What Does an L-Wave Represent on Echocardiography?
An L-wave on echocardiography represents mid-diastolic transmitral flow that occurs when markedly delayed left ventricular (LV) relaxation combines with elevated LV filling pressures, and it is a specific marker for advanced diastolic dysfunction with increased left atrial pressure (LAP). 1
Physiologic Mechanism
The L-wave appears as a distinct mid-diastolic flow velocity following the E-wave, occurring because:
- Severely impaired LV relaxation causes the LV diastolic pressure to continue declining slowly after mitral valve opening
- Elevated LAP maintains a persistent LA-to-LV pressure gradient throughout mid-diastole
- This combination allows ongoing LV filling in mid-diastole, creating the L-wave between the E and A waves 1
The L-wave typically has a peak velocity >20 cm/sec and is most commonly seen in patients with bradycardia 1
Clinical Significance
When present in patients with known cardiac disease (e.g., LV hypertrophy, hypertrophic cardiomyopathy, heart failure with preserved ejection fraction), the L-wave is highly specific for elevated LV filling pressures. 1 However, its overall sensitivity is low, meaning its absence does not exclude elevated filling pressures 1
Key Diagnostic Features:
- The L-wave can be visualized on mitral inflow Doppler, tissue Doppler imaging (as L' wave at the mitral annulus), and color M-mode echocardiography 1, 2
- It is associated with other markers of elevated filling pressures: short IVRT (<50 msec), high E/e' ratio, and enlarged left atrial volume 1
- In atrial fibrillation, L-waves are relatively common (34% prevalence) and indicate advanced diastolic dysfunction with distended, noncompliant left atrium 3
Important Caveats
Rarely, an L-wave may be seen in normal subjects with bradycardia, but in these cases it is usually <20 cm/sec. 1 This distinguishes physiologic from pathologic L-waves.
The L-wave should not be confused with E-A fusion that occurs with first-degree AV block or tachycardia—these represent merged early and late diastolic filling, not true mid-diastolic flow 1
Prognostic Implications
In patients with LV hypertrophy, the presence of an L-wave predicts future heart failure events and appears to be a marker of pseudonormal filling pattern, indicating more advanced disease than suggested by the E/A ratio alone 4