People with Wolff-Parkinson-White syndrome (WPW) are born with one or more extra conduction pathways between the atria and the ventricles. This allows the electrical impulses that control the heart rhythm to start going round in a circle. Most commonly the signals go down through the AV node and up the extra pathway.
Symptoms
During an episode the heart beats fast and regularly. This may be felt as palpitations, shortness of breath, dizziness and, in rare cases, fainting. Some manage to stop the episodes by holding their breath, pinching their nose and straining (the Valsalva manoeuvre), breathing heavily or straining as on the toilet. This works because these manoeuvres increase activity in the nerve that slows the AV node (the vagus nerve). Some have episodes during exertion, for others they come at random.
The delta wave
The properties of the extra pathway determine how dangerous it is. Some conduct so poorly that they cannot cause an arrhythmia, but only give a characteristic signature on the ECG called a delta wave. The delta wave shows that part of the ventricles is activated via the extra pathway before the rest of the ventricles is activated via the normal conduction system.
Concealed WPW
Other extra pathways only conduct from the ventricles to the atria, and many conduct both ways. If the pathway only conducts from the ventricles to the atria, it is not visible on the ECG when the heart beats normally. This is called a concealed pathway, or concealed WPW.
When can it be dangerous?
Episodes in which the signals circle can be very troublesome, but are rarely dangerous if you have no other diseases. It is more dramatic if you have an extra pathway that conducts well from the atria to the ventricles, and in addition develop a fast arrhythmia in the atria, for example atrial fibrillation. The extra pathway lacks the filtering properties of the AV node and can transmit the fast arrhythmia “unblocked” to the ventricles. In the worst case this can cause circulatory collapse and cardiac arrest.
Investigation and ablation
If you have WPW syndrome and it is certain that the pathway conducts poorly, treatment is usually not needed. The conduction properties can be examined with an exercise test, but there is often still uncertainty afterwards, and the patient is referred for an electrophysiological study at a regional hospital.
The procedure starts with local anaesthesia around the blood vessels in both groins. In our unit the veins are punctured in four places, and usually four catheters are passed up to the heart. Guided by X-ray and electrical signals, they are placed at specific sites. We then test the conduction properties of the extra pathway and try to induce the arrhythmia.
Sometimes we conclude that the pathway conducts poorly, or that it is located where the risk is too high for removal to be advisable. But most often we try to remove it. We locate it with the catheters, usually along the valve between atrium and ventricle on the right or left side, and burn it away with radiofrequency energy. If it is close to the normal conduction system, we use freezing instead, because this carries less risk of destroying the connection between the atria and ventricles. In return the risk of recurrence is somewhat higher.
The extra pathway is often located between the left atrium and ventricle. We then puncture the wall between the atria and continue searching around the mitral valve. On this side of the heart we always give a blood thinner (heparin) directly into the bloodstream, because clots can form on the instruments and where we ablate. Large blood vessels lead directly from the left side to the brain and other vital organs. Preventing clots must be weighed against an increased risk of bleeding, including into the pericardium. Fortunately we avoid such serious complications in up to 99 per cent of patients. On the few occasions when things go wrong, we get help from highly competent colleagues, and the complications rarely cause lasting harm.
After the procedure
You must stay in bed for 3–4 hours, depending on how extensive the procedure has been. On discharge we sometimes recommend mild blood thinning with acetylsalicylic acid (aspirin) for about a month. You should avoid lifting more than 4–5 kilos for the first two weeks. A follow-up at your local hospital or with your own doctor after a few months is routinely requested.
Medication
Most people with WPW syndrome are referred for an electrophysiological study and possibly ablation, but for some, medication can be a good alternative. In concealed WPW many respond to a beta blocker or verapamil. Verapamil must not be used in WPW syndrome with a delta wave on the ECG. Many of these respond well to flecainide, but this requires that the heart otherwise functions normally.