The heart works by following a sequence of electrical signals that cause the heart chambers to contract in a certain order. Normally, the atrioventricular node acts like a junction box and controls the electrical impulses that pass between the upper and lower chambers of the heart (the atria and ventricles). In Wolff-Parkinson-White (WPW) syndrome, the normal electrical activity of the heart is disrupted. There is a risk of developing a tachycardia (a fast heart rate) from time to time and other arrhythmias (heart rhythm disturbances). This sometimes causes serious problems. Radiofrequency ablation (destruction) of the accessory pathway is the common treatment. Medication is an alternative option.
The function of the heart and some anatomy
Your heart is a muscular pump that pushes blood through blood vessels around your body. Your heart is considered to have two sides - the right side and the left side. It has four chambers - an atrium and ventricle on each side. The atria receive large blood vessels that bring blood to the heart. Atria have special valves that open into the ventricles. The ventricles also have valves but in this case they open into blood vessels. The walls of the heart chambers are made mainly of special heart muscle. The different sections of the heart have to contract (squeeze) in the correct order for the heart to pump blood efficiently with each heartbeat.
The right side of the heart receives deoxygenated blood (lacking oxygen) from the body. After passing through the right atrium and right ventricle, this blood is pumped to the lungs. Here blood picks up oxygen and loses another gas called carbon dioxide. Once through the lungs, the blood flows back to the left atrium. It then passes into the left ventricle and gets pumped into the aorta - the main artery supplying the body. Oxygenated blood is then carried though blood vessels to all the body's tissues. Here oxygen and other nutrients pass into the cells where they are used to perform the body's essential functions.
Understanding the normal electrical activity of the heart
The heart works by following a sequence of electrical signals that cause the muscles in each chamber to contract in a certain order. If these electrical signals change, the heart may not pump as well as it should. The sequence of each heartbeat is as follows:
The sinoatrial node (SA node) in the right atrium is like a tiny in-built timer. It fires off an electrical impulse at regular intervals (about 60-80 per minute when you are resting and faster when you exercise). Each impulse spreads across both atria, which causes them to contract. This pumps blood through one-way valves into the ventricles.
The electrical impulse then gets to the atrioventricular (AV) node at the lower right atrium. The AV node acts like a junction box between the atria and ventricles. It can limit the number of electrical impulses that conduct from the atria to the ventricles and it also slows down the electrical impulse slightly. Most of the tissue between the atria and ventricles does not conduct the impulse. However, a thin band of conducting fibres called the atrioventricular bundle (AV bundle) acts like wires and carries the impulse from the AV node to the ventricles.
The AV bundle splits into two - a right and left branch. These then split into many tiny fibres (the Purkinje system) which carry the electrical impulse throughout the ventricles. The ventricles contract and pump blood through one-way valves into large arteries.
- The arteries going from the right ventricle take blood to the lungs.
- The arteries going from the left ventricle take blood to the rest of the body.
The heart then rests for a short time (diastole). Blood coming back to the heart from the large veins fills the atria during diastole.
- The veins coming into the left atrium are from the lungs (full of oxygen).
- The veins coming into the right atrium are from the rest of the body (depleted of oxygen).
The sequence then starts again for the next heartbeat. So, the timing of the electrical impulses that travel through your heart is important for your heart to beat regularly and normally.
What is Wolff-Parkinson-White syndrome?
In Wolff-Parkinson-White (WPW) syndrome there is an accessory pathway (an extra connection) between the atria and ventricles. This means that as well as electrical impulses passing normally between the atria and the ventricles at the AV node, electrical impulses can also pass abnormally along the accessory pathway.
This accessory pathway is essentially a strand of extra heart muscle tissue passing between the atria and the ventricles. The accessory pathway in WPW syndrome is known as the bundle of Kent. It is a congenital problem which means that it is present from birth. The majority of people with WPW syndrome have no other heart abnormalities.
An electrical impulse that passes along the accessory pathway can arrive at the ventricles more quickly than normal. There is not the usual impulse delay that occurs at the AV node and no limiting of the electrical impulses that pass through. This can cause the heart rate to speed up. The accessory pathway can also sometimes transmit electrical impulses backwards from the ventricles to the atria.
So, in WPW syndrome, the normal electrical activity of the heart is disrupted. There is a risk of developing a tachycardia (a fast heart rate) from time to time and other arrhythmias (heart rhythm disturbances). This can sometimes cause serious problems (see below).
Because the muscle of the ventricles can contract early, WPW syndrome is known as a pre-excitation syndrome. It can lead to what is called a supraventricular tachycardia because the abnormal electrical impulse starts in the atria (the accessory pathway starts here). Tachycardia is a heart rate over 100 beats per minute. Supra means above and because the atria are above the ventricles, the tachycardia is supraventricular.
