Perfusion-only Q-SPECT as a rule-out tool for CTEPH in resource-limited settings: a feasibility study on reducing unnecessary referrals to tertiary centers

BACKGROUND AND AIM: To evaluate the diagnostic performance of perfusion-only Q-SPECT in suspected chronic thromboembolic pulmonary hypertension (CTEPH) and to assess its potential role in reducing unnecessary referrals in resource-limited settings. METHODS: Between January 2022 and February 2024, 42 patients with suspected CTEPH underwent perfusion-only Q-SPECT at a secondary care center. Patients were stratified into Group 1 (no defect) and Group 2 (defect present). Defect-positive cases were further assessed with computed tomography pulmonary angiography (CTPA) and multidisciplinary follow-up, whereas defect-negative cases were verified by structured clinical and imaging follow-up. Final diagnoses were established using a composite reference standard based on imaging, clinical assessment, and multidisciplinary evaluation. A validated single-patient preparation method for 99mTc-MAA was applied to enable daily imaging. Diagnostic performance was analyzed using sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy. RESULTS: Of the 42 patients, 18 (43%) were male, with a median age of 56.5 years. Confirmed CTEPH was diagnosed in 7 patients (16.6%). Patients older than 50 years tended to have a higher prevalence of perfusion defects (61% vs. 32%), (χ², p = 0.059) and a positive correlation was found between age and defect count (rho = 0.315, p = 0.042). Twenty-two patients (52.4%) had normal Q-SPECT results (Group 1), yielding an NPV of 100%. Among defect-positive patients (Group 2), nine had ≥ 5 typical wedge-shaped defects, while atypical or non-segmental defects were classified as non-embolic in three patients. For the entire cohort, diagnostic performance was as follows: sensitivity 85%, specificity 77%, PPV 43%, NPV 96%, and overall accuracy 79%. CONCLUSION: In this single-center cohort, perfusion-only Q-SPECT was feasible as an initial imaging approach for suspected CTEPH at a secondary care level. Patients without perfusion defects did not demonstrate findings consistent with CTEPH during structured follow-up, allowing more than half of suspected cases to be managed locally. Defect-positive patients required further diagnostic verification with CTPA and, when indicated, invasive assessment. Overall, these findings support the feasibility of a pragmatic, stepwise diagnostic strategy incorporating perfusion-only Q-SPECT in resource-limited settings, pending confirmation in larger prospective studies.