Pre-excitation syndrome

Revision as of 20:15, 28 August 2020 by Shivam Singla (talk | contribs) (Natural history)
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Pre-excitation syndrome Microchapters

Overview

Historical Perspective

Classification

Pathophysiology

Differentiating Pre-excitation Syndrome from other Diseases

Epidemiology and Demographics

Risk Factors

Natural History, Complications, and Prognosis

Diagnosis

Treatment

Prevention

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Associate Editor-In-Chief: Shivam Singla, M.D.[2]

Overview

Pre-excitation syndrome is a condition where ventricles of the heart depolarize earlier than the normal leading to premature contraction. Normally the atria and the ventricles are isolated electrically and only electrical passage existing in between atria and ventricles is at Atrioventricular Node. In all pre-excitation syndromes, there is also present an additional conducting pathway beside the AV junction. So the electrical impulses pass to the ventricles even before the normal wave of depolarization that is about to conduct through the AV node. This mechanism of depolarization of ventricles through an additional accessory pathway ( Bundle of Kent) much earlier than the usual depolarization pathway (through AV node) is referred to as "Pre- Excitation". The secondary conduction pathways are generally named as Bundle of His.

The typical ECG findings are shortened PR interval and widened QRS interval with a slight slurring in the upstroke region. The clinical syndrome of the above clinical finding of ECG and history of SVT is referred to as Wolff-Parkinson-White syndrome. pre-excitation syndromes are getting more common in the pediatric population as well. The main component is the presence of an additional accessory bypass pathway in the heart through which the impulse conducts faster than the physiological conduction through AV node, resulting in quick depolarization ofventricles and leads to dangerous arrhythmias. The most common subtype is Wolf-Parkinson -White syndrome. The severe consequences range from arrhythmias, SVT, and sudden cardiac death. The main therapeutic measures for managing the patients are pharmacotherapy and ablation therapy.

Historical Perspective

Classification

Type Conduction pathway QRS interval PR interval Delta wave
Wolff-Parkinson-White syndrome Bundle of Kent Wide/long Usually short yes
Lown-Ganong-Levine syndrome "James bundle" (atria to bundle of His) Normal/Unaffected Short no
Mahaim-type Mahaim fibers long normal


Pathophysiology

Basics of Pre excitation sydrome

Basic concept of Pathophysiology in pre-excitation syndrome lies in the concept of bypassing the AV node conduction and letting the impulse conduct faster through atria to ventricles via accessory pathways.

These accessory pathways Usually called Bundle of Kent in WPW syndrome, James fiber in LGL syndrome and Mahaim fibers in Mahaim type pre-excitation syndrome. These conducts impulses in forward (not common), backward ( around 15-20%) and in both directions ( Most common type) as well.

The accessory pathways mediate the occurrence of tachyarrhythmia by forming a re-entry circuit and commonly known as AVRT. The direct conduction of impulses from atria to ventricles can also result in the development of tachyarrhythmia's when there is a development of Atrial Fibrillation with RVR


WPW Syndrome


Lown-Ganong-Levine(LGL)Syndrome


Mahaim-Type Pre-excitation

  • ECG findings are usually normal

Differentiating Pre-excitation Syndrome from other Diseases

Arrhythmia Rhythm Rate P wave PR Interval QRS Complex Response to Maneuvers Epidemiology Co-existing Conditions
Atrial Fibrillation (AFib)
  • Absent
  • Less than 0.12 seconds, consistent, and normal in morphology in the absence of aberrant conduction
  • 2.7–6.1 million people in the United States have AFib
  • 2% of people younger than age 65 have AFib, while about 9% of people aged 65 years or older have AFib
Atrial Flutter
  • 75 (4:1 block), 100 (3:1 block) and 150 (2:1 block) beats per minute (bpm), but 150 is more common
  • Varies depending upon the magnitude of the block, but is short
  • Less than 0.12 seconds, consistent, and normal in morphology
  • Conduction may vary in response to drugs and maneuvers dropping the rate from 150 to 100 or to 75 bpm
Atrioventricular nodal reentry tachycardia (AVNRT)''''
  • 140-280 bpm
Multifocal Atrial Tachycardia
  • Irregular
  • Atrial rate is > 100 beats per minute
  • Less than 0.12 seconds, consistent, and normal in morphology
Paroxysmal Supraventricular Tachycardia
  • Regular
  • 150 and 240 bpm
  • Absent
  • Hidden in QRS
  • Absent
  • Narrow complexes (< 0.12 s)
Premature Atrial Contractrions (PAC)
  • 80-120 bpm
  • Upright
  • Usually narrow (< 0.12 s)
Wolff-Parkinson-White Syndrome
  • Regular
  • Atrial rate is nearly 300 bpm and the ventricular rate is at 150 bpm
  • Less than 0.12 seconds
Ventricular Fibrillation (VF)
  • Irregular
  • 150 to 500 bpm
  • Absent
  • Absent
  • Absent (R on T phenomenon in the setting of ischemia)
Ventricular Tachycardia
  • Regular
  • > 100 bpm (150-200 bpm common)
  • Absent
  • Absent
  • Initial R wave in V1, initial r > 40 ms in V1/V2, notched S in V1, initial R in aVR, lead II R wave peak time ≥50 ms, no RS in V1-V6, and atrioventricular dissociation
  • Wide complex, QRS duration > 120 milliseconds
  • 5-10% of patients presenting with AMI

