There are two main arteries that bring blood to the heart muscle. Each of them is about the size of the tip of a pen or about 3 mm. This is how blood flow gets to the heart muscle so it can pump blood.
Diseases of these arteries are known as coronary artery disease. What happens is that over time they begin to narrow, frequently started by cholesterol buildup or damage from high blood pressure, diabetes or cigarette use. They will subsequently develop scar formation and calcify. They narrow down and limit how much blood flow reaches the heart muscle.
When the blood flow does not get to the heart muscle as efficiently as needed, people typically get symptoms of coronary artery disease. Some get chest pain. Some get shortness of breath. Some people develop heart rhythm irregularities or arrythmias. And some people may actually have a heart attack if there’s an artery blocked off entirely.
By performing stress tests and having a patient either walk on a treadmill or get an IV injection of a medication which can mimic walking exercise by dilating these arteries, we can test the body’s ability to provide an efficient amount of blood flow to the heart muscle. The way we can tell whether it is inadequate is through nuclear imaging.
Just prior to peak exercise, we give an IV injection through an IV that has already been placed. It contains a chemical called technetium which is a naturally occurring substance. It is the same agent used for gallbladder scans and bone scans. No one is allergic to it. It is not a dye and it’s not harmful to the kidneys. The technetium distributes proportional blood flow to the heart muscle so we can determine whether the flow is normal and that there is no significant blockage in the arteries.
If there is a blockage, the flow of technetium to that portion of the heart muscle downstream of the blockage is decreased. We know this because after the patient gets off the treadmill, we take a picture of the heart with a camera. This camera is essentially a chair the patient sits on with a two-headed camera that rotates around the patient and takes pictures of the heart. We can visualize where the flow is going and where it is not. This is how we can determine whether or not there is a diminished amount of blood flow to the heart muscle. It is a very sensitive way to identify an abnormality, and it is quite reproducible and accurate.
This is how a nuclear stress test is performed. A picture is taken prior to exercise, which is called a resting image. Subsequently, we take another picture after exercise to determine the blood flow under stress. By comparing these two, Dr. Peterson can accurately determine whether or not there is any abnormality inside the heart muscle, which may be responsible for symptoms that the patient may be having. In addition, it can sometimes point out areas of abnormality which are currently not causing any symptoms.
The test in our office takes about 2.5 to 3 hours. After the test, we process the images and let the patient go home. The patient can also drive, go back to work, etc. Dr. Peterson will typically call them that afternoon or the next morning and go over the results with them, using this information to devise a treatment plan.
As mentioned, the test can be done without walking on a treadmill. Some people are unable to walk on the treadmill because of orthopedic problems, lung disease or other issues. In this instance we give a medicinal IV called adenosine, which mimics the stress of exercise. In this way, even those unable to walk on a treadmill can have stress tests and avail themselves of all the information we get from them.