What is a Stress Test/Nuclear Stress Test?
A “STRESS TEST” – (medical names include, Cardiac Stress Test, Cardiac Diagnostic Test, and Cardiopulmonary Exercise Test) is a diagnostic tool used by a cardiologist to determine if a patient has developed CAD (Coronary Artery Disease). It is the first-line diagnostic test for those at risk for CAD because it is a non-surgery procedure.
A stress test measures the heart’s ability to respond to external stress in a controlled environment. “Stress” is defined as “exercise“. Developed by Dr. Robert A. Bruce in 1963, the stress test (following either the Bruce Protocol or a “Modified” Bruce Protocol) consists of placing a patient on a treadmill or stationary bicycle while connected to an EKG (Electrocardiograph) and monitoring cardiac output during no work load, light work load, and high work load.
The BRUCE PROTOCOL has to do with how hard you are expected to exercise during the test. The MODIFIED BRUCE PROTOCOL is gentler in that it starts the test with a lower workload.
Additionally use of an ECHOCARDIOGRAM (ECG) machine or the use of an injected radiotracer (radioactive element) which is filmed with a special gamma camera may be included.
Stress tests are helpful in determining issues with arrhythmias and abnormalities with the heart’s structure and function, but they are limited in their ability to detect CAD.
According to the American Heart Association about 65% of men and 47% of women will present with a heart attack or sudden cardiac arrest as their first symptom of CAD. A stress test given shortly before these events cannot provide relevant predictive evaluation of an impending heart attack.
Stress tests, however, in individuals who have already suffered a heart attack; can be valuable in determining the extent and nature of any residual heart damage (nuclear stress test).
NUCLEAR STRESS TEST – MYOCARDIAL PERFUSION IMAGING
Heart attacks often cause heart damage. Cardiac tissue is deprived of oxygen and cells die. When this happens the heart is not able to regenerate these dead cells and a scar is left. The scarred areas of a heart do not function.
A nuclear stress test can show a cardiologist a number of things about a person’s post heart attack heart. It can show how many scarred, damage areas a heart has developed. I can show how large they are and how they affect the heart’s ability to function.
Because healthy cardiac tissue will absorb blood/oxygen equally, using a radioactive dye to determine how well your heart tissue is absorbing blood and oxygen is very effective in determining an accurate heart damage assessment.
NUCLEAR STRESS TESTING – THE PROCESS – WHAT TO EXPECT
It is important for your cardiologist to see your heart at rest and at peak stress from exercise. This means you will be expected to exert yourself.
The typical series of events in a nuclear stress test are:
- You’ll be injected with a very trace amount of radioactive dye – through an IV. You’ll keep this IV inserted through the length of the test.
- Once the dye is in your bloodstream you’ll sit in a machine that will shoot images of your heart from multiple angles. This is to get images of your heart at rest – to see how well it absorbs oxygen without stress.
- You’ll be connected to an EKG machine. You’ll stay connected to it through the rest of the test.
- You’ll have a baseline set of tests completed – blood pressure, heart rate, and an EKG.
- You’ll be asked to walk on a treadmill or to ride a stationary bike. Most cardiologists prefer the treadmill so they can control the amount of exertion you are expect to output.
- The exercise part of the test typically takes 12 to 17 minutes. As you are taking this portion of the test the treadmill will be slowing increased. You’ll go from walking slowly to normally to fast, then to jogging and running. Your doctor may also increase the pitch of the treadmill to simulate you running uphill. This puts even more stress on your heart.
- During the last minute of the test you’ll receive a second injection of radioactive material.
- You’ll then slow down gradually – this is so your heart can recover from the exertion of the exercise.
- Once your heart is back to normal you’ll get your vitals checked again before getting a second series of images taken with the gamma camera.
- Your cardiologist will review all of the before, during, and after data.
Above are some clips from my nuclear stress test – taken in May of 2018.
The results of your stress test will show several important things if you are a heart attack survivor.
- Visual confirmation of any damaged/scarred tissue – the images taken with the gamma camera will show any areas of your heart that are not functioning as they should. This is helpful in cases where a CARDIAC NODE may have been damaged. CARDIAC NODES are clusters of nerves which receive an electrical impulse, causing your heart muscle to contract. A damaged cardiac node can cause a number of heart arrhythmias – where the heart doesn’t beat in proper sync.
- The speed with which your heart rate increases during exercise/stress – this is important because a healthy heart will react rapidly to ensure oxygen needs are met when the body is under stress.
- Maximum Heart Rate – Your max heart rate decreases as you age but the averages for healthy adults are well established. If your heart cannot reach an acceptable output during exercise/stress it is a sign of heart damage.
- EKG Abnormalities – Your heart’s 4 chambers have to work in a precise order to be effective. An EKG is a diagnostic tool that reads the electrical output of the heart during its beat sequence.
- Lung/Heart Output – Your lungs and heart work together during exercise/stress to ensure enough oxygenated blood reaches all of your body’s organs. A stress test can detect issues with lung functioning as well as heart health.
- Heart Muscle Thickening (Hypertrophic cardiomyopathy) – When a portion of heart muscle becomes thicker than normal that area of the heart ceases to function correctly.
- LVEF – Left Ventricular Ejection Fraction – This is very important in post heart attack patients. Your left ventricle is responsible for sending oxygen rich blood to the rest of your body. It is the largest chamber of your heart and is the chamber most often affected by CAD. The LAD – Left Anterior Descending Coronary Artery – AKA – The Widowmaker – when blocked (partially or completely) during a heart attack; will result in damage to the left ventricle.
The LVEF (Left Ventricular Ejection Fraction) is a standard used to determine the effectiveness of the left ventricle. Each heart beat the left ventricle ejects blood into the aorta to be distributed through your body. Because of the size of the left ventricle it cannot expel all of the blood in its chamber in any single beat. Instead a fraction or percentage of the fresh blood in the ventricle is ejected. In a healthy person this is over 55%. If the fraction is between 50-55% it is borderline low. If it is below 50% it is low and a sign of heart damage.
WHY I AM SO LUCKY
The very reason I started Summit4CAD – I survived the Widowmaker – with my life and zero residual heart damage. My Nuclear Stress Test revealed a perfectly normal heart with no scarring, no damage, and a normal EKG, tissue profusion, and LVEF.