Stress tests are generally ordered by your doctor to assess whether you might have a problem with the blood supply to your heart. Although an angiogram can look at the blood supply directly, it carries risk and it’s also invasive, so to avoid that, we can do these tests first to see whether your symptoms are related to your heart.
The term ‘stress’ just refers to putting your heart under more work, to see how it performs – sometimes the problem doesn’t reveal itself when the heart doesn’t have to work very hard – the same way that you may not get symptoms until you start walking for some distance, or carrying something heavy.
Determining your risk
So how do we decide if you need one? It’s based on determining your risk level.
If your symptoms sound very much like they are not related to your heart, and you are of low risk, you usually don’t need a stress test. This may still mean we need to control your risk factors however, by keeping your blood pressure under control and encouraging a healthy diet and plenty of exercise.
If your symptoms sound very much like they are related to your heart, and you are high risk, then you may be referred straight on to have an angiogram. This is the gold standard test to exclude blockages in the heart arteries.
But if you fall somewhere in between – intermediate risk – then a stress test can help define whether you are low or high risk, depending on whether the test is negative (no signs of ischaemia) or positive (there are signs of ischaemia).
Sometimes, people need stress tests because of their work requirements however, even if they don’t have symptoms, to make sure that their heart will not be an issue when they are doing something physically challenging.
How we stress your heart
There are a few different types of stress test – both in how your heart gets stressed, and how we can look at the heart when it is under stress.
Ways to stress the heart include:
Exercise is most commonly performed with a treadmill or using an exercise bicycle. With the treadmill, you will be walking at a slow speed initially, then every few minutes (each stage) the treadmill will get faster and the incline will go up. This is performed according to a specific protocol (usually, the Bruce protocol).
Medications can test out the heart’s blood supply in a few ways. It can make your heart beat faster and harder (using a drug called dobutamine), or it can change how the blood is distributed around your heart (dipyridamole and adenosine). This means you don’t have to do exercise – although sometimes both exercise and the medication can be used together. The disadvantage is that the test is not as accurate when using the medication, and so if you can exercise, that is by far the preferred method.
And we can look at your heart in a few different ways too:
An echocardiogram involves an ultrasound probe being placedon your chest to look at your heart. A set of images is taken before you exercise, and then immediately following exercise you are escorted back to the bed while your heart is pumping fast, to be able to take another set for comparison. If the test is done with dobutamine (a dobutamine stress echocardiogram), then you will remain on the bed the entire time while the medication is give to you via a cannula (intravenous drip) in your arm.
- Nuclear medicine
A nuclear stress test involves the injection of a specially labelled compound (radiotracer), that can be seen by a gamma camera, to allow us to visualise the blood flow into the heart muscle. Images are taken before and after exercise, or before and after a medication is given (like dipyridamole or adenosine). If there is an area that isn’t receiving blood, a gap will appear.
A CT coronary angiogram is not a stress test in the traditional sense – you don’t have to exercise or have a medication to make the heart work harder, however it is often ordered in the same circumstances, to determine if there are narrowings in the heart arteries, and to decide whether you are low risk, or whether you need a coronary angiogram.
A stress test is not a definite result – although it can help either decide whether you are low or high risk, the gold standard investigation is a coronary angiogram, however that is an invasive test that does carry some risk.