House Call: Heart and the electrical system
The heart’s electrical system controls all the events that occur when your heart pumps blood.
The system is comprised of three main parts including the sinoatrial (SA) node, located in the right atrium, the atrioventricular (AV) node, located in the interatrial septum close to the tricuspid valve, and the His-Purkinje system, located along the walls of the heart’s ventricles.
The SA node works as our natural pace maker, receiving messages from other parts of the body and directing the heart to function accordingly, while sending the signals throughout the rest of the electrical system.
This explains why your heart rate usually slows during sleep, and may speed up when frightened—the SA node is receiving these signals from the body and reacting. Arrhythmia (irregular heart beat) is the most common abnormality of the heart’s electrical system. Many arrhythmia disorders are benign, but some increase risk of stroke and other life-threatening conditions.
Therefore, if you are feeling symptoms such as ongoing heart palpitations it is important to get the condition assessed by a medical professional. Most often, arrhythmia and abnormalities of the heart’s electrical system are treatable conditions.
Irregularly fast heart rhythms can be treated with catheter ablation, in which the cardiologist destroys the abnormal tissue. Irregularly slow heart rhythms are most often treated with a pacemaker.
The exceptional team of cardiologists and related healthcare professionals at Cone Health Heart and Vascular Center are dedicated to continuous education and training on the Heart’s Electrical System and methods of treating abnormalities of the system.
Dr. James Allred is a cardiologist and member of the Cone Health medical staff. He is a 2002 graduate of Medical College of Virginia, completing a residency in internal medicine at Duke University Medical Center.
Dr. Allred is a leading expert in electrophysiology and treating arrhythmia, completing a fellowship in cardiovascular disease and electrophysiology at University Alabama-Birmingham.
Your Heart’s Electrical System[i]
Your heart’s electrical system controls all the events that occur when your heart pumps blood. The electrical system also is called the cardiac conduction system. If you’ve ever seen the heart test called an EKG (electrocardiogram), you’ve seen a graphical picture of the heart’s electrical activity.
Your heart’s electrical system is made up of three main parts:
- The sinoatrial (SA) node, located in the right atrium of your heart
- The atrioventricular (AV) node, located on the interatrial septum close to the tricuspid valve
- The His-Purkinje system, located along the walls of your heart’s ventricles
A heartbeat is a complex series of events. These events take place inside and around your heart. A heartbeat is a single cycle in which your heart’s chambers relax and contract to pump blood. This cycle includes the opening and closing of the inlet and outlet valves of the right and left ventricles of your heart.
Each heartbeat has two basic parts: diastole and systole. During diastole, the atria and ventricles of your heart relax and begin to fill with blood.
At the end of diastole, your heart’s atria contract (atrial systole) and pump blood into the ventricles. The atria then begin to relax. Your heart’s ventricles then contract, (ventricular systole), pumping blood out of your heart.
Each beat of your heart is set in motion by an electrical signal from within your heart muscle. In a normal, healthy heart, each beat begins with a signal from the SA node. This is why the SA node sometimes is called your heart’s natural pacemaker. Your pulse, or heart rate, is the number of signals the SA node produces per minute.
The signal is generated as the vena cavae fill your heart’s right atrium with blood from other parts of your body. The signal spreads across the cells of your heart’s right and left atria.
This signal causes the atria to contract. This action pushes blood through the open valves from the atria into both ventricles.
The signal arrives at the AV node near the ventricles. It slows for an instant to allow your heart’s right and left ventricles to fill with blood. The signal is released and moves along a pathway called the bundle of His, which is located in the walls of your heart’s ventricles.
From the bundle of His, the signal fibers divide into left and right bundle branches through the Purkinje fibers. These fibers connect directly to the cells in the walls of your heart’s left and right ventricles (see yellow on the picture in the animation).
The signal spreads across the cells of your ventricle walls, and both ventricles contract. However, this doesn’t happen at exactly the same moment.
The left ventricle contracts an instant before the right ventricle. This pushes blood through the pulmonary valve (for the right ventricle) to your lungs and through the aortic valve (for the left ventricle) to the rest of your body.
As the signal passes, the walls of the ventricles relax and await the next signal.
This process continues over and over as the atria refill with blood and more electrical signals come from the SA node.
To learn more about the heart, its electrical system and the services offered at Cone Health Heart and Vascular Center visit http://www.conehealth.com/heart or call 336.832.7000.
Cone Health Heart and Vascular Center is located on the campus of Moses H. Cone Memorial Hospital at 1200 N. Elm Street Greensboro, NC 27401.
[i] The National Heart, Lung and Blood Institute, Your Hearts Electrical System, http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/electrical.html