Abstract 13470: RV Ejection Efficiency Measured in the Phasic Pulmonary Flow; a CMR Approach in PAH

Introduction: Measurements of RV function, such as RVEF and RV-measured ventricular-vascular coupling (VVC), maybe important in predicting survival in PAH, but are dependent on load and mathematical assumptions. However, independent measures, such as flow efficiency (FEI) within the main PA may be better predictors. FEI is dependent on the natural ratio between MPA area to pulsatile blood wavelength (λ), where λ is proportional to the product of λ velocity and the pulse time, but is difficult to measure directly. Hypothesis: We hypothesize pulmonary FEI will correlate with the VVC and RVEF. Methods: CMR was performed on 18 pts with PAH to assess RV function. Eight pts additionally underwent RV CMR during physiologic stressors: 1) inhaled NO 2) dobutamine (20μ/kg/min) and 3) volume challenge (500ml NaCl). MPA flow was measured via phase velocity mapping (PVM). The RVEF, VVC ratio and ejection time (ET) were calculated from CMR. The MPA area was measured from the PVM images along with avg velocity (Vel avg . Pulmonary FEI = (average Vel avg x ET) / MPA area. Results: A total of 38 unique measures of RVEF (52±12%), VVC (0.89±.3) and MPA flow conditions were measured: Vel avg (49±15cm/s), MPA area (51±11mm 2 ) and ET (295±61ms). The FEI correlated with RVEF and VVC via log term: RVEF = 11.5 log nat (FEI) + 37.2; and VVC = 0.34 log nat (FEI) + 1.17.Bland-Altman analysis of the measured RVEF vs. the FEI modeled RVEF (Fig 1) has an offset bias of 0, a four SD range of ±14.4; r=0. 0.8, while the measured VVC vs. modeled has a bias of 0 and a 4 SD range of ± 0.45; r = 0.74. Conclusions: The linear combination of average pulmonary blood velocity, ejection time and MPA area combine to form a pulmonary FEI that strongly correlates with RVEF and VVC. Importantly, it is devoid of the afterload/preload assumptions of RVEF and the multitude of assumptions of V 0 and RVEDP in VVC. As such, this index may provide additional clinical value since it reflects the directly measured intrinsic efficiency of integrated RV-PA conditions.