What is an arrhythmia?
An arrhythmia (also called dysrhythmia) is an abnormal rhythm of the heart, which can cause the heart to pump less effectively.
Arrhythmias can cause problems with contractions of the heart chambers by:
Not allowing the ventricles (lower chambers) to fill with an adequate amount of blood, because an abnormal electrical signal is causing the heart to pump too fast.
Not allowing a sufficient amount of blood to be pumped out to the body, because an abnormal electrical signal is causing the heart to pump too slowly or too irregularly.
In any of these situations, the heart may not be able to pump an adequate amount of blood to the body with each beat due to the arrhythmia's effects on the heart rate. The effects on the body are often the same, whether the heartbeat is too fast, too slow, or too irregular.
What are the symptoms of arrhythmia?
The following are the most common symptoms of arrhythmias. However, each child may experience symptoms differently. Symptoms may include:
Low blood pressure
The symptoms of arrhythmias may resemble other medical conditions or heart problems. Always consult your child's doctor for a diagnosis.
Another indication of an arrhythmia is a change in the electrocardiogram (ECG or EKG) pattern. However, ECG changes are not seen unless an ECG test is performed or a child is being monitored in the hospital or other facility. Because symptoms such as those listed above may indicate the presence of an arrhythmia, an ECG is commonly done on children with one or more of the symptoms.
The heart's electrical system
The heart is, in the simplest terms, a pump made up of muscle tissue. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart.
How does the heart beat?
An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), which is a small mass of specialized tissue located in the right atrium (right upper chamber of the heart). The sinus node generates an electrical stimulus regularly (60 to190 times per minute, depending on the age of the child and his or her activity level). This electrical stimulus travels down through the conduction pathways (similar to the way electricity flows through power lines from the power plant to your house) and causes the heart's lower chambers to contract and pump out blood. The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart).
The electrical impulse travels from the sinus node to the atrioventricular node (also called AV node), where impulses are slowed down for a very short period, then continue down the conduction pathway via the bundle of His into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to the right and left ventricles.
Normally, at rest, as the electrical impulse moves through the heart, the heart contracts about 60 to 140 times a minute, depending on a child's age. Each contraction of the ventricles represents one heartbeat. The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract.
Under some abnormal conditions, certain heart tissue is capable of starting a heartbeat, or becoming the "pacemaker," just like the sinus node. An arrhythmia (abnormal heartbeat) may occur when:
The heart's natural pacemaker (the sinus node) develops an abnormal rate or rhythm.
The normal conduction pathway is interrupted.
Another part of the heart takes over as pacemaker.
What is an electrocardiogram (ECG)?
The electrical activity of the heart is measured by an electrocardiogram (ECG or EKG). By placing electrodes at specific locations on the body (chest, arms, and legs), a graphic representation, or tracing, of the electrical activity can be obtained. Changes in an ECG from the normal tracing can indicate arrhythmias, as well as other heart-related conditions.
What does an ECG mean?
Almost everyone knows what a basic ECG tracing looks like. But what does it mean?
The first little upward notch of the ECG tracing is called the "P wave." The P wave indicates that the atria (the two upper chambers of the heart) are electrically stimulated to pump blood to the ventricles.
The next short flat segment is called the "PR interval." The PR interval represents the delay in the conduction of the electrical signal from the atria to the ventricles.
The next part of the tracing is a short downward section connected to a tall upward then downward section. This part is called the "QRS complex." It indicates that the ventricles (the two lower chambers of the heart) are electrically stimulated (undergo depolarization) to pump out blood to the body.
The next short flat segment is called the "ST segment." The ST segment indicates that the ventricles are depolarized and that the electrical signal for ventricular contraction is completed.
The next upward curve is called the "T wave." The T wave indicates the electrical recovery period of the ventricles in preparation for the next electrical depolarization and mechanical contraction.
When your child's doctor studies your child's ECG, he or she looks at the size and length of each part of the EKG. Variations in size and length of the different parts of the tracing may be significant.