The common arrhythmia that occurs in WPW syndrome is a paroxysmal (intermittent) supraventricular tachycardia (PSVT). Other arrhythmias that can also occur include atrial fibrillation, atrial flutter and atrioventricular re-entrant tachycardia (AVRT). Rarely, another arrhythmia called ventricular fibrillation can develop.
How common is Wolff-Parkinson-White syndrome?
WPW syndrome probably affects somewhere between 1-3 in 1,000 people. It is more common in men. There does seem to be some genetic basis, as WPW syndrome can run in families. However, most cases of WPW syndrome occur in people with no known family history.
What are the symptoms of Wolff-Parkinson-White syndrome?
Symptoms are caused by the episodes of rapid heart rate (tachycardia). How often these episodes occur can vary from person to person. In some people, the rapid heart rate only ever occurs once or twice. In others, it can occur a few times per week. Many people are not aware that they have WPW syndrome because their symptoms are mild or infrequent.
If symptoms are present, some people first notice them during childhood. In others, they may not be obvious until middle age.
Symptoms can also vary from person to person. They can include palpitations (a sensation of feeling, or being aware of, your heartbeat) and mild dizziness or light-headedness. Chest pain or chest tightness can also sometimes occur.
In some people, symptoms can be more severe. For example, an episode of a very rapid heart rate (up to about 250 beats per minute) can occur. If your heart is beating this quickly, your blood pressure can drop because your heartbeats become less effective and this can lead to collapse (blackout). If your heart is beating very fast, this can also lead to a build-up of fluid in your lungs and shortness of breath. In extreme cases, your heart can stop beating altogether (a cardiac arrest). However, this is rare.
How is Wolff-Parkinson-White syndrome diagnosed?
It may be diagnosed by doing an electrocardiogram (ECG). There are classic changes on the ECG that can be seen in some people with WPW syndrome. These are essentially the signs of the pre-excitation of their ventricles due to the accessory pathway. One such ECG change is known as a delta wave.
If you are having an episode of tachycardia, this can also be seen on an ECG. Occasionally, WPW syndrome may be picked up on a routine ECG recording done for another reason such as a medical check-up. Sometimes an ambulatory ECG may be suggested. This is an ECG recording device that you wear usually over a 24-hour period. It can monitor your heart whilst you are going about your normal activities. See separate leaflets called 'Electrocardiogram (ECG)' and 'Electrocardiogram (ECG) - Ambulatory' for more details.
Special tests called electrophysiology studies may be carried out in some people. They can help to find the precise area in the heart where the accessory pathway is located.
What is the treatment for Wolff-Parkinson-White syndrome?
Most people diagnosed with WPW syndrome (either picked up on an ECG or because they have symptoms) will be referred to a cardiologist (heart specialist). If you have no symptoms and are at low risk of complications you may need no treatment. Radiofrequency ablation is the treatment of choice but if you don't want it or are not considered suitable, other options are available. Treatment options include the following.
A treatment called radiofrequency ablation may be suitable for many people with WPW syndrome. It is usually the first treatment that is offered to those who have symptoms. It may even be considered in some people with no symptoms.
A thin tube called a catheter is inserted into an artery near your groin through a small cut in your skin. The tube is passed from here up to your heart. When the tip of the tube reaches the small area in your heart that causes the fast heart rate (the accessory pathway), this area is destroyed using a type of energy called radiofrequency. When carried out, radiofrequency ablation can have very good results and can cure the condition in the majority of people.
Long-term treatment with a medicine may be advised in some people to prevent episodes of rapid heart rate. For example, for people who don't wish to have radiofrequency ablation, or in those where this has failed. Medicines may also be given in an emergency situation to slow down your heart rate, interrupt the accessory pathway and restore a normal heart rhythm. In the rare case that you are unwell with very low blood pressure, you may need treatment with oxygen and a shock to your heart using a defibrillator to restore a normal heart rhythm.
Traditional heart surgery
This type of treatment used to be done more commonly in the past for WPW syndrome. It has now been replaced by radiofrequency ablation in most cases. However, traditional heart surgery is still used in some cases - for example, in people in whom radiofrequency ablation has failed who do not wish to take medication for the rest of their life. The surgery is open heart surgery which aims to find and destroy the accessory pathway that causes the fast heart rate.
Further reading & references
|Original Author: Dr Michelle Wright||Current Version: Dr Laurence Knott||Peer Reviewer: Dr Adrian Bonsall|
|Last Checked: 15/03/2012||Document ID: 13158 Version: 2||© EMIS|
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