CONGENITAL HEART DISEASE
UPDATE ON THE NORWOOD PROCEDURE FOR
HYPOPLASTIC LEFT HEART SYNDROME
Richard A. Jonas*, M.D.
Children’s Hospital, Harvard Medical School, Boston,
MA, USA
Hypoplastic left heart syndrome (HLHS) is not
rare. In the New England Regional Infant Cardiac
Program report of 1980 (1) the incidence of hypoplastic
left heart syndrome was 7.5% among children with
congenital heart disease. Before the advent of
prostaglandin El (2) and reconstructive surgery
in the late 1970s, HLHS was responsible for 25%
of deaths from congenital heart disease in the
first week of life (3). It has been estimated
by Morris et al (4) that approximately 600 infants
are born each year with HLHS in the United States.
There is no single generally agreed
upon definition of hypoplastic left heart syndrome.
However, a reasonable definition is that this
is an anomaly in which there is normal segmental
anatomy and that the left heart structures are
inadequately developed to support the systemic
circulation. Because the right heart is usually
normally developed, it can be connected surgically
to become the single functional systemic ventricle
through application of the Norwood procedure.
HLHS involves various degrees of underdevelopment
of left heart structures. The mitral valve may
be either stenotic or atretic as may the aortic
valve. Therefore, HLHS can be subcategorized into
four main anatomic subtypes based on the morphology
of the left heart valves: aortic and mitral stenosis,
aortic and mitral atresia, aortic atresia and
mitral stenosis, and aortic stenosis and mitral
atresia. The most serious, aortic atresia and
mitral atresia, is the most common anatomical
subtype of HLHS representing approximately 35%
of cases. Aortic stenosis with mitral stenosis
generally represents approximately 20% of cases.
Aortic atresia tends to be associated with a more
severe degree of hypoplasia of the ascending aorta
than does aortic stenosis. Patients in the aortic
stenosis subgroup are part of a continuum of patients
with critical neonatal aortic valve stenosis.
Differentiating these two anomalies can be difficult
and is discussed below.
Typically the ascending
aorta in the neonate with aortic atresia type
of HLHS is 2.5 mm in diameter whereas in the neonate
with aortic stenosis who has HLHS, the ascending
aorta is often 4 to 5 mm in diameter. The arch
of the aorta is quite variable in length and is
hypoplastic to various degrees. It may be interrupted.
A coarctation shelf is present opposite the junction
of the ductus with the proximal descending aorta
in at least 80% of patients(5,6). The ductus
itself is large, often close to 10 mm in diameter.
It is a direct extension of the main pulmonary
artery which is even larger. The right pulmonary
artery arises very proximally from the main pulmonary
artery, usually no more than 2 to 3 mm beyond
the tops of the commissures of the pulmonary valve.
The left atrium is usually smaller than normal
which is exacerbated by leftward displacement
of the atrial septum primum which is often heavily
muscularized. Occasionally the foramen ovale is
severely restrictive. The left atrium may have
a thickened and fibrotic endocardium analogous
to that seen in endocardial fibroelastosis. Occasionally
this process extends into the pulmonary veins
resulting in an obliterative generalized stenosis
of these veins.
Two reports from Children’s Hospital of Philadelphia,
one in 1988 and one in 1990 (7,8), have suggested
that there is an important incidence of extracardiac
anomalies associated with hypoplastic left heart
syndrome including diaphragmatic hernia, hypospadias
and omphalocele. Brain anomalies included malformations
such as agenesis of the corpus collosum and microcephaly.
In contrast to these reports, however, the clinical
impression at Children’s Hospital Boston has been
that major associated anomalies are rare. On the
other hand developmental studies (see below) suggest
that cognitive and motor skills may be below normal
though it remains unclear whether this is related
to perioperative insults which will decrease as
in utero diagnosis becomes more prevalent and
perioperative support methods are improved.
Following birth, the child’s survival is dependent
on continuing ductal patency. In addition there
must be a reasonable balance between pulmonary
and systemic vascular resistance. As pulmonary
resistance falls in the first days and weeks of
life, the child’s oxygen saturation progressively
increases but the child develops congestive heart
failure and may acquire metabolic acidosis.
On
the other hand, if total pulmonary resistance
is very high, for example because of a restrictive
foramen ovate, which prevents free egress of blood
from the left atrium to the right atrium, the
child will be severely hypoxic.
Although it is
possible to increase pulmonary resistance by adding
carbon dioxide or nitrogen to the gas mixture
inhaled by the child, if pulmonary resistance
is too low, a preferable approach is to proceed
with surgery.
