Transcatheter Right Ventricular Outflow Tract Stenting in Children With Postoperative Infundibular Stenosis and Preserved Pulmonary Valve Function

ABSTRACT: Recurrent or residual right ventricular outflow tract obstruction after early surgical repair of congenital heart disease is one of the most frequent indications for either surgical or transcatheter reintervention. Transcatheter stent implantation across the stenotic right ventricular outflow tract or conduit is a safe and effective alternative to surgical reintervention. However, chronic deleterious effects of pulmonary regurgitation can potentially counterbalance the early improvement in clinical and hemodynamic parameters, sometimes necessitating further intervention. While there are several studies documenting safe and effective palliation by transcatheter right ventricular outflow tract stenting in infants with tetralogy of Fallot, literature on isolated infundibular stent implantation sparing the normal pulmonary valve in postoperative infundibular restenosis is very scant. We report our experience of safety and feasibility of transcatheter right ventricular outflow tract stent implantation while preserving the native pulmonary valve function in two children with infundibular stenosis after surgical repair of congenital heart disease.

J INVASIVE CARDIOL 2013;25(7):E151-E154

Key words: pediatric interventions, infundibular stenting, transcatheter

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As the complete surgical repair of various forms of congenital heart disease (CHD) at a very young age has become common practice, postoperative right ventricular outflow tract (RVOT)-infundibular obstruction is not uncommon in children. Reintervention is sometimes necessary in symptomatic patients with significant obstruction. RVOT obstruction is one of the most common indications for reintervention after tetralogy of Fallot (TOF) repair.¹ Surgical reintervention rate varies from 3%-17%, depending upon age at operation, surgical technique, and follow-up duration.^1,2 Although surgical resection or reconstruction is the standard approach, it is not without risk and occasionally not desirable due to either previous or anticipated surgical procedures.^1,2 Transcatheter RVOT reconstruction is a well-described procedure as a palliative intervention;^3-5 however, the experience of transcatheter intervention as definitive repair of severe infundibular stenosis by percutaneous stent implantation with preservation of competent native pulmonary valve (PV) is very limited,⁴ and in fact has not been reported in postoperative patients. 

We report our experience of successful transcatheter RVOT stent implantation while preserving the native pulmonary valve in two children with severe infundibular restenosis after surgical repair of CHD. 

Case Report. Since 2010, two children with severe postoperative infundibular restenosis and normal competent PV have undergone percutaneous infundibular stent implantation at our institute. Clinical profile, echocardiography records, and angiography data were analyzed retrospectively. Both patients’ parents denied the second surgical intervention, and consented to the transcatheter intervention. After ethics committee approval, therapeutic intervention was attempted based on angiographic and hemodynamic observations. In both patients, balloon-expandable stents were used with intent to perform balloon redilatation so that stent size can be optimized to somatic growth of the children. Hand-crimped, balloon-mounted, stainless-steel Palmaz stents (Cordis Corporation) were used in each case. Both patients were followed to ensure the hemodynamic status of RVOT, tricuspid valve (TV) function, and PV function and stent integrity by regular echocardiography and fluoroscopy. 

Patient 1. The first patient, a 10-year-old female, was apparently asymptomatic except for mild effort intolerance. Her body weight of 16 kg was inadequate for her age. In 2002, at the age of 1 year and a weight of 3.4 kg, she underwent successful complete repair of TOF at a different institute. Her clinical evaluation in 2010 at our institute for effort intolerance and persistent low body weight revealed pansystolic 4/6-grade murmur at the left parasternal region with soft second heart sounds. Her chest roentgenogram and electrocardiogram (ECG) were normal except for the predominant right ventricle (RV) forces on ECG. Her resting room air oxygen saturation was 98%. Transthoracic echocardiography revealed subaortic patch in situ, no residual septal defect, and normal left ventricular (LV) systolic function. However, she had severe infundibular restenosis, with peak systolic gradient (PSG) of 76 mm Hg and mild tricuspid regurgitation (TR) (measured RV systolic pressure by TR jet was 4.6 mV/second). RV angiogram in lateral and right anterior oblique view confirmed the echocardiographic finding of severe membranous infundibular stenosis, with normal pulmonary valve morphology and large dilated subpulmonic infundibulum. Hemodynamic tracing on catheter pullback across the PV and infundibulum revealed peak systolic gradient of 72 mm Hg.

