Stroke Volume (SV) is calculated by multiplying the cross-sectional area (CSA) of a flow region by the Velocity Time Integral (VTI) of the flow through it.
LVOT Area: Measured by assuming a circular shape. The LVOT diameter is measured in the PLAX view at mid-systole, 5–10 mm proximal to the aortic annulus. Area = πr².
LVOT VTI: Obtained by tracing a Pulse Wave (PW) Doppler signal at the LVOT.
Example: Diameter = 2.0 cm, VTI = 24 cm. Area = 3.14 cm². SV = 3.14 cm² × 24 cm = 75 ml.
The LVOT diameter is the most common source of error because any error is squared during the area calculation. Since the LVOT is often oval, 3D or biplane 2D tracing is more accurate but time-consuming and should be used when routine measurements seem inconsistent.
Represents forward flow across the mitral valve.
Measurements: The mitral annular diameter is measured in the apical 4-chamber view at mid-diastole before atrial contraction (leaflet insertion to leaflet insertion), assuming a circular shape. The annular VTI is obtained with PW Doppler with the sample volume at the level of the annulus. For more accuracy, the annular area can be traced using 3D.
Utility: Not routine but helpful in valvular pathology quantification.
Calculation: Uses the same principle as the left side. RVOT diameter and VTI are measured in PSAX or RVOT views proximal to the pulmonic valve.
Rationale: When both semilunar valves are competent and no shunt is present, left and right ventricular SVs are equal because blood flows in a closed circuit. RV SV can be used when LV SV cannot be obtained.
Aortic Regurgitation: Aortic SV includes forward flow from the right side plus regurgitant volume.
Pulmonic Regurgitation: Pulmonic SV includes forward flow from the left side plus regurgitant volume.
Key Limitation: This method cannot be used if both aortic and pulmonic valves are regurgitant.
Interpretation: Left-to-right shunt: Pulmonic SV is higher → Qp/Qs > 1. Right-to-left shunt: Aortic SV is higher → Qp/Qs < 1.
In Patent Ductus Arteriosus, blood shunts from the aorta to the pulmonary artery, but the shunted blood is distal to the RV. Therefore, the shunted volume does not affect the Pulmonic SV, resulting in Qp/Qs < 1 despite being a left-to-right shunt.
ASD Shunt Volume: With good 3D TEE imaging, the ASD area can be traced, and flow across it can be pulsed and traced to directly calculate the shunt volume. For a left-to-right shunt: Right side SV = Left side SV + Shunt Volume.
Shunt Examples: PFO, VSD, ASD, PDA, and anomalous pulmonary vein.
Based on the principle of conservation of mass (volume in = volume out).
Solving for the smallest area (Area₂):
Measurement: Since the smallest area has the highest velocity, Continuous Wave (CW) Doppler is used to measure VTI₂. Peak velocity can be used instead of VTI but is less accurate due to timing differences.
If both Mitral and Aortic valves are regurgitant: RVOT SV can be used if the pulmonic valve is competent and there is no shunt. (AR Volume = Aortic SV − RVOT SV; MR Volume = Mitral SV − RVOT SV).
The continuity principle is not valid when significant valvular regurgitation occurs in one area but does not flow through the other (e.g., in MR, mitral SV cannot be used to calculate aortic valve area). Exception: In AR, LVOT SV can still be used for aortic valve area because regurgitant flow goes through both areas.
As flow converges towards a narrow orifice, its velocity increases, forming hemispheric shells. The velocity at the surface of a shell equals the set Nyquist limit.
Derived from the continuity equation (Flow rate in = Flow rate out).
V₁ × A₁ = V₂ × A₂, where:
If the area represents a regurgitant orifice, it is called the Effective Regurgitant Orifice Area (EROA). If it represents a stenotic orifice, it is called the Effective Orifice Area (EOA). Multiplying EROA by the flow VTI yields the regurgitant volume.
1. Decrease the Nyquist limit in the direction of flow to visualize the aliasing hemisphere.
2. Measure the radius (r) from the orifice to the aliasing surface. Crucially, measure the radius parallel to the Doppler beam to avoid underestimation due to angle dependency.
3. The selected frame for measuring the flow convergence must match the timing of the peak velocity on the CW Doppler tracing.
Measurement: Visualize the IVC in the subcostal view and measure it inner edge-to-inner edge, 1–2 cm from the junction with RA. Assess collapsibility with a sniff.
| IVC Diameter (cm) | Collapsing with Sniffing | RA Pressure (mmHg) |
|---|---|---|
| ≤2.1 | >50% | 3 |
| ≤2.1 | <50% | 8 |
| ≥2.1 | >50% | 8 |
| ≥2.1 | <50% | 15 |
Measures central venous pressure (CVP) in cmH₂O, which is a surrogate for RA pressure.
Requirements: The TR signal must be adequate with a complete spectral envelope. Use the highest velocity from all available windows (average of 3–5 beats if arrhythmia). Do not report if the signal is inadequate. In severe TR, the method is inaccurate due to a distorted RV-RA gradient.
If no aortic stenosis, LV systolic pressure equals the systolic blood pressure. VSD flow is systolic and left-to-right.
1. Mean Formula:
PADP = PR end-diastolic pressure + RA pressure.
2. Acceleration Time (AT): Measured by PW Doppler proximal to the pulmonic valve.
3. PR Early Diastolic Pressure:
4. Mean TR Gradient:
(Provided no pulmonic stenosis).
PR Dip (Loss of): A normal dip in the pulmonic regurgitation flow coincides with atrial contraction. Its presence indicates normal pulmonary pressure. The loss of this dip in sinus rhythm signifies pulmonary hypertension, as the RA contraction cannot cause a noticeable change in the PA-RV gradient.
Pulmonary Systolic Flow Notch: A mid-to-late systolic notch in the RVOT PW Doppler flow profile is a sign of significant pulmonary hypertension.
From Aortic Regurgitation (AR):
In the absence of Mitral Stenosis (MS): LA End-Diastolic Pressure (LAEDP) = LVEDP. If MS is present: LA pressure = LVEDP + MS Mean Gradient.
From Mitral Regurgitation (MR):
(Assuming no Aortic Stenosis). In Aortic Stenosis (AS): Correct the gradient.
Then, LA pressure = LV Systolic Pressure − MR Peak Gradient.
From ASD/PFO:
Phase 1 (Onset of strain): Decreased RV filling allows the LV to fill more freely and eject more, causing an increased BP and a reflex decreased heart rate.
Phase 2 (5–15 seconds of strain): Decreased right-sided filling is transmitted to the left side, causing a decreased LV stroke volume, a decreased BP, and a reflex increased heart rate.
Phase 3 (Release of strain): The congested systemic veins gush blood to the RA, causing RA pressure to exceed LA pressure, decreasing LV filling. This is associated with an increased heart rate.
Phase 4 (Post-release): The LV becomes well-filled, increasing stroke volume and BP, with a reflex decreased heart rate.
Phase 2: Requires a decrease in LV filling. Used for provoking dynamic LVOT obstruction in HOCM (when resting gradient is <30 mmHg) and for estimating LV filling pressure.
Phase 3: Requires an abrupt increase in RA pressure that exceeds LA pressure. Used to demonstrate a right-to-left inter-atrial shunt with saline contrast study in PFO/ASD.
Clinical: Distension of neck veins, flushing of the face, increased abdominal muscle tone.
Echocardiographic:
• Phase 2: A decrease in mitral peak E velocity by 20 cm/s (e.g., from 80 cm/s to 30 cm/s).
• Phase 3: A leftward shift of the inter-atrial septum upon release of strain.