Cardiac arrhythmia is any of a group of conditions in which the electrical activity of the heart is irregular or is faster or slower than normal.
Some arrhythmias are life threatening and can cause cardiac arrest and sudden death. Others cause symptoms, such as an awareness of a different heartbeat, or palpitation, which can be unpleasant. Some are simply normal variants. Most people have experienced a skipped beat or a sudden fast heart rate. In adults the normal resting heart rate ranges from 60 beats per minute to 100 beats per minute. A small area in the upper chamber of the heart called the senatorial node or sinus node controls the normal heartbeat. The sinus node contains specialized cells that have spontaneous electrical activity that starts each normal heartbeat.
Faster and slower arrhythmias
In an adult, a resting heart rate faster than 100 beats/minute is considered tachycardia. This number varies with age, as the heartbeat of a younger person is naturally faster than that of an older person's. During exercise the sinus node increases its rate of electrical activity to increase the heart rate developing what is called sinus tachycardia. In contrast, arrhythmias that are due to fast, abnormal electrical activity can cause tachycardia that are dangerous. If the ventricles of the heart experience one of these tachycardia for a long period of time, there can be deleterious effects. Individuals may sense a tachycardia as a pounding sensation of the heart, known as palpitations. If a tachycardia lowers blood pressure it may cause lightheadedness or dizziness, or even fainting (syncope). If the tachycardia is too fast, the pump function of the heart is impaired, and may lead to sudden death.
Most tachycardia is not dangerous. Causes of tachycardia include stress, ingested or injected substances (i.e.: caffeine, amphetamines, alcohol, and an overactive thyroid gland (hyperthyroidism).
A slow rhythm, known as bradycardia (less than 60 beats/min), is usually not life threatening, but may cause symptoms. It may be caused by reversible causes (low oxygen, electrolyte abnormalities), or be more permanent (heart block). When it causes symptoms implantation of a permanent pacemaker may be needed. Either dysrhythmia requires medical attention to evaluate the risks associated with the arrhythmia.
Fibrillation
A serious variety of arrhythmia is known as fibrillation. The muscle cells of the heart normally function together, creating a single contraction when stimulated. Fibrillation occurs when the heart muscle begins a quivering type of motion due to a lack of synchrony among contractile cells. Fibrillation can affect the atrium (atrial fibrillation) or the ventricle (ventricular fibrillation); ventricular fibrillation is life threatening.
Atrial fibrillation is the chaotic motion in the upper chambers of the heart, known as the atria. Atrial fibrillation is often due to serious underlying medical conditions, and should be evaluated by a physician. Atrial fibrillation is associated with connexin dysfunction in the cardiac conduction system.
Ventricular fibrillation occurs in the ventricles (lower chambers) of the heart; it is always a medical emergency. If left untreated, ventricular fibrillation (VF, or V-fib) can lead to death within minutes. When a heart goes into V-fib, effective pumping of the blood stops. V-fib is considered a form of cardiac arrest, and an individual suffering from it will not survive unless cardiopulmonary resuscitation (CPR) and defibrillation are provided immediately.
Diagnosis
Cardiac arrhythmias are often first detected by simple nonspecific means: auscultation of the heartbeat with a stethoscope, or feeling for peripheral pulses. These cannot usually diagnose specific arrhythmias, but can give a general indication of the heart rate and whether it is regular or irregular. Not all the electrical impulses of the heart produce audible or palpable beats; in many cardiac arrhythmias, the premature or abnormal beats do not produce an effective pumping action and are experienced as "skipped" beats.
The simplest specific diagnostic test for assessment of heart rhythm is the electrocardiogram (abbreviated ECG or EKG). A Halter monitor is an EKG recorded over a 24-hour period, to detect arrhythmias that may happen briefly and unpredictably throughout the day.
There are many types of arrhythmias this is a list of common cardiac arrhythmias
Atrial Rhythms
Ventricular Rhythms
Junctional Arrhythmias
Heart Blocks, also known as AV blocks
Arrhythmias may also be treated electrically. Cardioversion is the application of electrical current across the chest wall to the heart and it is used for treatment of supraventricular or pulsed ventricular tachycardia. Defibrillation differs in that it is used for ventricular fibrillation and pulseless ventricular tachycardia, and more electricity is delivered with defibrillation than with cardioversion. In cardioversion, the recipient is either sedated or lightly anesthetized for the procedure. In defibrillation, the recipient has lost consciousness so there is no need for sedation.
Electrical treatment of arrhythmia includes cardiac pacing. Temporary pacing may be done for very slow heartbeats, or bradycardia. A pacemaker may be placed when the bradycardia is not expected to recover.
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