Patient 2. The patient was a 2.7-year-old male who weighed 14 kg. In 2009, at the age of 6 months and body weight of 6.8 kg, the patient underwent complete surgical repair of large perimembranous ventricular septal defect (VSD), tubular patent ductus arteries (PDA), severe infundibular stenosis, and partially obstructive subaortic membrane. His predischarge echocardiography reported mild residual infundibular stenosis. His regular cardiovascular examination revealed increasing intensity of pansystolic murmur at left parasternal region, consistent with worsening RVOT stenosis. Though his subsequent follow-up revealed gradual increase in the infundibular gradient, he was managed conservatively due to asymptomatic status. In 2011, at 22 months after surgical intervention, infundibular gradient was 96 mm Hg on follow-up echocardiography. In addition, he had moderate TR with consequent RA and RV dilatation. Diagnostic RV angiography in lateral and right anterior oblique views showed 8 mm band-like fibromuscular circular narrowing at the infundibulum with well preserved RV and PV function (Figures 1A and 1B). There was no gradient across the valve, while gradient across the stenosed infundibulum was 84 mm Hg.

Procedure. Both patients had angiographic and echocardiographic evidence of discretely narrow circumferential stenotic segment with near-normal sized peristenotic segment between the pulmonary and tricuspid valves. Diastolic dimension of the subpulmonic dilated infundibulum was used as reference for the selection of stent size. In both children, procedures were performed under general anesthesia via femoral venous access. The RVOT was crossed using a 0.032˝ hydrophilic Terumo guidewire (Terumo Corporation), which was then exchanged for a 260 cm, super-stiff, 0.035˝ guidewire (Amplatz Super Stiff; Medi-Tech/Boston Scientific Corporation), allowing a long, 10 Fr and 12 Fr sheath (Cook, Inc) in patients 1 and 2, respectively, to be positioned in the pulmonary trunk. In patient 1, a 10-mm diameter Palmaz Genesis XD stent (PG3910P; Cordis Corporation) was delivered on a 10 mm OptaPro PTA dilatation catheter (Cordis Corporation). In patient 2, a 14-mm diameter Palmaz XL stent (P4014) was delivered on a 14 mm Maxi LD PTA dilatation catheter (Cordis Corporation). After delivery of the mounted stent to the infundibulum, the sheath was withdrawn to leave the stent uncovered. The stent position was confirmed 1-2 mm below the pulmonary valve by hand injection of contrast through the sheath and the balloon was then inflated (Figure 2). In patient 1, the stent was redilated with 14 mm Maxi LD PTA dilatation (Cordis Corporation) to facilitate the stent alignment to optimize the stent alignment with the RVOT. Prophylactic antibiotic treatment was given for 48 hours. There was no new pulmonary regurgitation (PR) in either patient, while TR severity was persistent in both patients. Predischarge cardiac fluoroscopy did not reveal any stent fracture in either case. They were discharged from hospital 3 days after stent implantation. Both patients were treated with low-dose aspirin for an indefinite period.

Results. Stent implantation was successful in both children without any periprocedural complications. The fluoroscopy time was 18 minutes and 22 minutes in patients 1 and 2, respectively. The hemodynamic results are summarized in Table 1.

Follow-up. At mid-term follow-up (30 months for patient 1 and 18 months for patient 2), both patients experienced subjective improvement in their exercise capacity in addition to enhanced weight gain (22 kg in patient 1 and 18 kg in patient 2). Periodic echocardiographic assessment showed RVOT gradient of 22 mm Hg and RV systolic pressures of 38 mm Hg in patient 1 and RVOT gradient of 18 mm Hg and RV systolic pressures of 35 mm Hg in patient 2. There was no evidence of stent fracture, distortion, or displacement on fluoroscopy during follow-up. Therapeutic transcatheter reintervention in patient 2 confirmed the echocardiographic evidence of intact stable stent across the infundibulum with mild gradient across the stent. Although the hemodynamic parameters were acceptable, the stent was redilated with 16 mm Maxi LD PTA dilatation catheter to optimize the luminal diameter and match the stent size to growing RVOT dimension. While, in patient 1, there was mismatch of stent and RVOT dimension on echocardiography, therapeutic catheterization revealed well-aligned stent position with intact stent struts without significant gradient across the infundibulum and therefore, balloon dilatation was deferred.

