Subaortic Stenosis

by Denisa Muraru, MD, PhD; Patrizia Aruta, MD, Luigi Badano, MD, PhD
Department of cardiac, thoracic and vascular sciences, University of Padua, School of Medicine, Padua, Italy

Clinical Case

  • Female, 51-year-old woman
  • Mild dyspnea on exertion
  • Paroxysmal atrial fibrillation
  • Systolic heart murmur

Two-dimensional echocardiography, with zoom on aortic valve, showing an echo-reflective, linear structure in the LV outflow tract. The aortic valve appears thickened, moderately calcified and with limited systolic opening.

Spectral CW Doppler recording across LV outflow, showing an increased systolic velocity (Vmax = 3.7 m/s) and a dense signal of associated aortic regurgitation.

Color Doppler imaging, showing turbulent ejection flow with acceleration at the level of the linear subaortic structure and backward diastolic flow originating at aortic valve level with visible proxymal convergence zone at 72 cm/s Nyquist limit, suggesting significant associated valvular regurgitation.

Although there are signs of obstruction at both subvalvular and valvular level, their severity cannot be reliably quantified by CW Doppler methods in case of multiple stenoses. In addition, since there is a significant associated aortic regurgitation, area planimetry is the best method for assessing stenosis severity in this case.

By cropping a transthoracic 3D data set of the aortic valve acquired from the apical approach and visualizing it en face from the ventricular perspective, the anatomy of the subaortic membrane and its residual orifice size, shape and dynamics could be appreciated throughout the cardiac cycle.

Planimetry of 3D rendered orifice allowed an estimation of the residual orifice area of the membrane, suggesting a severe obstruction at subaortic level (0.5 cm2)

After positioning the cropping plane in the aortic root, at the tips of the aortic cusps in fully open position, and changing the viewing perspective from the left ventricle to the aortic root, it was possible to visualize the aortic valve en face, and to appreciate its three-cusp morphology and its limited systolic opening.

As an alternative to measurements performed directly on rendered images (which may be affected by gain settings or limited in case of a non-planar geometry of residual orifice), stenotic orifice areas can be reconstructed en face as a 2D slice using multi-planar method (Flexi-slice), which enables to closely control the alignment and position of the cutting plane exactly at the narrowest orifice.

Subaortic membrane orifice measurement by multi-planar method (Flexi-slice). Subaortic orifice planimetry is shown in the bottom right image.

Aortic stenotic orifice measurement by multi-planar method (Flexi-slice). Aortic valve orifice planimetry is shown at the bottom right image.

Discussion

Volume-rendering display of multi-beat, full-volume 3D data sets provides a complete, anatomically sound visualization of the heart valves in the beating heart. By 3D echocardiography the valves can be viewed from both sides (perspectives), and not just from the ventricular perspective as it happens with conventional two-dimensional echocardiography.

Thus, aortic valve can be visualized by 3D echo both from the left ventricular outflow tract and from the aortic root (“surgical view”).

The choice between transthoracic or transoesophageal approach for assessing the subaortic and aortic morphology depends on patient’s acoustic window and on the clinical indication. In patients with suboptimal acoustic window, if obstruction severity is still doubtful or if more detailed information is needed (i.e. assessing suitability for percutaneous interventions), transeosophageal 3D echocardiography should complement the primary transthoracic approach.

In this particular case, however, the patient had an optimal acoustic window from apical approach, which allowed to obtain an estimation of the anatomic area of both obstructions by 3D transthoracic echo and to obtain relevant information regarding their severity, despite the known limitations of conventional Doppler echocardiography in such cases.

Cardiac surgery (membrane resection and aortic valve replacement) was indicated.

Key Messages

3D echocardiography:

  • Enabled en face visualizations from both aortic and ventricular perspectives for a more detailed anatomic characterization of the subaortic membrane and aortic valve in the beating heart
  • Instead of the traditional parasternal approach, a non-conventional apical approach allowed to obtain information on aortic valve morphology (three-cusp, thickened, limited opening) and to perform area planimetry
  • En face 3D dynamic reconstruction of LV outflow enabled a confident diagnosis of a discrete subaortic membrane and to reliably differentiate from other types of subaortic obstruction (tunnel-like, fibro-muscular ridge, abnormal mitral valve attachments etc)
  • En face 3D visualizations were key for quantifying the anatomic area of subaortic and aortic valve stenoses by transthoracic echocardiography, despite the limitations of conventional Doppler echocardiography in such case

References

  • Muraru D, Badano LP, Vannan M, Iliceto S. Assessment of aortic valve complex by three-dimensional echocardiography: a framework for its effective application in clinical practice. Eur Heart J Cardiovasc Imaging. 2012 Jul;13(7):541-55.
  • Simpson JM, Miller O. Three-dimensional echocardiography in congenital heart disease. Arch Cardiovasc Dis 2011; 104: 45-56
  • Lang RM, Badano LP, Tsang W et al. EAE/ASE Recommendations for image acquisition and display using three-dimensional echocardiography. Eur Heart J Cardiovasc Imaging 2012; 13(1):1-46