Genesis XD*

•

10–12 (−18)

19–59 13–80

Saxx

•

4–12 (−18)

CP stent 6 zig

•

6–15 (−18)

16–45

Double Strut LD

•

5–8 (−18)

16–36

Mega LD

•

5–8 (−18)

16–36

•

6–25 (−28)

30–50

•

6–25 (−28)

22–45

5–8 (−26)

16–36

Extra large stents Palmaz XL (10 series) CP stent 8 Maxi

zig*

LD*

Andrastent XL & XXL

• •

•

14–32

13–57

Table 1b. Currently used Self-Expendable Stents in CHD.* Stent

Diameter (mm)

Length (mm)

Sheath

Dynalink

5–10

28–100

5 Fr

Protégé GPS

6–14

20–80

6F

S.M.A.R.T

9–14

30–80

6–7 F

Wallstent

8–10

40–100

8F

Cook Zilver

6–10

20–80

5–7 Fr

∗

Modified from Peters et al. [24].

(10%). The death reported in this study was due to vessel disruption related to stent implantation over a fresh 3-dayold suture line of a unifocalization procedure in tetralogy of Fallot patient with pulmonary atresia. The incidence of complications tends to be higher with the use of non-premounted stents compared to premounted stents, although this comparison may not be valid as the smaller premounted stents were not selected for use in larger vessels [22]. Nonetheless, the reason for fewer complications in premounted stents may be their relative ease of use and the more secure attachment of the balloon–stent system [36]. Operator inexperience with stenting may also contribute to higher a major complication rates. McMahon et al. [37] in a 12-year retrospective single centre study demonstrated no morbidity or mortality in the last five years. Moreover, two studies conducted two years apart by O’Laughlin et al. [25,29] showed a

decreased complication rate in the second study possibly arising from increased operator experience (Table 3). Modifications in stenting techniques and refinement of balloon–stent systems over the last two decades have lead to reduced complications. The avoidance of overdilation of the vessel [18,38,39], the use of simultaneous implantation in adjacent vessels with pulmonary artery stenosis [40] so called bifurcation stenosis [24], and the use of front-loading techniques [37] have heralded a reduction in vessel dissection, pulmonary oedema, and stent migration incidence respectively. The introduction of ‘balloon in balloon’ technique using the BIB balloon (Numed Inc., New York) allows for inflation of the inner balloon first allowing for repositioning of the stent if need be, prior to inflation of the outer balloon to fully expand the stent [37]. This technique may also help prevent protrusion of the stent strut into the vessel wall and/or “peeling off”

Heart, Lung and Circulation 2013;22:56–70

Table 2. Summary of Studies Investigating Stent Implantation in PAS. Study

Clinical setting

No. of patients (no. of stents)

Age (years)

Vessel diameter (mm)

Pre

Post

Pressure gradient across the stenosis (mmHg) Pre

RV:systemic pressure ratio

Post

Pre

Post

Unselected

23 (35)

16.7 (median)

4.6 ± 2.8

O’Laughlin 1993 [29]

Unselected

58 (80)

11.8 (median)

4.6 ± 2.3

11.3 ± 3.2**

55.2 ± 33.3

14.2 ± 13.5**

0.69 ± 0.23

0.43 ± 0.15**

Mendelsohn 1993 [34]

Intraoperative and percutaneous SI

13 (14)

9.4 (mean)

5.6 ± 0.7b

11.5 ± 1.0b,*

43 ± 4.0++

8 ± 3.0++,*

NA

NA

Nakanishi 1994 [16]

Unselected

5 (6)

12.3 (mean)

5.6 ± 2.2

10.6 ± 1.8

56 ± 26.0

22 ± 16.0

NA

NA

Fogelman 1995 [18]

Unselected

42 (55)

6.1 (mean)

5 ± 2.0 (ns = 46)

10 ± 3.0** (ns = 48)

28 ± 21.0 (ns = 45)

7 ± 9.0** (ns = 45)

0.56 ± 0.22 (ns = 21)

0.48 ± 0.16** (ns = 13)

Moore 1995 [45]

After cavopulmonary anastomosis

8 (10)

