Download Nonsurgical pulmonary valve replacement: Why, when, and how?

Catheterization and Cardiovascular Interventions 62:401– 408 (2004)
PEDIATRIC AND CONGENITAL HEART DISEASE
Core Curriculum
Nonsurgical Pulmonary Valve Replacement:
Why, When, and How?
Sachin Khambadkone,*
MD,
and Philipp Bonhoeffer,
MD
Percutaneous transcatheter interventions for valve replacement or implantation is one of
the most exciting developments in the field of interventional cardiology. Valvular stenosis
has been treated by balloon dilatation with early and late results; however, treatment for
valvular regurgitation has remained surgical until now. Most new designs have been
investigated for implantation of valves in the left or right ventricular outflow tracts.
Patients with surgery on the right ventricular outflow tract for congenital heart disease
constitute the most common group for reoperations during late follow-up. Surgical
pulmonary valve replacement can be performed with low mortality; however, it sets up a
substrate for future operations. Also, the risk of cardiopulmonary bypass, infection,
bleeding, and ventricular dysfunction remains. A transcatheter technique is likely to have
more acceptance and may expand the indications for early intervention for right ventricular outflow tract dysfunction. Catheter Cardiovasc Interv 2004;62:401– 408.
©
2004 Wiley-Liss, Inc.
Key words: transcatheter; pulmonary valve; regurgitation
INTRODUCTION
Nonsurgical cardiac valve replacement is one of the
most exciting developments in the field of interventional
cardiology [1– 4]. Despite transcatheter treatment of valvular stenosis being well established [5–7], treatment of
valvular regurgitation remains entirely surgical. The
prospect of nonsurgical transcatheter treatment of valvular regurgitation holds great promise in view of the
inherent advantages to patients and the medical community alike. There have been various developments in the
designs of implantable valves and systems to deploy
them through percutaneous route with variable success
[4,8,9]. Most of these developments are designs for treatment of semilunar valve regurgitation. The basic principle consists of use of a valve that can be mounted on a
balloon-expandable stent using standard catheter techniques. However, the underlying morphological differences between the left and right ventricular outflow tracts
provide major challenges to these designs. The right
ventricular outflow tract commonly requires intervention
during correction of congenital heart disease. While relief of stenosis was considered the main strategy during
the early repair of conditions such as tetralogy of Fallot,
only recently has the importance of maintaining a com© 2004 Wiley-Liss, Inc.
petent pulmonary valve been emphasized [10 –12]. Despite the fact that surgical pulmonary valve replacement
can be performed with low mortality, there still exists the
morbidity of reoperations and the need to replace these
valves surgically, particularly when they are implanted at
a young age.
We describe our approach in embarking on treatment
of pulmonary regurgitation secondary to surgical or
transcatheter intervention on the pulmonary valve in congenital heart disease.
Department of Cardiology, Great Ormond Street Hospital, London, United Kingdom
*Correspondence to: Dr. Sachin Khambadkone, Department of Cardiology, Great Ormond Street Hospital, Great Ormond Street, London,
United Kingdom. E-mail: [email protected]
Received 13 January 2004; Revision accepted 2 March 2004
DOI 10.1002/ccd.20122
Published online in Wiley InterScience (www.interscience.wiley.com).
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Khambadkone and Bonhoeffer
WHY?
Despite acceptance of early postoperative pulmonary
regurgitation as a benign lesion in the early era of congenital heart surgery, long-term follow-up has revealed
the detrimental hemodynamic effects on the right and left
ventricular function [11–13]. Chronic volume overload
of the right ventricle leads to ventricular dilatation and
impairment of systolic and diastolic function [14,15].
The tricuspid annulus dilates and may lead to onset of
new or worsening of preexistent triscuspid regurgitation.
The combination of these two valvular lesions is responsible for right heart dilatation. In the long term, this
causes atrial and ventricular arrhythmia, heart failure,
and increases the risk of sudden death. Prolongation of
QRS duration, risk of malignant ventricular arrhythmia,
and sudden death are all linked to pulmonary regurgitation during late follow-up after tetralogy of Fallot repair
[16]
Impaired exercise capacity after repair of tetralogy of
Fallot has been shown to be related to pulmonary regurgitation [17]. Right ventricular diastolic dysfunction due
to restrictive physiology, however, protects the ventricle
from dilatation and maintains better exercise performance compared to patients without restrictive physiology [10]. Preservation or restoration of pulmonary valve
competence at an appropriate time has resulted in improvement in right ventricular function, incidence of
arrhythmias, and effort tolerance [13,18 –20].
WHEN?
