Treadmill Stress Test

How does a Regular Stress Test Work?

Patients with coronary artery blockages may have minimal symptoms and an unremarkable or unchanged EKG while at rest. However, symptoms and signs of heart disease may become unmasked by exposing the heart to the stress of exercise.

During exercise, healthy coronary arteries dilate (develop a more open channel) than an artery that has a blockage. This unequal dilation causes more blood to be delivered to heart muscle supplied by the normal artery. In contrast, narrowed arteries end up supplying reduced flow to it's area of distribution. This reduced flow causes the involved muscle to "starve" during exercise. The "starvation" may produce symptoms (like chest discomfort or inappropriate shortness of breath), and the EKG may produce characteristic abnormalities. Most commonly, a motorized treadmill is used for exercise, while a stationary bicycle is used in some exercise laboratories.

When is a Regular Stress Test ordered?

A regular stress test is considered in the following circumstances:
    •Patients with symptoms or signs that are suggestive of coronary artery diseases (CAD).
    •Patients with significant risk factors for CAD.
    •To evaluate exercise tolerance when patients have unexplained fatigue and shortness of breath.
    •To evaluate blood pressure response to exercise in patients with borderline hypertension.
    •To look for exercise-induced serious irregular heart beats.

Please remember that the regular stress test is heavily dependent upon interpretation of EKG changes produced by exercise. Therefore, the reliability drops drastically if there are significant EKG changes at rest (for example in patients with long standing high blood pressure, an artificial cardiac pacemaker, use of medications like digitalis, or presence of a bundle branch block pattern, etc.). In all such cases, the physician will usually order an Echo Stress Test or a Nuclear Stress Test, particularly if he or she is suspecting coronary artery disease. However, a regular stress may be sufficient in stable patients or those with a low suspicion of coronary artery disease who are being assessed for exercise tolerance (for example, prior to undergoing a structured exercise or rehab program).

How is a Regular Treadmill Stress Test Performed?
The patient is brought to the exercise laboratory where the heart rate and blood pressure are recorded at rest. Sticky electrodes are attached to the chest, shoulders and hips and connected to the EKG portion of the Stress test machine. A 12-lead EKG is recorded on paper. Each lead of the EKG represents a different portion of the heart, with adjacent leads representing a single wall. 

The treadmill is then started at a relatively slow "warm-up" speed. The treadmill speed and it's slope or inclination are increased every three minutes according to a preprogrammed protocol (Bruce is the commonest protocol in the USA, but several other protocols are perfectly acceptable). The protocol dictates the precise speed and slope. Each three minute interval is known as a Stage (Stage 1, Stage 2, Stage 3, etc. Thus a patient completing Stage 3 has exercised for 3 x 3 = 9 minutes). The patient's blood pressure is usually recorded during the second minute of each Stage. However, it may be recorded more frequently if the readings are too high or too low.

As noted earlier, the EKG is constantly displayed on the monitor. It is also recorded on paper at one minute intervals. The physician pays particular attention to the heart rate, blood pressure, changes in the EKG pattern, irregular heart rhythm, and the patient's appearance and symptoms. The treadmill is stopped when the patient achieves a target heart rate (this is 85% of the maximal heart rate predicted for the patient's age). However, if the patient is doing extremely well at peak exercise, the treadmill test may be continued further.

The test may be stopped prior to achievement of the target heart rate if the patient develops significant chest discomfort, shortness of breath, dizziness, unsteady gait, etc., or if the EKG shows alarming changes or serious irregular heart beats. It may also be stopped if the blood pressure (BP) rises or falls beyond acceptable limits. Please note that the systolic BP (upper number) may normally rise to 200 at peak exercise. At the same time, the diastolic BP (lower number) remains unchanged or falls to a slight degree. In contrast, the BP of patients with hypertension or high BP will show a rise of both systolic and diastolic readings. The latter may rise above 90 - 100.
 

Preparing for the Regular Stress Test
The following recommendations are "generic" for all types of cardiac stress tests:
    •Do not eat or drink for three hours prior to the procedure. This reduces the likelihood of nausea that may accompany strenuous exercise after a heavy meal. Diabetics, particularly those who use insulin, will need special instructions from the              physician's office.
    •Specific heart medicines may need to be stopped one or two days prior to the test. Such instructions are generally provided when the test is scheduled.
    •Wear comfortable clothing and shoes that are suitable for exercise.
    •An explanation of the test is provided and the patient is asked to sign a consent form.
    •How long does the entire test take? A patient should allow approximately one hour for the entire test, including the preparation.

Isotope Stress Test

How does an Isotope Stress Test Work?
An isotope stress test is also known as a nuclear, thallium, Cardiololite, Myoview or dual isotope stress test, depending upon the method used.

