Peninsula Cardiology

Arrhythmias

How the Heart Works

The normal heart is a strong, muscular pump a little larger than a fist. It pumps blood continuously through the circulatory system. Each day the average heart beats (expands and contracts) 100,000 times and pumps about 2,000 gallons of blood. In a 70-year lifetime, an average human heart beats more than 2.5 billion times.

The circulatory system is the network of elastic tubes through which blood flows, carrying oxygen and nutrients to all parts of the body. The system includes the heart, lungs, arteries, arterioles (small arteries) and capillaries (minute blood vessels), as well as venules (small veins) and veins, which return the blood to the heart. If all these vessels were laid end-to-end, they would extend for about 60,000 miles — far enough to encircle the earth more than twice.

Circulating blood takes oxygen and nutrients to all the body's organs and tissues, including the heart itself. It also picks up waste products from the body's cells. These waste products are removed as they are filtered through the kidneys, liver and lungs.

What is the structure of the heart?

The heart has four chambers. The upper two are the right and left atria — the lower two, the right and left ventricles. The heart also has four valves that open and close to let blood flow in only one direction when the heart contracts (beats). The four heart valves are:

• Tricuspid valve, located between the right atrium and right ventricle
• Pulmonary or pulmonic valve, between the right ventricle and the pulmonary artery
• Mitral valve, between the left atrium and left ventricle
• Aortic valve, between the left ventricle and the aorta

Each valve has a set of flaps (also called leaflets or cusps). The mitral valve has two flaps; the others have three. Under normal conditions, the valves permit blood to flow in only one direction. Blood flow occurs only when there's a difference in pressure across the valves, which causes them to open.

How does the heart pump blood?

The heart pumps blood to the lungs and to all the body's tissues by a sequence of highly organised contractions of the four chambers. For the heart to function properly, the four chambers must beat in an organised way. This is governed by an electrical impulse or signal that starts in a small bundle of highly specialised cells located in the right atrium — the sinoatrial node (SA node, also called the sinus node). When this electrical impulse moves across the heart's chambers, they contract, or beat. That's why the SA node is called the "natural pacemaker." Normally, electrical impulses are generated at a given rate, but emotional reactions and hormonal factors can affect the rate of discharge. This lets the heart rate respond to varying demands.

What Are Arrhythmias?

The heart is a muscle that works like a pump. It's divided into four chambers — two atria at the top of the heart and two ventricles at the bottom. The heart beats (contracts) when an electrical impulse from the heart's "natural pacemaker" — the sinoatrial or SA node — moves through it. The normal sequence, called the sinus rhythm begins in the right atrium, spreads throughout the atria and to the atrioventricular (AV) node. From the AV node, the impulses (signals) travel down a group of specialized fibers (the His-Purkinje system) to all parts of the ventricles. This exact route must be followed for the heart to pump properly. As long as the electrical impulse is transmitted normally, the heart pumps and beats at a regular pace. A normal heart beats 60 to 100 times a minute.

The term arrhythmia refers to any change from the normal sequence of electrical impulses, causing abnormal heart rhythms. This can cause the heart to pump less effectively. Some arrhythmias are so brief (for example, a temporary pause or premature beat) that the overall heart rate or rhythm isn't greatly affected. But if arrhythmias last for some time, they may cause the heart rate to be too slow or too fast or the heart rhythm to be erratic.

The term tachycardia refers to a heart rate of more than 100 beats per minute. Bradycardia describes a rate of less than 60 beats per minute.

Tachycardia

A fast heart rate is called tachycardia. Tachycardias fall into two major categories. Ventricular tachycardia involves only the ventricles. Supraventricular tachycardia involves both the atria and the ventricles. The definition of "too fast" usually depends upon the person's age and physical activity.

What causes tachycardia?

Under certain conditions, the automatic firing rate of secondary pacemaker tissue may become too fast. If such an abnormal "focus" fires faster than the sinus node, it may take over control of the heart rhythm and cause tachycardia.

In another type of abnormal conduction, impulses get caught in a merry-go-round-like sequence. This process, called reentry, is a common cause of tachycardias. Regardless of their cause, tachycardias are classified by where they arise. Thus, ventricular tachycardias start in the heart's ventricles (lower chambers). Supraventricular tachycardias arise higher in the heart — either in the upper chambers (atria) or the middle region (AV node or the very beginning portion of the His-Purkinje system.)

What are the symptoms and treatments for tachycardia (rapid heart beating)?

Rapid heart beating can produce symptoms of palpitations, rapid heart action, dizziness, lightheadedness, fainting or near fainting. Heartbeats may have either a regular or irregular rhythm. Rapid heart beating in the ventricles — called ventricular tachycardia — can be life-threatening. The most serious cardiac rhythm disturbance is ventricular fibrillation, where the lower chambers quiver and the heart can't pump any blood. Collapse and sudden death follows unless medical help is provided immediately.

