Discordance Between Gated Single-Photon Emission Computed Tomography Myocardial Perfusion Imaging and Coronary Angiography in Dilated Cardiomyopathy.

Background Gated single-photon emission computed tomography myocardial perfusion imaging (SPECT-MPI) provides functional information that may help distinguish ischemic from nonischemic dilated cardiomyopathy (DCM). However, its classification may differ from that of coronary angiography (CAG). Examining these discordant cases may improve SPECT-MPI interpretation in patients with DCM. This study aimed to assess the pattern of discordance between gated SPECT-MPI and CAG in patients with DCM and describe the features of false-positive and false-negative SPECT-MPI findings. Methodology This cross-sectional secondary analysis included 89 patients who underwent CAG and gated SPECT-MPI during the same diagnostic sitting at the National Institute of Cardiovascular Diseases, Dhaka, Bangladesh, from October 2023 to August 2025, minimizing the possibility of intervening clinical events or therapeutic changes. We used CAG as the reference standard. We categorized patients as true-positive, true-negative, false-positive, or false-negative based on agreement between SPECT-MPI and CAG. We compared clinical, echocardiographic, angiographic, and quantitative SPECT-MPI parameters between groups. Results CAG classified 48 patients as ischemic cardiomyopathy and 41 as nonischemic DCM. SPECT-MPI agreed with CAG in 57 (64.0%) patients and disagreed in 32 (36.0%) patients, including 19 false-positive and 13 false-negative cases. The agreement was fair (κ = 0.269), although the association between modalities was significant (χ² = 6.545, p = 0.011). Using CAG as the reference standard, SPECT-MPI demonstrated a sensitivity of 72.9% (35/48), a specificity of 53.7% (22/41), and an overall accuracy of 64.0% (57/89). False-positive cases had higher summed stress scores, summed rest scores, summed difference scores, and transient ischemic dilation than true-negative cases. False-negative cases had lower summed stress scores, summed rest scores, and summed difference scores than true-positive cases, and most had double- or triple-vessel coronary disease. Conclusions In patients with DCM, gated SPECT-MPI and CAG showed discordant classification in more than one-third of cases. False-positive and false-negative patterns suggest that the two modalities provide complementary rather than fully interchangeable information. SPECT-MPI should be interpreted alongside the clinical profile, echocardiographic findings, and pre-test probability of CAD, particularly when imaging findings do not match the overall clinical picture.