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years (mean 12.7 years). Twenty-three had an initially abnormal exercise response and 38 converted to an
abnormal response during the follow-up period. There were nine coronary events in the first group and 12
in the second. In the much larger normally responding group, there were 44 events. The positive
predictive accuracy was 25.3 per cent, but there was only one sudden death in the initially abnormal
group. There were seven sudden deaths in the much larger “normal” group.
1 Bayes’ theorem: A simple mathematical formula used for calculating conditional probabilities. In a medical
context, it can be paraphrased as ‘the rarer the condition for which we are testing, the greater the percentage of the
positive tests will be false positives’. After British cleric Thomas Bayes (1702-1761)
ICAO Preliminary Unedited Version — October 2008 III-1-9
Middle-aged males in the Seattle Heart Watch programme1 who had more than one abnormal exercise
ECG response in the presence of vascular risk factor(s) had an annual coronary event rate >5 per cent. By
comparison, the risk of an event was only 0.22 per cent if there were no vascular risk factors and the
exercise recording was normal. If there was one abnormal recording and no vascular risk factor present
the risk of an event was 0.42 per cent per annum. Under such circumstances, the finding of a normal
exercise ECG identifies a group in whom the risk of event is acceptably <1 per cent per annum.
The American College of Cardiology (ACC)/American Heart Association (AHA) guidelines state that in
patients with suspected coronary artery disease with a low or high pre-test probability of its presence,
exercise ECG is less appropriate than if the probability is intermediate. This is based on greatest value in
terms of diagnostic outcome: low-risk subjects are likely to have a normal response and high-risk subjects
the reverse. In a study of 5103 patients with symptoms suggestive of angina pectoris in whom the overall
sensitivity of the investigation was 70 per cent and specificity 66 per cent, there was a progressive
increase in positive predictive value – 21 per cent, 62 per cent and 92 per cent for low, intermediate and
high pre-test probability, respectively – and a fall in the negative predictive value – 94 per cent, 72 per
cent and 28 per cent, respectively. Although this group is not representative of the pilot population in
terms of prevalence of disease, it emphasizes the usefulness of exercise ECG in returning aircrew to
flying when the probability of coronary artery disease is low (i.e. lack of symptoms, unremarkable
vascular risk burden (including age), non-specific ECG changes) due to the high negative predictive
value.
Further investigation should be carried out when the probability of coronary disease is high (i.e.
symptoms, significant vascular risk (including age), possibly significant ECG changes, known coronary
artery disease), irrespective of the result of the exercise test. With the intermediate group, exercise
evaluation alone may be insufficient as some authors have noted a statistically significant difference
between the pre-/post-test predictive values (P < 0.0001). A significant false-negative rate following
investigation does not sit easily in the regulatory environment.
Although aviation used to be an almost exclusively male preserve, increasing numbers of females
recruited over the past three decades have brought the need for investigation for coronary artery disease in
a group in which its prevalence, overall, is low. One meta-analysis of exercise testing for coronary artery
disease in women revealed an overall sensitivity of 61 per cent and a specificity of 70 per cent,
comparable to males, but of limited value due to the high number of both false-positive and false-negative
results. Additional guidance should be sought, depending on the clinical situation.
Some examples of normal and abnormal exercise ECG responses are illustrated in Appendix 2
Pharmacological stress echocardiography
In a subject with a low probability of coronary artery disease, routine resting ECG anomalies are initially
best assessed by exercise ECG. When an exercise recording is equivocal or abnormal, and the probability
of coronary artery disease is intermediate or high, then further evaluation will be clinically indicated.
Of the techniques available, stress echocardiography is the least invasive but the one with which, in many
centres, there is the least experience. Using exercise or a beta-agonist (such as dobutamine)
to increase myocardial oxygen requirement, stress echocardiography demonstrates ventricular wall
motion abnormality in the presence of myocardial ischaemia. In one study, the three year event free
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Manual of Civil Aviation Medicine 1(74)
