After the introduction of the Blalock-Thomas-
Taussig (BTT) shunt in 1944, it garnered significant
interest from both surgeons and the general public,
becoming a widely adopted palliation method until
it was eclipsed by direct corrective surgery. Later,
Lord Russell Claude Brock innovated a closed
transventricular pulmonary valvotomy technique,
subsequently incorporating closed infundibular
excision with a custom valvutome, which directly
addresses outflow restriction and represents a genuine
partial repair of the deformity.[
2-
4,
13] The procedure was
the first direct intracardiac intervention prior to the development of echocardiography and CPB; however,
this operation has not been widely adopted since then
due to concerns about long-term survival, including
recurrence of RVOT obstruction, arrhythmias,
sudden cardiac mortality, and gradual biventricular
dysfunction and failure, despite favorable short-term
results, as indicated by reports.[
6-
12]
Right ventricular outflow tract stents, which have
recently gained in popularity and are promoted as
providing better hemodynamics and perhaps lower
death rates compared to modified BTT (mBTT)
shunts or ductal stenting, could be regarded as a
transcatheter synthesis of a variant Brock procedure
with an intracardiac Sano-type shunt, executed
without CPB.[14-17] Therefore, surgical palliative
procedures targeting RVOT have gained popularity
recently. We employed the modified Brock procedure
for patients with hypoplastic pulmonary arteries that
hindered their ability to endure a full repair, as this
technique offers advantages over BTT shunts. First,
it facilitates antegrade flow via the natural pathway,
promoting optimal uniform and symmetrical growth
of the pulmonary arteries without distortion and
gradually prepares the pulmonary bed for increased
pulmonary blood flow. In extreme cases of TOF,
it may facilitate the possibility of total correction.
Second, the infundibulum and the RV cavity can
also undergo further growth. Third, there may be a
reduction in coronary steal attributed to decreased
diastolic runoff. Fourth, the operation can also
be repeated if necessary and facilitates further
catheter interventions.[11,12,18] In our cohort, we
managed to safely palliate patients with hypoplastic
pulmonary arteries with a median SO2 above 90%
at mid-term follow-up. Mortality was low (7%)
with a straightforward postoperative course, and we
were able to achieve complete repair in 30% of the
patients during follow-up in a median of 17.5 months
after the modified Brock procedure. Similarly, a
retrospective study from Germany with 11 patients
reported that there was no perioperative mortality,
and 10 patients underwent elective complete repair.[8]
They determined that palliative RVOT construction
may offer the potential for complete repair in a
severe form of TOF. The Paris group reported an
early mortality rate of 2.7%, an interstage attrition
rate of 6.6%, and successful biventricular repair
in 84 (77%) patients with the use of a similar
technique. They also reported that a Nakata index of
74 mm2/m for the mBTT shunt and 102 mm2/m for the right ventricle-to-pulmonary artery connection,
indicating that the right ventricle-to-pulmonary
artery connection appeared to facilitate superior
pulmonary artery growth compared to the mBTT
shunt.[9,10] Batlivala et al.[11] reported their experience
of 17 patients who underwent modified RVOT
procedure as palliation, and they concluded that it is
a viable alternative that produces satisfactory results
by preventing the possibility of sudden mortality
associated with a shunt. Another study from China
reported that the modified Brock procedure appears
to be a more effective strategy that ensures safety and
promotes satisfactory pulmonary arterial growth until
complete repair compared to the mBTS procedure.[12]
On the other hand, disadvantages can be listed
as the requirement of CPB and cardioplegia, and the
challenging nature of the technique that requires
precise division and resection (risk of pulmonary
overflow).[18] If the valve is excessively opened,
physiological issues may arise, particularly in the
context of a large VSD, when a double outlet
ventricle is present. In TOF, pulmonary stenosis
prevents most left ventricular output from diverting
to the low pressure pulmonary vascular system. The
protective mechanism is abruptly removed when the
valve is opened via the Brock technique. Subsequent
extensive postoperative pulmonary mucosal edema,
difficult tracheal extubation, and even heart failure
are possible.[11,12,18,19] Therefore, it is crucial to open
the pulmonary valve to an appropriate extent. Proper
adjustment of the valve may produce sufficient
pulmonary blood flow without significant blood
shunting to the lungs. We did not encounter any of
these problems as a result of our meticulous surgical
technique, including restricted muscle resection,
restricted RVOT enlargement, preservation of the
annulus, and leaving a pressure gradient between the
right ventricle and pulmonary artery. Furthermore,
the fine-tuning of the RVOT patch size according to
immediate hemodynamic parameters after weaning
off CPB helped us prevent pulmonary overcirculation,
which can result in sudden left ventricular dilation,
bradycardia, and cardiac arrest. We strongly believe
that all these preventive measures helped us achieve
low mortality and straightforward postoperative
recovery. Classically, it was often accepted that TOF
management required total alleviation of obstruction
in the RVOT. Recently, an emphasis has been
placed on the preservation of the pulmonary valve
and annulus, and a greater residual RVOT gradient after surgery may be tolerated to prevent early and
long-term complications.[19,20] Similar considerations
are crucial when addressing RVOT for palliation, as
frequently highlighted in previous articles.[6-12] As we
managed to preserve the annulus in our cohort, we
believe that pulmonary regurgitation would not be a
significant problem after complete repair.
