Sir

We read with interest the original article by Wren et al about the trends in diagnosis of major congenital cardiovascular malformations published in the fetal and neonatal issue of the journal1. The paper discusses the difficulties which we are still experiencing in diagnosing the cardiovascular (CVS) abnormalities. It is evident that we continue to miss life threatening abnormalities despite efforts to improve our detection rates.

The authors in their discussion suggest that better early diagnosis of serious congenital cardiac malformations is likely to be achieved by further improvements in antenatal diagnosis and more wide spread use of routine pulse oximetry. Whether such is indeed the case is open to debate and discussion.

Firstly how can we realistically advance the antenatal detection rate? The current practice is to perform a detailed scan of the foetus at around 19 weeks of gestation to look for foetal abnormalities. This is done by trained sonogarphers who routinely do a 4- chamber view of the heart. The additional view of the outflow tracts is still not routine practice in all units and remains optional. It is envisaged that by obtaining the latter view the detection rate of the CVS malformation would be improved from 25 % to up to 75% as per the RCOG2 guidelines for mid- trimester scans. The malformations which were noted to be undetected in the author’s study include coarctation of the aorta, interruption of the aortic arch, aortic valve stenosis and total anomalous pulmonary venous connection. These malformations are unlikely to be detected on routine anomaly scans and are likely to evolve as the foetus grows. Identifying them may well need another scan later in gestation. This at present is not a recommended practice and has considerable additional resource implications. There is of course the alternative of seeking early input from the experts in cardiac scanning, namely paediatric cardiologists with expertise in foetal cardiac scanning. Again the resource implications make this highly improbable if not impossible. Thus with the current system of screening for foetal abnormalities, we are unsure how the antenatal detection rates for CVS abnormalities can be improved.

Secondly there is paucity of high-quality evidence supporting the role of pulse oximetery for early detection of congenital heart disease. The report of the Tennessee task force, which the authors have referenced in their discussion was based on the analysis of four major studies using pulse oximetry screening3. The task force recommended against mandatory implementation of screening and stated that a very large prospective study is needed to define sensitivity and false positive rates of lower limb pulse oximetry screening in asymptomatic newborn population. More recently a systematic review identified pulse oximetery as a potentially useful tool for diagnosis of congenital heart disease in asymptomatic neonates. The reviewers however in addition concluded that although pulse oximetery is highly specific it has highly variable sensitivity with wide confidence intervals. They also commented on the quality of the various studies included in the review stating that this was generally compromised due to the differential verification used in identifying positive and negative cases. Moreover the absence of blinding, and absent or poor description of the test or reference standard was deemed to have affected the results of the review. The reviewer’s conclusion was that large, well-conducted and robust studies are essential to confirm the value of pulse oximetry as a screening test, in isolation or in combination with clinical examination to obtain precise estimates of its sensitivity4.

It may sound disappointing but it seems rather implausible that detection rates of congenital heart disease in the foetal or neonatal period are going to improve notably in the foreseeable future.

References

1. Wren C, Reinhardt Z, Khawaja K. Twenty-year trends in diagnosis of life-threatening neonatal cardiovascular malformations. Arch Dis Child Fetal Neonatal Ed 2008;93:F33-F35. 2. Ultrasound Screening for Fetal Abnormalities. Report of the RCOG Working Party (2000). RCOG, London. 3. Liske MR, Greeley CS, Law DJ, et al. Report of the Tennessee task force on screening newborn infants for critical congenital heart disease. Pediatrics 2006; 118: e1250–6. 4. Thangaratinam S, Daneils J, Ewer AK, Zamora J, Khan KK. Accuracy of pulse oximetry in screening for congenital heart disease in asymptomatic newborns: as systematic review. Arch Dis Child Fetal Neonatal Ed 2007;92:F176-F180.