An arrhythmia is any type of irregular heartbeat. It may present itself as a skipped beat, a rapid or slow heart rate, or a continuous irregular heartbeat. Each year, millions of people are affected by arrhythmias, most of which can be treated and are not life-threatening. However, many arrhythmias can be very dangerous and contribute to approximately 500,000 deaths in the US each year. Early and appropriate diagnosis and treatment can help decrease the number of deaths from arrhythmias between 15 percent and 25 percent annually.
How does the heart beat?
The heart consists of four chambers, the right and left atria and the right and left ventricles. The heart beats, or contracts, because of electrical stimulation of heart muscle tissue. Electrical impulses originate in the sinus node (the heart's natural pacemaker), which is a group of special cells located in the high right atrium. The sinus node, in turn, sends the electrical signal throughout both atria to the atrioventricular (A-V) node. The A-V node transmits the signal to a group of fibers throughout the ventricles. Stimulation of muscle in the ventricle is ultimately what causes the familiar sensation of a heartbeat. A normal heart rate for an adult is between 60 beats and 100 beats per minute. In order for the heart to beat properly, the signal must follow an exact course throughout the heart.
When does an arrhythmia occur?
The heart's natural pacemaker (sinus node) usually determines the heart rate, however almost all other heart muscle is capable of assuming a pacemaker role (e.g., where the electrical impulse begins).
An arrhythmia can occur under several conditions: when a part of the heart other than the sinus node acts as the pacemaker, when the regular path for electrical conduction is altered, when the sinus node develops an abnormal rhythm, or when a patient develops heart block along the normal electrical pathway. Heart block usually occurs at the site of the atrioventricular node, prelcuding part or all of the impulse from traveling from the atria to the ventricles. The incidence of arrhythmias increases with age, occurring most frequently in middle-aged adults. People with a history of heart disease, blood chemistry imbalances, and some metabolic diseases are at a greater risk for the development of arrhythmias and their complications.
Certain medications and substances can also cause an irregular heartbeat, including caffeine, tobacco, alcohol, cold and cough supressing medications, appetite suppressants, cocaine, psychotropic drugs (used to treat certain mental illnesses), antiarrhythmics, and beta blockers. Stress may also trigger an arrhythmia. Some of these arrhythmias can be dangerous, while others are not. Frequently, there is no obvious cause to an arrhythmia.
Types of arrhythmia
Doctors diagnose arrhythmias based on two factors: where it occurs in the heart - the atria or ventricles - and the effect it has on the heart's rhythm.
Sinus tachycardia: The heart rate is increased because of fast conduction speed from the sinus node.
Sick sinus syndrome: The heart rate is decreased because of improper signals from the sinus node. Occasionally the heart rate fluctuates between a rapid and slow heart rate (if this occurs, the condition is referred to as tachycardia-bradycardia syndrome).
Atrial flutter: Electrical signals originate in the atria and are fired quickly, usually resulting in a regular and fast heart rate.
Atrial fibrillation: The atria fire rapid and sporadic signals to the ventricles resulting in an irregular heartbeat.
Sinus arrhythmia: The heart rate changes consistently with breathing.
Premature supraventricular or atrial contractions (PACs): The atria generate an early heartbeat preceding the next regular heartbeat.
Supraventricular tachycardia (SVT): The heart rate is increased after a succession of continual beats in the atria.
Paroxysmal atrial tachycardia (PAT): Periodic and frequently unpredicatable intervals of rapid heartbeats initiated by atrial-generated impulses.
Wolff-Parkinson-White syndrome: Electrical signals arrive to the ventricles via an "accessory pathway" from the atria (e.g., the signal bypasses the atrioventricular node), creating a potentially dangerous situation whereby the heart rate can become excessively rapid.
Ventricular arrhythmias are usually more serious than atrial arrhythmias and include the following:
Ventricular tachycardia: Electrical impulses originate from a site in the ventricles causing the heart rate to become excessively rapid.
Ventricular fibrillation: The ventricles fire rapid and erratic signals. This condition causes an entirely uncoordinated, ineffective contraction that is best regarded as a tremor rather than a beat.
- Premature ventricular complexes (PVCs): A premature heartbeat arising from the ventricles causes the heart to pause somewhat before the next regular heartbeat.
