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FONTANCIRCULATION
Dr Bijilesh uSenior Resident,
Dept. of Cardiology,Medical College, Calicut
• Normal mammal cardiovascular system double circuit connected in series—systemic—pulmonary
• powered by a double pump —the right and left heart
• Many complex cardiac malformations - one functional ventricle
• Maintain systemic and pulmonary circulation - not connected in series but in parallel
• Major disadvantages– arterial desaturation– chronic volume overload to single ventricle - in
time impair ventricular function
• 1971, Fontan and Baudet
• Goal was to create a circulatory system in which the systemic venous blood enters the pulmonary circulation, bypasses the right ventricle, and thus places the systemic and pulmonary circulations in series driven by a single ventricle
• All shunts on the venous, atrial, ventricular and arterial level are interrupted
• Advantages of a Fontan circuit include – (near) normalisation of the arterial saturation– abolishment of the chronic volume overload
• Cost for such a circulation includes – Chronic hypertension and congestion of the
systemic veins– decreased cardiac output
• Cardiac output is no longer determined by the heart,but rather by transpulmonary flow
INDICATIONS FOR A FONTAN CIRCUIT
• Cardiac malformation and a single functional chamber– dysfunctional heart valve – absent or inadequate pumping chamber
• Tricuspid atresia• Pulmonary atresia with intact ventricular septum • Hypoplastic left heart syndrome• Double-inlet ventricle
SELECTION OF PATIENTS 1978, Choussat et al
• 10 criteria for optimal results following the Fontan
1. age at operation between 4 and 15 years2. presence of normal sinus rhythm3. normal systemic venous connections4. normal right atrial size5. normal pulmonary arterial pressure (mean≤ 15 mmHg)6. low pulmonary vascular resistance (4 Woods units/m2)7. adequate-sized PA with diameter ≥75% of the aorta8. normal left ventricular ejection fraction ≥ 60%9. absence of mitral valve insufficiency10. absence of complicating factors from previous surgeries
• Refined by many centres
• After repair – LA pressure must be low (determined by good LV fn)– transpulmonary gradient must be low (determined by
the pulmonary vasculature)
• Cardiac requirements nowadays are– unobstructed ventricular inflow (no atrioventricular
valve stenosis, no regurgitation)– reasonable ventricular function– unobstructed outflow (no subaortic stenosis, and no
coarctation
• Pulmonary requirements – non-restrictive connection from systemic veins to
the PA– good sized PA without distortion– a well developed distal vascular bed– (near) normal PVR - 2.5 U/m2– unobstructed pulmonary venous return
– Marc Gewillig , Heart 2005;91:839–846. doi: 10.1136/hrt.2004.051789
Fontan Procedure
• Since its original description, the Fontan circuit has known numerous modifications
• Early modifications of the Fontan procedure connected pulmonary arteries to the right atrium
• Original procedure included
– SVC to RPA anastomosis (Glenn shunt) – Anastomosis of RA appendage to LPA directing IVC flow
through a valved homograft– Placement of a valved homograft at the IVS-RA junction – Closure of the atrial septal defect
• RA was included to - improve pulmonary blood flow, being a pulsatile chamber
• Instead RA dilated and lost contractile function – Turbulence and energy loss – Decreased pulmonary blood flow
de Leval et al
• Right atrial–pulmonary circuits - obsolete • Replaced with newer techniques - direct
connection between each vena cava and PA• Bypass the right atrium and right ventricle• More efficient cavopulmonary blood flow to
the lungs – reduce risk for arrhythmia and thrombosis
• Modern Fontan procedure involves connecting SVC and IVC to the RPA
• Originally performed at the same time• Resulted in a marked increase in blood flow to
the lungs - pulmonary lymphatic congestion, and pleural effusions
• No longer performed together
• Currently total cavopulmonary Fontan circulation done in two stages – To allow body to adapt to different hemodynamic states – Reduce overall surgical morbidity and mortality– Allows a better patient selection and intermediate preparatory
interventions
