Stress and Test October 16, 2007Posted by tomography in Nuclear Medicine, Picture of the week, SPECT.
The stress test shows if your heart receives enough blood from its own arteries to work harder, safely. Taking the stress test also helps your doctor know what type of exercise and how much is right for you.
The resting heart muscle’s blood supply needs are usually well met even in the presence of blocked arteries. When the heart is stressed either by exercise or chemicals, the demand for blood increases. The blood flow through the blocked arteries – while adequate at rest – may not be able to keep up with the demands of a stressed heart. This can show up on the pictures of the heart taken after stress. This is the principle behind all the stress tests. The word stress test is used for any means used to increase heart muscle’s demand for blood. This can be done by exercise or by chemical means.
The patient either walks on a treadmill, or is given iv. (intravenous) medication which simulates exercise, while connected to an ECG machine, used to record a 12-lead ECG. The level of exercise is increased by 3 minute stages, of progressively increased grade (incline) and speed. The patient’s symptoms, and blood pressure (BP) response are repeatedly checked.
However, some patients cannot exercise adequately. Patients with lung disease, arthritis, or disease in the leg vessels may not be able to walk. Patients with some medical conditions should not walk on the treadmill. For these patients the doctor can use a drug to affect the blood supply to the heart and simulate the effects of exercise.
It is done to identify the cause of chest pain or chest discomfort which can occur with blockages in blood flow to the heart, to monitor heart function in people with known heart disease, and to determine the response to medications or after angioplasty or bypass surgery.
If radioactive isotopes are also used (commonly, Technetium Tc99m Sestamabi and rarely, Thallium-201), then it is usually called a Nuclear Stress Test (NST).
It is similar to excersize stress test except for the fact that a medicine called Dobutamine is used to stress the heart. During this test, Dobutamine is infused at a gradually increasing rate to increase the heart rate to a desired level. This drug has the effect of increasing the force of contraction of the heart, the heart rate and blood pressure. This stresses the heart muscle, which simulates exercise.
“Cardiolite is a short-lived, radioactive element that is absorbed by the heart muscle and allows your heart to be seen by the camera. Cardiolite images allow the physician to indirectly look at the blood flow to your heart.”
Areas that do not have adequate blood supply pick up the tracer very slowly or not at all.
Take a look at one of the “picture of the week”s.
Cardiolite is injected while you are at rest and while your heart is under stress. Rest and stress images are taken to allow doctors to compare how much blood flows through the heart muscle during stress and at rest.
(Most patients experience no side effects.)
“Persantine is a coronary vasodilator that is used as a diagnostic agent in nuclear stress testing. Persantine works by increasing the blood vessel circumference of the coronary arteries (arteries that feed the heart) in order to increase blood flow to the heart.”
Adenosine is an antiarrhytmic agent, works as a vasodilatator, similar to Persantine. Side effects include: chest pain/pressure, headache, nausea, dizziness, shortness of breath. Some patients experience a burning or stinging sensation at their IV site because Persantine is more acidic than your blood. Persantine is contraindicated in patients who have a hypersensitivity to this drug. If needed, the antidote Aminophylline is given to the patient.