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Echo after single ventricle repair
echo in ped and adult congen ht dis
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12/17/2013

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Term
What is meant by Fontan physiology?
Definition

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.

Term
What is a healthy central venous pressure in Fontan physiology?
Definition
10-12 mmHg
Term
In a patient with a single ventricle (or effective single ventricle), what are the two benefits of creating a Fontan circulation?
Definition

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

2. Reducing the volume overload on the single ventricle

 

Term
How was the first Fontan pathway constructed?
Definition

1. Connection of the SVC to the RPA

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

n[image]

Term
What are the complications of the early (atrio-pulmonary) Fontan pathway?
Definition

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

Term
In patients with a Fontan pathway, what other sources of systemic embolus exist?
Definition

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)

Term
How can RA dilatation be avoided when creating a Fontan pathway for the IVC?
Definition

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

[image]

Term
What is a fenestration?
Definition
A fenestration is a hole made on purpose in the IVC conduit. It is usually 3-5 mm in diameter.
Term
What are the advantages of a fenestrated conduit?
Definition

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)

Term
What are the disadvantages of IVC conduit fenestration?
Definition

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 

Term
What are the hemodynamic benefits of a Fontan pathway?
Definition

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

[image]

Term
The fenestration in an ivc conduit opens into the functional left atrium. (Sometimes both anatomic atria empty into the systemic ventricle and sometimes the atrial septum has to be excised.) So, the fenestration is a kind of ASD. Is the shunt created left to right or right to left?
Definition

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

Term
What is the optimal gradient across the IVC conduit gradient?
Definition

5-8 mmHg. 

<5, co volume depletion

>8 co increased pulmonary resistance

Term
Is flow across the fenestration phasic or constant?
Definition

Phasic.

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

 

Term
What is the effect of atrial and ventricular contraction on flow across the fenestration of an extracardiac Fontan conduit?
Definition

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.

[image] 

Term
How do the hemodynamics (and doppler wave form) of an atriopulmonary Fontan pathway differ from an extra-cardiac Fontan pathway?
Definition

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. 

[image]

Term
What effect does the loss of A-V synchrony have on Fontan hemodynamics in patients with extracardiac IVC-PA conduits?
Definition

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.

 

Term
When is a Fontan (single ventricle) palliation a good idea?
Definition

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)

 

Term
What physiology would make the Fontan a grave mistake?
Definition
Any resistance to flow along the pathway between the cava and the LV.
Term
What cardiac factors would cause resistance to caval-pulmonary flow?
Definition

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

Poor systolic function of any cause

AV valve malfunction-stenosis or regurgitation

 

 

Term
What pulmonary factors would make a Fontan a mistake?
Definition

Elevated pulmonary resistance (>2.5 WU)

Hypoplastic PAs

Abnormal pulmonary parynchema

pulmonary venous stenosis

 

Term
When a Fontan pathway is created, what is the immediate effect on LV contractility and pulmonary blood flow?
Definition

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. 

 

 

Term
What is meant by "staging" a Fontan?
Definition

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.

Term
What are the determinants of early and late mortality?
Definition
Any of the conditions described above that restrict blood flow anywhere along pathway from cavae to aorta. Pts with even borderline contraindications who are accepted for surgery do less well than pts who are ideal candidates.
Term
What is the functional status after a successful Fontan?
Definition
Most pts are asymptomatic or mildly symptomatic. 02 consumption is about 70% of normal.
Term
Which pt is more likely to experience ventricular failure after Fontan palliation, a pt with a hypoplastic left ventricle or a double inlet left ventricle?
Definition

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.

Term
AV valve regurgitation is poorly tolerated after Fontan palliation. Which is more likely, tricuspid or mitral regurgitation?
Definition

Tricuspid regurgitation

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

Term
Are pts with Fontan palliation at risk for ventricular arrythmias and sudden death?
Definition
No, unless severe systemic ventircular function is present.
Term
Which Fontan pathways are associated with atrial arrythmias?
Definition
Atrial arrythmias are common in pts with either atriopulmonary or lateral tunnel Fontan surgeries. Both surgeries lead to atrial dilatation. Long term fu is not yet available for extracardiac conduits. We hope that arrythmia will be less common after that surgery.
Term
In pts with atriopulmonary or lateral conduit Fontan pathways, what factors increase the risk of arrythmia?
Definition

Atriotomy

Damage to the sinus node or the sinus node artery

Increased pulmonary resistance or any other cause of increased pulmonary resistance

Term
Which atrial arrythmias are most common in pts with with Fontan pathways?
Definition
atrial tachycardia due to reentry or atypical atrial flutter
Term
What is the best way to deal with atrial tachycardia or atrail flutter acutely?
Definition

Cardioversion.

