Pre-excitation syndrome

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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 & 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

Risk Factors

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

Natural History, Complications and Prognosis

Natural History

Complications

Prognosis

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

HEMODYNAMICALY UNSTABLE PATIENT -- DIRECT SYNCHRONIZED CARDIOVERSION, BIPHASIC ( 100 J INITIAL LATER ON 200j OR 360J.


HEMODYNAMICALLY STABLE PATIENTS -- FOLLOWING ALGORITHM CAN BE FOLLOWED,

GENERAL PROTOCOL

  • Antiarrhythmic drug
    • Helps in slowing the accessory pathway conduction and thus plays a major role in the acute events.
  • AV Nodal blocking agents should NOT be used
    • As they aggravate WPW by increasing the conduction through the accessory pathway.
  • Address the underlying cause triggering dysrhythmias which includes
    • Coronary artery disease
    • Cardiomyopathy
    • Electrolyte derangement
    • Anemia
    • Thyroid disease

IN CASE OF ACUTE AVRT/AVNRT

  • Treated by blocking the AV nodal conduction
    • Help in blocking the pathways responsible for causing dysrhythmias through the involvement of the AV node (AVRT/AVNRT).
    • Vagal Maneuvers - Valsalva maneuver, immersing the face in cold water or ice water, carotid sinus massage
    • IV Adenosine- very short half-life and commonly used in dose around 6-12 mg
    • IV Verapamil- this is a calcium channel blocker and commonly used as 5-10 mg.

ATRIAL FLUTTER/FIBRILLATION

  • If wide complex tachycardia is present
    • Use IV Amiodarone or Procainamaide

RADIOFREQUENCY ABLATION

  • This modality has replaced drug therapy and other surgical treatment options by showing promising results. Best results are studied these days when it is used in conjunction with cryoblation (commonly used for septal Accessory pathways and for accessory pathways near small coronary arteries)
  • This technique is used widely with best results in:
    • Patients with AVRT showing symptoms of dysrhythmias
    • Patients with impaired functional daily activities having no symptoms with ventricular preexcitation
    • Patients with WPW and family history of sudden cardiac death in first or second-degree relatives.
    • Patients with AVRT OR A.FIB with RVR
    • Patients with h/o Pre-excited A.FIB
  • Patients who are not willing to undergo radiofrequency ablation can be managed on medical management with the use of Anti-arrhythmics. Though its role in the prevention of future episodes of arrhythmias is limited still this is the most commonly used modality of choice.

Class 3 Antiarrhythmics and class Ic drugs are used with AV nodal blocking agents in patients with a history of atrial flutter or A.Fib.Sotalol and Flecainide would be the safe options to use in pregnancy.

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