2.3 (median)

4.4 ± 0.4

9.9 ± 1.0**

NA

NA

NA

NA

Hatai 1995 [47]

Less than 1 year of age

10 (17)

0.2 (median)

2.2 ± 0.6

5.8 ± 1.4

40a

2a

0.85 ± 0.19

0.51 ± 0.12

Hijazi 1996 [17]

Unselected

36 (55)

7.0 (median)

4.8 ± 1.6

10.5 ± 2.6**

43 ± 20.4

13 ± 13.9**

0.74 ± 0.2

0.52 ± 0.19**

Shaffer 1998 [19]

Post operative PAS

136 (237)

10.5 (median)

5.6 ± 2.6 (ns = 229)

12.1 ± 3.0** (ns = 229) 46 ± 25 (ns = 223)

10 ± 12.8** (ns = 223)

0.63 ± 0.2 (ns = 127)

0.41 ± 0.02** (ns = 127)

71 ± 45 (ns = 26)

15 ± 20** (ns = 26)

0.71 ± 0.3 (ns = 13)

0.55 ± 0.35 (ns = 13)

Congenital PAS

15 (NA)

Spadoni 1999 [32]

Unselected

29 (49)

Formigari 2000 [51]

After arterial switch operation

7 (10)

Hwang 2000 [20]

Postoperative residual stenosis of PAS

7 (10)

3.3 ± 1.2 (ns = 27)

8.9 ± 1.2** (ns = 27)

50.6 ± 24.0

15.9 ± 13.4*

NA

NA

5.8 ± 1.9

10.9 ± 2.3**

54 ± 19

42 ± 13*

0.51 ± 0.17

0.36 ± 0.11**

4.3 (mean)

5.3 ± 1.6

11.9 ± 2.1

44.9 ± 10

13 ± 6.0

0.74 ± 0.11

0.42 ± 0.08

10.1 (mean)

6.7 ± 3.4

11.3 ± 3.0**

31 ± 9.9

11.4 ± 4.6**

NA

NA

12 (mean)

Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

O’Laughlin 1991 [25]

10.9 ± 4.2*

59 REVIEW

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60

Study

Clinical setting

No. of patients (no. of stents)

Age (years)

Vessel diameter (mm)

Pre Pass 2002 [35] Vranicar 2002 [33] McMahon 2002 [37] Mitropoulos 2007 [52] Kretschmar 2009 [46]

Stapleton 2009 [40] Tomita 2010 [54] Law 2010 [21]

Without the use of long vascular sheath Pulmonary atresia with VSD Unselected

RV:systemic pressure ratio

Post

Pre

Post

10 (13)

0.8 (median)

2.5 ± 1.5

5.7 ± 1.4*

10 (17)

1.3 (median)

1.5

3.4*

NA

NA

0.65 (n = 6)

0.66 (n = 6)

5.4

11.2*

41

8.7*

0.66

0.45*

7.6 (ns = 20)

10.9 (ns = 20)

45.4 (ns = 20) 16.1 ± 2.8

4.3 (ns = 20) 11.4 ± 2.1

NA

NA

NA

NA

37 ± 26.9

9.2 ± 13.0**

0.75 ± 0.29

0.53 ± 0.24**

30 ± 22 (ns = 162) 41 ± 25.0

12 ± 12* (ns = 162) 9 ± 11.0**

NA

NA

NA

NA

338 (664)

12.2 (mean)

Intraoperative 22 (23) SI SVM, before 12 (17) and after completion of partial and total CPC Simulataneous 49 (108) SI in bifurcation PAS Unselected 199 (253)

9.3 (mean)

Unselected

Post

Pressure gradient across the stenosis (mmHg) Pre

55 (79)

4.5 (mean)

3.1 ± 2.1

10.9 (mean)

5.7 ± 2.4

11 (median)

4.7 ± 2.1 (ns = 205)

12.6 (mean)

4.6 ± 2.1

8.1 ± 3.3**

11 ± 3.6**

8.8 ± 2.7* (ns = 205) 12.2 ± 3.2**

44 ± 22

14 ± 11.6*

NA

NA

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Vessel diameters, pressure gradients, and RV:systemic pressure ratios are expressed as mean ± SD unless indicated. a values are expressed as median. b Values are expressed as mean ± SEM. Values are obtained from the number of stents implanted (no. of stents) instead of the number of patients, unless indicated. ∗ p < 0.05. ∗∗ p < 0.001. ns, number of stents observed; RV, right ventricle; SI, stent implantation; VSD, ventricular septal defect; PAS, pulmonary artery stenosis; SVM, single ventricle malformation; CPC, cavopulmonary connection; and NA, not available.

