Correlation Between Automated Quantification of V/Q SPECT Mismatch and Haemodynamics in Chronic Thromboembolic Pulmonary Hypertension

M. Kural (Köln)¹, H. Weis (Köln)², J. Weindler (Köln)³, N. Westphal (Köln)³, J. Hertel (Köln)³, T. Kramer (Köln)⁴, A. Drzezga (Köln)³, S. Baldus (Köln)⁴, M. Schmidt (Köln)², S. Rosenkranz (Köln)^5
1Universitätsklinikum Köln Klinik III für Kardiologie, Angiologie, Pneumologie und Internistische Intensivmedizin Köln, Deutschland; ²Universitätsklinik Köln Nuklearmedizin Köln, Deutschland; ³Universitätsklinikum Köln Nuklearmedizin Köln, Deutschland; ⁴Herzzentrum der Universität zu Köln Klinik für Kardiologie, Angiologie, Pneumologie und Internistische Intensivmedizin Köln, Deutschland; ⁵Herzzentrum der Universität zu Köln Klinik III für Innere Medizin Köln, Deutschland

Introduction: Accurate diagnosis of chronic thromboembolic pulmonary hypertension (CTEPH) is crucial in standardised pulmonary hypertension (PH) work up. Ventilation/perfusion single-photon emission computed tomography (V/Q SPECT/CT) is essential in CTEPH assessment due to its high sensitivity. The extent of detected mismatches can be automatically quantified using a newly validated software-assisted method (Hermes^TM, Lung SPECT V/Q tool), aiming to improve diagnostic accuracy and reproducibility in CTEPH evaluation. This study aimed to evaluate correlations between quantitative V/Q mismatch and haemodynamics in V/Q SPECT/CTs of CTEPH patients.
Methods: We conducted a software-assisted, retrospective analysis of 256 V/Q SPECT/CT scans, which were performed on patients with suspected PH. For our analysis, only patients with a first-time diagnosis of CTEPH who also underwent right heart catheterisation (RHC) within three months were included, resulting in a cohort of 42 patients. Automated, observer-independent quantification was performed using Hermes^TM - Lung SPECT V/Q tool software yielding extent of V/Q mismatch (V/Qvol>5) and its heterogeneity (logSDV/Q). Analyses were performed for attenuation corrected (AC) scans as well as no-AC scans. Statistical analysis was performed using Pearson correlation testing between V/Q parameters and haemodynamic measurements including mean pulmonary arterial pressure (mPAP), pulmonary vascular resistance (PVR) and transpulmonary pressure gradient (TPG). 
Results: The extent of V/Q mismatch and its heterogeneity, both with and without AC, correlated significantly (p<0.05) with all major haemodynamic parameters. Specifically, the correlation to mPAP prevailed with r=0.52 and 0.6 for no-AC and 0.58 for AC. The correlation to PVR prevailed with r=0.8 and 0.84 for no-AC and  r=0.52 and 0.63 with AC. Similarly, mismatch showed correlation to TPG (r=0.64 and 0.68 without AC and r=0.67 and 0.78 with AC). Interestingly, no-AC V/Q scans tended to show slightly higher r-values compared to those with AC. 
Conclusion: In our study, both the extent and heterogeneity of V/Q mismatch measured with an observer-independent software based method were significantly correlated with haemodynamic parameters in CTEPH. Our findings underscore the potential of this objective analysis and quantification of mismatch findings as a valuable non-invasive tool for assessing disease severity in CTEPH. Our findings should be validated in lager-scale studies.