Arrhythmias

Definition

An arrhythmia is any disorder of heart rate or rhythm.

Causes, incidence, and risk factors

Arrhythmias are caused by a disruption of the normal electrical conduction system of the heart. Normally, the 4 chambers of the heart (2 atria and 2 ventricles) contract in a very specific, coordinated manner. When the heart beats faster than normal, it is called tachycardia. Bradycardia is a slower-than-normal rhythm.

The electrical impulse that signals the heart to contract in a synchronized manner begins in the sinoatrial node (SA node), which is the body's natural pacemaker.

The signal leaves the SA node and travels through the 2 upper chambers (atria), stimulating them to contract. Then the signal passes through another node (the AV node), and finally, through the lower chambers (ventricles), stimulating them to contract in synchrony.

Problems can occur anywhere along this conduction system, causing various arrhythmias. There may be a problem in the heart muscle itself, causing it to respond differently to the signal, or causing the ventricles to contract independently of the normal conduction system.

Tachycardia that originates in the atria is called supraventricular tachycardia, and ventricular tachycardia when it originates in the ventricles. The most common supraventricular tachycardias are atrial fibrillation, atrial flutter, and atrioventricular nodal reentry tachycardia.

Bradycardia is due either to altered pacemaker function of the SA node or an interrupted impulse conduction through the natural electrical pathways of the heart.

The incidence of tachycardia and bradycardia varies greatly, depending on the condition of the heart itself, the history of prior heart attack, blood chemistry imbalance, or endocrine abnormalities.

Arrhythmias may also be caused by some substances or drugs. These include beta blockers, psychotropics, sympathomimetics, caffeine, amphetamines, and cocaine. Sometimes antiarrhythmic medications -- prescribed to treat one type of arrhythmia -- can actually cause another type of arrhythmia.

Some types of arrythmias may be life-threatening if not promptly and adequately treated.

Symptoms

• Fast or slow heart beat (palpitations)
• Skipping beats
• Fainting
• Light-headedness, dizziness
• Chest pain
• Shortness of breath
• Changes in the rate, rhythm, or pattern of the pulse
• Paleness
• Sweating

The person may not have symptoms. The first symptom may be sudden cardiac arrest (loss of heartbeat), which requires CPR.

Signs and tests

A doctor will listen to your heart with a stethoscope and feel your pulse. Your blood pressure may be low or normal.

Tests that reveal arrhythmias and identify the type of arrhythmia include:

• ECG
• Ambulatory cardiac monitoring (for example, a Holter monitor, used for 24 hours, or loop recorders that may be worn for 2 weeks or longer)
• Echocardiogram
• Electrophysiology study (EPS)
• Coronary angiography

Various tests are appropriate to confirm or rule out suspected causes of the arrhythmia. EPS testing may be performed to locate the origin of the arrhythmia and determine the best treatment, especially if a pacemaker implantation or catheter ablation procedure is being considered.

Treatment

When an arrhythmia is serious and not well-tolerated, urgent intervention may be required to restore normal rhythm.

Electrical "shock" (defibrillation or cardioversion), the implantation of a temporary pacemaker to interrupt the arrhythmia, or antiarrhythmic drugs may be used.

Most supraventricular arrythmias can be treated and cured with radiofrequency ablation, eliminating the need for lifelong drug therapy.

Increasingly, most ventricular tachycardias are treated with an implantable cardioverter-defibrillator (ICD). As soon as arrhythmia begins, the ICD detects it, and sends either an automatic electrical shock to terminate it, or a burst of pacing activity to overdrive it.

Symptomatic bradycardias and heart blocks are treated with the implantation of a pacemaker.

Expectations (prognosis)

The outcome is dependent on several factors:

• The kind of arrhythmia -- whether it is supraventricular tachycardia, or a more dangerous arrhythmia such as ventricular tachycardia or ventricular fibrillation, which are potentially fatal
• The overall pumping ability of the heart
• The underlying disease and its treatability

With bradycardias that are treated with a permanent pacemaker, there is usually good outcome.

Complications

• Angina (chest pain caused by imbalance of supply and demand for oxygen in the heart muscle)
• Heart attack
• Heart failure
• Stroke
• Sudden death

Calling your health care provider

Call your provider if you develop symptoms indicating a possible arrhythmia.

Call your provider if an arrhythmia has been diagnosed and symptoms worsen or do not improve with treatment.

Prevention

Using methods of preventing coronary artery disease may in turn decrease the likelihood of developing an arrhythmia. These methods include not smoking, eating a well-balanced, low-fat diet, and exercising regularly.

Illustrations

Heart, section through the middle

Heart, front view

Atrioventricular block,EKG tracing

Normal heart rhythm

Bradycardia

Ventricular tachycardia

Conduction system of the heart

Page Content:

Dysrhythmias; Abnormal heart rhythms ; dysrhythmias; cardiac dysrhythmias; basic dysrhythmias; abnormal heart rhythm