Geeking Out on the Fontan: A technical discussion between brothers

Signed heart pillow

A conversation started between Colin (software engineer) and his brother Jared (dental Ph.D.) when Colin described Maddie’s Fontan procedure and its findings over email. These two brilliant guys went on to discuss the benefits of one method over another using some articles* that detailed the debate. Did I mention neither one is a cardiologist?

Some of you have asked what the surgery involved this time around. Here is the dialogue that ensued between the brothers. This is more technical than you would ever need as a layperson but I love it and am always eager to learn more. Feel free to “geek out” on the fascinating medical technology with us.

Dr. Wells (the surgeon who performed her first two surgeries) left her in good condition. Dr. Chen was able to follow what he had done and had no complications due to previous surgeries. He was able to widen the pulmonary vein somewhat, but the entire system is stenotic. He was not concerned about the stenosis as the pressure differentials were equal across both lungs. Instead of passing the Fontan through the atrium, due to the location of confluence of her major veins, they needed to have the Fontan go around the heart.

Post operation, her oxygen saturation was 97%. Pre-operation, her saturation was 83%.

-Colin

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One is a study¹, the other is a commentary² on the study from a cardiologist/electrophysiologist perspective. The study looks at the arrhythmia risks down the road of the different variations in fontan. The extracardiac conduit appears to have the best results a decade out relative to atrial arrhythmias.

-jared

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Thanks. I read both, now I just need to find out if they did an extracardiac lateral tunnel or an extracardiac conduit.

-Colin

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I read these two papers from both sides of the argument for and against extracardiac conduit placement. The decision was made in the moment by the surgeon, so reading these is obviously not for reaching a decision, but they do highlight the debate in the field concerning the long-term issues. I haven’t had a chance to follow up on the additional heterotaxy-based literature, which will be more pertinent to Maddie’s case.

-jared

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A quick read. 🙂 Maddie has a fenestrated extracardiac fontan which, according to the article, is the optimal extracardiac fontan in case they need to treat arrythmia through a catheterization procedure. The fenestration allows them access to the atrium. Now that I have a tiny background, I’m more curious about the exact anatomy. Specifically the orientation of her heart in relation to the fontan hardware as well as the relative position of the fontan hardware and glenn hardware as they enter the pulmonary artery. Also, does the pulmonary artery have to be disconnected from the “right” ventricle for this whole thing to work? It seems that there would no longer be any blood flow through the right structures and, if so, it would be oxygenated blood only except what small amount comes through the fenestration.

Now I’m hooked. I guess I just like engineering problems no matter what shape they take. Today I redesigned the bed to solve the problem of cord and tube entanglement, I helped the nurse better understand and utilize the vital statistics monitor UI, and I helped two men find their way through the hospital.

-Colin

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Nice work, you sound like Doctor Who.

[The girls] and I sat and discussed all the tubes, needles, and bands in the picture you posted of Maddie. We tried to figure out why everything was in place. We look forward to seeing her up and moving around again, and hopefully soon enjoying some chocolate milk.

-jared

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She’s past chocolate milk and moved on to soda. She had some sprite last night and kept it down while soaking in the wonders of original Scooby-Doo episodes. She’s off her pacer as of this morning. She is starting to feel a little homesick today though. If you guys have questions about any of the tubes, let me know. I know most of them now.

To add upon my education, I spoke with Maddie’s cardiologist last night. Some things weren’t making sense and Dr. Meg (her cardiologist) loves to geek out with me about her anatomy, so I got information from the person who knows Maddie’s anatomy second-best (assuming the surgeon knows it best). Her structures are reversed, but even for a heterotaxy kid her heart is different. The apex is not down, but to the right and the confluence of veins into the IVC occurs deep within the walls of her “right” atrium on the left side. Post Fontan, all systemic return is routed around the heart with gore-tex other than the fenestration into the “right” left atrium. I was confused because then the “right” left ventricle would seem to be a useless structure given that her pulmonary artery was severed from her heart during the Glenn procedure. I asked Dr. Meg about that and she said it would be, except Maddie’s heart has a double-exit ventricle. Her aorta is connected to both ventricles. Originally her right ventricle pumped to both arteries.

We speculated on the relative position of the Glenn entry and Fontan entry into the pulmonic artery (she didn’t know). Usually they put them right opposite each other and aim them straight at the artery so flow does not prefer one side over the other. We speculated on the fluid dynamics of that setup including churning and backflow. She agreed that there usually is some and swelling of the head after the Glenn and of the body after the Fontan is evidence of that.

Other risks of the fenestration include stroke, given that clots that are generated in the venous system have a path to the aorta through the fenestration and could get pumped to the brain. That is the main reason they often suggest to come back and close the fenestration a while after surgery. However, her liver–which is now already experiencing additional pressure–would experience even more pressure without the fenestration and would be susceptible to failure, so there is debate on which risk is greater.

I didn’t do any more Dr. Whoian deeds last night, but stay tuned…

-Colin

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I think you should make a 3D model of Maddie’s heart. I’m getting lost in all the ‘rights’. I’m glad Maddie is awake and doing well. Is she loaded up on pain medication? I imagine most movements are painful anyway. I hope the fenestration is helpful to her liver. How much fluid exudate is coming out of her lungs now? What causes it to eventually stop?

It looks like she has a picc line in her jugular. Were they using that in the OR, or is it more for just-in-cases afterwards (or both)?

-jared

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The IJ line is for taking pressure readings and administering drugs directly to her heart as needed. It is currently being used. She has been off most of her medications since yesterday morning. During the day yesterday they were administering morphine as needed. Today they have her on Ketoralac instead, and it is administered constantly.

I would love a 3D model, they should have one because they did an MRI a few months ago. I wonder if they would be willing to share a soft-copy of it, and I wonder what format it would be in. Her heart returned to irregular beats, so the pacer has been hooked back up.

She still has a lot of fluid coming out. The pressure change is so great with the Fontan that they expect the fluid to continue for many days to come.

-Colin

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*Extracardiac vs. Intracardiac debate: pro¹ vs. con²

See here for more “light reading” on the Fontan procedure: Intracardiac, lateral-tunnel Fontan has superior hemodynamics to the TCPC (extracardiac) and Hydrodynamic power loss of Glenn (and Hemi-Fontan) is considerably lower than that of the final completed TCPC

7 thoughts on “Geeking Out on the Fontan: A technical discussion between brothers”

  1. Love this! So interesting to read … and yes I am being serious {I suppose you can tell I am a former Biology teacher}! I even did my own “geeking” out the day of her surgery so I could better understand everything:

    http://www.lhm.org.uk/filestore/publications/fontan%20bookletfweb.pdf

    I enjoyed gleaning more info on how Maddie is doing from these email exchanged – you should keep posting them periodically 🙂 !! Maddie is a fighter for sure! Her poor little body has been through the wringer!

    XOXOXO

  2. I was somehow able to follow their “geeking out”… Although I must admit, I sometimes had to read what they wrote a few times before I understood it – hahaha ????. Where would this world be without Colins and Jareds ????

  3. Thanks so much for sharing! I agree a model of her heart would be interesting. She is quite the miracle girl! Sending you guys our prayers!

  4. I love my “geeky” brothers, their shared fascination with all things scientific, and the ability they have to make sense of seriously complex information.

    Thank you for sharing this conversation Jeanne. Your appreciation for the family “geek” ness is always a breath of fresh air.

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