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Table 2. (Continued)

Study

Clinical setting

No. of patients (no. of stents)

Age (years)

Complications

Total (%)

Major (%)

Minor (%)

Nature of complications

Stent related death (n)

Stent malpositioning, migration, embolization

Balloon rupture

Vessel dissection

Other

O’Laughlin 1991 [25]

Unselected

23 (35)

16.7 (median)

40

3

37

1

1 (3%)

6 (17%)

1 (3%)

6 (17%)

O’Laughlin 1993 [29]

Unselected

58 (80)

11.8 (median)

17

1

1

1

1 (1%)

6 (8%)

1 (1%)

6 (8%)

13 (14)

9.4 (mean)

14

14

0

0

–

1 (7%)

–

1(7%)

12.3 (mean)

0

0

0

0

–

–

–

–

Mendelsohn Intraoperative 1993 [34] and percutaneous SI Unselected

5 (6)

Fogelman 1995 [18]

Unselected

42 (55)

6.1 (mean)

5

0

5

0

2 (4%)

–

–

1 (1%)

Moore 1995 [45]

After cavopulmonary anastomosis

8 (10)

2.3 (median)

0

0

0

0

–

–

–

–

Hijazi 1996 [17]

Unselected

36 (55)

7.0 (median)

11a

4a

7a

0

1 (2%)a

–

1 (2%)a

Shaffer 1998 [19]

Post operative and congenital PAS

136 (237)

10.5 (median)

7

2

5

2

4 (2%)

–

8 (3%)

4 (2%)

Spadoni 1999 [32]

Unselected

29 (49)

12 (mean)

8

0

8

0

3 (6%)

–

–

1 (2%)

4 (7%)a

Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

Nakanishi 1994 [16]

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Table 3. Summary of Studies Investigating Short Term Complications of Stent Implantation in PAS.

61 REVIEW

REVIEW

62

Study

Clinical setting

No. of patients (no. of stents)

Age (years) Total (%)

Formigari 2000 [51] Hwang 2000 [20] Pass 2002 [35] Vranicar 2002 [33] McMahon 2002 [37] van Gameren 2006 [22] Mitropoulos 2007 [52] Kretschmar 2009 [46]

Stapleton 2009 [40]

4.3 (mean)

7 (10)

10.1 (mean)

0

Major (%)

After arterial switch operation Postoperative residual stenosis of PAS Without the use of long vascular sheath Pulmonary atresia with VSD Unselected

10 (13)

0.8 (median)

8

8

10 (17)

1.3 (median)

29

338 (664)

12.2 (mean)

Unselected

NA (223)

Intraoperative SI SVM, before and after completion of partial and total CPC Simulataneous SI in bifurcation PAS Unselected

Stent malpositioning, migration, embolization

Balloon rupture

Vessel dissection

Other

–

–

–

–

0

–

–

–

–

0

1

–

–

1 (8%)

–

23

6

0

–

1 (6%)

–

4 (23%)

4

1

3

4

8 (1%)

8.7 (mean)

17

6

10

2

18 (8%)

22 (23)

9.3 (mean)

0

0

0

0

12 (17)

4.5 (mean)

0

0

0

0

49 (108)

10.9 (mean)

22a

6a

16a

1

2 (4%)a

199 (253)

11 (median)

22

2

20

0

24 (9%)

0

0

Stent related death (n) 0

0

0

Minor (%)

0

– –

NA

9 (1%)

12 (2%)

6 (3%)

1 (1%)

12 (5%)

