Word count: 4367 Electrocardiography In Elite Athletes F. CARRE and J.C. CHIGNON* Department of Physiology, Pontchaillou Hospital 35003 Rennes, France *National Institute of Sports, 11 Avenue du Tremblay, 75012 Paris, France. Electrocardiographic (ECG) features commonly observed in top ranking sportsmen were first described in 1929 by Hoogerwerf. The development of new non-invasive exploration methods (i.e. cardiac echocardiography and magnetic resonance imaging) in the early 1970s offered physiologists the means of investigating the so-called "Athlete's Heart Syndrome" recognized by its specific ECG features. Standard ECG tracings have the advantage of low cost, ready availability and ease of use and remain an essential investigation tool. In trained subjects, ambulatory ECG monitoring and stress testing ECG are particularly important as they provide supplementary information to the classical 12-ECG which records only a brief period of cardiac electrical activity. The features of the athlete's ECG basically reflect the heart's normal physiological adaptation to repetitive physical training. However several unusual patterns appear
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Word count: 4367
Electrocardiography In Elite Athletes
F. CARRE and J.C. CHIGNON*
Department of Physiology, Pontchaillou Hospital
35003 Rennes, France
*National Institute of Sports, 11 Avenue du Tremblay,
75012 Paris, France.
Electrocardiographic (ECG) features commonly observed in top
ranking sportsmen were first described in 1929 by Hoogerwerf. The
development of new non-invasive exploration methods (i.e. cardiac
echocardiography and magnetic resonance imaging) in the early
1970s offered physiologists the means of investigating the so-called
"Athlete's Heart Syndrome" recognized by its specific ECG features.
Standard ECG tracings have the advantage of low cost, ready
availability and ease of use and remain an essential investigation
tool. In trained subjects, ambulatory ECG monitoring and stress
testing ECG are particularly important as they provide
supplementary information to the classical 12-ECG which records
only a brief period of cardiac electrical activity.
The features of the athlete's ECG basically reflect the heart's
normal physiological adaptation to repetitive physical training.
However several unusual patterns appear to be quite similar to
pathological aspects occurring in different heart diseases. It is thus
essential to acquire a full understanding of the ECG patterns in the
elite athlete.
2
Interpretation of the athlete's ECG
A highly trained athlete is usually defined as a subject who
practices at least ten hours a week at a level of intensity reaching at
least 60 percent of his maximal oxygen consumption (Use Word 6.0c or later to
view Macintosh picture.
O2max).
Consequently, and athlete's ECG must always be interpreted in light
of his individual level of training, both qualitatively and
quantitatively, and in accordance with the physical examination,
functional signs and his personal and familial cardiovascular risk
factors, including age.
The most common ECG features described in elite athletes can
be observed in all age groups and in both men and women, however
they are not always found in every elite athlete. They result from
physiological adaptations to physical conditioning and should not be
immediately interpreted as markers of heart disease. The
mechanisms underlying the disturbances observed on the athlete's
ECG are not yet fully understood although modifications in
autonomic nervous system tone and cardiac hypertrophy are often
proposed as significant explanations.
Modifications in autonomous nervous system tone have been
described in the athlete's heart syndrome on the basis of
biochemical and pharmacological tests. Another way of evaluating
the effect of changes in parasympathetic and sympathetic tone is to
study heart rate variability. Characteristically, there is an increase in
parasympathetic tone and a decrease in sympathetic tone (perhaps
through the effect of lower baroreceptor sensitivity). At rest,
vagotonia appears to predominate whereas during exercise the
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deceased sympathetic drive results in the slower heart rate observed
in athletes compared with untrained subjects performing the same
work load.
Cardiac hypertrophy in the athlete was first suspected by
Henschen in 1899 on the basis of chest percussion and has been
confirmed by non-invasive morphology investigations including
radiology, echocardiography and more recently magnetic resonance
imaging. It is described as a four-chamber harmonious wall
hypertrophy-chamber dilation which can be observed at all ages and
appears to be totally reversible after deconditioning.
