Sindfgle

1. SINGLE VENTRICLE & FONTAN
PHYSIOLOGY

2. Formation of the cardiac loop

3. Molecular regulation of cardiac
development
Dependent on the
activation of two
transcription factors
• NKX2.5
• Specifies
cardiogenic
field
• Septation
• Conduction
system
• TBX5
• Septation

4. Formation of the cardiac septae
The major septae are formed between the 27 and 37th days
of development
It is a simultanuous process if the following areas
• Septum formation in the common atrium
• Septum formation in the atrioventricular canal
• Septum formation in the truncus arteriosus and conus
cordis
• Septum formation in the ventricles

5. Septum formation of the ventricles
End of the fourth week the two primitive ventricles start to expand.
The medial walls of the expanding ventricles become apposed and gradually
merge, forming the muscular interventricular septum

6. • Univentricular heart (UVH) is a term used to describe a wide variety
of structural cardiac abnormalities associated with a functional
single ventricular chamber.
• The consensus of the STS- Congenital Heart Surgery and the
European study group database proposed that the nomenclature of
UVH should include
• double inlet left and right ventricles,
• absence of one AV connection,
• common AV valves
• hearts with only one well developed ventricle as unbalanced AV
canal and complex conditions with heterotaxy syndromes

7. • Double Inlet Left Ventricle
• DILV is the most common form of single ventricle described in all series
and represents the classically described form of single ventricle.
• The Van Praagh classification also distinguished four subgroups of DILV
based on the great artery relationships: I, normally related great arteries;
II, right-anterior aorta; III, left-anterior aorta; and IV, left-posterior aorta
(inverted). By combining the criteria distinguishing the types of DILV, three
clinically observed forms occur (A-I, A-II, and A-III).
• DILV with Normally Related Great Arteries (A-I Single Ventricle, “Holmes
Heart”)
• DILV with right-sided hypoplastic subaortic right ventricle (A-II Single
Ventricle)
• DILV with left-sided subaortic hypoplastic right ventricle (A-III Single
Ventricle) is the most common type of univentricular connection observed
in most reviews

8. • A double inlet AV connection is almost always associated with a dominant
morphologic LV. In this situation, both atria connect to the dominant
ventricle by two distinct AV valves, which are usually mirror-image
morphologic mitral valves, thus fulfi lling the embryologic concept that AV
valve morphology always corresponds to the morphology of the ventricle
to which they connect.
• In contrast, in hearts with a common inlet AV connection, the dominant
ventricle is almost always of right ventricular morphology. It should be
noted that common inlet right ventricle occurs much less frequently than
double inlet LV
• The third form of univentricular AV connection is a single inlet ventricle,
which includes tricuspid atresia and mitral atresia .These are characterized
either by an imperforate valve orifice with a fibrous plug or by absence of
the AV connection such that the corresponding atrium and ventricle are
completely separated.

9. • Subaortic obstruction usually occurs with ventricular–great artery (VA) discordance
and is located primarily at the VS (bulboventricular foramen type).
• Pulmonary outflow tract obstruction frequently occurs in DILV and may occur with
either concordant or discordant VA connections. When subpulmonary obstruction
occurs within the left ventricular chamber, it most frequently is due to posterior
deviation of the infundibular septum.
• In the setting of univentricular heart of left ventricular morphology, the majority
of patients will have discordant ventriculoarterial connections, with the aorta
arising from the rudimentary outlet chamber of right ventricular morphology, and
the pulmonary artery arising from the dominant ventricular mass of left
ventricular morphology

10. • Conduction abnormalities similar to those described with AV and VA discordance
(corrected transposition of the great arteries) can be present. When the AV
connection is double inlet, the connecting AV node always is located
anterolaterally at the acute margin of the right AV valve orifice . It subsequently
perforates the annulus of the right AV valve to enter the main left ventricular
chamber. The nonbranching bundle courses along the right-sided rim of the VSD
(outlet foramen) to reach the trabecular septum.
• If the hypoplastic right ventricle is right-sided, the right margin of the VSD is
adjacent to the anterolateral node, and the nonbranching bundle passes down
directly onto the right rim of the VSD.

11. The physiology of UVH in a neonate depends upon
certain key anatomical factors.
1. Obstruction to systemic or pulmonary outflows.
2. Obstruction to ventricular inflow and atrial septum
and abnormal systemic or pulmonary venous return.
3. Amount of pulmonary blood flow and pulmonary
vascular resistance.
4. A-V valve regurgitation.

