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Section
4: Pediatric Exercise Testing
Overview
of the Test
Exercise
testing in the pediatric population and in patients
with congenital heart defects is fundamentally different
from routine adult stress testing. This difference is
due to both the population undergoing testing and the
types of testing required in each population 7,35,36.
Therefore, not surprisingly, many of the standards for
testing in the adult population have little relevance
for pediatric exercise testing.
Ischemic
heart disease is rare in the pediatric population. Most
pediatric patients who undergo exercise testing do so
to evaluate nonischemic heart disease. The most common
reason is the evaluation of exercise performance in
preoperative or, more commonly, postoperative congenital
heart defects. Other common indications include cardiomyopathy
and exercise-induced arrhythmia or syncope. Increasingly,
pediatric cardiologists are also being called on in
their role as exercise physiologists to evaluate non––cardiac-exercise–related
abnormalities such as exercise-induced bronchospasm
or other pulmonary and/or musculoskeletal abnormalities
36. Recommendations
regarding the indications for exercise testing in the
pediatric population have been published previously
7.
Exercise
performance and aerobic capacity can be inferred in
the pediatric population from endurance time on ergometers.
Although this type of testing does not directly measure
such values as maximal oxygen consumption or anaerobic
threshold, these values can be estimated from such studies.
In addition, assessment of ECG changes, the presence
of arrhythmias, and blood pressure response to exercise
are readily assessed.
Because
physical working capacity and aerobic capacity are often
the most important measurements in a pediatric exercise
testing, direct measurement of metabolism by gas exchange
is frequently performed as part of pediatric exercise
testing 36,37.
Commonly measured values include maximal oxygen consumption,
maximal carbon dioxide production, maximal respiratory
exchange ratio, and maximal cardiac output, as well
as measurements of oxygen consumption at anaerobic threshold.
Maximal work rate, heart rate, and blood pressure responses
are also measured. Pulmonary function studies that evaluate
performance both at rest and during exercise are important.
This is not only to assess for pulmonary dysfunction
but also because many congenital heart defects have
associated pulmonary abnormalities. Resting spirometry
is often performed. During exercise, minute ventilation,
tidal volume, respiratory rate, and the ratio of physiological
dead space to tidal volume are frequently monitored.
Normal
values for all the above measurements vary with age
and often with sex. Interpretation of these data requires
that the physician be familiar with the changes in children’s
responses to exercise as a consequence of age and pubertal
status 35.
In addition, the physician needs to be familiar with
many of the expected variations in response to exercise
seen in various types of congenital heart defects 7,35,36.
In
the actual performance of exercise testing in the pediatric
population, wide differences in age and size must also
be taken into account. Protocols and ergometers must
be adapted to children as young as 4 years of age up
through adolescence and young adulthood. Equipment needs
(such as mask size, dead space in equipment, and size
of rebreathing bags) vary with patient size. Protocols
frequently used in adult patients to assess myocardial
ischemia are often inadequate to assess the working
capacity of young children with congenital heart defects.
Likewise, a protocol well suited to measure aerobic
fitness in a young child may be inadequate to measure
aerobic fitness in an adolescent 36.
Recommendations
Regarding Training and Competence for Pediatric Exercise
Testing
Recommendations
regarding clinical competence in pediatric exercise
testing present a number of difficulties. There are
no large pools of data available nationwide regarding
the types of exercise testing performed and the manpower
usage in pediatric practice groups. Data available from
surveys of adult exercise testing are not generally
applicable to the pediatric population. In addition,
far fewer pediatric studies are performed, and there
are far fewer pediatric cardiologists than adult cardiologists
performing exercise tests. It is therefore difficult
to make generalized recommendations for a relatively
small group of physicians.
To
obtain some insight into the type of testing performed
in the pediatric population, an informal survey of 10
medium to large academic pediatric cardiac programs
was performed for this committee. The centers had a
median of 9 cardiologists (range 5 to 27). A median
of 380 tests per year (range 100 to 850) was performed
at these institutions, with 88% of tests (range 0% to
100%) using metabolic measurements. These studies were
usually read by a single physician in each center (range
1 to 9). In the 7 centers with active fellowship programs,
the median number of studies observed by an individual
fellow in the course of training was 40 (range 18 to
60).
The
large number of patients undergoing metabolic exercise
testing in this survey would suggest that a very large
percentage of pediatric exercise testing is at least
in part directed at assessing working capacity and aerobic
capacity. These tests are read by a very small number
of individuals (usually just 1) at any center. This
tends to reflect the very subspecialized body of knowledge
in exercise physiology required to accurately interpret
metabolic data from pediatric exercise testing. More
physicians appear to participate in exercise testing
involving nonmetabolic measurements that focus primarily
on ECG and blood pressure responses.
