What is the difference between aortic valve area calculations using Velocity Time Integral (VTI) and maximum velocity (Vmax), and which method is more representative of valve opening?

From the Guidelines

The aortic valve area (AVA) calculated using velocity time integral (VTI) is more representative of the valve opening compared to maximum velocity (Vmax), as it incorporates the entire flow profile across the valve throughout systole, providing a more comprehensive assessment of the valve's hemodynamic performance. The VTI method uses the continuity equation, which has been well validated in both clinical and experimental studies 1. This approach is particularly valuable in patients with irregular heart rhythms, varying stroke volumes, or low-flow, low-gradient aortic stenosis. In contrast, the Vmax method relies on peak instantaneous gradients and only captures the maximum velocity at a single point in time, potentially overestimating stenosis severity in certain conditions like hypertrophic cardiomyopathy or underestimating it in low-flow states.

Some key points to consider when calculating AVA using VTI or Vmax include:

• Accurate Doppler alignment and careful LVOT diameter measurement are crucial for both methods 1
• The VTI method better reflects the physiological reality of blood flow across the valve throughout the entire cardiac cycle 1
• The continuity equation used in the VTI method measures the effective valve area, which is the area of the flow stream as it passes through the valve, rather than the anatomic valve area 1
• The Vmax method may be limited by its reliance on peak instantaneous gradients, which may not accurately reflect the valve's hemodynamic performance in certain conditions 1

Overall, the VTI method is the preferred approach for calculating AVA and assessing aortic stenosis severity, as it provides a more comprehensive and accurate assessment of the valve's hemodynamic performance 1.

From the Research

Aortic Valve Area Calculations

The difference between aortic valve area calculations with VTI (Velocity-Time Integral) and with Vmax (maximum velocity) lies in the method of calculation and the parameters used.

• VTI is calculated by integrating the velocity of blood flow over time, providing a measure of the volume of blood that flows through the valve [ 2 ].
• Vmax, on the other hand, is the maximum velocity of blood flow through the valve.

Comparison of VTI and Vmax

Studies have compared the two methods, with one study finding that the dimensionless index (DI) calculated using Vmax is more consistent over time than DI calculated using VTI [ 3 ].

• The coefficient of variation was significantly better when DI was calculated using Vmax than VTI (12.6% vs 25.4%, p < 0.0001).
• However, another study found that the most accurate effective orifice area (EOA) after transcatheter aortic valve replacement is calculated using preimplantation left ventricular outflow tract diameter and VTI [ 2 ].

Representative of Valve Opening

The choice of method depends on the specific context and the parameters being measured.

• VTI may be more representative of the valve opening in certain situations, such as in the calculation of EOA after transcatheter aortic valve replacement [ 2 ].
• Vmax, on the other hand, may be more suitable for serial measurement in real-world aortic stenosis follow-up [ 3 ].