Exercise Treadmill Test (ETT) or Stress Test
What is a ‘stress test’ and
why is this called a stress test?
The resting heart muscle’s
blood supply needs are usually well met even in the
presence of blocked arteries. When the heart is
stressed either by exercise or chemicals, the demand
for blood increases. The blood flow through the
blocked arteries- while adequate at rest- may not be
able to keep up with the demands of a stressed
heart. This can show up on the pictures of the
heart taken after stress. This is the principle
behind all the stress tests. The word stress test is
used for any means used to increase heart muscle’s
demand for blood. This can be done by exercise or by
chemical means.
What is an exercise
treadmill test?
For this test, your chest area
is cleaned and if need be, shaved. Some stick-ons
called electrodes are placed on the chest. After
this, you are asked to walk on the treadmill. Most
of the treadmill tests are done according to certain
set protocols. These protocols have different names
like modified Bruce protocol, Bruce protocol,
McNaughton, Balke protocol etc. The speed and
incline of the treadmill increase by preset degree
at preset time intervals governed by each protocol.
While you are walking on the treadmill, your heart
rhythm is watched, blood pressure is measured and
serial EKGs are taken. EKG or ECG stands for
electrocardiogram. It appears as lines on a piece of
paper. The person doing the test needs to know if
you are having chest pain, dizziness or any other
unusual symptoms during the test. You will be asked
to walk on the treadmill till one or more of the
following are achieved:
-
You cannot keep walking due to variety of
reasons including shortness of breath, dizziness,
joint pains, fatigue, leg pain, chest pain etc.
-
The person doing the test sees some signs
that may mean that continuing the test could be
harmful. These include: very high blood pressure,
chest pain, plummeting blood pressure, significant
rhythm or other EKG changes.
-
For a test to be useful, you should achieve
at least 85% predicted heart rate. Predicted heart
rate is calculated by a formula: 220 minus age. You
should achieve at least 85% of this number.
The person doing this test will
study the following:
-
Any symptoms you may have during the test
including chest pain, shortness of breath, etc.
-
The EKG changes that could be suggestive of
blockages in heart arteries.
-
Rhythm changes.
-
Blood pressure response and heart rate
response to exercise.
-
Exercise capacity.
How do I prepare for this
test?
You should wear comfortable
shoes and clothes. Simply put, wear clothes that you
will wear if you were going exercising.
How does this test help?
This test can give indication
toward blockage in heart arteries. It also helps
measure exercise capacity. In certain cases, it can
tell us about propensity toward certain arrhythmias.
Are there any shortcomings
of exercise treadmill test?
This test cannot be done in
patients who cannot walk. Because this test studies
EKG changes that appear on exercise, it will not be
useful if your baseline EKG is abnormal. This test
is also not helpful if you are on a medicine called
digoxin. The sensitivity of this test is around 70%.
That means that this test can miss up to 1/3 of the
cases with blockages of heart arteries. This test
cannot help us localize the area of blockages.
Because of some of these factors, simple exercise
treadmill test may not be the right test for you.
Can you die during a stress
test?
With well-selected cases,
incidence of death during any stress test should be
extremely rare.
Return to stress tests
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