12. Systemic Outflow Obstruction
• Hypoplastic left heart syndrome (HLHS)
• Tricuspid atresia with transposed great
arteries, DORV (some variations), Double-inlet
left ventricle associated with critical AS, severe
CoA, or IAA

13. Systemic Outflow Obstruction
• Complete mixing of systemic and pulmonary venous
return
• Ventricular outflow directed primarily to the PA
• Systemic blood flow (Qs)
– Largely by right-to-left ductal shunting
– Dependent on the relative PVR and SVR
• Systemic outflow obstruction is poorly tolerated
• Usually accompanied by signs or symptoms of shock

14. • When there is severe obstruction to systemic outflow (HLHS and its
variants, UVH with severe aortic valve or arch obstruction), the neonate is
dependent on the ductus arteriosus for maintaining systemic output. The
baby started on prostaglandin E2 (PGE1) immediately after birth, in order
to maintain ductal patency.
• Physiologically, there is complete mixing of blood within the heart at the
atrial and ventricular levels, with all the blood ejected through the
pulmonary valve and distributed to the pulmonary and systemic beds by
the pulmonary artery branches and PDA respectively

15. Pulmonary Outflow Obstruction
• Tricuspid atresia + PS
• Pulmonary atresia with IVS
• TOF with pulmonary atresia
• Severe Ebstein’s anomaly of the tricuspid valve
• Critical PS
• DORV (some variations) + PS

16. Pulmonary Outflow Obstruction
• Complete mixing of systemic and pulmonary venous
return
• Ventricular outflow predominantly directed out the
aorta
• Low pulmonary blood flow (Qp) in single-ventricle
patients implies an obligate right-to-left shunt
(generally atrial level)
• Clinical consequences of low Qp are variable

17. • OBSTRUCTION TO PULMONARY OUTFLOW:
• UVH with critical pulmonary outflow obstruction (usually in the form of
pulmonary atresia) presentation is usually not as catastrophic as with
HLHS, as the neonatal cyanosis is often apparent as the PDA starts to close
• In this situation, there is complete mixing of blood within the heart and
the degree of cyanosis depends on the severity of pulmonary stenosis.
Once the ductus is opened using PGE1, the pulmonary and systemic
circulations become interdependent on each other, and the resistances in
the two circulations determine the amount of flow. Additionally, anatomic
obstructions along the pulmonary vascular tree would further influence
pulmonary blood flow and distribution.

18. • OBSTRUCTION TO SYSTEMIC OR PULMONARY VENOUS RETURN OR
VENTRICULAR INFLOWS:
• Systemic and pulmonary venous abnormalities are often seen in association with
other complex congenital cardiac anomalies and especially with heterotaxy
syndrome.
• Pulmonary venous obstructions cause severe pulmonary hypertension because of
backpressure into the pulmonary capillary bed and need to be detected early and
corrected during surgery.
• In order to ensure unobstructed communication between the two venous inflows
and the single ventricular chamber, an unrestricted atrial septal defect is necessary
for egress of blood from the atrial chamber with the obstructed valve. In the
presence of mitral atresia, a restrictive ASD acts physiologically similar to
pulmonary venous obstructionand leads to elevated pulmonary vascular resistance
from back pressure.
• Similarly, in tricuspid atresia, a restrictive ASD causes signs of systemic venous
obstruction. The atrial septal defect needs to be widened either by balloon
septostomy prior to surgery or by surgical resection of the atrial septum during the
first stage of repair

19. • An ideal patient with UVH should have good ventricular function, unobstructed
venous return, unrestrictive ASD and “optimal” pulmonary blood flow. This
situation is rarely found in patients with UVH variants and PS, where the amount
of pulmonary blood flow is just enough to prevent severe cyanosis as well as avoid
development of pulmonary vascular disease.
• Patients with tricuspid atresia and pulmonary stenosis occasionally have “optimal”
pulmonary flow which allows for the patient to wait and undergo a superior cavo-
pulmonary connection or even a direct “Fontan” procedure during early
childhood, without going through staged repair.
• In patients with aortic obstruction, often pulmonary blood flow is unrestricted
and since the pulmonary and systemic outputs are interdependent, this situation
leads to excessive pulmonary blood flow and consequently, low cardiac output and
hemodynamic decompensation. Similarly, when the ductus is kept open, to supply
either the systemic or pulmonary circulation, the patient’s pulmonary blood flow
has to be very carefully fine tuned in the pre-operative period in order to maintain
appropriate cardiac output