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

Term

True or False

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

Definition

True

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

Term
Is anticoagulation indicated in pts with Fontan pathways and atrial tachycardia?
Definition

Yes

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

Term
Why are bradyarrhythmias common after Fontan palliation?
Definition
Damage to the sinus node or its artery during surgery leads to sinus node dysfunction. Escape junctional rhythms  may be the consequence. Loss of atrial synchrony leads to venous congestion and decreased ventricular preload. Pacemakers are often required.
Term
How would you place the leads for a pacemaker in a pt with a Fontan pathway?
Definition
Epicardial leads are preferred.
Term
You see a pt with an extracardiac Fontan pathway. The pt feels well. The surgcial report says that all right to left shunts were closed and no fenestration was created. But the arterial 02 sat is only 92%. What do you make of this?
Definition
Mild desaturation is the rule even when Fontan pathway is functioning well. In pts with lateral tunnel or extracardiac pathways, the coronary sinus drains to the left atrium resulting in a small right to left shunt and desaturation.
Term
What are some causes of hypoxemia in pts with Fontan pathways?
Definition

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

Term
What are some causes of left to right shunts in pts with a Fontan pathway?
Definition

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.

Term
Should a left to right shunt be closed. If so, why? If not, why not?
Definition
Left to right shunts should be closed. They are usually small enough that they do not pose a threat to the systemic ventricle. But any increase in pulmonary blood flow may increase in pulmonary pressure and resistance and can be harmful.
Term
Which intervention will increase cardiac output the most: administration of dobutamine at 8 mcg/kg/min or balloon dilatation of a PA narrowing with a gradient of 5 mmHg?
Definition
Dilatation of a narrowed PA will have the most effect on cardiac output. Cardiac output is dependent on preload in a Fontan circulation. Dobutamine may increase ejection fraction, but end diastolic volume will fall as there is no increase in venous tone to augment pulmonary blood flow. Even if venous tone increased (as it does during exercise), unless pulmonary resistance is low, there can be no increase in pulmonary venous flow.
Term
A pt with a Fontan palliation has high caval pressures. As an infant, a modified Blalock-Taussig shunt had been created on the left side to augment pulmonary blood flow.It had been "taken down" when the pt completed the Fontan pathway. What complication should you consider?
Definition

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.

Term
he lymphatic system has its own circulation, ending in the thoracic duct. In what structure does the thoracic duct drain?
Definition

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

[image]T

Term
Why is lymphedema a danger in pts with a Fontan circulation?
Definition
High venous pressures impede emptying of the thoracic duct leading to high lymphatic pressures.
Term
Where my might lymph collect and how might it manifest?
Definition

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

Term
What is protein losing enteropathy? (PLE for short)
Definition
PLE results from intestinal lymphangectasia and consists of loss of proteins ( including albumin and immunoglobulins), lymphocytes, and chylomicrons through the bowels.
Term
What is the prognosis of patients with PLE?
Definition
Poor. Over half are dead within 5 years.
Term
Why to pts with a Fontan circulation develop PLE?
Definition

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.

Term
What treatments are available for PLE?
Definition

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

Term
Is pregnancy contraindicated in women with Fontan circulation?
Definition

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.

Term
What complications might arise in a woman with Fontan circulation during pregnancy?
Definition

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

Term
What is the risk of congenital heart disease in the child of woman with Fontan circulation?
Definition

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%

Term
What coagulation factors are frequently abnormal after Fontan palliation?
Definition
Like any pt with hepatic congestion, proteins C, S, and antithrombin are decreased.
Term
How can a pt with pulmonary embolus present?
Definition

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

However, multiple microemboli can result in subacute pulmonary htn. 

Term
Should all pts with a Fontan circulation by anticoagulated?
Definition

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

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