–

–

–

–

–

–

4 (8%)a

2 (4%)a

5 (10%)a

17 (7%)

2 (1%)

12 (5%)

Complications were classified as major, when death, a life-threatening event, or the need for surgical intervention occurred. Complications that were transient and un-anticipated were defined as minor. Vessel dissection included the incidence of retroperitoneal haemorrhage, haemoptysis, and other extravasations following stent implantation. Rates (%) are described as the number of complications per implanted stents, unless indicated. a Rates are defined as the number of complication per patients. SI, stent implantation; VSD, ventricular septal defect; SVM, single ventricle malformation; CPC, cavopulmonary connection; and NA, not available.

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Tomita 2010 [54]

7 (10)

Nature of complications

Complications

Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

Table 3. (Continued)

of the stent from the inflating balloon. McMahon et al. [37] reported that improvement of these practices has led to no further complication in stent migration, pulmonary oedema, haemoptysis, or death over the last three years (1998–2001) of their experience.

Intermediate and Long Term Effectiveness Studies investigating intermediate and long term follow up of stent implantation for pulmonary artery stenosis demonstrated that vessel diameter, systolic pressure gradient, and right ventricular to systemic blood pressure ratio were significantly improved at follow up catheterisation [18,21,38,41]. These results, however, required repeated interventions for stent redilation to ensure good long-term clinical outcomes following implantation. RESTENOSIS. A small degree of neointimal proliferation normally covers the inner surface of the stent within six months of implantation [19,34,41]. Neointimal proliferation is considered mild/physiologic when only 1–2 mm thick [19,38]. A greater degree of neointimal proliferation may cause restenosis of the vessel [39]. The incidence of restenosis has been reported between 1.5% and 4% [19,21,32,38,41]. Of note, these studies used balloon expandable stents. Yet Cheung et al. [42] reported a restenosis incidence of 28% (7 of 25 patients) with the use of self expanding stents. The suggested aetiology of this high incidence related to the design of the stent and the degree of adherence of the stent to the vessel wall, which resulted in increased thrombogenicity and friction with the vessel wall ultimately leading to neointimal proliferation. Fogelman et al. [18] reported various degrees of neointimal proliferation in all 29 followed-up PAS patients. Risk factors for restenosis include: (1) abrupt variation in vessel-to-lumen diameter (residual waist), in which the vessel diameter proximal or distal to the stent is less than the stent diameter [18,19,41], (2) overdilation of stents [18,38,39], (3) minimal stent overlap [38,41], (4) abnormal underlying vascular tissue [38], and (5) sharp angulation of the stent to the vessel wall [38]. These factors are thought to result in an increase of neointimal proliferation as an “attempt” to achieve a uniform vessel diameter and to “smooth-out” turbulent blood flow [19,41]. A higher incidence of restenosis is also observed in stent implantation in specific clinical settings. Stent implantation in bifurcation pulmonary artery stenosis was reported to develop a high incidence (32%) of restenosis [40]. The proposed mechanism was related to vessel distortion, increased exposed metallic surface of the two stents, or increased turbulent flow at bifurcation points. Moreover, restenosis of small stents in small pulmonary arteries of infants is also common (>50% of followed up patients) [33]. Regardless of restenosis occurrence, stent redilation can be carried out to treat restenosis [19,21,38,39,41,43]. Improvements in stent characteristic have also allowed greater flexibility for better vessel-stent alignment, which tends to reduce restenosis [38]. REDILATION. Excellent long term outcomes of stent implantation are closely related to stent redilation. Indications