• As no ventricular contraction to pump blood through the lungs, elevated PAH is an absolute contraindication for Fontan procedure
• At birth, it is impossible to create a Fontan circulation– PVR is still raised for several weeks – Caval veins and pulmonary arteries - too small
• Initially in the neonatal period, management must aim to achieve
• Unrestricted flow from the heart to the aorta – coarctectomy– Damus- Kaye-Stansel– Norwood repair
• Well balanced limited flow to the lungs – pulmonary artery band– modified Blalock-Taussig
• Unrestricted return of blood to the ventricle – Rashkind balloon septostomy
Bidirectional Glenn Shunt / Hemi-fontan
• At 4–12 months of age• First half of creating a total cavopulmonary
circulation circuit
• End-to-side anastomosis between SVC & RPA• RPA is not divided, resulting in blood flow from the
SVC into the right and left PA • Children may remain cyanotic because blood from
the IVC is not directed to the lungs
Bidirectional Glenn Shunt / Hemi-fontan
• Cardiac end of the divided SVC is attached to MPA or the under surface of RPA
• Lower stump of SVC is connected to IVC with a conduit
• Open end of the SVC is either oversewn or occluded with a polytetrafluoroethylene patch
• Allows Fontan circulation to be completed later
• When patients reach 1–5 years of age total cavopulmonary Fontan circuit is completed
• IVC connected to pulmonary artery with a conduit
• Modified Fontan directing IVC flow through the lateral portion of the RA into PA via an anastomosis to the underside of the RPA
• SVC flow is already directed into the RPA by a previous bidirectional Glenn shunt
• Internal conduit - pass through the right atrial chamber
• External conduit - run completely outside the heart to the right side of the right atrium
Intraatrial tunnel method
• Conduit is constructed with both the lateral wall of the right atrium and prosthetic material
• Inferior aspect of the tunnel is anastomosed to the IVC and the superior aspect is anastomosed to the pulmonary arteries
• Conduit enlarges as the child grows - may be used in children as young as 1 year old
• Internal conduit may lead to atrial arrhythmia
Extracardiac conduit method
• Usually performed only in older than 3 years• PTFE tube graft is placed between the transected IVC
and the pulmonary artery, bypassing RA• Entire atrium is left with low pressure - less atrial
distention, arrhythmia, and thrombosis
• Cannot enlarge as the patient grows• Performed only in patients who are large
enough to accept a graft of adequate size to allow adult IVC blood flow
Fenestrated fontan
• small opening or fenestration may be created between the conduit and the right atrium
• Functions as a pop-off valve (a right-to-left shunt) – prevent rapid volume overload to the lungs– Limit caval pressure– Increase preload to the systemic ventricle– Increase cardiac output
• cyanosis may result from the right-to-left shunt
• Fenestrations decrease postop pleural effusions• May be closed after patients adapt to new
hemodynamics
• Now, fenestrations are seldom created during the completion of the Fontan – improved patient selection and preparation– improved staging
• FONTAN PHYSIOLOGY
Early increase in preload
• Fontan circulation provides definitive palliation for complex cardiac lesions not suitable for biventricular repair
• Some form of palliation is done in early infancy • Results in a parallel pulmonary and systemic
circulation and a net increase in preload
• Most patients undergo a staged transition to their complete Fontan via Bidirectional Glenn
• BDG procedure leads to marked decrease in preload• Degree of reduction depends on prior pulmonary to
systemic flow ratio, which often exceeds 2:1• Reduction of preload results in reduced ventricular
dilation and work
Reduction of preload
• Abnormal systolic ventricular performance is rarely a problem in early years of palliation prior to Fontan – Is sustained or improved in most, after completion of
Fontan circuit• It was shown that restoration of normal systolic wall
stress was achieved in most individuals undergoing a Fontan procedure prior to the age of 10 years
• Sluysmans T et al. Natural history and patterns of recovery of contractile function in single left ventricle after Fontan operation. Circulation Dec 1992;86(6):1753–61.