There is some controversy in the literature as to the real
incidence of ECG disturbances. For example, in two studies based on
a large sample population (Venerando published a series of 12,000
subjects and in our own personal unpublished work we investigated
6,487 subjects) the global prevalence of ECG disturbances was found
to be 13 and 44 percent respectively. This difference could be
explained by differences in methodology in the training level since
the ECG criteria for diagnosis of cardiac hypertrophy have not been
standardized.
The mean ± SD values of classical ECG criteria as observed in
our study are given in Table I in comparison with the ranges
classically described in a standard population. In general, the ECGs of
athletes lie within standard limits. A few trends which increase with
training level can however be seen. The durations of the PR interval,
the QRS complex and the corrected QT interval increase with the
Sokolow-Lyon Index and frontal QRS axis turns to the left. Even
though the ECGs of elite athletes lie within normal limits, different
patterns of ECG disturbances have been described.
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For the purposes of this review, we have divided these changes
into rhythm disorders, atrio-ventricular conduction impairment,
cardiac hypertrophy related ECG criteria and disturbed
repolarization. Finally, we shall try to specify the potential differences
observed in endurance versus resistance in the trained athlete.
Changes in cardiac rhythm
Hypokinetic Arrhythmias
The respective incidences of changes in cardiac rhythm and
hypokinetic arrhythmias are summarized in Table II.
Resting sinus bradycardia is the most common finding among
trained athletes. It is difficult to determine the real incidence of
athlete's bradycardia due to the lack of a common definition of
bradycardia. The incidence varies from 8 to 85% in studies using the
cut-off of 60 beats per minute, and in our study, we found only 9% of
our athletes with a resting heart rate below 50 beats per minute.
Controlled Holter recordings have shown a significantly lower mean
hourly heart rate. Training undoubtedly affects the incidence of
bradycardia but the role of individual sensitivity and the mechanisms
of training-induced bradycardia have yet to be established.
Classically, the alterations in the autonomous nervous system
described above would have an effect, but some studies have shown
that lower intrinsic heart rate is also related to athlete's bradycardia.
In most cases, the bradycardia is benign as confirmed by normal
rhythms recorded during stress testing and also by the persistence of
physiological circadian variations (lower nocturnal heart rate) on
Holter recordings. Rarely, the bradycardia is associated with
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dizziness, syncope or hyperkinetic arrhythmias due to vagal tone. In
general, these symptoms disappear with deconditioning. Electrical
stimulation is rarely needed and usually concerns older athletes in
whom a latent sinus node disease is unmasked by the increased
vagal tone. The resting heart rate in individuals with athlete's
bradycardia correlates with their individual level of peak training,
and is used as a criteria for evaluating their level of training although
it is not well correlated with performance or Use Word 6.0c or later to
view Macintosh picture.
O2max. A better index
of training level would be the heart rate recovery curve. The rapidity
at which the heart rate returns to the basal level (or near basal level)
would be an indication of a good level of training. An unusual
disturbance of the resting sinus rate which cannot be explained by a
change in the training regimen, is commonly considered to be a
feature of overtraining.
Other hypokinetic dysrhythmias also concern the sinus rhythm
and are related to altered autonomous tone. They disappear during
stress training. These modifications are frequently observed on
ambulatory ECG recordings, particularly at night. They are of no
prognostic significance.
The prevalence of sinus dysrhythmia , the so-called
"respiratory arrhythmia", would appear to be significantly higher in
athletes than in the standard population, but in fact the apparent
sinus dysrhythmia disappears when the variability of R-R interval as
a function of basal heart rate is taken into account (R-R interval
variation increases with decreasing heart rate). This is a well-
recognized ECG pattern on ambulatory ECGs where the sinus pauses
during both awake and (especially) sleeping hours are significantly
longer on athlete's recordings than on control recordings.
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Ectopic atrial rhythm including the wandering atrial pacemaker
or coronary sinus rhythm have also been described.
Nodal rhythm is more frequent in elite athletes. The escape threshold
varies from 45 to 65 beats per minute and in some cases (in 15% of
the subjects in our study) escape rhythm totally disappears only
above 100-120 beats per minute.
Idioventricular rhythm (Figure 1) is the event of a low sinus
rate and/or of sinus pauses. This cardiac rhythm originates in
pacemaker cells at a rate of 40 to 100 beats per minute.