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of stent redilation include: (1) somatic growth of the child [19,38,39,44], (2) neointimal proliferation that significantly reduces lumen size [19,38,39,44], (3) external compression of the stent [19,44], (4) stenosis which prevents optimal stent expansion [39], and (5) elective expansion through staged, serial dilation to avoid initial overdilation [38,39]. Studies summarised in Table 4 have demonstrated the long term effectiveness and safety of stent redilation across different pulmonary artery stenosis patient groups and in various clinical settings. Redilation of stents in pulmonary artery stenosis was shown to be safe and effective in providing significant increases in vessel diameter and significant decreases in the pressure gradient at the stent implantation site. Right ventricular to systemic pressure ratios were also shown to improve significantly after repeated dilation. Complications of stent redilations encompass stent fracture, balloon rupture, vessel dissection, pulmonary oedema, and arrhythmias. Complications were reported to be rare in all studies reviewed, with the highest total, major and minor complication rates of approximately 9%, 5%, and 8%, respectively (Table 4). Major complications were reported in no more than 5% of all studies with only Law et al. [21] reporting a patient death following redilation. This death was due to vessel rupture related to the suspected patient’s chronic steroid therapy. The stent redilation occurred 6.6 years following the stent implantation. In order to achieve optimal outcomes from redilation, several authors have suggested the following approach. In redilating small distal branch pulmonary artery stenosis, great care should be exercised along with the use of a short balloon [39]. Although vessel rupture is rare, if it does occur the operator should be prepared to insert a covered stent to stop further bleeding [39]. Such an insertion should be undertaken quickly with the ready availability of suitable covered stent in the catheter lab and which may also be used to cover up a previous stent fracture. In addition, to attain safe redilation and reduce vascular disruption, it is essential not to overdilate the initial implant [19,39].

Effectiveness of Stent Implantation in Specific Clinical Setting CAVOPULMONARY CONNECTIONS (CPC). The efficacy and safety of stent implantation has been demonstrated in children with PAS after cavopulmonary anastomosis, as pulmonary artery stenosis is an added risk factor when completing the Fontan procedure. Stent implantations have shown good relief of the pressure gradient and an increase in the arterial diameter with no complications noted [45,46]. Of note, the subclavian or internal jugular vein may become an alternative access pathway in patients where there was limited or no access to the superior vena cava from the inferior vena cava route [45]. Kretschmar et al. [46] suggested that previously implanted stents in patients with CPC should be left in place or changed to a larger diameter through a hybrid procedure because restenosis may recur after surgery and stent removal.

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64

Study

Clinical setting

Follow up after stent implantation (years)

Effectiveness

No. of patients (no. of stent redilations) Follow up data

Post

Complications

After redilation

Total (%)

Major (%)

Minor (%)

Death (n)

Nature of complications Stent fracture, embolization

O’Laughlin 1993 [29]

Fogelman 1995 [18]

Unselected

Unselected

0.9 (mean)

1.3 (median)

20.4 ± 16.5

10 ± 12.1*

Diameter

9 ± 2.6

11.8 ± 2.2*

RV:systemic

NA

NA

Gradient

23 ± 13

14 ± 12**

7±2

10 ± 2**

RV:systemic

NA

NA

Gradient

14b

8b,**

Diameter

9.5b

12.2b,**

RV:systemic

0.53b

0.46b,*

Gradient (n = 51)

19 ± 15.7

6 ± 7.3**

Diameter (n = 98)

9.6 ± 2.8

12.3 ± 3.4**

RV:systemic (n = 30)

0.48 ± 0.14

0.34 ± 0.09

Gradient (n = 5)

34 ± 9.8

19 ± 14.6**

Diameter (n = 6)

6.7 ± 0.8

8.8 ± 1.0**

RV:systemic (n = 6)

0.74 ± 0.15

0.70 ± 0.14

11 (16) Diameter

Ing 1995 [41]

Shaffer 1998 [19]

Unselected

1.1 (mean)

Postoperative PAS 1.6 (mean) Congenital PAS

20 (30)

Vessel dissection, vascular disruption

Other

6

0

6

0

1 (6%)

–

–

–

0

0

0

0

–

–

–

–

6

0

6

0

–

2 (6%)

–

–

1

0

1

0

–

–

1 (1%)

– Heart, Lung and Circulation 2013;22:56–70

Gradient 14 (17)

Balloon rupture

Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

Table 4. Summary of Studies Investigating Clinical Outcomes of Stent Redilation in PAS.

