1. Who Should Have a Stress Test?
Stress testing is a common office and hospital cardiology procedure. These tests are ordered by all types of physicians and cardiologists. The most common reason to have a stress test is to determine if chest pain is a sign of poor circulation to the heart muscle. A typical patient may have pain with exertion or discomfort that doesn't seem like the typical "elephant sitting on my chest" description that some patients give. A stress test is ideal for patients that have a complaint of chest pain and risk factors like diabetes, hypertension, peripheral arterial disease, smoking, elevated lipids and family history of premature coronary artery disease. Of course, if the story is so impressive that it is clear to the physician that the patient has a very high likelihood of having a grossly abnormal test it is less useful and more invasive testing might be indicated. The test is really best for a patient with a moderate chance of disease where the results will change the doctor's management with medications or a procedure like an angiogram. Cases where the test can be very helpful is prior to surgery in high risk patients to determine if they have a greater chance of having a peri-procedural heart attack or in patients presenting to the hospital with symptoms that might repesent a heart attack with no objective laboratory abnormalities to indicate heart muscle injury. A stress test is also used in patients with known arterial blockages to determine how well medications and implanted stents are performing.
2. What Types of Stess Tests Are There?
The easiest and most widely used type of stress test is a simple treadmill exercise test. In this test the patient walks at varying speeds and inclines on the treadmill. The speed and incline change every 3 minutes. The heart's electrical activity (Electrocardiogram or ECG) is monitored during the exercise and recorded at every 3 minute stage. Changes in the baseline of the ECG help determine if there might be a obstruction to blood flow in the heart's circulation. In some cases the ECG is not sensitive enough to determine if a blockage is present. In these cases an image of the heart is also obtained. This can be done with and ultrasound of the heart (echocardiogram or echo) or by nuclear perfusion imaging. A stress echo is similar to a treadmill stress test in that the patient will exercise as long as possible on the treadmill (sometimes a bike is used). After exercise, the patient has pictures taken to look at the contractile pattern of the heart. These pictures are then compared to images taken at rest. Heart muscle under low blood flow doesn't contract correctly and this can be seen by echo. In a similar fashion a nuclear stress test (known as Thallium or Mibi stress testing) obtains pictures of the heart with a special camera after injection of a weakly radioactive substance that binds to normal heart muscle. With exercise the same substance or a slightly different one is injected. Before and after images are compared. If the blood flow is decreased there will be less tracer uptake with stress. Both of these tests are more than 90 percent accurate to determine if a significant blockage is present.
3. What to Expect During a Stress Test
The day of the test, you should not eat within 6 to 8 hours of the study. Many doctors will ask you to not take certain medications that can slow the heart rate within 12 hours of the test (beta blockers, digitalis, or calcium channel blockers). The goal of an exercise test is to raise the heart rate to at least 85 percent of the predictied maximum. Wear good shoes and comfortable clothes that you can move easily in. The technician will obtain consent for the study. There is minimal risk to the study and it is very rare (less than 1 percent chance) that testing can result in a heart attack. A resting ECG will be obtained lying down and standing up. If a left bundle branch block is present, a nuclear stress test with adenosine will have to be performed. The patient then slowly starts walking on the treadmill. Blood pressure and ECG tracings are recorded every 2 to 3 minutes. If an irregular heartbeat develops, the technician will record the ECG tracings. If you have any symptoms of chest discomfort or breathing difficulty let the technician know. In general, the longer you stay on the treadmill the better the prognosis. In most cases if you can exercise more than 6 1/2 minutes without chest pain or significant ECG changes, you have a very low chance of significant narrowing in your arteries.
4. What if I Can't Exercise?
Not every patient can walk on a treadmill. Examples include patients with arthritis or orthopedic injuries or patients with chronic lung disease. Other medical conditions can affect your ability to reach an adequate heart rate to lower the diagnostic yield of the study. Many patients that have significant cardiovascular risk factors such as diabetes, peripheral arterial disease or older age can't keep up with a standard treadmill test. In these cases a pharmacological stress test coupled with imaging is the study of choice. The heart stimulant dobutamine can be used to increase the heart rate during and intravenous infusion. This can be used to achieve an adequae heart rate with nuclear imaging or echo stress testing. Adenosine is the most common agent used with nuclear stress testing. Adenosine is slowly infused over 4 minutes after resting images are obtained. After infusion the second tracer is given as described above. Adenosine dilates the arteries in the heart. This effect is more pronounced in normal arteries. An artery with a blockage dilates less, therefore less tracer flows to the muscle. If you have asthma or use inhalers be sure and let your doctor know. Both adenosine and dobutamine can induce an asthma attack and your doctor will take special precautions during the test.
5. What if My Stress Test is Abnormal?
If the stress test is abnormal, you can expect to start several important medications. They include aspirin, cholesterol lowering medications (statins most commonly), beta-blockers, angiotesnin converting enzyeme inhibitors, and nitrates. Many patients with a mildly abnormal stress test do very well with medications and close clinical follow-up. I often start these medications on lower risk patients and repeat the test in 1 or 2 months. If it normalizes, this constitutes adequate medical therapy. If the patient is already on these medications and the test is positive, or the test is severely abnormal with high risk findings (low heart function, many muscle segments involved, unstable heart rhythms, low exercise tolerance and severe symptoms) a coronary angiogram is needed.