If treated in time, ventricular tachycardia and ventricular fibrillation can be converted into normal rhythm with electrical shock. Rapid heart beating can be controlled with medications and by identifying or destroying the focus of rhythm disturbances. One effective way of correcting these life-threatening rhythms is by using an electronic device called an implantable cardioverter defibrillator.

Bradycardia

A heart rate that's "too slow" is called bradycardia. What's "too slow" depends upon a person's age and physical activity.

What are the symptoms and treatments for bradycardia (slow heartbeat)?

A heart rhythm that's too slow can cause fatigue, dizziness, lightheadedness, fainting or near-fainting spells. These symptoms can be easily corrected by implanting an electronic pacemaker under the skin to speed up the heart rhythm as needed.

Arrhythmias Originating in the Atria

Atrial fibrillation

Sometimes your heart's electrical signals can lose their regular pattern. In the condition called atrial fibrillation (AF), many parts of the atria, the heart's two upper chambers, start emitting uncoordinated electrical signals. The atria pump too fast and unevenly and won't fully contract. In fact, they may contract 5–7 times faster than normal — up to 300–400 beats per minute. Not all these signals go to the ventricles, so although their rate is irregular, it won't be this fast and the ventricles can still pump out blood.

An estimated 2.2 million Americans are living with AF. That makes it the most common "serious" heart rhythm abnormality.

AF isn't life-threatening, but it can lead to other rhythm problems, chronic fatigue, congestive heart failure and worst of all — stroke. When your left atrium pumps too fast and unevenly, blood doesn't empty completely into your left ventricle. Instead, leftover blood "pools" in the atrium. This blood can form clots. If a clot breaks loose, enters the bloodstream and travels to the brain, it can plug an artery and cause a stroke. This doesn't happen to everyone with AF, but your chances of having a stroke are five times higher if you have AF. About 15–20 percent of all strokes occur in people with AF.

Atrial flutter

This condition occurs when rapidly fired signals cause the muscles in the atria to contract quickly, leading to a very fast, steady heartbeat.

Premature atrial contraction (PAC)

Premature beats or extra beats most often cause irregular heart rhythms. Those that start in the upper chambers are called premature atrial contractions (PACs). If you've ever felt your heart "skip a beat," it was probably from this type of arrhythmia. In reality, the heart doesn't skip a beat. Instead an extra beat comes sooner than normal.

Premature beats are very common in normal children and teenagers — most people have them at some time. Usually no cause can be found and no special treatment is needed. The premature beats may disappear later. Occasionally premature beats may be caused by disease or injury to the heart. Your doctor may recommend more tests to make sure your heart is OK.

Sick sinus syndrome

When the sinus node doesn't fire its signals properly, the heart rate slows down. This is called sick sinus syndrome. In this condition, the rate sometimes changes back and forth between a slow rate (bradycardia) and a fast rate (tachycardia).

Sinus arrhythmia

This refers to cyclic changes in the heart rate during breathing. It's common in children and often found in adults.

Sinus tachycardia

Sinus tachycardia is a normal increase in the heart rate caused when the sinus node (the heart's natural pacemaker) sends out electrical signals faster than usual. It occurs with fever, excitement and exercise. No treatment is needed. Rarely, diseases such as anemia (low blood count) or increased thyroid activity cause this fast heart rate. In these cases, when the disease is treated, the tachycardia goes away.

Supraventricular tachycardia (SVT)

Supraventricular tachycardia (SVT) is also called paroxysmal atrial tachycardia (PAT) or paroxysmal supraventricular tachycardia (PSVT). In this condition a series of early beats in the atria speeds up the heart rate. Many people with it don't need medical therapy. Treatment is considered if episodes are prolonged or occur often. This is the most common form of arrhythmia in children.

Wolff-Parkinson-White (WPW) syndrome

Abnormal pathways between the atria and ventricles cause the electrical signal to arrive at the ventricles too soon and to be transmitted back into the atria. Very fast heart rates may develop as the electrical signal ricochets between the atria and ventricles. Many people with WPW syndrome don't have symptoms or episodes of tachycardia.

Arrhythmias Originating in the Ventricles

Premature ventricular contraction (PVC)

Premature beats or extra beats most often cause irregular heart rhythms. Premature ventricular contractions (PVCs) start in the ventricles. If you've ever felt your heart "skip a beat," it was probably from this type of arrhythmia. The heart doesn't really skip a beat. Instead an extra beat comes sooner than normal. Then there's a pause that causes the next beat to be more forceful. You felt this more-forceful beat.

