Wolf Parkinson White Syndrome Effect On The Heart Biology Essay

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In a normal heart, the electrical impulses that signal the heart to beat flow along one pathway, which begins in the sinoatrial node, or SA node, located in the right atrium. When the SA node fires, the single impulse spreads through the right and left atria causing the chambers to contract. The impulses then travel through the atrioventricular node, AV node, which is the bridge that allows the impulses to flow from atria to the ventricles. The AV node slows down the electrical signal before allowing the signal to travel to the ventricles. This slight delay allows the ventricles to fill with blood before contracting. When electrical impulses reach the ventricles, they contract, causing them to pump blood to the lungs, or through the body. When the electrical signal reaches the ventricles, the chamber then contracts.

Wolf-Parkinson-White syndrome, or WPW, is a disease in which an additional conduction pathway is present. This can cause pre-mature ventricle contraction, as well as abnormal heart rhythm, because in addition to the normal AV node pathway, the extra pathway allows impulses to travel via a circular pattern. This circular pattern that causes the heart to beat abnormally is called arrhythmia. Arrhythmias are considered electrical abnormalities called "pre-excitation syndromes,"; they have many forms. In Wolff-Parkinson-White syndrome, the most common form of arrhythmia is known as paroxysmal supraventricular tachycardia. Many people with WPW also experience atrial fibrillation, an irregular rapid heart rhythm.

Wolff-Parkinson-White syndrome is present at birth, but the first symptoms often appear in teens. WPW is one of the most common causes of fast heart rate in infants and children. The syndrome affects approximately 1 to 3 people in 1,000 people worldwide, but many people with the syndrome never experience symptoms (MedicineNet). In China, 70 percent of cases of abnormal heart rhythm is due to WPW (MedicineNet).

The syndrome has been studied for many years. Wolff-Parkinson-White syndrome was named in 1930, after Drs. Wolff, Parkinson, and White, who fully described the syndrome. Wolff, Parkinson, and White described a distinct electrocardiograph (ECG) pattern in healthy young people with short bursts of tachycardia. In 1944, Dr. David Scherf is thought to have described the current understanding of the WPW syndrome in terms of the presence of extra pathways.

There has been much research over the years about why this disease occurs. The extra electrical pathway of Wolff-Parkinson-White syndrome is present at birth. Little is known regarding why the extra pathway develops, but can be caused by sporadic occurrence, and is linked to abnormal gene inheritance, which only accounts for a small percentage of cases. In most cases, the cause of Wolff-Parkinson-White syndrome is unknown. Most WPW occurs sporadically in the general population, occurring in about 0.1 to 3.1 per 1,000 persons (Cleveland). Men have a higher incidence of WPW than women do, for unknown reasons

A small percentage of cases of WPW are caused by a mutation of the PRKAG2 gene. The mutation of the gene is also linked to hypertrophic cardiomyopathy, a form of heart disease that enlarges and weakens the cardiac muscle of the left ventricle. The PRKAG2 gene codes for a protein that is part of the AMP-activated protein kinase (AMPK). AMPK is believed to be involved in the development of the heart before birth and helps manage the energy demands within the heart.

Researchers are uncertain how PRKAG2 mutations lead to the development of WPW, but it is believed to be due to the altered activity of AMP-activated protein kinase in the heart. It is unclear whether the changes cause over-activation of the enzyme or reduce enzyme activity. It is known though that the AMPK mutation allows glycogen to build up abnormally within cardiac muscle, as well as being related to changes in the regulation ion channels in the heart, which play critical roles in maintaining the heart's normal rhythm.

Only a small amount of cases of Wolff-Parkinson-White syndrome occur in people with apparent family history of the condition (MedicineNet). The inherited disorder typically has an autosomal dominant pattern of inheritance. Research has indicated that the incidence of pre-excitation in first-degree relatives could be as high as 5.5 per 1,000 persons (Cleveland). About 7 to 20 percent of patients with WPW also have congenital defects within the heart (Cleveland).

