Introduction: Right ventricular (RV) function is a major determinate of mortality in patients with pulmonary arterial hypertension (PAH). RV coupling obtained from full conductance derived pressure-volume (PV) loops are difficult to obtain in clinical settings. Thus, simplified methods have been introduced but are limited as they rely on end-diastolic (ED) and end-systolic (ES) volumes. Presented is a novel method to measure full PV loops using cardiac magnetic resonance (CMR) images to generate volumetric data. We hypothesize that it is feasible to generate full clinical PV loops from CMR images to more accurately measure RV coupling than simplified methods.
Methods: PV loops were generated in 9 subjects (5 control, 4 PAH) who had a CMR exam and right heart catheterization (RHC) within 48 hours. RV volumes were derived by propagating manually traced RV endocardium in the ED and ES frames throughout the cardiac cycle using an automated dynamic programming technique (Fig. 1A). RV volumes were matched with RHC-measured RV pressure using linear interpolation. Treatment naïve patients underwent repeat RHC/CMR following the initiation of parenteral treprostinil.
Results: PAH patients demonstrated increased mean pulmonary arterial pressure (mPAP) (57 ± 10 mmHg vs 20 ± 5 mmHg) and decreased RV ejection fraction (RVEF) (26 ± 11% vs 55 ± 4%) when compared to controls. Representative PV loops for a control and a moderate PAH (middle) and severe PAH (right) demonstrate the late-systolic increase in RV pressure, previously observed using conductance catheters (Fig. 1B). The response to treprostinil therapy (Figs. 1C-D) consisted of a decrease in mPAP, an increase in RVEF and a patient-specific change in RV volumes. ES and ED volumes decreased in (Fig. 1C) but only the ES volume decrease in (Fig. 1D).
Conclusion: Full RV PV loops obtained by our CMR-RHC method show the contour is significantly altered in PAH; this is not easily estimated using the simplified rectangular PV loop approach.