Nuclear Stress Test

A nuclear stress test is used to identify any blockages in a patient's coronary arteries.

When resting it can be difficult to identify the symptoms of cardiac disease. A stress test increases the heart's load and monitors some of the vital signs of the patient.

But what is the difference between a regular cardiac stress test and a nuclear stress test?

One of the main differences is that a perfusion tracer is intravenously injected which travels to the heart muscle.

In this article we look at:

  • what is a nuclear (or thallium) stress test
  • how this stress test is conducted
  • how accurate are the stress test results

What is a nuclear (or thallium) stress test

There are a variety of cardiac stress tests that a patient can have done. The nuclear stress consists of the regular cardiac stress test with the addition of an intravenous injection of an isotope (usually thallium and technetium).

Hence this type of test can also be called a thallium stress test.

The intravenous injection of the isotope or "perfusion tracer" allows images of the blood flow to be captured at rest and after exercise.

The thallium stress test identifies areas of the heart that have adequate blood flow or inadequate blood flow. Those areas that take up the nuclear isotope quickly have adequate blood flow compared to those areas that respond slowly if at all.

This can help to identify ischemia.

How is a nuclear stress test conducted?

There are three parts to this stress test that typically takes 2-4 hours.

  1. The regular exercise cardiac stress test involves the walking on a treadmill or riding a stationary bike.
  2. A few minutes prior to the end of the stress test and intravenous injection captures images after exercise.
  3. Depending on the isotope used, images are also captured at rest either before the stress test or 2-4 hours after the stress test.

The typical procedure for this stress test involves the following steps:

  • The patient will come into the exam room and be asked to change from the waist up into a gown.
  • The heart rate and blood pressure are measured at rest.
  • An EKG machine with electrodes are attached to the hip, shoulder and chest.
  • The patient will begin by walking on the treadmill and the technician will slowly increase the speed and the incline of the treadmill based on the protocol they are using.

    The protocol being used determines the speed and slope of the treadmill during the test.

    The goal is to get the patient to reach and maintain their target heart rate. The target heart rate is typically 85% of the patients maximal heart rate based on age of the patient.

  • Heart rate, blood pressure and EKG readings will be monitored repeatedly during the stress test.

    If the EKG shows irregular or serious abnormal rythm, or blood pressure goes outside the acceptable limits, or their is significant chest pain, or breathlessness, the administrator may stop the stress test.

    An alternative stress test for people unable to reach the target heart rate may be a chemical stress test such as the adenosine stress test.

  • One to two minutes prior to the termination of the exercise stress test a perfusion tracer is injected. The tracer is taken up by the heart.
  • During the nuclear (or thallium) stress test the administrator is interested in capturing images of the heart and associated blood flow following exercise and at rest.

    Depending on the isotope being used resting images may be captured before the exercise stress test or a few hours after the stress test.

    The images that are taken are compared to cases of a normal heart. This allows the physician to identify the extent (if any) of coronary heart disease.

    Are the stress test results an accurate measure of stress?

    First it is important to understand that a stress test does not measure stress!

    A stress test measures the heart's ability to manage load. More specifically the nuclear stress test compares coronary artery flow with data from normal hearts and compares the differences that may arise.

    With good images and if the patient is able to reach their target heart rate, the accuracy of the thallium stress test is about 85%.

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