Pre-excitation syndrome

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

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Overview

Pre-excitation syndrome is a condition where ventricles of the heart become depolarized too early, which leads to their partially premature contraction.

Normally, the atria (chambers taking venous blood) and the ventriculi (chambers pro-pulsing blood towards organs) are electrically isolated, and only electrical passage exists at "atrioventricular node". In all pre-excitation syndromes, there is at least one more conductive pathway is present. Physiologically, the electrical depolarization wave 'waits' in atrioventricular node to allow atria contract before ventriculi. However, there is no such property exists in abnormal pathway, so electrical stimulus passes to ventricle by this tracts far before normal atrioventricular-his system, and ventricles are depolarized (excited) before (pre-) normal conduction system. The term pre-excitation derives from this condition.

It is usually caused by a secondary conduction pathway (other than the bundle of His).

Historical Perspective

  • First described by Louis Wolff, John Parkinson and Paul Dudley White in 1930
  • They found the association of these conditions with a small risk of sudden cardiac death

Classification

  • pre-excitation syndrome may be classified into sub-types[1]
Type Conduction pathway PR interval QRS interval Delta wave?
Wolff-Parkinson-White syndrome Bundle of Kent (atria to ventricles) short long yes
Lown-Ganong-Levine syndrome "James bundle" (atria to bundle of His) short normal no
Mahaim-type Mahaim fibers normal long


WPW Syndrome

WPW is a combination of the presence of congenital accessory pathways along with episodic tachyarrhythmias. Here the accessory pathways are referred to as Bundle of Kent or AV bypass tracts.

The features of pre-excitation are subtle, intermittent, and are aggravated by an increase in vagal tone ( Valsalva maneuver, AV blockage by drugs).

ECG Features of WPW

  • Shortened PR interval (Less than 120ms)
  • Delta wave – slow/slurring in the rise of an initial portion of the QRS
  • Widening of QRS complex
  • ST Segment and T wave discordant changes – i.e. in the opposite direction to the major component of the QRS complex
  • WPW is mainly categorized as type A or B.
    • Type A: positive delta wave in all precordial leads with R/S > 1 in V1
    • Type B: negative delta wave in leads V1 and V2

Lown-Ganong-Levine (LGL) Syndrome

Here the Accessory pathway are composed of James fibers.  

ECG features:

The important point to be noted is that this tern is not relevant or shouldn't be used in the absence of paroxysmal tachycardia. Its existence is disputed and it may not exist.

Mahaim-Type Pre-excitation

Right-sided accessory pathways connecting either AV node to ventricles, fascicles to ventricles, or atria to fascicles

ECG features:

  • Sinus rhythm ECG may be normal
  • May result in variation in ventricular morphology
  • Reentry tachycardia typically has LBBB morphology
Basics of Pre excitation sydrome

Pathophysiology

  • Pathophysiology of Pre-Excitation syndrome
    • Pre-excitation refers to the early activation of the ventricles as a result of impulses bypassing the AV node via an accessory pathway. The latter are abnormal conduction pathways formed during cardiac development. These can conduct impulses either
      • towards ventricles (Anterograde conduction, rarely seen) ,
      • Away from the ventricles (Retrograde conduction, in approx 15%),
      • in both the directions ( Majority of cases).
    • In WPW syndrome which is a type of pre-excitation syndrome the abnormal conduction pathways are called Bundle of Kent or AV bypass tract.
    • The accessory pathways facilitate the formation of Tachyarrhythmias by mainly forming a reentry circuit, termed as AVRT (80%). Even in cases of direct conduction through the accessory pathways from A to V ( Bypassing AV node), there can be the resultant formation of Tachyarrhythmias, seen most frequently in the condition of A. Fib with RVR.


Clinical Features

People with Pre- Excitation syndromes may be asymptomatic, however, the individual may experience following symptoms


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)[2][3]'
  • Irregularly irregular
  • Absent
  • Fibrillatory waves
  • 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[4]
  • Regular or Irregular
  • 75 (4:1 block), 100 (3:1 block) and 150 (2:1 block) beats per minute (bpm), but 150 is more common
  • Sawtooth pattern of P waves at 250 to 350 bpm
  • Biphasic deflection in V1
  • 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)[5][6][7][8]
  • Regular
  • 140-280 bpm
  • slow-fast AVNRT:
    • Pseudo-S wave in leads II, III, and AVF
    • Pseudo-R' in lead V1.
  • Fast-Slow AVNRT
  • Slow-Slow AVNRT
  • Inverted, superimposed on or buried within the QRS complex (pseudo R prime in V1/pseudo S wave in inferior leads)
  • Absent (P wave can appear after the QRS complex and before the T wave, and in atypical AVNRT, the P wave can appear just before the QRS complex)
  • Less than 0.12 seconds, consistent, and normal in morphology in the absence of aberrant conduction
  • QRS alternans may be present
'Multifocal Atrial Tachycardia[9][10]
  • Irregular
  • Atrial rate is > 100 beats per minute
  • Varying morphology from at least three different foci
  • Absence of one dominant atrial pacemaker, can be mistaken for atrial fibrillation if the P waves are of low amplitude
  • 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)[11][12]
  • Regular except when disturbed by premature beat(s)
  • 80-120 bpm
  • Upright
  • > 0.12 second
  • Maybe shorter than that in normal sinus rhythm (NSR) if the origin of PAC is located closer to the AV node
  • Ashman’s Phenomenon:
  • Usually narrow (< 0.12 s)
'Wolff-Parkinson-White Syndrome[13][14]
  • Regular
  • Atrial rate is nearly 300 bpm and the ventricular rate is at 150 bpm
  • Less than 0.12 seconds
  • A delta wave and evidence of ventricular pre-excitation if there is conduction to the ventricle via ante-grade conduction down an accessory pathway
  • A delta wave and pre-excitation may not be present because bypass tracts do not conduct ante-grade.
Ventricular Fibrillation (VF)[15][16][17]
  • Irregular
  • 150 to 500 bpm
  • Absent
  • Absent
  • Absent (R on T phenomenon in the setting of ischemia)
Ventricular Tachycardia[18][19]
  • 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

