Is stress-only SPECT myocardial perfusion imaging with attenuation correction an effective laboratory strategy in patients with no known CAD?

Objectives Stress-only myocardial perfusion imaging (SO MPI) with attenuation correction has been proposed as an effective tool to reduce radiation exposure and improve laboratory efficiency. Outcomes data are limited as is the necessity to perform rest imaging in such patients. The objective of this study was to evaluate cardiac events and the need for rest imaging in patients undergoing clinically-indicated SO MPI.

Methods Consecutive patients without known CAD referred for chest pain were scheduled for stress-only Tc-99m MPI (n= 1384 ). Resting images S/(R) were acquired on a subset of these patients if requested by the interpreting physician (n= 128). Images were interpreted using the ASNC 17-segment model and summed stress scores (SSS) were calculated. A SSS > 0 was considered an abnormal result. All Patients were followed for mean of 2.1 + 1.3 yrs for occurrence of cardiac events (coronary revascularization, non-fatal MI or cardiac death). Annualized event rates (AER) were calculated for both groups with normal and abnormal images.

Results A subsequent rest study was required in 128 patients (9.2%). In the SO group, 50 patients (3.9%) had abnormal images whereas 86 patients (67%) in S/R group had abnormal images.. The mean SSS in SO was significantly lower than S/R (0.2 + 1.5 vs 3 + 1.5; p<0.001). There were a total of 38 events during follow- up. AER were similar among groups for normal images and very low. An abnormal SO image was associated with significantly higher event rates as compared to S/R group.

Conclusions Stress-only SPECT MPI with attenuation correction effectively risk stratifies patients at risk for CAD. In our study population, an abnormal study without rest was associated with a significantly higher cardiac event rate primarily in the form of revascularization. A normal study was found to be safe, efficient, and associated with low cardiac events. The need for subsequent rest studies was low, and usually associated with an abnormal result