Download Aortic atresia

Aortic Atresia or Hypoplastic
Left Heart Physiology
Seoul National University Hospital
Department of Thoracic & Cardiovascular Surgery
Hypoplastic Left Heart Syndrome
• Definition
A developmental anomaly in which the aortic valve
is atretic and the ascending aorta is hypoplastic
* With few exceptions, there is in additional mitral atresia or mitral
valve hypoplasia, severe left ventricular hypoplasia, & intact
ventricular septum, called Hypoplastic left heart syndrome.
• History
Canton
: 1st description of aortic atresia in 1850
Brockman
: Coexisting maldevelopment of left side of heart
Noonan & Nadas : Hypoplastic left heart syndrome in 1958
Cayler
; RPA-ascending aorta, bilateral PA bands in 1977
Norwood
: Neonatal reconstructive surgery of HLHS in 1980
Bailey
: Allograft heart transplantation in 1985
Hypoplastic Left Heart Physiology
1. Inability of the left heart to sustain an adequate cardiac output
following birth because of underdevelopment of one or more
left heart structures despite surgical or medical intervention
2. The term hypoplastic left heart physiology rather than the more
common and entrenched term hypoplastic left heart syndrome
because it more accurately describes the entities
3. Definition of hypoplastic left heart is physiologic, not
morphologic, despite morphologic abnormalities being the
underlying cause of left heart inadequancy.
4. An important implication of the term hypoplastic left heart
physiology is that the left heart is incapable of sustaining
systemic cardiac output, thereby limiting therapeutic options
to reconstructions of single ventricular pumping or to
transplantation
Hypoplastic Left Heart Syndrome
Classification
Class I : Isolated cardiac anomaly
Class II : Two congenital anomalies affecting left
ventricular outflow
Class III : More than two anomalies, or two with coexisting
LV or ascending aortic or aortic arch hypoplasia
Class IV : Aortic atresia
* Anomalies : Congenital MV disease
LV hypoplasia.
Subvalvar, valvar, supravalvar AS
Ascending aortic or arch hypoplasia
IAA or COA
Hypoplastic Left Heart Syndrome
Pathophysiology
• HLHS is characterized by marked hypoplasia or absence
of the left ventricle, and severe aortic hypoplasia places
the work of the pulmonary and systemic perfusion solely
on the right ventricle.
• Pulmonary venous return enters the right atrium via an
interatrial communication and systemic perfusion is
dependant on a PDA.
• Cyanosis, congestive heart failure, and systemic
hypoperfusion results as pulmonary vascular resistance
decreases and pulmonary blood flow increases at the
expense of systemic blood flow.
Hypoplastic Left Heart Syndrome
Morphogenesis & morphology
• Currently, it is not clear whether the etiology of
hypoplastic left heart physiology is similar an all cases.
• Primary morphologic abnormalities at the aortic valve,
mitral valve level, left ventricular myocardial level, or
atrial septal level could all in theory lead ultimately to
hypoplasia of the entire left side of the heart as gestation
progresses
• In hypoplastic left heart physiology, the heart is enlarged
to about twice normal weight for age.
• Among the 4 major categories defined by the left-sided
valves, aortic atresia and mitral atresia is the most
common form , representing two third, & aortic stenosis
with mitral atresia is the least common form ( 5% ).
Morphology of HLHS
Morphology of HLHS
Hypoplastic Left Heart Syndrome
 Morphology
1. Aortic valve & ascending aorta
Absent valve, diminutive sinus, coarctation in 80%
2. Left ventricle & mitral valve
Hypoplastic & intact ventricular septum in 95%
Mitral valve atretic in 1/3, hypoplastic in 2/3
Variable degree of endocardial fibroelastosis, hypertropic muscle
Normal LV cavity with VSD in 5%
3. Right ventricle ; enlarged and diffuse hypertrophy, variable TR
4. Atria & atrial septum
Left atrium : small, thick walled, Right atrium : large
Atrial septum : thick, interatrial communication ( PFO)
5. Other associated cardiac anomalies ;
Uncommon
Juxtaposed atrial appendages & double tricuspid orifice
6. Associated noncardiac anomalies ; frequently ( 25 -40%)
Hypoplastic Left Heart Syndrome
 Clinical Features & Diagnosis
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Mild cyanosis & respiratory distress in newborn
Rapid deterioration with CHF & death within
a week of birth, ductal closure is inevitable with
variable times
Hyperactive RV precordial impulse & midsystolic
murmur with S2 accentuation, poor peripheral pulse
Chest X ray : cardiomegaly with pulmonary plethora
EKG : RVH, RAD
Echocardiography
Cardiac catheterization & cineangiography
Hypoplastic Left Heart Syndrome
 Natural history
1. Incidence
4th common CHD ( 4~7% of CHD), 70% male
2. Death
40% survive beyond neonatal period,
Uncommon survival beyond 6 weeks of age
25% of cardiac deaths during 1st week of life
15% of cardiac death during 1st month of life
3. Perinatal survival is dependent on PDA
4. Associated genetic & extracardiac anomalies
in 20~40% (Chromosomal & major, minor CNS
abnormalities, esp. micrencephaly in 25% in autopsy)
Hypoplastic Left Heart Syndrome
Preoperative management
• After diagnosis, resuscitation & PGE1 is initiated
• Avoiding supplemental inspired oxygen is critical to
overall strategy; 21% oxygen or even lower FiO2 helps
maintain tone in the pulmonary microvascularture
• Reasonable balance of Qp & Qs include PaO2 about
40mmHg, and systemic diastolic pressure greater than
30mmHg
• Ideal time for surgery is about age 3 to 5 days.