• Increase in wall thickness coincident with the acute reduction in end-diastolic volume
• Result s in abnormalities of early relaxation & characteristically reduced early rapid filling
• Consequently, much of diastolic filling is dependent on atrial systole
• Early diastolic dysfunction negatively impact recovery after subsequent Fontan operation
Early diastolic dysfunction
• Persistently abnormal early relaxation with worsening ventricular compliance markedly reduces ability of the ventricles to fill
• Reduces pulmonary blood flow • Accounts for some of late failure seen in these
patients• Worsen naturally with age as in the normal heart
• Avoidance of factors known to lead to worsening compliance (persistent LV outflow tract obstruction, hypertension) is of fundamental importance
• While diastolic abnormalities predominate early-on , systolic failure also becomes apparent in some patients late after the procedure
Systemic vascular bed
• Many studies have reported uniformly elevated systemic vascular resistance after Fontan
• Senzaki H, Masutani S, Kobayashi J, et al
Use of ACE inhibition in Fontan patients
• Enalapril or placebo was given for 10 weeks in 18 patients approximately 14 years after the Fontan operation
• Tendency to worsen exercise performance. • Reduced incremental cardiac index during exercise in
the patients receiving enalapril• Kouatli et al ,Enalapril does not enhance exercise capacity in patients after
Fontan procedure. Circulation Sep 2 1997;96(5):1507–12.
• Many patients continue to receive ACE inhibition, in the hope of a beneficial effect when given chronically
• It is possible that there are subgroups that may benefit e.g. severe systolic dysfunction
• Presently no evidence for this therapy being beneficial
The veno-pulmonary circuit
• Major evolution in the hemodynamic design of the Fontan operation since its inception
• Initial right atrial to pulmonary connection has been abandoned in favor of more streamlined versions
• Cardiac output - using respiratory mass spectrometry and an acetylene re-breathing method
• There was no difference between the patient group at rest
• Cardiac output & respiratory rate higher in the lateral tunnel group than the atriopulmonary group at low and moderate workloads
• Rosenthal M et al Comparison of cardiopulmonary adaptation during exercise in children after the atriopulmonary and total cavopulmonary connection Fontan procedures. Circulation Jan 15 1995;91(2):372–8.
• Work of breathing is a significant additional energy source to circulation in Fontan
• Normal negative pressure inspiration has been shown to increase PBF after the atrial pulmonary connection and TCPC
• Redington AN, Penny D, Shinebourne EA. Pulmonary blood flow after total cavopulmonary shunt. Br Heart J Apr 1991;65(4):213–7
• Philadelphia group, using magnetic resonance flow measurements,have estimated that approximately 30% of the cardiac output can be directly attributed to the work of breathing in patients after the TCPC
• Fogel MA,Weinberg PM, Rychik J, et al. Caval contribution to flow in the branch pulmonary
arteries of Fontan patients Circulation Mar 9 1999;99 (9):1215–21.
Positive pressure ventilation
• Increasing levels of PEEP during positive pressure ventilation is adverse to Fontan circulation
• Higher the mean airway pressure, lower cardiac index• Maintain with minimum mean airway pressure
compatible with normal oxygenation and ventilation
• Williams DB, Hemodynamic response to positive end-expiratory pressure following right atrium-pulmonary artery bypass (Fontan procedure). J Thorac Cardiovasc Surg Jun 1984;87(6):856–61y
The pulmonary vascular bed
• Low PVR is a prerequisite for early success after Fontan operation
• Lower the total pulmonary resistance (PVR , pulmonary venous resistance and LA
resistance) the better• LA resistance is influenced by the abnormal
ventricular response
• Structural pulmonary venous abnormalities – Naturally occurring– May evolve as a result of abnormal hemodynamics
• Atriopulmonary anastomosis- gross enlargement of RA may compress adjacent pulmonary veins
• Abnormalities of arteriolar resistance adversely influence early outcome, in terms of morbidity and mortality
• Few data available regarding the long-term effects of the Fontan circulation on the pulmonary vascular bed.
