Advanced Imaging of the Fontan, What is Driving Fontan Failure: New Horizons...
With Dr. Andrew Crean & Dr. Mike Takahashi · StayCurrentMD
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Single Ventricle / HLHS 37 items
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What the experts said
In adult Fontan patients, ventricular function is either moderately or severely dysfunctional but often does not change very much over the years.
A change in ventricular function in a Fontan patient is an indicator to look at the ventricle more carefully, as this is not frequently seen.
Embolic ventricular dysfunction is not a common feature of Fontans, but embolic complications are seen roughly once a year in the Toronto center.
Thrombus imaging in Fontan circuits is generally not done very well, particularly in adult Fontan circulations.
Timing is everything in imaging of the Fontan circulation, and usually imaging is performed too quickly, leading to false-positive thrombus diagnoses.
Premature contrast timing is a particular problem with on-call PE studies done in the middle of the night.
Radiologists imaging the chest typically want to image in the pulmonary arterial phase, which is too early to adequately opacify the IVC portion of Fontan circuits.
In large atriopulmonary Fontans, it can take up to 7 minutes for contrast to fully opacify the circuit and confidently exclude thrombus.
Late gadolinium enhancement imaging performed 10 minutes after contrast administration is effective for detecting thrombus in Fontan circuits.
Both CT and MRI are exquisitely good at looking at the presence of thrombus in Fontan circuits, and CT allows easy volumetric measurement of thrombus over time.
The tried and tested approach to managing large atrial thrombus in Fontan patients involves anticoagulation with heparin.
Resolution of Glenn shunt thrombus with TPA was associated with normalization of albumin levels, suggesting a link between venous obstruction and protein-losing enteropathy.
Fontan patients in their mid-80s oxygen saturation without open fenestrations are unusual and warrant investigation for causes of desaturation.
Veno-venous collaterals and arteriovenous malformations are easily seen by CT or MRI angiography but very difficult to detect in any other way.
The spatial resolution of cross-sectional imaging, particularly CT, allows detection of very subtle features such as highly stenotic coronary sinus drainage to the left atrium.
A Fontan patient presenting with a heart failure phenotype, particularly edema, does not necessarily have pump failure; conduit stenosis can present with anasarca.
Plastic bronchitis has not been seen in adult Fontan patients in 10 years at the Toronto center, though it is easy to detect by CT.
In adult patients, echocardiography is not adequate for thrombus detection in a Fontan circuit.
Transesophageal echo for detecting thrombus in an atriopulmonary Fontan is a waste of time and should not be done prior to cardioversion.
It took roughly 10 years and many cases where CT or MR were right and echo was wrong to convert colleagues in Toronto away from routine TEE for Fontan thrombus assessment.
Cardiac CT can be obtained within about 1 hour, which is more practical than organizing space on the CCU for a TEE in a sick Fontan patient.
The spatial resolution of cardiac CT is at worst 0.5 millimeters isotropic, which is sufficient to detect small thrombi.
In 10 years of practice, there have been no cases requiring escalation from CT to echo based on doubt about thrombus detection.
T1 mapping in adolescent Fontan patients shows fibrosis content is higher than in normal controls and significantly higher in those with systemic right ventricles compared to systemic left ventricles.
There are large series in the adult AF population with outcomes up to about a year suggesting no increased stroke risk when CT is used instead of TEE for pre-cardioversion thrombus assessment.