The optimal timing of establishing pulmonary competence before irreversible dysfunction of right ventricle
has not yet been determined. The conventional indications of surgery for pulmonary regurgitation have been
onset of symptoms, effort intolerance, arrhythmias, progressive dilatation of right ventricle, worsening right
ventricular function, or associated lesions that exacerbate
pressure or volume overload to the right ventricle (residual ventricular septal defect, outflow obstruction, severe
tricuspid regurgitation) [19,21,22]. However, there are
concerns that this may be too late and irreversible
changes in the right ventricle may already set in. Therrien
et al. [20] reported no improvement in right ventricular
volumes, right ventricular (RV) function, and exercise
performance after late pulmonary valve replacement performed more than 20 years after the initial repair. They
concluded that late intervention for pulmonary regurgitation might compromise the recovery of right ventricular function. Also, other investigators have clearly shown
that pulmonary valve replacement can improve right
ventricular function, control arrhythmias, and improve
exercise performance if performed at an appropriate time
[18,23,24]. However, there is no single investigation that
gives a reliable indication from the currently available
data. Onset of right ventricular dysfunction, tricuspid
regurgitation, and worsening symptoms may all be markers of diminished reversibility and probably are not justified as indicators for appropriate time of intervention.
Based on the current knowledge, it is arguable that the
most appropriate time of intervention would be before
the onset of symptoms, or significant right ventricular
dilatation in patients with severe pulmonary regurgitation
where serial cardiopulmonary exercise testing indicates
diminishing effort tolerance.
HOW?
Surgical pulmonary valve replacement can be performed with very low mortality [25,26]. Despite this,
adolescents and adults are reluctant to have reoperations
where the longevity of the new valved conduit does not
guarantee freedom from further operations [27].
We have developed a new percutaneous technique for
pulmonary valve implantation with a bovine jugular venous valve sutured inside a stent and implanted using a
delivery system designed to track a front-loaded device
without difficulty. After initial animal studies, we have
implanted this valved stent in humans [8].
The most common indications for surgical pulmonary
valve replacement are pulmonary regurgitation with or
without stenosis, right ventricular dilatation, malignant
arrhythmias, and residual hemodynamic lesions [28].
The majority of patients referred for surgical pulmonary
valve replacement have diagnosis of tetralogy of Fallot
with pulmonary stenosis or pulmonary atresia or have
surgical treatment for critical pulmonary valve stenosis
[24,29]. Other diagnostic groups included transposition
of great arteries with ventricular septal defect and pulmonary stenosis who had Rastelli operation and placement of a right ventricle to pulmonary artery conduit, as
well as patients with Ross operation with dysfunction of
the pulmonary homograft [30]. The conventionally accepted intervention has been surgical with use of homografts (aortic or pulmonary) [31], monocusp valves
(pericardial or Gore-Tex) inside Gore-Tex tubes [32–34],
and conduits with xenograft valves [35,36] and mechanical valves [37]. Recently, bovine jugular venous valved
conduits [38,39] have been used for reconstruction of the
right ventricular outflow tract. Despite major advances in
terms of durability, the life span of the prosthetic conduits is limited. Calcification, stenosis, intimal proliferation, and graft degeneration cause progressive stenosis
or regurgitation. Indeed, these patients are committed to
multiple reoperations for life. Though these procedures
can be carried out with reasonably low risks, one still had
to consider risks of reoperations in these patients, includ-
Nonsurgical Pulmonary Valve Replacement
Fig. 1.
403
Angiograms in lateral projection showing complete abolition of pulmonary regurgitation.
ing bleeding, infection, and the risk of graft failure or
prosthetic valve dysfunction. The graft failure always
sets up need for reoperations and the risk increases with
the number of previous conduit implantations [40]. Also,
right ventriculotomy could lead to right ventricular dysfunction and form a substrate for malignant ventricular
arrhythmias [41].
A transcatheter intervention for pulmonary valve replacement would be less invasive, avoid the risks of
ventriculotomy and cardiopulmonary bypass, and avoid
the risks of bleeding and infection associated with reoperation and reduce the costs by avoiding postoperative
intensive care. The procedure would have to provide a
comparable safety and efficacy to established surgical
procedures.
Transcatheter implantation of cardiac valves is evolving as one of the most exciting developments in the field
of interventional cardiology. Hufnagel et al. [42] first
reported the use of a ball valve prosthesis designed for
rapid insertion into descending aortal for treatment of
aortic regurgitation. Andersen et al. [43] described a
valve mounted inside a stent, which could be implanted
with percutaneous transluminal techniques in the ascending aorta and the aortic root. Bonhoeffer et al. [1,44]
described a similar model with a bovine jugular venous
valve sutured inside a stent, which was deployed using a
custom-made delivery system into the right ventricular
outflow tract. After a series of successful animal experiments to show the feasibility, safety, and efficacy of this
technique and device, human implantation was performed in patients with pulmonary valve dysfunction for
regurgitation and stenosis (Fig. 1).