There are a wide range of symptoms linked to WPW. The accessory pathway allows electrical signals to bypass the atrioventricular node and move from the atria to the ventricles faster than usual. The accessory pathway also can transmit electrical impulses abnormally from the ventricles back to the atria, causing an additional contraction of the atria, leading to abnormally fast heartbeats, tachycardia, or other arrhythmias. About 80 percent of people with symptoms first have them between the ages of 11 and 50 (American). Complications of Wolff-Parkinson-White syndrome can occur at any age, although some individuals born with an accessory pathway in the heart never experience any health problems associated with the condition. Symptoms of the arrhythmias are often dizziness, a fluttering sensation, chest palpitations, shortness of breath, fainting. Cardiac arrest and death are also rarely symptoms. The most common arrhythmia associated with Wolff-Parkinson-White syndrome is called paroxysmal supraventricular tachycardia. A person experiencing a tachycardia episode will have a heart rate greater than 230 beats per minute and normal blood pressure (MedlinePlus). An episode of tachycardia often happens during exercise; it begins abruptly and lasts for a few seconds to several hours. Wolff-Parkinson-White syndrome often occurs with other structural abnormalities of the heart, or underlying heart disease. Additionally, Wolff-Parkinson-White syndrome can be a component of several other genetic syndromes, such as hypokalemic periodic paralysis, which is periods of extreme muscle weakness, Pompe disease, and a disease linked to storage of excess glycogen, and tuberous sclerosis, which results in noncancerous tumor growth.

Tachycardia may correct itself, but often needs treatment. The goal of treatments for WPW is to slow a fast heart rate when it occurs, and prevent future episodes. Ways to slow heartbeat include vagal maneuvers, medications and surgeries. Whether a person will be treated with medication or with a surgical procedure depends on several factors. These include the severity and frequency of symptoms, risk for future arrhythmias and patient preference.

Vagal maneuvers affect the vagus nerve, which is the same nerve that regulates heartbeats, and is usually the first treatment tried. Vagal maneuvers, which include coughing, squeezing of the abdominals, and placing an icepack on the face, are often performed during an episode of a fast heartbeat (MayoClinic.com). These actions sometimes result in slowed conduction of electrical impulses through the AV node.

If vagal maneuvers do not stop the fast heartbeat, medicine may be required. Often an injection of an anti-arrhythmic medication, or pill versions of drugs, may be prescribed for treatment of an episode of tachycardia. Anti-arrhythmic medications may prevent a fast heart rate all together when taken regularly. Medications are usually given to people who experience frequent arrhythmias and who cannot, or who cannot, or will not, undergo surgery.

In people with WPW, whose symptoms cannot be controlled with medications or vagal maneuvers, surgery is the last type of treatment that can improve symptoms and cure the abnormal arrhythmias. The most common procedure used to interrupt the abnormal pathway is catheter ablation. This procedure involves inserting a catheter in an incision in the groin area and running the catheter to the heart. Radiofrequency is then placed on to the pathway. Electrodes at the catheter tips are heated to damage the extra electrical pathway and prevents it from sending electrical signals. When the catheter reaches the heart, the extra electrical pathway is destroyed using radiofrequency. This procedure is highly effective with a success rate for the procedure, ranging between 85 - 95% with uncommon complications (MedlinePlus). Successful ablation ends the need for medication.

Another procedure done to alleviate the symptoms of Wolff-Parkinson-White syndrome is cardioversion. Cardioversion is a procedure where a shock is delivered to the heart through paddles on your chest. The shock affects the electrical impulses in your heart and restores a normal rhythm.

When other forms of treatment have not worked, open-heart surgery is almost 100 percent (MayoClinic). However, because radiofrequency catheter ablation is almost as effective, and less invasive, surgery for WPW is rare. Open-heart surgery is usually done only if the patient must have surgery for other reasons.

A person with WPW has several social implications they must deal with. Since Wolff-Parkinson-White syndrome often occurs with other structural abnormalities of the heart or underlying heart disease, a person must monitor their heart health carefully. The other genetic syndromes that are sometimes associated with WPW must also be monitored. Common substances of caffeine, tobacco, alcohol, and pseudoephedrine need to be avoided since they can cause a tachycardia episode (MayoClinic). These substances can restrict or dictate where a person can go in public. While caffeine, alcohol, and pseudoephedrine can be more easily avoided, consumption or use of tobacco and tobacco smoke is more of a social conflict. Smoky buildings or areas may need to be avoided to prevent symptoms from arising. The relatively new smoking ban around the US helps eliminate this social issue with smoking since public areas are now smoke-free. Exercise must also be monitored since it may trigger episodes. This might mean that a person has to avoid exercise.