What is Fontan Paradox?

What is Fontan Paradox?

The term Fontan Paradox was coined by Marc de Leval in 2005 as paradox seen in Fontan circulation with caval hypertension, mainly in the splanchnic region and relative pulmonary arterial hypotension [1,2]. According to him, in a normal biventricular circulation, the mean caval pressures are less than 10 mm Hg and the mean pulmonary arterial pressure is at least 15 mm Hg to keep the pulmonary vasculature patent. He further suggested that a mechanical device capable of producing a step down in pressure energy of 5 mm Hg in the inferior vena cava and producing a step up of 5 mm Hg in the pulmonary arteries could potentially reverse the Fontan paradox.

Different computational models have been demonstrated for such a device, but none has been deployed clinically so far, to the best of my knowledge [3,4]. An editorial commentary on a proposed device mentioned that the concept is similar to that of a venovenous extracorporeal membrane oxygenator without the oxygenator part and hence would be suitable for short term support like a bridge to transplant. It was pointed out that it would not help in case of failing Fontan circulation due to ventricular dysfunction. Another downside suggested was that the presence of a large cannula in the superior vena cava could cause obstruction to superior vena caval flow [5].

Cavopulmonary assist device is proposed to be implanted in situ in the total cavopulmonary connection (TCPC) [4].

References

1. de Leval MR. The Fontan circulation: a challenge to William Harvey? Nat Clin Pract Cardiovasc Med. 2005 Apr;2(4):202-8. doi: 10.1038/ncpcardio0157. PMID: 16265484.
2. Kutty S, Jacobs ML, Thompson WR, Danford DA. Fontan Circulation of the Next Generation: Why It’s Necessary, What it Might Look Like. J Am Heart Assoc. 2020 Jan 7;9(1):e013691. doi: 10.1161/JAHA.119.013691. Epub 2019 Dec 19. PMID: 31852419; PMCID: PMC6988165.
3. Rodefeld MD, Coats B, Fisher T, Giridharan GA, Chen J, Brown JW, Frankel SH. Cavopulmonary assist for the univentricular Fontan circulation: von Kármán viscous impeller pump. J Thorac Cardiovasc Surg. 2010 Sep;140(3):529-36. doi: 10.1016/j.jtcvs.2010.04.037. Epub 2010 Jun 18. PMID: 20561640; PMCID: PMC2924921.
4. Rodefeld MD, Marsden A, Figliola R, Jonas T, Neary M, Giridharan GA. Cavopulmonary assist: Long-term reversal of the Fontan paradox. J Thorac Cardiovasc Surg. 2019 Dec;158(6):1627-1636. doi: 10.1016/j.jtcvs.2019.06.112. Epub 2019 Aug 28. PMID: 31564543.
5. Hsia TY. Commentary: The Fontan paradox: A de Leval challenge. J Thorac Cardiovasc Surg. 2019 Nov;158(5):1434-1435. doi: 10.1016/j.jtcvs.2019.04.066. Epub 2019 Apr 30. PMID: 31128901.