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recovery phase.
The subject should be exercised to symptom limitation and be expected to complete at least three stages
— nine minutes — of the protocol or achieve an oxygen uptake equivalent to 11 metabolic equivalents
(METs)2. The age-predicted maximum heart rate is calculated by subtracting the age in years from 220
(beats/minute (bpm)). The test is most sensitive when taken to symptom limitation rather than any
percentage of the age-predicted maximum. The reason for discontinuing the test should be recorded,
together with the presence or absence of any symptoms.
In some countries, bicycle ergometry is still employed widely. This suffers from the relative disadvantage
that the subjects do not have to bear their own weight, and there is no imperative to maintain speed.
Furthermore, some people are not used to riding a bicycle. The bicycle protocol that approximates to the
Bruce treadmill protocol is the 20 Watt protocol. The subject is seated and the workload increased from
zero by 20 Watts every minute to the same symptom/heart-rate endpoints. Neither of the two test methods
1 Bruce treadmill protocol: standardized treadmill test for diagnosing and evaluating heart and lung diseases,
developed by Robert A. Bruce, American cardiologist (1916-2004).
2 1MET is the resting oxygen requirement of a 70-kg 40-year-old male (3.5 ml/min/kg).
ICAO Preliminary Unedited Version — October 2008 III-1-8
are completely sensitive — they do not detect non-flow-limiting lesions, nor are they completely specific
— they may falsely suggest the presence of coronary artery disease. Thus:
• Sensitivity = true positives/(true positives + false negatives). It reflects the percentage of all
subjects with coronary disease with an abnormal test.
• Specificity = true negatives/(false positives + true negatives). It reflects the percentage of negative
tests in subjects without coronary disease.
• Positive predictive accuracy = true positives/(true positives + false positives). It reflects the
percentage of abnormal responses in subjects with coronary disease.
• Negative predictive accuracy = true negatives/(true negatives + false negatives). It reflects the
percentage of negative responses in subjects without coronary disease.
Interpretation of exercise ECG data has been reviewed widely. There remains an excessive interest with
interpretation of the ST segment, the depression (or elevation) of which is measured at 60ms after the J
point - the junction of the S wave and the ST segment. Its pattern needs to be examined closely at rest and
in the early stages of exercise, during the recording and especially during the early stages of recovery -
the recovery ECG should be recorded for 10 minutes. It is at its most sensitive and specific when the
resting ECG is normal and at its least when it is abnormal, e.g. in left bundle branch block. Often 2 mm
of plane ST segment depression is referred to as “positive” (i.e. for coronary artery disease), but this is a
confusing term as such disease may not be present with this observation. The skilled interpreter will be
more influenced by the walking time, symptoms (if any) and pattern of change, rather than numerical
values.
Ventricular function is a good predictor of outcome, and its surrogate, the exercise walking time reflects
this. A walking time > 10 minutes using the standard Bruce treadmill is associated with an annual event
rate of <1 per cent, even if the ECG response is not completely normal. This predictive capability also
applies following myocardial infarction, coronary surgery, angioplasty and coronary stenting. The
argument against routine exercise ECG scrutiny of aircrew is as follows and depends on the Bayesian
theory of conditional probability:1
• In an average middle-aged pilot, the prevalence of significant coronary artery disease may be
only one to two per cent.
• The exercise ECG is only 60 to 70 per cent sensitive, i.e. it detects only this percentage of those
subjects with coronary artery disease — the true positives.
• If 1 000 pilots underwent such a study, then 10 to 20 (1 to 2 per cent) might have the disease, but
only 6 to 14 (60 to 70 per cent of 1 to 2 per cent) would be detected.
• With 95 per cent specificity of the test (at best, and it may be much lower than this), 5 per cent
(perhaps 50 pilots) would have diagnostic changes but no disease, i.e. would be false positives.
• The false-positive responders to exercise could thus outnumber the true-positive responders by a
factor of up to seven or more.
This effect was demonstrated in one study of healthy police officers with a mean age similar to the pilot
population (38 years) of whom 916 were followed up with serial exercise ECG for between 8 and 15
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Manual of Civil Aviation Medicine 1(73)
