Combined magnetic resonance and positron emission tomography imaging of the right ventricle to assess disease severity in arterial pulmonary hypertension.

Background: Pulmonary arterial hypertension (PAH) is defined by a mean pulmonary arterial pressure (mPAP) higher than 25 mmHg at rest in the presence of a normal wedge pressure at right heart catheterization. Absolute levels of mPAP and pulmonary vascular resistance (PVR) are commonly used to measure hemodynamic impairment and define short term prognosis in these patients. Mixed venous oxygen saturation (Sv02) commonly expresses disease severity. Aim of the study was to assess whether the extent of the pulmonary hemodynamic impairment and disease severity in PAH can be predicted by right ventricular mass index (RVMI) and myocardial blood flow (MBF) as non-invasive indicators of RV overload frorn magnetic resonance imaging (MRI) and positron emission tomography (PET). Methods: Twenty-four patients with moderate-severe PAH (19 females, age 54±15 yrs, mPAP 42±1 OmmHg, wedge pressure 6±3 mmHg) were evaluated by right heart catheterization, MRI and PET within 6 days. PAH was idiopathic (N=8), postembolic (N=9) or associated with scleroderma (N=7). At time of catheterization, mPAP, PVR and arterial blood gases were measured. RV mass index (MI) and ejection fraction (EF) were obtained from MRI study. RV myocardial blood flow (MBF) was measured at rest by PET and 13N-Ammonia as a flow tracer. Results: In PAH patients, RVMI was directly related with mPAP (r 0.48, P<0.05) or PVR (r 0.58, P<0.01) and inversely related with Sv02 (r -0.52, P<0.05). RV MBF was not related with mPAP and PVR and was inversely related with RVMI (r -0.57, P