Abstract
Introduction: Patient survival with pulmonary arterial hypertension (PAH) is determined from right ventricular (RV) function. CMR feature tracking (CMR-FT) is used to assess RV function. It is not determined, however, whether CMR-FT can assess RV functional reserve in patients with PAH. Hypothesis: We assessed the hypothesis that CMR-FT can estimate RV functional reserve in rats with PAH. Methods: Rats were received injections with monocrotaline (MCT-rats, n=19) or solvent (Ctr-rats, n=5). After four weeks, retrospective ECG-gated cine MR (16 phases/beat) was imaged using a 7-T MRI scanner, and RVEF, RV global longitudinal strain (RVGLS) and RV global circumferential strain (RVGCS) were measured before and after addition of 0.5~3 nmol endothelin-1 (ET-1). After the measurements, trabeculae were dissected from the RVs and electrically stimulated with 2-s intervals ([Ca 2+ ] o 2.0 mM, 24°C). Force and maximum dF/dt (dF/dt max ) were obtained using a silicon strain gauge in the absence and presence of 0.1 μM ET-1. Results: MCT-rats showed higher RV pressure (RVP), lower RVEF, lower RVGLS, lower developed force and lower dF/dt max . RVGLS showed a liner correlation with dF/dt max (r=0.53, p<0.05) and had already been reduced in 5 MCT-rats with preserved RVEF (>50%), suggesting that RVGLS reflects RV contractile properties and is reduced earlier than RVEF. Addition of ET-1 increased RVP in MCT-rats (49.0±19.3 to 59.7±16.8 mmHg, n=6) and Ctr-rats (17.3±7.5 to 20.4±7.8 mmHg, n=2) and increased developed force and dF/dt max in MCT-rats (12.2±5.7 to 17.4±3.1 mN/mm 2 , 0.08±0.03 to 0.14±0.06 mN/mm 2 /sec, n=6). When MCT-rats with preserved-RVEF (>50%) were divided into 2 groups depending on RVGCS, addition of ET-1 further reduced RVGCS in reduced-RVGCS (>-20%) group but not in increased-RVGCS (<-30%) group, suggesting that RVGCS can reflect RV functional reserve. In addition, ET-1 killed MCT-rats with reduced-RVGCS and reduced-RVEF just after its addition. In contrast, ET-1 did not change RVGCS and RVEF in Ctr-rats. Conclusions: CMR-FT can estimate RV functional reserve earlier and more accurately with RVGLS and RVGCS in rats with PAH. Therefore, RV strain with CMR may become an important parameter to assess RV functional reserve in patients with PAH.
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