From the Guidelines
The normal range for left ventricular outflow tract (LVOT) velocity measured with Doppler by transthoracic echocardiography (TTE) is typically 0.7 to 1.1 meters per second (m/s). This measurement represents the blood flow velocity through the LVOT during systole. Values above this range may suggest obstruction or increased cardiac output, while lower values might indicate reduced cardiac function. When measuring LVOT velocity, the Doppler sample volume should be placed approximately 0.5-1.0 cm proximal to the aortic valve in the apical five-chamber or apical long-axis view. The measurement is important for calculating stroke volume, cardiac output, and aortic valve area using the continuity equation. Factors that can affect LVOT velocity include heart rate, contractility, preload, and afterload. Proper technique is essential for accurate measurements, including appropriate gain settings, proper alignment of the ultrasound beam with blood flow, and averaging measurements over multiple cardiac cycles, especially in patients with irregular rhythms. According to the 2020 ACC/AHA guideline for the management of patients with valvular heart disease 1, echocardiographic imaging allows reliable evaluation of valve anatomy and motion and the degree of valve obstruction.
Some key points to consider when measuring LVOT velocity include:
- The outflow tract–to–aortic velocity ratio is independent of body size and eliminates potential errors in calculated valve area related to measurement of LV outflow tract diameter or area 1.
- A normal ratio is close to 1.0, whereas a ratio of ≤0.25 corresponds to a valve area 25% of normal for that patient, which is consistent with severe AS and is a predictor of symptom onset and adverse outcomes 1.
- Echocardiography is recommended for the diagnosis and assessment of AS severity, as well as for the assessment of LV wall thickness, size, and function 1.
It is essential to follow proper technique and consider the potential factors that can affect LVOT velocity to ensure accurate measurements and reliable assessment of aortic stenosis severity.
From the Research
Normal Range for LVOT Velocity
The normal range for left ventricular outflow tract (LVOT) velocity measured with Doppler by transthoracic echocardiography (TTE) can vary depending on the specific population and device being used.
- In a study of 79 subjects free of clinical heart disease, the peak systolic velocity in the LVOT was measured to be 98 +/- 16 cm/s in the medial margin, 89 +/- 14 cm/s in the midline, and 79 +/- 14 cm/s in the lateral margin 2.
- A study of patients with left ventricular assist devices (LVADs) found that the average outflow cannula peak velocity for the normal Heartmate II (HM2) cohort was 1.86 ± 0.44 m/s, with upper and lower reference limits of 2.73 m/s and 0.98 m/s, respectively 3.
- The same study found that the average outflow cannula peak velocity for the normal Heartware (HW) cohort was 2.36 ± 0.53 m/s, with upper and lower reference limits of 3.42 m/s and 1.3 m/s, respectively 3.
Factors Affecting LVOT Velocity
Several factors can affect LVOT velocity, including:
- The shape of the LVOT, which can be ovoid rather than circular 4
- The location of the measurement, with velocities varying across the LVOT 2
- The type of device being used, with different devices having different reference limits 3
- The presence of cardiac disease or other conditions, which can affect LVOT velocity 5, 6
Clinical Implications
Understanding the normal range for LVOT velocity is important for diagnosing and managing cardiac conditions, such as aortic stenosis and LVAD malfunction.
- A study found that the ratio of LVOT velocity-time integral to descending thoracic aorta velocity-time integral can be used to validate LVOT measurements and estimate LVOT velocity 5.
- Another study found that cardiovascular magnetic resonance (CMR) can provide a non-invasive and reliable alternative to Doppler-echocardiography for quantifying aortic stenosis severity, with good concordance between TTE-derived and CMR-derived effective orifice areas 6.