• Pulmonary thromboembolism is not infrequent - lead to adverse changes in vascular resistance
• Pulmonary artery flow in Fontan is relatively low velocity, laminar
• Different to the normal pulsatile flow of pulmonary vascular bed in normal circulation
• Release of nitric oxide from the endothelium is dependent on pulsatile flow in the normal circulation
• Experimentally, reducing pulsatility leads to reduced NO production and an increase in vascular resistance
• Nakano T et al, Pulsatile flow enhances endothelium-derived nitric oxide release in the peripheral vasculature. Am J Physiol Heart Circ Physiol Apr 2000;278(4):
• COMPLICATIONS OF FONTAN CIRCULATION
• Creation of Fontan circulation is palliative by nature• Proved good results with ideal hemodynamics
• Substantial morbidity and mortality – in those with unfavorable hemodynamics – those who underwent older surgical techniques
• Risk factors for complications include – elevated pulmonary artery pressure– anatomic abnormalities of the right and left
pulmonary arteries– atrial-ventricular valve regurgitation– poor ventricular function
Late mortality
• Late death is directly related to the number of risk factors for a Fontan operation
• Unfavourable haemodynamics and risk factors are associated with an increased early and late attrition
Functional status and exercise tolerance
• Most patients with a Fontan circulation to lead a nearly normal life, including mild to moderate sport activities
• More than 90% of all hospital survivors are in NYHA functional class I or 2
• However, with time there is a progressive decline of functional status in some subgroups
Ventricular dysfunction
• Ventricle of a functionally univentricular heart– Dilated, hypertrophic and hypocontractile
• May fail after years of systemic loading
• congenital malformation itself• original hemodynamic state of volume overload• Systemic ventricle may be a morphologic right or an
indeterminate primitive ventricle• previous surgical interventions• High RA pressure may impair coronary blood flow - affect
myocardial perfusion and function
• During the first months after birth - ventricle will always be volume overloaded
• Leads to dilation and hypertrophy of LV• After unloading at the time of a Fontan operation,
some regression to normalisation will occur - frequently incomplete
• Currently only a small shunt is allowed to persist for several months
• Ventricle thus evolves from being volume overloaded and overstretched, to overgrown and (severely) underloaded
• Low preload results in remodelling, reduced compliance, poor ventricular filling, and eventually continuously declining cardiac output
• Lack of reaction to classic treatment strategies has given the ventricle in a Fontan circuit a very bad reputation
• Little impact on ventricular function of – inotropes, afterload reducing agents, vasodilators,
and b blockers
• no impact on the reduced preload which is the dominant limiting factor
Arrhythmia
• Many old circuits have atrial wall incorporated into the circuit causing atrial dilation
• Dilatation predispose to– arrhythmia – swirling of blood in the enlarged atrium - stasis &
clot formation – results in poor blood flow to the lungs
• May have undergone atriotomy injure the sinus node or conducting fibers cause atrial arrhythmia
• Occur in up to 40% of the patients 10 years after surgery
• Most common atrial tachycardia is intra-atrial re-entry or atrial flutter
• Immediate direct current DC version• Anticoagulation in view of the significant risk of a
right atrial thrombus
• Long term treatment of atrial arrhythmia can involve medication and ablation
• Conversion of the old Fontan circuit to an extracardiac cavopulmonary connection
• Together with a right atrial maze and a reduction plasty
Collateral Vessels and Shunts
Collateral vessels and shunts may lead to substantial right-to-left shunts and cyanosis
• Incomplete closure or a residual atrial septal defect • Surgically created fenestration between the surgical
conduits and RA • Surgical redirection of coronary sinus blood flow to LA • Formation of pulmonary AV malformations• Patent collateral vessels between systemic and
