Speculum - University of Melbourne

12
SPECULUM
AN AFFAIR OF THE HEART
M. L. Powell
High upon the uppermost shelves of THE
LIBRARY there rests in placid content
Vol. XLVI of the Annals of Surgery which
was published in the year 1907. On page
335 is an article of rare prophecy. It is
titled "Ligation of the Ductus Arteriosus"
and is written by one John C. Munro M.D.,
of Boston, Massachussetts, U.S.A. Though
this paper was presented on May 6th, 1907,
the idea was. born 19 years before — exactly
55 years before Gross ligated the first ductus
in, perhaps not strangely, Munro's home
city of Boston.
In 1888, Munro, who appears to have
been surgically minded but with considerable
medical interest, saw a girl baby (note
that this first case was of the fair female sex
which later was to prove three times more
inept at closing that particular channel than
the male) "with symptoms of some cardiac
lesion. Ascultation at this time revealed
a cardiac murmur with pulmonary rales but
cyanosis was not• a marked feature. After
death, which took place without oedema or
marked cyanosis, examination showed an
open ductus arteriosus lying easily within
reach behind the sternum without any other
defect except a dilated right ventricle". This
in itself was a profound observation for it
is certain there have been many autopsies
since that time, done in well equipped post
mortem rooms in which the open ductus has
not been found or certainly its significance
missed as the cause of death.
Munro found "the simplicity of the
remedy so striking" that he made further
dissections and felt it should be possible to
ligate the duct during life if a diagnosis
could be made. But in this his hopes seem
to have been dimmed for his "paediatric
advisers were not reassuring", but he urged
"those skilled in the diagnosis of infantile
lesions to lend their aid".
Munro noted that cyanosis was wanting
(as we now appreciate befits a left to right
shunt) that an anaemia or waxy appearance
is shown which well describes the pallor
which is in fact often non-anaemic, but
rather due to poor peripheral flow due to
the shunt through the ductus, and that "a
loud systolic whir conducted into the cervical
vessels may be heard but, as a matter of fact
there are no definite auscultatory signs established
as yet". Here in this last observation,
is indicated for the first time that
wonderful diagnostic sign, the continuous
or machinery murmur heard high in the left
chest close to the sternum which actually
had been described by Gibson of Scotland
seven years earlier.
This is the murmur which when all its
facets are appreciated instruct the clinician
in terms of certitude unusual in the game of
chance which we call diagnosis, that the
Ductus Botalli is anachronistically open.
This small arteriovenous communication
usually about 15 m.m. long and 5 m.m. in
diameter is a useful channel during the
intrauterine sojourn when oxygen derived
from the placenta, short circuits the nonfunctioning
lungs, and is shunted to the
systemic circulation, a process which is
assisted by the hypertension of the foetal
pulmonary circuit. With expansion of the
lungs at birth the pulmonary arterial pressure
falls and after about two weeks the
ductus has closed.
No clear cut answer has been provided
to the question "Why does it close?". It
is not unreasonable to suggest that at some
time during the first two weeks of extra
uterine life the pulmonary and systemic
pressures are fairly well in balance and that
there is little flow either way through the
ductus for several days.
Such stasis must conduce to contraction
of the ductus, thrombus formation and
ultimate obliteration. But it is not easy to
suggest why on occasions it does not close
and is thus responsible for a new branch of