The tracing for each lead of a 12-lead ECG will look different, but will have the same basic components as described above. Each lead of the 12-lead ECG is "looking" at a specific part of the heart from different angles. Variations in a lead may indicate a problem with the part of the heart associated with that particular lead.
What are the different types of arrhythmias?
An atrial arrhythmia is an arrhythmia caused by abnormal function of the sinus node or the atrioventricular node, or by the development of another atrial pacemaker within the atrium that takes over the function of the sinus node.
A ventricular arrhythmia is an arrhythmia caused by an abnormal electrical focus within the ventricles, resulting in abnormal conduction of electrical signals within the ventricles. The sinus node and atrioventricular node may function normally.
Arrhythmias can also be classified as slow (bradyarrhythmia) or fast (tachyarrhythmia). "Brady-" means slow, while "tachy-" means fast.
Listed below are some of the more common arrhythmias:
Sinus arrhythmia. A condition in which the heart rate varies with breathing. Sinus arrhythmia is commonly found in children; adults may often have it as well. This is a benign (not dangerous) condition.
Premature ventricular contractions (PVCs). A condition in which an electrical signal originates in the ventricles and causes the ventricles to contract before receiving the electrical signal from the atria. PVCs are not uncommon and typically do not cause symptoms or problems. However, if the frequency of the PVCs increases significantly, symptoms such as weakness, fatigue, dizziness, fainting, or palpitations may be experienced.
Sinus tachycardia. A condition in which the heart rate is faster than normal for the child's age because the sinus node is sending out electrical impulses at a rate faster than usual. Most commonly, sinus tachycardia occurs as a normal response of the heart to exercise when the heart rate increases to cope with increased energy requirements. Sinus tachycardia can be completely appropriate and normal, such as when a child is exercising vigorously. However, it may cause symptoms, such as weakness, fatigue, dizziness, or palpitations if the heart rate becomes too fast to pump an adequate supply of blood to the body. Sinus tachycardia is often temporary, occurring when the body is under stress from exercise, strong emotions, fever, or dehydration, to name a few causes. Once the stress is removed, the heart rate will return to its usual rate.
Ventricular tachycardia (VT). A life-threatening condition in which an electrical signal is sent from the ventricles at a very fast but often regular rate. If the heart rate is sustained at a high rate for more than 30 seconds, symptoms such as weakness, fatigue, dizziness, fainting, or palpitations may be experienced. A person in VT may require an electric shock or medications to convert the rhythm to back normal sinus rhythm.
Sick sinus syndrome. A condition in which the sinus node sends out electrical signals either too slowly or too fast. There may be alternation between too-fast and too-slow rates. This condition may cause symptoms if the rate becomes too slow or too fast for the body to tolerate. This condition is not common in children.
Ventricular fibrillation (VF). A condition in which many electrical signals are sent from the ventricles at a very fast and erratic rate. As a result, the ventricles are unable to fill with blood and pump. This rhythm is life-threatening because there is no pulse and complete loss of consciousness. A person in VF requires prompt defibrillation to restore the normal rhythm and function of the heart. It will result in sudden cardiac death if not treated within seconds.
Premature supraventricular contractions or premature atrial contractions (PAC). A condition in which an atrial pacemaker site above the ventricles sends out an electrical signal early. The ventricles are usually able to respond to this signal, but the result is an irregular heart rhythm. PACs are common and may occur as the result of stimulants such as coffee, tea, alcohol, cigarettes, or medications.
Wolff-Parkinson-White Syndrome (WPW). A condition in which an electrical signal may arrive at the ventricle too fast due to an extra conduction pathway or a shortcut from the atria to the ventricles. Tachycardia is a common symptom.
Supraventricular tachycardia (SVT), paroxysmal atrial tachycardia (PAT). A condition in which the heart rate speeds up due to a series of early beats from an atrial or junctional pacemaker site above the ventricles. PAT usually begins and ends rapidly, occurring in repeated periods. This condition can cause symptoms such as weakness, fatigue, dizziness, fainting, or palpitations if the heart rate becomes too fast. This condition is the most common type of abnormal tachycardia in children, and is sometimes referred to as paroxysmal supraventricular tachycardia (PSVT).
