Potts Shunt and Pulmonary Hypertension
Typically, creation of a post-tricuspid shunt involves an anastomosis
between the descending aorta and the left pulmonary artery, a surgical
technique first described in 1946 by Dr. Willis
Potts.14 The original goal of his eponymous shunt was
to provide pulmonary blood flow to a child with tetralogy of Fallot at a
time when cardiopulmonary bypass was not available. The procedure fell
out of favor once primary repair became standard. However, in 2004, a
group from Hôpital Necker-Enfants Malades in Paris, France resurrected
the Potts shunt to treat two boys suffering from severe, suprasystemic
right ventricular systolic pressures.15 Their
insightful theory postulated that by creating an unrestrictive
pulmonary-to-systemic shunt, the afterload on the right ventricle would
be reduced to systemic levels and thereby recapitulate the
pathophysiology seen in patients with Eisenmenger’s syndrome. By doing
so, the researchers hoped to confer upon these children the relatively
superior life expectancy purported for patients with Eisenmenger’s
syndrome.16,17 One immediate consequence of the shunt
would be to send deoxygenated blood to the lower half of the body, while
preserving the highest oxygenated blood for the upper half and the brain
in particular. This contrasts with an AS that leads to global
deoxygenation. The two children experienced significant improvement both
clinically and hemodynamically with follow-up at 6 and 18 months
respectively.
This initial success led the way for their publication of 24 consecutive
children with PH treated with a Potts shunt in 2012.18In this series, children’s ages ranged from 1.5 to 17 years with the
majority classified as severely compromised with WHO-FC IV. Nineteen of
the children had a traditional shunt via a left thoracotomy and direct
anastomosis of the pulmonary artery and the aorta. Five had
transcatheter shunts through the stenting of a restrictive patent ductus
arteriosus (PDA). There were 3 procedural deaths (12.5%). Children that
went home had a median follow-up of 2.1 years with 7 children having
over 8 years follow-up post-procedure. There was rapid clinical and
hemodynamic improvement with better WHO-FC (from a median FC IV to II),
longer 6 minute walk distances, lower brain natriuretic peptide (BNP)
levels and improved echocardiographic findings. Perhaps most remarkable,
these improvements occurred while weaning PH medications. Indeed, 6 of
the children that were on intravenous epoprostenol pre-operatively were
weaned completely off post-shunt. This contrasts with studies of
patients undergoing AS for palliation where medical regiments often
increased post-procedure.10,13 Overall, this series
demonstrated that a child with severe PH, WHO-FC IV on intravenous
prostacyclin therapy, could experience a sustained, prostacyclin-free,
improved quality of life by means of a Potts shunt.
In 2016, a group from Washington University in St Louis, USA published a
series of five consecutive children who had undergone a surgical Potts
shunt for severe PH.19 Their findings mirrored that of
the Parisian group, demonstrating in 4 of the children, with less
follow-up (mean ~10 months), an improvement in
functional class and BNP levels. Since that publication, the St Louis
group has performed a total of 23 Potts shunts in children with a mean
age of 10.3 years (range 0.3-20 years) with diagnoses including
idiopathic PH, heritable PH, PH associated with congenital heart disease
and PH associated with lung disease (personal observation). Twenty had
surgical shunts, either through 1) direct anastomosis, 2) the use of a
short inter-arterial graft or 3) with a valved conduit placed via a
sternotomy. Three children had catheter-based interventions, two with
PDA stenting and one with reopening a previously device-closed duct.
Four of the children died (17%) within 30 days of the procedure. Three
of these early mortalities were children who presented in extremis,
requiring veno-arterial ECMO prior to their shunt. The fourth child died
from progressive hypoxia due to interstitial lung disease. Nineteen of
the children were discharged home with a mean follow-up of 2.5 years
(range 0.5-6 years). Seventeen of these children showed improvement
clinically with lower WHO-FC scores, lower BNP levels and a reduction in
overall PH medications. There were four late deaths and two lung
transplants post-shunt. Reasons for death or transplant included
worsening right ventricular failure, acute infection and one due to
accidental tracheostomy tube dislodgement.
The data from Paris and St Louis demonstrate, with a combined mean
follow-up of 2-3 years, that a Potts shunt can provide symptomatic
improvement in children with severe PH. The question of longer-term
benefits, however, remains open. The original idea behind utilizing a
Potts shunt was to “convert” a child to Eisenmenger-like physiology
and possibly confer the purported survival benefits seen with
Eisenmenger patients. This conferral of benefit assumes that a child
with PH due to an etiology distinct from Eisenmenger’s syndrome would
respond similarly to right ventricular decompression. In adult series,
median survival with Eisenmenger syndrome has been estimated as long as
40-60 years, far better than that reported in children with
PH.2,3,16,17 The survival rate for children with
Eisenmenger’s syndrome, however, may not be as robust as seen in adults,
with one estimate of 77% survival at four years.20Nonetheless, even this reduced survival projection would still compare
favorably to that of children who typically present for Potts shunt
consideration, specifically, those who are WHO FC IV despite PH specific
therapy. These compromised children have a purported median survival of
less than two years.21
To address survival benefits and other aspects regarding the use of a
Potts shunt in treating children with PH, an international registry with
at least fourteen centers has begun to compile data. Even without
registry results, however, there are relevant observations and
discussions that can be made regarding the Potts shunt and PH. From the
St. Louis experience, three children were sick enough prior to their
shunt procedure to require veno-arterial ECMO (personal observation).