Although 30% of our cohort has undergone total
repair, nine individuals were still awaiting full repair,
with satisfactory growth of the pulmonary artery. Our
institutional strategy for complete repair in patients
with hypoplastic pulmonary arteries is to achieve
a McGoon ratio of no less than 1.8. Consequently,
although there was growth in pulmonary arteries,
individuals awaiting complete repair still exhibited a
McGoon ratio below 1.8. Their functional state and
oxygen saturation levels were decent during the most
recent follow-up. We employed a proactive approach
during follow-up to assess pulmonary arterial growth.
In terms of the reoperations following the modified
Brock procedure, only one patient necessitated
reaugmentation of the patch. Late reoperation for
restrictive flow is typically not the result of an initial
technical failure, as is widely recognized. It is often the
result of the progressive relative stenosis of the initial
procedure, which was caused by somatic growth, and
the lack of development of the pulmonary artery to
facilitate a full repair. Interestingly, few case reports
have recently been published presenting long-term
follow-up after the classical Brock procedure. One
of the earliest patients who underwent the Brock
procedure, a four-year-old child, was reported to
have survived an additional 43 years without further
surgical intervention.[21] Other patients have been
reported to remain active and asymptomatic 43, 52,
and even 63 years after the Brock procedure with good
biventricular function.[22-24] Brock's[2] initial hypothesis
that the pulmonary arteries would endure substantial
development as a result of enhanced flow through the
natural channel is also supported by these patients.
This would suggest that a smaller number of patients
would require total correction.[4,6,13]
This study was limited by the fact that it was
conducted retrospectively and observationally at a
tertiary referral center and with a small sample size
over an extended period of time. The generalizability
of our findings was also limited by the significant
anatomical heterogeneity within the patient
population. In addition, no comparison was made
with other palliative procedures. Comprehensive statistical analysis was ultimately limited by the
number of deaths, reoperations, and complications. It
is imperative to collect additional data consistent with
surgical techniques in a larger population of patients to
derive association metrics.
In conclusion, we believe that palliative repair of
RVOT with the modified Brock procedure appears
to be a viable option and should be the primary
palliative therapy, as opposed to conventional
aortopulmonary shunts, for patients whose
pulmonary artery anatomy prevents complete repair.
The modified Brock procedure contributes to the
preservation of RV function by maintaining an
appropriate pressure gradient between the right
ventricle and pulmonary artery, as well as enhancing
pulmonary arterial growth through pulsatile flow.
The potential drawback of pulmonary overcirculation
was not a significant problem in our experience.
Close follow-up of patients after palliative RVOT
augmentation is essential.
Data Sharing Statement: The data that support the
findings of this study are available from the corresponding
author upon reasonable request.
Author Contributions: Conseptualisation, methodology,
editing: S.A., M.Y.; Writing, data curation: S.A.
Conflict of Interest: The authors declared no conflicts
of interest with respect to the authorship and/or publication
of this article.
Funding: The authors received no financial support for
the research and/or authorship of this article.
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