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KEY POINTS
Incidental non-cardiac findings are present in up to 30% of myocardial perfusion scans and may vary in clinical significance.
A strong understanding of the normal patterns of radiotracer activity by non-cardiac structures during myocardial perfusion imaging (MPI) is paramount as a deviation of these patterns may be suggestive of pathology.
To increase the likelihood of detecting incidental findings, when reading MPI, a stepwise, integrated approach should be utilized paying attention to all the images acquired (both the nuclear and computed tomography [CT] images [when present]).
Several logistical factors surround the over reading of attenuation-corrected CT images and non-cardiac nuclear images obtained during MPI, which calls for a need for increased training and lab accreditation.
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On average, more than 9.1 million myocardial perfusion scans are performed in the United States each year as a part of the evaluation of coronary artery disease.1,2 While these studies focus primarily on the assessment of key cardiac functions and structures, such as myocardial blood flow and myocardial contractility and viability, several incidental cardiac and non-cardiac findings may be discovered simultaneously. These discoveries may be either identified via abnormal radiotracer activity (and in some case inactivity) or may be detected via concomitant computed tomography (CT) images that are acquired to facilitate attenuation correction and performance of coronary artery calcification scoring.3,4
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The importance of incidental non-cardiac findings discovered during myocardial perfusion imaging (MPI) varies from trivial findings to potentially life-threatening. In some instances, the incidental finding may be the source of the patient’s symptoms which were previously incorrectly attributed to cardiac ischemia.
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While incidental non-cardiac findings may be present in as many as 20% to 30% of MPI studies performed with CT, evidence suggests that these findings are not often life-threatening.5 Due to this, there is some debate as to whether the downstream effects of the identification of these non-cardiac findings are universally justified, as they may act as a source of subsequent patient anxiety and costly follow-up investigations with an overall low yeild.5
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Though this concern is valid, in some circumstances, failure to appropriately triage concerning non-cardiac findings present on MPI could have dire consequences and should be avoided. Beyond the obvious implications to the patient, failure to adequately identify incidental findings may expose the reading physician to litigation if these omissions result in negative patient outcomes.
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Given these factors, there is an increased need for cardiologists reading radionuclide MPI studies and their accompanying CT attenuation correction scans to have an appreciation of how to navigate and triage the numerous clinically significant non-cardiac findings that may be captured during these studies.6
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Normal Radiotracer Activity
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Myocardial perfusion imaging takes advantage of the fact that functioning well-perfused cardiac myocytes will uptake radiotracers proportional to blood flow to that region of the heart. ...