When a patient is resting it is difficult to
diagnose heart disease because while at rest the patient's physical
examination and
ECG are often viewed as normal. In these cases, cardiac abnormalities
may become apparent only when the heart is asked to perform at increased
workloads. 
The stress test is used to evaluate the heart
and vascular system during exercise. It helps answer to two general
questions: 1) Is there occult underlying heart disease that only becomes
apparent when the heart is stressed by exercise? 2) If there is
underlying heart disease, how severe is it? (Image is of an actual
beating heart.)
How is a stress test performed?
The patient is attached to an ECG machine, and
a blood pressure cuff is placed on one arm. Sometimes a clothespin-like
sensor is attached to the finger to measure the amount of oxygen in the
blood. 
After a baseline ECG is obtained, the patient begins to perform a
low level of exercise, either by walking on a treadmill, or pedaling a
stationary bicycle. The exercise is "graded" - that is, every three
minutes, the level of exercise is increased. At each "stage" of exercise,
the pulse, blood pressure and ECG are recorded, along with any symptoms
the patient may be experiencing.
With a "maximal" stress test, the level of
exercise is gradually increased until the patient cannot keep up any
longer because of fatigue, or until symptoms (chest pain, shortness of
breath, or lightheadedness) prevent further exercise, or until changes on
the ECC indicate a cardiac problem. Maximal stress tests should be
performed when the goal is to diagnose the presence or absence of coronary
artery disease.
With a "sub maximal" stress test, the patient
exercises only until a pre-determined level of exercise is attained.
These tests are used in patients with known coronary artery disease, to
measure whether a specific level of exercise can be performed safely.
After the test, the patient remains monitored
until any symptoms disappear, and until the pulse, blood pressure and ECG
return to baseline.
What kinds of heart disease can the stress
test help to evaluate?
The stress test is useful chiefly in the
diagnosis of coronary artery disease. Coronary artery disease produces
blockages in the coronary arteries, the arteries that supply blood to the
heart muscle. If a partial blockage is present, the heart muscle supplied
by that partial blockage may be getting all the blood it needs in the
resting state. But if the patient exercises, the partially blocked artery
may not be able to supply all the blood the heart muscle needs to perform
at the high level now needed. When a portion of the heart muscle is
suddenly not receiving enough blood flow, it becomes oxygen-starved, or
ischemic. Ischemic heart muscle often causes chest discomfort (a symptom
called "angina") and characteristic changes on the ECG. It can also cause
changes in the heart rhythm, or in the blood pressure. By placing the
stress of exercise on the heart, the stress test can bring out
abnormalities caused by partial blockages in the coronary arteries -
abnormalities that are often completely unapparent at rest.
Because exercise raises adrenaline levels,
stress tests can also be useful in diagnosing certain cardiac arrhythmias
that tend to occur at times when adrenaline levels are increased.
Stress tests are also useful in measuring the
"functional capacity" of patients with heart disease. If a patient has
coronary artery disease, for instance, the stress test can help assess the
significance of partial blockages. If signs of ischemia occur at a low
level of exercise, the blockages are likely to be very significant. But
if ischemia does not occur, or if it occurs only at very high levels of
exercise, the blockages are likely to be much less significant.
Performing periodic stress tests can be a
useful way of monitoring the progress of patients with congestive heart
failure. If the peak level of attainable exercise is worsening over time,
either the underlying heart disease may be worsening, or the patient's
medical therapy may need to be re-adjusted.
What are some of the variations used with
stress tests?
The accuracy of the stress test in diagnosing
coronary artery disease is greatly increased by performing a
nuclear
perfusion study in conjunction with the stress test. A radioactive
substance called thallium
(or a similar substance called sestamibi or
Cardiolite) is injected into a vein during exercise. The thallium
collects in the parts of the heart that have good blood flow. Pictures of
the heart are taken with a special camera that can image the radioactivity
of the thallium. From these pictures, portions of the heart that are not
receiving good blood flow (because of blockage in the coronary arteries)
can be identified. The thallium study greatly increases the accuracy of
the exercise study in diagnosing coronary artery disease. The amount of
radioactivity the patient receives from thallium is less than that from a chest x-ray.
Basic Cardiac Stress Tests take approximately one
hour for the total procedure, with nine to twelve minutes being the
average exercise time. The patient's fitness level and how fast he or
she achieves target heart rate determines the exercise time. Heart rate,
heart rhythm, blood pressure and electrical changes on the 12-lead
electrocardiogram are monitored throughout the testing procedure. A
four-hour fast is required, as well as comfortable clothing and shoes.
Nuclear Stress Testing Using Cardiolite as the imaging agent
increases the accuracy of the basic cardiac stress test to detect
coronary artery disease. An intravenous catheter is placed in the arm to
allow the administration of Cardiolite during the rest and exercise
phase of the test. Rest images using a SPECT camera are obtained in the
nuclear medicine department by a registered nuclear
medicine technologist. After the rest images are obtained, the patient
is brought to the cardiology department, where the treadmill stress test
is performed. Heart rate, heart rhythm, blood pressure and electrical
changes on the 12-lead electrocardiogram are monitored throughout the
testing procedure. A cardiologist, cardiac technologist and nuclear
medicine technologist are present throughout the exercise testing phase.
Post-exercise images are collected in the nuclear medicine department. A
staff of experienced radiologists compare the rest and exercise images,
the results of which are sent to the referring physician. A four-hour
fast is required, as well as comfortable clothing and shoes. The testing
procedure lasts approximately four hours.
Pharmacological Stress
Testing
is used when a person is unable to exercise on a treadmill long enough to
achieve their target heart rate. We offer two types
of pharmacologic stress testing:
Pharmacological cardiac nuclear stress tests are performed using
Persantine, which is administered through an intravenous catheter placed
in the arm. Rest images of the heart using a SPECT camera are first
obtained in the nuclear medicine department by a registered nuclear
medicine technologist. The stress test, using Persantine as the
stressing agent, is performed in the cardiology department. Persantine
may be administered lying down, sitting or during low-level exercise.
Heart rate, heart rhythm, blood pressure and electrical changes on the
12-lead electrocardiogram are monitored throughout the testing
procedure. A four-hour fast is required, as well as comfortable clothing
and shoes. This procedure lasts approximately four hours.
12-Lead Electrocardiograms
are used to monitor the heart's electrical activity at rest and are
performed using a computerized EKG cart. This procedure requires no
fasting, is pain free and last approximately fifteen minutes. An on-site
staff cardiologist interprets the results of this test.
Sometimes patients are not able to perform
exercise because of physical limitations. The drugs persantine and
dobutamine can be used in these cases to simulate the effects of exercise
on the heart.
What are the limitations of the stress
test?
In some patients, ECG changes suggestive of
ischemia can occur even in the absence of coronary artery disease. (In
other words, "false positive" stress tests are not uncommon.) In other
patients, no significant ECG changes are seen even in the presence of
coronary artery disease. (So "false negative" stress tests can be seen.)
False positive and false negative studies can significantly limit the
usefulness of the stress test in many patients. By adding a nuclear
perfusion study to the stress test, this limitation is minimized, and the
diagnostic capacity of the stress test is greatly improved.
What are the risks of having a stress
test?
The stress test has proven to be remarkably
safe. It poses about the same level of risk as taking a brisk walk or
walking up a hill. While it is possible that the ischemia provoked by such
stress can lead to a myocardial infarction (heart attack) or to serious
heart rhythm disturbances, in practice this event is rare. Further, when
these serious events do occur during a stress test, they occur in the
presence of trained medical personnel who can deal with them immediately.