20. • All patients with single ventricle physiology who have severe hypoplasia of one ventricle will
ultimately be staged down the single ventricle pathway to Fontan physiology.
• Patients with single ventricle physiology and two wellformed ventricles will be able to
undergo a two-ventricle repair. In some cases (truncus arteriosus Type 1 and 2, tetralogy of
Fallot with pulmonary atresia, severe aortic stenosis) the two-ventricle repair will be
complete. In others (type 3 and 4) significant residual lesions (VSD, aortopulmonary
collaterals) may remain.
• With single ventricle physiology the arterial saturation (SaO2) will be determined by the
relative volumes and saturations of pulmonary venous and systemic venous blood flows that
have mixed and reach the aorta. This is summarized in the following equation: Aortic
saturation = [(systemic venous saturation) (total systemic venous blood flow) + (pulmonary
venous saturation) (total pulmonary venous blood flow)]/[total systemic venous blood flow +
total pulmonary venous blood flow]. From this equation, it is apparent that with single
ventricle physiology, three variables will determine arterial saturation:

21. • The ratio of total pulmonary to total systemic blood flow (Qp:Qs). A greater proportion of
the mixed blood will consist of saturated blood (pulmonary venous blood) than of
desaturated blood (systemic venous blood) when Qp:Qs is high. An increase in arterial
saturation that occurs in complete mixing lesions with increases in pulmonary blood flow
relative to systemic blood flow.
• Systemic venous saturation. For a given QP:QS and pulmonary venous saturation, a decrease
in systemic venous saturation will result in a decreased arterial saturation. Decreases in
systemic venous saturation occur as the result of decreases in systemic oxygen delivery or
increases in systemic oxygen consumption. Systemic oxygen delivery is the product of
systemic blood flow and arterial oxygen content. Arterial oxygen content, in turn, is
dependent on the hemoglobin concentration and the arterial saturation.
• 3. Pulmonary venous saturation. In the absence of large intrapulmonary shunts and/or V/Q
mismatch pulmonary venous saturation should be close to 100% breathing room air. In the
presence of pulmonary parenchymal disease, pulmonary venous saturation may be reduced.
The V/Q mismatch component of pulmonary venous desaturation will be largely eliminated
with a FiO2 of 1.0 while the intrapulmonary shunt contribution will not be eliminated. For
any given systemic venous saturation and QP:QS a reduction in pulmonary venous saturation
will result in a decreased arterial saturation.

22. THE GOAL OF CORRECTIVE PROCEDURES
• The single most important principle in UV
circulation is that the systemic and pulmonary
circulations balance each other and this critical
balance is maintained by the ratios of the
respective resistances. The goal of initial surgical
palliation is to provide unobstructed systemic
outflow, restricted pulmonary blood flow to
maintain normal pulmonary pressures and
unobstructed systemic and pulmonary venous
return to the heart.

23. Postoperative Anatomy
• Goal of initial palliative surgery to establish
– Unobstructed pulmonary and systemic venous
return
– Unobstructed systemic outflow
– Limited Qp and PA pressure

24. Ventricular Dysfunction
• Single ventricle is volume loaded
• Low Qs, particularly with low diastolic blood pressure
(large PDA) or a high end-diastolic ventricular
pressure (volume-loaded heart or after CPB) can
cause coronary perfusion pressure to become
critically low
• Compromise systolic ventricular function and further
raise EDP and lower SAP  profound hemodynamic
decompensation

25. Manipulation of Delivered Oxygen
• Goal of management:
– Ensure adequate DO2, not to maximize SaO2
• Optimization of DO2:
– Maintenance of cardiac inotropy while balancing
Qp and Qs and maintaining adequate BP and SaO2

26. Management
• Manipulation of Qp/Qs by manipulation of PVR
• Management of total CO and SVR may be more
effective
• Keeping Hb 13-15 mg/dL can have a positive
influence on DO2
• Increased Hb increases SmvO2 and SaO2 and
decreases Qp/Qs in single-ventricle physiology

27. Manipulation of PVR and SVR
• Subatmospheric oxygen (FiO2 0.17-0.19) or
respiratory acidosis can effectively raise PVR,
decrease SVR, and thus decrease Qp/Qs in infants
with unrestricted Qp
• Subatmospheric oxygen may be associated with PV
desaturation (particularly postoperative)
• Inhaled CO2 in HLHS: increased cerebral and systemic
DO2

