Arrhythmia, also called dysrhythmia, is a disturbance of the heart's normal rhythm. When the heart beats, the electrical impulses that cause it to contract must follow a precise pathway through the heart. Any interruption in these impulses can cause an arrhythmia. Arrhythmias cause the heart to pump blood less effectively.
In an arrhythmia, the heart beats may be too slow (bradycardia, slower than 60 beats per minute), too rapid (tachycardia, greater than 100 beats per minute), too irregular (atrial or ventricular fibrillation), or too early (premature contraction).
Each day, a normal heart contracts about 100,000 times, at a rate anywhere from 60-100 times a minute. Changes in rate brought about by variations in activity, diet, medications, and age are normal and common. During intense exercise, a heart may speed up to 160-180 or more beats a minute. Running up a flight of stairs or being startled by a noise account for normal increases in heart rates as well. The rapid-fire contractions in all these situations are faster than the normal resting heart rate range, yet they pose no danger.
In most people, arrhythmias are minor and are not dangerous. A small number of people, however, have arrhythmias that are dangerous and require treatment. Arrhythmias are also more serious if the individual has other heart problems, such as atherosclerosis (hardening of the arteries) or high blood pressure.
The hollow center of the heart is divided into four sections, called chambers. The two upper chambers in the heart are called the atria (or atrium for one chamber). The two lower chambers in the heart are called ventricles.
The rhythm of the heart is normally generated and regulated by specialized tissue within the sinoatrial (SA) node, which is located within the wall of the right atrium of the heart. SA nodal pacemaker activity normally governs the rhythm of the atria and ventricles. Signals arising in the SA node stimulate the atria to contract and travel to the AV node. The atrioventricular node (AV node) is an area of specialized tissue between the atria and the ventricles of the heart, which conducts the normal electrical impulse from the atria to the ventricles.
Normal rhythm is very regular, with minimal changes. Atrial contraction is always followed by ventricular contraction in the normal heart. When this rhythm becomes irregular, tachycardic (too fast) or bradycardic (too slow), or the frequency of the atrial and ventricular beats are different, it is called an arrhythmia.
In general, arrhythmias that start in the ventricles are more serious than those that start in the atria.
About 14 million people in the United States have arrhythmias.
The most common arrhythmias are atrial fibrillation (also called atrial flutter). As many as two million Americans are living with atrial fibrillation. The number of atrial arrhythmias is related to age and the presence of underlying heart disease. The prevalence approaches 30% following open heart surgery.
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types of arrhythmia
Arrhythmias are classified not only by where they originate but also by the speed of heart rate they cause.
Tachycardia refers to a fast heart rate (beat), greater than 100 beats a minute.
Bradycardia refers to a slow heartbeat, or a resting heart rate less than 60 beats a minute.
Not all tachycardias or bradycardias indicate disease. Sinus arrhythmia refers to the normal increase in heart rate that occurs when the individual breathes in. During exercise, it is normal to develop sinus tachycardia as the heart speeds up to provide body tissues with more oxygen-rich blood.
Atrial fibrillation: Atrial fibrillation is a common arrhythmia and affects mainly older people (60 years and older). Atrial fibrillation is due to normal wear and tear on the heart muscle and also due to cardiovascular problems such as hypertension (high blood pressure). During atrial fibrillation, the electrical activity of the atria becomes uncoordinated. The atria beat so rapidly, as fast as 350-600 beats a minute, that instead of producing a single, forceful contraction, they fibrillate (quiver). Atrial fibrillation can be intermittent, lasting a few minutes to an hour or more, before returning to a regular heart rhythm. Atrial fibrillation can also be chronic, causing an ongoing problem. Atrial fibrillation is seldom a life-threatening arrhythmia.
Atrial flutter: Atrial flutter is similar to atrial fibrillation and both can coexist in the heart. The key distinction is that atrial fibrillation is characterized by 350-600 beats per minutes and atrial flutter is characterized by 200-400 beats per minute.
Supraventricular tachycardia (SVT): Supraventricular tachycardia (SVT) is a broad term that includes many forms of arrhythmia originating above the ventricles. SVTs usually cause a burst of rapid heartbeats that begin and end suddenly and that can last from seconds to hours. SVT may cause the heart to beat 160-200 times a minute. Symptoms of SVT are generally not life-threatening in an otherwise normal heart, although these arrhythmias may feel quite uncomfortable. SVTs are common in young people.
Wolff-Parkinson-White syndrome: One cause of SVT is known as Wolff-Parkinson-White syndrome. This arrhythmia is caused by an extra electrical pathway between the atria and the ventricles. This pathway may allow electrical current to pass between the atria and the ventricles without passing through the atrioventricular node (AV node) leading to short circuits and rapid heartbeats.
Ventricular tachycardia (VT): Ventricular tachycardia (VT) is a fast, regular beating of the heart that is caused by abnormal electrical impulses originating in the ventricles. Often, VTs are due to a short circuit around a scar from a previous heart attack. VTs can cause the ventricles to contract more than 200 beats a minute. Sometimes, ventricular tachycardias last for 30 seconds or less and are usually harmless, although they cause inefficient heartbeats. Still, an unsustained VT may be a predictor for more serious ventricular arrhythmias, such as longer lasting (sustained) VT. An episode of sustained VT is a medical emergency. It may be associated with palpitations, dizziness, fainting, or possibly death. Without prompt medical treatment, VT often turns into ventricular fibrillation. Rarely, VT occurs in a normal heart.