Premature beats are very common in normal children and teenagers — most people have them at some time. Usually no cause can be found and no special treatment is needed. The premature beats may disappear later. Occasionally premature beats may be caused by disease or injury to the heart. Your doctor may recommend more tests to make sure your heart is OK.

Ventricular tachycardia (VT)

Ventricular tachycardia (VT) is a fast heart rate that starts in the heart's lower chambers (ventricles). VT may result from serious heart disease; it usually requires prompt treatment. If treatment is required, it includes medicines and treating the cause, if possible. The type and length of treatment depends on what's causing the problem. In some people radio frequency ablation or surgery may be needed to control the tachycardia.

Ventricular fibrillation

Ventricular fibrillation is a condition in which disordered electrical activity causes the ventricles to contract in a rapid, unsynchronized, uncoordinated fashion. When this occurs, little or no blood is pumped from the heart. Collapse and sudden death follows unless medical help is provided immediately. If treated in time, ventricular tachycardia and ventricular fibrillation can be converted into normal rhythm with electrical shock. Rapid heart beating can be controlled with medications by identifying or destroying the focus of rhythm disturbances. One effective way of correcting these life-threatening rhythms is by using an electronic device called an implantable cardioverter defibrillator in high-risk persons.

If someone may be experiencing ventricular fibrillation, get help immediately. This problem can be corrected with a defibrillator, which gives an electrical shock to the heart. This must be done very soon after the start of fibrillation even when blood flow is partially maintained through CPR (cardiopulmonary resuscitation.).

Electrophysiologic testing This method has become extremely valuable for provoking known but infrequent arrhythmias and for unmasking suspected arrhythmias. This procedure is done using local anesthesia. Temporary electrode catheters are placed through peripheral veins (or arteries) into the heart using a fluoroscope. Then these catheters are positioned in the atria, ventricles or both, and at strategic locations along the conduction system. They record cardiac electrical signals and "map" the spread of electrical impulses during each beat, thus showing where the heart block is (AV node vs. His-Purkinje system). It also shows where tachycardia originates (supraventricular vs. ventricular) far better than an ECG usually does.

The ability to electrically stimulate the heart at programmed rates and induce precisely timed premature beats lets a doctor assess electrical properties of the heart's conduction system. Most significantly, it also triggers latent tachycardia or bradycardia. Induced tachycardias can usually be stopped by rapid pacing via the electrode catheters. Sometimes an externally applied shock may be required if the patient loses consciousness during the tachycardia. Being able to "turn on" and "turn off" tachycardias during electrophysiologic studies allows antiarrhythmic drugs to be tested quickly for effectiveness. This can be done during a single study using intravenous therapy or during short follow-up studies with oral medication. Electrophysiologic testing has been performed safely worldwide; complications only rarely occur.

Diagnosing Arrhythmias

Diagnostic methods

Electrocardiographic techniques

An arrhythmia is considered documented if it can be recorded on an electrocardiogram (ECG or EKG.) This is the standard clinical tool for diagnosing arrhythmias. It records the relative timing of atrial and ventricular electrical events. It can be used to measure how long it takes for impulses to travel through the atria (the heart's upper chambers), AV conduction system and ventricles (the heart's two lower, pumping chambers). Often, though — because of the fleeting nature of arrhythmias — someone who complains of symptoms that suggest arrhythmia has an ECG that appears normal. Electrocardiographic techniques are passive; they require an arrhythmia to occur spontaneously.

Small patches or stickers called electrodes are placed on different parts of the body. One is put on each arm and leg and several across the chest. They don't hurt. With various combinations of these electrodes, different tracings of the heart's electrical activity can be made and permanently recorded on paper or in a computer.

Three major waves of electric signals appear on the ECG. Each one shows a different part of the heartbeat.

• The first wave is called the P wave. It records the electrical activity of the atria.
• The second and largest wave, the QRS wave, records the electrical activity of the ventricles.
• The third wave is the T wave. It records the heart's return to the resting state.

Doctors study the shape and size of the waves, the time between waves and the rate and regularity of beating. This tells a lot about the heart and its rhythm.

Holter monitor

Suspected arrhythmias sometimes may be documented by using a small, portable ECG recorder, called a Holter monitor (or continuous ambulatory electrocardiographic monitor). This can record 24 hours of continuous electrocardiographic signals. While an ECG is sort of a 12-second "snapshot" of the heart's electrical activity, the Holter monitor is more like a "movie." For suspected arrhythmias that occur less than daily, a patient can wear an event monitor. It has a continuously updated memory loop and can allow the heart to be monitored by telephone.

In Holter monitoring, electrodes are taped to the chest. The wires are connected to a portable, battery-operated recorder that can run for 24 to 48 hours. You can do most normal activities while being tested. Then the tape is analyzed on a computer that rapidly identifies rhythm disturbances.

