How does the shape of the Doppler (Doppler ultrasound) spectrum change as Aortic (aortic valve) Stenosis worsens?

From the Guidelines

As aortic stenosis worsens, the Doppler spectrum changes, with the peak velocity increasing and the curve becoming more rounded in shape, reflecting a high gradient throughout systole, as noted in the 2017 European Heart Journal study 1.

Key Changes in Doppler Spectrum

• The peak velocity increases progressively, often exceeding 4 m/s in severe stenosis compared to normal values of 1-2 m/s.
• The spectrum develops a more rounded shape with a slower upstroke and prolonged deceleration time, reflecting the increased resistance to blood flow through the narrowed valve.
• With mild obstruction, the peak is in early systole with a triangular shape of the velocity curve, compared with the rounded curve with the peak moving towards mid systole in severe stenosis, upward in early systole, as described in the 2017 European Heart Journal study 1.

Clinical Implications

• These changes directly correlate with the increasing pressure gradient across the valve, which is calculated using the modified Bernoulli equation (pressure gradient = 4v²).
• The spectrum alterations occur because as the valve opening becomes progressively smaller, blood must accelerate to higher velocities to maintain cardiac output, creating greater pressure differences and more disturbed flow patterns.
• The 2017 European Heart Journal study 1 and the 2015 Circulation study 1 provide guidance on the assessment of aortic stenosis severity using Doppler echocardiography, highlighting the importance of combining features of the history, physical examination, and echocardiogram in evaluating the severity of AS.

Assessment of Aortic Stenosis Severity

• The 2017 European Heart Journal study 1 recommends using the peak jet velocity, mean aortic transvalvular pressure gradient, and valve area by continuity equation to evaluate AS severity.
• The 2015 Circulation study 1 provides a table summarizing the severity of aortic stenosis by Doppler echocardiography, including jet velocity, mean gradient, and aortic valve area.

Importance of Accurate Assessment

• Accurate assessment of aortic stenosis severity is crucial for determining appropriate timing for intervention and for predicting clinical outcomes, as noted in the 2016 Circulation study 1.
• The 2017 European Heart Journal study 1 and the 2015 Circulation study 1 emphasize the importance of using multiple acoustic windows for the CW Doppler assessment of AS and of considering the limitations of each echocardiographic measure.

From the Research

Doppler Ultrasound Spectrum Changes in Aortic Stenosis

• The shape of the Doppler ultrasound spectrum changes as aortic stenosis worsens, with increases in peak jet velocity and mean gradient across the aortic valve 2, 3.
• The continuity equation is used to calculate the effective aortic valve area, which decreases as aortic stenosis worsens 2, 3.
• Transesophageal and multidimensional echocardiography can be used to measure geometric aortic valve area and cardiac dimensions, providing additional information on the severity of aortic stenosis 2.
• The Doppler evaluation of aortic stenosis has improved our understanding of the prevalence and natural history of this disease, and can be used for clinical decision making regarding the need for valve replacement in symptomatic adults 3.

Classification of Aortic Stenosis by Flow and Gradient Patterns

• Aortic stenosis can be classified into different patterns based on flow and valve gradients, including high-gradient/normal flow, high-gradient/low flow, low-gradient/normal flow, and low-gradient/low flow 4.
• These different patterns can provide insights into the pathophysiology of the disease and help identify patients with less severe aortic stenosis 4.
• The classification of aortic stenosis by flow and gradient patterns can also help guide treatment decisions, including the use of transcatheter aortic valve implantation in patients with severe aortic stenosis 5.

Changes in Coronary Flow with Aortic Stenosis

• Patients with severe aortic stenosis have reduced coronary flow, which can increase after transcatheter aortic valve implantation 6.
• The change in coronary flow is associated with a decrease in left ventricular end-diastolic pressure, and can be measured using pulse-wave Doppler echocardiography 6.
• The increase in coronary flow after transcatheter aortic valve implantation can have important implications for patient outcomes and quality of life 6.