Glenn shunt a review

PRESENTATION OVERVIEW
 Introduction
 History
 Indications for Surgery
 Surgical Technique
 Postoperative Physiology
 Postoperative Issues
GLENN SHUNT-A REVIEW

INTRODUCTION
 Atresia of an atrioventricular or semilunar valve results in single-ventricle
anatomies that have complete mixing of the systemic and
pulmonary venous circulations
 Structural defects that are generally managed with a staged
palliation include variations of single left ventricle and variations
of single right ventricle.

GENERAL PRINCIPLES OF SUPERIOR AND TOTAL
CAVOPULMONARY CONNECTIONS
 Goal of surgical palliation in single-ventricle lesions - to
separate the systemic and pulmonary circuits, resulting in
normal or near normal oxygen saturation.
 Cavopulmonary connections -used to divert systemic venous
return directly into the pulmonary vascular bed, providing more
“effective” pulmonary blood flow and reducing the volume load
on the single ventricle.

 After these procedures, the single ventricle ejects blood only to the
systemic circuit, with pulmonary blood flow derived by “passive
flow” into the pulmonary vascular bed at the expense of higher
central venous pressure.
 Although cavopulmonary connections improve cyanosis and
minimize ventricular work, the elevated PVR in the neonate
precludes their use until approximately 3 months of age

 The cavopulmonary connections used to stage the single-ventricle
patient to the modified Fontan
1)BDG
2)Hemi-Fontan.
 Staging to Fontan performed because of the high incidence of
pleural effusions and low-output myocardial failure when taken
directly for fontan procedure..

Single left ventricle physiologies
 Tricuspid atresia with normally related great arteries
 Double-inlet left ventricle with normally related great arteries
 Transposition of the great arteries with PS
 Malaligned atrioventricular canal with hypoplastic right ventricle
 Pulmonary atresia with intact ventricular septum

TRICUSPID ATRESIA

Single right ventricle physiologies
 Hypoplastic left heart syndrome [HLHS]
 Double-outlet right ventricle with mitral atresia
 Malaligned atrioventricular canal with hypoplastic left ventricle
 Heterotaxy syndromes

HYPOPLASTIC LEFT HEART SYNDROME

GOALS OF STAGE 1 PALLIATION
Unobstructed systemic blood flow
Limited pulmonary blood flow
Undistorted pulmonary arteries
Unobstructed pulmonary venous return
Minimal atrioventricular valve regurgitation

 Surgical palliation allows the neonate to survive into infancy but is
not a stable anatomic or physiologic long-term solution.
 Children with single-ventricle anatomy will ultimately undergo
some variation of the Fontan operation as their final surgical
palliation

Selecting Patients with Tricuspid Atresia for the
Fontan Procedure: The “Ten Commandments”
1. Minimum age, 4 years
2. Sinus rhythm
3. Normal caval drainage
4. Right atrium of normal volume
5. Mean pulmonary artery pressure ≤ 15 mm Hg
6. Pulmonary arterial resistance < 4 U/m2
7. Pulmonary-artery-to-aorta-diameter ratio ≥ 0.75
8. Normal ventricular functions (ejection fraction > 0.6)
9. Competent left atrioventricular valve
10. No impairing effects of previous shunts

History
 In the 1950s and 1960s in Italy, the United States, and Russia, many
surgeons were concurrently discovering and harnessing the utility
of the cavopulmonary connection.
 An experimental model of the cavopulmonary anastomosis was
used in dogs by Carlon in the 1950s.
 This model identified many of the hemodynamic and surgical
advantages of the cavopulmonary anastomosis relative to the
Blalock-Taussig shunt.

 The first significant clinical use of the cavopulmonary anastomosis
in the United States was performed by Glenn.
 He used unidirectional (classic) and bidirectional superior
cavopulmonary anastomoses and inferior cavopulmonary
anastomosis (inferior vena cava [IVC]-to-PA connection).
 Interim palliation with a BDG shunt has now become the standard
of care over the past decade, typically in infancy (4 to 9 months of
age).