The patient selection for percutaneous transcatheter
pulmonary valve implantation was crucial to the success
of this technique in human subjects. The animal studies
confirmed that the valve stent assembly could be safely
anchored in the native right ventricular outflow tracts of
lambs. When considering the patient groups referred for
percutaneous pulmonary valve implantation, we had to
identify first the diagnostic groups and then the nature of
the right ventricular outflow tracts within these groups.
Tetralogy of Fallot and its variants remains the most
common diagnostic group in clinical practice requiring
pulmonary valve implantation for pulmonary regurgitation during late follow-up. When associated with pulmonary atresia, a valved conduit is used to establish continuity between the right ventricle and the pulmonary
artery. Homografts and porcine bioprosthetic valves are
the commonly used means of establishing this continuity.
The right ventricular outflow tract dysfunction during
late follow-up results from degeneration of the valve
leaflets with or without stenosis related to fibrous or
fibromuscular proliferation at the anastomotic site at the
proximal end involving the ventriculotomy or at the
distal end involving the pulmonary artery or its branches.
Calcification of the homograft also contributes to the
reduction of the luminal diameter. For relief of right
ventricular hypertension due to stenotic lesions, balloon
dilatation and stent implantation have been successfully
used in the conduits [45,46]. However, this does not
provide relief from regurgitation and may in fact result in
the exacerbation of the regurgitant component of right
ventricular outflow tract dysfunction [47,48].
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Khambadkone and Bonhoeffer
Fig. 2.
ment.
MRI showing dilated right ventricular outflow tract, which would be unsuitable for nonsurgical pulmonary valve replace-
We believe that the homograft provides an excellent
bed for implantation of our device. In most cases, the
homograft degeneration provides a combination of stenosis and regurgitation. The stenotic component is helpful for creating an implantation point for the valve, which
leads to successful anchoring. Most conduit stenosis have
been shown to respond favorably to balloon dilatation
and stenting despite heavy calcification, and there is no
reason to believe that this would not be the case with our
device [45]. The limiting factor in these patients would
then be the size of the conduit. A large conduit, which is
larger than the fully expanded dimension of the valve
stent assembly, would clearly be unsuitable for this technique. So would a small conduit (⬍ 16 mm), which
cannot be dilated to the diameter of the device and lead
to an incompletely expanded valve-stent assembly with a
large profile.
In contrast, patients with a native outflow tract with
repair of tetralogy of Fallot involving only a valvotomy
or valvectomy may not provide a very discrete implantation point at the site of the pulmonary valve annulus. If
there is augmentation of the right ventricular outflow
with an outflow tract patch or transannular patch, the
outflow tracts tend to be dilated and may not have any
secure implantation point at all (Fig. 2). The outflow tract
in such cases appears dilated and may in fact form a part
of the right ventricular outflow tract aneurysm [48]. The
patch, being a noncontractile part of the outflow tract,
moves paradoxically to the rest of the ventricle and
increases in dimension in systole. These are the most
unfavorable outflow tracts for transcatheter techniques
with currently available devices. The dimensions of the
outflow do not provide any secure anchorage to the
valve-stent assembly. Also, the paradoxical motion of a
noncontractile patch leads to further increase in dimension during systole. The right ventricle is usually dilated
in these patients and they may have additional patch or
extension of the transannular patch on the right ventricular wall.
The valve-stent assembly and their dimension also
limit their use in the dilated outflow tracts. The bovine
jugular venous valve are usually not more than 18 mm in
diameter. However, the leaflets have a much larger area
than in homografts and tend to have a larger coaptation
surface. Because of this, the valve leaflets still remain
competent despite the dilatation of the venous wall. This
has been shown by in vitro dilatation of the bovine
venous valved conduit [1]. Similar phenomenon is seen
in patients who have surgical implantation of the bovine
jugular venous wall for the reconstruction of the right
ventricular outflow tract and there is dilatation of the
conduit. This is commonly associated with distal stenosis
of the branch pulmonary arteries or due to stenosis of the
distal anastomosis. Nevertheless, severe dilatation would
lead to disruption of the valvular mechanism and dysfunction of the conduit. The stent also limits the overdi-
Nonsurgical Pulmonary Valve Replacement
Fig. 3.
405
MRI showing extrinsic compression of conduit.
latation of the venous valve up to a certain limit beyond
its natural diameter due to the inherent external constraint provided by the size of the stent. Due to these
reasons, we believe that the currently available device
would not be suitable for use in patients with outflow
tract dimensions beyond 22 mm.
