Usefulness of Exercise Test and Myocardial Perfusion–Gated Single Photon Emission Computed Tomography to Improve the Prediction of Major Events

Abstract

Background-The incremental prognostic value of myocardial perfusion-gated single photon emission computed tomography (MPGS) compared with exercise test has not yet been properly evaluated. Methods and Results-Five thousand six hundred seventy-two consecutive patients with known or suspected coronary disease undergoing exercise MPGS between 1997 and 2007 were included. Three-year predictive models for total death and death from cardiovascular causes or acute myocardial infarction (ie, major cardiovascular events [MCE]) were built using Cox-regression modeling, including only the clinical information. Then the exercise and MPGS information was sequentially added. The added discriminative ability of exercise test information and MPGS was assessed by net reclassification improvement and integrated discrimination improvement. The increase in predictive ability of exercise information for death and MCE was high as assessed by net reclassification improvement (0.199 and 0.263) and integrated discrimination improvement (0.042 and 0.021). The only variable of MPGS associated with total death was ejection fraction (hazard ratio, 0.84; 95% confidence interval, 0.79-0.89; P<0.001). Global stress ischemic score emerged as an additional variable associated with MCE (hazard ratio, 1.07; 95% confidence interval, 1.02-1.12; P=0.007). Adding MPGS information barely improved the prognostic value for total death (net reclassification improvement, 0.017; integrated discrimination improvement, 0.013), but it increased for MCE (net reclassification improvement, 0.122; integrated discrimination improvement, 0.033). Conclusions-Adding

Net Reclassification Improvement and Integrated Discrimination Improvement

“…Only a handful of recent nuclear cardiology publications have applied this approach. [12][13][14] The present study by Candell-Riera et al 6 can be added to this small group of important studies.…”

“…Additionally, the results of NRI can demonstrate how many patients are shifted into different clinical risk categories (low, moderate, high) by using a different model. The application of these principles is illustrated in the article by Candell-Riera et al 6 These authors show the conventional results of their study in Table 1 (univariable associations between clinical, exercise, and MPGS variables and outcome end points), Table 2 (important variables in each of the respective multivariable models), and Figure 2 (receiveroperating characteristic curves and c-statistic results). The more novel results from applying NRI and IDI are provided in Figure 3 and Table 3.…”

“…In this issue of Circulation: Cardiovascular Imaging, CandellRiera et al 6 report on the prognostic value of exercise MPGS in 5672 patients with known or suspected coronary artery disease. The authors apply the c-statistic, net reclassification improvement (NRI), and integrated discrimination improvement (IDI) to examine the incremental prognostic value of MPGS compared with clinical and exercise test variables for predicting the end points of all-cause death and the major cardiovascular end point of combined cardiovascular death and nonfatal myocardial infarction.…”

“…The major contribution of the article by Candell-Riera et al 6 is the application of NRI and IDI. The standard approach of examining the association between a variable of interest (in this case MPGS) and clinical outcome consists of applying a series of tests of increasing statistical rigor.…”

“…Even assuming that the correct reclassification of some patients into a higherrisk category could lead to an intervention that could be lifesaving, the cost per year-of-life-saved would be substantially higher than the imaging costs of reclassification provided by Candell-Riera. 6 The concept of applying nuclear imaging for reclassifying patient risk is not new. [8][9][10] More recently, this concept has been popularized through the work of Pencina et al 11 and the introduction of the terms NRI and IDI.…”