Myocardial changes in the right ventricular insertion point and septum have been identified with late gadolinium enhancement MRI in patients with pulmonary hypertension and this is associated with disease advancement [1]. Additionally, animal models of pulmonary hypertension demonstrate elevated native T1 and late gadolinium enhancement in the right ventricular insertion point, which correlated with right ventricular remodelling and function metrics [2].The motivation of this study was to establish whether patients with pulmonary hypertension had elevated T1 indicating myocardial changes, and to establish whether T1 correlated with and invasive catheter measurements and established functional cardiac MRI markers of RV remodelling.

All patients and volunteers underwent cardiac MR and MOLLI (modified Look-Locker inversion recovery) sequences on a 1.5 T GE scanner. 141 patients with pulmonary hypertension were recruited from a National clinical referral centre underwent MRI and right heart catheter measurement of mean pulmonary artery pressure and pulmonary vascular resistance.

Acquired MOLLI images were registered for cardiac motion using pair-wise image registration to synthetic images based on the method of Xue et al [3]. Regions of interest were drawn manually on each post-registration T1 map in the right ventricular free wall, right ventricular insertion point and ventricular septum from a short axis slice of the heart. Regions of interest were small, central and conservative to eliminate partial volume effects (see Figure 1). Cardiac MR volume, mass and function measurements were recorded and were corrected for age, sex and BSA.

112/141 patients and 34/34 healthy volunteers were successfully imaged and analysed, of the 26/29 patients whose data was not useful the primary cause was inability of the algorithm to effectively register the images, the remainder were significantly affected by image artefact. 100/112 patients had a diagnosis of PH and were included in subsequent analysis.

Healthy volunteer T1 values were consistent with previously published values (right ventricular insertion point T1 =0.93±0.07s, septal T1 =0.94±0.08s) [5], see Figure 2. In patients with PH T1 was significantly elevated in the right ventricular insertion points (T1= 1.00±0.11s, p<0.001), and left ventricular free wall (T1=0.90±0.12s, p=0.013), compared to healthy volunteers, see Figure 3. Right ventricular free wall was found to be 0.95±0.16s in patients with pulmonary hypertension.

Right ventricular insertion point T1 correlated significantly with load independent arterial elastance (r=0.406, p=0.016), pulmonary arterial right ventricular coupling ( $$$ Elastance(Ea)/Contactility(Emax) $$$ ) (r=0.361, p=0.036) and mean pulmonary artery pressure (r=0.374, p=0.025), among patients with PH and a right heart catheter within 24 hours of cardiac MRI (n=35).

A strong positive correlation was found with RVFW and patient age (r=0.389, p<0.001, see Figure 4). RVFW T1 and septal T1 correlated positively with age and sex corrected RV diastolic mass index (r=0.305, p=0.003 and r=0.281, p=0.006 respectively). No other correlations were found between myocardial T1 and cardiac MR measures of function and remodelling.

Septal (100/100), LV free wall (92/100) and RV insertion point T1 (98/100) could be measured in the majority of patients. RV free wall could be reliably measured in patients (97/100), but was found to be in accurate in healthy volunteers, likely because the free wall of healthy volunteers is thin and poorly spatially resolved.

Patients with pulmonary hypertension had elevated T1 in the right ventricular insertion point and left ventricular free wall. RV free wall was measured in 97/100 patients using small regions of interest to be 0.95±0.16s. Right ventricular free wall was not measured in healthy volunteers due to poor spatial resolution of the RV free wall.

Significant correlations were found between RV insertion point T1 and mean pulmonary artery pressure, and load-independent measures of elastance and right ventricular-pulmonary arterial coupling. A strong correlation was found between RF free wall T1 and age which may indicate normal age related alterations in RV myocardial tissue characteristics with advancing age; an alternative explanation is poor adaption of the RV with RV fibrosis as a result of elevated afterload in older subjects who typically have worse outcome.

Both RV free wall T1 and interventricular septal T1 correlated with RV mass, which may indicate that T1 most closely reflects myocardial hypertrophy and provides less information of RV volume or function.