Do you understand what is meant by heart failure? As the name implies, people with heart failure have a heart that is failing. The term most often refers to the abnormal functioning of the left ventricle, the chamber of the heart that forcefully pumps blood to all parts of the body. When something is wrong with the pumping mechanism of the left ventricle, it translates into symptoms patients feel; weakness, fatigue, shortness of breath, lightheadedness, fluid retention (ankle edema), and even chest pain. The net effect of a failing heart is that blood doesn’t circulate through the body as it should and oxygen is not supplied to the tissues and organs in sufficient quantities. When organs and tissues are starved of oxygen, they fail to function optimally and may suffer damage.
Heart failure has many causes. Anything that weakens the heart muscle (myocardium) or makes the heart work harder can cause heart failure. There are four main categories of disease that comprise the majority of causes. These are the following:
- High Blood Pressure—the heart has to work harder and pump blood against a higher than normal pressure. This is called peripheral resistance. High BP causes the wall of the left ventricle to thicken and the ventricle dilates (balloons in size) and pumps less effectively.
- Cardiomyopathy—the heart muscle is either infected with a virus (myocarditis) or it weakens for reasons unknown and fails to pump effectively.
- Heart Valve Problems—the mitral and aortic valves on the left side of the heart either leak or are narrowed restricting outflow. The heart has to pump harder against resistance and has a larger volume to pump each beat. The heart tires and fails.
- Heart Attack—blockage in a coronary artery results in damage to the heart muscle. The damaged heart muscle forms scar tissue that pumps blood poorly or not at all.
- Other less common causes are diabetes, smoking, obesity, aging, alcohol, arrhythmias
Heart failure is diagnosed and quantified by the procedure called echocardiography. The test result is called an echocardiogram. An “echo” (short for echocardiogram) is a sonar-like study of the heart that clearly demonstrates the functioning of the heart valves and the flow of blood through the four chambers. The cardiologist is able to see in real time the valves opening and closing, and myocardium actually pumping. A “color echo” is able to visibly demonstrate the flow of blood through the heart. Included in the echocardiographic assessment of the heart is a quantitative measurement called the left ventricular ejection fraction (LVEF). This is where the diagnosis of heart failure is made. Through amazing technology, LVEF measures the percentage of blood within the left ventricle that is pumped out to the body with each beat. A low left ventricular ejection fraction (LVEF) is a diagnostic criterion for heart failure.
When the left ventricle pumps, it doesn’t expel all of the blood within it. Instead, each beat normally expels (ejects) only 52%-72% of the blood within. So, the normal value for the LVEF is between 52-72%. That means that any percentage outside that range is abnormal, and the heart is failing. Those abnormal percentages are as follows:
Mild heart failure: the LVEF is 41%-51%
Moderate heart failure: the LVEF is 30%-40%
Severe heart failure: the LVEF is lass than 30%
A high left ventricular ejection fraction of 75% or greater is also possible. A genetic condition called hypertrophic cardiomyopathy (HCM) is the usual cause. Here, the heart muscle is hypertrophic (thickened). HCM is associated with a high frequency of arrhythmias, some of which have fatal consequences.
Understanding the concept of left ventricular ejection fraction requires a knowledge, at least in passing, of heart failure, its causes and effects. I cannot tell you how LVEF is determined except to say its an echocardiographic measurement just as are chamber size and wall thickness. It’s done by the device. Other diagnostic studies—cardiac catheterization, MRI, and CT may also be done, adjunctively. Ultrasound (echocardiography) technology has improved greatly in the past 50 years, and doctors now have hand-held devices they employ for bedside diagnostic purposes. Auscultation (listening to the heart) is an art that has all but been replaced by the accuracy and precision of echocardiography. With echo, guessing the cause of a murmur, etc. is no longer necessary. It’s now possible to see heart valves functioning, or malfunctioning, and directly see the pumping of the left ventricle. Plus precise measurements that were previously possible only during cardiac catheterization are now possible.
Determination of the ejection fraction is a valuable tool in the assessment of a patient with fatigue, weakness, and shortness of breath, and should be used without hesitation. Its use is important diagnostically, and it is very helpful for assessing the success of treatment. Since it is non-invasive, patient acceptance is high.
References: https://www.pennmedicine.org/updates/blogs/heart-and-vascular-blog.
Fukata H, Little WC. The Cardiac Cycle and the Physiological Basis of Left Ventricular Contraction, Ejection, Relaxation, and Filling. Heart Fail Clin 2008 January;4(1):1-11.
