The Single Ventricle
Karim Rafaat, M.D.
The title “single ventricle” includes those
lesions designated as both
HLHS
HRHS
HLHS is far more common, and the
strategy for palliation of both lesions
similar, so I will not mention HRHS
HLHS - History
First described in 1952 by Lev as the
pathologic complex “hypoplasia of the
aortic tract”, included cases of:
hypoplasia of the aorta and VSD
hypoplasia of the aorta with aortic stenosis or
atresia, with or without mitral stenosis or
atresia
In 1958, Noonan and Nadas termed these
lesions as “hypoplastic left heart
syndrome”.
Embryology
The embryologic cause is not fully
understood.
It probably results from a limitation of
either LV inflow or outflow, such as the
development of severe AS early
Decreased antegrade flow through LV
most common cause is mitral atresia
decreased division of cardiac myocytes
Genetics
Familial inheritance:
Autosomal recessive and multifactorial inheritance
have both been postulated.
Sibling recurrence risk: 0.5%
Sibling recurrence for all other cardiac malformations:
2.2%
Definable genetic disorder (28%):
Turner Syndrome
Noonan Syndrome
Trisomy 13, 18, 21, or other microdeletion syndromes
Epidemiology
Uniformly lethal prior to 1980
Each year, approximately 1000 infants with
HLHS are born in the US.
Prevalence: 1 per 6000-7000 live births.
In pathologic series, it accounts for 1.4-3.8% of
congenital heart disease.
Third most common cause of critical CHD in the
newborn.
23% of all neonatal mortality from CHD
Male predominance: 57-70%.
Anatomy
Underdevelopment of
the left side of the
heart
atresia of the aortic or
mitral orifice
hypoplasia of the
ascending aorta.
The left ventricle may
be small and
nonfunctional or
totally atretic
Pulmonary venous
return from LA to RA
through a large PFO
or ASD
Systemic venous
blood mixes with
pulmonary venous
blood in the RA and
RV
RV ejects blood into a
large MPA
Systemic circulation is
supplied in parallel
with pulmonary
circulation through a
PDA
Multiple obstructions
to systemic flow
Aortic valve atresia
Arch hypoplasia
Place systemic flow at
risk
Blood flow to the
coronary and cerebral
circulations is retrograde
Usually little or no flow
through aortic valve
Postnatal decline in PVR
places systemic, and
especially the ductal
dependant and
retrogradely supplied
coronary and cerebral
vascular beds at risk for
hypoperfusion secondary
to pulmonary run-off
Pathophysiology
Relative Qp and Qs
determined via
resistances of
respective vascular
beds
Ventricle must supply
both Qp and Qs
Single right ventricle
has at least twice the
volume load of an in
series ventricle
Significantly volume
overloaded
The aim of initial management is to
optimize Qp and Qs in a manner that
provides adequate end organ oxygen
delivery without overloading the single
ventricle
Remember my last lecture?
This balancing act is only temporizing and
serves to allow pt to survive to definitive
treatment
Treatment options
Supportive care
Only option up to 25 years ago
Is still main option of treatment in many
countries
Staged reconstruction
Stage I Norwood Procedure
Stage II Bi-directional Glenn or Hemi-Fontan
Stage III Fontan Procedure
Transplant
Goals of Surgery
Unobstructed systemic blood flow
To maximize oxygen delivery and minimize
ventricular hypertrophy
Limited pulmonary blood flow
To minimize ventricular volume load and the risk of
pulmonary hypertension
Unobstructed pulmonary venous return
To minimize secondary pulmonary artery
hypertension
Minimize likelihood of pulmonary artery
distortion
Avoid dysrhythmias
All these goals, achieved in a timely fashion,
circumvent the major risk factors for poor
outcome post-Fontan:
Ventricular hypertrophy causing diastolic dysfunction
Elevated PVR or pulmonary artery pressure
AV valve regurgitation
Ventricular systolic dysfunction
The reasons why the above hurt the post-fontan
heart will be discussed later
Stage I – Norwood palliation
The goal of the Norwood is to stabilize and
balance the parallel circuit, protect the
pulmonary vascular bed and preserve
ventricular function
Adequate oxygen delivery allows for the
growth necessary for a hemi-fontan or BDG to
be performed
Native ascending and transverse
aortic arch is incorporated into a neoaorta
Neo-aorta created by augmenting
native arch with autologous
pulmonary homograft
Neo-aorta is attached to the proximal
pulmonary artery trunk
Neo-aorta provides systemic outflow
Important that the neo-aorta is free of
obstruction
Obstruction is poorly tolerated by the
single ventricle and is associated
with increased interstage mortality
Distal MPA is closed
Pulmonary flow is
provided by a
restrictive shunt from
the right innominate
artery to the RPA
Modified BTS
Post-Norwood Anatomy
Post-Norwood issues
The hope is that now
RBTS + Rp = Rs
So the circulations are
balanced and volume
work is minimized
Meaning for a given
required Qs, total Q can
be less as the ratio is
more favorable
But……
The ventricle has just been through hypothermic
cardiopulmonary bypass with myocardial
ischemia/arrest
Vascular endothelium of the systemic and
pulmonary circulations have also been subjected
to bypass and injury
Combined effect is a systemic inflammatory and
adrenergic stress response
The ventricle can also exhibit a low cardiac
output syndrome in the first 12-24 hours post op
All vascular beds show signs of
endothelial dysfunction
Evidenced by increased resistance
This may tip the balance of flow towards the
pulmonary circulation
Systemic oxygen demands may be unable
to be met by the post-op ventricle
Leading to anaerobic metabolism, acidosis
and worsening function
LCOS
Low Cardiac Output
Low systemic cardiac output can be due to
Globally decreased ventricular function
Elevated Qp:Qs
AV valve regurgitation
How to discern between the above?
