Heart arrhythmias

Anatomy
To understand arrhythmias, it's helpful to have some basic knowledge of the heart's structures and its electrical conduction system.
The heart is a hollow, muscular organ. The valves inside the heart help direct blood flow in and out of the heart, as well as regulate the movement of blood between the heart's chambers. The heart has four chambers. The upper chambers -- the right atrium and the left atrium -- are the receiving chambers. The lower chambers -- the bigger and thicker right ventricle and left ventricle -- are the discharging chambers, or the heart's actual pumps.

With each heartbeat, the heart contracts and pumps blood through the heart and to the rest of the body. Between each heartbeat, the heart relaxes and fills with blood, getting ready for the next contraction.

The heart has an electrical conduction system that controls heart rate and rhythm. The heart's natural pacemaker is called the sinus node. It's located in the right atrium. When the heart's electrical system works as it should, electrical impulses travel from the sinus node to the atrioventricular node (or AV node), which is located between the atria and the ventricles. At the AV node, the impulse slows to give the ventricles time to fill with blood before contracting. Then, the impulse travels over a network of fibers known as the bundle branches, which branch down to both ventricles. When the impulse reaches the ventricles, it sends the heart a signal to contract. An abnormal heart rhythm, or arrythmia, may develop if the impulse travels a different path, is blocked or delayed, or the fibers conducting it are damaged.

A normal resting heart rate is 60 to 100 beats per minute. An arrhythmia may cause the heart to beat irregularly -- either too slow (a condition known as bradycardia, or less than 60 beats per minute) or too fast (a condition known as tachycardia, or more than 100 beats per minute).





Types of arrhythmias
There are many types of arrhythmias, including:
Atrial fibrillation (AF): A fast, irregular, chaotic heartbeat that prevents the heart from pumping blood throughout the body adequately. Atrial fibrillation is the most common chronic arrhythmia. Sometimes, there are no symptoms. If symptoms are present, they may include palpitations, chest pain, shortness of breath or fatigue. Atrial fibrillation is often more serious when it accompanies heart disease. In this case, it may lead to enlargement of the heart, heart failure and blood clots, which increase the risk of stroke.

Atrial flutter (AFL): A rapid and ineffective heart rhythm. An atrial flutter gives a characteristic flutter wave on an electrocardiogram (EKG, a diagnostic test used to record the electrical activity of the heart). An atrial flutter may occur with atrial fibrillation. Like atrial fibrillation, it also increases the risk of stroke.

Supraventricular tachycardia (SVT): A fast heart rate that originates above the ventricle. Atrial fibrillation and atrial flutter are both types of supraventricular tachycardia.

Paroxysmal atrial tachycardia (PAT): A rapid heart rate that stops and starts unpredictably. It originates from the atria. PAT is also referred to as paroxysmal supraventricular tachycardia (PSVT).

Wolf Parkinson White syndrome (WPW): A congenital condition in which an extra electrical conduction system develops between the atria and ventricles. With this syndrome, impulses can be conducted without following the normal path through the AV node. Like atrial fibrillation and atrial flutter, WPW is a type of supraventricular tachycardia.

Premature atrial contraction (PAC): An extra heartbeat that originates from the atria before it should. PACs are quite common and typically not serious.

Ventricular tachycardia: A rapid heart rhythm that originates in the ventricles. This is a serious arrhythmia that can be life-threatening without emergency treatment.

Ventricular fibrillation: A fast, chaotic heart rhythm that prevents the heart from pumping blood. This life-threatening arrhythmia requires immediate emergency treatment.

Premature ventricular contraction (PVC): An extra beat that originates from the ventricles before it should. Like premature atrial contractions, PVCs are quite common and typically don't require treatment. If you have a PVC, it may feel as though your heart skips a beat.

Heart block (or AV block): A group of several arrhythmias, some more dangerous than others. Heart block is characterized by a defect in the electrical conduction of the AV node. With first-degree AV block, heart rate is normal but the prolonged conduction time through the AV node can be detected through an EKG. With second-degree AV block, impulses may be blocked occasionally or as frequently as every other beat. If many impulses are blocked, the heart rate will slow down. Third-degree AV block, or complete heart block, is more serious. With this condition, impulses from the sinus node don't reach the ventricle at all. Instead, impulses from the ventricles initiate heart contraction but the heart rate is very slow. Third-degree AV block requires emergency treatment.

Bundle branch block: A defect in the conduction of the impulse in the bundle branches of the ventricles. It may occur in the right or left bundle branches. This rhythm may be caused by damage to the heart from a heart attack.