Epidemiology and Demographics

  • WPW is commonly found with an incidence of around 0.1-3.0 per thousand population
  • More common in the male population as compared to females.
  • Familial studies are done to found its association proved that around .55% more commonly found in first degree relatives.
  • More common in young and healthy individuals and as the age advances the prevalence of disease decreases because of loss of pre-excitation.
  • WPW can be considered as a congenital anomaly in some cases where it is usually present since birth and in others and in others it is regarded as a developmental anomaly. Studies proved its lower prevalence in children aged between 6-13 than those in the age group of 14-15 years of age.

Risk Factors

High-risk population for development of atrial fibrillation or sudden cardiac death include:

  • Policemen
  • Athletes
  • Firemen
  • Pilots
  • Steelworkers
  • Male gender
  • Age (peak ages for the development of atrial fibrillation include 30 years and 50 years)
  • Past history of syncope

Natural History, Complications and Prognosis

Natural History

  • There are a lot of studies being done in the past to describe the natural history or the disease course of pre-excitation syndrome. But data from a recent study- "Long term natural history of patients with WPW treated with or without catheter ablation" showed some promising results in explaining the reduced long-tern mortality rates in WPW patients who are matched for age and gender. Also explained the lower mortality rates in catheter ablated patients as compared to non ablated ones.

Complications

  • Most common complications studied in patients having accessory pathway conduction are Arrhythmias and Sudden cardiac death
  • Tachyarrhythmias:
    • If there is a development of atrial fibrillation or flutter then there is fast conduction across the tracts leads to an increased risk of dangerous ventricular arrhythmias.
    • AV nodal blocking agents may also be the factor responsible for the increased conduction through accessory pathways causing life-threatening ventricular arrhythmias or hemodynamic instability resulting and with a worse prognosis.
  • Sudden cardiac death:
    • Sudden cardiac death as a complication in patients with AP conduction is more common in a young male with age less than 35, history of arrhythmias in the past, anatomical location of accessory pathway- that is the septal location of the accessory pathway, having multiple accessory pathways.
    • The studies proved the risk of sudden cardiac death related to the pre-excitation syndrome is around 1.5% in childhood with the highest risk in the first two decades of life.

Prognosis

  • Prognosis is usually very good till the time patient is getting managed and treated appropriately. Catheter ablation showed promising results in the curative treatment of patients suffering from this disorder.
  • Sudden cardiac death is rarely seen in patients with this syndrome but when it happens it is most commonly related to arrhythmias.
  • The most common misconception about the prognosis of WPW syndrome is related to symptoms of the patient but the most important determinant of prognosis is dependent on the electrophysiologic properties of the accessory pathways
  • The conduction through accessory pathways usually decreases with age. This is due to fibrotic changes that happen with time.

Diagnosis

AVRT ( Orthodromic and Antidromic)

WPW Syndrome

Lown-Ganong-Levine(LGL) Syndrome

Mahaim-Type Pre-excitation

  • ECG findings are usually normal

History and Symptoms

People with Pre- Excitation syndromes may be asymptomatic, however, the individuals commonly experience the following symptoms:

Treatment

Medical Treatment


Orthodromic AVRT

  • Hemodynamically Unstable patients (Low BP, Altered mental state, pulmonary edema)- Synchronized DC Cardioversion.
  • Hemodynamically stable- Vagal maneuvers, Adenosine, CCB, and DC cardioversion as a last resort only if the patient not responding to medical therapy.
Antidromic AVRT
  • Hemodynamically unstable patients:- Urgent synchronized DC cardioversion.
  • Hemodynamically stable patients:- Amiodarone, procainamide, or ibutilide.
AF with WPW
  • Hemodynamically unstable patients: Urgent synchronized DC cardioversion
  • Hemodynamically stable patients:- Procainamide or ibutilide.
  • Caution: Adenosine, CCB, Beta-blockers enhances conduction via accessory pathway resulting in worsening & possible degeneration into VT or VF

Surgery

  • Surgery is the mainstay of therapy for [disease name].
  • [Surgical procedure] in conjunction with [chemotherapy/radiation] is the most common approach to the treatment of [disease name].
  • [Surgical procedure] can only be performed for patients with [disease stage] [disease name].


Prevention

For preventing the recurrence of episodes major options available are

  • Radio frequency ablation
  • Surgery.
    • Success rate for surgical ablation is around 100 percent along with lower complication rates. Radiofrequency ablation is a less invasive option and preferred over surgery.
    • Surgery can be considered if a patient is undergoing cardiac surgery for other reasons such as CABG or other heart valve surgery.
  • Medications
    • Although Medications can prevent recurrent episodes of tachycardia they are only used on patients who are not the candidates for ablation or surgery.
    • These patients must be taught to perform Valsalva maneuvers that can relieve tachycardia during the episodes.

References