Echocardiography
Evaluates pump function and rules out AV
valve regurg
Arterial-venous oxygen saturation
difference
An A-V DO2 more than 40% suggests
inadequate tissue delivery of oxygen and low
systemic cardiac output
OR…Lactate level plus base deficit
Good echo function plus high A-V DO2 =
Qp>Qs
Treatment
One must pay attention to both TOTAL CO
and the Qp:Qs ratio
The ratio can be altered by maneuvers
discussed in my last talk
Total CO can be increased by careful
selection of vasoactive agents
Want to avoid tachycardia and increasing afterload
Milrinone
Nesiritide
Dopamine
Hypoxemia
Pulmonary Venous desaturation
Atelectasis
pulmonary edema
pneumothorax
Systemic venous desaturation
Anemia
Low cardiac output
Decreased pulmonary blood flow
Elevated PVR
Pulmonary venous hypertension
Pulmonary artery distortion
Restrictive systemic to pulmonary shunt
Gotta rule out the top two, then, think about echo or cath
to rule out the anatomic causes
Which need a surgeon….
Coronary circulation
Single right ventricle coronary blood flow
occurs predominantly in diastole
Like an in series LV
When pulmonary flow is supplied by a
shunt from a systemic artery, increases in
SVR lead to increased pulmonary flow,
and increased diastolic pulmonary run-off
This can lead to myocardial
ischemia….and sudden death
Which is why
“Leaving a kid in Norwood physiology is like
taking a walk through Watts at midnight”
Dr. Cocalis
The Wall of Wo
Sudden death post Norwood
Unpredictable and sudden
Experienced centers report survival between 63-94%1
Inter-stage mortality of 10-15%2
Rapid fall in PVR, or increase in SVR
Steal from coronary arteries
lower pressure in pulmonary circulation throughout cardiac
cycle
The Journal of Thoracic and Cardiovascular Surgery 2003;126(2) 504-509
Arch Dis Child Fetal Neonatal Ed 2005;90:F97-102.
• Bartram et al, Causes of
Death after the Modified
Norwood procedure: A study
of 122 postmortem cases,
Ann Thorac Surg, 1997
122 cases over 15 years
The leading causes of death
largely correctable surgical
technical problems
associated with perfusion of
the lungs (36%), of the
myocardium (27%), and of
the systemic organs (14%).
The proposed solution to
surgical manipulation of the coronary arteries
the pulmonary diastolic run-off through the
modified BTS
Is an RV to PA conduit
First described by Norwood in 1981
Reintroduced by Japanese surgeon Sano in
the late 1990’s
The Sano modification
Directly supplies pulmonary
flow via the RV
Aortic diastolic runoff does
not occur
Post-op diastolic BP is higher
Coronary perfusion is
improved
Blood flows only during
systole
Reducing total pulmonary
blood flow
Improves Qp:Qs, thus
protecting pulmonary
vascular bed and decreases
volume load on the RV, giving
it a greater chance to return
to normal size and function
Less distortion of the
pulmonary arteries
than is seen with a
BTS
Improved growth of
PA’s
Trade off’s
Ventriculotomy
Increases potential for low cardiac
output syndrome
The damage to the ventricular wall
may be offset by the better
coronary perfusion…..
