Cardiac Disease Screening in Down Syndrome: Is the Fox Guarding the Henhouse?
DrBudWiedermann, MD, MA, Evidence eMended Editor, Grand Rounds
Guidelines can be biased, particularly if the guideline developers stand to gain from
some of the recommendations. In most cases this isn't an intentional bias, but rather
implicit bias hovering beneath the clinician's consciousness. Is implicit bias influencing
screening for heart disease in Down Syndrome children?
In 2011, the AAP Committee on Genetics provided us with guidelines on Health Supervision for Children with Down Syndrome. Of course there are many screening and health supervision issues for these children
that are different from children without Down syndrome, so guidance from experts is
really valuable. When I look at any guideline, one of the first things I do is look
for strength of evidence ratings to help me understand whether what I'm reading is
just expert consensus or a stronger recommendation supported by clinical trials or
other high quality studies. For this guideline, there are no evidence ratings, and
I know that at the time of publication the AAP hadn't agreed on criteria for evidence
ratings, so their absence is lamentable but not surprising.
Secondly, I try to ascertain if there is any implicit bias present - whether any of
the authors have a financial or professional stake in the recommendations. Well, if
you want a guideline written by experts in the field, you can't help but have some
degree of conflict of interest. I'd want a cardiologist to weigh in on how to screen
children with Down syndrome for cardiac disease. However, it raises my antennae just
a bit, analogous to articles funded and/or authored by the pharmaceutical industry.
They may be perfectly honest in their writing, but it's hard to contain implicit bias
since the individual isn't aware of its presence. Guess how many of the 7 Committee
on Genetics members are cardiologists: exactly zero. So much for my fox/henhouse idea.
But what is the best way to screen for heart disease in children with Down syndrome?
The recommendation for screening for congenital heart disease, in the section covering
infants from birth to 1 month of age contains this advice:
"Heart defects (∼50% risk). Perform an echocardiogram, to be read by a pediatric cardiologist,
regardless of whether a fetal echocardiogram was performed. Refer to a pediatric cardiologist
for evaluation any infant whose postnatal echocardiogram results are abnormal."
That's clearly money in the cardiologist's pocket, but also it could present a major
hurdle for a family that doesn't have ready access to a pediatric cardiologist. So,
I was pleased to see the current study, a retrospective chart review of how 408 Down
syndrome children were evaluated for heart disease, and whether screening efforts
short of echocardiogram could be effective. The authors found that the combination
of physical exam, electrocardiogram, and chest radiograph identified 95% of children
with major congenital heart disease. They calculated that, if echocardiogram were
performed only on infants who failed screening, 17% fewer echocardiograms would have
That's pretty good, but not good enough. Major congenital heart disease is of course
a serious condition, and I'd want a screening test to be 100% sensitive. Raising the
sensitivity bar to that level will absolutely result in many false positive results,
meaning that some children would have an echocardiogram but wouldn't benefit from
it, but if it still resulted in significantly less children needing an echocardiogram,
it could be worth it.
Of course there are several other issues that should prevent anyone from implementing
these results in clinical practice tomorrow. First, the fact that it was retrospective
and based on chart review can introduce many sources of bias. For example, did the
cardiologists or radiologists interpreting the electrocardiograms or radiographs have
any clinical information about the children? If they were aware of clinical information
suggesting a high (or low) likelihood of congenital heart disease, that might influence
their interpretation of borderline findings. I wish the authors had used blinded observers
to re-interpret these studies to see if the results would change.
Still, this study raises the question about whether unnecessary echocardiograms are
being performed in children with Down syndrome. I hope we see an ambitious prospective
study of this question in the near future. For now, stick with the 2011 guidelines;
they aren't perfect, but they're the best we have at the moment.