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Table 4 (Continued ). Study

Clinical setting

Follow up after stent implantation (years)

No. of patients (no. of stent redilations)

Complications

Effectiveness

Follow up data

Post

After redilation

Total (%)

Major Minor Death (%) (%) (n)

Nature of complications Stent fracture, embolization

McMahon 2001 [38]

After repair TOF and PA

CBPS

3.8 (mean)

After Fontan operation

9 (NA)

Stanfill 2008 [43]

Unselected

6b,**

Diameter RV:systemic Gradient Diameter RV:systemic Gradient

9.4b 0.48b 19b 8.3b 0.59b 3b

13.2b,** 0.4b,** 8b,* 11.2b,** 0.46b 0.5b,*

Diameter RV:systemic Gradient Diameter RV:systemic

10.5b NA 27b 8b 0.52b

14b,* NA 7b,* 12.6b,* 0.35b,*

3 (median)

12 (31)

Gradient

24a (ns = 13)

12**,a (ns = 19)

8.5 (median)

13 (27)

8.8a,** Diameter (ns = 19) 6.9a RV:systemic 0.53a (ns = 7) 0.45a,* (ns = 9) Gradient

NA

NA

Diameter RV:systemic

7 ± 1.4 NA

9 ± 2.2** NA

Vessel dissection, vascular disruption

Other

5

0

5

0

–

–

1 (1%)

3 (4%)

0

0

0

0

–

–

–

–

0

0

0

0

–

–

–

–

0

0

0

0

–

–

–

–

6

3

3

0

–

–

1 (3%)

1 (3%)

0

0

0

0

–

–

–

–

Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

7 (NA) Unselected

20b

6 (NA)

After ASO

Duke 2003 [39]

Gradient 72 (NA)

Balloon rupture

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66

Study

Clinical setting

Follow up after stent implantation (years)

Effectiveness

No. of patients (no. of stent redilations) Follow up data

Post

Complications

After redilation

Total (%)

Major (%)

Minor (%)

Death (n)

Nature of complications Stent fracture, embolization

Kretschmar 2009 [46]

Tomita 2010 [54]

Unselected

Unselected

Law 2010 [21] Unselected

4.4 (mean)

5 (6)

2 (median)

NA (157)

7.2 (mean)

36 (66)

Gradient

NA

NA

Diameter RV:systemic

5.8 ± 2.1 NA

8.5 ± 2.7** NA

Gradient (n = 125)

24 ± 16

14 ± 11*

Diameter (n = 137) 6.1 ± 2.5 NA RV:systemic

8.3 ± 2.7* NA

Gradient Diameter RV:systemic

NA

NA

Balloon rupture

Vessel dissection, vascular disruption

Other

0

0

0

0

–

–

–

–

9

1

8

0

2 (1%)

9 (6%)

1 (1%)

1 (1%)

6

5

1

1

–

1 (2%)

2 (3%)

1 (2%)

Heart, Lung and Circulation 2013;22:56–70

Definitions of major complications, minor complications, and vessel dissection are as in Table 2. Gradients are reported in mmHg. Diameters are reported in mm. Vessel diameter, pressure gradient, and RV:FA pressure ratio are expressed as mean ± SD unless indicated. a Values are expressed as median. b Values are expressed as mean. ∗ p < 0.05. ∗∗ p < 0.001. Complication rate (%) is described as the number of complication per implanted stents. RV:systemic, right ventricle to systemic pressure ratio; PAS, pulmonary artery stenosis; TOF, tetralogy of Fallot; PA, pulmonary atresia; CBPS, congenital branch pulmonary stenosis; ASO, arterial swith operation; n, number of patients; ns, number of stents; and NA, not available.

Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

Table 4 (Continued ).