The diagnosis of HLHS is being made with increasing
frequency by prenatal ultrasound. In many cases
the diagnosis can be made confidently by 16 to
18 weeks gestation. This has opened the possibility
of prenatal intervention by balloon dilation of
the stenotic or atretic aortic valve. It is important
to remember however that although prenatal echo
is sensitive to the diagnosis of HLHS it is not
highly specific and can over diagnose the problem.
We have seen a number of cases where babies required
only coarctation or aortic valve intervention,
and on occasion, no intervention at all despite
a prenatal diagnosis of HLHS.
The diagnosis of
HLHS after birth is made by echocardiography.
The physical findings of a slightly cyanotic neonate
in respiratory distress with a variable degree
of general circulatory collapse are non-specific.
Likewise, the appearance of the chest X ray of
a slightly enlarged heart with congested lung
fields does not help distinguish this anomaly
from many others.
The problem of distinguishing HLHS from critical
stenosis of the neonatal aortic valve is one of
the major diagnostic challenges in managing this
anomaly. The Congenital Heart Surgeons has developed
a calculator (available at www.chssdc.org) (9),
which is the most helpful tool for determining
whether an individual child should be managed
with a Norwood procedure or if the left heart
structures are sufficiently well developed to
attempt to achieve a biventricular circulation
by performing a balloon aortic valvotomy.
Our current technique for first stage palliation
of hypoplastic left heart syndrome is based on
the procedure described by Norwood et al in 1983
but now incorporates the shunt modification described
by Sano (10). Approach is through a median sternotomy.
The thymus is partially excised to allow access
to the aortic arch. It is not necessary to dissect
the arch vessels at all. It is important to place
a 6/0 marking suture on the right side of the
tiny ascending aorta to help guide the aortotomy
which will be made later.
Following heparinization. an 8 French flexible arterial cannula is inserted
in the mid-ductus and an 18 French venous cannula
is placed in the right atrium through the atrial
appendage. Immediately after beginning bypass,
a 5/0 prolene suture ligature is tied around the
proximal ductus. We no longer place tourniquets
around the branch pulmonary arteries or around
the arch vessels as these may cause intimal injury
and subsequent stenosis. The child is cooled over
about 15 to 20 minutes to a rectal temperature
of less than 18C.
During cooling, the proximal
main pulmonary artery is divided 2 to 3mm above
the tops of the commissures of the pulmonary valve.
The distal divided main pulmonary artery is closed
obliquely by direct suture. Although many recommend
using a patch for closure of the distal pulmonary
artery, we believe that long term growth of the
central pulmonary arteries is improved if only
autologous arterial tissue is used. This also
avoids a central bulge of the pulmonary arteries
which can result in tortion and kinking of the
branch pulmonary artery origins.
Fig 1:
The stage 1 Norwood procedure involves anastomosis
of the proximal divided main pulmonary artery
to the ascending, arch and proximal descending
aorta. A small “v” is cut in the proximal pulmonary
artery to facilitate the side to side anastomosis
between the tiny ascending aorta and main pulmonary
artery. The remainder of the anastomosis is supplemented
with a cuff of cryopreserved homograft. The distal
anastomosis of the Sano shunt can be performed
to the site of closure of the distal divided main
pulmonary artery or to a separate longitudinal
arteriotomy close to the origin of the left pulmonary
artery. 6/0 Gortex suture is employed.
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Fig 2:
The reconstruction of the neoaorta using a cuff
of homograft tissue has been completed. The proximal
anastomosis of the Sano shunt is fashioned to
an oblique incision in the infundibulum of the
right ventricle.
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The distal anastomosis of the Sano shunt is now
constructed as shown in Figure 1 or to a longitudinal
arteriotomy, which is made between the left pulmonary
artery takeoff and the main pulmonary artery closure.
For neonates between 2.0 and 3.5 kg, a 5 mm stretch
Gortex tube graft should be selected.
By that time, an appropriate homograft
would have been selected and thawed. It should
be shaped for the arch reconstruction according
to the length and diameter of the arch. Bypass
is then discontinued and cardioplegia is infused
through a side arm on the arterial cannula.
During perfusion, the head vessels and distal
aorta are temporarily occluded with forceps.
The arterial cannula is removed and the venous
cannula is left open to drain. The ductus
is divided at its junction with the descending
aorta and redundant ductus tissue is excised.
