Heart Beat

A heartbeat is a two-part pumping action that takes about a second. As blood collects in the upper chambers (the right and left atria), the heart's natural pacemaker (the SA node) sends out an electrical signal that causes the atria to contract. This contraction pushes blood through the tricuspid and mitral valves into the resting lower chambers (the right and left ventricles). This part of the two-part pumping phase (the longer of the two) is called diastole.

The second part of the pumping phase begins when the ventricles are full of blood. The electrical signals from the SA node travel along a pathway of cells to the ventricles, causing them to contract. This is called systole. As the tricuspid and mitral valves shut tight to prevent a back flow of blood, the pulmonary and aortic valves are pushed open. While blood is pushed from the right ventricle into the lungs to pick up oxygen, oxygen-rich blood flows from the left ventricle to the heart and other parts of the body.

After blood moves into the pulmonary artery and the aorta, the ventricles relax, and the pulmonary and aortic valves close. The lower pressure in the ventricles causes the tricuspid and mitral valves to open, and the cycle begins again. This series of contractions is repeated over and over again, increasing during times of exertion and decreasing while you are at rest. The heart normally beats about 60 to 80 times a minute when you are at rest, but this can vary. As you get older, your resting heart rate rises. Also, it is usually lower in people who are physically fit.

Your heart does not work alone, though. Your brain tracks the conditions around you—climate, stress, and your level of physical activity—and adjusts your cardiovascular system to meet those needs.

The human heart is a muscle designed to remain strong and reliable for a hundred years or longer. By reducing your risk factors for cardiovascular disease, you may help your heart stay healthy longer

Heart Valves

Four valves regulate blood flow through your heart:

* The tricuspid valve regulates blood flow between the right atrium and right ventricle.

* The pulmonary valve controls blood flow from the right ventricle into the pulmonary arteries, which carry blood to your lungs to pick up oxygen.

* The mitral valve lets oxygen-rich blood from your lungs pass from the left atrium into the left ventricle.

* The aortic valve opens the way for oxygen-rich blood to pass from the left ventricle into the aorta, your body's largest artery, where it is delivered to the rest of your body

Coronary Arteries

Diagram of the Coronary Arteries

Coronary Circulation

The heart muscle, like every other organ or tissue in your body, needs oxygen-rich blood to survive. Blood is supplied to the heart by its own vascular system, called coronary circulation.

The aorta (the main blood supplier to the body) branches off into two main coronary blood vessels (also called arteries). These coronary arteries branch off into smaller arteries, which supply oxygen-rich blood to the entire heart muscle.

The right coronary artery supplies blood mainly to the right side of the heart. The right side of the heart is smaller because it pumps blood only to the lungs.

The left coronary artery, which branches into the left anterior descending artery and the circumflex artery, supplies blood to the left side of the heart. The left side of the heart is larger and more muscular because it pumps blood to the rest of the body.

Bundle Branch Block

Your heart has a natural "pacemaker" called the sinoatrial (SA) node. The SA node is a specialized group of cells at the top of your heart's upper-right chamber (the right atrium). Anywhere between 60 and 100 times a minute, the SA node sends an electrical impulse throughout your heart to cause it to beat (contract).

When the SA node sends an electrical impulse, that impulse first travels through the heart's upper chambers (the atria). It then passes through a small group of cells called the atrioventricular (AV) node. The AV node checks the impulse and sends it along a track called the bundle of His. The bundle of His divides into a right bundle branch and a left bundle branch, which lead to your heart's lower chambers (the ventricles)

Sometimes the electrical impulse cannot travel throughout the heart because part of the heart's conduction system is "blocked." If an impulse is blocked as it travels through the bundle branches, you are said to have bundle branch block.

What causes bundle branch block?

For the left and right ventricles to contract at the same time, an electrical impulse must travel down the right and left bundle branches at the same speed. If there is a block in one of these branches, the electrical impulse must travel to the ventricle by a different route. When this happens, the rate and rhythm of your heartbeat are not affected, but the impulse is slowed. Your ventricle will still contract, but it will take longer because of the slowed impulse. This slowed impulse causes one ventricle to contract a fraction of a second slower than the other.

