As people age, plaque can accumulate in the blood vessels of the heart, narrowing the space through which blood must flow. This process is called atherosclerosis, or hardening of the arteries, because the buildup thickens and stiffens artery walls. When enough plaque accumulates inside a person's coronary arteries to reduce or block blood flow to the heart, that person is said to have coronary heart disease, or CHD.
To detect stress-induced blood flow defects caused by CHD, doctors use echocardiographic stress testing, also called exercise echocardiography, echo, stress testing. During echo stress testing, high-frequency sound waves, called ultrasound waves are used to produce a real-time moving image of the heart, called an echocardiogram. Although primarily used to confirm a diagnosis of CHD, an echo stress test can also identify one of more of the following:
- Ischemia (lack of oxygenated blood reaching the heart);
- Diseased heart valves;
- Septal defects;
- The pumping efficiency of the heart;
- The damage caused by a heart attack; or
- The results of angioplasty or coronary artery bypass surgery.
PRE-TEST GUIDELINES
The physician often provides written instructions before the test, which the patient should follow closely. Typically it is recommended that people wear clothing that is comfortable to exercise in and avoid strenuous exercise and eating or drinking for approximately 4 hours before the test. The testing center may also request that the person refrain from using tobacco, certain prescription and nonprescription drugs, and alcohol or caffeine for 24 hours before the test. It is also recommended that people refrain from applying lotions, oils, or powder because these substances can interfere with a conductive gel used as well as electrocardiographic electrodes.
RISK FACTORS
Echocardiography is painless, has no risk, and does not use radiation.
WHAT TO EXPECT
Approximately 10 electrocardiographic (ECG) electrodes will be placed on the person's chest and back, which the physician will use to monitor the patient's heart function throughout the test. Next, a resting echocardiogram is recorded for later comparison with the stress test. The stress test begins with the patient walking slowly on a treadmill (a stationary bicycle may also be used). The speed and incline of the treadmill increase every 3 minutes, and exercise typically lasts from 5 to 15 minutes. The physician monitors the exercise level, and makes recordings until the person's heart reaches a maximum predicted heart rate, which is determined by an age-based formula.
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| A typical treadmill exercise test setup. |
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Because the effects of exercise-induced ischemia will show up in the echocardiogram for only a few minutes, exercise stops as soon as the person's maximum predicted heart rate is nearly reached and the echocardiography begins immediately. To ensure image quality, a conductive gel is applied to the patient's chest, and the patient is instructed to lie quietly and exhale fully. In addition, the physician may order the use of an echocardiogram contrast solution that will further improve image clarity. Once the test is complete, the physician analyzes the images.
Medication-induced stress echocardiography is available for people who cannot exercise. Medications that stress the heart temporarily for testing include:
- Dipyridamole (unless the patient has asthma);
- Adenosine; and
- Dobutamine.
Dipyridamole and adenosine may cause brief side effects, including:
- Headache;
- Dizziness;
- Nausea; and
- Flushing.
