Myocardial perfusion imaging using only stress is safe in patients of low probability pre-test of coronary artery disease and reduces radiation exposure

Abstract

Introduction: A normal Myocardial Perfusion Imaging (MPI) provides a prognosis and current guidelines recommending to perform the exam under the standard resting / stress (R / S) protocol to confirm that a MPI is normal. Purpose: To
evaluate the prognosis of MPI using the protocol of only stress in selected population of low risk. Methods – It was prospectively studied 46 consecutive patients through a MPI. The patients whom meeting the following admission criteria performed the stress phase first: 1. Low pretest probability (<50%) of significant CAD based on Diamond and Forrester criteria; 2. Capacity to perform stress in treadmill; 3. Do not have a previous diagnosis of Coronary Artery Disease (CAD); 4. Have interpretable rest ECG. The MPI indication was an abnormal prior exercise test due to ST changes in 63% and atypical angina in 22%. The mean pre-test probability of CAD was 11.25% (4-46%). The mean age was 40 years (30 - 49), 60% were female. The patients underwent the stress phase, under the Bruce protocol; the mean heart rate (HR) achieved was 92.9% of the predicted maximum HR for age. All Patients achieved a workload ≥ 6 METS (average 9.4 METs). If the stress image was normal unambiguously, the examination was finished. Any suspicion of artifacts and
/ or presence of perfusion defects on stress, the patients were submetted to the resting phase and were excluded from the study. Results: Stress ECG revealed changes in ST segment in 30% of the patients, with an ascending pattern in 35%, horizontal in 7% and descending in 57%. No patients reported angina in the stress phase. The mean duration of the examination was 115 min (standard protocol R / S 240
min). The dose of the radiopharmaceutical (Tc99m-MIBI) injected was significantly lower than that predicted for the standard protocol (9.2 mCi, vs 33.9 mCi-p <0.00001) with a reduction in radiation exposure of 77% (2.5 mSv vs 11.4 mSv). Follow-up was obtained on all patients with an average of 19.9 months (ranging from 6 to 34 months). No hard events (death, fatal or non-fatal MI) or myocardial
revascularization occurred during the follow-up period. Conclusion: The normal MPI using the stress-only protocol in low-probability pre-test of CAD, gives a good prognosis, and there were no hard events and / or revascularization in a follow-up of 19.9 months, with a significant reducing exposure to radiation, and with a shorter protocol.