28. PEEP
• PEEP increases PVR by compressing the interalveolar
pulmonary arterioles in normal lung compliance
• The nadir of PVR occurs at FRC rather than at zero
PEEP
• Initial PEEP applies radial traction forces and aids
vascular recruitment
• Increases PEEP may prevent PV desaturation by
optimizing lung gas exchange and therefore decrease
Qp/Qs

29. Manipulation of SVR
• Intravenous vasodilator
– Relatively greater effect on the systemic vasculature in
poor systemic perfusion and low PVR
– Nitroprusside, phenoxybenzamine, inamrinone, milrinone
• b-stimulation of myocardium with vasodilation can
further increase total CO without associated
vasoconstriction
• Inappropriate SVR  Qp, Qs (BP, SaO2 ),
masking potential warning signs of low Qs

30. Inotropic Support
• Inotropic support that increases Qs may also increase
SaO2 simply by increasing SmvO2
• Dobutamine (5 and 15 mg/kg/min):  Qp/Qs
• Epinephrine (0.05 and 0.1 mg/kg/min):  Qp/Qs
• Low-dose epinephrine (0.05 mg/kg/min): greatest 
in PVR/SVR ratio, largely because of  SVR
• DO2 is increased dramatically by increasing total CO
and is optimized by adjusting Qp/Qs

31. Combination of inotropic support
and decreasing SVR is potentially
the optimal strategy to maximize
DO2.

32. High PVR
• Not all pulmonary overcirculation
• Very low Qp (PaO2 < 30 mmHg)
–  pulmonary dead space and impair minute ventilation
– Respiratory acidosis further  PVR
• Alveolar recruitment strategies of ventilation in atelectasis or
pulmonary disease
• Minimum airway pressure, high-frequency jet ventilation
• Supplemental inspired oxygen, hyperventilation, and alkalosis
• Inhaled NO, iv PGE1
•  BP by vasoconstriction may  Qp and usually  SaO2 but at
the expense of some systemic perfusion

33. SUPERIOR CAVOPULMONARY SHUNT OR
BIDIRECTIONAL GLENN (BDG) PHYSIOLOGY
• The BDG directs systemic venous blood from the SVC directly to the
pulmonary circulation. The BDG is normally undertaken at 3-6 months of
age at which point the PVR has decreased to point where pulmonary
blood flow can be provided with systemic venous pressure as the driving
pressure. Patients who have outgrown their PA band, RV to PA conduit, or
MBTS and have a low SaO2 and patients who are not tolerating the
additional volume on their ventricle with a loose PA band or large MBTS
will be staged to a BDG earlier in this interval

34. Glenn procedure
• SVC to pulmonary artery
• Patient selection: good candidate
– Pulmonary arterial pressure (PAP) mean < 20 mmHg
– Size of branch pulmonary arteries
Special considerations for Glenn
• Additional sources of pulmonary blood flow
• Bilateral BDG
• Kawashima operation
• Hemi-Fontan procedure

35. • Modifications of the BDG have been devised to potentially simplify
the ultimate conversion to a Fontan. The hemi- Fontan refers
specifically to a procedure in which atriopulmonary anastomosis is
constructed between the dome of the right atrium at the RA/SVC
junction and the inferior surface of the right pulmonary artery. A
Gortex baffle is used to supplement the central pulmonary artery
area and to isolate the cavopulmonary connection from the RA.
• Another modification incorrectly called a hemi-Fontan involves
creation of a double cavopulmonary anastomosis. The cranial end
of the divided SVC is anastomosed to the superior surface of the
right pulmonary artery. The cardiac end of the divided SVC is
anastomosed to the inferior surface of the right pulmonary artery.
The internal orifice of the superior vena cava is closed with a Gortex
patch

36. Operations: pre-Fontan palliation
• Pulmoanry artery banding
• Modified BT shunt
• Atrioventricular valve repair
• Correction of TAPVC (if present)
• DKS or Norwood principle
• Glenn’s shunt: superior cavopulmonary
connection

37. • The Fontan procedure is generally performed in staged
patients at 1-2 years of age. Fontan physiology is a
series circulation that can be described as follows:
• There is one ventricle with sufficient diastolic, systolic,
and atrioventricular valve function to support systemic
circulation. This ventricle must in turn: Be in
unobstructed continuity with the aorta & Be in
unobstructed continuity with pulmonary venous blood
• There is unobstructed delivery of systemic venous
blood to the pulmonary circulation (total
cavopulmonary continuity).