Treadmill testing

This is an option that provokes arrhythmias and makes their diagnosis (and thus their proper treatment) easier. A treadmill test may be used for people whose suspected arrhythmias are clearly exercise-related. It is important to know if exercise makes an arrhythmia worse. To test this, you will walk and run on a treadmill — or ride a stationary bicycle — while your heart rate and rhythm are monitored.

Tilt table studies

A tilt test may be advised for some people who've had recurrent fainting spells (syncope). This test shows how your heart rate and blood pressure respond to a change in position from lying down to standing up. In this test, an intravenous line (a small plastic tube in a vein) is usually started. A catheter also may be placed in the artery to monitor blood pressure. In some cases medications are given through the intravenous line. If a cause of the fainting spells is found, medications can be given through the intravenous line to help prevent the episodes. This information will help your doctor find the best way to treat these episodes.

Transtelephonic monitor (or event recorder)

Sometimes arrhythmia symptoms happen infrequently, or pass so quickly that you can't get to a doctor or hospital. In these cases, a "transient event monitor" may be used. These small recorders are sent home with a person for a month or two. When you have symptoms, attach the recorder with bracelets, finger clips or patches under the arms. The ECG will be recorded and stored. When it's convenient, you can transmit the ECG by phone to the cardiologist to be analyzed.

Echocardiogram

Echocardiography works much like sound waves used to study solid objects in the sea (sonar). You may only think of ultrasound being used to monitor a baby's growth, but ultrasound waves can also show the heart's size, structure and motion. This simple, painless test often provides valuable information about a heart with an arrhythmia.

Arrhythmia Medications

When taken exactly as prescribed, medications can do wonders. They can help prevent heart attack and stroke. They can also prevent complications and slow the progression of coronary heart disease. Make sure that your doctor knows all the drugs you're taking, including over-the-counter drugs and natural supplements. Discussing all the drugs you take will help you prevent serious side effects and help the medications have their desired effects.

In this list of medications used to treat arrhythmias, we've included generic names as well as some major trade names. If your prescription isn't on this list, don't hesitate to ask you doctor or pharmacist about your medication.

Antiarrhythmic drugs

Symptomatic tachycardias and premature beats may be treated with a variety of antiarrhythmic drugs. These may be given intravenously in an emergency situation or orally for long-term treatment. These drugs either suppress the abnormal firing of pacemaker tissue or depress the transmission of impulses in tissues that either conduct too rapidly or participate in reentry. In patients with atrial fibrillation, a blood thinner (anticoagulant or antiplatelet agent such as aspirin) is usually added to reduce the risk of blood clots and stroke.

When tachycardias or premature beats occur often, the effectiveness of antiarrhythmic drug therapy may be gauged by electrocardiographic monitoring in a hospital, by using a 24-hour Holter monitor or by serial drug evaluation with electrophysiologic testing.

The relative simplicity of antiarrhythmic drug therapy must be balanced against two disadvantages. One is that the drugs must be taken daily and indefinitely. The other is the risk of side effects. While side effects are a risk of all medication, those associated with antiarrhythmic drugs can be very hard to manage. They include proarrhythmia, the more-frequent occurrence of preexisting arrhythmias or the appearance of new arrhythmias as bad as or worse than those being treated.

Ablative Techniques

Radiofrequency ablation

This nonsurgical procedure is used to treat some types of rapid heart beating, such as atrial fibrillation, atrial flutter and atrial tachycardia. It's most often used to treat supraventricular tachyarrhythmias. These are rapid, uncoordinated heartbeats starting in the heart's upper chambers (atria) or middle region (AV node or the very beginning portion of the heart's electrical system).

How is radiofrequency ablation done?

A physician guides a catheter with an electrode at its tip to the area of heart muscle where the damaged site is located. Then a mild, painless radiofrequency energy (similar to microwave heat) is transmitted to the site of the pathway. Heart muscle cells in a very small area (about 1/5 of an inch) die and stop conducting the extra impulses that caused the rapid heartbeats.

How effective and safe is this procedure?

Radiofrequency ablation has a success rate of over 90 percent, a low risk of complications and the patient can resume normal activities in a few days. It causes little or no discomfort and is done under mild sedation with local anesthesia. For these reasons, it's now widely used and is the preferred treatment for many types of rapid heartbeats.

Transcatheter approach

Newer advances now permit therapeutic ablations using a transcatheter approach. In this technique, an electrode catheter inserted through a blood vessel during electrophysiologic studies is used to perform targeted electrocautery in the heart. A patient may be cured of tachycardia through ablative therapy, so antiarrhythmic medication is no longer needed. Transcatheter ablation is rapidly becoming the treatment of choice for many supraventricular tachycardias.