Minimum
Requirements Needed to Achieve and Maintain Clinical
Competence
Exercise
Testing Without Metabolic Measurements
The
skills necessary to perform this type of stress testing
in a pediatric population are similar to those requirements
in adult testing for ischemia and arrhythmias. In addition,
the healthcare provider must be familiar with the unique
ECG, heart rate, and blood pressure responses in the
pediatric populations 35,36,38. These include
both differences in healthy children compared with healthy
adults and the changes that occur in the healthy pediatric
population in response to aging 38.
The physician should be familiar with the expected response
to exercise in types of patients who routinely undergo
exercise testing with the types of congenital heart
disease that produce arrhythmias 7,35.
The individual responsible for the supervision of the
exercise test should be familiar with the indications
and contraindications for exercise testing in the pediatric
population; they should also be familiar with the indications
for termination of a pediatric exercise study 36.
(See Table 5.)
Trainees
in the task force survey listed above participate in
a median of 40 tests during the course of their fellowship.
Although these numbers would appear adequate to achieve
competence, the caveats listed in the section on adult
testing seem to hold true for pediatric testing. Individual
training circumstances must be taken into account when
adequacy of training is judged.
Requirements
for maintenance of clinical competence should be similar
to those for physicians who test adults. Because of
the generally lower number of studies performed in the
pediatric population, the total number of studies a
physician performs in the pediatric population may be
fewer. It is nevertheless important to perform testing
regularly to maintain an adequate level of clinical
competence.
Exercise
Testing with Metabolic Measurements
Supervision
Because
many of the data needed for interpretation of metabolic
measurements in an exercise test require posttest computer
processing, there are many instances in which it may
not be required that the physician who interprets these
data be present for the exercise test. The physician
who supervises the test, in many instances, does not
need to be able to interpret the metabolic data. He/she
should be competent to assess all data acquired in a
routine nonmetabolic exercise test as outlined in the
above section. Most importantly, the monitoring individual
should be familiar with all the indications and contraindications
for exercise testing, as well as the indications for
termination of a pediatric exercise test 36.
The need for the presence of a physician familiar with
interpretation of metabolic data during an exercise
test must be made on an individual basis. There will
be tests for which the physician’s presence is
necessary to ensure proper collection and subsequent
interpretation of the metabolic data.
Interpretation
Interpretation of pediatric metabolic exercise testing
is a very subspecialized field in exercise testing.
As the committee survey indicates, the number of pediatric
cardiologists who interpret these studies is quite small.
Therefore, it is extremely difficult to set any specific
guidelines regarding how to obtain the fund of knowledge
necessary for metabolic exercise interpretation. Trainees
wishing to learn these skills generally study metabolic
exercise testing as an adjunct to the normal clinical
skills that must be mastered as a part of a pediatric
cardiology fellowship. Pediatric cardiologists who have
completed training usually gain this knowledge by a
combination of direct mentoring and texts. Minimal recommendations
are summarized in Table 6.
It
is not possible to give recommendations about specific
numbers or types of studies that an individual should
perform to achieve clinical competence. In most cases,
this decision would appear to be best made by the individual
physician who mentors the trainee. These decisions should
obviously take into account the clinical circumstances
under which the trainee is likely to function subsequent
to completion of training.
Requirements
for maintaining clinical competence are also difficult
to establish. The physician should be familiar with
the data outlined in the overview section of this report
for pediatric metabolic exercise testing 7,35–39.
Given the specialized nature of this fund of knowledge,
there are no data that would suggest how many studies
per year are necessary to maintain clinical competence.
The information from the committee survey is reassuring,
however, suggesting that most physicians who interpret
pediatric metabolic exercise tests evaluate a substantial
number of studies on a yearly basis.
Stress
Echocardiography, Nuclear Imaging, and Pharmacological
Stress Testing in Pediatric Patients
These
studies are performed in very small numbers in the pediatric
population. They are performed to evaluate conditions
associated with potential coronary insufficiency, such
as Kawasaki disease, cardiac transplant graft vasculopathy,
the arterial switch operation, and supervalvular aortic
stenosis. These conditions may be due to either an acquired
or a congenital cardiac abnormality. In most cases,
these studies are performed with the same protocols
and measurement techniques as in adult studies.
Very
few pediatric centers perform significant numbers of
these studies. At these centers, the numbers performed
may be insufficient to provide adequate training for
these types of studies during fellowship. It may also
be difficult to maintain clinical competence with such
a small number of studies. It would therefore appear
advisable that a pediatric cardiologist who wishes to
perform these types of procedures have a relationship
with an adult cardiology center, which could serve as
a resource for additional expertise in both the performance
and interpretation of certain studies.
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