Aortic valve morphology influences regurgitant volume in aortic regurgitation: in vitro evaluation

Effect of three-dimensional valve shape on the hemodynamics of aortic stenosis: three-dimensional echocardiographic stereolithography and patient studies

OBJECTIVES

This study tested the hypothesis that the impact of a stenotic aortic valve depends not only on the cross-sectional area of its limiting orifice but also on three-dimensional (3D) valve geometry.

BACKGROUND

Valve shape can potentially affect the hemodynamic impact of aortic stenosis by altering the ratio of effective to anatomic orifice area (the coefficient of orifice contraction [Cc]). For a given flow rate and anatomic area, a lower Cc increases velocity and pressure gradient. This effect has been recognized in mitral stenosis but assumed to be absent in aortic stenosis (constant Cc of 1 in the Gorlin equation).

METHODS

In order to study this effect with actual valve shapes in patients, 3D echocardiography was used to reconstruct a typical spectrum of stenotic aortic valve geometrics from doming to flat. Three different shapes were reproduced as actual models by stereolithography (computerized laser polymerization) with orifice areas of 0.5, 0.75, and 1.0 cm(2) (total of nine valves) and studied with physiologic flows. To determine whether valve shape actually influences hemodynamics in the clinical setting, we also related Cc (= continuity/planimeter areas) to stenotic aortic valve shape in 35 patients with high-quality echocardiograms.

RESULTS

In the patient-derived 3D models, Cc varied prominently with valve shape, and was largest for long, tapered domes that allow more gradual flow convergence compared with more steeply converging flat valves (0.85 to 0.90 vs. 0.71 to 0.76). These variations translated into differences of up to 40% in pressure drop for the same anatomic area and flow rate, with corresponding variations in Gorlin (effective) area relative to anatomic values. In patients, Cc was significantly lower for flat versus doming bicuspid valves (0.73 +/- 0.14 vs. 0.94 +/- 0.14, p < 0.0001) with 40 +/- 5% higher gradients (p < 0.0001).

CONCLUSIONS

Three-dimensional valve shape is an important determinant of pressure loss in patients with aortic stenosis, with smaller effective areas and higher pressure gradients for flatter valves. This effect can translate into clinically important differences between planimeter and effective valve areas (continuity or Gorlin). Therefore, valve shape provides additional information beyond the planimeter orifice area in determining the impact of valvular aortic stenosis on patient hemodynamics.

Measurement of aortic valve anatomic regurgitant area using transesophageal echocardiography: implications for the quantitation of aortic regurgitation

BACKGROUND

Various echocardiographic methods for the assessment of the severity of the aortic regurgitation (AR) by have been described with no general consensus.

AIM

To assess the feasibility and reproducibility of direct planimetric measurement of the end-diastolic gap between aortic cusps on the transesophageal echocardiography (TEE) images in patients with AR. We also analyzed the correlation of this anatomic aortic regurgitanty area with angiographic AR severity.

METHODS

Ninety patients (38 males, 52 females, mean age 41 +/- 24 years) with AR who underwent TEE and contrast aortography in a single institution. The AR was graded angiographically as mild (n = 45), moderate (n = 31), and severe (n = 14). The anatomic regurgitant area was measured on the end-diastolic short-axis TEE images of the aortic valve by planimetering the central gap bordered by the commisural edges of the aortic cusps.

RESULTS

The intraobserver and interobserver variability for the measurement of aortic anatomic regurgitant area were small (mean absolute differences 0.01 +/- 0.01 cm(2), and 0.015 +/- 0.013 cm(2), respectively). The average values of anatomic regurgitant area for angiographically mild, moderate, and severe AR were 0.15 +/- 0.05 cm(2), 0.30 +/- 0.08 cm(2), and 0.68 +/- 0.33 cm(2), respectively (P <.001). When the anatomic regurgitant area was graded as small (> 0.2 cm(2)), moderate (> 0.2 and > 0.4 cm(2)) and large (> 0.4 cm(2)), the sensitivity, specificity, positive and negative predictive value, and the diagnostic accuracy for predicting the angiographically mild AR were 85%, 97%, 97%, 87%, and 91%, respectively. For the moderate angiographic AR the same values were 84%, 92%, 81%, 93%, and 90%, and for the severe angiographic AR they were 98%, 93%, 93%, 98% and 97%.

