Low Prevalence of Non-Response to Vasodilator Stress during Dynamic CZT SPECT MPI

Introduction: The prevalence of non-response (NR) to regadenoson (Reg), which is one potential mechanism for false negative stress myocardial perfusion imaging (MPI), is unknown. Myocardial blood flow quantification is feasible with dynamic CZT SPECT and allows confirmation of reg-induced hyperemia.

Methods: A convenient sample of patients referred for Reg-MPI underwent dynamic imaging on the DSPECT camera. Patients were instructed to abstain from caffeine containing products and methylxanthine drugs for 12 hours by a nurse the day prior to their scheduled MPI. Compliance was checked verbally on the day of the test and the test was rescheduled in cases of non-compliance. Patient positioning was accomplished with a hand-injected 1mCi Tc-99m sestamibi (MIBI) pre-scan. Reg stress, and rest/ stress MIBI injection using an automated injector were performed with the patient under the camera. 9mCi and 30mCi of MIBI in 2ml saline followed by a 40 mL saline flush for the rest and stress studies were administered respectively, with the tracer injection performed 50s after Reg stress. Data acquired in list mode were processed on either an INVIA 4DM® or Cedars Sinai QGS/QPS ® platform by re-binning into 32 frames consisting of 21 × 3-sec, 1 × 9-sec, 1 × 15-sec, 1 × 21-sec, 1 × 27-sec and 7 × 30-sec frames, using an OSEM algorithm with 4 iterations and 32 subsets. Manual adjustments were routinely made to the ROI position in each frame for arterial input and myocardial activity curve derivation. A myocardial flow reserve (MFR) of ≤ 1.2 ml/g/min in the absence of extensive coronary disease or known microvascular disease was considered to represent a lack of response to Reg.

Results: 222 of 269 dynamic Reg-MPI patients were analyzed after patients with cardiac amyloidosis (17) who are known to have severe microvascular disease, studies with QA issues (2), and cases with incomplete data (28) were excluded. 36 patients with SPECT infarct or ischemia were also excluded. Of the remaining 186 patients, only 5 patients (2.7%) had an MFR of ≤ 1.2 ml/g/min. As part of a sensitivity analysis, patients with abnormal MPI demonstrated a lower global peak stress flow and MFR compared to normal MPI (2.09 vs. 2.41, p value = .029 and 2.16 vs. 2.58 p value =.005).

Conclusions: In non-consecutive SPECT MPI patients carefully instructed to abstain from caffeine, a very low MFR which might indicate non-response to Reg is rare.