Wolff-Parkinson White Syndrome

Classic electrocardiogram triad is a short PR interval, slurred QRS upstroke, and a prolonged QRS complex.

Estimated prevalence of 0.1 to 0.3 percent.

Lifetime incidence estimated to be about 3-4%.

Conduction occurs over an accessory atrioventricular pathway exciting the ventricle ipsilateral to where the accessory pathway enters the myocardium.

Antegrade conduction through the accessory pathway during sinus rhythm, can inscribe a slurred QRS upstroke associated with a short PR interval known as Wolff-Parkinson-White pattern.

This slurred QRS of stroke occurs because ventricular depolarization through the accessory pathway occurs earlier than through the native conduction system-ventricular pre-excitation.

Most common arrhythmia associated with this syndrome is an atrioventricular reciprocating tachycardia.

Sudden death from ventricular fibrillation may occur in young, previously asymptomatic people.

The estimated incidence of sudden cardiac death is 2.4 per 1000 person-years.

Prophylactic radiofrequency ablation improves outcome in high-risk adult patients.

In high-risk children with Wolff-Parkinson White syndrome prophylactic catheter radiofrequency ablation reduces the risk of life threatening arrhythmias.

One of several disorders of the electrical system of the heart that are commonly referred to as pre-excitation syndromes.

Caused by the presence of an abnormal accessory electrical conduction pathway between the atria and the ventricles.

Electrical signals traveling down this abnormal pathway, known as the bundle of Kent, may stimulate the ventricles to contract prematurely, resulting in a unique type of supraventricular tachycardia referred to as an atrioventricular re-entrant tachycardia.

Affects between 0.1 and 0.3% in the population.

Sudden cardiac death with WPW is rare, occurring less than 0.6% of cases and is usually caused by the propagation of an atrial tachydysrhythmia to the ventricles by the accessory pathway.

Usually asymptomatic.

Patients may experience palpitations, dizziness, shortness of breath, or syncope during episodes of supraventricular tachycardia.

A diagnostic “delta wave” may sometimes be seen on an electrocardiogram

Electrical activity in the normal human heart begins when a cardiac action potential arises in the sinoatrial (SA) node, which is located in the right atrium.

From the sino atrial node the electrical stimulus is transmitted to the atrioventricular (AV) node.

After a brief delay at the AV node, the stimulus travels through the bundle of His to the left and right bundle branches and then to the Purkinje fibers and the endocardium at the apex of the heart, then finally to the ventricular myocardium.

The AV node functions to limit the electrical activity that reaches the ventricles.

When the atria generate excessively rapid electrical activity, as occurs with atrial fibrillation or atrial flutter, the AV node limits the number of signals conducted to the ventricles.

The AV node slows down individual electrical impulses, and is manifested on the electrocardiogram as the PR interval, which is usually shortened to less than 120 milliseconds in duration.

The PR INTERVAL,Is the time from electrical activation of the atria to electrical activation of the ventricles.

Individuals with WPW have an accessory pathway that communicates between the atria and the ventricles, in addition to the AV node.

The bundle of Kent is the accessory pathway and it does not share the rate-slowing properties of the AV node, and may conduct electrical activity at a significantly higher rate than the AV node.

Extremely rapid heart rates may result in hemodynamic instability or shock.

The combination of an accessory pathway and abnormal heart rhythms can trigger ventricular fibrillation, a leading cause of sudden cardiac death.

WPW may be associated with PRKAG2, a protein kinase enzyme encoded by the PRKAG2 gene.

The bundle of Kent is an abnormal extra or accessory conduction pathway between the atria and ventricles that is present in a small percentage, between 0.1 and 0.3%, of the general population.

The bundle of Kent pathway may communicate between the left atrium and the left ventricle, in which case it is termed a type A pre-excitation, or between the right atrium and the right ventricle, in which case it is termed a type B pre-excitation.

Problems arise when this pathway creates an electrical circuit that bypasses the AV node.

The AV node is capable of slowing the rate of conduction of electrical impulses to the ventricles, whereas the bundle of Kent lacks this capability.

When an aberrant electrical connection is made via the bundle of Kent, tachydysrhythmias may result.

Commonly diagnosed on the basis of the electrocardiogram in an asymptomatic individual.

