To understand what occurs in heart failure, it is useful to be familiar with the how the heart works and its anatomy. The heart is composed of two independent pumping systems, one on the right side, and the other on the left. Each has two chambers, an atrium and a ventricle. The ventricles are the major pumps in the heart.
The Right Side of the Heart. The right system receives blood from the veins of the whole body. This is "used" blood, which is poor in oxygen and rich in carbon dioxide.
- The right atrium is the first chamber that receives blood.
- The chamber expands as its muscles relax to fill with blood that has returned from the body.
- The blood enters a second muscular chamber called the right ventricle.
- The right ventricle is one of the heart's two major pumps. Its function is to pump the blood into the lungs.
- The lungs restore oxygen to the blood and exchange it with carbon dioxide, which is exhaled.
The Left Side of the Heart. The left system receives blood from the lungs. This blood is now oxygen rich.
- The oxygen-rich blood returns through veins coming from the lungs (pulmonary veins) to the heart.
- It is received from the lungs in the left atrium, the first chamber on the left side.
- Here, it moves to the left ventricle, a powerful muscular chamber that pumps the blood back out to the body.
- The left ventricle is the strongest of the heart's pumps. Its thicker muscles need to perform contractions powerful enough to force the blood to all parts of the body.
- This strong contraction produces systolic blood pressure (the first and higher number in blood pressure measurement). The lower number ( diastolic blood pressure) is measured when the left ventricle relaxes to refill with blood between beats.
- Blood leaves the heart through the ascending aorta, the major artery that feeds blood to the entire body.
The Valves. Valves are muscular flaps that open and close so blood will flow in the right direction. There are four valves in the heart:
- The tricuspid regulates blood flow between the right atrium and the right ventricle.
- The pulmonary valve opens to allow blood to flow from the right ventricle to the lungs.
- The mitral valve regulates blood flow between the left atrium and the left ventricle.
- The aortic valve allows blood to flow from the left ventricle to the ascending aorta.
Click the icon to see an image of the internal structures of the heart.
The Heart's Electrical System. The heartbeats are triggered and regulated by the conducting system, a network of specialized muscle cells that form an independent electrical system in the heart muscles. These cells are connected by channels that pass chemically caused electrical impulses.
Click the icon to see an image of the conduction system of the heart.
Description of Heart Failure
Heart failure is not a disease. It is a condition or process in which the heart is unable to pump enough blood to meet the needs of the body's tissues. The heart doesn't "fail" in the sense of ceasing to beat (as occurs during a heart attack). Rather, it weakens, usually over the course of months or years, so that it is unable to pump out all the blood that enters its chambers. As a result, fluids tend to build up in the lungs and tissues, causing congestion. This condition used to be called "congestive heart failure," but the name was officially changed to heart failure in 2005.
Ways the Heart Can Fail. Heart failure can occur in several ways:
- The muscles of the heart pumps (ventricles) become thin and weakened. They stretch (dilate) to the extent that they cannot pump the blood with enough force to reach all the body's tissues.
- The heart muscles stiffen or thicken. Here, they lose elasticity and cannot relax. Insufficient blood enters the chamber, so not enough blood is pumped out into the body to serve its needs.
- Sometimes the valves of the heart are abnormal. (Valves open or close to control the flow of blood entering or leaving the heart). They may narrow, such as in aortic stenosis, causing a back up of blood, or they may close improperly so that blood leaks back into the heart. The mitral valve (which regulates blood flow between the two chambers on the left side of the heart) often becomes leaky in severe heart failure -- a condition called mitral regurgitation.
Click the icon to see an image of the valves of the heart.
- The very mechanisms that the body uses to compensate for inefficient heart pumping can, over time, change the architecture of the heart (called remodeling) and finally lead to irreversible problems.
The specific effects of heart failure on the body depend on whether it occurs on the left or right side. Over time, however, in either form of heart failure, the organs in the body do not receive enough oxygen and nutrients, and the body's wastes are removed slowly. Eventually, vital systems break down.
Failure on the Left Side (Systolic Failure). Failure on the left side of the heart is the more common event. The failure can be a result of abnormal systolic (contraction) or diastolic (relaxation) action.
- This failure is often caused by a systolic abnormality (called systolic failure). In such cases, the heart muscles weaken and cannot keep up with the demands of the body. The left ventricle is usually dilated. Fluid backs up and accumulates in the lungs. Systolic heart failure typically occurs in men between the ages of 50 and 70 years who have had a heart attack.
- Between 20 - 50% of heart failure cases have abnormal diastolic actions, in which there is an abnormality in the way the heart relaxes. Most often in failure on the right side, the heart muscles thicken so that the muscles relax abnormally. In this case, fluid entering the heart backs up. This causes the veins in the body and tissues surrounding the heart to swell. It is often a precursor to systolic failure. Patients with diastolic failure are typically women, overweight, and elderly, and have high blood pressure and diabetes.
In both cases, with the weakened pump, fluid builds up in the lungs, and from there it builds up in tissues throughout the body, causing congestion.
Failure on the Right Side. Failure on the right side of the heart is most often a result of failure on the left. Because the right heart receives blood from the veins, failure here causes the blood to back up. As a result, the veins in the body and tissues surrounding the heart to swell. This causes swelling in the legs.
Ejection Fraction. To help determine severity, doctors use a calculation called an ejection fraction. This is the percentage of the blood pumped out during each heartbeat. An ejection fraction of 50 - 75% is considered normal, and, in general, a low percentage is considered an indication of failure. The ejection fraction in left-side heart failure typically falls below 40%. In severe failure it may drop as low as 5%.
Of note, between 20 - 50% of patients with heart failure have a normal ejection fraction, an indication of diastolic heart failure.