There are many symptoms associated with arrhythmias. The most common symptoms include the following: chest pain, palpitations (racing heart or a fluttery feeling in your chest), dizziness, lightheadedness or a faintness sensation, and shortness of breath. Other symptoms can include fatigue and clammy or pale skin. The pulse rate or rhythm may change. Sometimes a person may be asymptomatic (no symptoms). Unfortunately, many of the life-threatening arrhythmias begin with no warning signs at all. Rather, they rapidly progress to a state of unconciousness, that if uncorrected emergently, frequently results in sudden cardiac death.
Diagnosis and tests
Doctors diagnose arrhythmias in several ways. A patient may develop symptoms that prompt the seeking of medical attention. Alternatively, a routine physical exam may reveal an irregular heart beat. Your physician will begin with a complete medical history that includes all past and ongoing medical problems and assess your current medications. He/She will inquire about any recent ingestion of caffeine or other stimulants, tobacco, and over-the-counter cold remedies and assess your stress level and sleep habits.
Occasionally, an arrhythmia can be discovered by feeling changes in pulse rate and rhythm or by listening to the heart with a stethoscope. Sometimes an arrhythmia does not occur during the physical exam. Other tests may allude to the diagnosis of an arrhythmia that was the cause of symptoms experienced previously.
The noninvasive electrocardiogram (ECG) is the most accurate way to diagnose an arrhythmia. An ECG measures the electrical activity that occurs in the heart. Leads are attached to the chest and body to record the electrical signals created by the heart. The signals are recorded on a strip of paper that is then interpreted by your physician. There are several types of ECGs that can be performed:
A resting ECG is performed while the patient is lying down. Leads are attached to the chest, arms and legs. Electrical impulses are recorded for several minutes.
An exercise ECG, also known as a stress test, involves exercise during the ECG. A patient may be on a treadmill or bicycle. This test can indicate whether exercise has an effect on the heart's conduction activity.
A patient may have to wear a holter monitor. The patient has leads attached to the chest and carries the monitor like a purse over a 24 to 48 hour period. The monitor measures electrical activity that occurs during a typical day. If the patient is asked to wear the monitor for a longer period of time, a transmission of the recording can be made to a specific site. This is called transtelephonic monitoring and is used for patients who have infrequently occurring arrhythmias.
Another noninvasive test frequently used is an echocardiogram. A transducer passed over the patient's chest uses ultrasound waves to form an image of the heart. It helps to visualize the chambers and their response to the electrical activity in the heart.
The heart's electrical activity can be mapped to detect the source of an arrhythmia by performing a procedure called an electrophysiology study. If a specific area is identified as the root of the arrhythmia, a technique called radio frequency catheter ablation may be used as therapy. Radio waves emitted from the tip of the heart catheter destroy the tissue that was responsible for the arrhythmia. The catheter is guided to the heart through a vein.
Treatment and patient education
Treating arrhythmias depends on its cause and point of origin in the heart. Sometimes treatment is not indicated.
Circumstances may dictate emergency treatment. For life-threatening arrhythmias, an electrical counter shock can quickly return the heart back to its regular rhythm. When cardioversion is performed, paddles apply a shock to the chest wall.
Medication therapy is generally indicated following cardioversion to prevent recurrence of the arrhythmia. Drugs are chosen to prevent possible side effects and interactions with other medications. It is important to understand how your medication works, when and how often it should be taken, and what its interaction can be when taken with other medications.
Patients taking medications for arrhythmia should know how to take their pulse. Ask your health care provider to instruct you. Remember to take your medication exactly as prescribed, at the same time each day. Never self-discontinue your medication suddenly. Report any side effects to your health care provider.
Several implanted devices are also frequently used to correct arrhythmias. A pacemaker is indicated when the heart's natural pacemaker (sinus node) is not functioning correctly. A pacemaker is a device that is implanted just below the surface of the skin. A lead is permanently attached from the pacemaker directly into the right atrium.
Automatic implantable defibrillators are used to correct both atrial and ventricular arrhythmias. Also surgically implanted, these devices are able to quickly detect an arrhythmia and shock the heart into a regular rhythm. The advent of automatic implantable defibrillators has been a major revolution in the field of cardiology for patients at high risk for suffering serious, potentially life-threatening arrhythmias.
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