38. Ten commandments
(Fontan and Baudet)
 Age above 4 years
 No distortion of pulmonary arteries from prior shunt
surgery
 Normal systemic venous drainage
 Normal ventricular function
 Adequate pulmonary artery size
 Minimum atrio-ventricular valve regugitation
 Low pulmonary artery pressure (below 15 mmHg)
 Low PVR
 Normal sinus rhythm
 Adequate size of right atrium

39. Completion of TCPC
• On CPB or Off-pump
• Dissection of IVC and PA
• Tailoring the PTFE conduit (at least size 16
mm should be selected for adequate IVC flow)
• Anastomosis: the IVC anastomosis is done
first.
• Side-to-side fenestration

40. Challenges
Anatomical and technical
• Branch pulmonary artery stenosis and
disconnected pulmonary artery
• Dextrocardia and Mesocardia
• Abnormal anatomy or position of the IVC
• Fenestration or non-fenestration
Physiological
• Pulmonary hypertension

41. Advantage of fenestration
• Debate on routine fenestration
• Beneficial in high-risk Fontan
• Standard-risk group  controversial
• Randomised-controlled trial
• 49 cases underwent Fontan (< 2 risk factors)
• 25 fenestrated, 24 non-fenestrated
• 6 LT, 43 ECC
• Fenestrated group: less hospital stay, shorter
duration of pleural drainage and less
additional procedures
Lemler MS, Scott WA, Leonard SR, et al.
Circulation 2002; 105; 207-212

42. Factors associated with
poor outcome
• Systemic ventricular dysfunction (EDP > 12)
• Increased pulmonary arterial pressure (mean
> 15)
• Increased pulmonary vascular resistance (>2)
• Atrioventricular valve regurgitation
• Distorted pulmonary artery
• Anomalous pulmonary venous connection

43. Candidate for Fontan
• Body size
• Systemic ventricular function
End diastolic pressure < 10 mmHg
• Mean PAP < 15 mmHg
• PVR < 2.5 Woods unit (2)
• Unrepairable pulmonary artery
distortion ???
Abnormal IVC course: proceed to
Fontan operation???

44. Sequelae of Fontan procedure
• Low cardiac output
• Pleural effusion
• Arrhythmia
• Protein losing enteropathy (PLE)  immunity loss
• Hepatic dysfunction
• Pulmonary arteriovenous malformation (AVM) in
Kawashima
• Progressive cyanosis
• Chronic exercise intolerance
• Plastic bronchitis

45. • Systemic Outflow obstructions associated with UVH usually
necessitate “Norwood Procedure” or its variations for repair.
• The Norwood repair involves conversion of the pulmonary artery
into the systemic artery or “neo-aorta”. The small native aorta is
anastomosed to the neo aorta and serves to carry blood retrograde
to the coronary arteries. The aortic arch is augmented and then
connected to the “neoaorta”.
• A recent modification of this procedure, popularized by Sano et al
involves using a RV to PA Gore-Tex shunt to supply the pulmonary
arteries.
• The RV to PA shunt avoids the diastolic run-off that happens in
aorto-pulmonary shunts, which lead to compromised coronary flow
and poor ventricular myocardial perfusion and ultimately death.

46. • The smallest shunt size to supply enough
pulmonary blood flow to maintain normal PA
pressures and systemic circulation in the high 70s
to low 80s is placed.
• The baby is ventilated in the post operative
period with a strategy to maintain the PCO2 in
the 50s and PO2 in the 40s range. This ensures
that the pulmonary arterial resistance is
maintained on the higher side, to prevent
pulmonary over circulation, which would be at
the expense of systemic output.

47. • A combined catheterization and surgical approach to achieve the same
goals has been performed in some centers.In this “hybrid” approach, the
neo-aortic arch is created by stenting the ductus .
• This ensures continued presence of a “ductal arch” to function as a new
systemic arch. The arch vessels and coronaries are perfused by
reterograde flow.
• The atrial septal defect is widened by septostomy or stenting the ASD if
required.
• The branch pulmonary arteries are initially individually banded in a
“closed heart” procedure, to limit pulmonary blood flow.
• This “hybrid” procedure offers the physiological results of a Norwood
surgical procedure, without subjecting these ventricles to cardio-
pulmonary bypass, and the neonate to deep hypothermic circulatory
arrest.