Non-invasive myocardial work in aortic stenosis: validation and improvement in left ventricular pressure estimation

Abstract

Aims: The non-invasive myocardial work index (MWI) has been validated in patients without aortic stenosis (AS). A thorough assessment of methodological limitations is warranted before this index can be applied to patients with AS.

Methods and results: We simultaneously measured left ventricular pressure (LVP) by using a micromanometer-tipped catheter and obtained echocardiograms in 20 patients with severe AS. We estimated LVP curves and calculated pressure-strain loops using three different models: (i) the model validated in patients without AS; (ii) the same model, but with pressure at the aortic valve opening (AVO) adjusted to diastolic cuff pressure; and (iii) a new model based on the invasive measurements from patients with AS. Valvular events were determined by echocardiography. Peak LVP was estimated as the sum of the mean aortic transvalvular gradient and systolic cuff pressure. In same-beat comparisons between invasive and estimated LVP curves, Model 1 significantly overestimated early systolic pressure by 61 ± 5 mmHg at AVO compared with Models 2 and 3. However, the average correlation coefficients between estimated and invasive LVP traces were excellent for all models, and the overestimation had limited influence on MWI, with excellent correlation (r = 0.98, P < 0.001) and good agreement between the MWI calculated with estimated (all models) and invasive LVP.

Conclusion: This study confirms the validity of the non-invasive MWI in patients with AS. The accuracy of estimated LVP curves improved when matching AVO to the diastolic pressure in the original model, mirroring that of the AS-specific model. This may sequentially enhance the accuracy of regional MWI assessment.

Keywords: aortic stenosis; myocardial function; myocardial work index; valvular heart disease.

Graphical Abstract

Synopsis of the study design, key findings, and conclusions. Estimations and calculations based on Model 1 (red-dashed line) and Model 2 (blue-dashed line), where the pressure at AVO is adjusted to the diastolic cuff pressure and invasively measured LVP (grey line). AVC, aortic valve closure; AVO, aortic valve opening; MVC, mitral valve closure; MVO, mitral valve opening; LVP, left ventricular pressure; STE, speckle-tracking echocardiography.

Figure 1

Normalized pressure reference curve. (A) Invasive left ventricular pressure traces from patients with aortic stenosis. Valvular events: circle, mitral valve closure; square, aortic valve opening; diamond, aortic valve closure; triangle, mitral valve opening. (B) Traces from A are normalized (light grey curves) and averaged (blue curve) with the corresponding valvular events.

Figure 2

Reference curves and estimation models. (A) The original reference curve used previously in patients without aortic stenoisis shown together with the new aortic stenosis–specific reference curve, where phase intervals were set to the average for the patients. Notice that the pressure at AVO relative to peak pressure is substantially lower in patients with aortic stenosis. Furthermore, the reference curves differ in length/duration, reflecting increased ejection times in aortic stenosis patients. (B) Estimated LVP (all three models) compared with invasive LVP (representative patient). Estimations differ mainly around the time of AVO. Early systolic pressure overestimation with the original reference curve is corrected when AVO is adjusted vertically to diastolic pressure, illustrated in Panel 2. Arrows mark adjustment to AVO. AVC, aortic valve closure; AVO, aortic valve opening; MVC, mitral valve closure; MVO, mitral valve opening; LVP, left ventricular pressure.

Figure 3

Schematic illustration of the estimated pressure–strain loop area. (A) Pressure–strain loop ‘closed’ in diastole with a straight (blue) line from MVO to MVC. (B) Pressure–strain loop when assuming zero pressure during filling shown with vertical blue lines from MVO and MVC down to the x-axis. The blue-coloured area illustrates the small relative difference in loop area if filling pressure, in a thought scenario, increases from 10 to 20 mmHg. MVC, mitral valve closure; MVO, mitral valve opening.

Figure 4

Comparison and accuracy of LVP curve estimation. (A and B) Compare measured (continuous line) and estimated LVP (dashed line) traces and point-by-point correlation from a representative patient illustrating the difference in LVP estimations with different reference curves. (C) The agreement between estimated and measured LVP (for all the patients) with the mean difference shown as a thick bright red line. Note the improvement of early systolic pressure estimation following AVO pressure adjustment (1C vs. 2C). AVO, aortic valve opening; LVP, left ventricular pressure.

Figure 5

Correlation and agreement of MWI based on invasive and estimated LVP curves. (A and B) Correlation and agreement for MWI as represented by pressure–strain loop areas calculated with measured and estimated LVP. (C) Pressure–strain loops from a selected patient, calculated with estimated (dashed line) and measured LVP (continuous line). AVO, aortic valve opening; LVP, left ventricular pressure; STE, speckle-tracking echocardiography.

Figure 6

Difference in MWI. (A) Agreement between estimated and measured MWI for all three models as a function of time. (B) The cumulative difference in MWI estimations as a function of time. The mean value is depicted with a red line. AVC, aortic valve closure; AVO, aortic valve opening; MVC, mitral valve closure; MVO, mitral valve opening; MWI, myocardial work index.

Figure 7

MWI analysis with and without AVO pressure-adjusted reference curve. Regional analysis of MWI in two patients with severe aortic stenosis and an ischaemic region (upper panel) and a dyssynchronous region (lower panel). (A) Estimated LVP curves and recorded strain trace. (B) Strain–pressure loops with direction of systolic motion marked with arrows. (C) MWI as a function of time. Estimations with (blue-dashed line) and without (red-dashed line) AVO pressure adjustment. Regional longitudinal strain (green line). AVO, aortic valve opening; MWI, myocardial work index; LVP, left ventricular pressure.