CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 7, August 2012
406
AFRICA
medical practitioners to identify murmurs that have a high
probability of structural heart disease. CAA promises to address
this need by providing a decision support tool on the likelihood
of the presence of pathological murmur.
CAA as a teaching aid for cardiac auscultation
In the past decade, numerous reports have expressed concern
over the training of healthcare professionals in cardiac
auscultation.
3,9,10
Despite the fact that directors of USA-based
medical school programmes interviewed considered auscultation
an important clinical skill, only 27% of internal medicine and
37% of cardiology programmes offered any structured teaching
of auscultation.
10
A multi-centre study testing medical students,
trainees, physicians and teaching faculty more comprehensively
demonstrated low ability to recognise systolic and diastolic
murmurs.
11
These studies indicate the need for more directed
teaching of cardiac auscultation.
The ability of a digital stethoscope to record sounds, replay
them at different speeds, provide a visual display and develop a
database of heart sounds for on-going review creates a unique
vehicle for teaching auscultation and is a major incentive for the
addition of CAA into current teaching programmes.
The development of computer-assisted auscultation
The pursuit of a quantitative and objective stethoscope has
occupied investigators for decades, and electronic stethoscopes
have been available commercially for some time.
12
Early
criticisms related to difficulty of use, distortion of sound and
cumbersome designs. However, over the past decade, rapid
advances have been made not only in the electronic stethoscopes
themselves, but also in the associated computer analysis.
13
The CAA provides a spectral and temporal analysis of heart
sounds and a graphic display of the energy profiles relating
to systolic and diastolic murmurs (Fig. 1).
14
The quantitative
measurement of the intensity of the heart sounds and murmurs
in the spectral display, which is recorded simultaneously with
the waveform of the sounds, allows objective classification
into normal and abnormal sounds (Fig. 2).
15
Signals obtained
electronically may be subjected to objective visual and numerical
analysis, transmitted to distant sites, and stored for medical and
research purposes.
The Food and Drug Administration (FDA) has approved
the first CAA system as an aide to the physician for the
detection of abnormal heart murmurs. Using this software, the
sensitivity for detection of murmurs increased from 77 to 89%,
while the referral sensitivity increased from 87 to 93% among
primary-care physicians.
16
Another decision support system,
aimed at the paediatric population and utilising novel signal-
processing techniques, recently reported a specificity of 94% and
a sensitivity of 91% for the detection of murmurs associated with
structural heart disease.
17,18
Opportunities for clinical application
CAA is a promising decision support tool for the identification
of pathological murmurs and appropriate referral of cases
for further investigation. Primary-care physicians assessing
asymptomatic patients with heart murmurs were able to increase
the sensitivity of pathological murmurs detected with the use of
CAA from 77 to 89%, while referral sensitivity increased from
87 to 93%, and specificity increased from 64 to 79%.
16
The clinical utility of the digital stethoscope and associated
software in detecting cardiac disease has great potential
(Table 1). A recent article described an autonomous auscultation
system which could be used to screen for cardiovascular disease
in the rural areas of Africa.
19
The performance of the system was
impressive, with a sensitivity of 82% and a specificity of 88%
for the identification of pathological murmurs, demonstrating
its potential benefit as a screening tool in a rural healthcare
environment.
The need for a method to detect athletes at risk of sudden
cardiac death due to hypertrophic obstructive cardiomyopathy
led to a pilot study examining the level of agreement between
auscultation by a cardiologist and the results of CAA.
20
This
study was able to identify ejection systolic murmurs that are
louder in standing than in reclining positions: a cardinal sign of
hypertrophic obstructive cardiomyopathy.
The third heart sound is an early abnormality in adult patients
with heart failure. It is frequently missed in a cursory examination
of the heart, but is easily recorded by means of CAA.
21
The most common cause of acquired heart disease in
the world, rheumatic heart disease, has long been neglected
due to its waning incidence in the developed world.
22
A
landmark study in Mozambique and Cambodia, however,
Fig 1. The computer interface, as displayed on a laptop
computer, depicts the areas of auscultation, visual
display of heart sounds and murmurs, as well as ECG.
(Reproduced with the permission of Mr Thys Cronje.)
Fig 2. In this display, analysis has determined that
pathological murmurs were detected in the tricuspid,
aortic and pulmonary areas. The computer interface also
displays the level of confidence (90%) and the heart rate.
(Reproduced with the permission of Mr Thys Cronje.)
Auscultation
sequence
Patient
information
ECG
Visual display
of heart sounds
and murmurs
