Discussion
The recognition of need for atrial septal intervention after HP remains
relatively controversial, with little evidence to support a consistent
approach when there is such wide heterogeneity of the interatrial
communication (2-4). It is well recognised that initially unrestrictive
interatrial communications may become increasingly restrictive, and also
that a degree of atrial restriction may be acceptable, and indeed
important, for those where biventricular repair may be possible in the
future (7). It is an important decision as if a child is well-balanced
even in the face of flow acceleration seen on echocardiography, they may
become less well balanced after a septal intervention.
There are many factors affecting echocardiographic assessment of the
atrial septum in HLHS. A colour and 2D approach will highlight aliasing,
but this can be present even with a generous communication in the
context of high pulmonary blood flow. Sometimes application of the
pulmonary artery bands may reduce the pulmonary flow sufficiently to
reduce the perceived transatrial gradient. Pulmonary vein Dopplers were
not included in this study as they were not reliably measured in all
studies and measurement can be positional. Additionally, we have noted
that the A wave reversal can be absent in severe restriction only
becoming obvious after relief of the obstruction which may be to do with
reduced pulmonary flow in the face of obstruction.
The Doppler of the left pulmonary artery band appears to be the most
affected by increasing atrial restriction. The left pulmonary artery
often falls in a better plane for Doppler interrogation compared to the
right and therefore Doppler traces may be more accurate. It may also
relate to the left pulmonary artery band being generally looser. Access
to the left pulmonary artery can be challenging (a short
intra-pericardial length)(8) both during HP and when it comes to
pulmonary artery reconstruction at the subsequent stage. A looser band
may therefore be more representative of acute changes in the pulmonary
vascular bed, although it should be noted that a similar waveform is
seen when the band is too loose.
As the HP population is small, there are a relatively small number of
patients in this cohort which did not therefore allow comparison between
the groups with and without forward flow. Not all measurements were
available for all scans at all time-points, and some (albeit few) scans
were performed >48 hours after the procedure.
Additionally, some patients had the atrial septostomy as a proactive or
opportunistic intervention, when another intervention was performed.
Invasive catheter data was not available for all patients as many had
septostomies performed under echocardiographic guidance only, if there
had been more invasive data, we may have been able to correlate this
with some of the echocardiographic parameters.