The resulting arteriotomy is extended at least
5 mm distally into the descending aorta.
Proximally, the arch and ascending
aorta are filleted open to the level of division
of the main pulmonary artery (Figure 1).
An anastomosis is fashioned between the proximal
portion of the divided main pulmonary artery and
the filleted aorta with a supplementary cuff of
arterial wall (Figure 2) (11).
After division of the main pulmonary artery.
a 2 to 3 mm V-shaped incision is made on the proximal
pulmonary artery. At least three interrupted 7/0
sutures are placed at the apex of the descending
aortotomy.
The atrial septum primum must be completely excised.
The septectomy is usually performed through the
venous cannulation site in the right atrial appendage.
Many different shunts have been described during
the 20 years that the Norwood procedure has been
used (10-12). Our current preference is a Sano
shunt from the right ventricle to the pulmonary
bifurcation using a stretch Gortex tube graft.
The important advantage of the Sano shunt is that
flow occurs only during systole. There is no competition
between pulmonary and coronary blood flow during
diastole as is the case with the Blalock shunt.
This is the most likely explanation for the very
much improved stability of neonates which is seen
following a Sano shunt.
Norwood’s original technique did not include
use of a cuff to supplement the aortic to pulmonary
anastomosis. Recently the technique has been repopularized.
However, the important disadvantage of this modification
is that it can create a bowstring effect of the
reconstructed aorta over the left main bronchus,
which can result in either bronchial compression
or left pulmonary artery stenosis.
Many ingenious technical variations have been
described which permit the circulatory arrest
time to be reduced or eliminated. Many of these
methods involve retrograde perfusion through a
Blalock shunt. However, these methods involve
a risk that the surgical team will have a false
sense of safety and will extend the total repair
time to a dangerous degree. It is unclear how
homogeneously blood is distributed. In the future,
it will be important for proponents of these techniques
to demonstrate that they are as safe as a limited
period of deep hypothermic circulatory arrest
using appropriate neurodevelopmental studies.
An oblique incision is made in the infundibulum
of the right ventricle being careful to avoid
injury to pulmonary artery branches and the pulmonary
valve (Figure 2). The muscular edges can be undermined
if necessary. The anastomosis of the beveled Goretex
tube graft is performed with continuous 5/0 Gortex
suture.
If there is any doubt as to the child’s
stability, the sternum should not be approximated. Since
we began using the Sano shunt, we have found that
it is usually possible to close the chest unlike
the experience with the Blalock shunt where it
was frequently necessary to leave the sternum
open.
Management of the neonate following the Norwood
procedure which incorporates a Sano shunt has
been very much simplified relative to the management
with a Blalock shunt. The child with a Blalock
shunt frequently has a tendency to excessive pulmonary
circulation. Maneuvers must be applied to maximize
systemic blood flow relative to pulmonary blood
flow. Monitoring of systemic venous saturation
can be a helpful adjunct to assess the success
of such maneuvers. However, when a Sano shunt
has been performed, management is very much more
routine. When bleeding no longer appears to be
a problem as can be facilitated by routine use
of aprotinin, then the child should be withdrawn
from anesthesia and weaning from the ventilator
can start. Generally, a spontaneous diuresis is
established within 24 to 48 hours by which time
extubation can be performed.
The principles of follow-up after stage 1 surgery
for HLHS are identical to those applied to any
child with single ventricle physiology in whom
a Fontan procedure is anticipated. Attention should
be directed towards optimal pulmonary artery development,
maintenance of ventricular function and maintenance
of low pulmonary vascular resistance, including
absence of restriction at the level of the atrial
septal defect. It is important to recognize that
the infant is likely to outgrow a Sano shunt earlier
than a Blalock shunt because flow is limited to
systole. All patients should be catheterized or
undergo MRI scan by 4 to 5 months of age irrespective
of clinical progress. If there is a suspicion
by echocardiography that there is a problem with
development, either of the aortic arch or pulmonary
artery, then catheterization should be performed
sooner. If the catheterization demonstrates a
problem such as distortion of the pulmonary arteries,
then a bidirectional cavopulmonary (Glenn) shunt
should be undertaken including an associated pulmonary
arterioplasty. Other indications for early application
of a cavopulmonary shunt have included the need
for aortic arch reconstruction, the need for atrial
septal defect enlargement, early outgrowth of
the Sano shunt resulting in unacceptably low oxygen
saturation (less than 70 to 75%) and the development
of tricuspid regurgitation or right ventricular
dysfunction secondary to excessive volume load
on the ventricle. Cavopulmonary shunt procedures
have been successfully performed in infants as
early as 2.5 to 3 months.
