Variation of Identification of Ventricular Septal Defects Between Fetal Echocardiogram and Postnatal Transthoracic Echocardiogram in Complex Congenital Heart Defects

Background: Prenatal diagnosis of congenital heart disease (CHD) using fetal echocardiogram (FE) has been demonstrated to improve outcomes in CHD. Ventricular septal defects (VSD) are the second most commonly occurring CHD, with a prevalence of 0.5-5% of live births. The development of the ventricular septum is a complex embryologic process that requires appropriate ventricular looping, adequate fusion of the endocardial cushions, and accurate involution and development of subaortic and subpulmonic conus, respectively. Interruption of this process results in a wide spectrum of CHD including the development of a VSD. Complex VSDs are those subtypes of inlet, outlet, and malaligned. In the setting of complex CHD accuracy in diagnosing the size and location of VSD is crucial when determining the type of surgical intervention that will be needed. There is a paucity about the classification of VSDs on fetal echo. This is the first study to investigate and understand the differences of complex VSDs on FE and postnatal transthoracic echocardiogram (TTE)

Methods: A retrospective study was performed to assess variations in complex VSD diagnosis between FE and paired TTE between January 2014 – January 2021. We reviewed initial and follow-up FE reports for description of the VSD and categorized the VSD using the International Society of Nomenclature of Pediatric and Congenital Heart Disease Classification Scheme for Ventricular Septal Defects. Paired postnatal TTE images were then reviewed and the VSDs were classified using the same classification system. Surgical description of the defect were also collected to query echocardiographic diagnosis. Any additional heart defects were noted.

Results: 85 FEs with complex VSDs were analyzed. Of those 43 were initial scans and 42 were follow-up scans. The average gestational age of the initial fetal scans was 28.5 (20.2 – 39) weeks gestation with the average for follow-up scans at 32.4 weeks. The average gestational age of postnatal TTE was 37.3 (28.2 – 40.1) weeks gestation, and average birth weight was 2807g (820-5200g). VSD location differed 47% (n=40) of the time between FE and postnatal TEE. (Figure 1) Of the wrongly categorized fetal VSDs 70% (n=28) of the errors were a reported perimembranous vsd, with the majority being diagnosed either inlet (n=13) or outlet (n = 13) postnatally. All scans included additional congenital heart diagnoses.

Conclusion: In the setting of complex congenital heart disease, we found that variation between FE and postnatal TEE in VSD location exists. The most common discrepancy occurred with fetal diagnosis of a perimembranous with postnatal diagnosis of either an inlet or outlet VSD.