|
 |
| |
Stress testing is done to screen for heart disease, also known as coronary
atherosclerosis or "blocked arteries". This is usually done in patients with symptoms of chest pain, shortness of breath,
or fatigue. Sometimes stress testing is done in very high risk individuals (diabetics) to screen for abnormalities
before symptoms start. The test consists of two parts: stressing the heart and imaging the heart for abnormalities.
Stress may be performed with exercise
on a treadmill or with medications such as adenosine or dobutamine. Medications are used in patients unable to
walk on a treadmill adequately. The EKG is monitored for changes. Imaging of the heart is often performed in addition
to EKG evaluation for improved detection of heart disease. Imaging can be done with either with an echocardiogram
(ultrasound) or with nuclear perfusion.
Treadmill Stress Test
A Treadmill Stress Test is generally chosen in patients
at low risk of significant heart disease, who can exercise, and have a normal baseline EKG. This test stresses the heart
with exercise, using a treadmill. The speed and incline are predetermined, following the Bruce protocol.
We monitor for changes in the EKG called ST depression. If this is abnormal, will will refer you on to another stress
test or to angiography. If findings are normal, the probability of significant heart disease is generally low.
However, this is only a screening test, and may not always detect significant heart disease. Patients at higher
risk (diabetics, smokers, previous disease) or with recurrent episodes of chest pain may benefit from a more sensitive test
(echo or nuclear).
For the treadmill, you will undress from the waist up, and will be provided
a hospital gown. Men may need their chest shaved in a small area. Electrodes are placed on the chest to monitor
the EKG. The treadmill starts very slow, and every 3 minutes the treadmill goes faster and the incline becomes steeper.
Most people can exercise for 6-8 minutes on the Bruce protocol, while patients in very good shape can go for 12 minutes
or more. The test takes approximately 30 minutes. The doctor will usually review and discuss the test results with
you before you leave.
An example of a patient walking on the treadmill, with a technician
monitoring the EKG and blood pressure, is shown above.
Stress Echo
A stress echo is chosen for patients with an abnormal baseline EKG or abnormal treadmill test,
those with higher risk of having heart disease, and in patients who also need an echocardiogram to evaluate for valve disease,
cardiomyopathy, or pulmonary hypertension. A stress echo can also be used to detect the severity of valve disease, and
followed over time to determine when surgery should be performed. A stress echo is more sensitive than the treadmill
in detecting significant heart disease, at about 85%. This stress test is also the most specific, meaning when it is
abnormal, the probability of actually having disease is very high. However, like the treadmill, a stress echo
can miss detecting heart disease in some patients. Sometimes adequate pictures are not available, or equivocal
abnormalities are present, and a nuclear test will be scheduled. If the stress echo is normal, the probability of having
a heart attack in the next year is 1% or less. If the study is abnormal, the probability of a heart attack in the next
year is substantially higher, and coronary angiography is generally recommended. A trial of medical therapy can be considered,
and these options should be discussed with your physician after the stress test.
For the procedure, patients will have a baseline echo to evaluate heart and valve function.
Patients then proceed with a treadmill stress test as above. Immediately after exercise, another echo is taken. The movement
of the heart before and after exercise are compared. When there is blockage of blood flow to the heart, the muscle
function weakens, and is detected for 1-2 minutes after completing the treadmill.
Patients who cannot exercise on the treadmill, can have the heart stressed with dobutamine.
This medication is given through the IV for 5-10 minutes, and causes the heart to speed up. This increases the heart
rate similar to exercise, and can also detect blocked arteries. Echo imaging is performed throughout the study to evaluate
for heart muscle changes.
An example of echo imaging immediately after exercise.
Nuclear Stress Test
A nuclear stress test is chosen for patients with an abnormal baseline EKG,
patients unable to exercise, and in those at higher risk of having heart disease. The nuclear test is currently the
most sensitive stress test, detecting disease in 90% of patients, but is slightly less specific than the stress echo, meaning
an abnormal result may not always indicate blocked arteries. A normal nuclear stress test indicates a very low risk
of heart attack in the next year. However, an abnormal test indicates an increased risk of heart attack or death.
These risks may be reduced with treating these blocked arteries- see coronary angiography.
The stress test is performed by taking baseline images of the heart. A radioactive tracer
(Cardiolyte) is injected in the vein to allow us to take pictures of the heart. These pictures are obtained by lying down
under the nuclear camera. A large number of data points are collected and then processed on a computer.
The heart is then stressed with exercise or medications, Cardiolyte is injected again, and pictures are taken again.
We then compare the two sets of pictures. In patients with blocked arteries, a lack of blood flow can be seen on the
stress pictures, but not on the resting pictures. Patients with a previous heart attack will have lack of blood flow
on both resting and stress pictures.
Our nuclear technician is processing data on the computer for interpretation
by the physicians.
Instructions Prior to Test
On the day of your stress test you should arrive to the designated clinic with:
- Comforable shoes to walk in
- No food consumption for 4 hours before your exam
- No caffeine for 12 hours if you are scheduled for a nuclear stress test
- You may take all of your usual medications in the morning with water with the following exceptions:
- Do not take a beta-blocker on the day of your stress test or the night before unless directed
to do so by your physician. Beta-blockers include atenolol (Tenormin), metoprolol (Toprol), carvedilol (Coreg), propranolol
(Inderol), labetalol, timolol, nadolol, and acebutalol.
- Do not take calcium channel blockers on the day of the test until after you complete the exam,
unless directed by your physician. This includes: verapamil (Calan, Covera, Tarka), diltiazem (Cardizem, Diltia), amlodipine
(Norvasc, Lotrel), felodipine (Plendil), nisoldipine (Sular), and nifedipine (Procardia, Adalat).
Links:
Wikipedia
Answers.com
|
|
|
