Evaluation of Pulmonary Artery Flow Reserve in Patients With Chronic Thromboembolic Pulmonary Hypertension: A Pilot Study

Background Pressure‐wire fractional flow reserve (FFR) can guide balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension, but lesion crossing with a distal wire increases cost and procedural risk. We developed an angiography‐derived physiologic index—pulmonary artery flow reserve (PFR)—computed from selective pulmonary angiography using fluid‐dynamic modeling without distal pressure‐wire advancement. Methods In this prospective observational study, selective pulmonary angiography was acquired in 2 projections for type A (ring‐like), type B (web lesion) and type C (subtotal) pulmonary artery lesions. Proximal pressure (Pa) was measured at the target vessel ostium using a pressure‐sensor catheter; flow velocity was estimated by frame counting; pressure drop (ΔP) was computed by a proprietary computational fluid dynamics approach, and PFR was derived as (Pa − ΔP)/Pa. Pressure‐wire FFR (Pd/Pa) served as the reference standard (FFR ≤0.80). Diagnostic performance was assessed by receiver operating characteristic analysis and agreement by Bland–Altman analysis. Results Fifty‐two vessels in 29 patients were analyzed. Mean FFR and PFR were 0.57 ± 0.23 and 0.58 ± 0.24; 44 vessels had FFR ≤0.80. PFR showed excellent discrimination for FFR ≤0.80 (area under the curve 0.981, 95% CI 0.935–1.000), with sensitivity 94.1% (95% CI 80.9%–98.7%) and specificity 87.5% (95% CI 64.0%–97.0%) at an optimal PFR cutoff of 0.77. Agreement was high (bias 0.0076; 95% limits of agreement −0.1037 to 0.1190), and correlation was strong ( r =0.970, P <0.001). At 3‐month follow‐up (n=45 vessels), PFR maintained high performance (area under the curve 0.985; bias 0.0071; r =0.967; all P <0.001). Conclusions Angiography‐derived PFR demonstrated strong agreement with pressure‐wire FFR for physiologic assessment of pulmonary artery stenoses in chronic thromboembolic pulmonary hypertension and may provide a simpler alternative to distal pressure‐wire measurements to support physiology‐guided balloon pulmonary angioplasty.