Hemodynamics by Echo

Doppler echocardiography estimates pressure gradients, flow, stroke volume, cardiac output, valve area, and intracardiac pressures.

These measurements depend heavily on Doppler alignment, loading conditions, rhythm, and measurement accuracy.

Pressure Gradients¶

Using the simplified Bernoulli equation:

\[ \Delta P = 4V^2 \]

where velocity is measured in m/s and gradient in mm Hg.

The calculated value is the peak instantaneous gradient, which may exceed the peak-to-peak gradient measured during catheterization.

Do not apply the simplified equation when proximal velocity is elevated. Use:

\[ \Delta P = 4(V_2^2 - V_1^2) \]

Stroke Volume and Cardiac Output¶

\[ CSA_{LVOT} = \pi\left(\frac{D_{LVOT}}{2}\right)^2 \]

\[ SV = CSA_{LVOT} \times VTI_{LVOT} \]

\[ CO = SV \times HR \]

\[ CI = \frac{CO}{BSA} \]

Measure LVOT diameter in midsystole and PW Doppler immediately proximal to the aortic valve.

Because LVOT area depends on the squared diameter, small diameter errors produce large stroke-volume errors.

Continuity Equation¶

Assuming conservation of flow:

\[ AVA = \frac{CSA_{LVOT} \times VTI_{LVOT}} {VTI_{AV}} \]

The Doppler velocity index avoids measuring LVOT diameter:

\[ DVI = \frac{VTI_{LVOT}} {VTI_{AV}} \]

The same principle may be applied to prosthetic valves and selected other stenotic lesions.

Right Atrial Pressure¶

Estimate RAP from IVC size and inspiratory collapse:

IVC	Collapse	RAP
≤2.1 cm	>50%	3 mm Hg
>2.1 cm	<50%	15 mm Hg
Indeterminate pattern	—	8 mm Hg

IVC-based estimates are less reliable with mechanical ventilation, elevated intra-abdominal pressure, athletic adaptation, or poor inspiratory effort.

RVSP and PASP¶

\[ RVSP = 4(TRV)^2 + RAP \]

In the absence of pulmonic stenosis or RVOT obstruction:

\[ PASP \approx RVSP \]

Use the highest complete TR envelope from multiple windows.

Severe TR may underestimate RVSP because RA and RV pressures equalize early. An absent TR jet does not exclude pulmonary hypertension.

Pulmonary Artery Pressures¶

From pulmonic regurgitation:

\[ PADP = 4(PR_{ED})^2 + RAP \]

\[ mPAP = 4(PR_{peak})^2 + RAP \]

These estimates require a complete and well-aligned PR envelope.

Left Atrial Pressure¶

No single Doppler parameter directly measures LA pressure.

Elevated filling pressure is supported by integration of:

Mitral inflow
Tissue Doppler e′
E/e′
TR velocity
LA volume
Pulmonary venous flow
Clinical context

E/e′ should not be used in isolation and becomes less reliable in significant mitral valve disease, prosthetic valves, constriction, and several other special populations.

Shunt Flow¶

Pulmonary-to-systemic flow ratio may be estimated as:

\[ Q_p/Q_s = \frac{CSA_{RVOT} \times VTI_{RVOT}} {CSA_{LVOT} \times VTI_{LVOT}} \]

A ratio >1 indicates net left-to-right shunting.

Small errors in outflow-tract diameter are amplified because the diameter is squared.

Common Errors¶

Poor Doppler alignment underestimates velocity and gradient.
Tracing an incomplete envelope produces unreliable measurements.
PW sample placement too close to the valve may include acceleration.
LVOT diameter errors substantially alter calculated AVA and stroke volume.
Tachycardia and irregular rhythm affect gradients and filling measurements.
High flow increases gradients without necessarily indicating severe obstruction.
Low flow may conceal severe stenosis.
Pressure estimates should be interpreted with the entire examination.

Suggested Reporting¶

Estimated RVSP is ___ mm Hg based on a peak TR velocity of ___ m/s and estimated RAP of ___ mm Hg.

Cardiac output is ___ L/min with a cardiac index of ___ L/min/m².

Stroke-volume index is reduced at ___ mL/m².

Pulmonary pressure cannot be estimated because an adequate TR Doppler envelope is not present.

Doppler findings suggest elevated left atrial pressure.

Key Points¶

Doppler velocity must be parallel to flow.
Bernoulli provides an instantaneous rather than peak-to-peak gradient.
LVOT diameter error is squared in flow calculations.
Severe TR may cause underestimation of RVSP.
Use integrated findings rather than a single parameter to estimate filling pressure.