INFANCY (<1 YEAR OR <10 KG). Stents in small infants with pulmonary artery stenosis may play an important role as either a palliative or staged treatment. Hatai et al. [47] (Table 2) reported ten infants less than 1 year of age with seventeen implanted stents who showed clinical improvements in symptoms, avoiding or delaying surgical repair, and making an inoperable situation operable in eight out of 10 patients. Poor results arose from diffuse hypoplasia of the distal pulmonary arteries. Major complications observed were two stent malpositions in a total of seventeen stent implantations. The investigators therefore concluded stent implantation was a feasible technique for infants, which provided acute clinical improvement. A retrospective study conducted by Ashwath et al. [48] in eight PAS infants with a mean weight of 6.1 kg demonstrated successful palliative treatment following stent implantation in all infants. The investigators used premounted Genesis stents. Improved vessel diameter and reduced pressure gradients were observed across the stenosed vessel following stent implantations. One stent migrated. However, the stent was recaptured and implanted at the target site. Regardless of successful implantation, restenosis is common in small pulmonary arteries [33,49]. In addition, the use of larger stents (iliac size) is less acceptable for implantation in infants and small children, as these may lead to difficulties in implantation and may also compromise pulmonary blood flow by compressing the adjacent vessel in the small and confined areas in the pulmonary outflow [47,50].

OTHER CLINICAL SETTINGS. Stent efficacy for pulmonary artery stenosis has also been reported in bifurcation pulmonary artery stenosis [40], after arterial switch repair [51], and severe pulmonary artery stenosis in pulmonary atresia/ventricular septal defect [33]. In bifurcation pulmonary artery stenosis, Stapleton et al. [40] reported that simultaneous stent implantation provided significant gradient relief, reduced systolic pressure and increased diameter of the stenotic segment (Table 2). However, a high rate of stenosis (31.8%) and severe complications (6.2%) were reported (Table 3). Balloon expandable stents have also been suggested as the primary treatment for pulmonary artery stenosis after an arterial switch procedure as these were considered safe (no complications reported) and more effective compared to balloon angioplasty (124% vs. 15% increased mean diameter of stenosis; 71% vs. 10% decreased pressure gradient across stenosis and 43% vs. 10% decrease in the RV:systemic pressure) [51] (Tables 2 and 3). Less favourable results regarding stent effectiveness have been reported for rehabilitation of severe pulmonary artery stenosis in pulmonary atresia with ventricular septal defect. Vranicar et al. [33] working with infants reported that, although stent implantation resulted in immediate improvement in vessel size and blood flow, there was a high incidence of complications (29%) and long term restenosis (>50% of patients followed up) (Tables 2 and 3). They concluded that further stenting should be reserved

Krisnanda et al. Stent Implantation for Pulmonary Artery Stenosis

67

only for infants who are unresponsive to other interventions.

Potential Problems Related to Stent Implantation Despite the benefits of stent implantation in pulmonary artery stenosis, there are still a number concerns when it is used in the paediatric setting. The concerns include growth of the child [19,22,38,52], followed by vessel access and stent delivery to the designated site [35,48].

Difficulties Related to Somatic Growth of Infant, Child, and Adolescent As the child grows, the final diameter of the pulmonary artery achieved at implantation may not be adequate. Although stents have the capability for further dilation, the critical question is whether redilation alone can attain the optimal diameter required following growth of the child, or whether it is possible to achieve an adult vessel lumen size. In particular, the use of smaller stents in younger children may result in a limited capacity for further dilation [53]. Inevitably, surgical removal may be required if subsequent angioplasty fails to achieve sufficient increase in calibre. Three studies have evaluated the long term effectiveness and safety of stent use in relation to the growth of the child. Each concluded that stent implantation was effective and safe, and serial redilation was possible to keep pace with the growth of the child [21,43,54]. Of note, large size nonpremounted Palmaz stents were used in these studies. Stanfill et al. [43] reported the long term follow up of 15 patients (19 stents). One late death was reported due to plastic bronchitis. Post-mortem findings revealed patency of the stent with no evidence of stenosis. Two stents from one patient were electively removed following a planned surgery. Thirteen patients (15 stents) underwent 27 redilations and were followed up for a median of 8.5 years (Table 4). A mean increase in the children’s weight of 25.7 kg (300%) from initial implantation and significant somatic growth were reported. No significant obstruction was observed in these stents. The remaining 14 patients remained alive and well. Thus, stent redilation was shown to be effective and safe for “adapting” to somatic growth. A survey of stent implantation collected from 14 leading hospitals in Japan described 157 effective stent implantations with a median follow up of 24 months, the longest being 144 months (12 years) (Table 4). Although 13 minor and 1 major complication were reported, the authors concluded stent redilation may overcome problems associated with the growth of the child [54]. The effectiveness of stent implantation in adapting to somatic growth was further confirmed by Law et al. [21] Thirty six patients (55 stents) were followed up for a mean of 7.2 years (Table 3). All patients underwent 1.2 ± 0.9 stent redilation. The final catheterization data reported significant improvement in pulmonary artery diameter, decreased gradient and right ventricle to femoral artery systemic ratio. This study concluded that stents were ‘amenable’ to further dilation for somatic growth.

