How is myocardial ischemia risk stratified prior to nuclear myocardial scan?

Updated: Aug 07, 2019
  • Author: Thomas F Heston, MD, FAAFP, FASNC, FACNM; Chief Editor: Eugene C Lin, MD  more...
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Answer

This principle makes creating a rough risk stratification system easy and straightforward: in all patients with chest pain who undergo myocardial perfusion scanning, the pain should be categorized as nonanginal, atypical, or typical. The definitions of these categories must be rigorously followed. All too often, clinicians loosely use a description of atypical chest pain to mean a nebulous categorization of intermediate risk according to the clinician's gut feeling. This approach is unacceptable because these terms have been precisely defined and, when used correctly, carry significant meaning regarding the pretest likelihood of CAD. [19, 26, 27, 28, 29, 30, 31, 11]

Categorization of pretest CAD probability should include not only the patient's symptoms but also the clinical risk factors and the results of the stress test. Data from the Framingham Heart Study have enabled a more precise risk stratification according to age, cholesterol levels, blood pressure, presence of diabetes, and smoking history. [32] The value of exercise treadmill testing in risk stratification is optimized by using the Duke Treadmill Score. [33, 34] Several online risk calculators are available. An especially good site is maintained by the Stanford University Cardiology Department.

Using the clinical symptoms criteria developed by Diamond and Forrester for risk stratification can show that in patients with an intermediate-to-high pretest likelihood of disease, an exercise treadmill test alone is insufficient for excluding CAD. [25] As seen in the image below, of 1000 American men older than 60 years who have nonanginal chest pain, the exercise stress test causes clinicians to miss CAD in almost one third.

An exercise stress test is inadequate for excludin An exercise stress test is inadequate for excluding CAD when the pretest probability of disease is intermediate to high. Of 1000 American men older than 60 years who have nonanginal chest pain, the exercise stress test causes clinicians to miss almost one third of CAD cases.

Adding nuclear cardiac imaging to the stress electrocardiography (ECG) greatly increases the clinical value of the test; as seen in the image below, of 1000 American men older than 60 years who have nonanginal chest pain, CAD is misdiagnosed with nuclear scanning in only 25 of the 281 patients with CAD. Additionally, of these 25 patients misidentified as not having CAD, the annual rate of myocardial infarction or cardiac death is still less than 1% per year.

Adding nuclear cardiac imaging to the stress ECG t Adding nuclear cardiac imaging to the stress ECG test greatly increases the clinical value of the test. Of 1000 American men older than 60 years who have nonanginal chest pain, CAD is misdiagnosed in 25 of the 281 men who have the disease; however, of these 25 patients, the annual rate of severe cardiac events (myocardial infarction or cardiac death) is still less than 1% per year.

Because determining the pretest likelihood of disease greatly affects the final risk categorization, nuclear myocardial scanning reports are most useful when they include notes regarding the type of pain the patient is experiencing and the results from the stress test and clinical risk factors. Usually included are the patient's type of chest pain, whether ECG and/or clinical evidence of ischemia was noted on the stress test, and a list of the important risk factors. Including these notes as part of the nuclear myocardial scanning report takes little time and makes the report more useful to the clinician who ordered the test.


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