Speculum - University of Melbourne

SPECULUM 15
E.C.G. DIAGNOSIS OF CONGENITAL
HEART DISEASE
Dr. E. R. Trethewie M.D., D.Sc., M.B., M.R.A.C.P.
Reader in Physiology, University of Melbourne
The lesion in congenital heart disease is
frequently able to be diagnosed by considering
the stethoscopic and electrocardiographic
findings alone. In many instances a bruit is
heard in the vicinity of the second left interspace
close to the sternum and it may be
heard over a wide area. The bruit of pulmonary
stenosis is harsh, superficial, and
occupies a considerable period of systole
(fig. 1). The bruit of interatrial defect has
a rumbling crescendo quality with rapid
diminuendo and occupies the early stage of
systole (fig. 4). The bruit of interventricular
defect may be harsh or soft and is
frequently best heard in the fourth left interspace
close to the sternum. The classical
bruit of patent ductus can never be mistaken;
it is a continuous machine-hum murmur;
but of course, it may not produce this
classical sound. It may even only be
systolic in time and sometimes we think we
are listening to an atypical patent ductus
murmur when in reality we hear the bruit of
aorto-pulmonary communication.
Having decided we have heard a basal
bruit, usually in a young person, often, btit
not necessarily, of inferior physique and one
who has never had rheumatic fever, an examination
of the electrocardiogram is
Pig. 1—Phonocardiogram of the bruit in pure
pulmonary stenosis. (i), (ii) timing of first
and second heart sounds. Note the prolonged,
well-sustained, late systolic bruit.
usually very illuminating. Interatrial and
interventricular septal defect become diagnosed
almost always. Pure pulmonary
stenosis can be confirmed. The combination
of pulmonary stenosis and interventricular
defect can commonly be recognised.
Patent ductus in a young person
produces only a slight degree of right axis
deviation with perhaps some strain pattern.
The pressure in the right ventricle can be
estimated approximately in all instances.
The lesion of coarctation of the aorta,
already largely diagnosed by the absence of
femoral pulses, can also be recognised.
However, to make a satisfactory electrocardiographic
diagnosis it is essential to
perform three dimensional electrocardiography.
The leads chosen here are the
ABC leads where lead A: manubrium sternum
(M) to xiphisternum (X); B: left axilla
(L) to xiphisternum (X); C: right chest at
base (R) to xiphisternum (X); such that
MXL = LXR = RXM = 1 rt. angle.
We shall consider the types of tracings
for the following defects:
1. Pulmonary Stenosis.
2. Interatrial Defect.
3. Interventricular Defect.
4. Patent Ductus Arteriosis.
5. Coarctation of the Aorta.
For comparison the normal electrocardiogram
is shown in fig. 2. Note the large
P(A) and the normal distribution of R to S
potentials. Large R- and small S-waves
occur in right axis deviation and large S-
and small R-waves in left axis deviation.
This applies to all leads. Another normal
electrocardiogram is shown in fig. 10, the
E.C.G. after tying a patent ductus, while the
prior tracing is shown in fig. 9; note the
inverted normal T(B), which is found in
more than half the subjects.