Clinical role of the Duke Activity Status Index in the selection of the optimal type of stress myocardial perfusion imaging study in patients with known or suspected ischemic heart disease

Abstract

Background

Exercise treadmill stress myocardial perfusion imaging (MPI) with single photon emission computed tomography is commonly used to evaluate the extent and severity of inducible ischemia as well as to risk stratify patients with suspected and known coronary artery disease (CAD). Failure to reach adequate stress, defined as not attaining age-appropriate metabolic equivalents (METs), can underestimate the extent and severity of ischemic heart disease, resulting in false negative results. This study evaluates the efficacy of the Duke Activity Status Index (DASI), a simple self-administered 12-item questionnaire, as a predictor of METs achieved by treadmill stress testing.

Methods

The DASI was prospectively administered to 200 randomly selected men and women referred to the nuclear cardiology laboratory at New York University Langone Medical Center for stress MPI. Each patient was asked to complete the 12-item DASI questionnaire independently. 136 patients underwent treadmill exercise with MPI and 64 had pharmacologic stress with MPI. The association between exercise capacity in METs as estimated by the DASI questionnaire and performance on the Bruce treadmill protocol in METS was compared using chi-square statistics.

Results

Over 70% of those patients whose DASI score predicted the ability to perform <10 METs were unable to exercise beyond stage 2 of the Bruce protocol (7 METs). For those whose DASI score predicted ability to perform >12.5 METs, over 80% of patients reached >stage 2 of the Bruce protocol with 40% reaching beyond stage 3 (10 METs). When patient age was incorporated into the calculation, a more linear relationship was observed between predicted and obtained METs.

Conclusion

The DASI is a simple self-administered questionnaire which is a useful pretest tool to determine a patient’s ability to achieve appropriate METs. In the nuclear cardiology laboratory, the DASI has the potential to guide selection of exercise treadmill vs pharmacologic stress and ultimately improve laboratory efficiency.

Introduction

Cardiac stress testing with myocardial perfusion imaging (MPI) is a valuable technique in the diagnostic and prognostic evaluation of patients with known or suspected ischemic heart disease.1, 2, 3, 4 MPI combined with treadmill exercise is often the preferred modality of testing to evaluate the physiological significance of CAD, extent and severity of inducible ischemia, to evaluate functional capacity, hemodynamic parameters, and patient symptoms.^1,2 The sensitivity, specificity, and prognostic accuracy of exercise stress MPI, however, are dependent on achieving adequate exercise stress.^5,6 Failure to reach adequate stress, defined as not attaining age-appropriate metabolic equivalents (METs), can underestimate the extent and severity of ischemic heart disease and lead to false negative results.^5,7,8

In clinical practice, a growing number of patients referred for exercise stress MPI have limited functional capacity due to obesity or orthopedic problems and are unable to achieve an exercise stress level that is sufficient to reach age-appropriate METs. This can result in failure to render a diagnostic test.^6,9 In clinical practice, the exercise stress MPI for this patient population is often aborted and the patients are converted to pharmacologic stress MPI test.¹⁰ Pharmacologic stress testing is increasingly being utilized for stress MPI, accounting for nearly half of all nuclear stress tests performed in the United States.

The selection of the appropriate type of nuclear stress test, exercise treadmill stress MPI vs pharmacologic stress MPI, is crucial not only for diagnostic accuracy and prognostic evaluation, but also for clinical decision making and management strategies. Research has shown that those patients who require pharmacologic testing because they are unable to exercise adequately for a stress test have an increased risk of cardiac events.¹¹ Functional capacity should play an important role in the selection of the optimal nuclear stress test in the patient with known or suspected ischemic heart disease. The Duke Activity Status Index (DASI) is a 12-item questionnaire that utilizes self-reported physical work capacity to estimate peak METs and has been shown to be a valid measurement of functional capacity.^12,13 It allows gender specific risk-stratification and may improve identification of the higher-risk, functionally impaired patients who would benefit from pharmacologic stress testing.⁹ We hypothesized that the pretest use of the DASI questionnaire in patients referred for stress MPI could help in the selection of patients who would be more accurately evaluated using pharmacologic stress testing vs exercise treadmill stress. For patients noting significant limitations on their activities of daily living, defined as an estimated METs <5, referral to pharmacologic stress may be warranted as the initial stress test.