The study aim to assess right atrial (RA) remodeling, in terms of RA fibrosis, in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension patients. This will be investigated in detail with in-depth cardiac magnet resonance imaging (CMRI). A cohort with exclusion of pulmonary hypertension which underwent CMRI due to dyspnoe of unkown reason will be the control group.

Right atrial (RA) function consists of a reservoir, conduit, and active contractile function and can serve as a tool for the evaluation of the severity of RV dysfunction and prognosis in pulmonary hypertension according to recent data. In-depth evaluation of phasic RA function was previously undertaken either by echocardiographic speckle tracking or by cardiac magnetic resonance (CMR) imaging-derived feature tracking. However, it is currently unknown if right atrial remodeling is present.

As described for left atrial fibrosis, the presence and extent of atrial fibrosis can be quantified using CMR late gadolinium enhancement. The protocol for the assessment of left atrial fibrosis will be used and adapted to the RA. Patients will undergo 3-dimensional late gadolinium enhancement CMRI along with a contrast-enhanced magnetic resonance angiography and cine imaging in order to define the anatomy of the RA and the superior and inferior vein. High-resolution late gadolinium enhancement images of the RA will be acquired 15 to 30 min after gadolinium-based contrast agents administration using a 3-dimensional inversion-recovery prepared, respiration navigated, and electrocardiogram triggered gradient-echo pulse sequence with fat saturation. Following acquisition of the scans, the endocardial borders of the RA will be defined in each slice by manual tracing. After manual adjustment of the epicardial RA surface, the quantification of fibrosis based on the relative intensity (signal intensity) of late gadolinium enhancement will be performed. Finally, a 3-dimensional model of the RA will be rendered with the maximum enhancement intensities being projected on the model surface.

Inclusion Criteria:

• Confirmed diagnosis of pulmonary arterial hypertension, WHO group 1 or chronic thromboembolic pulmonary hypertension, group 4
• Invasive exclusion of pulmonary hypertension
• Age ≥ 18 years
• Signed informed consent
• planned right heart catheterization based on clinical grounds

Exclusion Criteria:

• Other etiologic groups of pulmonary hypertension (WHO group 2, 3, 5)
• Patients with congenital heart disease
• Atrial septal defects
• Clinical relevant left heart disease
• Atrial fibrillation / Atrial flutter
• Ablations of the right atrium
• History of major cardiac surgery
• Atrial occlude
• Metallic implants
• Pacemakers
• Severe renal impairment (eGFR < 30 ml/min)
• Other severe disease with a life expectancy below 12 month
• Pregnancy
• Any known factor or disease that might interfere with treatment compliance, study conduct, or interpretation of results
• Intolerance to a contrast agent containing gadolinium
• Inability to perform a cardiac magnetic resonance imaging (claustrophobia or similar)

40 subjects with pulmonary arterial hypertension, group 1 and chronic thromboembolic pulmonary hypertension, group 4; Patients with invasive exclusion of pulmonary hypertension undergoing diagnostic right heart catheterisation due to dyspnoe will serve as control

Upon reasonable request