Pulmonary hypertension (PH) is a hemodynamic and pathophysiological condition defined by a mean pulmonary artery pressure (mPAP) greater than 20 mmHg at rest, as confirmed by right heart catheterization (RHC) (1). The global prevalence of PH is estimated at approximately 1% of the adult population, rising to 10% or more in individuals over 65 years of age.Pre-capillary pulmonary hypertension, which includes pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH), is characterized by a pulmonary arterial wedge pressure (PAWP) ≤15 mmHg and an elevated pulmonary vascular resistance (PVR) ≥2 Wood units (2)

Computed tomography pulmonary angiography (CTPA) is routinely performed in the diagnostic workup of PH and offers a non invasive alternative that can generate multiple quantitative metrics from a single scan (3). Traditional CTPA metrics, including main pulmonary artery diameter (MPAd), the ratio of MPAd to ascending aortic diameter, central pulmonary arteries, and right ventricular to left ventricular diameter (RV/LV ratio) were previously studied in PH patients (4,5,6) Most existing studies have evaluated CTPA metrics in isolation or within single PH subgroups, limiting generalizability across the broader pre-capillary PH population (7).

Therefore, this study aims to systematically investigate the correlation between multiple quantitative CTPA metrics and key invasive hemodynamic parameters derived from RHC in patients with confirmed pre-capillary pulmonary hypertension

This is a prospective, cross-sectional , analytical study. All eligible patients referred to the Pulmonary Hypertension Clinic and Catheterisation Laboratory at Assiut University Hospital who undergo both CTPA and RHC as part of standard clinical care will be enrolled consecutively after providing an informed consent.

The hospital maintains a dedicated Pulmonary Hypertension Multidisciplinary Team (MDT) comprising chest physicians, cardiologists, and cardiothoracic radiologists, and performs regular right heart catheterizations.

1. Demographic and clinical

   • Age, sex , vital signs, body mass index and 6 min walking test.
   • Comorbidities: hypertension, diabetes mellitus, coronary artery disease, chronic kidney disease, liver disease, prior DVT, recent surgery, arrhythmia .

2. CTPA Morphometric Measurements:

   All CTPA measurements will be performed independently by two trained radiologists (Reader 1 and Reader 2) who are blinded to the RHC hemodynamic results Vascular Measurements : Main PA Diameter (mPAD), Ascending Aorta Diameter Same axial level as mPAD, PA : Ao Ratio (mPAD ÷ Aortic diameter) Calculated value, RV Maximum Transverse Diameter, LV Maximum Transverse Diameter Same axial slice as RV measurement, RV : LV Diameter Ratio (RV ÷ LV), RA diameters, and lung parenchymal affection

3. Right Heart Catheterization :

   All right heart catheterization procedures will be performed in the Cardiac Catheterization Laboratory at Assiut University Hospital by an accredited cardiologist or chest physician with dedicated PH catheterization experience. The procedure will be conducted in accordance with the 2022 ESC/ERS Guidelines on PH.

   Equipment

   • 7-French balloon-tipped thermodilution Swan-Ganz catheter.
   • Multi-channel pressure transducer system, zeroed at mid-axillary line at the level of the right atrium.
   • Continuous ECG, SpO₂, and non-invasive blood pressure monitoring throughout.
   • Fluoroscopy with stored images confirming catheter position at RA, RV, PA, and PAWP RHC Hemodynamic Parameters: Right atrial pressure, Right Ventricular Pressure - systolic (RVSP), Right Ventricular End-Diastolic Pressure (RVEDP), Pulmonary Arterial Pressure - systolic (sPAP), Pulmonary Arterial Pressure - diastolic (dPAP), Mean Pulmonary Arterial Pressure (mPAP), Pulmonary Arterial Wedge Pressure - mean (PAWP), Cardiac Output ,Cardiac Index, Stroke Volume , Systemic Vascular Resistance (SVR), and Mixed Venous O₂ Saturation (SvO₂)

4. ECHOCARDIOGRAPHY Comprehensive transthoracic echocardiography (TTE) will be performed within ± 2 weeks of the RHC date by a certified echocardiographer, following the American Society of Echocardiography (ASE) and European Association of Cardiovascular Imaging (EACVI) guidelines. Echocardiography will be performed independently from CTPA and RHC result review (blinded acquisition).

   Parameters: Estimated RVSP, TAPSE (M-mode, apical 4-chamber, lateral tricuspid annulus), RV Fractional Area Change, RV S' - Tissue Doppler, lateral tricuspid annulus peak systolic velocity ,RV Free Wall Longitudinal Strain (GLS, 3-segment or 6-segment), TAPSE / sPAP Ratio , RV and LV dimensions, and RA dimensions.

5. Laboratory investigations:

The following routine laboratory investigations will be performed as part of the study baseline assessment. All samples will be collected on the day of enrolment or within 48 hours.

Parameters: Hemoglobin (Hb), Hematocrit (Hct),White Blood Cell Count (WBC),Platelet Count, MCV, renal and liver function, serology, arterial blood gases and coagulation profile

Inclusion Criteria:

1-Age ≥ 18 years at time of enrolment. 2-Confirmed pre-capillary pulmonary hypertension on RHC performed at Assiut University Hospital: mPAP > 20 mmHg AND PAWP ≤ 15 mmHg AND PVR ≥ 2 Wood Units.

3-WHO PH Clinical Group 1 (PAH), Group 3 (PH due to lung disease/hypoxia), or Group 4 (CTEPH / chronic thromboembolic PH) classification assigned by the PH-MDT.

4-Both CTPA and RHC performed within a maximum interval of 4 weeks. b. Exclusion criteria:

1. WHO PH Group 2 (PH due to left heart disease) or Group 5 (PH with unclear/multifactorial mechanisms) .
2. Active malignancy.
3. Pregnancy, confirmed or suspected.
4. Contraindication to iodinated contrast agent: eGFR < 30 mL/min/1.73m² OR documented history of severe anaphylactic contrast reaction.
5. Inability to sustain breath-hold of ≥ 8 seconds (impairs CTPA quality).
6. Initiation or dose escalation of pulmonary vasodilator therapy (endothelin receptor antagonist, PDE5 inhibitor, soluble guanylate cyclase stimulator, or prostanoid) in the interval between CTPA and RHC, or within 4 weeks prior to CTPA.
7. Patient refusal to consent or inability to provide informed consent

adults with precapillary PHTN with contraindications to CTPA