CONCLUSION

The planimetric measurement of aortic anatomic regurgitant area by TEE is feasible and reproducible for the assessment of the severity of AR.

Assessment of aortic regurgitation by transesophageal color Doppler imaging of the vena contracta: validation against an intraoperative aortic flow probe

OBJECTIVES

This study was performed to validate the accuracy of color flow vena contracta (VC) measurements of aortic regurgitation (AR) severity by comparing them to simultaneous intraoperative flow probe measurements of regurgitant fraction (RgF) and regurgitant volume (RgV).

BACKGROUND

Color Doppler imaging of the vena contracta has emerged as a simple and reliable measure of the severity of valvular regurgitation. This study evaluated the accuracy of VC imaging of AR by transesophageal echocardiography (TEE).

METHODS

A transit-time flow probe was placed on the ascending aorta during cardiac surgery in 24 patients with AR. The flow probe was used to measure RgF and RgV simultaneously during VC imaging by TEE. Flow probe and VC imaging were interpreted separately and in blinded fashion.

RESULTS

A good correlation was found between VC width and RgF (r = 0.85) and RgV (r = 0.79). All six patients with VC width >6 mm had a RgF >0.50. All 18 patients with VC width <5 mm had a RgF <0.50. Vena contracta area also correlated well with both RgF (r = 0.81) and RgV (r = 0.84). All six patients with VC area >7.5 mm2 had a RgF >0.50, and all 18 patients with a VC area <7.5 mm2 had a RgF <0.50. In a subset of nine patients who underwent afterload manipulation to increase diastolic blood pressure, RgV increased significantly (34 +/- 26 ml to 41 +/- 27 ml, p = 0.042) while VC width remained unchanged (5.4 +/- 2.8 mm to 5.4 +/- 2.8 mm, p = 0.41).

CONCLUSIONS

Vena contracta imaging by TEE color flow mapping is an accurate marker of AR severity. Vena contracta width and VC area correlate well with RgF and RgV obtained by intraoperative flow probe. Vena contracta width appears to be less afterload-dependent than RgV.

Progressive enlargement of the regurgitant orifice in patients with chronic aortic regurgitation

The severity of aortic regurgitation is dependent on the size of the regurgitant orifice, the left ventricular response to volume overload, and the diastolic pressure difference across the aortic valve. The purpose of this study was to test the hypothesis that the aortic regurgitant orifice increases over time in patients with audible chronic aortic regurgitation. To assess serial changes in aortic regurgitant severity by the use of two-dimensional and Doppler echocardiography, 59 patients (29 men and 30 women) with audible chronic aortic regurgitation were prospectively identified and evaluated annually with two-dimensional and Doppler echocardiograms. Patients were followed for a median of 38 months. We measured two separate indicators of the size of the regurgitant orifice: the color Doppler regurgitant jet width and the Doppler-derived regurgitant orifice area. Jet width increased with time (0.5 +/- 0.4 cm at baseline, 0.04 +/- 0.01 cm/year slope, p < 0.001). The regurgitant orifice area also increased (0.12 +/- 0.14 cm2 at baseline, 0.01 +/- 0.01 cm2/year, p = 0.05). Changes in regurgitant orifice area were related to changes in left ventricular end-diastolic dimension (p < 0.001). There were no significant changes in left ventricular chamber dimensions, volumes, and regurgitant volume over time in this cohort. Increases in jet width and orifice area occurred in patients with all degrees of baseline disease severity, with bicuspid or tricuspid leaflet morphology, and with male or female sex. In this prospective study of chronic aortic regurgitation, both jet width and Doppler-derived regurgitant orifice area increased over time. These findings suggest that one factor in the progression of chronic aortic regurgitation is enlargement of the orifice.

