Fontan repair has to be done under three stages
Stage 1- Neonatal palliation
• In immediate postnatal period
• Goal - To maintain unobstructed systemic outflow and pulmonary venous return to the ventricle and create a stable and regulated source of pulmonary blood flow
Principles in neonatal palliation
• Protect the lung: prevent pulmonary HTN with PA banding(fig 4)
• Correct cyanosis: BT shunt(fig 5,fig 6b)/sano shunt
• Atrial septostomy/septectomy- to allow mixing of blood at atrial level
• Relieve systemic outflow tract obstruction – Norwood procedure(fig 6) , Damus-Kaye-Stansel (DKS) procedure[1](fig 7)
• Correct AV valve regurgitation and pulmonary venous stenosis
• No neonatal palliation-some situations, such as tricuspid atresia with normally related great arteries with no obstruction to aortic outflow, and appropriately restrictive pulmonary blood flow
Stage 2 : Superior Cavopulmonary connection through Bidirectional Glenn shunt(BDG) or Hemifontan
Ø BDG Procedure-
• In this, SVC is divided and the cardiac end is oversewn. Then its cephalic end is anastomosed end to side to the ipsilateral PA(fig 8). It is called bidirectional because blood from SVC flows into both Right pulmonary artery(RPA) and left pulmonary artery(LPA)
Ø Hemifontan procedure
• Right atrium(RA) is connected to pulmonary arteries, to augment them and a baffle is placed in the right atrium, directing SVC flow to the pulmonary arteries
Timing –usually at 3-4months of age as pulmonary vascular resistance (PVR) falls by this age.
Ø Prerequisites before the BDG procedure (Table 4 )
Ø Post BDG physiology
• After BDG, blood to the lungs is solely from SVC which will bypass the right heart and reaches lungs
• This results in reduction of the volume work of the SV and also a predictable Qp:Qs of approximately 0.6 to 0.7(>50% in young infants because of the relative large size of the head and the upper extremities).
• As there is less mixing of blood in the heart, SaO2 also gets improved and maintained at a range of 75% to 85% with more efficient O2 delivery to the body.
• As the required cardiac output to achieve a given tissue oxygen delivery is reduced, workload on the single ventricle also decreases.
Clinical presentations of various complications after BDG(Table 5)
Stage 3: Total Cavopulmonary connection through Fontan procedure
Ø Directs flow from the IVC to the pulmonary arteries with either a lateral tunnel or extracardiac Fontan procedure
Ø Three types of Fontan(fig 10 ) (Table 6) [2]
Ø Timing - 1-2 yrs after BDG shunt
Ø Prerequisites for a Fontan procedure
Ø Similar to BDG(table 4)
Ø Additionally, normal sinus rhythm, adequate right atrial size( if classic and lateral tunnel fontan), no veno-venous collaterals
Post Fontan Physiology
• Completion of total Cavopulmonary connection was done. Total systemic venous return is directed to Pulmonary circulation. So patients will be in a state of systemic venous hypertension
Complications-
• Almost similar to post BDG procedure
• Other complications [3]–[5]( Table 8)
• Algorithm for management of different types of single ventricle heart (fig 11, 12,13, 14,15)
Role of cross sectional Imaging (CT and MRI)
• CT and MRI usually not indicated prior to neonatal palliation surgery(only indicated if associated with heterotaxy syndromes)
• They have role only after neonatal palliation surgery
• CT and MRI has their own advantages and disadvantages(table 7)
MDCT(Multidetector CT)
CT techniques
• Maximum volume of contrast that can be given to child is 2ml/kg (up to 3 mL/kg of 300 mg of iodine per milliliter[6]
In post BDG
u Lower extremity intravenous access to prevent streak artifact from SVC
u Bolus tracking performed over the lower neck or the superior mediastinum.
u Imaging is initiated when contrast material peaks in the IJVs or SVC during the venous return phase(fig 16a)
u Aortic angiogram may be required to assess the MAPCAs. Alternatively using different rates and volumes of contrast at different timings may be used(fig16 b,c) to opacify all the structures.
After Fontan
Dual injection dual phase technique
Injection from both antecubital vein in the upper extremity and dorsal foot vein in the lower extremity simultaneously opacifies the Fontan pathway and pulmonary arteries.
Due to the preferential filling of RPA from SVC and LPA from IVC, Pulmonary arteries may not opacify at the same time. So delayed scan after 60- 70s can be done to see the opacification of IVC and LPA
Single injection single phase
Single injection from lower extremity with delayed phase imaging (initiate at the time of opacifcation of IJVs or after a delay of 70s)
MRI
MRI protocols shown in table 9
What to report - depends on the clinical question and timing of imaging
1. Post Neonatal palliation surgery imaging
v For Follow up
• Coarctation of aorta repair – residual stenosis/occlusion, anastomosis leak
• Aorta reconstruction-any stenosis/leak/occlusion/abscess collection
v For Complications
• Any modified BT shunt thrombosis (may present with severe cyanosis and saturation drop)
• PDA stent stenosis/occlusion
• MAPCAs- in case of hemoptysis and elevated pulmonary pressures
2. Assessment for Stage 2(BDG) repair (fig 17) -
· Retrosternal anatomy
· PA status- size adequacy, stenosis or obstruction
· Caval anatomy - unilateral or bilateral SVC, left SVC with dilated coronary sinus, interrupted IVC with azygous continuation, any communicating veins
· Coronary cameral fistulas
· MAPCAs- number, size and course of MAPCAs. Communicating ( joining any pulmonary artery)or noncommunicating MAPCAs( directly supplying pulmonary parenchyma without any communication with pulmonary arteries). If noncommunicating, they have to be ligated or embolized; if communicating unifocalisation can be done
After Stage 2-BDG
v For complications
• SVC thrombosis (fig 18)
• Shunt and PA thrombosis(fig 19)
• Stenosis of the cavopulmonary anastomosis(fig 20)
• Venovenous collaterals (fig 21 )
• Pulmonary AVMs (fig 22,24 )
• MAPCAs (fig 23,24)
• Lung pathology
• Residual aortic obstruction
v For Fontan completion
• PA anatomy
• BDG patency
• IVC and hepatic veins - distance between IVC –RA junction and RT PA(fig 25) ,any IVC anamolies, whether all hepatic veins opening into IVC or not
• Apicocaval juxtaposition - means apex of the heart and IVC on the same side
• RA anatomy
• Pulmonary vein stenosis
• AV valve regurgitation
• Ventricular function
• MAPCAs
After Fontan
Complications
• Liver- altered echotexture, focal lesions, portal hypertension and splenomegaly
• Right atrium- dilatation, clot formation
• Pulmonary circulation- stenosis ,dilatation or thrombosis
• Left ventricle- ejection fraction and ventricular volumes
• Shunts – shunt thrombosis/occlusion
• Venovenous collaterals
• Pulmonary AV malformations (fig26)
• MAPCAs
• Lung pathology(fig 27)-pneumonia, cavity
• Lymphatic system –
• Plastic bronchitis- hyperdensites in tracheobronchial tree with downstream obstruction
Pericardial and pleural effusions