pulmonary veins • Patent systemic veins that extend directly into LA
Left-to-right shunts
• Aortopulmonary collateral vessels - common • May lead to hemodynamic shunting - results in volume overload of the systemic ventricle
- increased PBF and pulmonary pressure• Arise from the thoracic aorta, internal mammary
arteries, or brachiocephalic arteries
Blood Vessels
• Increased frequency of pulmonary thromboembolic events– Dilated atrium – low cardiac output– coagulation abnormalities associated with hepatic
congestion – chronic cyanosis–induced Polycythemia
• Massive pulmonary embolism is the most common cause of sudden out-of hospital death in patients with Fontan circulation
• Reported incidences of venous thromboembolism and stroke are 3%–16% and 3%–19%, respectively
Pulmonary Circulation
• Fontan circulation results in a paradox of systemic venous hypertension (mean pr >10 )
pulmonary artery hypotension ( <15 mm Hg)
• Due to absence of the hydraulic force of RV
• Absence of pulsatile blood flow and low mean pressure in the PA underfill the pulmonary vascular bed and increase PVR
• Pulmonary arteries may be morphologically abnormal (small, discontinuous, or stenosed)
• PVR is an important determinant of cardiac output in Fontan circulation
• Stenosis or leakage of surgical anastomoses between the venae cavae and pulmonary arteries may adversely affect pulmonary blood flow
• Patients with borderline haemodynamics have been reported to deteriorate acutely after moving to altitude above 2000 m
Lymphatic System
• Fontan circulation operates at or sometimes beyond the functional limits of the lymphatic system
• Affected by high venous pressure and impaired thoracic duct drainage
• Increased pulmonary lymphatic pressure may result in interstitial pulmonary edema or lymphedema
• Leakage into the thorax or pericardium may lead to pericardial and pleural effusions (often right-sided) and chylothorax
Protein-losing enteropathy
• Relatively uncommon manifestation of failing Fontan circulation
• Cause is unclear• Loss of enteric protein may be due to elevated
systemic venous pressure that is transmitted to the hepatic circulation
• Lead to hypoproteinemia, immunodeficiency, hypocalcemia, and coagulopathy,
• May occur in the long term
• PLE is a relatively rare complication• In an international multicentre study involving
35 centres and 3029 patients with Fontan repair between 1975 and 1995, PLE occurred in 114 patients - 3.8%
• Mertens L et al. Protein losing enteropathy after the Fontan operation J Thorac and Cardiovasc Surg 1998;115:1063–73
• Very poor prognosis• Five year survival rate was 59%
Treatment options for PLE
• Diet high in calories• High protein content• Medium chain triglyceride fat supplements • Diuretics • Several surgical options have been reported– relief of obstruction– conversion to streamlined cavopulmonary
connection– atrioventricular–valve repair/replacement
Plastic bronchitis
• Rare but serious complication• 1%–2% of patients• Noninflammatory mucinous casts form in
tracheobronchial tree and obstruct the airway• Dyspnea,cough, wheezing, and expectoration
of casts - may cause severe respiratory distress with asphyxia, cardiac arrest, or death
• Exact cause unknown
Plastic bronchitis
• High intrathoracic lymphatic pressure or obstruction of lymphatic flow may lead to the development of lymphoalveolar fistula and bronchial casts
• Medical management is difficult - often require repeat bronchoscopy to remove the thick casts
• Surgical ligation of the thoracic duct may cure plastic bronchitis by decreasing intrathoracic lymphatic pressure and flow
Reproduction: pregnancy
• Most females after Fontan repair have normal menstrual patterns
• Increased systemic venous pressure may trigger complications of right heart failure such as atrial arrhythmias, oedema, and ascites
• Right-to-left shunt through a residual ASD will Increase - decrease in arterial saturation • Increased risk for venous thrombosis and pulmonary embolus• Successful pregnancy with delivery of normal children is
possible.
