Clinical research: cardiac imaging
Utility of myocardial perfusion imaging in patients with low-risk treadmill scores

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Abstract

Objectives

The purpose of this study was to determine whether a previously validated clinical score (CS) could identify patients with a low-risk Duke treadmill score who had a higher risk of adverse events and, therefore, in whom myocardial perfusion imaging would be valuable for risk stratification.

Background

Current American College of Cardiology/American Heart Association guidelines recommend using a standard exercise test without imaging as the initial test in patients who have an interpretable electrocardiogram and are able to exercise.

Methods

We studied 1,461 symptomatic patients with low-risk Duke treadmill scores (≥5) who underwent myocardial perfusion imaging. The CS was derived by assigning one point to each of the following variables: typical angina, history of myocardial infarction, diabetes, insulin use, male gender, and each decade of age over 40 years. A CS cutoff ≥5 or <5 was used to categorize patients as high risk (n = 303 [21%]) or low risk (n = 1,158 [79%]). Perfusion scans were categorized as low, intermediate, or high risk on the basis of the global stress score (GSS).

Results

High-risk scans were more common in patients with a high-risk CS (26.4% vs. 9.5%, p < 0.0001). The CS and GSS were significant independent predictors of cardiac death. However, in patients with a low CS, seven-year cardiac survival was excellent, regardless of the GSS (99% for normal scans, 99% for mildly abnormal scans, and 99% for severely abnormal scans). In contrast, patients with a high CS had a lower seven-year survival rate (92%), which varied with GSS (94% for normal scans, 94% for mildly abnormal scans, and 84% for severely abnormal scans; p < 0.001).

Conclusions

In symptomatic patients with low-risk Duke treadmill scores and low clinical risk, myocardial perfusion imaging is of limited prognostic value. In patients with low-risk Duke treadmill scores and high clinical risk, annual cardiac mortality (>1%) is not low, and myocardial perfusion imaging has independent prognostic value.

Abbreviations

ACC/AHA
American College of Cardiology/American Heart Association
CAD
coronary artery disease
CS
clinical score
ECG
electrocardiogram/electrocardiographic
GDS
global difference score
GRS
global rest score
GSS
global stress score
MI
myocardial infarction
SPECT
single-photon emission computed tomography

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