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In order to overcome the somatic growth problem, particularly in small children and infants, new concepts of stent design have been developed. These promising alternatives include the biodegradable stent and the growth stent. The biodegradable stent offers the greatest hope with the stent material degrading over months, thus allowing the possibility of growth and remodelling of the vessel [55,56]. The growth stent involves a modification of a balloon-expandable stent, with two longitudinal halves connected by bioabsorbable sutures so that a circular stent is created [57]. The stent halves are expected to separate over time as the suture material is absorbed. These two stents may reduce the need for reintervention but will allow subsequent ballooning and further stent implantation once the child has grown. However, further evidence is required to confirm these potential advantages compared to existing stents. An alternative strategy that involves purposely fracturing maximally dilated smaller calibre stents, prior to implanting a larger calibre stent, has been an option that some units have considered but there is no published data on the results of this approach.

Difficulties Related to Vessel Access and Stent Delivery to the Lesion Site A further important consideration in stent implantation relates to vessel access and stent delivery to the stenotic site in infants and small children. The use of stents in small children has been hampered due to the large sheaths needed to accommodate the balloon catheter and stent combinations [35]. Another limiting factor is associated with the rigidity of the stent, which may hinder delivery to the lesion site [48]. These difficulties are especially important in infants as they have smaller vessels and an increased likelihood of complications. Importantly, when larger stents are to be used in small infants in order to avoid future surgery, placement of the larger stents is often considered too difficult, if not, impossible [47,50]. Advances in stent design to achieve more flexible stents but maintaining stent integrity have been the focus of several manufacturers. We also now have available low profile, premounted stent–balloon systems that allow for stent delivery without the need of a long sheath, especially important if the route is circuitous [24,35]. In addition, the possibility of translumbar and transhepatic approaches for stent implantations offers an alternative access in selected cases [58,59]. Ashwath et al. [48] have suggested that the introduction of low profile and premounted stent–balloon systems has made stent implantation possible in small infants. They have reported successful stent implantations in 10 PAS patients weighing less than 10 kg using premounted Palmaz-Genesis stents (Cordis, Johnson and Johnson, Miami, FL). Significant increases in the stenosed vessel diameter and significant decreases in pressure gradient across the lesion were observed. Complications included one stent migration, which was recaptured and implanted at the target site. No surgical intervention or procedural related mortality was reported. They further concluded

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that percutaneous stent implantation was safe and may provide successful palliation in small, high-risk patients.

Imaging of Infants and Children with Pulmonary Artery Stents Both CT and MRI scans may provide adequate imaging of pulmonary artery stents [60] though CP stents may produce gross artefact in CT. Palmaz stents may be well seen on MRI with T-1 weighted imaging.

Conclusions Pulmonary artery stenosis, whether congenital or acquired, is a challenging problem. Intravascular stent implantation is an effective and safe therapeutic approach in both short, as well as long term pulmonary artery stenosis management not successfully treated by balloon dilation alone and not easily amenable to surgery. Long term efficacy, however, requires repeated intervention with stent redilation, which is considered safe and effective to accommodate somatic growth and to treat restenosis. The further development/refinement of balloon and stent designs with the aim to increase efficacy and safety of stent implantation in infants and young children but allows for the expected growth of the target vessels remain the goal of clinicians. The use of novel techniques, using either biodegradable or growth stents, or a strategy of purposely fracturing maximally expanded small calibre stent to allow implantation of larger calibre stents needs further study to judge the efficacy of these alternatives to conventional stent implantation.

Conflict of Interest There was no conflict of interest or external financial support.

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