Increased volume load secondary
to reversed diastolic flow in a nonvalved conduit
Possibility of shunt occlusion
Concern of RV arrhythmias post
ventriculotomy
Not confirmed by present studies,
though
Januszewska et al, RV to PA shunt and modified BTS in
preparation for hemi-Fontan procedure in children with
HLHS, European Jour Cardiac Surg, 27, 2005
78 children –
27 underwent Norwood with BTS
51 underwent Sano modification
Those who underwent Sano, at time of hemi-fontan
Larger pulmonary arteries
Which means lower resistance to the passive flow that will be
supplying the lungs after the BDG or Fontan
Less RVH
Better diastolic function, and so lower filling pressures required
Lower Qp:Qs (0.8 vs 1.27)
Less pulmonary vascular remodeling and less ventricular volume
load
Pizzaro et al, Right Ventricle to Pulmonary Artery
Conduit Improves Outcome after stage I Norwood for
HLHS, Circulation, 2003; 108
Retrospective cohort review
36 RV to PA conduits
20 BTS
Those with RV to PA conduits
Higher diastolic BP
Lower PaO2
Indicating lower Qp:Qs secondary to less diastolic run-off
Less ventilatory manipulations were required for Qp:Qs
management
33/36 survived to BDG vs 14/20 in the BTS group
Other Considerations
Risk for shunt occlusion
Low sats lead to high Hct’s, which increases risk of
thromboembolic complications
Need to be well hydrated
Shunt failure
Slowly occurs as pt grows, but shunt does not
Leads to slowly progessive cyanosis as oxygen consumption
increases in a growing pt
VENOUS ACCESS
Any venous embolus may reach systemic vascular
beds
Watch for air bubbles, clots, meticulously….
Glenn Hughes – A Village Person
Bidirectional?
Stage II – Partial Cavopulmonary
Anastomosis
After stage I, there are two problems
Cyanosis
Excessive ventricular volume load
The Fontan fixes both of the above, but
must come after an intermediate step…
Why?
Reasons for a staged repair
The fontan requires low PVR to allow for
passive pulmonary flow
PVR does not reach nadir until 6-8 months
Furthermore, following the high Qp:Qs state of prenorwood, the pulmonary vasculature can be
reactive
Which is exacerbated by the stress of bypass
The parallel circulation
single ventricle is relatively
hypertrophied and dilated
secondary to volume
overload
Shifts Frank-Starling curve
down and to the right
Means the norwood
ventricle is very volume
sensitive
A loss of ventricular filling
secondary to increases in
PVR would lead to critically
decreased CO
The solution is a staged procedure that
allows for more gradual ventricular
unloading and remodeling
Also allows for adjustment of the upper
body venous and lymphatic systems to
deal with an increase in venous pressure
prior to the Fontan
Usually performed around 4-6 months of
age
Bidirectional Glenn
The RV/PA or BT shunt is
removed
This volume unloads the
ventricle
Critical in improving
outcome in single ventricle
palliation
SVC is anastomosed end
to side with the RPA
Is more compatible with
an extracardiac fontan
procedure down the line
Hemi-Fontan
Similar to BDG
physiologically
Has additional
proximal SVC and
inferior RPA
anastomosis
RA communication
closed with a patch
More suited for
eventual lateral baffle
Fontan
Stage II Physiology
Half the blood to the heart
comes from the IVC, half
from the pulmonary veins
Qp:Qs is now 0.5
SaO2 about 75-85%
Infants with bigger heads
have higher sats
Excessive volume load is
now eliminated
Ventricle now pumps only
Qs
Decreased cavity
dimension and increased
wall thickness improves
tricuspid function
Preload is not critically dependant upon
unimpeded pulmonary flow
Increases in PVR won’t significantly affect
systemic circulation
Qp driving force is now SVC pressure
Qp must pass through two highly
regulated vascular beds
Pulmonary and cerebral
Transpulmonary pressure gradient
Mean pulmonary
arterial pressure –
mean atrial pressure
Represents the
driving force through
the lungs
Low PVR allows for
a low delta P
Which means lower
SVC pressures
Pulmonary flow can
be impaired by
High PVR
Increased atrial
pressures
AV valve dysfunction
Ventricular diastolic
dysfunction
A low transpulmonary
gradient with a good
CO means good
things for sleep….
Post-Op issues – Ventilator Management
Excessive Paw
will limit systemic venous return via increased intrathoracic
pressure
increase PVR, potentially decreasing pulmonary flow AND
increases SVC pressure
Minimize iT, PIP and choose PEEP that allows for
maintenance of FRC
Remember that Qp comes through the cerebral
vascular bed…
So maneuvers like alkalosis and hyperventilation to decrease
PVR may INCREASE cerebral vasc resistance, decreasing
flow and further exacerbate hypoxemia
Low Cardiac Output
Low systemic cardiac output can be due to
Globally decreased ventricular function
Elevated Qp:Qs
AV valve regurgitation
Loss of AV synchrony
Low Cardiac Output
Careful choice of inotropes
Passive pulmonary blood flow occurs mostly
during diastole
Tachycardia is bad
Alpha agonists work on both pulmonary and
systemic vascular beds
Increase in PVR will decrease preload
Increase in SVR increases afterload
Both bad in the post-op single ventricle
Low dose dopamine and milrinone are good
choices
Elevated SVC Pressure
As evidenced by upper compartment plethora and
edema
DDx
Obstruction at anastomosis
Pulmonary artery distortion
Elevated PVR
Elevations in SVC pressure limit cerebral blood flow
CPP = MAP – SVC pressure
Combined with hyperventilation / alkalosis to maintain
low PVR, perfusion decrease is more marked
Prolonged SVC pressure elevation can lead to cerebral
edema, worsening the above
3% NaCl / Mannitol
Hypoxemia
Three broad categories of cause:
Pulmonary Venous desaturation
Systemic venous desaturation
Decreased pulmonary blood flow
I just brought these up again because I
like the organization of thinking here…I’m
trying to ram this one home..
