Non-Invasive Determination of Left Ventricular Workload in Patients with Aortic Stenosis Using Magnetic Resonance Imaging and Doppler Echocardiography

Abstract

Early detection and accurate estimation of aortic stenosis (AS) severity are the most important predictors of successful long-term outcomes in patients. Current clinical parameters used for evaluation of the AS severity have several limitations including flow dependency. Estimation of AS severity is specifically challenging in patients with low-flow and low transvalvular pressure gradient conditions. A proper diagnosis in these patients needs a comprehensive evaluation of the left ventricle (LV) hemodynamic loads. This study has two objectives: (1) developing a lumped-parameter model to describe the ventricular-valvular-arterial interaction and to estimate the LV stroke work (SW); (2) introducing and validating a new index, the normalized stroke work (N-SW), to assess the global hemodynamic load imposed on the LV. N-SW represents the global hemodynamic load that the LV faces for each unit volume of blood ejected. The model uses a limited number of parameters which all can be measured non-invasively using current clinical imaging modalities. The model was first validated by comparing its calculated flow waveforms with the ones measured using Cardiovascular Magnetic Resonance (CMR) in 49 patients and 8 controls. A very good correlation and concordance were found throughout the cycle (median root mean square: 12.21 mL/s) and between the peak values (r = 0.98; SEE = 0.001, p<0.001). The model was then used to determine SW using the parameters measured with transthoracic Doppler-echocardiography (TTE) and CMR. N-SW showed very good correlations with a previously-validated index of global hemodynamic load, the valvular arterial impedance (), using data from both imaging modalities (TTE: r = 0.82, SEE = 0.01, p<0.001; CMR: r = 0.74, SEE = 0.01, p<0.001). Furthermore, unlike , N-SW was almost independent from variations in the flow rate. This study suggests that considering N-SW may provide incremental diagnostic and prognostic information, beyond what standard indices of stenosis severity and provide, particularly in patients with low LV outflow.

Normalized left ventricular workload using phase-contrast magnetic resonance imaging in patients with aortic stenosis

“…This threshold was used to divide AS patients into two groups (<1.5 cJ/mL and >1.5 cJ/mL which indicates LV load increase due to AS). A For specific values please see references [17] and [18].…”

“…Traditional TTE and CMR imaging methods fail to estimate the LVSW which is typically measured invasively by cardiac catheterization and may cause cerebral embolism [16]. However, we recently introduce and validate a simple lumped-parameter model able to evaluate LVSW using TTE/CMR measurements [17], [18]. We hypothesized that LVSW, as calculated by our model using CMR in-vivo data, may detect LV load alterations due to AS severity.…”

Semiautomated Analysis of Aortic Stenosis Parameters on Velocity-Encoded Phase-Contrast MR Images in Patients with Severe Aortic Stenosis: A Comparison with Echocardiography

“…The VENC PC sequence is an established and non-invasive tool used to quantify the velocity and blood flow based on the accumulated phase of moving protons [14,15]. Previous studies have manually assessed AVA on cine sequences and used in-house or customized software to assess hemodynamic parameters from a VENC PC sequence in valvular stenosis [3,8,[16][17][18]. We only used VENC PC sequences and commercial software for easy access in daily clinical practice.…”

Elimination of Transcoarctation Pressure Gradients Has No Impact on Left Ventricular Function or Aortic Shear Stress After Intervention in Patients With Mild Coarctation

“…Vascular hemodynamic parameters : the systemic arterial compliance (SAC) and the systemic vascular resistance (SVR) (7,17); $$\mathit{SAC}={SV}_i/PP$$ $$\mathit{SVR}=80\mathit{MAP}/CO$$…”

“…All input parameters were obtained from transthoracic echocardiography (TTE) measurements (Table 1). Sub-models have already been used and validated against in vivo MRI data in previous works (7,17,55,56). Moreover, in this study, the lumped parameter model is validated against cardiac catheterization data in thirty-four patients with mild COA (see Figures 3 to 6 for examples).…”