A persistent left superior caval vein (LSVC) is present in about 0.3% of the population at necropsy and in adults undergoing pacing.¹ Although it may occur in up to 9% of necropsies of children with congenital heart disease (CHD),² its prevalence in the fetus at increased risk of, or with, CHD has not yet been determined. We document the incidence, associations, and outcome of LSVC in 1678 consecutive fetuses referred for echocardiography to a fetal medicine unit between January 1997 and December 2002.

METHODS

Fetal echocardiograms were performed (Acuson Sequoia C256/Siemens Medical Solutions, Acuson Ultrasound Department, Mountain View, California) using a 6C2, 8C4 or 5V2c probe and persistence of the LSVC documented from routine views of the four chambers and transverse arch (the three vessel view). Postnatal diagnosis was confirmed by echocardiogram, at surgery, or at necropsy.

The odds ratio (95% confidence intervals (CI)) for CHD in the presence of LSVC and the odds ratio of an associated cardiac defect being coarctation of the aorta (CoA) were calculated.

RESULTS

Of 1678 cardiac referrals, 1230 were normal with an LSVC detected in four patients (0.3%). Cardiac abnormality was present in 448 cases (27%), with persistent LSVC in 12 cases (2.7%). Thus, the odds ratio of a fetus having a cardiac defect if a LSVC is detected is 8.43 (95% CI 2.71 to 26.29).

Table 1 details the cardiac diagnosis, associations and outcomes of the 16 fetuses with persistent LSVC. It was associated with situs inversus in one fetus, and five fetuses showed interruption of the inferior vena cava (IVC) with azygous/hemiazygous continuation to a persistent LSVC which drained to the coronary sinus in all but one fetus. All five fetuses had the usual arrangement of the atrial appendages, confirmed postnatally.³ LSVC was seen in five of the 10 fetuses with aortic arch hypoplasia (50%), nine of whom required surgery for CoA, and one with Turner syndrome and arch hypoplasia was managed conservatively. The odds ratio of the cardiac defect being a CoA in fetuses with LSVC is 61.57 (95% CI 14.48 to 261.74).

DISCUSSION

This study has documented persistent LSVC in 1% of a consecutive series of fetuses selected for detailed echocardiography. While the 0.3% prevalence of LSVC in those with structurally normal hearts was similar to previous population studies, LSVC was associated with an eightfold increase in CHD in this fetal population, and strongly associated with CoA.

The prevalence of LSVC in the fetal population remains uncertain. The importance of the three vessel view, where the LSVC is most easily identified, is only now becoming recognised by obstetric sonographers as part of complete fetal screening. However, fetuses with LSVC may be referred with four chamber disproportion caused by an enlarged coronary sinus, or as suspected atrioventricular or atrial septal defect. Furthermore, in our series 25% had important extracardiac malformations and three had aneuploidy that may have been detected sonographically.

The prevalence of LSVC in 2.7% of fetuses with CHD is less than the 9% reported from pathological series where atrioventricular septal defect, cor triatriatum, and mitral atresia were common associations.² However, there was a 6% prevalence of LSVC in the 107 fetuses in our cohort with serious malformations associated with ventricular or arterial disproportion. Of particular importance was the association with CoA or arch hypoplasia. This lesion remains the one with most diagnostic uncertainty in fetal life and in common with others, we found an 89% specificity of diagnosis before 24 weeks of gestation but only 17% after.⁴

Cardiac growth velocities are well documented in the fetus⁵ but early growth may differ in those with LSVC. Necropsy associations with cor triatriatum and mitral atresia suggest that the mechanism responsible for failure to close the LSVC may be associated with abnormal left sided connections or abnormal early flow patterns that reduce left ventricular filling and may explain in part the association with CoA, unbalanced atrioventricular septal defect, and total anomalous pulmonary venous connections reported here. Serial scans in this series suggest that it exerts less haemodynamic influence later in gestation, and left sided growth proved adequate for a biventricular repair in all cases where surgery was necessary, with important implications for first trimester counselling.

This study suggests that sonographic detection of LSVC is a powerful indicator of fetuses with probable CHD in whom CoA was the most common diagnosis. LSVC is easily recognised on standard cardiac screening views and we recommend its detection should prompt referral for detailed echocardiography.