Cardiac stress test
A cardiac stress test is performed to evaluate the ability of arterial blood flow to the left ventricular heart muscle, to increase with exercise, as compared to resting blood flow rates, and some indication of overall physical fitness. The test is not capable of detecting the presence/absence of the atheroma lesions of atherosclerosis, thus usually misses disease which
most commonly produces future angina or heart attack events. Also, it is not designed to evaluate the presence or influences of emotional stresses, even though these probably play a role in heart attacks.
The patient either walks on a treadmill or is given IV medications to "simulate exercise" while connected to an EKG machine, usually the standard 10 connections used to record a 12 lead EKG, and blood pressure response is repeatedly checked. Using EKG and blood pressure monitoring alone, the test is variously called a cardiac stress test, exercise stress test, exercise treadmill test or exercise EKG test. If radioactive isotopes are also used, then it is usually called a nuclear Thalium or Cardiolite (Technetium Tc99m Sestamibi) stress test or a Rubidium (Rubidium, RB-82) PET stress test.
The stress test is used to check both overall physical exercise capacity and is generally able to detect high grade, 75% or greater stenosis of the coronary arteries supplying the cardiac muscle. Stress tests are based on research, first done in the 1960s, which demonstrated that coronary artery blood flow rate must increase several fold and in proportion to heart muscle wall tension, reflected by systolic blood pressure and heart rate. Heart rate is the most important variable for stress testing because heart muscle contraction blocks heart muscle capillary blood flow during each heart beat and the time for blood flow between heart contractions progressively shortens as heart rate increases; e.g. about 40 seconds per minute, at heart rates of about 60 BPM, down to less than 10 seconds per minute, at heart rates in the 180 BPM range.
Generally, if one or more of the major epicardial heart arteries has a stenosis of 75% are greater, then abnormalities in the EKG waveforms, nuclear scan or echocardiographic images can usually be detected while the individual is at an elevated heart rate and exercise workload. Such high grade narrowing are typically responsible for angina episodes which reproducibly occur at a given level of exercise. However, most heart attacks result from rupture of atheroma lesions associated with only mild narrowing, 20-30% on average by IVUS clinical studies, thus the tests do not work well for detecting likelihood of impending heart attack.
Sometimes radioactive isotopes are injected intravenously at approximately one minute prior to the end of exercise. This protocol would be called a nuclear cardiac stress test. Either a gamma camera or PET imaging machine is used to create several 2 dimensional pictures, from different angles, of the radioactive particle decay emissions emanating from the radioactive isotopes which have been absorbed by the heart muscle cells from the blood after the intravenous injection. These images are compared with resting radioactive isotope emission distribution images for differences. Variations of nuclear cardiac stress tests include a thallium, technetium or rubidium (only used for PET machines) stress test, depending on the radioactive atomic element used. Sometimes heart muscle size, contraction and wall motion is physically evaluated before and immediately after the exercise phase using an echocardiography machine. This protocol would be called a echocardiographic cardiac stress test. Sometimes, if an individual is unable to perform enough physical exercise walking up an incline, then exercise is simulated using medications to stimulate faster heart rate, more intense contraction and/or peripheral arteriole vasodilatation.
Cardiac stress tests can be done in a clinic, a caregiver's office, or in a hospital. You may be asked to exercise using a bicycle or treadmill. A treadmill is a machine on which you can walk or jog.
Your heart is watched using a heart monitor. The heart monitor is part of an exercise stress test machine. This machine makes paper tracings of your heart while you exercise. An EKG (e-lek-tro-kar-d-o-gram) will be done several times during the stress test.If you cannot walk or exercise, you may be given medicine that causes your heart to work harder. You will get this medicine through an IV. An IV is a tube placed in your vein for giving medicine or liquids. You will be hooked to the heart monitor and the stress test machine. You may be asked to move your arms up and down. Your caregiver will see how your heart works on the medicine.
This test does not hurt, but it may make you tired. During the test, you will be asked to take off your shirt or blouse. You can wear a gown instead. Patches, called electrodes, will be stuck to your chest. These patches are then hooked to an exercise stress test machine, which has a heart monitor. Your heart rate will be counted for a minute. Your blood pressure will also be taken. Caregivers call these vital signs. They will be done many times during the test. Your caregiver will be watching you during this test. Tell your caregiver if you start getting tired, have trouble breathing, or start having chest pain.
Treadmill Stress Test: A treadmill stress test also is known as an exercise electrocardiogram. Before the test is started, electrodes are applied to 10 different locations on the arms and chest. An EKG and blood pressure are taken at rest to be compared with those taken during and after exercise. The treadmill is started, first at a slow speed, then faster and more elevated until enough information has been obtained. The EKG and blood pressure are monitored continuously and a physician is present throughout the exam. The procedure usually takes 60 minutes.
Oxygen Consumption Treadmill Stress Test: An oxygen consumption treadmill test is a stress test used to check how well the heart, lungs, blood vessels and muscles work together following diseases of the heart muscle (cardiomyopathy) and heart attack. The electrical activity of the heart and exhaled breath before, during, and after exercise is analyzed. Before the test is started, electrodes are applied to 10 different locations on the chest and arms. A disposable mouthpiece is used to analyze exhaled air and a small probe is attached to the forehead to monitor the level of oxygen in the blood. Baseline EKG, blood pressure and breath analysis are taken at rest; these are compared with those taken continuously during and after exercise. The treadmill is started, first at a slow speed, then faster and more elevated until enough information has been obtained. A physician is present throughout the exam. The procedure usually takes 90 minutes.