DR WILLIAM GLENN

Timing of shunt
 With a decrease in PVR, infants with single ventricle who have had a
neonatal palliation become candidates for the superior
cavopulmonary anastomoses by 3 to 6 months of age.
 Mahle and associates showed that early ventricular unloading after
neonatal single-ventricle palliation improved aerobic exercise
performance in preadolescents with the Fontan palliation.
 An additional advantage of an early superior cavopulmonary
anastomosis is the opportunity to address distorted pulmonary
arteries from previous bands or shunts and to create a better
distribution of PA blood flow and growth of the pulmonary vascular
bed.

Indications for early shunt procedure
 Cyanosis secondary to inadequate pulmonary blood flow after
neonatal palliation
Congestive heart failure from an excessive volume load caused by
severe atrioventricular valve regurgitation or by an elevated Qp:Qs.

 The benefits of early cavopulmonary anastomosis must be weighed
against the risks of elevated SVC pressure and cyanosis.
 Bradley and colleagues found that cavopulmonary anastomosis at
younger than 3 months was associated with lower oxygen saturation
in the early postoperative period and a risk of PA thrombosis.
 Some infants with severe ventricular dysfunction or
atrioventricular valve regurgitation may not be suitable for further
staged palliation and may require heart transplantation

Prerequisites before the procedure
 Echocardiogram
 Cardiac catheterization
For anatomic and hemodynamic assessment of the
 Pulmonary arteries,
 Aortic arch
 Ventricular and atrioventricular valve function
 Caval anatomy-Presence of decompressing veins that may
result in cyanosis after superior cavopulmonary
anastomosis.

CLASSIC GLENN SHUNT
Dr. Glenn described an anastomosis between the transected
distal end of the right pulmonary artery and the
side of the SVC, which is ligated distal to the anastomosis.
The azygous vein is ligated to prevent its
decompressing flow from the SVC.

BIDIRECTIONAL GLENN SHUNT
The BDG operation is performed via median
sternotomy . At the initiation of cardiopulmonary
bypass (CPB), the shunt is ligated with a vascular clip
or ligature. Preservation of the proper spatial
orientation of the SVC relative to the PA is essential.
Therefore the azygos vein is ligated but not divided.
The SVC is then divided, and the cardiac end is
oversewn. The cephalic end is anastomosed end to side
to the ipsilateral PA.

 As with the classic glenn shunt, the bi-directional cavo-pulmonary shunt
is far less likely to engender Pulmonary vascular obstructive disease
compared with systemic-pulmonary shunts, and there is minimal
Distortion of the pulmonary artery architecture.

Shunt between the Superior Vena Cava and Right Pulmonary Artery — Technic of Anastomosis.
Glenn WW. N Engl J Med 1958;259:117-120.

Angiogram Taken Two Months after Operation.

Arterial Oxygen Studies before and after the Shunt.*

Technique Without Cardiopulmonary Bypass
BDG may be performed without the utilization of CPB.
 Patients with sources of pulmonary blood flow that do not need
interruption as part of the cavopulmonary anastomosis (antegrade
flow through a stenotic pulmonary valve or banded PA) and have no
specific intracardiac pathology requiring revision are candidates for
cavopulmonary anastomosis without CPB.
 HLHS patients are not candidates for superior cavopulmonary
anastomosis without CPB because their pulmonary blood flow is
shunt dependent, and because they may require PA reconstruction
and other intracardiac procedures at the time of their superior
cavopulmonary anastomosis

HEMI FONTAN PROCEDURE

FONTAN PROCEDURE
d’Udekem Y et al. Circulation 2007;116:I-157-I-164
Copyright © American Heart Association, Inc. All rights reserved.

Postoperative Physiology
 After completion of the superior cavopulmonary anastomosis, the
circulation to the lungs is from the upper body systemic venous
return.
 The pulmonary blood flow results from upper body blood flow,all
SVC return must pass through the lungs to reach the heart in the
absence of decompressing venous collaterals.

 The principal physiologic advantage of conversion to a superior
cavopulmonary anastomosis at an early age is the reduction of the
volume work of the single ventricle and a predictable Qp:Qs of
approximately 0.6 to 0.7.
 This ratio is higher in young infants because of the relative size of
the head and the upper extremities in young infants as opposed to
those in older children, but in general, systemic arterial oxygen
saturations (SaO2) are 75% to 85%.

