A cardiac stress test, also known as an exercise stress test, is a diagnostic test that assesses the heart’s ability to respond to external stress in a controlled environment. The test is performed by having the patient exercise on a treadmill or stationary bike while hooked up to an electrocardiogram (ECG) machine. The test is used to evaluate symptoms such as chest pain, shortness of breath, or palpitations and to assess for the presence and severity of coronary artery disease (CAD).
Indications for a cardiac stress test include:
- Symptoms of chest pain, shortness of breath, or palpitations
- Suspected or known CAD
- Risk factors for CAD such as high blood pressure, high cholesterol, diabetes, or smoking
- Evaluation of the effectiveness of treatment for CAD
- Assessment of the ability to exercise safely before undergoing surgery or other procedures
Patients should avoid caffeine, nicotine, and heavy meals for several hours before the test, and should wear comfortable clothing and shoes. During the test, the patient will be connected to an ECG machine and asked to exercise on a treadmill or stationary bike while the heart’s electrical activity and blood pressure are monitored. The test will be stopped if the patient experiences symptoms such as chest pain, shortness of breath, or arrhythmias.
There are several different protocols used for cardiac stress tests, including:
- Bruce protocol: This is the most commonly used protocol, which starts with a low level of exercise and gradually increases the intensity over a period of several minutes.
- Modified Bruce protocol: This is similar to the Bruce protocol, but with a slightly lower starting level of exercise and a longer recovery period.
- Duke treadmill protocol: This protocol uses a series of stages with increasing levels of exercise intensity, and is used to evaluate patients with suspected or known CAD.
The outcome of a cardiac stress test will depend on the patient’s symptoms, risk factors, and the results of the test. If the test is normal, it suggests that the patient’s symptoms are not caused by CAD. If the test is abnormal, it may suggest the presence of CAD, and further tests such as a coronary angiography may be needed.
Here is a table that summarizes the different stages of the Bruce and Duke protocols:
| Protocol | Stage | Speed (mph) | Incline | Duration (min) |
|---|---|---|---|---|
| Bruce | 1 | 1.7 | 10% | 3 |
| Bruce | 2 | 2.5 | 12% | 3 |
| Bruce | 3 | 3.4 | 14% | 3 |
| Bruce | 4 | 4.2 | 16% | 3 |
| Bruce | 5 | 5.0 | 18% | 3 |
The limitations of a cardiac stress test include:
- False negative results in patients with CAD who have fixed or near-fixed stenosis (narrowing) in their coronary arteries. This means that the test may not detect CAD in these patients even if they do have it.
- False positive results in patients without CAD. This means that the test may suggest the presence of CAD in these patients even if they do not have it.
- The test may not be appropriate for patients who are unable to exercise, such as those with severe lung or heart disease.
- The test may not be reliable in patients with certain types of arrhythmias or other ECG abnormalities.
The accuracy of a cardiac stress test depends on the patient’s symptoms, risk factors, and the results of the test. The sensitivity and specificity of the test for different degrees of CAD can vary depending on the specific population and the test protocol used. However, in general, the sensitivity and specificity of a cardiac stress test for CAD are moderate to good.
Sensitivity refers to the proportion of true positive results (patients with CAD who test positive for CAD) out of all patients with CAD. Specificity refers to the proportion of true negative results (patients without CAD who test negative for CAD) out of all patients without CAD.
In general, the sensitivity of a cardiac stress test for CAD is around 80-90%, while the specificity is around 70-80%. This means that the test is good at detecting CAD in patients who have it, but not as good at ruling it out in patients who do not have it.
Alternatives for a cardiac stress test include, nuclear stress test, CT angiogram and MRI. These tests have higher sensitivity and specificity for detecting CAD than stress test. Although, cardiac stress test is not used as a screening tool for people without symptoms to detect underlying heart or coronary disease, but these alternatives are not used either.
The sensitivity of a cardiac stress test can vary depending on the stage of CAD. In general, the sensitivity of the test is higher for more severe CAD, and lower for mild or early stage CAD.
In patients with severe CAD, who have significant stenosis (narrowing) in one or more coronary arteries, the sensitivity of a cardiac stress test is high, with a positive test indicating a high likelihood of CAD. However, in patients with mild or early stage CAD, who have less significant stenosis, the sensitivity of the test is lower, and a negative test does not rule out the presence of CAD.
It’s worth noting that there is no consensus on what constitutes mild, moderate or severe CAD, but in general mild CAD is considered as less than 50% stenosis, moderate CAD is considered as 50-70% stenosis, and severe CAD is considered as more than 70% stenosis.
Additionally, the sensitivity of a cardiac stress test can also depend on the protocol used, as well as the population being tested. For example, studies have shown that the sensitivity of the test is higher in older patients and in those with a higher risk of CAD.
Therefore, when interpreting the results of a cardiac stress test, it is important to consider the patient’s symptoms, risk factors, and the results of other tests such as imaging studies, in addition to the results of the stress test itself. This allows for a more accurate assessment of the presence and severity of CAD.
Exercise stress echocardiography
Exercise stress echocardiography (ESE) is a variation of the traditional exercise stress test (EST) that involves performing an echocardiogram (ultrasound of the heart) during exercise. ESE is often used as an alternative to EST for the evaluation of CAD.
Studies have compared the sensitivity and specificity of EST and ESE in detecting different stages of CAD. The results of these studies have shown that ESE is generally more sensitive and specific than EST for detecting CAD, particularly in patients with intermediate or indeterminate results on EST.
Here is a summary of a few studies comparing the sensitivity and specificity of EST and ESE:
| Study | Sensitivity EST (%) | Specificity EST (%) | Sensitivity ESE (%) | Specificity ESE (%) |
|---|---|---|---|---|
| Fleg et al. (1995) | 69 | 96 | 96 | 96 |
| Hachamovitch et al. (1999) | 77 | 92 | 94 | 96 |
| DeMaria et al. (2001) | 72 | 87 | 91 | 96 |
The table shows that ESE tends to have higher sensitivity and specificity than EST in detecting CAD. However, it’s worth mentioning that these studies have some limitations and that the results may vary depending on the specific population and the protocols used.
In general, ESE is considered a more sensitive and specific test for the detection of CAD than EST. It may be particularly useful in patients with intermediate or indeterminate results on EST, as it can provide additional information on the function and structure of the heart during exercise. However, the availability and cost of ESE may be limited in some areas and therefore EST is still widely used.
