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Wolff-Parkinson-White Syndrome
What is Wolff-Parkinson-White syndrome?
Wolff-Parkinson-White syndrome (WPW) represents an abnormality of the heart's electrical system. In patients with WPW, there is an extra electrical connection between the atria (the upper chambers) and the ventricles (the lower chambers). This abnormal electrical connection can cause episodes of rapid heart rhythms called paroxysmal atrial tachycardia, preexcited tachycardia, or preexcited atrial fibrillation.
The syndrome usually occurs without other heart abnormalities. However, WPW has infrequently been associated with rare heart conditions such as Ebstein's anomaly and hypertrophic cardiomyopathy.
How does a normal heart function?
The heart is an organ consisting of four chambers that pump blood. The two upper chambers are called the right and left atria, and the two lower chambers are called the right and left ventricles. The right atrium receives venous blood (oxygen-poor blood) from the body and pumps it into the right ventricle. The right ventricle pumps the oxygen-poor blood to the lungs to receive oxygen. The oxygen-rich blood from the lungs then travels to the left atrium and is pumped by the left atrium into the left ventricle. The left ventricle delivers the oxygen-rich blood to the rest of the body. In addition to oxygen, the blood delivers other nutrients ( glucose , electrolytes , etc.) to the organs.
In order to keep a body healthy, the heart must deliver sufficient amount of blood to the body. As a pump, the heart is most efficient in delivering blood when functioning within a certain heart rate range. The heart is also most effective when the atria contract first to fill the ventricles with blood before the ventricles contract. The electrical system of the heart normally determines the heart rate as well as keeping the heart chambers contracting in an orderly and efficient manner.
There is a special tissue on the wall of the right atrium called the sino-atrial node (SA node). The SA node generates electrical signals at a regular pace and is the natural pacemaker of the heart. The rate of electrical signals generated by the SA node determines how fast the heart beats (the heart rate). These signals cause the atria to contract first. The signals then pass through the atrio-ventricular node (AV node) to reach the ventricles and cause the ventricles to contract next. The AV node is a small area of the heart that serves as an electrical relay station between the atria and the ventricles.
Normally, the AV node is the only electrical pathway which connects the atria to the ventricles. Electrical signals from the SA node must pass along the atria and through the AV node to reach the ventricles. This electrical pathway ensures the proper order of heart chamber contractions - first the atria, and subsequently, the ventricles.
What is the abnormality in WPW?
In WPW, there is an extra electrical connection (pathway) between the atria and the ventricles. This extra pathway allows electrical signals to pass from the atria to the ventricles and sometimes from the ventricles to the atria. This condition can create a "short circuit" in the heart's electrical system and lead to episodes of abnormally fast heart rates (tachycardias).
When the heart pumps too rapidly, the ventricles do not have enough time to fill their chambers with blood before the next contraction. The result is a decrease in the amount of blood delivered to the body. A short circuit in the heart can also disrupt the proper order of contraction of the heart chambers and cause the heart to pump inefficiently. Therefore, the tachycardia episodes associated with WPW syndrome interfere with the effective delivery of blood to the body.
How common is WPW?
WPW is present at birth and estimates suggest that the condition occurs in about 1 in 10,000 live births. However, the actual incidence of WPW syndrome is difficult to determine since many persons have mild and undiagnosed conditions. The condition can remain dormant for years without any symptoms of tachycardias, and therefore go undiagnosed for years.
Tachycardia episodes associated with WPW can occur at any age but generally begin in the teenage years or during early adulthood. In some women with WPW, the first tachycardia episode may occur during pregnancy.
What symptoms are caused by WPW?
Symptoms of tachycardias include palpitations , lightheadedness, loss of consciousness, chest pain, fatigue, and a general feeling of unwellness. Most of these symptoms are due to the diminished amount of blood transported by the heart to the brain and other organs.
Since symptoms only occur during tachycardia episodes, which occur infrequently, patients with WPW syndrome can remain symptom free most of the time.
What is the prognosis of patients with WPW?
The frequency and the severity of tachycardia episodes associated with WPW differ widely from patient to patient. Some patients have very infrequent tachycardia episodes that last only seconds to minutes. These patients experience minimal symptoms and may not need aggressive treatment. Other patients suffer frequent tachycardias which produce profound symptoms. In these patients, medications and other treatments are necessary to prevent repeated tachycardia episodes.
The pattern of tachycardia episodes also varies among patients with the syndrome. Some patients can go for years without any tachycardia symptoms only to be plagued by symptoms later in life. Conversely, some children and young adults that have frequent tachycardia episodes can have these tachycardias disappear spontaneously in later years. Changes in the conduction along the extra pathway are believed to be responsible for these altered patterns of tachycardia episodes.
