Each year, sudden cardiac death affects more than 300,000 people in the United States alone. Cardiac arrhythmias are responsible for many of these episodes of sudden death. The Cardiac Arrhythmias Research and Education Foundation Inc. (C.A.R.E.), has the mission to provide funding for research and to increase professional and public awareness of unexpected sudden cardiac death due to acquired heart disease and inherited rhythm disorders.
What are cardiac arrhythmias?
Cardiac arrhythmias are disturbances in the heart's natural rhythm. These disturbances are caused by disruptions in the normal conduction of electrical signals within the heart. For various reasons, electrical signals may be detoured, slowed, or blocked while traveling through certain parts of the heart. This can cause the heart's natural rhythm to speed up or slow down, affecting the flow of blood to the body's internal organs. There are many different types of arrhythmias.
What Causes Arrhythmias?
There are many known causes of arrhythmias, including scars in the heart muscle from a previous myocardial infarction (heart attack), lack of blood to the heart muscle from atherosclerosis, abnormalities in the electrical conduction system, or extra electrical connections within the heart. Other known causes include abnormalities in the heart's muscle or electrical system and the effects of certain medications.
The underlying mechanisms of certain arrhythmias remain unresolved. For example, inherited disorders can contribute to the onset of arrhythmias in several ways. First, single gene mutations may be directly responsible for the abnormality that causes the arrhythmia, such as in Long QT Syndrome. Second, inherited structural abnormalities may cause arrhythmias, such as in familial Hypertrophic Cardiomyopathy or familial mitral valve prolapse. Finally, certain inherited disorders may lead to premature coronary artery disease or cardiomyopathy, which may cause arrhythmias.
What are some common symptoms of arrhythmias?
Depending on the type of arrhythmia, the symptoms will vary. Some arrhythmias may be brief, lasting only a few moments, and others may be longer, causing sustained episodes. Arrhythmias may cause the heart to pump less effectively and may cause dizziness, chest discomfort, shortness of breath, or loss of consciousness. While many arrhythmias are not life-threatening, the most dangerous types can lead to sudden cardiac death. Although the severity of the symptoms is usually related to the seriousness of the arrhythmia, there are situations in which symptoms have not occurred but the potential for serious arrhythmias still exists.
What is being done to study arrhythmias?
Significant breakthroughs have occurred in the past several years that have greatly increased the understanding of the genetic basis of certain forms of sudden cardiac death. These breakthroughs form the foundation on which new testing techniques and treatments are being made available.
Inherited rhythm disorders, such as Long QT Syndrome, Hypertrophic Cardiomyopathy and Brugada Syndrome, are known as autosomal dominant genetic variations, which means that the child of a person with the gene for one of those disorders has a 50:50 chance of inheriting the same genetic mutation.
Talk to your doctor regarding the feasibility of genetic testing for inherited rhythm disorders. Cardiology genetic testing services are commercially available from GeneDx (www.genedx.com/site/cardiology_genetic_testing_services) and through several research programs in the United States.
Where can I learn more about arrhythmias?
The best person to talk to is a board-certified cardiologist or electrophysiologist. These specialists can evaluate symptoms and family histories and make recommendations based on their findings. You can also obtain additional information about arrhythmias by visiting the C.A.R.E. Foundation website at www.careforhearts.org or by calling C.A.R.E. at 800-404-9500 or e-mailing
Normal Heart Rhythm
A normal heartbeat is the result of the heart’s own rhythm working together with the nervous system to meet the body’s needs. The heart’s electrical system consists of a natural pacemaker, the Sinus (SA) Node, where each heartbeat originates and a network of specialized conduction pathways called the Purkinje fibers. These fibers transmit electrical signals throughout the heart’s chambers, causing them to contract in an orderly pattern. This results in a smooth flow of blood into and out of the heart.
Examples of Life-threatening Cardiac Arrhythmias
With cardiac arrhythmias, the orderly conduction of electrical signals is disrupted. This affects the heart's ability to pump blood to the rest of the body.
During ventricular tachycardia (VT), the electrical signal may be interrupted after it travels into the heart's lower chambers (right (RV) and left (LV) ventricles. The disrupted signal may then move erratically through the muscle, causing the heart to contract unusually fast. These rapid contractions prevent the heart from filling adequately with blood between beats. VT may cause dizziness and fainting and may be life-threatening if not treated properly.
In ventricular fibrillation (VF), the electrical signal moves chaotically throughout the chambers. This causes the heart muscle to quiver. Since the heart is not contracting, blood is not being pumped properly, and the body is quickly starved of oxygen. This can result in sudden cardiac death if not treated immediately.
The only effective treatment for a person in VF is to deliver an electrical shock to the heart muscle with a defibrillator. An external defibrillator may be automated (AED) or manual. Patients at high risk for VT and VF may also have an implanted cardioverter defibrillator (ICD).