High Doppler-derived gradients across the aortic valve may be misleading: potential causes of valve gradient overestimation

Transthoracic and transoesophageal echocardiography was performed on a 32-year-old, asymptomatic patient nine years after commissurotomy of a stenotic bicuspid aortic valve and supracoronary graft replacement of an aneurysmal ascending aorta. This exhibited increased continuous-wave (CW) Doppler-derived transaortic pressure gradients (max. / mean pressure differences 48/31 mm Hg, after correction for left ventricular outflow tract gradients; fig. 1), despite an aortic valve showing only mildly restricted opening (figs 2 and 3, videos A and B). Colour Doppler interrogation indicated supravalvular high-velocity flow, but no turbulent flow was seen in the left ventricular outflow tract or at the level of the aortic valve, indicating that the high gradients were not caused by stenosis at the subvalvular or valvular level (figs 4 and 5, videos C and D). Thoracic magnetic resonance (MR) angiography revealed a patent, but small-for-size 22-mm Dacron graft (fig. 6, video D). Doppler echocardiography is widely used to assess cardiac valve function. Underor overestimation of transvalvular gradients may occur with this technique. In the case presented, the observed transvalvular gradient overestimation is most likely of multifactorial genesis. The colour Doppler images showing high velocity turbulent flow in the aortic root suggest that the causative factors are mainly of supravalvular origin. Although MR imaging (MRI) of the thoracic aorta revealed no signs of graft obstruction, the non compliant, smallfor-size Dacron graft has almost certainly contributed to the increased Doppler gradients. More over, the pressure recovery phenomenon may have played an important role. Pressure recovery – the increase in pressure downstream from the valve caused by the reconversion of kinetic energy to potential energy – is a potential reason for gradient over estimation and, consequently, of valve area under estimation [1, 2]. Usually, it can be neglected if the ascending aortic diameter exceeds 30 mm,