A pressure-based single beat method for estimation of right ventricular ejection fraction: proof of concept

Abstract

The utility of considering right ventricular (RV) contractility and afterload as independent entities and summarising their balance or "coupling" using single beat methods has become widely appreciated [1][2][3]. Typically expressed as the ratio of end-systolic ventricular elastance (Ees, a load-independent measure of contractility), to arterial elastance (Ea, a lumped parameter measure of afterload) data suggest that when Ees/Ea reaches a critical threshold, the risk of cardiovascular decompensation begins to rise [4].Pressure-based single beat methods have two central features: prediction of Pmax, the theoretical pressure generated within the RV if contraction remained isovolumic, and definition of end-systolic pressure (ESP). These variables are then used to calculate Ees as (Pmax−ESP)/SV, and Ea as ESP/SV, where SV is the stroke volume. However, it remains unclear what a "normal" RV Ees/Ea value is, due in part to variation in how ESP is defined [5,6], a consideration highlighted in a recent clinical study comparing single and multi-beat determination of Ees/Ea [7]. Additionally, directly relating Ees/Ea to right ventricular ejection fraction (RVEF), a variable clinicians are more familiar with, is challenging. RVEF has been repeatedly shown to predict outcomes in patients with severe pulmonary hypertension (PH) [8], and while cardiac magnetic resonance imaging (cMRI) or three-dimensional echocardiography allow for direct measurement of RVEF, they are not routinely used for repeated measurement of RVEF during a clinically indicated right heart study. The present proof of concept study was designed to test the hypothesis that a method using readily available software and based entirely on analysis of the right ventricular pressure (RVP) waveform can effectively track acute changes in RVEF.Archived measurements of RVP and RV volume provided by conductance/micromanometer catheter were retrospectively analysed. Data had been acquired from 15 anaesthetised swine (∼55 kg) under Institutional Animal Care and Use Committee-approved protocols and in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. Prospective clinical data were acquired under a protocol approved by the Yale Human Investigation Committee. Input signals were sampled at 200 Hz and measured reference values for RVEF calculated from beat-to-beat RV volume as SV/end-diastolic volume. Experimental data had been recorded before and during interventions to alter RV afterload alone or in combination with inotropic depression or augmentation.The Dynamic Fit Wizard within SigmaPlot (version 13, Systat Software, Inc., San Jose, CA) was used to predict Pmax with a distribution function (the 4 parameter Weibull peak fit). In a pilot study involving 15 RVP waveforms with peak pressures ranging from ∼20 to 50 mmHg, the distribution function was found to yield Pmax values that were within 3±7 mmHg of those derived using a more conventional sinusoidal function (figure 1a). For ejection fraction estimation, an alternativ...

Dynamic right ventricular function response to incremental exercise in pulmonary hypertension

“…Because RV pressure waveforms were not available for all patients for conventional single beat analysis, a load-adjusted RV function, an alternative method based upon stroke work index (SWI) and PA elastance, Ea was developed based upon experimental pressure/volume data used in a previous study. 18 Briefly, archived measurements of RV pressure and RV volume, provided by a 5 Fr conductance/micromanometer catheter, and mPAP were used to define the relationship between SWI/Ea and RV–PA coupling (Ees/Ea) derived from both single beat and multi-beat methods. 18 Data had been acquired from 12 anesthetized swine (∼55 kg) under IACUC-approved protocols and in accordance with the NIH Guide for the Care and Use of Laboratory Animals.…”

When it all comes down to pressure: right ventricular ejection fraction at cardiac catheterisation

“…The theoretical hyperbolic decrease in EF with decreased Ees/Ea and progression from maladaptation to failure in pulmonary hypertension patients is illustrated in figure 1. Taken into account the error on the estimate determined by HEERDT et al [1] from animal experiments, there is a zone of uncoupling which actually corresponds to either higher EF or lower Ees/Ea than previously determined from direct measurements in pulmonary hypertensive patients [18]. This is possibly explained by the assumption of linearity of the ESP/ESV relationship leading to unrealistic unstressed volume extrapolation [7].…”

“…In the present issue of the European Respiratory Journal, HEERDT et al [1] report on the validation of right ventricularejection fraction (RVEF) calculated from a pressure curve at cardiac catheterisation. This is of great interest as right ventricular (RV) function is the main determinant of symptomatology and outcome in pulmonary hypertension [2], and RVEF accordingly adds significantly to risk stratification in these patients [3].…”

“…HEERDT et al [1] validated this pressure-only measurement of EF in 15 anaesthetised swine with RVEF ranging from 18 to 59% by manipulation of afterload or pharmacological interventions and in six patients, three with heart failure and three with pulmonary arterial hypertension (PAH) with RVEF ranging from 30 to 70%, who underwent standard diagnostic right heart catheterisations and magnetic resonance imaging [1]. Based on the experimental animal data, the prediction of EF from RV pressure curves was very good, with (in absolute values of EF) a small bias of −2% and limits of agreement of −9 to +13%, reduced to −3 to +7% when corrected for repeated measures.…”

“…In conclusion, measurement of RVEF is critically important to guide therapies in pulmonary hypertension. HEERDT et al [1] are to be commended for showing that this information can be obtained by RV pressure analysis at right heart catheterisation. The method will require automation in order to be routinely applicable in the catheterisation laboratory, and needs further validation against the gold standard of magnetic resonance imaging.…”