WPW syndrome (ventricular preexcitation, accessory pathway)

Wolff-Parkinson-White (WPW) syndrome is a cardiac condition with episodes of fast heart rate which may lead to palpitations, dizziness, blackouts and in extreme cases sudden death. The episodes of fast heart beat start and stop suddenly and last from seconds up to hours. WPW syndrome is a type of supraventricular tachycardia (SVT), i.e. abnormally fast heart beat originating in top heart chambers. The episodes may happen with no pattern, sometimes several times a day, in other cases only once in several months. Most people with WPW syndrome have just unpleasant palpitations but no serious problems. However in rare cases a combination of atrial fibrillation and WPW syndrome with an electrical pathway capable of very fast conduction can be life-threatening.

Mechanism and symptoms

Sinus node, a cluster of cells in the right atrium (one of the top heart chambers) is the natural pacemaker which sends electric signals to the atria and atrioventricular node (AV node). AV node is placed between the right atrium and right ventricle and under normal circumstances it is the only electrical connection between top and bottom heart chambers. Electrical impulses pass through the AV node and down the specialized fibres to the muscle of ventricles which respond by contraction. Cardiac contraction pumps blood into the body which can be felt as pulse.

In WPW syndrome, there is apart from the AV node an additional electrical connection between atria and ventricles. This additional connection is called accessory pathway and leads to premature activation of ventricles (ventricular preexcitation). AV node and accessory pathway can then create a short circuit which enables electrical impulses to travel around in a loop pattern, making the heart beat very fast. Contractions of heart muscle become so fast that heart muscle has not time to relax and fill with blood. The heart is therefore running almost empty, and the reduced amount of blood and oxygen pumped around the body may cause not only palpitations but also breathlessness, chest discomfort, dizziness and loss of consciousness.


Diagnosis

Some patients with abnormal (= accessory pathway) connecting atria and ventricles may have no symptoms at all and the condition may be diagnosed incidentally when ECG (electrocardiogram) is arranged for some other reason. ECG will show abnormal delta wave caused by premature activation of ventricles via the accessory pathway. In most cases, WPW is the only cardiac abnormality but sometimes it is related to other problems, e.g. congenital condition called Epstein anomaly.

Treatment and prognosis

In most of the cases, attacks of palpitations in WPW syndrome are benign, short-lived and settle without treatment. However, in rare cases WPW syndrome may lead to a collapse with loss of consciousness and sudden death. Every patient with WPW syndrome should be therefore assessed by a cardiologist and considered for EP study (catheter investigation of electrical pathways in the heart) to determine whether medication alone is sufficient or catheter ablation is advisable.

Catheter ablation is a permanent curative treatment of WPW syndrome. It is a procedure involving insertion of catheters through a vein in the groin to the heart. It is then possible to map the electrical signals in the heart and by delivering energy to destroy a small amount of tissue of the accessory pathway. The ablation therefore breaks the abnormal electrical circuit and in most people permanently cures WPW syndrome.

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