In this case, it is manifested as a delta wave, which is a slurred upstroke in the QRS complex that is associated with a short PR interval.

The short PR interval and slurring of the QRS complex is a result of the impulse making it through to the ventricles prematurely.

The impulse crosses the accessory pathway, without the usual delay experienced in the AV node.

WPW associated with atrial fibrillation, the ECG shows a rapid polymorphic wide-complex tachycardia, and the combination of atrial fibrillation and WPW is dangerous.

Most antiarrhythmic drugs are contraindicated with the combination of atrial fibrillation and WPW.

With a normal sinus rhythm, the ECG characteristics of WPW are a short PR interval (less than 120 milliseconds in duration), widened QRS complex (greater than 120 milliseconds in duration) with slurred upstroke of the QRS complex, and secondary repolarization changes (reflected in ST segment-T wave changes).

It’s electrical activity that is initiated in the SA node travels through the accessory pathway, as well as through the AV node to activate the ventricles via both pathways.

Since the accessory pathway does not have the impulse slowing properties of the AV node, the electrical impulse first activates the ventricles via the accessory pathway, and immediately afterwards via the AV node, giving the short PR interval and slurred upstroke of the QRS complex known as the delta wave.

In case of type A pre-excitation left atrioventricular connections, a positive R wave is seen in V1 (“positive delta”) on the precordial leads of the electrocardiogram.

In type B pre-excitation, right atrioventricular connections, a predominantly negative delta wave is seen in lead V1 (“negative delta”).

People with WPW may have more than one accessory pathway.

Sometimes associated with Leber’s hereditary optic neuropathy, a form of mitochondrial disease.

Treatment is based on risk stratification to determine which individuals with WPW are at risk for sudden cardiac death (SCD).

Previous episodes of unexplained syncope or palpitations may be due to earlier episodes of a tachycardia associated with the accessory pathway.

If delta waves disappear with increases in the heart rate, there is lower risk of SCD.

The delta wave shows that the accessory pathway cannot conduct electrical impulses at a high rate.

During episodes of atrial fibrillation, patients with WPW Sx usually do not have fast conduction down the accessory pathway.

Risk stratification is performed by programmed electrical stimulation (PES) in the cardiac electrophysiology laboratory during which the atria are stimulated to try to induce tachycardia.

Tachycardia involving the accessory pathway can be triggered, and its ability to conduct may be fast enough to trigger a lethal tachycardia

High-risk features of pre-excitation syndrome include an effective refractory period of the accessory pathway less than 250 ms, multiple pathways, septal location of pathway, and inducibility of supraventricular tachycardia.

With any high-risk features patients are considered at increased risk for sudden cardiac death or symptomatic tachycardia, and should be treated.

Some groups advocate programmed electrical stimulation in all individuals under 35 years old, others only offer it to individuals who have history suggestive of a tachydysrhythmia, since the incidence of sudden cardiac death is less than 0.6%.

With tachydysrhythmias patients may require synchronized electrical cardioversion if they are demonstrating severe signs or symptoms.

Patients with WPW syndrome with tachydysrhythmias but are relatively stable, pharmacologic treatment may be used.

With atrial fibrillation and rapid ventricular response patients are often treated with amiodarone or procainamide to stabilize their heart rate.

Procainamide and cardioversion are now accepted treatments for conversion of tachycardia found with

Amiodarone is no longer recommended in this clinical scenario.

AV node blockers are to be avoided in atrial fibrillation and atrial flutter with WPW or history of it.

AV node blockers include: adenosine, diltiazem, verapamil, other calcium channel blockers, and beta blockers.

AV node blockers can exacerbate the syndrome by blocking the heart’s normal electrical pathway, favoring 1:1 atrial to ventricle conduction through the pre-excitation pathway, potentially leading to unstable ventricular arrhythmias.

Definitive treatment is a destruction of the abnormal electrical pathway by radiofrequency catheter ablation.

This procedure the radiofrequency catheter ablation is not performed in all individuals with WPW because inherent risks are involved in the procedure.

Success rates of as high as 95% in people treated with radiofrequency catheter ablation for WPW.

Recurrence rates are typically less than 5% after a successful ablation.

Patients with underlying Ebstein’s anomaly may develop additional accessory pathways during progression of their disease.

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