Abstract
169
Introduction: Rest/Stress protocols with ECG and Tc-99m Sestamibi D-SPECT imaging are commonly used for the diagnosis of coronary disease, sometimes confounded by arrhythmias such as atrial fibrillation, or balanced ischemia from multivessel disease (1). More precise nuclear diagnostic techniques with higher specificity will be needed to localize heart microvascular stenosis and calcifications (3). Studies indicated that PET is the gold standard for the evaluation of microvascular dysfunction (CMD) in non-ischemic cardiomyopathies (2) (4). Rest/Stress N13 ammonia with PET/CT tests demonstrated increased accuracy namely due to the rapid and wide distribution of N13 ammonia to organs and as being extracted from coronary capillaries into myocardial cells. Both techniques were applied in sequence to the same case reviewed in this abstract.
Methods: Journal articles on the comparative use of Tc-99m Sestamibi with D-SPECT and N13 ammonia PET/CT in CMD were reviewed. In addition, a case of a 76 year old male who underwent MP MIBI on a D-SPECT followed by an N13 ammonia PET/CT 45 days later was reviewed.
Results: ECG readings of the reviewed case indicated atrial fibrillation (AF). This was followed with an MP study by injecting 6.6 mCi Tc-99m Sestamibi at rest. Forty-five minutes later, DSPECT images were taken as per the department protocol. For the stress portion of the exam, the patient exercised for 3:25 minutes of a Standard Bruce protocol and was injected at 85% of the maximum age-predicted heart rate (MPHR) with 18.4 mCi of Tc-99m Sestamibi. The symptomatic response to exercise was non-ischemic, and the ECG indicated no significant ST-T changes. Another set of images were acquired at stress after recovery as per the department protocol. The LV and RV sizes were found to be normal as well. No regional perfusion defects or ischemia were noted (Figure 1). As symptoms persisted a N13 ammonia with PET/CT was conducted after 45 days. A rest/stress protocol was performed with the patient having a rest dose of 3.9 mCi N13 ammonia and a stress dose of 13.2 mCi N13 ammonia. The patient was stressed with a pharmacologic vasodilator of 0.4 mg Regadenoson (Lexiscan). Both testing modalities confirmed the absence of large vessel coronary disease or prior infarct. However, the Gated N-13 ammonia PET/CT test detected 31% resting LV ejection Fraction (EF) while the minimal threshold is 50%, Global myocardial flow reserve (MFR) was also low (1.47 vs >2). Moreover, the PET/CT images revealed extensive multivessel coronary artery calcification after a calcium score with abnormal global stress MFR and abnormal global LV function (Figure 2). Overall, these imaging studies confirmed decreased LV function in the setting of microvascular disease, with an absence of large vessel disease.
Conclusions: The reviewed case had microvascular dysfunction due to calcification of coronary microvessels which was not detected by gated Tc-99m Sestamibi D-SPECT. The N13 ammonia PET/CT technique was shown to be more specific in diagnosing hidden CMD defects and multivessel CAD. Further reviews will be needed to verify the feasibility of early use of N13 ammonia with PET/CT in order to save time and reduce costs. Acknowledgements: The author recognizes the contribution and support provided by the technologists at the Dept. of Nuclear Medicine at Brigham and Women’s Hospital, Boston, MA.Special thanks for Leonas Nalivaika MBA,CNMT(RS),ARRT(N)(BD),FSNMMITSProgram Director/Assistant Professor Nuclear Medicine Regis College,Kyle Seaver, CNMT, RT(N), NMTCB(CT) Lead Nuclear Medicine Technologist,And Karla Sirianni Senior Clinical Exercise Physiologist, MS, RCEP Non-Invasive Cardiovascular Imaging.
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