Estimating the Accuracy of Dobutamine Stress Echocardiography and Single-Photon Emission Computed Tomography among Patients Undergoing Noncardiac Surgery

In this study, we demonstrated that the expected accuracy of DSE in the diagnosis of obstructive CAD among patients undergoing noncardiac surgery is higher than that of SPECT. This finding was true in both unselected patients and those selected by a perioperative risk of greater than 1%. The use of SPECT, compared with DSE, would likely result in greater numbers of false-positive tests in this patient population and less accurate results overall.

Cardiac stress testing, as with any diagnostic test, is most useful at intermediate probabilities. Insofar as stress testing offers diagnostic value, our analysis suggests that, in the range of the predicted risk of CAD found in patients undergoing noncardiac surgery, DSE is a more efficient testing strategy. To the extent that making a diagnosis of CAD informs the decision to proceed to surgery, a more accurate test would be preferable. The lower cost of DSE, the lack of ionizing radiation, and the information provided by echocardiography regarding diagnoses other than CAD, if considered, would further amplify that preference.

However, it is important to note that both modalities have limited positive predictive value. In the median patient who meets the currently recommended 1% perioperative event risk threshold, SPECT would lead to 2.74 false positive results for every true positive result. DSE would produce approximately two false positive results for every three true positive results. If lower rates of false-positive testing are desired, different patient selection criteria are required.

A few key limitations of this work warrant discussion. First, our results likely overestimate the probability of obstructive CAD in this population. We assumed that all patients have nonspecific chest pain at the time of the preoperative evaluation, though many patients do not, in fact, have chest pain. Tools to estimate the pretest probability of CAD (such as the ESC tool that we used or the older Diamond-Forrester prediction) are intended to stratify higher-risk patients than are seen in a preoperative setting. If asymptomatic patients seen in preoperative risk assessment clinics have lower risk of CAD than what we have predicted, we will have understated the case for DSE. Moreover, cases sampled from hospitals participating in NSQIP are not representative of the national surgical population. This likely further inflates our estimates of CAD risk compared with the “true” surgical population. Finally, we cannot comment on current practice from these data. Current guidelines recommend preoperative cardiac stress testing for patients whose risk of a perioperative cardiac event exceeds 1%, whose functional status is poor or unknown, and only if said testing will change management.⁵ Using these data, we cannot determine the pretest probability of patients referred for stress testing before noncardiac surgery.

Still, this analysis suggests that, among patients undergoing noncardiac surgery, selecting patients according to the risk of perioperative events would result in a population at an overall comparatively low risk of CAD, and that in this population, DSE would be more accurate than SPECT for making the diagnosis of CAD. If a diagnosis of CAD would change the decision to proceed to surgery, DSE is likely to be a more efficient test than SPECT.