Insights from three-dimensional echocardiographic laser stereolithography. Effect of leaflet funnel geometry on the coefficient of orifice contraction, pressure loss, and the Gorlin formula in mitral stenosis

BACKGROUND

Three-dimensional echocardiography can allow us to address uniquely three-dimensional scientific questions, for example, the hypothesis that the impact of a stenotic valve depends not only on its limiting orifice area but also on its three-dimensional geometry proximal to the orifice. This can affect the coefficient of orifice contraction (Cc = effective/anatomic area), which is important because for a given flow rate and anatomic area, a lower Cc gives a higher velocity and pressure gradient, and Cc, routinely assumed constant in the Gorlin equation, may vary with valve shape (60% for a flat plate, 100% for a tube). To date, it has not been possible to study this with actual valve shapes in patients.

METHODS AND RESULTS

Three-dimensional echocardiography reconstructed valve geometries typical of the spectrum in patients with mitral stenosis: mobile doming, intermediate conical, and relatively flat immobile valves. Each geometry was constructed with orifice areas of 0.5, 1.0 and 1.5 cm2 by stereolithography (computerized laser polymerization) (total, nine valves) and studied at physiological flow rates. Cc varied prominently with shape and was larger for the longer, tapered dome (more gradual flow convergence proximal and distal to the limiting orifice): for an anatomic orifice of 1.5 cm2, Cc increased from 0.73 (flat) to 0.87 (dome), and for an area of 0.5 cm2, from 0.62 to 0.75. For each shape, Cc increased with increasing orifice size relative to the proximal funnel (more tubelike). These variations translated into important differences of up to 40% in pressure gradient for the same anatomic area and flow rate (greatest for the flattest valves), with a corresponding variation in calculated Gorlin area (an effective area) relative to anatomic values.

CONCLUSIONS

The coefficient of contraction and the related net pressure loss are importantly affected by the variations in leaflet geometry seen in patients with mitral stenosis. Three-dimensional echocardiography and stereolithography, with the use of actual information from patients, can address such uniquely three-dimensional questions to provide insight into the relations between cardiac structure, pressure, and flows.

Dynamic change in mitral regurgitant orifice area: comparison of color Doppler echocardiographic and electromagnetic flowmeter-based methods in a chronic animal model

OBJECTIVES

The aim of the present study was to investigate dynamic changes in the mitral regurgitant orifice using electromagnetic flow probes and flowmeters and the color Doppler flow convergence method.

BACKGROUND

Methods for determining mitral regurgitant orifice areas have been described using flow convergence imaging with a hemispheric isovelocity surface assumption. However, the shape of flow convergence isovelocity surfaces depends on many factors that change during regurgitation.

METHODS

In seven sheep with surgically created mitral regurgitation, 18 hemodynamic states were studied. The aliasing distances of flow convergence were measured at 10 sequential points using two ranges of aliasing velocities (0.20 to 0.32 and 0.56 to 0.72 m/s), and instantaneous flow rates were calculated using the hemispheric assumption. Instantaneous regurgitant areas were determined from the regurgitant flow rates obtained from both electromagnetic flowmeters and flow convergence divided by the corresponding continuous wave velocities.

RESULTS

The regurgitant orifice sizes obtained using the electromagnetic flow method usually increased to maximal size in early to midsystole and then decreased in late systole. Patterns of dynamic changes in orifice area obtained by flow convergence were not the same as those delineated by the electromagnetic flow method. Time-averaged regurgitant orifice areas obtained by flow convergence using lower aliasing velocities overestimated the areas obtained by the electromagnetic flow method ([mean +/- SD] 0.27 +/- 0.14 vs. 0.12 +/- 0.06 cm2, p < 0.001), whereas flow convergence, using higher aliasing velocities, estimated the reference areas more reliably (0.15 +/- 0.06 cm2).

CONCLUSIONS

The electromagnetic flow method studies uniformly demonstrated dynamic change in mitral regurgitant orifice area and suggested limitations of the flow convergence method.

Hemodynamic assessment of aortic stenosis

The decision to operate in patients with aortic stenosis is based on the presence of symptoms and hemodynamically significant valvular obstruction. The strengths and limitations of cardiac catheterization and Doppler echocardiography are compared, and the concept of "critical" aortic stenosis is discussed. The recommendation of aortic valve replacement must take into account the symptom status, the hemodynamic significance of the lesion, and the size and type of valve to be implanted.