• It is not uncommon for organ systems to recover fairly
rapidly, but then plateau short of complete recovery.
Hypoplastic Left Heart Syndrome
Preoperative risk factors
• The impact of these risk factors on mortality
are institution dependent and include
noncardiac anomalies or genetic syndromes,
lower birth weight, postnatal diagnosis
• Additional cardiac risk factors including severe
preoperative obstruction to pulmonary venous
return, ventricular dysfunction, and moderate
to severe atrioventricular valve regurgitation.
• Earlier reports found aortic atresia to be a risk
factor for death
Hypoplastic Left Heart Syndrome
 Techniques of operation
1. Norwood first-stage procedure
Maintain PaCO2 40-45mmHg before operation
2. BCPC as interim procedure
3. Fontan operation
4. Cardiac transplantation
Norwood Operation
Autologous and interdigitating techniques.
Goals of Reconstructive Surgery
 The overall goal of reconstructive surgery is similar
to that for single ventricle physiology, that is ,
establishment in the neonatal period of an effective
mixed circulation in which pulmonary and systemic
blood flow are well balanced.
• A completely unobstructed systemic arterial pathway
from the right ventricle to all organs
• A restrictive connection between systemic and
pulmonary circulations such that Qp and Qs are
adequately balanced
• An unobstructed flow of pulmonary venous return
across the atrial septum to the right atrium
Norwood Operation
Surgical Process of HLHS
Norwood Operation
 Results
1. Survival
Early death & Time-related survival
2. Incremental risk factors for death
1) No morphologic risk factors
2) Small size of ascending aorta (< 2mm)
3) Tricuspid regurgitation
3. Hemodynamic and morphologic results
1) Nonrestrictive opening between two atria
2) Important tricuspid regurgitation
3) Systolic pressure gradient
4) Most patients have a Qp/Qs of 0.8~1.5, and
Pulmonary vascular resistance > 4u ; in 20%
Pulmonary artery distortion ; in 12%
RV end-diastolic pressure elevation ; in 10%
Norwood Operation
Pulmonary artery compromise
• Mechanisms contributing to pulmonary artery
compromise after the Norwood procedure are multiple,
and include narrowing at the ductal remnant site,
extrinsic compression by the neoaorta or the ductal
stump, and distortion by the modified Blalock-Taussig
shunt (BTS) insertion.
• Particularly at risk for these influences is the
retroaortic segment of the common pulmonary artery
and the left pulmonary artery (LPA).
• Compromised early flow to the LPA may contribute to
LPA hypoplasia over time, which can increase
morbidity of the subsequent bidirectional
cavopulmonary anastomosis & Fontan procedures
Modification of Shunt
Drawing representing the insertion point of a BTS onto the
pulmonary artery premodification (A), and postmodification,
with an oblique anastomosis to direct pulmonary blood flow
preferentially into the retroaortic pulmonary artery (B).
Norwood Operation
Survival
• Early deaths
Myocardial ischemia
Imbalance of systemic & pulmonary circulation
Subsequent multi-organ failure
• Late deaths
Not insignificant recently and reflects the delicately
balanced nature of circulation
Residual defects
Norwood Operation
Risk factors for deaths
1. Abnormal coronary flow patterns
2. Diminished coronary reserve
3. Neurologic complications
4. Residual lesions
5. Ventricular function
Hypoplastic Left Heart Syndrome
 Results of Fontan operation
1. Survival
Early deaths
Time-related survival
2. Incremental risk factors for death
1) Tricuspid regurgitation
2) Sudden reduction in ventricular volume
immediately after Fontan procedure
Indications for Operation
• The diagnosis of aortic atresia( hypoplastic left
heart physiology) indicates the presence of a
fatal disease ; death usually occurs within 1
month of birth and certainly within 1 year.
Surgical intervention is therefore advisable
unless contraindicated by economic,
institutional, legal problems
• The treatment begins as soon as the diagnosis
has been made, or the child is born.
