Nuclear Medicine Cardiac Stress Test

Authors: Dr Ghee Chew*
                            Dr Timothy Cain *

What is a Nuclear Medicine (NM) Cardiac Stress test?

A Nuclear Medicine (NM) cardiac stress test involves a scintigraphic (radioactive isotope) scan of the heart in conjunction with an exercise stress test to evaluate myocardial perfusion. The stress test usually uses treadmill exercise, but when the patient is unable to exercise then “stress” can be pharmacologically induced (intravenous dipyridamole (Persantin), adenosine or dobutamine).

Scanning is carried out at rest and also after cardiac stressing. Normal muscle takes up isotope, but non-viable cardiac muscle does not. In ischaemic cardiac muscle, uptake is reduced during stress, but is present at rest.

NM cardiac stress tests have been shown to have a higher accuracy in the detection of clinically significant coronary artery disease when compared to ECG stress tests alone. They have a proven value in predicting the risk of myocardial infarction.

What are the generally accepted indications for a NM cardiac stress test?

NM cardiac stress testing can be used for:

• Assessing fitness of patients with known coronary artery disease before major surgery.
• Assessing the viability of cardiac muscle after a previous or recent myocardial infarction. This information can help decide whether or not to proceed to coronary artery bypass surgery; that is, if the heart muscle is irreparably damaged, invasive surgery to improve the blood flow would not improve the heart function.
• Unexplained chest pain.
• Determining the extent of ischaemic coronary artery disease in patients with exercise-induced chest pain.
• Showing changes in cardiac muscle viability after revascularisation procedures (e.g. stenting or bypass grafting).

What are the prerequisites for having a NM cardiac stress test done?

There are no prerequisites for this study.

What are the absolute contraindications for a NM cardiac stress test?

Known allergy to any of the pharmacological stress agents (dipyridamole (Persantin), adenosine or dobutamine). More specific contraindications for dipyridamole and adenosine include:

• asthma and chronic airways limitation with a significant bronchospasm component;
• 2nd and 3rd degree atrioventricular block and sick sinus syndrome without an artificial pacemaker.

Caution is exercised when using dobutamine in patients with suspected tendency to ventricular tachyarrhythmias and in patients with atrial tachyarrhythmias (particularly if not on anticoagulation).

What are the relative contraindications for a NM cardiac stress test?

As the study relies on isotope radioactivity, it might not be suitable for pregnant women. The benefit versus risk from the small amount of radiation should be discussed with the NM specialist.

See InsideRadiology: Nuclear Medicine for further information about the precautions to take with NM studies for breast-feeding patients and those in close contact with children.

Claustrophobic and obese patients, whose weight exceeds the limits of the imaging bed, can be scanned with the patient sitting up and two-dimensional (planar instead of tomographic) images acquired.

Minor allergies to the pharmacological stress agents might be relative contraindications.

What are the adverse effects of a NM cardiac stress test?

The likelihood of an adverse reaction to the radiopharmaceutical is very remote, in the order of 1 in 10,000. The likelihood of a serious allergic event is even less likely. The adverse effects of the pharmacological stress agents are outlined above.

Is there any specific post-procedural care required following a NM cardiac stress test?

There is no post-procedural care required in an uncomplicated study. Women who are breast-feeding and people who are the primary or sole carer of small children might need to make special preparations after the test. Direct breast-feeding and close contact with young children should be avoided for 4 hours after the test. See advice given in InsideRadiology: Nuclear Medicine.

Are there alternative imaging tests, interventions or surgical procedures to a NM cardiac stress test?

The alternatives to NM cardiac stress tests in the assessment of myocardial perfusion are:

• Exercise stress test – lower accuracy compared to the addition of the nuclear scan and cannot be carried out in patients who are unable to exercise to an adequate level.
• Stress echocardiogram – similar to the nuclear scan, accuracy is dependent on the expertise of the sonographer or technical staff and the cardiologist interpreting the echocardiogram.
• Cardiac CT – relative contraindication in renal failure and hyperthyroidism. Scan quality reduced in patients whose heart rate cannot be adequately reduced.
• Cardiac MRI – contraindications of MRI apply. Relative contraindication in renal failure.
• Catheter coronary angiogram – invasive with higher risks. Relative contraindication in renal failure (See InsideRadiology: Iodine containing contrast medium).

References

Colquhoun D. CSANZ Position Statement: Clinical Exercise Stress Testing in Adults. 2014 Aug. Available from: http://www.csanz.edu.au/wp-content/uploads/2014/08/Clinical_Exercise_Stress_Testing_2014-August.pdf

*The author has no conflict of interest with this topic.

Page last modified on 24/8/2018.