Introduction:

To understand what occurs in heart failure, it helps to be familiar with the anatomy of the heart and how it works. 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 external structures of the heart include the ventricles, atria, arteries, and veins. Arteries carry blood away from the heart while veins carry blood into the heart. The vessels colored blue indicate the transport of blood with relatively low content of oxygen and high content of carbon dioxide. The vessels colored red indicate the transport of blood with relatively high content of oxygen and low content of carbon dioxide.

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 rich in oxygen.

• The oxygen-rich blood returns through veins coming from the lungs (pulmonary veins) to the heart.
• The heart receives the oxygen-rich blood 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 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 aorta.

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-triggered electrical impulses.

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 cardiac arrest). 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) and 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.

• 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 sides of the heart. 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 (Left-Ventricular Heart Failure). Failure on the left side of the heart is more common than failure on the right side. The failure can be a result of abnormal systolic (contraction) or diastolic (relaxation) action:

• Systolic. Systolic heart failure is a pumping problem. In systolic failure, the heart muscles weaken and cannot pump enough blood throughout the body. The left ventricle is usually stretched (dilated). Fluid backs up and accumulates in the lungs (pulmonary edema). Systolic heart failure typically occurs in men between the ages of 50 - 70 years who have had a heart attack.
• Diastolic. Diastolic heart failure is a filling problem. When the left ventricle muscle becomes stiff and cannot relax properly between heartbeats, the heart cannot fill fully with blood. When this happens, fluid entering the heart backs up. This causes the veins in the body and tissues surrounding the heart to swell and become congested. Patients with diastolic failure are typically women, overweight, and elderly, and have high blood pressure and diabetes.

Failure on the Right Side (Right-Ventricular Heart Failure). Failure on the right side of the heart is most often a result of failure on the left. Because the right ventricle 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 feet, ankles, legs, and abdomen. Pulmonary hypertension (increase in pressure in the lung's pulmonary artery) and lung disease may also cause right-sided heart failure.

Ejection Fraction. To help determine the severity of left-sided heart failure, doctors use an ejection fraction (EF) calculation, also called a left-ventricular ejection fraction (LVEF). This is the percentage of the blood pumped out from the left ventricle during each heartbeat. An ejection fraction of 50 - 75% is considered normal. Patients with left-ventricular heart failure are classified as either having a preserved ejection fraction (greater than 50%) or a reduced ejection fraction (less than 50%).

Patients with preserved LVEF heart failure are more likely to be female and older, and have a history of high blood pressure and atrial fibrillation (a disturbance in heart rhythm).