Wolff-Parkinson-White syndrome pathophysiology

https://https://www.youtube.com/watch?v=9MDRKId2d0Q%7C350}}

Wolff-Parkinson-White syndrome Microchapters
Home
Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Differentiating Wolff-Parkinson-White syndrome from other Diseases
Epidemiology and Demographics
Risk Factors
Natural History, Complications and Prognosis
Diagnosis
Approach
History and Symptoms
Electrocardiogram
EKG Examples
Other Diagnostic Studies
Treatment
Risk Stratification
Cardioversion
Medical Therapy
Catheter Ablation
Prophylaxis
Consensus Statement
Case Studies
Case #1
Wolff-Parkinson-White syndrome pathophysiology On the Web
Most recent articles
Most cited articles
Review articles
CME Programs
Powerpoint slides
Images
Ongoing Trials at Clinical Trials.gov
US National Guidelines Clearinghouse
NICE Guidance
FDA on Wolff-Parkinson-White syndrome pathophysiology
CDC onWolff-Parkinson-White syndrome pathophysiology
Wolff-Parkinson-White syndrome pathophysiology in the news
Blogs on Wolff-Parkinson-White syndrome pathophysiology
Directions to Hospitals Treating Deep vein thrombosis
Risk calculators and risk factors for Wolff-Parkinson-White syndrome pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Cafer Zorkun, M.D., Ph.D. [3]

Overview

In normal individuals, electrical activity in the heart is initiated in the sinoatrial (SA) node (located in the right atrium), propagates to the atrioventricular (AV) node, and then through the bundle of His to the ventricles of the heart. Individuals with Wolf-parkinson-White (WPW) have an accessory pathway, known as the bundle of Kent, that communicates between the atria and the ventricles. The conduction through the accessory pathway can be bidirectional (most commonly), only retrogarde (less common), or only antegrade (least common). The most common type of tachycardia associated with WPW is atrioventricular reciprocating tachycardia (AVRT). The accessory pathway does not share the rate-slowing properties of the AV node; therefore, the combination of an accessory pathway and cardiac arrhythmia can trigger ventricular fibrillation, a leading cause of sudden cardiac death.

Pathophysiology

Accessory Pathway

• Individuals with WPW have a congenital accessory pathway that communicates between the atria and the ventricles, in addition to the AV node.
• This accessory pathway is known as the bundle of Kent.
• 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.
• This 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".

The accessory pathway is characterized by:

• Conducting electrical stimulus faster than the AV node
• Longer refractory period compared to the AV node
• A non-decremental conduction in response to an increased paced rates

Electrical Activity

Normal Electrical Activity

• The electrical activity in the normal human heart is initiated when a cardiac action potential arises in the sinoatrial (SA) node, which is located in the right atrium.
• From there, the electrical stimulus is transmitted via internodal pathways to the atrioventricular (AV) node.
• After a brief delay at the AV node, the stimulus is conducted 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 theheart, then finally to the ventricular myocardium.

Shown below is an image depicting the conduction system in the normal heart.

The conduction system in the normal heart

• The AV node serves an important function as a "gatekeeper", limiting the electrical activity that reaches the ventricles.
• In situations where the atria generate excessively rapid electrical activity (such as atrial fibrillation or atrial flutter), the AV node limits the number of signals conducted to the ventricles.
• For example, if the atria are electrically activated at 300 beats per minute, half those electrical impulses may be blocked by the AV node, so that the ventricles are stimulated at only 150 beats per minute—resulting in a pulse of 150 beats per minute.

• Another important property of the AV node is that it slows down individual electrical impulses.
• This is manifested on the electrocardiogram as the PR interval (the time from electrical activation of the atria to electrical activation of theventricles), which is usually shortened to less than 120 milliseconds in duration.

Electrical Activity in WPW

• The accessory pathway communicates between the atria and ventricle.
• The accessory pathway can remain a bystander; however, problems may arise when this pathway creates an electrical circuit that bypasses the AV node. When an aberrant electrical connection occurs via the bundle of Kent, tachyarrhythmia may therefore result.

Shown below is an image depicting the normal conduction of electrical signals in the heart versus that in the presence of an accessory pathway.

[[File: Abnormal electrical pathway in WPW.jpeg|center| The normal conduction of electrical signals in the normalheart versus that in the presence of an accessory pathway

• The conduction through the accessory pathway can be:
• Bidirectional (most commonly): retrogarde (also known as concealed) as well as antegrade (also known as manifest, responsible for the ECG findings of delta wave and short PR interval)
• Only retrogarde (less common)
• Only antegrade (least common)

• When arrhythmia occurs in a patient with an accessory pathway, it defines as WPW syndrome.
• The most common type of tachycardia associated with WPW is atrioventricular reciprocating tachycardia (AVRT).
  • AVRT in WPW can be derived as follows:
• Orthodromic (~95%): the antegrade electrical signal moves from the atria to the ventricles through the AV node, whereas the retrograde electrical signal moves from the ventricles to the atria through the accessory pathway.
• Antidromic (~5%): the antegrade electrical signal moves from the atria to the ventricles through the accessory pathway, whereas the retrograde electrical signal moves from the ventricles to the atria through either the AV node or a second accessory pathway.

• Other supraventricular tachyarrhythmia may occur in patients with WPW, such as atrial tachycardia, atrial flutter, atrial fibrillation,AVNRT.
• In these arrhythmia, the accessory pathway may act as a bystander.
• The accessory pathway 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.
• The combination of an accessory pathway and tachyarrhythmia can trigger ventricular fibrillation and sudden cardiac death.
• If an individual had an atrial rate of 300 beats per minute, the accessory bundle may conduct all the electrical impulses from the atria to the ventricles, causing the ventricles to contract at 300 beats per minute. Extremely rapid heart rates such as this may result in hemodynamic instability or cardiogenic shock.
• The missense Mutation in PKRAG2 has been associated with the development of familiar WPW syndrome and cardiac hypertrophy , involving the gamma-2 subunit of AMPK pathway

Associated Conditions

WPW syndrome is associated with the following disorders:

• Ebstein's anomaly
• Mitral valve prolapse: This cardiac disorder, if present, is associated with left-sided accessory pathways.
• Hypertrophic cardiomyopathy: This disorder is associated with familial/inherited form of WPW syndrome.
• Hypokalemic periodic paralysis
• Pompe disease
• Tuberous sclerosis

References