  • Incidence 0.1 – 3.0 per 1000
  • LGL syndrome is a rare Man > woman.
  • prognosis is good with SCD is noted in only 0.1% (rare)

Risk Factors

High risk population for sudden cardiac death in Wolff-Parkinson-White syndrome include:

  • Policemen
  • Athletes
  • Firemen
  • Pilots
  • Steelworkers

Risk factors for the development of atrial fibrillation in WPW syndrome include:

  • 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[edit | edit source]

  • The majority of patients with [disease name] remain asymptomatic for [duration/years].
  • Early clinical features include [manifestation 1], [manifestation 2], and [manifestation 3].
  • If left untreated, [#%] of patients with [disease name] may progress to develop [manifestation 1], [manifestation 2], and [manifestation 3].
  • Common complications of [disease name] include [complication 1], [complication 2], and [complication 3].
  • Prognosis is generally [excellent/good/poor], and the [1/5/10­year mortality/survival rate] of patients with [disease name] is approximately [#%].


Diagnosis

Atrioventricular Reentry Tachycardia's (AVRT)

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AVRT is a form of PSVT. Reentry circuit results from the combination of signal transduction from normal conduction system and accessory pathway.( See: Diagram)[20]

  • During tachyarrythmias, the accessory pathway forms part of the reentry circuit that results in the disappearance of features of tachyarrhythmias.
  • AVRT are further divided into
    • Orthodromic or Antidromic conduction based on ECG morphology and direction of formation of re-entry circuit.


1) AVRT with Orthodromic Conduction

In this, the anterograde conduction occurs via the AV node and retrograde conduction occurs via an accessory pathway.

ECG features of AVRT with orthodromic conduction

  • Rate usually 200 – 300 bpm
  • P waves may be buried in QRS complex or retrograde
  • QRS Complex usually <120 ms unless pre-existing bundle branch block, or rate-related aberrant conduction
  • QRS Alternans – phasic variation in QRS amplitude associated with AVNRT and AVRT, distinguished from electrical altrens by a normal QRS amplitude
  • T wave inversion common
  • ST segment depression


2) AVRT with Antidromic Conduction

In this, the anterograde conduction occurs via the accessory pathway and retrograde conduction via the AV node. Occurring only in-app. 5% of patients with WPW.

ECG features are:


3) Atrial Fib/Atrial Flutter in WPW

  • In 20% of the patients WPW Atrial fibrillation can occur and in approx 7% of patients with WPW atrial flutter can occur. Accessory pathways plays major role by allowing the rapid conduction of impulses directly to the ventricles without involving AV node, in extreme cases may lead to VT or VF.

ECG features are:

  • Rate > 200 bpm
  • Irregular rhythm
  • Wide QRS complexes due to abnormal ventricular depolarisation via an accessory pathway
  • QRS Complexes change in shape and morphology
  • Axis remains stable unlike Polymorphic VT
  • Atrial Flutter presents with same features as atrial fibrillation in WPW except rhythm is regular and commonly mistaken for VT


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

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  11. Lin CY, Lin YJ, Chen YY, Chang SL, Lo LW, Chao TF, Chung FP, Hu YF, Chong E, Cheng HM, Tuan TC, Liao JN, Chiou CW, Huang JL, Chen SA (August 2015). "Prognostic Significance of Premature Atrial Complexes Burden in Prediction of Long-Term Outcome". J Am Heart Assoc. 4 (9): e002192. doi:10.1161/JAHA.115.002192. PMC 4599506. PMID 26316525.
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  13. Rao AL, Salerno JC, Asif IM, Drezner JA (July 2014). "Evaluation and management of wolff-Parkinson-white in athletes". Sports Health. 6 (4): 326–32. doi:10.1177/1941738113509059. PMC 4065555. PMID 24982705.
  14. Rosner MH, Brady WJ, Kefer MP, Martin ML (November 1999). "Electrocardiography in the patient with the Wolff-Parkinson-White syndrome: diagnostic and initial therapeutic issues". Am J Emerg Med. 17 (7): 705–14. doi:10.1016/s0735-6757(99)90167-5. PMID 10597097.
  15. Glinge C, Sattler S, Jabbari R, Tfelt-Hansen J (September 2016). "Epidemiology and genetics of ventricular fibrillation during acute myocardial infarction". J Geriatr Cardiol. 13 (9): 789–797. doi:10.11909/j.issn.1671-5411.2016.09.006. PMC 5122505. PMID 27899944.
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