What is the E/A (Early Diastolic Filling to Late Diastolic Filling) ratio?

E/A Ratio: A Key Measure of Diastolic Function

The E/A ratio is the ratio of early (E) to late atrial (A) diastolic filling velocities measured by Doppler echocardiography across the mitral valve, serving as a critical parameter for evaluating left ventricular diastolic function.

Definition and Physiological Basis

The E/A ratio represents two key components of ventricular filling:

• E wave (Early diastolic filling): Represents passive filling of the left ventricle during early diastole immediately after mitral valve opening
• A wave (Late diastolic filling): Represents active filling from atrial contraction during late diastole

This ratio reflects the relationship between passive and active ventricular filling phases during diastole 1.

Normal Values and Interpretation

• Normal E/A ratio: Typically 0.8-2.0 in healthy adults
• Age-dependent changes: The ratio naturally decreases with age as diastolic function gradually declines 2
• Interpretation requires context: Must be interpreted in the context of other echocardiographic parameters and the patient's age 3

Patterns of Abnormal E/A Ratio

1. Grade 1 (Mild) Diastolic Dysfunction:

   • E/A ratio < 0.8
   • Impaired relaxation pattern
   • Normal left atrial pressure

2. Grade 2 (Moderate) Diastolic Dysfunction:

   • E/A ratio 0.8-2.0 (pseudonormal)
   • Requires additional parameters for diagnosis
   • Elevated left atrial pressure

3. Grade 3 (Severe) Diastolic Dysfunction:

   • E/A ratio > 2.0
   • Restrictive filling pattern
   • Markedly elevated left atrial pressure 4

Clinical Significance

The E/A ratio has important clinical implications:

• Diagnostic value: Helps identify diastolic dysfunction, which often precedes systolic dysfunction
• Prognostic value: Abnormal patterns correlate with increased morbidity and mortality in various cardiovascular conditions
• Treatment guidance: Can help monitor response to therapies targeting diastolic function 1

Limitations and Considerations

• Pseudonormal pattern: Grade 2 diastolic dysfunction can mimic normal filling patterns, requiring additional parameters for accurate assessment
• Age dependence: Normal values decrease with age, necessitating age-adjusted interpretation 2
• Heart rate effects: Tachycardia can cause fusion of E and A waves, complicating interpretation
• Load dependence: Preload and afterload conditions can significantly affect the E/A ratio 1

Complementary Parameters

For comprehensive assessment, the E/A ratio should be evaluated alongside:

• E/e' ratio: Ratio of early mitral inflow velocity to early diastolic mitral annular velocity; better correlates with left ventricular filling pressures
• Deceleration time: Duration of E wave deceleration
• Isovolumic relaxation time (IVRT): Time between aortic valve closure and mitral valve opening
• Left atrial volume: Reflects chronicity of diastolic dysfunction
• Pulmonary vein flow patterns: Provides additional information about left atrial pressure 1, 4

Special Considerations

• Valvular disease: Mitral regurgitation or stenosis can affect E/A ratio interpretation
• Atrial fibrillation: Absence of organized atrial contraction makes A wave assessment impossible
• Pacemakers: Can alter normal filling patterns
• Transplanted hearts: Denervation and surgical factors complicate interpretation 1

The E/A ratio remains a fundamental parameter in the echocardiographic assessment of diastolic function, providing valuable insights when interpreted within the appropriate clinical and physiological context.