Homografts and other bioprosthetic conduits placed in
an extra-anatomic position after surgical correction of
transposition of great arteries with ventricular septal defect and pulmonary stenosis, common arterial trunk or
pulmonary atresia with ventricular septal defect and major aortopulmonary collaterals requiring unifocalization
provide a different challenge for surgical or transcatheter
intervention. The position of the valved conduit is determined by the variations in the morphology of the primary
lesion. The conduits could sometime lie behind the sternum and pose problems during reexploration. The position behind the sternum would also lead to external
compression by the sternum and adhesions to the anterior
chest wall (Fig. 3). Surgical exploration in these situations is fraught with risks of fatal hemorrhage due to
transection of the conduit during sternotomy and many
surgeons prefer to use femoral bypass during resternotomy.
Transcatheter course through an extra-anatomic conduit can be difficult, especially in the presence of severe
stenosis and calcification. However, with better catheters,
guidewires, and low-profile balloons with good tracking
capability, interventions on these conduits have become
less complicated. Despite this, positioning of large
sheaths and delivering stents could require long procedures with difficult manipulations. The current design of
the valve-stent assembly requires a specially designed
front-loading delivery sheath to deliver the valve-stent
assembly. The delivery sheath has a profile up to 22 Fr,
which requires dilatation of the femoral vein and may
pose difficulties in tracking it through a complex intracardiac course. Maintaining distal guidewire position can
be difficult during the tracking of the device to achieve an
appropriate position to deploy the valved stent. This
could increase the procedure times and screening times
and may require expert manipulation.
The conventional techniques to image the right ventricular outflow tract include echocardiography, angiography, and magnetic resonance imaging (MRI). Echocardiography provides hemodynamic information with
estimation of right ventricular systolic pressure from the
tricuspid regurgitation jet, assessment of right ventricular
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Khambadkone and Bonhoeffer
outflow tract (RVOT) gradient with continuous-wave
Doppler, and assessment of pulmonary regurgitation using color flow mapping and spectral Doppler analysis of
the pulmonary regurgitation (PR) jet for pressure halftime, half-time index, and deceleration slope [49,50].
Despite this, there are limitations in obtaining good morphological information due to the limited windows in
older patients. Angiography has been the traditional technique and has been replaced for diagnostic purposes by
MRI.
We believe that MRI is an excellent technique for
investigating the form and function of the right ventricular outflow tract and the consequences of its dysfunction
on the right ventricle [48,51]. Not only does it provide
excellent images to delineate the structure of the outflow
tract, it can provide hemodynamic information from the
tricuspid regurgitation (TR) jet velocity and RVOT velocity. In addition, assessment of RV volumes and systolic and diastolic function and regurgitant volume and
fractions helps in assessing the effects of intervention
short- and long-term follow-up [52–54]. Three-dimensional reconstruction of the right ventricular outflow adds
a completely different level of information that cannot be
obtained by echocardiography or angiography. The homografts and conduits have two sites of anastomosis that
are influenced by the morphology of structures at both
ends. The surgeons have to suture the conduits in optimum position to keep it away from external constraints
such as the sternum and to conform to anastomosis at the
distal pulmonary artery bifurcation. This can introduce
folds and twists in the conduit, which could lead to
stenosis and cause regurgitation by distortion of the valve
leaflets. The twists or folds can be underestimated by
angiography, as the decrease in caliber looks quite minimal (Fig. 4). Three-dimensional reconstruction of the
outflow tract by volume-rendered gadolinium images
delineates these types of stenosis extremely well.
We believe that with the currently available device,
homografts between 16 and 22 mm would form most
suitable outflow tracts for percutaneous pulmonary valve
implantation. The length of stenosis should not be greater
than 5 cm. Any additional stenosis close to the site of
implantation should be dealt with before the valve deployment. However, there would be concerns about rupturing the balloon of the delivery system for the valve, if
there are stents adjacent to the site of deployment. Proximity of the implantation point to the pulmonary artery
bifurcation with origin stenosis in the branches can provide a difficult combination for intervention on the outflow tract. Undilatable stenosis still remains a problem
with severely calcified homografts with extrinsic constraints due to retrosternal position.
Transcatheter implantation of pulmonary valves has
been the first clinical experience for nonsurgical manage-
Fig. 4. Lateral projection of a 3D image of right ventricular
outflow tract showing twists and folds in the conduits that
contribute to gradients.
ment of valvular regurgitation. Our group has shown the
feasibility, safety, and efficacy of pulmonary valve implantation in humans. There are still various unanswered
questions about the durability of this valve in the long
term. However, recourse to surgery still remains a viable
option for patients with valvular dysfunction. There are
limitations to the application of this technique in young
and small patients and patients with either too small or
too large outflow tracts. We are in the process of developing devices for providing anchoring for the valved
stent in patients with outflow tract aneurysms. With more
experience and the results of long-term follow-up, nonsurgical pulmonary valve implantation may expand the
boundaries of pulmonary valve replacement in patients
with pulmonary regurgitation and reduce the long-term
deleterious effects on the right ventricle.
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