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CMR for Functionally Single Ventricle: Decision Making in Borderline LV & CMR Approach for the Cyanotic Fontan

Posted By lauren small, Thursday, May 28, 2020

Post your questions on the CMR for Functionally Single Ventricle: Decision Making in Borderline LV & CMR Approach for the Cyanotic Fontan webinar by commenting below.


The recording will be posted in the webinar section of the Online Learning Portal soon after the live webinar.

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lauren small says...
Posted Wednesday, June 3, 2020
Q: How often have you seen LGE in young Fontan patients?
A: Unexpected LGE is uncommon, usually there is a known event or obvious dysfunction.

Q: Do you double injection/ upper and lower extremity in Fontan? What is your protocol for CT?
A: There are various proposed CT injection protocols. In our experience, the most consistent is to do total body opacification technique using a large amount (3-4 cc/kg) of contrast medium injected through any vein and wait more than 50 seconds for timing the homogeneous opacification of the Fontan track using Smartprep.

Q: Are you using 4D flow sequences or standard 2D flow phase contrast images when quantifiying flow?
A: We currently use 2D PC for quantifying flow, but expect to use more 4D flow in the future for clinical work.

Q: After occluding the connection between the Fontan circuit and the atrium, has the patient developed any signs of PLE? Any liver changes?
A: Too early to tell.

Q: Have you used 4D Flow to measure flow on these patients with one sequence ?
A: Not clinically yet.

Q: Please share some experience on how to measure the flow volume accurately.
A: Here is a good starting point:

Q: On the first case, how did you determine that a lower extremity injection would be needed prior to the MRI?
A: Part luck. The patient had an ultrasound showing patency of the upper extremity and central head/neck veins, so went for below (although SCV collaterals can still be missed if not careful on ultrasound). Our protocol is always to follow the dynamic time-resolved MRA with a 3D respiratory-navigated and cardiac-gated IR GRE MRA (all with extracellular contrast), so even if we missed it on the dynamic we would've seen it on the anatomic angio. A further clarification, we only perform the dynamic time-resolved MRA if we are looking for shunts, otherwise we just use our 3D IR sequence.

Q: Do the values (4D Flow) get affected since the venc is the same for all vessels?
A: Two acquisitions, one for the vein and the other for the arteries would be ideal. However, it would be more practically applicable if we can get all data from a single acquisition. To achieve the goal with a VENC setting, we still need to know the highest allowable VENC for assessment of all vessels. Although it was shown that anti-aliasing capabilities are better in 4D than in 2D flow, it should be tested carefully in a good number of cases before just believing. Newer multi-VENC sequences may also be of value.

Q: Can you please enlighten as to what happened to patient 2? The one with cut off LPA?
A: It was a complicated course and medical management was the choice, with the main problem later being PLE. The patient is now doing well several years after the CMR I showed and weaning from PLE medications. No interventions or surgeries were performed if you can believe that.

Q: Can you comment on how to trace the volumes in MRI in single ventricle patients, does hypoplasic ventricle has to be completely included in the tracing? Do you avoid the remanent portion of the interventricular septum in the volume calculation? Any tip for accurate tracing?
A: After Fontan, if the ventricles are not connected (by VSD) trace separately, otherwise trace as one. Before commitment to single ventricle pathway, can trace separately. Correlating with your other hemodynamic data and previous exams may improve your accuracy. Usually we include the remnant IVS as part of the myocardium, although depending on how deficient it is, it might not make sense practically to do so based on the specific morphology. Finally, when the ventricular septum is intact and the outflow tract of the hypoplastic ventricle is atretic or severely stenotic, we do not include the volume of the hypoplastic ventricle.

Q: It seems by the potential volume formula that what really matters is the mitral valve annulus. Why don’t just measure MV Z score?
A: Potential volume is more a concept than actual use. Of little doubt, the larger the potential volume, the higher the chance of biventricular repair. However, it would be very difficult to show the statistical significance of this concept as both actual and potential volumes vary significantly among the patients and the difference in numeric values is quite small. For ‘scientific’ evidence, many homogeneous groups of patients is required.

Q: How do you measure PDA flow?
A: In preoperative assessment, it is easy to target the PDA as it is large and usually rather long and so you can use a direct PC. If there is a stent, then the PDA can be calculated indirectly with PCs elsewhere, eg: Qp - MPA or AAO - Qs. This can get more complicated depending on the specific physiology and various potential sources of error due to technique/morphology.

Q: Do you use dual injection for time resolved MRA in Fontan patients?
A: Not usually.

Q: How is LVEDVi Z score being taken in consideration for uni or biventricular decision?
A: I am not aware of literature supporting use of Z-scores for this purpose. The recent paper: has normal population Z-scores for neonates, however, the segmentation method is different than what we currently do clinically so we have not used them. Therefore, we do not have a reference normal population for the current way we do segmentation at our institution.

Q: In case of extracardiac Fontan, the contrast injection will be in lower and upper limbs during the CMR exam?
A: We typically only place one IV for Fontan.

Q: When traced together in VSD, what about the amount of remnant septum that can change the volume estimation a lot.
A: We include it as part of the myocardium when possible.

Q: Do you utilize 4D flow as standard for the measurement of flows?
A: Not clinically yet.

Q: What Is the normal volumen and eyection frAccion in a Unique ventricle
A: I don't know about "normal", but volumes are usually larger and EF lower than normal. The way we segment, in the 150 ml/m2 and 40-45% range is typical.

Q: Do you utilize mitral inflow?
A: Not clinically as it is usually inaccurate with 2D phase contrast.

Q: Do you assess pulmonary venous flow individually by phase contrast in the Fontan patients ? I often find limitations related to the size of the pulmonary veins.
A: Yes, we do the pulmonary veins individually.

Q: Do you do CMR on all hypoplastic LV? Or only if there is uncertainty by echo.
A: Only if we are deciding between uni vs biventricular repair. Some HLHS are clearly single ventricle pathway.

Q: Have you used MR lymphography to characterize the source and potential treatment for chylous effusion?
A: Yes, but that would be another lecture!

Q: Chris: Do you routinely measure fenestration flow?
A: We measure the fenstration flow prior to Cath closure under the same GA (combined MRI-Cath suite). There are 2 methods to do so. 1) direct PC measurement. 2) Fontan above fenestration - Fontan below fenestration. Usually they are equal. Fenestration flow, at least the way we make our fenestrations at SickKids, tends to take all of the IVC flow and sometimes even some of the SVC flow, so basically, we find the physiology after Fontan fenestration at our institution is not much different than BCPC.

Q: How are you measuring successful bivent repair? A good fontan vs bad 2 vent repair?
A: If they can survive a biventricular repair without major short or mid-term re-intervention, or conversion back to single ventricle pathway, that would be a success for now. Agree that we still need to see long term outcomes.

Q: Shi-Joon: WE had a CMR done to evaluate LV volume for a HLHS child at Day decide on single pr bivent pathway....
A: Yes, we typically do in the 1st few days of life.
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