Getty
Cardiac stress tests look at how your heart reacts to the stress of an increased workload. There are several types of cardiac stress tests. But basically, the stress can come from two different stimuli—exercise or medicines. Exercise stress tests are the most common type. Doctors use chemical stress tests with medicines when people aren’t able to exercise.
The standard test is an ECG—or electrocardiogram—stress test. An ECG stress test monitors your heart’s electrical activity during exercise. Medical staff will also monitor your blood pressure and breathing. The exercise stress comes from walking on a treadmill or pedaling a stationary bike. In a chemical test, the stress comes from a medicine that stimulates the heart. Chemical stress tests use heart imaging along with an ECG. The imaging is necessary because stress changes from drugs may not be detectable by ECG alone.
A cardiologist interprets heart stress tests results. Your doctor will review them with you. Here’s a summary of the information doctors use in their interpretation and what their conclusions could mean.
Items in the Interpretation
There are several things doctors look at and use in their interpretation of heart stress test results. These items include:
- Baseline ECG: This is a recording of your heart’s electrical activity at rest. Doctor’s look for any abnormalities that show up without any stress. This may include changes in rhythm or rate with shifts in position, such as sitting, standing or lying.
- ECG changes: There are specific changes in the heart’s activity that can tell doctors about your heart health. When they are present during stress, it may mean your heart muscle isn’t getting enough oxygenated blood.
- Presence of arrhythmias: Changes in heart rhythm may or may not mean anything. If they are present during stress, doctors will look at the type of change and how often it happened. They will also want to know whether the changes disappeared with rest.
- Blood pressure response: Increases or decreases in blood pressure during stress can give doctors clues about your heart health. If systolic blood pressure drops by more than 10 mmHg, it can be a sign that the heart muscle isn’t getting enough blood supply.
- Symptoms during the test: Doctors will consider any symptoms you report during the test. This could include chest pain, fatigue, or shortness of breath.
- Exercise capacity: In exercise tests, it’s important for doctors to know how long the exercise lasted. They will also want to know how well you tolerated it. This may be reported as METS (metabolic equivalents). METs are an estimate of the amount of energy you are expending during exercise. They can tell doctors how intensely you are able to exercise.
- Imaging data: If imaging was part of the stress test, doctors will include this data. The main focus is perfusion—or the presence of adequate blood flow. They will look for areas with poor blood flow and note their size and location. Decreased or absent blood flow can indicate blockages or heart muscle damage or death.
- Reason for ending the test: There can be many reasons for stopping the test. Doctors will want to know if you asked to stop or experienced symptoms severe enough to stop it. Other reasons may include reaching the target heart rate or having ECG changes.
Possible Conclusions
After summarizing the items in the report, doctors will offer a conclusion based on their interpretation. There are several possible conclusions including:
- Positive or abnormal: Doctors may conclude the stress test is positive for cardiac ischemia—meaning the heart muscle wasn’t getting adequate oxygenated blood during the stress. There are certain ECG and imaging changes that would support this conclusion. There are also clinical findings that could support it. This includes chest pain, blood pressure drops, and the occurrence of a heart murmur during stress. Depending on which of these and how many of them were present, doctors may qualify the positive result as probably or strongly positive.
- Negative or normal: A negative test result lacks any of the things that could trigger a positive conclusion. There may still be ECG changes or symptoms, but they are what doctors would consider normal responses to stress.
- Equivocal: These results are inconclusive. This means there may have been changes with the test, but they aren’t diagnostic of cardiac ischemia. Additional testing will be necessary to find any problems with blood supply to the heart muscle.
- Uninterpretable: There are several reasons doctors may not be able to interpret a stress test. Sometimes, equipment malfunctions. Other times, people are unable to complete the test. Doctors may recommend alternative tests in this case.
- Goal achieved: Doctors will either conclude that the test was maximal or submaximal in this regard. A maximal test in one where you were able to meet the goals of the test. This may include a target heart rate, exercise level, or time. The target heart rate is usually 85% of your maximum heart rate. A submaximal test is one where these goals were not met. Alternative testing may be necessary when tests are submaximal because you aren’t able to tolerate the exercise.
What It All Means
Stress tests are an interpretive tool and no tool is perfect. ECG cardiac stress tests are not 100% accurate for diagnosing coronary artery disease (CAD) and other heart problems. About 15% of time, they can give false positive results, indicating heart disease which is not really there. So, positive results generally mean more testing is necessary to confirm if there is a real problem, or not, and guide treatment. This may involve either a stress echocardiogram or a nuclear stress test because these tests are more accurate. Sometimes, more invasive testing is necessary.
A negative ECG stress test doesn’t guarantee you won’t have a heart attack or other problem. ECG stress tests find severe blockages of 70% or more. Heart attacks can occur with smaller blockages that break off and form clots. These smaller blockages often don’t cause symptoms, like the larger ones do, until a heart attack happens. So even negative results may warrant more testing if other factors indicate you are at high risk of heart disease. Imaging stress tests can find smaller blockages.
The bottom line is stress tests give your doctor important information about the likelihood of a heart problem. And they can help your doctor recommend next steps for you. Ultimately, your doctor is the best source for information about interpreting your stress test results.
