Why is this test being ordered?
Nuclear Stress testing is used for the following reasons:
• Evaluate if chest pain or an abnormal EKG is being caused by unknown coronary artery disease (CAD), and if CAD is present, which vessels are being affected and to what extent is the disease.
See the video
• Determine if previous surgical intervention (Stents, bypass) requires any further attention
• Evaluate if previously known blockages require angioplasty
• Cardiac pre-operative clearance
• Follow progress of known CAD on a regular basis (usually every year or two depending on severity)
• Additional information: Click here
What to expect.
Nuclear stress testing is used to evaluate the blood flow to the heart muscle as well as additional structural information about the heart. The test has three steps: 1) rest images, 2) stress test and 3) stress images. The test will take anywhere from 2 to 4 hours. You will be offered a snack halfway through, so we won't starve you the entire time!!
1 - Rest Images
A small amount of liquid radiation is injected into an IV. This injection has to circulate for at least 15 – 45 minutes, depending on the exact type of radiation being used. Then the patient will sit on a rotating chair attached to a nuclear camera for a baseline set of images. These images will take 15 – 20 minutes. (The videos below will show a camera where you lay on a table, ALARA Imaging provides a chair which eliminates the need to raise your arms above your head and lay flat on a hard table.)
2 - Stress Test
The next step is to stress the patient. Stressing can be done through exercise on a treadmill or by a chemical that will simulate exercise. Leads are placed on the patients chest in order to monitor heart rhythms throughout the entire test.
EXERCISE STRESS: Our plan is to exercise the patient on a treadmill long enough to get their heart rate up to at least 85% of the maximum predicted heart rate – calculated: (220-age) * (0.85). Every three minutes the treadmill gets higher and faster. Once that heart rate is achieved another radioactive injection is given through the IV. It will bind with the heart upon injection, thus allowing us to take stress images later.
CHEMICAL STRESS: If the patient is unable to exercise due to certain EKG rhythms, joint issues, severe shortness of breath, or just an inability to stay on long enough, a chemical is used to stress the heart. It will be either Lexiscan or Dobutamine.
Lexiscan is used on patients unable to exercise on the treadmill. There are several reasons a patient couldn't walk the treadmill: certain EKG rhythms like left bundle branch block, injuries, severe arthritis, being severely out of shape, etc. In these cases, Lexiscan will be injected. It's a vasodilator – which means it will dilate/open the vessels in the heart. This is what the heart does on it's own during exercise. It's common to feel “weird” during this portion of the test. If patients complain of any symptoms it's usually the following: headache, pressure on chest, stomach slightly upset, jaw and neck tightening. The body uses up the Lexiscan pretty quickly so the symptoms should go away before you are disconnected from the EKG machine.
Dobutamine is used on patients with active lung disease like asthmas or steroid controlled COPD. Dobutamine will increase the heart rate as if you were exercising, so just like with the treadmill exercise we will continue the Dobutamine infusion until the heart rate has reached 85% of the maximum predicted heart rate. At this point the second radioactive injection is given again allowing us to take stress images later.
3 - Stress Images
Once the stress is complete, a recovery time is allowed so the patient's heart rate and blood pressures can return to their start points. At that point the EKG leads are removed and the patient is asked to get dressed and have a snack. Just like with the rest images the stress injection has to circulate for awhile before images are taken. This allows the gut to clear for beautiful images. So the patient waits in the waiting room until it's time for imaging. The second set of images will take 10 – 15 minutes.
Once completed the patient is free to go if nothing eminent is seen in the images and EKG portion of the test. The technologist will then download the data to the waiting cardiologist for interpretation. Once read, the ordering physician will have access to the report via the internet within 24 hours.
See a sample study.