Dis ees a fontan
Stage III - Fontan
The final step in single ventricle palliation
When is the stage II patient ready?
Usually about 6 months following stage II
Increasing growth and activity increases venous
return from lower limbs
When the ventricle has remodeled and displays good
function on echo
Good AV valve function
Small transpulmonary pressure gradient
Low ventricular end diastolic pressure
Most centers aim for completion between 12-24
months of age
Lateral baffle
Blood from IVC
directed into RPA via a
baffle in the lateral
portion of the RA
If the preceding
operation was a hemifontan, then IVC to
RPA continuity is
achieved by removing
the RA patch
Extracardiac Fontan
A conduit of PTFE tubing
or aortic allograft is
placed between IVC and
RPA
Advantages
Limited bypass
Atrial arrythmias less
common
Disadvantage
Conduit cannot increase
in size as pt. grows
In both operations,
poor ventricular
compliance or
increased PVR is a
concern
Both lead to
decreased pulmonary
flow, and, possibly,
decreased preload
Often a fenestration is
left in the baffle or
conduit
When systemic venous pressure
increases, increased shunting of blood
through the fenestration occurs
Maintains cardiac output when it is
compromised by decreased pulmonary
venous return
Fontan Physiology
Qp:Qs is equal
Ventricle supplies Qs
Systemic venous pressure
drives Qp
Shunt through
fenestration lowers SaO2
slightly
Pulmonary flow is nonpulsatile
Increases pulmonary
vascular bed impedance
Decreases capillary
recruitment
Flow through pulm vasc bed dependant upon
those factors that lend to a low transpulmonary
pressure gradient
Good ventricular systolic and diastolic function
AV valve competence
Low PVR
Elevated pulmonary artery pressures leads to
higher fluid replacement to maintain high SVC
pressures
Third spacing leads to effusions, ascites
Acsites increases required ventilator pressures,
decreases renal perfusion
Post-Op Issues - Ventilator Management
Pulmonary flow is impeded by a high PVR
Positive pressure ventilation increases
PVR
PEEP in excess of that required to
maintain FRC increases PVR
Minimal PEEP
Aim is usually to allow pt to do as much of
the work of breathing as possible
Low set rate with high PS
Low Cardiac Output
Discerning cause made
easier by “physiologic”
RA and LA lines
SVC/RPA and common
atrial pressure lines
Low Cardiac Output
Causes
Inadequate preload
Low SVC and atrial pressures
Elevated PVR
High SVC and low atrial pressure
Anatomic obstruction
Low atrial and high SVC pressures
Pump failure
High SVC and atrial pressures
Can be due to
AV valve regurgitation
Ventricular dysfunction
Loss of A-V synchrony
Ventricular outflow obstruction
Poor CO can lead to acidosis
Acidosis contributes to increased PVR, leading to
further desaturation, worse O2 delivery, more
acidosis….etc
Careful use of vasoactive agents that
increase pump function without increasing
afterload
Milrinone
Dopamine
nesiritide
Cyanosis
AGAIN……
Pulmonary Venous desaturation
Atelectasis
pulmonary edema
pneumothorax
Systemic venous desaturation
Anemia
Low cardiac output
Decreased pulmonary blood flow
Elevated PVR in those with fenestration
Pulmonary venous hypertension
Arrhythmias
Atrial and ventricular pacing wires are in place
Loss of AV valve synchrony is bad
Decreases CO, increases required transpulmonary
pressure gradient
Given the extent of this lecture, and how vast a
subject arrythmias are……
You got the wires….and the box…figure something
out.
Usual bothersome arrhythmias are atrial in nature, so
pacing the atria at a rate higher than the intrinsic rate
will fix the issue
Same goes for a fast junctional rate….
References
Chang et al, Pediatric Cardiac Intensive
Care, LWW, 1998
Schwartz S et al, Single Ventricle
Physiology, Critical Care Clinics
2003;19:393-411
Walker SG, et al, Single Ventricle
Physiology – Perioperative implications,
Seminars in Ped Surg, 2004, 188-202