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Indian Pediatr 2011;48:
17-18 |
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Clinical Screening for Congenital Heart
Disease at Birth: A Long Way to Go |
Jonathan D Reich
Watson Clinic LLP, Lakeland, FL, USA.
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There are many ways to express the problem
of undiagnosed congenital heart disease (CHD) in infants. Vaidyanathan,
et al. [1] describe the problem in a statistically detailed manner. I
prefer this analysis: for every 700,000 live births, there will be 4,500
infants with CHD, 25% of these children will leave the hospital without a
diagnosis, and roughly 30 infants will die from CHD before any cardiac
diagnosis is made [2]. This exceeds the total operative mortality from the
most complicated operation in CHD surgery, the Norwood [3,4]. If you
search hypoplastic left heart syndrome on PubMed you’ll get 1856 articles,
if you search for undiagnosed CHD you’ll get only 67 articles. This lack
of research interest is despite, even in an era of extensive fetal
diagnosis, the most common diagnosis made at autopsy for infants is CHD-nearly
40% [5].
Improving the diagnosis of CHD has received relatively
little attention perhaps because there isn’t much more we can do. There is
nearly an inverse correlation between the ease of diagnosis and the
morbidity of the cardiac lesion [6]. The cardiac diagnosis with the
highest likelihood of being diagnosed is pulmonic stenosis which has a
mortality rate near zero. The most difficult diagnosis to make is total
anomalous pulmonary venous return, which, in one series, had a nursery
diagnosis rate of 0% and an undiagnosed mortality rate of 30%. Hypoplastic
left heart syndrome had an undiagnosed mortality rate of 100%, but a
nursery detection rate of only 40% [7]. Fetal diagnosis has not really
reduced the overall mortality rate from undiagnosed CHD, and in most
studies really has a very small effect on rates of diagnosis [2,7,8]. It
is likely if we spent more time emphasizing the physical exam we would
just diagnose milder cases of pulmonic stenosis and other relatively
benign forms of CHD; thus we would have little effect on the problem of
morbidity and mortality from undiagnosed CHD.
For this reason, the use of pulse oximetry as a means
of detecting CHD has become a popular topic. In the last ten years, nearly
a sixth of all papers ever written on undiagnosed congenital heart disease
have studied pulse oximetry to detect CHD. Like all fields of medicine,
these studies have used varied methods rendering any conclusion subject to
problems. The first problem is that some papers express the sensitivity of
the test as the sensitivity of a combination of both the physical
examination and pulse oximetry [1,8,9]. This is superfluous; all newborn
infants should have a physical exam. No one writes papers assessing the
effectiveness of MRIs when combined with the physical exam; it is assumed
the patient had a physical exam before they had an MRI. The purpose of
pulse oximetry is to screen patients who wouldn’t be detected
otherwise. An abnormal physical exam means the patient is not a candidate
for a screening test. More importantly, it makes the study
non-reproducible as no two physicians do the same physical exam. Unless
the paper describes minute details of the physical exam, for example how
many minutes the physician listen and with which stethoscope, no two
researchers will obtain the same results.
Alternatively, there are studies which have
demonstrated that routine pulse oximetry has promising results. Riede,
et al. [8] managed to reduce the presentation of undiagnosed
congenital heart disease to 4.4% of CHD with routine pulse oximetry. This
compares favorably to other studies which calculated that 25% of infants
with CHD leave the nursery undiagnosed [2]. In order to achieve this
reduction, Riede, et al. like Meberg, et al. had nearly 4
times as many false positive pulse oximeter readings as true positives as
confirmed by echocardiography [7,8].
Vaidyanathan, et al. [1] arrived at similar
conclusions, that we did in our study eight years earlier. A few cases of
CHD were missed and in general the modality is limited in its ability to
detect CHD [9]. The authors report a low sensitivity and a specificity
below 90% [1]. This confirms our assessment that although pulse oximetry
is inexpensive and without side effects, it is difficult to recommend
universal adoption based on the available evidence. Pulse oximeters are
designed for long term use in critically ill patients, not spot checks in
healthy newborns. The software cycle lengths vary and various inputs are
averaged by the machine which produces a number which may not reliably
represent the patient’s oxygenation [10]. The research frontier is waiting
more for engineers to explore, than physicians. Pulse oximeters need to be
designed with short cycle lengths, specifically for infants, and produce a
paper trail for quality assurance. Otherwise, we’re generating numbers
from a black box and then reassuring parents their infants are healthy.
When it comes to screening newborns for congenital
heart disease it would appear there is not much difference between the
developed and developing world. It is difficult to resist the lure of a
cheap, safe test which holds out the promise of saving the occasional baby
which might be missed. Yet, screening populations is a complicated,
expensive endeavor which requires a test with reliability. We have a long
way to go to make a reality of the dream of diagnosing every baby with
congenital heart disease before they leave the hospital. I am not sure the
research on pulse oximetry has made the journey much shorter.
Funding: None.
Competing interests: None stated.
References
1. Vaidyanathan B, Sathish G, Mohanan S, Sundaram KR,
Warrier KKR, Kumar RK. Clinical screening for congenital heart disease at
birth: A prospective study in a community hospital in Kerala. Indian
Pediatr. 2011;48: 25-30.
2. 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:F33-5.
3. Ohye RG, Sleeper LA, Mahony L, et al.
Comparison of shunt types in the Norwood procedure for single-ventricle
lesions. New Engl J Med. 2010;362:1980-92.
4. Freedom RM, Black MD, Benson LN, Hypoplastic left
heart syndrome. In: Allen HD, Gutgesell HP, Clark ED, Driscoll DJ,
editors. Moss and Adams’ Heart Disease in Infants, Children, and
Adolescents: Including the Fetus and Young Adult. Philadelphia: Lippincott,
Williams, and Wilkins.2001.p.1011-26.
5. Weber MA, Ashworth MT, Risdon RA, et al.
Sudden unexpected neonatal death in the first week of life: autopsy
findings from a specialist centre. J Matern Fetal Neonatal Med.
2009;22:398-404.
6. Wren C. Presentation of CHD in infancy. Arch Dis
Child. 1999;80:F50.
7. Meberg A, Andreassen A, Brunvand L, Markestad T,
Moster D, Nietsch L, et al. Pulse oximetry screening as a
complementary strategy to detect critical congenital heart defects. Acta
Paediatr. 2009;98:682-6.
8. Riede FT, Wörner C, Dähnert I, Möckel A, Kostelka M,
Schneider P. Effectiveness of neonatal pulse oximetry screening for
detection of critical congenital heart disease in daily clinical
routine-results from a prospective multicenter study. Eur J Pediatr.
2010;169:975-81.
9. Reich JD, Miller S, Brogdon B, Casatelli J, Gompf TC,
Huhta JC, et al. The use of pulse oximetry to detect congenital
heart disease. J Pediatr. 2003;142:268-72.
10. Reich JD, Connolly B, Bradley G, Littman S, Koeppel
W, Lewycky P, et al. Reliability of a single pulse oximetry reading
as a screening test for congenital heart disease in otherwise asymptomatic
newborn infants: the importance of human factors. Pediatr Cardiol.
2008;29:371-6.
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