How does a normal heart beat?

The heart is a hollow muscular organ – approximately the size of your clenched fist – that beats 40 million times per year (between 60 and 100 beats per minute). The heart's pumping action is controlled by its electrical system, which gives rise to the heart rhythm.

Normal cardiac rhythm results from electrical impulses that begin in a special group of cells that form the sinoatrial (SA) node, also called the sinus node. Located in the right upper chamber of the heart, sinus node cells act as the heart's natural pacemaker. Impulses spread from the sinus node to the right and left atria (the upper chambers of the heart), causing them to contract at the same time. The impulses then travel to the AV (atrioventricular) node, the region that manages impulse traffic from the atria to the ventricles (the lower chambers of the heart). Here, impulses are slowed slightly to give the atria time to contract before the signal reaches the ventricles. From the AV node, the impulses travel through a system of specialized heart tissue. Located in the wall that separates the two ventricles, this conducting system splits to form the right and left bundle branches that travel to the respective ventricles. Via this conducting pathway, powerful electrical "jump-start" signals are delivered to the ventricular muscle of the heart. In the healthy heart, these impulses travel at the same speed so that the two ventricles contract at the same time, and oxygen-rich blood from the lungs is pumped throughout the body.

What is Wolf-Parkinson-White Syndrome?

Individuals with Wolff-Parkinson-White (WPW) Syndrome have an abnormal bridge of tissue that connects the atria and the ventricles. This tissue, known as an "accessory pathway," provides a second route – in addition to the normal path through the AV node – by which electrical impulses may reach the ventricles. In WPW Syndrome, the accessory pathway is often able to conduct in both directions: from the atria to the ventricles and from the ventricles to the atria. The accessory pathway allows electrical impulses to be conducted to the ventricles very rapidly, much more rapidly than by the AV node. In some cases, this rapid conduction can result in life-threatening abnormal heart rhythms.

Individuals with WPW Syndrome can have several types of arrhythmias. Most commonly, an abnormally fast heart rhythm, called supraventricular tachycardia, occurs when electrical impulses travel in an endless loop: down the AV node to the ventricles, back up to the atria using the accessory pathway, and then back down the AV node. WPW also predisposes the individual to atrial fibrillation, which can result in dangerously fast heart rates.

What causes WPW Syndrome?

The abnormal pathways that cause WPW Syndrome are formed because of a miscue in normal heart formation during fetal development. For reasons that are not well understood, even though people are born with accessory pathways, abnormal heart rhythms frequently do not develop until adolescence or adulthood.

What are the symptoms of WPW Syndrome?

People may feel palpitations (fluttering in the chest). If the heart rate is very rapid, it may result in fainting or near fainting.

How is WPW Sydrome Treated?

Catheter ablation provides a cure of the Wolff-Parkinson-White Syndrome and is the treatment of choice for any patient who has experienced a sustained abnormal heart rhythm, or a patient with symptoms suggestive of an abnormal heart rhythm (such as palpitations).