In the diagnosis of heart failure (HF), an echocardiogram is the most critical imaging tool. While a comprehensive report includes dozens of measurements, three specific metrics are considered the “keys” because they define the type of heart failure and provide the clearest evidence of how the heart is failing.
1. Left Ventricular Ejection Fraction (LVEF)
LVEF is the most widely recognized metric and is the primary factor used to classify the type of heart failure. It measures the percentage of blood pumped out of the left ventricle with each contraction.
- Normal: 50% – 70%
- HFrEF (Reduced EF): ≤40%. The heart muscle is weak and cannot contract effectively.
- HFpEF (Preserved EF): ≥50%. The heart contracts normally, but it is stiff and cannot fill properly.
- HFmrEF (Mildly Reduced EF – Mid Range): 41% – 49%. An intermediate zone often requiring close monitoring.
2. Diastolic Filling Pressures (E/e’)
As many patients have symptoms of heart failure despite a “normal” ejection fraction (HFpEF), we also look at the E/e’ ratio. This metric uses Tissue Doppler Imaging to estimate the pressure inside the left atrium.
- What it measures: The ratio between the speed of blood entering the ventricle (E) and the speed of the heart muscle moving (e’).
- Significance: A high ratio (typically > 14-15) indicates that the heart is “stiff”, requiring high pressures to fill. This is often the smoking gun for diagnosing heart failure when the EF is normal.
3. Left Atrial Volume Index (LAVI)
While EF looks at the “pump,” LAVI looks at the “reservoir.” The left atrium (LA) is highly sensitive to long-term pressure changes in the heart.
- Normal: < 34 mL/m2
- Significance: If the left ventricle is stiff or failing, pressure backs up into the left atrium, causing it to enlarge over time. An enlarged LA (LAVI > 34 mL/m2) is a strong marker of chronic diastolic dysfunction and is a key diagnostic criterion for HFpEF.
Comparison of Key Metrics
| Metric | Diagnostic Role | Key Threshold |
|---|---|---|
| LVEF | Defines “Weakness” (Systolic Function) | 40% (Reduced) |
| E/e’ Ratio | Defines “Stiffness” (Filling Pressure) | > 14 (High Pressure) |
| LAVI | Defines “Chronicity” (Atrial Size) | > 34 mL/m2 (Enlarged) |
Note: While these three are foundational, Global Longitudinal Strain (GLS) is useful to find “hidden” weakness and Tricuspid Regurgitant (TR) Jet Velocity will check for secondary pulmonary hypertension.