Association of Fetal Atrial Septal Aneurysm with Arrhythmia and Ventricular Hemodynamics

Atrial septal aneurysm (ASA) is characterized by a redundant atrial septum primum that bows >50% into the left atrium. Prior studies have suggested an association between ASA and the development of fetal arrhythmias. We aim to assess the association between ASA and arrhythmias in a large cohort of fetuses with isolated ASA. Our secondary aim is to evaluate for any changes in the cardiac output (CO) and/or aortic arch flow in the same cohort.

This was a single-center retrospective study of fetuses diagnosed with isolated ASA from January 1, 2016, to April 1, 2024, who were referred to our tertiary fetal center. All fetuses were identified by a coded diagnosis of ASA and evidence of a structurally normal heart. The presence and type of arrhythmia were assessed for each subject. Atrial septal aneurysm severity was measured as the atrial septal excursion index (ASEI) defined as the maximum excursion of the septum primum divided by the diameter of the left atrium. We also evaluated ASEI in correlation with hemodynamic changes assessed by left (LV) and right ventricular (RV) CO, chamber dimensions, RV CO/LV CO ratio, and flow reversal in the aortic arch using univariate linear regression. Comparisons in ASEI were made between fetuses with and without arrhythmias.

Among the 147 fetuses studied, arrhythmias were detected in 32 cases (22%). Premature atrial contractions were the most common type of arrhythmia (81%), followed by supraventricular tachycardia (13%) and then atrial flutter (6%). Only 1 patient with atrial flutter required transplacental therapy for rate control. The ASEI was higher in fetuses with arrhythmias (0.79 [0.74, 0.82] vs 0.69 [0.64, 0.73], P < .001). Our analysis identified an ASEI cutoff of 0.74, above which the likelihood of arrhythmias is significantly higher. Overall, there was good interrater reliability for ASEI measurements (intraclass correlation coefficient = 0.806; 95% CI, 0.681, 0.885; P value < .001). No significant correlation was observed between ASEI and absolute LV or RV CO Z score values, RV CO/LV CO ratio, LV internal diameter in diastole, or RV internal diameter in diastole Z scores, or flow reversal in the aortic arch.

In fetuses with ASA, higher ASEI correlates with incidence of fetal arrhythmias. While most arrhythmias are benign, 19% of fetuses with arrhythmias were found to have tachyarrhythmias in the form of SVT or atrial flutter. However, the majority of these patients did not meet the criteria for transplacental therapy. In addition, an ASEI threshold of 0.74 was identified as being associated with higher risk for fetal arrhythmias, with high sensitivity and specificity. The ASEI did not correlate significantly with the hemodynamic changes described in these fetuses.