Nov. 27, 2019
Congenital heart disease specialists have nearly 50 years of experience with palliative surgery for patients who have anatomy that will not accommodate a biventricular circulation, using variations of the Fontan operation to redirect blood flow. Multiple studies document encouraging survival rates in these patients — especially in early childhood. But over time, data show potential for long-term complications.
Original Fontan palliation and extracardiac conduit Fontan modification
The Fontan operation involves routing of systemic venous return directly into pulmonary circulation, bypassing the subpulmonary ventricle. The procedure has undergone several modifications since 1971, as illustrated in these schematics: A. The original Fontan procedure, which entailed anastomosis of the distal end of the right pulmonary artery to the superior vena cava; anastomosis of the right atrial appendage to the proximal end of right pulmonary artery by means of an aortic valve homograft; closure of atrial septal defect; insertion of a pulmonary valve homograft into the inferior vena cava; and ligation of the main pulmonary artery. B. Extracardiac conduit Fontan involving anastomosis of a vascular graft between the inferior vena cava and the pulmonary artery, which allows more uniform flow with less turbulence.
One emerging area of concern centers on pregnancy in women who have had a Fontan palliation. Placental insufficiency can be a cause of high preterm birth rate and small-gestational-age births. To understand the relationship of the Fontan circulation to placental health and pathology, a Mayo Clinic team evaluated a series of women with Fontan palliations treated at Mayo Clinic's campus in Rochester, Minnesota, who completed a pregnancy. The researchers published their results in the August 2019 issue of the International Journal of Cardiology, and a related editorial comment frames the issue.
Results show that select women can have successful pregnancies, but "Fontan physiology may not be compatible with good placental health," explains lead author Sabrina D. Phillips, M.D., a cardiologist at Mayo Clinic in Jacksonville, Florida.
Dr. Phillips expects the evidence presented in this case studies series to prompt further investigation of post-Fontan pregnancy outcomes and more rigorous pathological evaluation of placentas, particularly in women with congenital heart disease.
"More study is required regarding the pathology of the placenta in women with Fontan physiology. It may be that, similar to the liver, the placenta represents another site of end-organ damage," she says.
Post-Fontan pregnancy results
The team studied seven women with Fontan palliation who, between 2002 and 2013, had 13 deliveries. They concluded that, "similar to the liver, the placenta appears to sustain end-organ damage from the Fontan state of hypovolemia."
In addition, they found that high systemic venous pressure and low cardiac output typical of patients who have undergone Fontan operations may contribute to stagnation of placental blood flow and result in subchorionic fibrin deposition and variable villous hypoplasia.
Pregnancy results showed that:
- Of 13 births, only two were full term.
- Mean maternal age at last delivery was 27. 5 ± 3.2 years.
- Preeclampsia was noted during two pregnancies.
- At 24 and 35 weeks, two women had preterm premature rupture of membranes.
- Placental abruption with bleeding occurred in two pregnancies.
- Four pregnancies were complicated by intrauterine growth restriction.
- Placental weight varied greatly: Two were below the 10th percentile and five were above the 90th percentile for gestational age.
- Two umbilical cords contained a single umbilical artery.
- In all placentas, prominent subchorionic fibrin deposition was a consistent feature.
Combined, these findings suggest that post-Fontan pregnancies require close management across the pregnancy continuum, from preconception counseling that includes cardiology and obstetric evaluation to peripartum care and follow-up. "These evaluations need to be meticulous," Dr. Phillips says. "Preterm deliveries and small-for-gestational-age newborns should be expected in this population and, ideally, cared for at a multidisciplinary care center offering maternal-fetal medicine specialists, neonatologists and cardiologists."
She adds that analysis of placental pathology may be helpful in guiding decision-making about future pregnancies.
In 2015, Mayo Clinic published the largest single-center study of long-term outcomes of patients post-Fontan palliation, following up on 1,052 patients who underwent the modified Fontan operation at Mayo Clinic between 1973 and 2012. The findings were published in the Journal of the American College of Cardiology.
Despite remaining challenges of medical complications associated with long-term exposure to Fontan circulation, patient survival has improved as surgical techniques have been refined. Overall, 10-, 20-, and 30-year survival for the 1,052 Mayo patients was 74%, 61%, and 43%, respectively. More recent surgeries tend to have the best survival rates, such as the late survival of 95% at 10 years for the cohort that underwent a Fontan operation after 2001.
Fontan circulation effects
Developed separately in 1971 in France by Francois M. Fontan, M.D., and in Venezuela by Guillermo Kreutzer, M.D., the Fontan operation has become a foundational palliative surgery to redirect blood flow in infants born with a diverse group of congenital heart defects that share the trait of having only one functional ventricle.
The Fontan operation creates a circulation that appears to be well tolerated in childhood. But because the Fontan circulation is characterized by diminished cardiac output and elevated central venous pressure, over time and with demands of adult physiology, the Fontan circulation affects organ systems outside the heart. Studies document a range of effects beyond the heart. Among them:
- Change in liver architecture
- Alteration in renal function
- Increased incidence of protein-losing enteropathy
Combined, the results of Mayo Clinic's 2015 study of Fontan physiology and those of its recent placenta and pregnancy study will likely help lead to healthier mothers post-Fontan palliation and their babies. Says Dr. Phillips: "Evaluation of placental pathology may enhance our knowledge of the effects of Fontan physiology on neonatal outcomes."
For more information
Phillips AL, et al. The placenta: A site of end-organ damage after Fontan operation. A case series. International Journal of Cardiology. 2019;289:52.
Pundi KN, et al. 40-Year follow-up after the Fontan operation: Long-term outcomes of 1,052 patients. Journal of the American College of Cardiology. 2015;66:1700.
Goldberg, DJ. Editorial comment. The Fontan operation: Improved outcomes, uncertain future. Journal of the American College of Cardiology. 2015;66:1711.