 The immediate reduction in the volume load of the single ventricle
by removing the aortopulmonary shunt decreases the work of the
single ventricle and may improve long-term atrio-ventricular valve
and myocardial function.
 Atrioventricular valve regurgitation resulting from physiologic
rather than structural abnormalities may decrease as the
ventricular geometry normalizes

 After superior cavopulmonary anastomosis, oxygen is delivered
more efficiently to the body because only deoxygenated blood from
the SVC rather than admixed blood from the ventricle is presented
to the lungs for oxygen uptake.
 The net result of the more efficient oxygen uptake in the lungs is a
reduction in cardiac output needed to achieve a given tissue O2
delivery

DIASTOLIC DYSFUNCTION

 After the BDG or hemi-Fontan, ventricular filling is not absolutely
dependent on pulmonary venous return, because IVC flow is still
diverted directly to the single ventricle and maintains preload.
 As a result, the acute volume reduction noted after superior
cavopulmonary anastomosis is better tolerated than in the case of
transitioning a child from a neonatal palliation directly to the
Fontan completion without an intervening superior cavopulmonary
anastomosis

 SaO2 after creation of a BDG shunt tends to be lower in very young
younger than 3 months patients.
 Although some patients as young as 4 weeks have had satisfactory BDG
shunt creation, patients younger than 3 months have a higher incidence
of early cyanosis, PA thrombosis, and vascular congestion.
 Therefore a delay of the procedure until the child is older than 3 months
is generally recommended.
 By age 6 months, the mortality risk approaches 0 in many centers.

Postoperative Issues

Mechanical Ventilation
 Positive pressure ventilation with increased mean airway pressures
adversely affects PVR and ventricular filling
 Early institution of spontaneous ventilation improves
hemodynamics in the awake patient.
 Spontaneous breathing also increases pco2, which will promote
increased cerebral blood flow and, thereby, increase pulmonary
blood flow.

 “Physiologic” (3 to 5 cm H2O) positive end-expiratory pressure
(PEEP) is generally well tolerated, does not significantly affect PVR
or cardiac output, and may improve oxygenation by reducing areas
of microatelectasis, reestablishing functional residual capacity, and
improving ventilation/–perfusion matching.

Elevated Cavopulmonary Pressures
 The goal of postoperative cavopulmonary anastomosis management is
to minimize the transpulmonary gradient (PA mean pressure –
common atrium mean pressure) to allow passive pulmonary blood
flow through the lungs and back to the single ventricle.
 An elevated transpulmonary gradient may result from pulmonary
venous obstruction, elevated PVR, or pleural effusion, hemothorax, or
pneumothorax.
 Extubating the patient expeditiously will reduce the common atrial
pressure and promote flow through the lungs by creating a greater
transthoracic gradient from the extrathoracic space to the
intrathoracic space.
 Diminished cavopulmonary blood flow will reduce systemic SaO2

 Elevation of PVR from the inflammatory effects of CPB may be
minimized with pulmonary vasodilators such as nitric oxide at 5
to 20 parts per million in inspired gas.
 Mild facial edema after superior cavopulmonary anastomosis
may persist for up to 72 hours.
 Majority of pleural effusions after superior cavopulmonary
anastomosis will diminish over time with judicious diuretic use
and fluid restriction.

 Patients are typically given aspirin (5 mg/kg/day) after superior
cavopulmonary anastomosis to reduce the risk of thrombosis of
the superior cavopulmonary circuit

 Patients with clinical signs of significantly elevated SVC pressure
,upper extremity plethora and edema may have obstruction at the
cavopulmonary anastomosis, distal PA distortion, or marked
elevations in PVR.
 Significant elevations of pressure in the SVC may limit cerebral
blood flow.
 If the SVC pressure is more than 18 mm Hg, the etiology should be
promptly investigated, including early catheterization, if necessary

Hypertension and Bradycardia
 Transient postoperative hypertension and bradycardia have been
frequently observed in the first 24 to 72 hours after the
cavopulmonary shunt.
 Hypertension may be due to pain, catecholamine secretion,
intracranial hypertension, or a combination of these.
 The acute elevation of the central venous pressure may result in
a reflex similar to that seen in head trauma, such that systemic
hypertension is necessary to preserve adequate cerebral
perfusion.
 Therefore aggressive lowering of the blood pressure may
adversely affect the cerebral perfusion pressure, and vasodilators
should be used cautiously.