Discussion. Studies in patients with congenital pulmonary valvular stenosis who are treated with balloon pulmonary valvuloplasty have suggested that RVOT obstruction is well tolerated.6 These findings, however, do not apply to acquired RVOT obstruction in patients with complex congenital lesions, for whom this approach is not effective.⁷ In fact, it has been shown that relief of acquired RVOT obstruction with a bare stent reduces right ventricular systolic pressures, improves the symptoms, and defers reoperation, albeit with the consequence of pulmonary regurgitation.^8,9 Although the incidence of residual or recurrent RVOT stenosis necessitating reintervention is quite variable, 17% of patients in a series by Bacha et al1 had significant RVOT obstruction at long-term follow-up. Similarly, Adrian et al has reported 3.1% incidence of reoperation for double-chambered RV-like obstruction after TOF repair.² The indication for intervention is an RV pressure more than 3/4 of systemic arterial pressure or a gradient of >50 mm Hg across RVOT on echocardiography, with or without the presence of symptoms.⁸ The RVOT intervention or reconstruction, unless specified, implies surgical or transcatheter intervention to relieve the obstruction across the infundibulum, PV, and sometimes supravalvular segment.⁹ Transcatheter RVOT reconstruction by percutaneous stent implantation across the PV has definite potential as palliative intervention in patients with TOF.^3-5 Although the safety and feasibility of transcatheter stent release of infundibular stenosis as definite treatment is reported in few isolated cases of native infundibular stenosis,4 postoperative residual or recurrent isolated infundibular stenosis reconstruction by transcatheter stent implantation sparing the normal PV is not described. Gibbs et al had shown the feasibility and safety of palliative RVOT stent implantation in his experience of 4 patients. At 1-year follow-up, 2 patients with isolated de novo infundibular stenosis had stable stent position without any distortion or fracture.4 The optimal diameter of RVOT stent suggested by Dohlen et al is 1-2 mm larger than the infundibular diameter during diastole.³ The length of the stent should be enough to cover the entire stenotic RVOT, and careful attention is needed in the positioning.⁵ 

Anatomical and morphological assessment of infundibular segment by echocardiography and angiography in our patients showed discretely narrow membranous or fibromuscular infundibular with adequate-sized landing zone for complete stent deployment and normal pulmonary valve with mild pulmonary regurgitation. Therefore, stents with desired length could be deployed optimally without interfering with the pulmonary or tricuspid valves function in our patients. As continuous external compressive stress by hypercontractile hypertrophic RV was expected, the stents with the maximum radial strength were selected, and as far as possible larger size stents were deployed over lower normal recommended balloon size. Apart from stent dimensions and strength, prior to any definitive stent intervention in young children, it is always imperative to consider the possibility of future mismatch owing to growing infundibular dimension. Furthermore, isolated infundibular stenting, while sparing the PV in our approach, facilitated the sustained improvement in RV hemodynamics by avoiding the deleterious effects of chronic PR.¹⁰ Interestingly, intimal hyperplasia and subsequent intraluminal narrowing is rather infrequent with the infundibular stent, as compared to intravascular stent implantation. As observed in a study by Gibbs,⁴ both of our patients had sustained improvement in RV hemodynamics at mid-term follow-up.

Study limitations. Although it is less invasive and potentially free from surgical morbidities, transcatheter reintervention is predictably necessary in young children even after satisfactory acute and short-term results. Although the intact stent integrity and position with improvised chronic hemodynamics at 2-year follow-up in our report is least predictive of delayed stent complication, long-term vigilant follow-up is mandatory to exclude the possibility of late stent compression or fracture.

Conclusion. Transcatheter infundibular stent implantation may offer a safe and effective alternative to surgical reconstruction of stenosed RVOT in selected cases with normal pulmonary valve function. It is preferable to select larger, sturdy stents to maximize the radial strength of the deployed stent and to allow for redilatation if required to compensate for growing RVOT dimension.

From the UN Mehta Institute of Cardiology and Research Centre, Civil Hospital Campus, Asarwa, Ahmedabad, Gujarat, India.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted November 26, 2012, provisional acceptance given January 2, 2013, final version accepted January 31, 2013.

Address for correspondence: Dr Bhavesh M. Thakkar, Associate Professor and Pediatric Interventional Cardiologist, Department of Pediatric Cardiology, UN Mehta Institute of Cardiology and Research Centre, Ahmedabad, 380016 (Gujarat) India. Email: bthakkarin@yahoo.co.in

References

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From the UN Mehta Institute of Cardiology and Research Centre, Civil Hospital Campus, Asarwa, Ahmedabad, Gujarat, India.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted November 26, 2012, provisional acceptance given January 2, 2013, final version accepted January 31, 2013.

Address for correspondence: Dr Bhavesh M. Thakkar, Associate Professor and Pediatric Interventional Cardiologist, Department of Pediatric Cardiology, UN Mehta Institute of Cardiology and Research Centre, Ahmedabad, 380016 (Gujarat) India. Email: bthakkarin@yahoo.co.in