Principle
After transseptal access, the residual iASD shunts LA → RA when LAP > RAP.
Apply the simplified Bernoulli equation to the peak shunt velocity to recover the instantaneous
LA–RA pressure gradient, then add a measured/estimated RAP.
LAPpeak = RAP + 4 × Vpeak²
ΔPLA–RA = 4V² (mmHg, with V in m/s)
VpeakPeak L→R shunt velocity across the iASD by PW or CW Doppler (m/s)
RAPEstimated RA pressure (IVC method, ASE 2010): 3 / 8 / 15 mmHg
LAPpeakPeak left atrial pressure during the cardiac cycle (mmHg)
Acquisition Protocol
1
Locate the iASD. Subcostal or low parasternal short-axis at the AV groove gives the most parallel alignment to the L→R jet. TEE bicaval (90°) is the gold standard.
2
Color Doppler on the septum — identify the jet direction. Narrow the sector and lower Nyquist (~40–60 cm/s) to confirm continuous L→R flow.
3
Align the cursor with the jet (angle < 20°). Drop a PW sample on the RA side of the defect; switch to CW if velocities exceed PW Nyquist.
4
Set scale so the peak fits in the display — if the trace clips, extend the scale (do not estimate an aliased peak).
5
Trace the peak L→R velocity. Use the highest reproducible peak across ≥ 3 beats (or 5 in AF).
6
Estimate RAP from the IVC: collapsible & ≤2.1 cm = 3 mmHg; intermediate = 8; plethoric >2.1 cm with <50% collapse = 15.
Assumptions & When It Holds
- Restrictive defect. Small, post-transseptal puncture iASD — flow accelerates across a narrow orifice, so peak gradient reflects the LA–RA pressure difference. Large/non-restrictive ASDs equalize pressures and Bernoulli underestimates.
- Continuous L→R flow with a clear systolic-dominant peak. Bidirectional flow suggests near-equal pressures or RAP > LAP transiently.
- Good Doppler alignment. Off-axis sampling underestimates V; LAP estimate falls quadratically with V.
- Simultaneous RAP. Validated cohorts used invasive RA mean; bedside echo uses ASE IVC class.
- Validated against direct LA pressure in patients with post-MitraClip iASDs — r ≈ 0.90 with invasive measurement.
Worked Example
Post-transseptal iASD, parasternal short-axis with PW sample on the RA side of the defect. Scale extended to 2.0 m/s after the initial sweep aliased at 1.0 m/s.
Continuous L→R systolic-dominant flow. Peak velocity above baseline ≈ 1.5 m/s.
Inputs
Vpeak1.5 m/s (peak L→R, scale uncapped)
RAP5 mmHg (IVC small & collapsible)
Calculation
ΔP = 4 × V² = 4 × (1.5)² = 4 × 2.25 = 9 mmHg
LAPpeak = RAP + ΔP = 5 + 9 = 14 mmHg
ESTIMATED PEAK LA PRESSURE
14 mmHg
Interpretation
| LAPpeak | Clinical correlate |
|---|---|
| ≤ 12 mmHg | Normal LA pressure |
| 13–18 mmHg | Mild elevation — reassess loading, MR |
| 19–25 mmHg | Moderate — congestion likely; diurese |
| > 25 mmHg | Severe — pulmonary edema risk |
Quick Vpeak → LAPpeak: V > 1.6 m/s → LAPpeak > 15 mmHg · V > 1.9 m/s → LAPpeak > 20 mmHg
Tip: Combine with mitral inflow E (here 1.07 m/s, E/A 1.58, DecT 297 ms — consistent with normal-to-mildly-elevated filling pressure) for a coherent diastology read. The iASD gives you the quantitative anchor the rest of the algorithm lacks.
Pearls & Pitfalls
Aliased trace = unusable peak. If the spectral envelope is clipped at the Nyquist limit, extend the scale (or shift baseline). Reading velocity off a clipped trace systematically underestimates LAP. Page-2 trace in the source PDF illustrates this exact failure.
Off-axis underestimates. Cosine-θ error is squared by Bernoulli — a 20° off-axis cursor on a 1.5 m/s jet drops the LAP estimate by ~1 mmHg; 30° drops by ~2 mmHg.
Highest peak wins. L→R gradient peaks in late systole / early diastole at the LA v-wave — that instant is what the formula recovers. Bidirectional jet = near-equal LAP/RAP or transient RAP > LAP (severe TR, RV failure); flag result as uncertain.
Reference
Echo estimate of peak LAP in iatrogenic ASDs (vs. invasive LAP). Bernoulli: Hatle & Angelsen 1985. RAP: Rudski, ASE 2010.