During exercise, healthy coronary arteries dilate (develop a more open channel) more than an artery that has a blockage. This unequal dilation causes more blood to be delivered to heart muscle supplied by the normal artery. In contrast, narrowed arteries end up supplying reduced flow to it's area of distribution. This reduced flow causes the involved muscle to "starve" during exercise. The "starvation" may produce symptoms (like chest discomfort or inappropriate shortness of breath), and EKG abnormalities. When a "perfusion tracer" (a nuclear isotope that travels to heart muscle with blood flow) is injected intravenously, it is extracted by the heart muscle in proportion to the flow of blood.

The amount of tracer uptake helps differentiate normal muscle (which receives more of the tracer) from the reduced uptake demonstrated by muscle that is supplied by a narrowed coronary artery. In other words, areas of the heart that have adequate blood flow quickly picks up the tracer material. In contrast, muscle with reduced blood flow pick up the tracer slowly or not at all. Analysis of the images of the heart (taken by a scanning camera) can help identify the location, severity and extent of reduced blood flow to the heart. The reduced blood flow is known as ischemia (pronounced is-keem-ya).

How is an Isotope or Nuclear Stress Test performed?
The test is actually divided into three parts: A treadmill stress test, imaging at rest, and imaging after exercise. There are two common types of isotope used in the USA. They are thallium and technetium (which are marketed under the Trade names "Cardiolite" and "Myoview"). Some laboratories use a "dual isotope" technique, where thallium is used for the resting images and technetium is used for the stress pictures. Depending upon the isotope and protocol for the laboratory, resting images may be obtained either before stress or two to four hours after stress. The preparation for the test and the treadmill procedure is similar to that described under the Regular Treadmill Stress Test section. In patients who are unable to complete a high level of exercise because of physical limitations, stress to the heart is provided by pharmaceutical or chemical stimulation.

The patient is brought to the exercise laboratory where the heart rate and blood pressure are recorded at rest. Sticky electrodes are attached to the chest, shoulders and hips and connected to the EKG portion of the Stress test machine. A 12-lead EKG is recorded on paper. Each lead of the EKG represents a different portion of the heart, with adjacent leads representing a single wall (see Regular Treadmill for details). The treadmill is then started at a relatively slow "warm-up" speed. The treadmill speed and it's slope or inclination are increased every three minutes according to a preprogrammed protocol. Bruce is the commonest protocol in the USA, but several other protocols are perfectly acceptable (see Regular Treadmill for details). . It is the protocol that dictates the precise speed and slope. Each three minute interval is known as a Stage (Stage 1, Stage 2, Stage 3, etc. Thus a patient completing Stage 3 has exercised for 3 x 3 = 9 minutes). The patient's blood pressure is recorded during the second minute of each Stage. However, it may be recorded more frequently if the patient's reading is outside too high or too low.

The EKG is constantly displayed on the monitor. It is also recorded on paper at one minute intervals. The physician pays particular attention to the heart rate, blood pressure, changes in the EKG pattern, irregular heart rhythm, and the patient's appearance and symptoms. The treadmill is stopped when the patient achieves a target heart rate (this is 85% of the maximal heart rate predicted for the patient's age). However, if the patient is doing extremely well at peak exercise, the treadmill test may be continued further. The test may be stopped prior to achievement of the target heart rate if the patient develops significant chest discomfort, shortness of breath, dizziness, unsteady gait, etc., or if the EKG shows alarming changes or serious abnormal heart rhythm. It may also be stopped if the blood pressure (BP) rises or falls beyond acceptable limits.

Approximately one to 1 1/2 minutes prior to termination of exercise, the perfusion tracer or isotope is injected into the intravenous "plug" that had been placed in the forearm or hand. This is followed by a "flush" injection of saline (salt water) to make sure that all of the tracer is pushed into the blood circulation. After a brief waiting phase (that allows the tracer to be taken up by the heart muscle) the patient is placed under a scanning camera.

Two sets of isotope images are obtained. One at rest, and one following exercise. Depending upon the isotope used and the protocol for a particular laboratory, the resting images may be obtained before the stress test, or a few hours later. The scanning camera rotates around the patient's chest, stopping to take individual pictures. The patient needs to lay flat and still during the scanning period which takes approximately 11 to 20 minutes, depending upon the type of scanning camera. Patients with severe claustrophobia should notify their physician (a mild tranquilizer before the test may minimize discomfort).

The pictures or images are fed into a computer, which reconstructs them as "slices" of a three dimensional heart. These slices are presented in three views (vertical long axis or VLA, horizontal long axis or HLA and short axis or SA). It also computes the data and presents an aggregate "bull's eye" picture that compares the information to a data base of known normal cases. Areas that fall out side the expected normal range is presented as a blacked out area. In other words, your physician has an opportunity to view a three dimensional representation of your heart, examine individual "slices" and then compare the findings against those computed by the computer as "blackout plots. By comparing one wall against another, the physician can identify disease and assess its magnitude.