The medical terms for bundle branch block are derived from which branch is affected. If the block is located in the right bundle branch, it is called right bundle branch block. If the block is located in the left bundle branch, it is called left bundle branch block.

The block can be caused by coronary artery disease, cardiomyopathy, or valve disease. Right bundle branch block may also occur in a healthy heart.

What are the symptoms of bundle branch block?

If there is nothing else wrong with your heart, you probably will not feel any symptoms of bundle branch block. In fact, some people may have bundle branch block for years and never know they have the condition. In people who do have symptoms, they may faint (syncope) or feel as if they are going to faint (presyncope).

So why should we worry about bundle branch block? Because it can be a warning sign of other, more serious heart conditions. For example, it might mean that a small part of your heart is not getting enough oxygen-rich blood. Also, researchers have found that people who have left bundle branch block may be at greater risk for heart disease than are people who do not have the condition.

How is bundle branch block diagnosed?

Doctors can use an electrocardiogram (EKG or ECG) machine to record the electrical impulses of your heart. Bundle branch block shows up on the EKG tracing. The electrical patterns recorded by the EKG machine can even show your doctor whether the block is located in the right or left bundle branch.

How is bundle branch block treated?

In most cases, bundle branch block does not need treatment. But patients who have bundle branch block along with another heart condition may need treatment. For example, if bundle branch block develops during a heart attack, you may need a pacemaker. After a heart attack, your heart is fragile, and bundle branch block may cause a very slow heart rhythm (bradycardia). A pacemaker will help regulate the heart's rhythm after a heart attack.

For patients with both bundle branch block and dilated cardiomyopathy, a new type of pacing called cardiac resynchronization treatment (CRT) may be used. Normally, pacemakers pace only one of the lower heart chambers (the ventricles) at a time. But CRT re-coordinates the beating of the two ventricles by pacing them at the same time. Recent studies have shown that CRT works for certain patients with both bundle branch block and dilated cardiomyopathy.

Even if you do not have other conditions, you should still see your doctor regularly so that he or she can be sure there are no other changes in your heart

Conduction System

Electrical impulses from your heart muscle (the myocardium) cause your heart to beat (contract). This electrical signal begins in the sinoatrial (SA) node, located at the top of the right atrium. The SA node is sometimes called the heart's "natural pacemaker." When an electrical impulse is released from this natural pacemaker, it causes the atria to contract. The signal then passes through the atrioventricular (AV) node. The AV node checks the signal and sends it through the muscle fibers of the ventricles, causing them to contract. The SA node sends electrical impulses at a certain rate, but your heart rate may still change depending on physical demands, stress, or hormonal factors

Anatomy and physiology of the Heart

The heart weighs between 7 and 15 ounces (200 to 425 grams) and is a little larger than the size of your fist. By the end of a long life, a person's heart may have beat (expanded and contracted) more than 3.5 billion times. In fact, each day, the average heart beats 100,000 times, pumping about 2,000 gallons (7,571 liters) of blood.
Your heart is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone (sternum). A double-layered membrane called the pericardium surrounds your heart like a sac. The outer layer of the pericardium surrounds the roots of your heart's major blood vessels and is attached by ligaments to your spinal column, diaphragm, and other parts of your body. The inner layer of the pericardium is attached to the heart muscle. A coating of fluid separates the two layers of membrane, letting the heart move as it beats, yet still be attached to your body.
Your heart has 4 chambers. The upper chambers are called the left and right atria, and the lower chambers are called the left and right ventricles. A wall of muscle called the septum separates the left and right atria and the left and right ventricles. The left ventricle is the largest and strongest chamber in your heart. The left ventricle's chamber walls are only about a half-inch thick, but they have enough force to push blood through the aortic valve and into your bodthpulmonary arteries, which carry blood to your lungs to pick up oxygen.