Effort Electrocardiography
An effort test is performed during a standardized physical
activity that is gradually increased and strictly supervised. Its purpose is to
determine whether the patient has coronary insufficiency and to determine the
severity of the disease by means of some specific criteria.
During physical exertion, the patient's oxygen consumption increases. The increased
oxygen demand is met by an increase in the frequency of heart beats and thus an
increase in coronary blood flow.
The maximum oxygen consumption in each person is determined by the maximum
coronary blood flow, which is proportional to the theoretical upper limit of
the frequency of heart beats. The theoretical maximum heart rate is given by
the formula 220 - age of the patient (standard deviation ± 12). Accordingly, a
50-year-old patient's heart would theoretically beat a maximum of 170 beats per
minute. This is the number of beats to be progressively reached during the
effort test. 80 percent of this is considered "sub-maximal" (close to
maximal).
If the maximum rate is reached without any abnormalities on the
electrocardiogram (ECG) or symptoms such as pain or shortness of breath, the
coronary vessels are healthy.
On the other hand, if there is a blockage in the coronary arteries and this
blockage prevents the blood flow required for physical exertion, the ECG will
show abnormalities due to insufficient blood supply to the heart and
angina-like chest pains. The frequency of heart beats at which these symptoms
occur is called the "ischemia threshold", i.e. the local anemia
threshold.
There are other important criteria for determining coronary artery disease.
These include arterial pressure (blood pressure can become very high during
exertion), the duration of the exertion and the level of effort or strain
required to reach the critical pulse frequency. In this case, since the
examination is not limited to ECG data, it is more appropriate to call the
procedure a stress test rather than a stress ECG.
Localized anemia (ischemia) and the associated angina pain that occurs during
physical activity are caused by a disturbance in the balance between the oxygen
supply and the oxygen demand of the heart muscle. This is caused by narrowing
of the coronary arteries, which prevents increased blood flow.
Chest pain due to physical exertion does not give electrocardiographic symptoms
unless an ECG is performed during the attack, i.e. in normal times. In
contrast, it is almost always painful after the ECG shows typical signs of
ischemia.
MODE OF APPLICATION
Electrocardiography with effort does not require much equipment, but the
quality of the equipment used is very important for the test to give reliable
results.
The following devices are used during
the test:
- Ergometer bicycle. It is a bicycle with electromagnetic brakes adjusted
to allow precise measurement of the power expended to turn its pedals; it
stands in place like a gymnastic bicycle. Instead of this type of bicycle, a
treadmill can also be used; the patient walks or runs on this treadmill, the
speed and inclination of which can be adjusted. The Master's test, which is
based on continuous ascent and descent of two steps, is no longer practiced.
- An electrocardiograph device. Continuous recording during exertion.
- Mercury manometer. Used to measure arterial blood pressure.
- Electrodes. One end is attached to the body; the other end, connected to the
ECG, allows recording.
- Defibrillator, oxygen cylinder and medication for any malfunctions and severe
rhythm disturbances that may occur in the heart during the test. Used in
emergency situations.
APPLICATION CONDITIONS
The decision to use a stress test can only be made after careful clinical
examination and evaluation of a resting ECG. All these examinations should be
carried out by the physician responsible for the test. Sometimes a physician
may be asked to perform a test on a patient who has been referred to him/her
with very appropriate documentation.
may even detect new clinical symptoms or ECG changes and
conclude that the test may be dangerous.
After a resting ECG and blood pressure measurement, the patient begins the test
by expending 30 watts of power for three minutes. The power is increased by 30
watts every three minutes up to 210-270 watts. The three-minute period is the
time necessary for the organism to adapt to the new power. At the end of each
three-minute period, a long ECG is recorded without interrupting the patient's
power expenditure. This recording is checked for signs of ischemia, accelerated
heart rate and elevated blood pressure. If there are any signs of ischemia, or
if the test needs to be stopped, the next level of exertion is not started.
Peak power is the power that allows the heart rate to reach its theoretical
upper limit and varies according to the age, weight and sex of the patient.
If the heart rate is not fast enough to reach the theoretical upper limit, the
test should be stopped if the following symptoms occur
- Significant shortness of breath or muscle weakness;
- a drop or insufficient rise in blood pressure;
- significant rhythm disturbances;
- angina-type chest pain (even if there is no abnormality on the
electrocardiogram).
TEST RESULTS
Interpreting the test result as "normal" indicates normal
coronary blood flow and is not an easy decision to make. However, in some cases
the physician can make this decision with confidence. Negative response
An effort test gives a negative result in the following cases:
- If the chest pain the patient is experiencing is not due to exertion and
no changes in the ECG occur during exertion.
- There are so-called "atypical" abnormalities on the resting
ECG, which disappear during exertion and no symptoms occur.
- Various atypical symptoms occur only during exertion and over a certain
period of time (e.g. if pain occurs at the beginning of exertion and disappears
with further exertion, while the ECG remains normal and there are no abnormalities
in blood pressure).
Caution: A negative result of an exercise test is not an automatic
indication of the absence of coronary insufficiency, especially in men over 40
years of age with typical symptoms of angina pectoris. "Abnormal"
result
A test result may be considered "abnormal" if
- Heart rate increases with exertion, but blood pressure does not rise as
much as it should. This may be due to left ventricular failure suggestive of
coronary artery stenosis. If chest pain is also present during physical
activity or rest, the absence of a rise in blood pressure may be due to a
mitral valve defect or aortic valve stenosis. Methods such as echocardiography
should be used to investigate these possibilities in detail.
- If the EGK is normal but the patient has to discontinue the test because
of chest pain. In this case, the test result is positive and the only
indication of coronary insufficiency is chest pain that occurs with exertion
and disappears when the test is stopped.
- A negative test result does not necessarily indicate the absence of true
angina pectoris. Sometimes there is a typical angina, but it does not show up
during the effort test and does not cause abnormalities on the ECG.
