Abstract Introduction Angina with nonobstructive coronary arteries (ANOCA) is increasingly recognized and may affect nearly one-half of patients undergoing invasive coronary angiography for suspected ischemic heart disease. While invasive functional assessment with CFR and IMR remains the gold standard, emerging non-invasive methods, such as dynamic SPECT-MPI with myocardial flow reserve (MFR) measurement offer promising screening capabilities. Our institution has established a comprehensive microcirculatory assessment program to optimize patient selection and diagnostic pathways for INOCA/ANOCA evaluation. Aim Our aim was to evaluate the correlation between non-invasive SPECT-MFR and invasive coronary functional parameters (CFR, IMR). Methods First 10 consecutive patients enrolled in a systematic INOCA/ANOCA diagnostic program with both SPECT and invasive assessment. Inclusion criteria were: excluded obstructive CAD on invasive coronary angiography and either persistent symptoms suggestive of coronary dysfunction or suspected microcirculatory abnormalities on SPECT. All patients underwent dynamic stress SPECT-MPI using regadenosone, providing global and regional MBF and MFR quantification. Invasive assessment was performed using Pressure Wire X for CFR and IMR measurement, followed by acetylcholine provocation testing for VSA evaluation. Statistical analysis included Pearson correlation coefficients and descriptive statistics appropriate for pilot data. Results Mean age 64.8, 80% male. SPECT interpretation revealed abnormal studies in 3 patients, with induced perfusion defects in 4 and fixed defects in 1 patient. Mean SPECT-MFR was 2.27 ± 0.53, with normal TID values (0.975). Invasive assessment: CMD was identified in 7 patients, with mean CFR 3.33 and mean IMR 23.5. CMD was found in 4 patients, VSA was diagnosed in 4 patients, whereas 1 patient had combined CMD and VSA. Correlation: SPECT-MFR demonstrated correlation with CFR at r=-0.381, and with IMR at r=-0.277. These correlation coefficients approach values reported in larger validation studies, suggesting potential clinical utility of SPECT-MFR in our patient population. CMD-positive patients showed characteristically impaired microvascular parameters compared to CMD-negative patients (CFR: 2.83 vs 4.50 ; IMR: 28.0 vs 13.0). Conclusion Our experience demonstrates correlations between SPECT-MFR and invasive functional parameters. Observed correlation coefficients (r=-0.38 for CFR) are clinically relevant and consistent with published validation data, suggesting that SPECT-MPI can serve as an effective screening tool for patient selection prior to invasive assessment.For image description, please refer to the figure legend and surrounding text.
Harpula et al. (Sun,) studied this question.