Sinus bradycardia: A slow rhythm (less than 60 beats per minute) originating at the sinus node. This type of rhythm is normal in some conditioned athletes.

Sinus tachycardia: A fast rhythm (more than 100 beats per minute) originating at the sinus node. This increase in heart rate may be caused by increased demands on the heart, as you may experience with exertion or fever.

Sick sinus syndrome: A malfunctioning sinus node. The impulses may be initiated too slowly or too quickly. There may be long pauses between heart beats, or impulses may not be initiated at all. A pacemaker may be needed if symptoms are severe.

Causes/associated factors
Heart arrhythmias may have many causes. Heart disease -- including conditions such as heart valve disease, heart failure and heart attacks -- is the most common cause of serious arrhythmias. Other causes may include:
chronic disease, such as lung or thyroid disease
fever
infection
stimulants such as caffeine, tobacco or over-the-counter cold medications
You may be at risk for developing an arrhythmia if you're obese or have:

high blood pressure
high blood cholesterol
blood electrolyte imbalances
diabetes
pulmonary embolism
a collagen vascular disease, such as lupus and scleroderma
an infiltrative disease such as amyloidosis
Other risk factors include drug or alcohol abuse, stress, use of certain medications or supplements, a history of heart surgery, and a family history of heart disease. Generally, the risk increases as you get older.


Signs/symptoms
Some arrhythmias have no symptoms and may be left untreated. In other cases, symptoms may go unnoticed. When symptoms are noticeable, you may feel:
palpitations (a feeling of thumping, fluttering, skipping or racing of the heart)
faint or lightheaded
chest pain or tightness
shortness of breath
fatigue
anxiety
Sadly, some types of serious arrhythmia may be fatal with little or no warning.


Diagnosis
The doctor will review your medical history and do a physical exam. To detect an arrhythmia, heart disease or other underlying problems, you may need one or more diagnostic tests.
An electrocardiogram (EKG) may be done to record the electrical activity of the heart. This test will reveal any abnormal beats or arrhythmias that are present at the time of the recording.

Blood and urine tests may be done to provide information about your blood chemistry and hormone levels.

A chest X-ray can show whether the heart is enlarged, inflamed or surrounded with fluid.

An exercise stress test can help your doctor determine how well your heart is functioning. During the test, you'll exercise on a treadmill or exercise bike. While you're exercising, an EKG will record the electrical activity of your heart. Your heart rate and blood pressure will be monitored as well. Often, radioactive thallium is used during an exercise stress test. This substance will appear on an X-ray to help your doctor diagnose impaired blood flow in the heart. In this case, the test may be called a thallium stress test, a thallium scan or a nuclear scan. If you're unable to walk, medication may be used to stress your heart rather than exercise. This is known as a chemical stress test.

Various types of cardiac imaging may be done as well. For example:

An echocardiogram, or cardiac echo, is an ultrasound of the heart. This test uses sound waves to help the doctor study the heart structures, including the valves and walls. During an echocardiogram, the doctor will look for abnormalities such as reduced blood flow, clots, tumors and aneurysms. An echocardiogram is sometimes combined with an exercise stress test.

Electron beam computed tomography (EBCT) may be done to check for calcium deposits on the coronary arteries. With this test, an ultra thin X-ray beam is used to produce a computer-generated, cross-sectional picture of the heart.

A nuclear scan using a radioactive material, such as thallium or technetium, can help the doctor study heart function and blood flow, detect damage from heart attacks, and determine how well the coronary arteries are working. A nuclear scan may be referred to as a MUGA (multigated acquisition) scan or nuclear ventriculography.

SPECT (single-photon emission computed tomography) scans and PET (positron emission tomography) scans are specific types of nuclear scans that provide three-dimensional pictures of the heart. Often, PET scans are more expensive and not as readily available as SPECT scans.

Holter monitoring may be done to generate a continuous recording of the electrical activity of your heart for a period of 24 to 72 hours. During the test, you'll wear a small, portable monitor.

When symptoms or arrhythmias are infrequent, you may use an event recorder. You'll wear a small, portable monitor when symptoms are present and simply push a button to record the rhythm. In some cases, event recording is done in combination with Holter monitoring.

A coronary angiogram may be done to help the doctor study your blood vessels. During this imaging exam, you'll be given an injection of contrast dye to create various densities on the film.