All three had surgical shunts and all three died in house within 30 days
of their procedure. These results would suggest that in the severely
decompensated child, a Potts shunt might not be an effective option. In
fact, if these three children were excluded, acute mortality in the St
Louis series would drop from 17% to less than 5%. Thus, as with most
procedures, increased experience in patient selection can lead to
improved surgical outcomes. Certainly, if a child’s anatomy allows,
dilating and stenting a restrictive PDA would be the route of choice for
creating a shunt, avoiding the potential morbidity from surgery.
Unfortunately, this option is seldom available. Several centers have
reported on creating a transcatheter shunt through direct puncture from
the aorta to the pulmonary artery with subsequent placement of a covered
stent.22,23 Between the two series, a total of ten
patients underwent this transcatheter procedure with four deaths, an
early mortality more than double of that seen in the St Louis and Paris
experience. This relatively high risk may preclude the transcatheter
Potts shunt from gathering widespread acceptance.
Not all children with severe PH will benefit from a Potts shunt. In
theory, because the shunt is an unrestrictive communication between the
pulmonary and systemic circulations, it will only be effective in
reducing right ventricular afterload in those whose right ventricular
systolic pressures are higher than the left, i.e., suprasystemic.
Documenting suprasystemic right ventricular pressures can be done with
either echocardiography or cardiac catheterization. Relying on right
ventricular ejection fraction alone, however, is not sufficient. In the
St Louis series, one child had a calculated right ventricular ejection
fraction by MRI of 16% yet the echocardiogram still demonstrated
suprasystemic pressures. Post-procedure this child did well clinically
(personal observation). While a Potts shunt can successfully lower
suprasystemic right ventricular pressures, subsequent pressures will
still remain at abnormally high systemic levels. Consequently, a shunt
placed in a child whose right ventricle has lost the ability to generate
systemic to suprasystemic pressures may prove ineffectual. As a case in
point, one child, early on in the St Louis series, was diagnosed
initially with suprasystemic right ventricular
pressures.19 At the time of his shunt however,
echocardiograms demonstrated at most systemic right-sided pressures. The
child failed to improve post-procedure and eventually died three months
later from progressive right ventricular failure. Thus, intervening with
a Potts shunt should occur before the onset of frank right ventricular
failure, i.e., falling, sub-systemic, right ventricular systolic
pressures with rising RVEDP.
In theory, a post-tricuspid shunt like a Potts has the potential to
intercede relatively early in a child’s disease course, while systolic
function is still preserved at suprasystemic levels and diastolic
pressures are comparatively low. This contrasts with an AS which relies
upon an elevated RVEDP to be effective, a situation more typical of
end-stage disease. This potential advantage of a Potts shunt over AS,
leads to the interesting question as to how early in a child’s disease
course does one consider a shunt. Current recommendations suggest
considering a Potts shunt in a child with severe, symptomatic disease
who has failed aggressive medical therapy, including prostacyclin
infusion.11 However, does waiting for such a child to
develop symptoms reduce a shunts potential benefits and increase its
risks? Those answers are currently unclear. What is clear, however, is
that managing a 24-hour prostacyclin infusion places a substantial
burden upon a child and family and that a Potts shunt offers the hope of
easing that onus. Thus, perhaps intervention should be considered in a
child with severe PH who is still WHO FC I-II rather than III-IV. A
technical development that might provide impetus for employing a Potts
shunt earlier in a child’s course is the use of a valved conduit to
create the inter-arterial anastomosis. A shunt that allows for only
right-to-left flow might benefit the child who at rest has systemic to
even sub-systemic right ventricular pressures yet with exertion develops
suprasystemic pressures with resulting symptoms. A recently published
series demonstrates the feasibility of such an
approach.24 Managing the inevitable development of
valve incompetency and a conduit’s limitations in a growing child would
need to be considered.
For children with severe, progressive, medically recalcitrant PH,
bilateral lung transplantation remains the ultimate palliative option.
Whether a Potts shunt can provide a similar survival rate as lung
transplantation requires more data. A more immediate question, however,
is whether having a Potts shunt precludes further consideration for lung
transplantation. There is one reported case from the Paris series of a
child who had a Potts shunt and subsequently underwent successful lung
transplantation.25 This child initially did well
post-shunt with clinical improvement and weaning from her intravenous
epoprostenol. However, six years after her shunt, she developed severe,
persistent hemoptysis and was listed for transplant. On the day of her
transplant, her shunt was closed with a covered stent prior to her
operation. From the St Louis experience, three children post-shunt came
to transplant, two from progressive RV failure and one for hemoptysis
(personal observation). At the time of transplant, two were on
relatively high doses of IV prostacyclins and one was on veno-venous
ECMO. All three transplants were marked by severe bleeding which
resulted in two of the children dying post-operatively. The one survivor
recovered fully. Reasons for the profound bleeding are likely multifold
and include the known risk that prior thoracotomies have on chest wall
neo-vascularization and lung adhesions, failure to adequately control
the shunt at the time of transplant, and clotting derangements due to
medications such as prostacyclins. One technical modification that might
reduce these complications is to place a shunt through a sternotomy.
This approach could potentially reduce lung adhesions, provide better
control of the shunt at the time of transplant, and eliminate the need
for any additional peri-operative procedures.24Overall, while having a Potts shunt does not prevent future
consideration of lung transplantation, it does appear to increase the
risk and technical challenge of the operation. Lung transplantation in
of itself is a complex procedure. Consequently, performing one on a
child who has had a Potts shunt is not something every transplant center
is willing to consider. Therefore, before proceeding with a Potts shunt,
frank discussions with families about possible future limitations and
risks would obviously be important in helping them make informed
decisions.