Norwood Procedure
MBTS vs RV-PA conduit
• Advantages of mBTS include improved pulmonary
artery growth owing to the antegrade flow throughout
cardiac cycle.
• Lower diastolic pressures with the mBTS compromise
coronary blood flow & impact cardiac function.
• RV-PA conduit provides antegrade flow during systole
but diastolic flow reversal, adding to the ventricular
volume load & diminished pulmonary artery growth.
• MBTS has a recognized incidence of acute shunt
occlusion, less common with larger RV-PA conduit.
• Ventriculotomy carries an unknown risk for late
arrhythmia & diminished ventricular function
Norwood Procedure
Application of RV-PA conduit
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Low birth weight
Preoperative hypotension
Tricuspid regurgitation
Pulmonary venous obstruction?
Right ventricle dysfunction?
Small aorta
Norwood Procedure
Recent results
• It is well demonstrated that single-institution results
improve over time independent of significant changes in
surgical approach
• These improvements are thought to reflect an increased
incidence of prenatal diagnosis, surgical experience,
improvement in perioperative care with close attention
to low cardiac output syndrome, and less tangible
human factor.
• RV-PA conduit compared with more contemporary
mBTS controls showed no difference in survival, but
reported a more stable postoperative course
RV-PA Conduit
RV-PA Conduit
RV-PA Conduit
Norwood Procedure
RV-PA Conduit
RV-PA Conduit Procedure
1st_ Stage Reconstruction
• Choice of graft ; infant weight more than 3 Kg ; 6mm graft,
2-3Kg ; 5mm graft, less than 2 Kg; 4 mm graft. 50% of the
predicted normal size of the main pulmonary artery
Hybrid Palliation
• Hypoplastic left heart syndrome with aortic atresia is depicted after
bilateral pulmonary artery banding (stippled areas) and ductal stenting
(crosshatched area). MPA-IA shunt provides source of blood flow to
aortic arch (small arrows) in patients in whom retrograde flow across
aortic isthmus is obstructed (large arrow).
RV-PA Conduit
Advantages
• This novel procedure may be particularly beneficial to
low-birth-weight infants with HLHS.
• It would be reproducible for many less experienced
surgeons with application of the RV-PA shunt.
• The pulmonary bed was not subjected to nor dependent
on diastolic flow, and there should be less change in
pulmonary blood flow with pulmonary hypertensive
crises or during resuscitation
• Higher diastolic blood pressures and lower Qp/Qs ratios
are associated with a more stable and efficient systemic
circulation.
• Pulmonary perfusion restricted to systole leads to a
lower Qp/Qs ratio and demands more intensive
ventilatory support during the first postoperative days.
Norwood Procedure
 Questions in RV-PA conduit
• Optimal shunt size and shunt material
• Growth & distortion of pulmonary arteries
• Effects of the small ventriculotomy on right
ventricular function
• Potential risk of arrhythmia
• Ease of second stage palliation
• Potential injury of pulmonic valve
• Uncertainty to thrombosis & stenosis
Hypoplastic Left Heart Syndrome
Special situations & controversies
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Aortic atresia with large VSD
Borderline hypoplastic left heart syndrome
Use or avoidance of circulatory arrest
Use of RV-PA conduit
Valved conduit
Nonvalved conduit
Norwood Procedure
Laryngopharyngeal dysfunction
• Norwood procedure, like other operations on the aortic
arch, involves mobilization of the recurrent laryngeal
nerve, operative damage to the nerve is one potential
source of postoperative swallowing dysfunction.
• Postoperative vocal fold paralysis should generally be
considered to be permanent dysfunction.
• It should be noted that the voice of an infant can
improve despite persistence of vocal fold paralysis due
to the plasticity of the glottis and the ability of the
opposite vocal fold to compensate
Swallowing Function
Abnormalities
• Establishing adequate oral intake is generally the last
clinical hurdle to be overcome before hospital discharge
• Although we were unable to identify predictors of
swallowing dysfunction among our patients, its causes
are likely multiple.
• Normal infants can have swallowing abnormalities,
variability in suck and oral transit time, vallecular
residuals after swallowing, & hesitation of bolus transit
into the cervical esophagus
• Pharyngeal stage of swallowing, controlled by the
medulla oblongata, is not well developed in neonates
and might contribute to these findings
Swallowing Dysfunction
Management
• Risk factors for dysphagia included age less than 3
years, preoperative intubation, and transesophageal
echocardiographic probe in patients less than 5.5 kg.
• Routine assessment for swallowing dysfunction and
appropriate tailoring of feedings might decrease
interstage mortality.
• Aspiration is one of the most serious abnormalities of
swallowing function
• A nasogastric tube, compared with a gastrostomy tube,
might be more difficult to manage at home, impair
swallowing function and competence of esophageal
sphincters, and might worsen gastroesophageal reflux.