What is the normal left ventricular ejection fraction?
**Core Concept**
The left ventricular ejection fraction (LVEF) is a critical measure of the heart's pumping efficiency, reflecting the percentage of blood that is ejected from the left ventricle with each contraction. It is calculated by dividing the stroke volume by the end-diastolic volume.
**Why the Correct Answer is Right**
LVEF is an essential parameter for assessing cardiac function, and a normal value indicates that the left ventricle is pumping blood effectively. A normal LVEF ranges from 55% to 70%, with values above 55% typically considered normal. This range allows for efficient blood circulation to the body's tissues and organs. The LVEF is influenced by the contractility of the left ventricular muscle, the preload (the initial stretching of the cardiac myocytes prior to contraction), and the afterload (the resistance to blood flow that the left ventricle must overcome during ejection).
**Why Each Wrong Option is Incorrect**
* **Option A:** A value of 20% would indicate severe systolic dysfunction, which is not normal.
* **Option B:** A value of 90% is excessively high and may indicate conditions like hypertrophic cardiomyopathy.
* **Option C:** A value of 40% is below the normal range and may indicate mild systolic dysfunction.
**Clinical Pearl / High-Yield Fact**
A normal LVEF is crucial for maintaining adequate cardiac output and preventing complications such as heart failure. It is essential to monitor LVEF regularly in patients with cardiovascular disease, especially those with a history of myocardial infarction or heart failure.
**Correct Answer:** C. 55% to 70%.