An electrophysiology study (EP study, also known as cardiac mapping) may be another option. During this test, a catheter is inserted into a vein in your leg (or, rarely, your arm) and threaded into your heart. This catheter contains electrodes that can detect arrhythmias, as well as where the abnormal electrical impulses originate. An EP study may be used in conjunction with a procedure called radiofrequency ablation (described below) to treat arrhythmias.

Treatment
Some arrhythmias are harmless. In these cases, treatment is only needed if you have uncomfortable symptoms. More serious arrhythmias may be treated with medication or various procedures, as described below.
Medication
Your doctor may prescribe one or more medications to control your arrhythmia, depending on the type of arrhythmia and any other medical conditions that may influence your heart rhythm or overall health.

Sodium channel blockers
Sodium channel blockers suppress abnormal electrical impulses. They're used to treat supraventricular tachycardia, ventricular tachycardia and ventricular fibrillation. Examples include flecainide, procainamide and tocainide.

Benefits: They slow the heart's electrical impulses and prevent conduction through an abnormal pathway.

Risks: Common side effects include dizziness, lightheadedness, headache and fatigue. More serious side effects may include chest pain, shortness of breath, worsening of the arrhythmia, development of a new arrhythmia or heart failure.
Beta blockers
Beta blockers slow the heart rate by slowing atrioventricular conduction. They're used to treat supraventricular tachycardia and may help prevent the life-threatening arrhythmia ventricular fibrillation. Examples include propranolol and esmolol.

Benefits: They reduce the amount of oxygen needed by the heart and decrease the heart's workload.

Risks: Dizziness is a common side effect. Other possible side effects may include drowsiness, fatigue and lower libido or, for men, erectile dysfunction (impotence). Beta blockers aren't recommended for people who have certain respiratory problems, such as asthma.
Potassium channel blockers
Potassium channel blockers slow the heart rate and make the heart less likely to respond to abnormal electrical impulses. They're used to treat atrial fibrillation and flutter, supraventricular tachycardia, ventricular tachycardia and fibrillation. Examples include amiodarone and sotalol.

Benefits: They decrease the heart's workload.

Risks: Side effects may include dry mouth, nausea, vomiting and diarrhea. More serious side effects may include worsening of the arrhythmia, development of a new arrhythmia, or damage to the lungs, liver or eyes. Close monitoring may be needed while this drug is taken.
Calcium channel blockers
Calcium channel blockers prevent conduction of the sinus and AV node. They're used to treat supraventricular tachycardia. Examples include diltiazem and verapamil.

Benefits: They decrease the heart's workload.

Risks: Some calcium channel blockers aren't recommended for people who have heart failure or have survived a heart attack. In these cases, calcium channel blockers may increase the risk of fatal arrythmia complications.
Other medications
Other medications commonly used to treat arrhythmias include adenosine and digoxin. Both are used to treat supraventricular tachycardia. Warfarin, an anticoagulant, is used to prevent blood clots and stroke in cases of atrial fibrillation.

Cardioversion
Cardioversion is a procedure that uses electric current to convert an abnormal rhythm, such as atrial fibrillation, to a normal rhythm. Several weeks before the procedure, your doctor may prescribe anticoagulants to decrease the risk of clots forming in your heart. Cardioversion is done under a short-acting anesthetic. During the approximately 30-minute procedure, you'll receive one or more carefully timed and controlled electric shocks. You'll have an IV for fluids and breathe supplemental oxygen. Your vital signs will be monitored during the procedure and for several hours afterward.

Note: When an emergency electric shock is given to convert a life-threatening arrhythmia to a normal rhythm, the shock is much stronger. In this case, the procedure is called defibrillation.

Benefits: The procedure can be an effective treatment for supraventricular tachycardias and new cases of atrial fibrillation.

Risks: The skin on the chest may be mildly red or irritated after the procedure, and a reaction to the anesthesia is possible. Medication may be needed after the procedure to maintain a normal heart rhythm. Cases of long-term atrial fibrillation may not respond to this type of therapy.
Radiofrequency ablation
Radiofrequency ablation, also called catheter ablation, is a procedure done during an electrophysiology study. It's used to treat Wolf Parkinson White syndrome, as well as other types of arrhythmias. During the procedure, which is done under mild sedation, an electrode catheter is inserted through a vein in your groin and threaded into your heart. The catheter uses radiofrequency energy to ablate, or destroy, abnormal electrical pathways. The procedure usually lasts about three hours. When the catheter is removed, pressure will be applied to the puncture site. You'll need to lie in bed with your legs straight for several hours. During this time, your vital signs will be monitored and the puncture site will be checked often for bleeding.