The management of the child with hypoplastic
left heart syndrome following a bidirectional
Glenn is essentially generic as for the management
of any patient traversing a single ventricle pathway.
Cardiac catheterization is usually recommended
approximately 12 months following the bidirectional
Glenn shunt. A fenestrated Fontan procedure should
be performed within 6 months of the catheterization
procedure.
The largest and most comprehensive outcome analysis
of patients undergoing a stage-1 Norwood procedure
was reported by the Congenital Heart Surgeons
Society in 2003 (13). 985 neonates with either
critical aortic stenosis or atresia were enrolled
between 1994 and 2000. Seven hundred and ten of
the 985 patients underwent a stage-1 Norwood procedure.
Survival was 76% at one month, 60% at one year
and 54% at 5 years. Risk factors for death included:
patient specific variables such as lower birth
weight, smaller ascending aorta and older age
at the time of the Norwood procedure; institutional
variables including institutions enrolling less
than 10 neonates and also two institutions enrolling
more than 40 neonates; and procedure variables,
including shunt originating from the aorta, longer
circulatory arrest time, and the technique of
management of the ascending aorta.
Several reports
suggest that the results of the Norwood procedure
have improved markedly over the last 5 years.
For example, Daebritz reviewed 194 patients who
underwent a stage-1 Norwood procedure between
1990 and 1998 at Children’s Hospital Boston (14).
The operative mortality decreased from 38.5% between
1990 and 1994 to 21.4% after 1994 (p=0.02).
Introduction
of the Sano shunt at Children’s Hospital Boston
in 2002 has been associated with further reduction
in stage 1 mortality, which is now less than 10%.
The largest single institutional report is by
Mahle and colleagues from Children’s Hospital
of Philadelphia (15). 840 babies underwent the
Norwood procedure between 1984 and 1999. The hospital
mortality between 1984 and 1988 was 84% while
between 1995 and 1998, hospital mortality was
29%. Bove et al (16) described the outcomes for
253 patients who underwent the Norwood procedure
at the University of Michigan between 1990 and
1997. Hospital mortality was 24%. Mortality was
strongly influenced by the presence of associated
non-cardiac congenital conditions such as severe
preoperative obstruction to pulmonary venous return.
Survival following the second stage hemi-Fontan
procedure with bidirectional Glenn was 97% and
survival following the Fontan procedure was 88%.
In 2002, Twedell et al (17) described 115 patients
who underwent the Norwood procedure between 1992
and 2001. Hospital mortality was 47% between 1992
and 1996 but between 1996 and 2001 hospital survival
was 93%. Improving results have also been reported
by Azakie et al (18) from Toronto Canada as well
as Ishihino (19) from Birmingham UK.
In 2003, Malec et al (20) described 68 children
following a Stage 1 procedure. The mortality for
the 31 patients who had modified Blalock shunts
was 35%. In patients who had the Sano shunt the
mortality was 5%. Both Sano et al (10) and Norwood
et al have also described improved results with
the Sano modification relative to placement of
a modified Blalock shunt.
Wernovsky et al (21) reviewed 133 patients who
underwent developmental assessment following the
Fontan procedure. The mean full scale IQ was 95.7
+/- 17.4. A diagnosis of hypoplastic left heart
syndrome as well as other complex anatomical forms
of single ventricle were both associated with
a worse outcome. This study must be interpreted
carefully with the understanding that many of
these children underwent their stage 1 Norwood
procedure during the 1980s when long periods of
circulatory arrest were employed. Even more importantly,
the technique of circulatory arrest at that time
used a very alkaline pH, severe hemodilution,
rapid cooling and a relatively short period of
cooling.
Although it is possible that there is
an inherent association between suboptimal developmental
outcome and hypoplastic left heart syndrome, a
more likely explanation is that the technique
of cerebral protection employed during the sequence
of three operations was suboptimal in the time
frame during which these patients were managed.¨
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*Cardiovascular Surgeon-in-Chief, Children’s Hospital and William E.Ladd Professor of Surgery,
Children’s Hospital, Harvard Medical School
Correspondence to Dr. Richard A. Jonas, M.D., Children’s Hospital, Harvard Medical School, 300 Longwood
Avenue
Boston, MA 02115, USA. Phone: 617-355-7930 Fax: 817-730-0928 E-mail:richard.jonas@tch.harvard.edu
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