In Fontan physiology, all caval flow is directed to the pulmonary artery without the benefit of a ventricle. It is used when congenital heart disease  results in only a single usable ventricle or when there is aortic atresia. 

In Fontan physiology, the pressure to move blood across the pulmonary resistance vessels comes from central venous pressure.

1. Elimination of shunting = creation of a circulation in series

2. Reducing the volume overload on the single ventricle

1. Connection of the SVC to the RPA

2. Connection of the RAA appendage to the RPA near its junction with the MPA

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Atrial dilatation

Decreased atrial flow (swirling pressaging thrombus)

Thrombus and pulmonary embolus

Arrhythmia

For these reasons, the atriopulmonary pathway has been abandoned, tho some children with this surgery are now being followed as adults

Residual shunts 

PA stumps. In creating a Fontan pathway, the MPA is ligated to prevent shunting. If the MPA is closed above the pulmonic cusps, then a pouch is formed where thrombus might develop and have access (through pulmonic insufficiency, with the systemic circulation)

By using a conduit to join the IVC to the PA.

1. The conduit may be contained within the lumen of the RA and use the RA lateral wall as prosthetic material (dacron)

2. the conduit may be extracardiac and run along the outside of the RA

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1. higher cardiac output (filling is not limited by pulmonary resistance)

2. lower central venous pressure (the conduit can empty at a pressure lower than that of the PA)

Cyanosis created by the right to left shunt

In theory, the right to left shunt could result in systemic embolus, but I am not aware that this is a problem. A recent article in J Thoracic and cardiovasc Surgery in 2010 did not report any strokes during long term fu. Most patients were anticoagulated

Fenestration during Fontan palliation: Now the exception instead of the rule 

Fontan pathways preserve some of the pressure energy in the aorta and make it available to improve filling (preload) of the systemic ventricle. In single ventricles filling from the systemic and pulmonary veins, the filling pressure must be low enough to accomodate the systemic veins. Study the diagrams below from "The Fontan Circulation" by Gewillig in Heart '05

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Right to left! Central venous pressure must be higher than PA pressure which in turn must be higher than LA and LV diastolic pressure.

That is why fenestrations cause cyanosis even as they increase cardiac output

5-8 mmHg. 

<5, co volume depletion

>8 co increased pulmonary resistance

Phasic.

Flow across the fenestration is determined by venous return affected by respiration, and LA pressure affected by LA and LV contraction.

Since the conduit does not contract, left atrial contraction decreases the gradient by increasing the LA pressure (following Ac). Left atrial relaxation increases the gradient(just after Ar). 

Initially, LV contraction causes an increases in LA pressure as the AV valve bulges into the LA (c wave just after QRS). That decreases the gradient. As the ventricle contracts, it stretches the LA and LA pressure falls. As LA pressure falls, the gradient increases.

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Atriopulmonary Fontan pathways contain a right atrium. The RA will contract with various degrees of vigor (assuming sinus rhythm). When the RA contracts, the gradient across the lungs (and velocity) increase. When the RA relaxes, the gradient may decrease and even become negative as the RA draws blood from the PA. 

A rule of thumb: velocities in an atriopulmonary Fontan may reach zero or even reverse directions. Velocities in an extracardiac Fontan never reach 0. 

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Atrial contraction during ventricular systole results in a decreasae or even reversal of the LA-PA pressure gradient. Flow (and velocities) diminish or, depending on the timing of atrial contraction and the respiratory cycle, reverse.

The figure below is taken from a pt with CHB. In the PA, atrial contraction in late systole (near the height of the V wave) results in a cannon a wave. In the hepatic vien, cannon a waves are the rule except in the waveform above the letter "F". There, near A-V synchrony results in normal waveform with antegrade velocity and flow.

When part of the venous or systemic cardiac pathway is unusable. 

Tricuspid atresia

Pulmonary atresia with intact ventricular septum

Double inlet LV (with small RV)

Atrioventricular septal defects that are unbalanced---one of the AV valves overrides the septum such that both atria discharge into one ventricle

Hypoplastic LV (in which the RV becomes the systemic ventricle)

Diastolic LV dysfunction due to increased afterload (AS, LVOT obstruction, coarctation, hypertension)

Poor systolic function of any cause

AV valve malfunction-stenosis or regurgitation

Elevated pulmonary resistance (>2.5 WU)

Hypoplastic PAs

Abnormal pulmonary parynchema

pulmonary venous stenosis

By preventing mixing of caval and pulmonary venous blood in the systemic ventricle, the Fontan pathway decreases preload and with it contractility. 

