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symptomatic and 82.4 per cent were not. Fifteen per cent of pilots with the pattern alone developed the
1 Kent’s bundle: a muscular bundle in the heart, formimg a direct connection between the atrial and ventricular
walls. After Albert F.S. Kent, English physiologist (1863-1958).
2 Mahaim’s fibers: specialised tissue in the heart, connecting components of the conduction system directly to the
ventricular septum. After Ivan Mahaim, French cardiologist (1897-1965).
3 W-P-W syndrome: is the association of paroxysmal tachycardia (or atrial fibrillation) and pre-excitation, in which
the ECG shows a short P-R interval and a wide QRS complex. After Louis Wolff, American cardiologist (1898-?),
Sir John Parkinson, English physician (1885-1976) and Paul D. White, American cardiologist (1886-1973).
ICAO Preliminary Unedited Version — October 2008 III-1-26
syndrome over a mean of 22 years. The characteristic appearance of the QRS complex with a slurred
inscription of the R wave (the “delta” wave) and a short PR interval (but normal PT interval) is seen in
about 1.6 per 1000 routine resting ECGs. See ECG 20, Appendix 1b. It is more common in men than
women.
The prevalence of atrioventricular reciprocating tachycardia varies between five and 90 per cent in
hospital patients with the WPW pattern due to the phenomenon of “ascertainment bias” (individuals with
WPW pattern and a tachycardia are likely to be over-represented in the hospital population when
compared with the general population). If there is prograde (orthodromic) conduction through the slow
nodal pathway with retrograde conduction via the fast accessory pathway, the QRS complex will be
narrow. If there is prograde conduction via the accessory pathway with retrograde (antidromic)
conduction via the slow nodal pathway, the QRS complex will be broad. The appearance of the delta
wave may be intermittent, implying that it is refractory part of the time. This is usually associated with a
longer effective refractory period (ERF) - 300 to 500ms; and the term “safe” is applied, suggesting a low
risk of rapid atrioventricular reciprocating tachycardia. This also implies the absence of ability to conduct
at very fast rates in atrial fibrillation in which total anomalous conduction may occur via the accessory
pathway.
Although many subjects with preexcitation never experience an episode of tachycardia and in an
unknown number the pathway is concealed, the possibility of a re-entry tachycardia with abrupt onset at a
rapid rate, or of atrial fibrillation with anomalous conduction, gives rise to certificatory difficulties. Atrial
fibrillation with very rapid conduction may provoke ventricular fibrillation and sudden cardiac death, but
the risk is very low. There is also an association with other anomalies such as hypertrophic
cardiomyopathy and Ebstein’s anomaly1.
On first presentation with the WPW ECG pattern an aviator should be made unfit. Provided there is no
history of arrhythmia, and an echocardiogram, exercise ECG and 24-hour ambulatory ECG recording
are within normal limits, Class 1 restricted (OML) certification may be considered. The exercise
electrocardiogram in the presence of a delta wave may be associated with gross ST segment depression
which may mimic myocardial ischaemia. In this situation, further investigation with a thallium MPI or
equivalent may be indicated. In view of the generally more favourable outcome, it is helpful if, at least
part of the time, the accessory pathway is refractory.
For unrestricted certification, an electrophysiological study (EPS) is required demonstrating no inducible
re-entry tachycardia and an ante-grade ERF > 300 ms. If the subject has a history of re-entrant
tachyarrhythmia, certification is possible only following the demonstrated of ablation of the accessory
pathway. This may be accomplished by an adenosine challenge or further EPS.
ATRIOVENTRICULAR CONDUCTION DISTURBANCES
First degree atrioventricular block is present if the PR interval exceeds 210ms. It is present in at least one
per cent of asymptomatic aircrew applicants. In the absence of broadening of the QRS width >100ms, the
condition is very likely to be benign. The interval should shorten on exercise. Occasionally, very long PR
intervals are seen of up to 400ms; these, too, seem to be benign, provided the QRS width is normal, the
interval shortens on exercise, and following atropine. It is sometimes associated with Mobitz type I
atrioventricular block2 (decremental atrioventricular conduction), which should be of short periodicity
and occur only at night in young adults. The additional presence of a bundle branch disturbance,
1 Ebstein’s anomaly: atrialisation of the right ventricle with involvement of the tricuspid valve. After Wilheln
　
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