WPW can at times cause very rapid tachycardias. Very rapid tachycardias in WPW can result in loss of consciousness and, on rare occasions, cause ventricular fibrillation. Ventricular fibrillation is a chaotic heart rhythm that causes cardiac standstill (cardiac arrest) and sudden death. The chance of sudden death in WPW patients with tachycardia symptoms is estimated to be less than 1% over a lifetime.
How is WPW diagnosed?
The diagnosis of WPW is first suspected on an electrocardiogram (EKG). EKG is a paper tracing that records the heart's electrical activity. The EKG tracing is obtained by placing electrodes (small pads that conduct electricity) on the patient's chest and limbs. On an EKG tracing are waveforms that look like spikes which are called P waves and QRS waves. The P waves correspond to the electrical activation and contraction of the atria while the QRS waves correspond to the electrical activation and contraction of the ventricles.
In WPW, the extra electrical pathway causes the appearance of a "delta" wave inside the QRS wave. A finding of abnormal delta waves on an EKG alone is insufficient to establish the diagnosis of WPW. The presence of delta waves on an EKG must be accompanied by symptoms due to tachycardia episodes to establish a diagnosis of WPW. Patients found to have delta waves without symptoms related to tachycardias are diagnosed as having only ventricular preexcitation without actually having WPW.
Patients with WPW and some patients with ventricular preexcitation are usually evaluated by a cardiac electrophysiologist (a cardiologist with special training and expertise in electrical disturbances of the heart). Most of these patients undergo an electrophysiology study, which is a study of the electrical system of the heart. Electrophysiology studies are performed either in a cardiac catheterization laboratory or in a special electrophysiology laboratory.
Electrophysiology studies can locate the abnormal electrical pathway, characterize the conduction properties of the abnormal pathway, and assess the risk of life-threatening tachycardias. Also, at the time of electrophysiology study, selected patients with WPW can undergo radiofrequency ablation-a technique that destroys the abnormal electrical pathway using a catheter capable of delivering radiofrequency energy.
Who should be considered for treatment for WPW?
Patients suffering with significant symptoms of WPW and those found by electrophysiology studies to be at risk of developing life- threatening tachycardias require treatment. Examples include patients who have had a previous fainting or near fainting episode, an aborted cardiac arrest, or very rapid tachycardias.
WPW patients with no symptoms or infrequent mild symptoms and who are determined by electrophysiology testing to be at low risk for developing life-threatening tachycardias usually require no treatment. Patients who have only ventricular preexcitation without symptoms due to tachycardias also may not need treatment.
However, some patients with only ventricular preexcitation may need further evaluation and consideration for treatment. These include individuals in high-risk occupations such as airline pilots, school bus drivers, and competitive athletes. Athletes are considered higher risk because of the intense exertion. Airline pilots and school bus drivers have responsibility over public safety. Patients in this category may find it advisable to have further testing with an exercise treadmill and holter monitoring (wearing a monitor which records the heart rhythm over 24-48 hours) to help determine the need for treatment.
Treatment decisions are best made by electrophysiology cardiologists experienced in the electrical systems of the heart.
What is the treatment of WPW?
Although medications that prevent abnormal rhythms were used extensively in the past, most specialists now recommend radiofrequency catheter ablation (destruction) of the abnormal electrical pathway as the treatment of choice. In experienced hands, radiofrequency ablation can be performed safely with minimal discomfort. The procedure has an over 95% success rate in eradicating the abnormal pathways. The estimated rate of procedure related deaths is less than 0.2%. The overall complication rate is between 1%-4%. Wolff-Parkinson-White Syndrome At A Glance - Wolff-Parkinson-White syndrome (WPW) is a condition that can cause episodes of abnormally rapid heart rhythms (tachycardias).
- WPW is caused by an abnormality of the heart's electrical system which consists of an extra electrical pathway connecting the atria and the ventricles of the heart.
- Symptoms (such as palpitations, lightheadedness, and loss of consciousness) of WPW occur only during tachycardia episodes.
- Diagnosis of WPW is based on an abnormal electrocardiogram (EKG) tracing along with symptoms of tachycardias.
- In rare instances, WPW related tachycardias could lead to sudden cardiac death.
- Although medications that prevent tachycardias were used extensively in the past, most specialists recommend radiofrequency catheter ablation (destruction) of the extra electrical pathway as the treatment of choice for WPW.
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