Balloon pulmonary angioplasty (BPA) treats patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH). Intra-procedural markers of success to guide the intervention are lacking. The investigators propose to measure right ventricular (RV) pressure volume loops invasively and measure biomarkers at intervals during the course of a course of BPA. These data will be analysed to define load independent indices of RV functional improvement, cross correlated with biomarker data and be used to calibrate non-invasive assessment of ventriculo-arterial coupling by cardiac magnetic resonance imaging (CMR) to better detect responders of BPA and pulmonary endarterectomy (PEA).

Patients who have Chronic Thromboembolic Pulmonary Hypertension (CTEPH) can treated surgically or by undergoing minimally invasive balloon pulmonary angioplasty (BPA). However not all patients have resolution of their pulmonary hypertension following these procedures, and some patients who don't have pulmonary hypertension derive substantial benefit nonetheless from surgical clearance of their thromboembolic disease.

Thus better understanding of the interaction between the blood vessels, the right heart workload, and symptoms and outcomes is required to predict treatment response. Ventriculo-arterial coupling is one such measure, quantifying the efficiency of transfer of energy from the right ventricle to the pulmonary arteries. Traditionally this has required invasive procedures involving intracavity conduction catheterisation of the right ventricle to simultaneously measure flow and pressure whilst altering preload. Not only is this invasive, but it is not routinely performed in clinical practice due to its complexity and requirement for specialised expertise and equipment. As CMR can simultaneously assess right ventricular and pulmonary function it may be able to assess function and ventriculo-arterial coupling non-invasively and allow for a more detailed and accessible mode of disease quantification and stratification.

The investigators will measure how the right heart function changes during BPA in patients with inoperable CTEPH, measured using a conductance catheter placed within the pumping chamber on the right side of the heart (right ventricle). This will generate pressure volume loops to detect intra-procedural changes of ventriculo-arterial coupling that can be used to quantify treatment success. The investigators will also monitor the levels of a newly discovered vessel inflammatory marker in the blood - Angiopoietin 2 (Ang2), and N-terminal pro-brain natriuretic peptide (NT-Pro BNP) that may also be useful in identifying responders to treatment and help define the optimal treatment protocol for BPA.

This participants will have CMR as standard of care. Data from CMR and invasive measurements of ventriculo-arterial coupling will determine the best CMR measures of coupling efficiency. These measures will then be applied within a large well-characterised cohort with long term follow-up to determine its association with symptoms, and outcomes following surgical intervention.

Inclusion Criteria:

• >18 years old
• Able to provide informed consent
• Inoperable CTEPH eligible for BPA treatment

Exclusion Criteria:

• Severe co-morbidity (expected life <6months)
• Women of child bearing age
• Significant known left to right shunt
• Permanent pacemaker
• Atrial fibrillation
• Severe lung parenchyma disease ( eg emphysema, Interstitial Lung Disease (ILD)).
• Retained metallic foreign body

Patients with inoperable CTEPH undergoing BPA

IPD data will not be shared