Diastolic right ventricular (RV) function has recently been shown to be of high clinical and prognostic relevance in patients with pulmonary arterial hypertension (PAH). However, current methods to determine accurate measures of diastolic stiffness require the same-day completion of a right heart catheterization (RHC) combined with cardiac magnetic resonance imaging (CMR) and rely on assumptions about RV volume at zero pressure (V0). We investigated the feasibility of determining a clinically meaningful measure of RV diastolic stiffness from a standard RHC without advanced imaging.
Treatment-naïve PAH patients (n=31, 55±12 years, 26 female/5 male) were initiated on parenteral treprostinil therapy and after 3 months, underwent same-day RHC and CMR. Diastolic stiffness coefficient, β, was estimated by fitting the end-diastolic pressure-volume relationship (EDPVR), P=α(eβV-1) to both pressure points (0, beginning diastolic pressure, end-diastolic pressure) and volume points: (V0, end-diastolic volume (EDV)–stroke volume (SV), and EDV). SV was calculated from cardiac output and heart rate (SVRHC) or the difference between EDV and end-systolic volume (SVCMR). Bland-Altman analysis was used to compare β when V0 = 0 (Figure 1A) or estimated using single-beat analysis (Figure 1B).
Using CMR-derived stroke volumes, average β was similar under conditions when V0 equals zero (0.047±0.022 ml-1; SVCMR, V0=0) as well as when V0 was calculated (0.049 ± 0.021 ml-1; SVCMR, V0). The bias and confidence intervals (CI) were 0.002 ml-1 and -0.002-0.006 ml-1, respectively (Figure 1C). Using SVRHC, average β was also similar whether V0=0 (0.043±0.019 ml-1) or was calculated (0.045±0.018 ml-1). The latter bias and CI were 0.002 ml-1 and (-0.002-0.006 ml-1). SV significantly influenced estimates of β whether V0=0 (Figure 1D) or was calculated (bias: -0.005, CI: -0.03-0.02).
In contrast to V0, the current study suggests that stroke volume contributes to the precision but not the accuracy of calculating RV diastolic stiffness.