What are E and e' in echocardiography (echo)?

Understanding E and e' in Echocardiography

E and e' are key echocardiographic parameters used to assess left ventricular diastolic function, with the E/e' ratio being one of the most reliable indicators of left ventricular filling pressures. 1

Definitions and Physiological Basis

E Wave (Early Diastolic Filling)

• E represents the early diastolic transmitral flow velocity measured by conventional Doppler echocardiography 1
• It reflects the pressure gradient between the left atrium and left ventricle during early diastole 1
• E wave is influenced by left ventricular relaxation, restoring forces, and left atrial pressure at mitral valve opening (lengthening load) 1

e' Wave (Early Diastolic Mitral Annular Velocity)

• e' is the early diastolic mitral annular velocity measured by tissue Doppler imaging (TDI) 1
• It primarily reflects left ventricular relaxation with minimal influence from loading conditions when relaxation is impaired 1
• The three main determinants of e' are:
  1. LV relaxation (rate of active fiber force decay)
  2. Restoring forces (diastolic suction)
  3. Lengthening load (left atrial pressure at mitral valve opening) 1
• e' decreases with aging and is reduced in patients with impaired relaxation 1

Clinical Significance and Interpretation

E/e' Ratio

• E/e' ratio is used to estimate left ventricular filling pressures 1
• Values for average E/e' ratio < 8 usually indicate normal LV filling pressures 1
• Values > 14 have high specificity for increased LV filling pressures 1
• Values between 8-14 represent a "gray zone" where other parameters should be considered 1

Measurement Technique

• e' should be measured at both septal and lateral mitral annulus sites 1
• Proper sample volume positioning is critical - common errors include:
  1. Placing sample volume in LV cavity
  2. Positioning in basal segment of lateral wall
  3. Placing partly outside the heart
  4. Positioning in left atrium above mitral annulus 1

Clinical Applications

Assessment of Diastolic Dysfunction

• When E/A ratio ≤ 0.8 with peak E velocity ≤ 50 cm/sec, mean left atrial pressure is normal/low (grade I diastolic dysfunction) 1
• When E/A ratio ≥ 2, left atrial pressure is elevated (grade III diastolic dysfunction) 1
• For intermediate values, additional parameters including E/e' are needed for accurate assessment 1

Prognostic Value

• E/e' is a powerful predictor of cardiac events in hypertensive populations 2
• A unit rise in E/e' ratio has been associated with a 17% increment in risk of cardiac events in hypertensive patients 2
• E/e' provides both diagnostic and prognostic information about LV diastolic dysfunction 1

Limitations and Caveats

• E/e' has limited accuracy in:
  • Normal subjects
  • Patients with heavy annular calcification
  • Mitral valve disease
  • Pericardial disease
  • Coronary artery disease with regional dysfunction 1
• Different cutoff values apply depending on the sampling site (septal vs. lateral) 1
• The correlation between E/e' and invasively measured filling pressures is modest (pooled correlation coefficient r = 0.56) 1
• There is insufficient evidence that E/e' can reliably assess LVFP changes in response to exercise or other interventions 3

Automated Measurement

• Recent advances in deep learning algorithms have enabled automated measurement of E/e' with similar accuracy to manual measurements by expert sonographers 4
• Automated workflows may accelerate access, improve quality, and reduce costs in diagnosing and managing heart failure 4