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

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. 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. 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%. 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.