Coagulopathies
• Protein C, protein S, and antithrombin III deficiency• Most common cause of sudden out-of-hospital death
in patients with a Fontan circuit• Chronic multiple pulmonary microemboli may lead to
pulmonary vascular obstructive disease, a late complication– particularly lethal in a Fontan circulation.
• Some clinicians recommend anticoagulating every patient with a Fontan circuit
• Subgroups of patients with a very low risk• Full anticoagulation in– previous thrombi– poor cardiac output – congestion, dilation of venous or atrial structures, – arrhythmia
• All patients having undergone Fontan surgery and follow-up at Children’s Hospital Boston were included if they were born before January 1, 1985, and lived
• Type of Fontan surgery was classified into the following 4 categories: – Right atrium (RA)–to–PA anastomosis– RA–to–right ventricle (RV) connection– Intraatrial lateral tunnel (LT)– Extracardiac conduit (ECC)
Baseline Characteristics
• A total of 261 patients, 121 female (46.4%)• had their first Fontan surgery at a median age
of 7.9 years • 33 (12.6%) of which were fenestrated• Type of first Fontan – RA-PA connection in 135 (51.7%),– RA-RV in 25 (9.6%)– LT in 98 (37.5%) ECC in 3 (1.1%)
Mode of Death
• Over a median follow-up of 12.2 years years• 76 patients (29.1%) died• 5 (1.9%) had cardiac transplantation• 5 (1.9%) had Fontan revision• 21 (8.0%) Fontan conversion - LT in 16 or ECC in 5
• Overall, 52 deaths (68.4%) were perioperative• 7 (9.2%) were sudden• 6 (7.9%) were thromboembolic• 5 (6.6%) were due to heart failure• 2 (2.6%) were secondary to sepsis
Perioperative Mortality
• Of 52 perioperative deaths, 41 (78.9%) were early and 11 (21.1%) were late
• Importantly, perioperative mortality rates decreased steadily over time
• First Fontan surgery – Before 1982 -36.7%– 1982 to1989 - 15.7% – 1990 or later - 1.9%
Long-Term Survival
• Actuarial event-free survival rates at 1, 10, 15, 20, and 25 years were 80.1%, 74.8%, 72.2%, 68.3%, and 53.6%
• Significant disparities between Fontan categories mainly due to periop deaths in an earlier surgical era
• In perioperative survivors, freedom from death or cardiac transplantation was comparable among all types
• In early survivors, overall actuarial freedom from death or cardiac transplantation at 1, 5, 10, 15, 20, and 25 years was 96.9%, 93.7%, 89.9%, 87.3%, 82.6%, and 69.6%, respectively
• Death resulting from thromboembolism occurred at a median age of 24.9 years
• 8.7 years after Fontan surgery• Actuarial freedom from thromboembolic
death was 98.7% at 10 years and 90.8% at 25 years
• All patients had RA-PA Fontan surgeries except for 1 patient with an LT
Predictors of Thromboembolic Death in PerioperativeSurvivors
• Atrial fibrillation • Lack of aspirin or warfarin therapy • Thrombus within Fontan
Heart failure
• Heart failure–related deaths occurred at a mean age of 22.9
• 4.3 years after Fontan surgery• Actuarial freedom from death caused by heart
failure was 99.5% at 10 yrs and 95.8% at 25 yrs• Risk factors were single RV morphology, higher
postoperative RA pressure, and protein-losing enteropathy.
Sudden death
• Sudden death occurred at a median age of 20.2 years in 7 patients
• 3 with RA-PA, 3 with LT, and 1 with RA-RV • 2.9 years after Fontan surgery.
Conclusions
• Leading cause of death was perioperative, particularly in an earlier era
• Gradual attrition was noted thereafter, predominantly from thromboembolic, heart failure–related, and sudden deaths
• 70% actuarial freedom from all-cause death or cardiac transplantation at 25 years
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