Benefits: This procedure can treat atrial arrhythmias caused by an extra pathway in the heart. Lifelong medication isn't needed, and recovery time is much shorter than conventional surgery.

Risks: It's possible for a blood vessel or the heart itself to be perforated during the procedure. Other rare risks may include arrhythmias, blood clots, bleeding, stroke and heart attack.
Pacemaker
A cardiac pacemaker is an electrical device that senses your heart rate and stimulates your heart to beat when it beats too slowly or not at all. A pacemaker is used to treat bradycardia, partial heart block and complete heart block.

A pacemaker has two parts -- the lead wire and the pulse generator. The lead wire conducts electrical impulses from the pacemaker's pulse generator to your heart muscle. The pulse generator is a surgically implanted device that weighs about 2 to 4 ounces. It's powered by a lithium battery that can last from five to 10 years, depending on how often the pacemaker stimulates your heart and its specific features. Eventually, the pacemaker batteries will need to be surgically replaced. Sometimes the leads must be surgically replaced as well.

Benefits: A pacemaker can relieve symptoms of dizziness, fainting and shortness of breath. A pacemaker can help you enjoy an improved or even normal activity level.

Risks: Problems with pacemakers are uncommon, but may include:

reaction to the anesthesia used during surgery
puncture of the lung, vein or heart by a needle or the lead wires
infection or bleeding of the pacemaker pocket
mechanical or electrical failure of the leads or device
movement or damage to the leads
Implantable cardioverter defribrillator
An implantable cardioverter defibrillator (ICD) is a surgically implanted device that detects life-threatening arrhythmias and delivers an electrical shock to the heart to convert the rhythm back to normal. ICDs may be used to treat sustained or symptomatic ventricular tachycardia.

Like a pacemaker, an ICD has a generator and leads. An ICD typically lasts four to six years, depending on how often shocks are given. Newer models may last longer, but eventually the ICD will need to be surgically replaced.


Benefits: An ICD can reduce the risk of dying from cardiac arrest (a condition in which your heart stops beating) or a dangerous arrhythmia, such as ventricular tachycardia.

Risks: Problems with ICDs are uncommon, but may include:

reaction to the anesthesia used during surgery
puncture of the lung, vein or heart by a needle or the lead wires
infection or bleeding of the pacemaker pocket
mechanical or electrical failure of the leads or device
movement or damage to the leads
Surgery
Surgery may be considered if medication or other procedures aren't successful in controlling an arrhythmia. For atrial fibrillation, an open-heart procedure known as the maze procedure may be done. Incisions are made in the atria to redirect the electrical impulses on a normal pathway. The procedure typically takes about three hours.

Benefits: This procedure can cure atrial fibrillation.

Risks: Medication may be needed after the surgery to maintain a normal heart rhythm. Sometimes a pacemaker is needed as well. Other possible surgical complications include bleeding, infection, blood clots or stroke.

Complications
Again, some type of arrhythmias aren't serious. Without proper treatment, however, certain types of arrhythmias may lead to life-threatening complications. For example, atrial fibrillation can lead to blood clots that lodge in the heart or the brain, causing a heart attack or stroke. Untreated complete heart blocks or very slow bradycardias can lead to low blood pressure, fainting or death. Sustained ventricular tachycardia and ventricular fibrillation can be fatal without immediate emergency treatment.

Pregnancy-specific information
Palpitations may increase during pregnancy, although most are harmless and don't need treatment. Medication to treat arrhythmias during pregnancy must be prescribed with caution. The medication amiodarone may harm a developing baby, and some beta blockers have been associated with poor fetal growth and low blood sugar in newborns.

Senior-specific Information
The risk of developing arrhythmias, particularly atrial fibrillation, increases with age. In fact, atrial fibrillation affects an estimated 10 percent of Americans older than age 80.

Prevention
Again, the most common cause of serious arrhythmias is heart disease. To keep your heart healthy, consider the following lifestyle choices:
Reduce the amount of fat and cholesterol in your diet.
Exercise regularly. (Discuss with your doctor safe ways to increase your physical activity if you have any medical conditions or you're planning to add strenuous exercise to your routine.)
Lose excess weight, or maintain a normal weight for your age and height.
If you smoke, quit.
Limit the amount of alcohol you drink. The general recommendation is no more than 2 to 3 ounces a day.
Limit the amount of caffeine you drink.
Keep your stress under control.
Follow your doctor's recommendations for managing any medical conditions you may have.