EXPLANATION


The Fontan procedure is the final operation in the single ventricle palliative pathway. Fontan physiology is characterized by the absence of a subpulmonary ventricle and drainage of systemic venous blood directly into the pulmonary arterial circulation, resulting in passive blood return to the lungs for oxygenation. With surgical and perioperative advancements, Fontan patients are reaching reproductive age due to an estimated survival rate nearing 80% at 20 years. However, morbidity remains high as a result of the deleterious consequences of Fontan physiology, such as elevated systemic vascular resistance (SVR), high arrhythmia burden, single ventricular diastolic dysfunction, chronic elevation in central venous pressure (CVP), and reduced preload/filling of the single ventricle from the cavo-pulmonary anastomosis. Additionally, Fontan physiology is characterized by low cardiac output despite higher central venous pressures, high pulmonary vascular resistance, and increased preload dependence. The physiologic effects of pregnancy, positive pressure ventilation and sustained arrhythmias can lead to negative hemodynamic effects.


During pregnancy, neurohormonal activation causes increased heart rate, blood volume, cardiac output, as well as vasodilation to favor uteroplacental perfusion. These factors add considerable hemodynamic stress to patients with Fontan physiology, who may already have tenuous cardiopulmonary function/reserve. The pregnancy-induced decrease in SVR may not completely offset the intrinsic arterial stiffness present in Fontan patients, thereby increasing the work required from the single ventricle to meet the new metabolic requirements. The 45% increase in blood volume is usually well tolerated and contributes to increased cardiac output. The expansion in blood volume load typically reaches a maximum during labor, delivery, and the early post-partum period due to autotransfusion from uterine contractions and subsequent uterine involution.


However, in some patients with elevated pulmonary vascular resistance (PVR), cavo-pulmonary pathway obstruction/stenosis, valvular regurgitation, or diastolic dysfunction, the expansion in blood volume may precipitate heart failure (HF). Garcia Romero et al. conducted a systematic review to evaluate maternal and fetal outcomes in pregnant Fontan patients. The study analyzed outcomes in 225 pregnancies in 133 women that resulted in 115 live births. Supraventricular tachyarrhythmia was the most common adverse event affecting 8.4% (3% to 37%) of Fontan patients. The underlying mechanism is attributed to pregnancy-induced adrenergic activation and atrial stretch from fluid loading in individuals prone to tachyarrhythmias. Heart failure was the second most common complication affecting 3.9% (3% to 11%) of the pregnant Fontan patients. The low occurrence of heart failure is explained by the low rate of systolic ventricular failure and low incidence of severe Fontan-related complications in those Fontan patients who are able to get pregnant. Reassuringly, no maternal deaths were reported in this analysis. Whilst the Fontan circulation creates a prothrombotic state, exacerbated during pregnancy, thromboembolic events such as strokes and pulmonary embolism were infrequent in the study population.


Obstetric complications are common in the Fontan population. Both antepartum and post-partum bleeding are estimated to occur in roughly 15% of pregnant Fontan patients, compared to 2-11% in the general population. This is attributed to underlying liver disease, anticoagulation, a higher incidence of cesarian section delivery, and the restrictive use of uterotonics. Interestingly, Fontan patients without significant liver disease and higher resting saturation were more likely to become pregnant. Over 50% of Fontan patients who become pregnant experience miscarriages. Furthermore, 50% of live births occur prematurely, and 20% of these neonates are small for gestational age. These complications are thought to be caused by a chronically low cardiac output state and neuro-hormonal activation, leading to uteroplacental insufficiency.


The literature suggests many single-ventricle patients can safely carry a pregnancy close to term. According to the modified WHO classification of maternal cardiovascular risk, Fontan patients who do not have protein-losing enteropathy, systolic ventricular dysfunction, or atrioventricular valve regurgitation are considered to be at moderate-to-high risk of adverse cardiac or obstetric events (Class III) whereas those who do have the complications listed above are at extremely high risk (class IV).


The correct answer is C, arrhythmias, which occur more frequently than heart failure or thromboembolic events in pregnant Fontan patients with few other comorbidities.


REFERENCES


Garcia Ropero A, Baskar S, Roos Hesselink JW, et al. Pregnancy in Women With a Fontan Circulation: A Systematic Review of the Literature. Circ Cardiovasc Qual Outcomes. 2018;11(5):e004575. doi:10.1161/CIRCOUTCOMES.117.004575


Maisat W, Yuki K. The Fontan Circulation in Pregnancy: Hemodynamic Challenges and Anesthetic Considerations. J Cardiothorac Vasc Anesth. 2024;38(11):2770-2782. doi:10.1053/j.jvca.2024.07.021


Breviario S, Krishnathasan K, Dimopoulos K, et al. Pregnancy in women with a Fontan circulation: Short and long-term outcomes. Int J Cardiol. 2024;415:132445. doi:10.1016/j.ijcard.2024.132445


van Hagen IM, Roos-Hesselink JW. Pregnancy in congenital heart disease: risk prediction and counselling. Heart. 2020;106(23):1853-1861. doi:10.1136/heartjnl-2019-314702


Cannobio MM, Warnes CA, Aboulhosn J et al. Management of pregnancy in patients with complex congenital heart disease: A scientific statement for healthcare professionals from the American Heart Association. Circulation. 2017;135(8):e50-e87. doi:10.1161/CIR.0000000000000458