Original ArticleClinical 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
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.
Section snippets
Methods
200 patients, 134 men and 64 women, were prospectively recruited from those referred to New York University Langone Medical Center for stress testing. Subjects were enrolled after completing a written informed consent which was approved by the Institutional Review Board. Each patient was asked to complete the 12-item DASI questionnaire (Table 1) independently. Each question in the questionnaire had been assigned a numerical value based on the estimated peak oxygen uptake of the inquired
Clinical Characteristics of the Patient Cohort (Table 2)
A total of 200 patients completed the DASI questionnaire and underwent MPI between April 2009 and January 2010. 138 patients underwent exercise stress tests with MPI (68%) and 62 patients underwent pharmacologic stress with MPI (32%). 64 (32%) of the patients were women and 136 (66%) of the patients were men. Coronary artery disease (CAD) risk factors were seen with high frequency in this patient subset with a majority of the patients carrying a diagnosis of hypertension (59%) and
Discussion
In this study, we evaluated the predictive value of the DASI, a brief self-administered questionnaire of functional status, in the identification of patients referred for stress testing who were likely to achieve adequate level of stress, defined as attaining age-appropriate METs. Failure to obtain age-appropriate METS can underestimate the extent and severity of ischemic heart disease, resulting in false negative results. In addition, prospectively identifying the appropriate type of test
Conclusion
This study adds to the body of evidence that the DASI questionnaire can predict a patient’s exercise capacity during an exercise stress test using the Bruce protocol.9,12 Utilization of the DASI questionnaire to predict exercise capacity in METs has important clinical use in determining patients’ eligibility for exercise stress testing. Future studies can also identify patients who are sent for pharmacologic stress testing who may be able to adequately participate in an exercise MPI stress
Disclosures
Lawrence Phillips—Speaker’s Bureau, Astellas Pharma (2009-2010).
Funding
Investigator Initiated Research Grant from Astellas Pharma.
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