Atrial flutter. A condition in which the electrical signals come from the atria at a fast but regular rate, often causing the ventricles to contract faster and increase the heart rate. When the signals from the atria are coming at a faster rate than the ventricles can respond to, the ECG pattern develops a signature "sawtooth" pattern, showing two or more flutter waves between each QRS complex. The number of waves between each QRS complex is expressed as a ratio, i.e., a two-to-one atrial flutter means that two waves are occurring between each QRS.
Atrial fibrillation. A condition in which the electrical signals come from the atria at a very fast and erratic rate. The ventricles contract in an irregular manner because of the erratic signals coming from the atria.
The symptoms of various arrhythmias may resemble other medical conditions or heart problems. Always consult your child's doctor for a diagnosis.
How are arrhythmias diagnosed?
In addition to a complete medical history and physical examination of your child, there are several different types of procedures that may be used to diagnose arrhythmias. Some of these procedures include the following:
Electrocardiogram (ECG or EKG). An electrocardiogram is a measurement of the electrical activity of the heart. By placing electrodes at specific locations on the body (chest, arms, and legs), a picture, or tracing, of the electrical activity can be obtained as the electrical activity is received and interpreted by an ECG machine. An ECG can indicate the presence of arrhythmias or other types of heart conditions. There are several variations of the ECG test, including the following:
Resting ECG. For this procedure, the clothing on the upper body is removed and small, sticky patches called electrodes are attached to the chest, arms, and legs. These electrodes are connected to the ECG machine by wires. The ECG machine is then started and records the heart's electrical activity for a minute or so. The child is lying down during this ECG.
Exercise ECG, or stress test. The child is attached to the ECG machine as described above. However, rather than lying down, the child exercises by walking on a treadmill or pedaling a stationary bicycle while the ECG is recorded. This test is done to assess changes in the ECG during stress such as exercise.
Signal-averaged ECG. This procedure is done in the same manner as a resting ECG, except that the heart's electrical activity is recorded over a longer period of time, usually 15 to 20 minutes. Signal-averaged ECGs are done when arrhythmia is suspected but not seen on a resting ECG. The signal-averaged ECG has increased sensitivity to abnormal ventricular activity called "late potentials." Signal-averaged ECG is used in research and seldom used in clinical practice.
Holter monitor. An ECG recording done over a period of 24 or more hours. Three electrodes are attached to the child's chest and connected to a small, portable ECG recorder by lead wires. The child goes about his or her usual daily activities (except for activities such as taking a shower, swimming, or any activity causing an excessive amount of sweating which would cause the electrodes to become loose or fall off) during this procedure. There are two types of Holter monitoring, including the following:
The ECG is recorded continuously during the entire testing period.
Event monitor, or loop recording
The ECG is recorded only when the patient starts the recording when symptoms are felt or when an abnormal rhythm is detected.
Holter monitoring may be done when an arrhythmia is suspected but not seen on a resting ECG. Arrhythmias may be short-lived in nature and not seen during the shorter recording times of the resting ECG.
Electrophysiologic study (EPS). An invasive test in which a small, thin tube (catheter) is inserted in a large blood vessel in the leg or arm and advanced to the heart. This gives the doctor the capability of finding the site of the arrhythmia's origin within the heart tissue, thus determining how to best treat it. Another procedure called an esophageal electrophysiologic study may be ordered where a soft, thin flexible plastic tube is inserted in the nostril and placed in the esophagus (close to the atria) to provide a more precise ECG recording.
Tilt table test. A test recommended for children who have frequent fainting (syncope) episodes. The test displays how the heart rate and blood pressure respond to a change in position--lying down to standing up. During this test, medication may be given intravenously to help prevent a fainting episode once the cause has been identified by the doctor.