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Recordings made on apparatus in which A/D conversion1 is sub-optimum, or if filtering and/or damping
is inappropriate, may demonstrate artefacts. These often involve the important ST-segment and T-wave.
The standard presentation of a resting electrocardiogram is upon A4 graph paper; the faint lines on both
axes measure 1 mm. On the x-axis this represents 40 ms at the standard paper speed of 25 mm/s. The
heavy lines are 5 mm apart and represent 200 ms on the x-axis at the standard paper speed. On the y-axis
10 mm is standardised as reflecting 1 mV (see above).
Lead systems
The leads are divided into the limb leads — S1, S2, and S3 (also named leads I, II and III); the augmented
vector leads — aVR, aVL, aVF; and the chest leads. The first six leads are known as the hexaxial leads
and are used to define the PQRS and T-wave angles in the frontal plane — the “mean manifest frontal
QRS-axis”.
Basic definitions and limits
Heart rate (without definition of rhythm).
60 to 100 bpm2 – normal limits.
50 to 60 bpm – bradycardia
<50 bpm – significant bradycardia
>100 bpm – tachycardia
The PR interval: 120 to 210 ms.
Longer PR intervals (up to 280 ms) are not infrequently encountered and, provided the QRS-complexes
are of normal width, likely to be unimportant. Shortening with exercise to the normal range is to be
expected without decrement in AV conduction. Shorter PR-intervals (<120 ms) need to be examined for
the presence or absence of early depolarisation – pre-excitation. In the absence of this, they are likely to
reflect a normal variant unless particularly short (< 100 ms) or unless there is a history of atrioventricular
nodo reentrant tachycardia (the Lown-Ganong-Levine syndrome) or atrioventricular
reciprocating(reentrant) tachycardia (the Wolff-Parkinson-White syndrome).
1 A/D conversion: conversion from analog to digital signals for transmission and further computer
storage/processing.
2 bpm: beats per minute
ICAO Preliminary Unedited Version — October 2008 III-App. 1A-2
The QRS duration: 70 to 90 ms.
.
The QRS width may be non-specifically prolonged (>100 ms) but is not absolutely prolonged until 120
ms, often by the presence of right or left bundle branch aberration and sometimes by ventricular
hypertrophy or dilatation.
The QTc: 340 to 440 ms - up to 460 ms in the female
The QT-interval and the QTc. The QTc is used to adjust QT-interval for heart rate. It is calculated by
using Bazett’s formula (see page 31) As the T-wave may fuse with the U-wave, precise description of the
QT-interval may be difficult or impossible and such measurements need to be treated with caution.
The ST-segment is fused with the T-wave and commences at the J-point where it takes off from the
return deflection of the S-wave. Depression of the ST-segment, particularly on exercise, may be
attributable to myocardial ischaemia. However, the exercise walking time and the pattern of evolution of
ST-segment displacement in exercise and recovery is more important than a numerical measurement of
ST-segment displacement.
The T-waves are in the same direction as the dominant deflection of the QRS in the hexaxial leads (i.e.
normally within 30º of the mean frontal QRS-axis). They should be asymmetric with a slow upstroke and
relatively sharper down stroke. They are normally upright in the hexaxial leads and the left chest leads.
They may be inverted in V1 as a normal variant, and sometimes in V2. Loss of amplitude is a nonspecific
observation. Inversion is potentially important but may be a normal variant in young individuals
in whom “normalisation” with exercise is the rule.
U-waves
U-waves follow the T-wave, are generally of lower amplitude, and should always be in the same direction
of the T-wave. U-wave inversion is commonly abnormal and may represent systolic overload in the left
ventricle, or myocardial ischaemia.
Epsilon waves
Epsilon waves are seen on the ST segments of leads V1 and V2 as small “crinkles”. They are best seen in
Fontaine leads (SI, SII, SIII in the parasternal position). They are not diagnostic of ARVC and may be
seen in right ventricular hypertrophy and sarcoidosis. They probably represent late potentials in the right
ventricle.
Delta Waves
Delta waves are seen in at the onset of the QRS complex in the WPW pattern. There is preexcitation of
the ventricle which has the effect of shortening the PR interval whilst the QT interval remains normal.
They may be positive or negative, their polarity depending on the lead and also the delta vector which
reflects the position of the accessory pathway.
Osborn Waves
　
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