Ventricular fibrillation: About 300,000 Americans die every year of sudden cardiac death believed to be caused by ventricular fibrillation. With ventricular fibrillation, rapid, chaotic electrical impulses cause the ventricles to quiver uselessly instead of pumping blood. Without an effective heartbeat, the blood pressure falls rapidly, cutting off blood supply to vital organs, including the brain. Most individuals lose consciousness within seconds and require immediate medical assistance including cardiopulmonary resuscitation or CPR. The chances of survival may be increased if CPR is given until the heart can be shocked back into a normal rhythm with a machine called a defibrillator. Without CPR or defibrillation, death results in minutes. Most cases of ventricular fibrillation are linked to some form of heart disease. Ventricular fibrillation is frequently triggered by a heart attack.
Long QT syndrome: Long QT syndrome is a rare arrhythmia that can either be an inherited condition or one that occurs naturally. In older adults, long QT syndrome may be triggered by certain medications, including antibiotics and antifungals, antidepressants, antihistamines, antipsychotics, cholesterol-lowering drugs, diabetes medications, diuretics, and heart medications. Individuals with low potassium, magnesium, or calcium blood levels, such as those with the eating disorder anorexia nervosa, may be susceptible to prolonged QT intervals.
Although a heart rate below 60 beats a minute while at rest is considered bradycardia, a low resting heart rate does not always signal a problem. If an individual is physically fit, they may have an efficient heart capable of pumping an adequate supply of blood with fewer than 60 beats a minute while at rest. However, if the individual has a slow heart rate and the heart is not pumping enough blood, bradycardias may develop.
Sick sinus: If the pace-making sinus node is not sending impulses properly, the heart rate may be too slow or it may speed up and slow down intermittently. If the sinus node is functioning properly, sick sinus can be caused by an impulse block near the sinus node that is slowing, disrupting, or completely blocking conduction.
Conduction block: Conduction block of the heart's electrical pathways can occur in or near the AV node or along pathways that conduct impulses to each ventricle. Depending on the location and type of block, the impulses between the atria and ventricles may be slowed or partially or completely blocked. If the signal is completely blocked, certain cells in the AV node or ventricles are capable of initiating a steady, although usually slower, heartbeat. Some blocks may cause no signs or symptoms and others may cause skipped beats or bradycardia. Even without signs or symptoms, a conduction block is usually detectable on an electrocardiogram (ECG), which is a machine that detects and visually shows heart rhythm. Since some blocks are caused by heart disease, an ECG showing a block may be an early sign of heart problems.
Premature heartbeats can originate in either the atria or the ventricles. Although it often feels like a skipped heartbeat, a premature heartbeat is actually an extra beat between two normal heartbeats.
Premature heartbeats may indicate a more serious heart condition. However, a premature beat can trigger a longer lasting arrhythmia, especially in individuals with heart disease such as hypertension (high blood pressure). These types of arrhythmias are commonly caused by stimulants, such as caffeine from coffee, tea, soft drinks, over-the-counter cold remedies containing pseudoephedrine, and some asthma medications such as albuterol (Proventil®).
Fainting (syncope): Fainting or syncope is a sudden loss of consciousness. It most often occurs when the blood pressure is too low (hypotension) and the heart does not pump a normal supply of oxygen to the brain. Typically, a faint lasts only a few seconds or minutes and then the individual regains consciousness. Syncope (fainting) is a common problem that affects one million people in the United States every year. About one-third of individuals will faint at least once during a lifetime. A single fainting spell usually is not serious. It may be explained by factors such as stress, grief, overheating, dehydration, exhaustion, illness, or arrhythmias.
Mitral valve prolapse: The mitral valve is between the heart's left atrium and left ventricle. It has two flaps that open and close together like a pair of swinging doors. When the heart beats, the left ventricle pumps blood out to the body and the flaps swing shut. This keeps the blood in the ventricle from going back into the left atrium. In an individual who has mitral valve prolapse (MVP), one or both of the valve's flaps swing up into the atrium as they close. In some individuals, the flaps will still close completely, but in others, they may not shut properly. When the flaps don't close correctly, blood can leak back into the left atrium. This can happen because the flaps are too floppy, too big, or have the wrong shape.
Usually MVP does not cause health problems. Most individuals will continue to lead normal lives and many have no symptoms. In some individuals, the flaps of the mitral valve make a clicking sound when they close. A doctor may hear this when listening to the heart with a stethoscope. Individuals with MVP may also have a heart murmur. A heart murmur is the sound caused by the leaking blood. Individuals with MVP may also may feel dizzy or light-headed, feel anxious, be really tired, be out of breath when playing or exercising, feel that their heart is skipping beats or beating very fast, have chest pain, or have fainting episodes. Symptoms of MVP in children may go away as they age.