 Transient bradycardia is typically seen after a cavopulmonary
connection and may be due to the acute reduction of the volume
load of the single ventricle, or may be due to injury to the sinus
node or its arterial supply.

Low Cardiac Output
 When the child has preexisting ventricular dysfunction or severe
atrio-ventricular valve regurgitation.
 In these volume-loaded ventricles, which need high filling
pressures to generate adequate output, volume reduction and the
effects from CPB may significantly reduce cardiac output and
oxygen delivery to the tissues.

Cyanosis
 Excessive hypoxemia (SpO2 <75%) should be investigated promptly.
 The differential diagnosis of excessive or unexplained cyanosis can
be grouped into three broad categories: pulmonary venous
desaturation, systemic venous desaturation, or decreased
pulmonary blood flow.

Pulmonary venous desaturation
 Pleural effusion
 Pneumothorax
 Hemothorax
 Chylothorax
 Pulmonary edema
 Atelectasis
 Bacterial pneumonia/viral pneumonitis
 Arteriovenous malformation

Systemic venous desaturation/Decreased
oxygen delivery
 Anemia
 Low cardiac output
 Decreased ventricular function
 Severe atrioventricular valve regurgitation
 Pericardial tamponade

Increased oxygen consumption
 Sepsis
 Venovenous collateral from superior cavopulmonary circuit via the
systemic venous circuit to the systemic ventricle
 Baffle leak

Decreased pulmonary blood flow
 Pulmonary venous hypertension
 Restrictive atrial communication
 Decompressing vein

 Decreased pulmonary blood flow may be due to decompressing
venovenous collaterals, an undiagnosed contralateral (usually left)
SVC.
 Factors related to the development of decompressing venous
collaterals include bilateral superior vena cava, a higher early
postoperative transpulmonary gradient, and elevated pressure in
the SVC.

 A left SVC to coronary sinus, which appeared closed on the cardiac
catheterization before the superior cavopulmonary anastomosis,
may re-canalize, resulting in significant desaturation after superior
cavopulmonary anastomosis.
 Successful transcatheter coil embolization of these vessels can be
accomplished with good results

PULMONARY AV MALFORMATIONS
 A cause of pulmonary venous desaturation after a BDG is the
development of pulmonary arteriovenous malformations,
particularly in patients with heterotaxy syndrome.
 Diversion of normal hepatic venous flow from the pulmonary
circulation may be related to development of these abnormal
pathways,and some have been noted to regress after
incorporation of hepatic venous flow into the lungs.
 Pulmonary arteriovenous malformations have been associated
with young age at the time of the superior cavopulmonary
anastomosis, polysplenia (interrupted IVC with azygos
continuation to the SVC).

 Pulmonary arteriovenous malformations typically cause gradual
hypoxemia months to years after the surgical procedure, rather
than in the immediate postoperative period.
 Studies have shown that a pulsatile second source of pulmonary
blood flow may minimize the development of pulmonary
arteriovenous malformations.
 In most cases, the malformations diminish or disappear
completely after fontan completion.
 Although theoretic advantages exist to an ivc-pa cavopulmonary
anastomosis relative to the formation of pulmonary
arteriovenous malformations, the elevation in hepatic venous
pressure and the detrimental effects on liver function may be
prohibitive GLENN SHUNT-A REVIEW

 Song and colleagues reported that long-term aspirin (a
cyclooxygenase inhibitor) therapy has successfully prevented the
development of cyanosis, possibly by preventing pulmonary AV
fistula formation.
 Transcatheterembolisationwhen feeding artery greater than 3mm.
 Surgery-Fistulectomy/Lobectomy

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Glenn shunt a review

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