By removing the "shortcut" allowing blood to bypass the PAs, pulmonary blood flow increases. PA pressure and resistance may rise as well. 

To allow the pulmonary vasculature and systemic ventricle to adapt to the new flow and loading conditions, the Fontan pathway is created in two steps. During the first year of life, after pulmonary resistance has fallen, the superior vena cava is attached to the right pulmonary artery. (That is called a, "bidirectional Glenn".)

After a couple of years during which the PAs grow with the help of extra flow and the LV adapts to a loss of preload, the IVC conduit is added.

Hypoplastic left ventricle

When the systemic ventricle is an anatomic right ventricle, ventricular dysfunction is likely. The anatomic right ventricle lacks a middle, circumferential layer of muscle unlike the anatomic left ventricle. Perhaps that is why the higher pressures of the systemic circulation lead to dsyfunction.

Tricuspid regurgitation

Functional TR is a consequence of RV dysfunction and RV dysfunction is more likely than LV dysfunction.

Atriotomy

Damage to the sinus node or the sinus node artery

Increased pulmonary resistance or any other cause of increased pulmonary resistance

Cardioversion.

The loss of AV synchrony can diminish ventricular preload resulting in hypotension.

True or False

The onset of atrial tachycardia in pts with atriopulmonary or lateral tunnel Fontans may signify increased resistance within the Fontan pathway

True

Adverse hemodynamics are often the trigger for arrythmia. In particular pulmonary emboli from the dilated RA should be excluded.

Yes

The dilated RA is prone to thrombus. Should pulmonary embolus develop, severe venous congestion and hypotension can result.

Fenestrations in lateral tunnel or extracardiac pathways may cause hypoxemia if venous pressures rise. 

Don't assume that all anatomic abnormalities had been found and corrected prior to creation of the Fontan pathway. Common problems include

pulmonary avm

left SVC to coronary sinus or directly to LA

hepatic veins entering the anatomic RA directly that were not incorporated into the ivc tunnel

Fontan pathways are often used in the setting of pulmonary atresia or other conditions of diminished pulmonary blood flow. Left to right shunts are either created by the body (aortopulmonary collaterals) or the surgeon (Waterston, Potts, Blalock Taussig shunts). Also, in creation of the Fontan pathway, the surgeon may not ligate the MPA completely.

The persistence of any of the above will result in a left to right shunt.

Kinking of the LPA.

Systemic-pulmonary shunts fix the PA in a particular position. As the pt (and PA) grow, that may result in kinking.

The thoracic duct enters the left subclavian vein at its junction with internal jugular vein.

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pericardium or pleural space---chylous effusion (usually in periop period)

Bowels----protein losing enteropathy (most common)

bronchi---plastic bronchitis (often diagnosed at autopsy)

 legs---lymphedema

The most common problem is hemodynamic.

Myocardial dysfuntion

AV valve regurgitation

pulmonary venous stenosis

pulmonary parenchymal disease

pulmonary thrombus

hypoplastic pulmonary arteries or kinking due to prior shunt

conduit stenosis or anastamoses that cause excessive turbulence and wasted energy

In some patients, infectious or autoimmune processes seem to be the trigger for PLE.

A search of the Fontan circulation from stem to stern for ways to reduce resistance to flow

Creation of a fenestration to reduce caval pressure (at the expense of cyanosis)

Diuretics for edema

A high calorie, high protein diet with medium chain triglycerides

Albumin and immunoglobulin infusions

Treatment of infection

Steroids

Transplantation

Not if the woman in question has good ventricular function, no more than mild desaturation, and a venous pressure of 12 or less. 

Pregnancy often results in children who are always a nuisance.

Increased blood volume and cardiac output as well and a mild hypercoagulable state can lead to

atrial arrythmias

edema and ascites

increased right to left shunting through a fenestration

venous thrombosis or pulmonary embolus

There is not much information yet since Fontan palliation has not been around long enough to let a large number of women with lesions treated with a Fontan palliation go through pregnancy.

A reasonalbe guess is 5-10%

Because of the lack of a right ventricle, pulmonary emboli may present with shock

However, multiple microemboli can result in subacute pulmonary htn. 

No, but by the time you are through going down the list of indications, most will be anticoagulated

atrial arrythmia

low cardiac output (spontaneous echo contrast, poor lv function)

Known thrombus or embolus

markedly dilated RA

Oral contraceptives are relatively contraindicated