Ejection fraction (EF) is calculated using a simple formula: EF = (Stroke Volume / End-Diastolic Volume) x 100. This result is expressed as a percentage.
Here's a breakdown:
- Ejection Fraction (EF): Represents the percentage of blood pumped out of the left ventricle with each contraction. It's a key indicator of heart health.
- Stroke Volume (SV): The amount of blood ejected from the left ventricle during each heartbeat (contraction). It's measured in milliliters (mL).
- End-Diastolic Volume (EDV): The volume of blood in the left ventricle at the end of diastole (when the heart is relaxed and filled with blood). It is also measured in milliliters (mL).
The Formula Explained
The formula EF = (SV / EDV) x 100 tells you what proportion of the blood filling the ventricle is actually pumped out with each beat. Multiplying by 100 expresses this proportion as a percentage.
Example Calculation
Let's say:
- Stroke Volume (SV) = 70 mL
- End-Diastolic Volume (EDV) = 120 mL
Then,
EF = (70 mL / 120 mL) x 100
EF = 0.5833 x 100
EF = 58.33%
In this example, the ejection fraction is approximately 58.33%.
Methods for Determining SV and EDV
Determining SV and EDV usually involves medical imaging techniques, such as:
- Echocardiogram (Echo): Uses ultrasound to create images of the heart.
- Cardiac MRI: Provides detailed images of the heart using magnetic resonance imaging.
- Cardiac Catheterization: An invasive procedure where a catheter is inserted into a blood vessel and guided to the heart.
- Nuclear Medicine Scans: Use radioactive tracers to assess heart function.
A trained healthcare professional uses these imaging techniques to measure the volumes needed for the calculation. You cannot directly measure your ejection fraction at home.
What is a Normal Ejection Fraction?
A normal ejection fraction is generally considered to be between 55% and 70%. Values below 55% may indicate heart failure or other heart conditions. Values above 70% may indicate a heart condition such as hypertrophic cardiomyopathy. Your doctor is best suited to explain what your ejection fraction means.
