Exploring Your Heart’s Electrical Conduction

Your heart has four chambers, four valves, two nodes, and a system of fibers known as the His-Purkinje system. The four chambers consist of two atria (upper chambers) and two ventricles (lower chambers). Your four valves consist of a tricuspid valve, pulmonary valve, mitral valve, and aortic valve.

The tricuspid and mitral valves are known as inlet valves; they sit between the left atrium and ventricle and right atrium and ventricle, respectively. Your pulmonary and aortic valves are known as outlet valves; they allow blood to leave your heart from the right and left ventricles, respectively.

The two nodes are the sinoatrial (SA) and atrioventricular (AV) nodes. The former is located near the top of your right ventricle; the latter is located between the atria and ventricles. Lastly, the His-Purkinje system spreads throughout your ventricles’ walls.

Below, you’ll discover how your heart’s electrical system regulates your heartbeat through the organ’s chambers, valves, nodes, and His-Purkinje network of fibers.

The Essence Of A Heartbeat

Each time your heart beats, it goes through a multi-step process that accepts blood, oxygenates it, and sends it out to the rest of your body. This occurs as the four chambers relax (known as diastole) and contract (known as systole). When the chambers relax, they fill with blood. When your atria contract, they pump blood through the tricuspid and mitral valves into the ventricles. When your right ventricle contracts, it pumps blood through the pulmonary valve to your lungs. When your left ventricle contracts, it pumps blood through the aortic valve to the rest of your body.

This cycle represents your heartbeat. It is triggered by electrical signals from your SA node.

The Path Of Electrical Signals

Your right atrium fills with blood supplied by the inferior and superior vena cavae. Once the chamber has filled, your SA node generates an electrical signal. The signal spreads throughout both atria and causes them to contract, pushing blood into their corresponding ventricles. The signal then reaches your AV node and pauses while your ventricles fill with blood.

Once your ventricles have completely filled, the signal advances to the bundle of His, a group of cells located throughout your ventricles. The signal travels downward through the bundle of His and splits into two directions. It continues to travel through the Purkinje fibers, which are located in the inner walls of your ventricles. As the signal travels, your ventricles contract and push blood outward. The right chamber sends blood through the pulmonary valve to your lungs while the left chamber sends blood through the aortic valve to the rest of your body.

There are many potential heart problems that can affect the organ’s ability to pump blood effectively. For example, a regurgitant mitral valve can cause leaking between the left atrium and ventricle. An atrial septal defect can allow blood to travel between the left and right atria. Fortunately, these problems can be resolved with surgery. If you suspect you may be suffering from a heart problem, ask your doctor whether minimally invasive surgery can be performed.

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How Congenital Heart Defects Are Diagnosed

If a congenital heart defect is severe (for example, as in the case of tetralogy of Fallot), it will likely be diagnosed when a mother-to-be is pregnant. If it is not diagnosed during pregnancy, there is a high likelihood that it will be detected within weeks after she gives birth to the child. If the defect is less severe, it can remain hidden for years. In those cases, a physical exam, X-rays, and other tests will eventually expose it.

In this article, we’ll provide a brief overview of the types of tests that physicians, pediatrists, and pediatric cardiologists will use to diagnose congenital heart defects.

Physical Examination

A doctor may stumble upon signs of a defect through conducting a routine physical exam. He may listen to the child’s heart activity by using a stethoscope, and detect a problem. Or, if symptoms of a heart defect manifest, he might try to identify cyanosis (a warning sign of complex defects), breathing difficulties, or other signs. A physical exam is rarely adequate for accurately diagnosing heart problems in children.

Echocardiography

An echocardiogram generates a moving image of the child’s heart through ultrasound. Sound waves create the image and allow the physician to examine the muscle’s function. The doctor can not only identify defects, but can also determine how the muscle is adapting to them. Echocardiography can be performed while the mother is still carrying the child in her womb. If a congenital problem is identified, a treatment path can be formulated before childbirth.

Electrocardiogram

An electrocardiogram (ECG) can be used to study the electrical signals generated in the sinus node as they travel throughout the heart’s four chambers. It can highlight the rhythm, pace, and strength of the heartbeats as the signals travel from the atria to the ventricles.

X-Ray Of The Chest

While X-rays are limited in their scope when compared to an echocardiogram or ECG, they can help the physician identify an enlarged heart. They can also provide clues (e.g. fluid in the lungs) that imply the child is suffering from mild heart failure.

Cardiac Catheterization

Cardiac catheterization is a slightly invasive procedure. A catheter is inserted into the groin or arm, and threaded through a blood vessel to the heart. Once the catheter arrives at the site, a dye is released into one of the heart’s four chambers. The dye is used to create an X-ray image of the area that lets the doctor examine the flow of blood through the targeted chamber.

This same technique can be used to identify the level of oxygen and blood within certain chambers. If the levels are low or high, they may imply the presence of an atrial or ventricular septal defect. These are characterized by a hole in the septum, the wall separating the left and right sides of the heart.

Once a congenital heart defect has been identified, your doctor can determine whether treatment is necessary. If it is, treatment can include medications, catheter-based procedures, and even open-heart surgery.

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