Preparing for an Isotope Stress Test: The following recommendations are "generic" for all types of cardiac stress tests:
    •Do not eat or drink for three hours prior to the procedure. This reduces the likelihood of nausea that may accompany strenuous exercise after a heavy meal. Diabetics, particularly those who use insulin, will need special instructions from the             physician's office.
    •Specific heart medicines may need to be stopped one or two days prior to the test. Such instructions are generally provided when the test is scheduled by the doctor's office. Call if you have any questions.
    •Wear comfortable clothing and shoes that are suitable for exercise.
    •An explanation of the test is provided and the patient is asked to sign a consent form.
 

How long does the entire test take?
A patient should allow approximately two to four hours for the entire test, including the preparation. Dual isotope and technetium stress testing takes less time than thallium. You will be allowed to leave the lab and get a light snack or lunch in cases of thallium stress testing.
 

How safe is an Isotope Treadmill Stress Test?
The patient is exposed to a very small amount of radiation and the risk is minimal, if any. The risk of the stress portion of the test is very small and similar to what you would expect from any strenuous form of exercise (jogging in your neighborhood, running up a flight of stairs, etc.). As noted earlier, experienced medical staff is in attendance to manage rare complications like sustained abnormal heart rhythm, unrelieved chest pain or even a heart attack. In such cases, the patient is better off having the problem in the presence of experienced staff, rather than have it happen when they are exercising alone.

What is the reliability of an Isotope Stress Test?

If a patient is able to achieve the target heart rate and good quality images are obtained, an isotope treadmill stress test is capable of diagnosing important disease in approximately 85% of patients with coronary artery Approximately 10% of patients may have a "false-positive" test (when the result is falsely abnormal in a patient without coronary artery disease). Technical problems can occur when a patient is markedly overweight. Women may have an abnormality in the front portion of the heart because of overlying breast tissue. Some men may demonstrate an inferior wall abnormality because of a prominent diaphragm (muscular partition that separates the chest cavity from the abdomen). Patients who have a left bundle branch block on their EKG may also have a false abnormal test.

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Chemical Stress Test

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How does a Chemical Stress Test work?
A chemical or pharmacological stress test combines an intravenous medication) with an imaging technique (isotope imaging or echocardiography) to evaluate the LV. In these cases, the medication serves the purpose of increasing the heart load instead of using exercise. Stress causes normal coronary arteries to dilate, while the blood flow in a blocked coronary artery is reduced. This reduced blood flow may decrease the movement of the affected wall (as seen by echo), or have reduced isotope uptake in a nuclear scan. Agents that are commonly used in pharmacologic stress testing include dipyridamole, dobutamine and Adenosine (Trade name).
 

How is a Chemical Stress Test performed?
The imaging portion of the test is identical to that used during Stress Echocardiography or Isotope Stress Testing (depending upon the technique employed) and is performed either in a cardiologists office, a satellite lab or the hospital. An intravenous line is started in the arm, the blood pressure is checked and an EKG recorded. The EKG is also constantly monitored on the screen. If Stress Echo is being performed, an echocardiogram is obtained before and immediately after administration of the stress producing medication. In cases of stress isotope testing, the resting images may be obtained before or approximately two hours after the stress (depending upon the lab and the employed isotope). The stress-producing medication is given intravenously, as per protocol. In cases of dobutamine, drug is given as a continuous drip with a gradual increase in the rate (at three minute intervals). The patient's heart rate accelerates and the isotope is given when 85% of the target heart rate is achieved. In cases of dipyridamole, the medication is usually given over four minutes, through the IV line. A drop in the diastolic (lower number) blood pressure is generally awaited before administration of the isotope.
If a patient is able to perform mild exercise, he or she may be asked you to walk on a treadmill for a minute or so after the injection of dipyridamole.
 

How long does the entire test take?
A patient should allow approximately two to four hours for the entire test, including the preparation. Dual isotope and technetium stress testing takes less time than thallium. The first part of the test generally takes an hour. The second part takes anywhere from 15 to 30 minutes. Between the two parts of a thallium test, you will be allowed to leave the lab and get a light snack or lunch.

How safe is a chemical Stress Test?
The patient is exposed to a very small amount of radiation and the risk is minimal, if any. The risk of the chemical stress portion of the test is very small and similar to what you would expect from any strenuous form of exercise (jogging in your neighborhood, running up a flight of stairs, etc.). As noted earlier, experienced medical staff is in attendance to manage the rare complications like sustained irregular heart beats, unrelieved chest pain or even a heart attack. In such cases, the patient is better off having the problem in the presence of experienced staff, rather than have it happen when they are exercising alone. Also, the stress medicine like Dobutamine can be immediately stopped if there are problems, The effects of dipyridamole (which can occasionally cause nausea or a headache can be reversed by aminophylline (an anti-asthma medication). Please also see the caution about asthma under the "Preparing..." section.