Estimating the Accuracy of Dobutamine Stress Echocardiography and Single-Photon Emission Computed Tomography among Patients Undergoing Noncardiac Surgery
When cardiac stress testing is ordered prior to noncardiac surgery, the optimal test modality is unknown. Therefore, we conducted this study to compare the diagnostic accuracy of dobutamine stress echocardiography (DSE) and single-photon emission computed tomography (SPECT) in a representative sample of patients undergoing noncardiac surgery without an existing diagnosis of coronary artery disease (CAD). The predicted accuracy of DSE was greater than that of SPECT in around 60.5% of cases above the current guideline-recommended risk threshold. In this population, DSE is likely to be more accurate than SPECT in the diagnosis of obstructive CAD. To the extent that making a diagnosis of obstructive CAD changes the decision to pursue noncardiac surgery, DSE likely represents a more efficient testing modality. However, in the range of pretest probabilities among this population, positive results from either test are more likely to represent false positives than true positives.
© 2018 Society of Hospital Medicine
Cardiac complications account for at least one-third of perioperative deaths, and lead to substantial morbidity and cost.1-4 Current guidelines recommend that patients undergo assessment of cardiac risk and functional status prior to noncardiac surgery.5 Preoperative cardiac stress testing is recommended for patients whose predicted cardiac risk exceeds 1%, whose functional status is limited, and for whom testing may change management.5
However, patients are not specifically selected according to risk of coronary artery disease (CAD) in current guidelines. The pretest probability of CAD may vary widely in this patient population, and the resultant accuracy of cardiac stress testing in making the diagnosis of CAD may vary as well.5 Meanwhile, CAD is a clear risk factor for perioperative cardiac events.6-8
Because the pretest probability of CAD is heterogeneous, the optimal modality of cardiac stress testing in this population is unclear. False-positive results would likely lead to inflated estimates of operative risk, expensive and high-risk downstream testing, and potentially cancellation of otherwise beneficial surgeries. Meanwhile, false-negative results would lead to overly optimistic estimates of surgical risk and potentially to surgical intervention at higher levels of risk than would be desirable. Current guidelines leave the selection of either dobutamine stress echocardiography (DSE) or pharmacological stress myocardial perfusion imaging to the clinician.5 To inform decisions regarding the selection of cardiac stress testing modality prior to noncardiac surgery, we conducted this study to estimate the diagnostic accuracy of DSE and single-photon emission computed tomography (SPECT) among this patient population.
METHODS
Surgical Cohort
The American College of Surgeons’ National Surgical Quality Improvement Program (NSQIP) samples patients undergoing surgery at participating hospitals and collects standardized clinical data on preoperative risk factors and postoperative complications.9 We acquired public use data from the 2009 NSQIP cohort, which included more than 336,000 surgical cases from 237 hospitals (principally in the United States). We excluded from our analysis patients undergoing cardiac surgery, patients with a prior diagnosis of CAD, and patients undergoing experimental surgeries. This left a sample of 300,462 for analysis.
Prediction of Dyslipidemia
The model we used to predict the presence of obstructive CAD required the presence or absence of dyslipidemia. A number of variables are common to both NSQIP and the National Health and Nutrition Examination Survey (NHANES), including age, weight, sex, tobacco use, diabetes, and prior stroke.10 Using those common variables, we developed a logistic regression to predict a diagnosis of dyslipidemia, applied that regression to the NSQIP cohort, and dichotomized. To assess the potential impact of misclassification, we performed separate sensitivity analyses in which either no patients or all patients had dyslipidemia.
