Cardiac MRI Differentiates Classical Idiopathic Pulmonary Arterial Hypertension from Lung Phenotype and Group 3 Pulmonary Hypertension

Practical application of the classification of pulmonary hypertension (PH) occasionally presents challenges, particularly for idiopathic pulmonary arterial hypertension (iPAH) with a lung phenotype, which can overlap with group 3 PH. This study aimed to evaluate cardiac MRI as a discriminatory tool between classical iPAH, iPAH with a lung phenotype and group 3 PH. This retrospective study included incident patients diagnosed with iPAH or group 3 PH referred to a PH reference center. All included patients underwent cardiac MRI, right heart catheterization, and chest computed tomography within 48 hours of diagnosis. The analysis included 34 patients, 11 with classical iPAH, 11 with iPAH and a lung phenotype (per predefined criteria) and 12 with group 3 PH (7 with chronic obstructive pulmonary disease and 5 with interstitial lung disease). No significant differences were observed regarding ventricular functions and flow rates. T1 mapping values in the interventricular septum and inferior ventricular insertion point were significantly higher in patients with classical iPAH compared to patients with iPAH and a lung phenotype (1305 [1234 – 1365] ms versus 1210 [1194 – 1251] ms, p=0.028 and 1398 [1355 – 1604] ms versus 1229 [1201 – 1289] ms, p=0.007, respectively. T1 mapping measurements were similar in the iPAH and a lung phenotype compared to group 3. cardiac MRI with T1 mapping, specifically targeting fibrotic areas, effectively discriminated classical iPAH and iPAH and a lung phenotype. These MRI measurements revealed divergent patterns that could explain the different treatment responses and prognoses observed across these PH subtypes. This trial was registered before inclusion and analyses in www.clinicaltrial.gov (NCT05624242).