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LGL syndrome and WPW syndrome are a form of AVRT both are due to accessory pathway.

• Patients with bypass tract have two limbs of reentry circuit,

  • the AV node (normal)

  • the bypass tract with connections at the atrial & ventricular ends by myocardial cells.

• Rentry can take place in either way , but usually it occurs anterograde via AV node & retrograde via bypass tract thus producing narrow QRS complex (orthodromic conduction). Retrograde conduction through AV node and anterograde conduction through accessory bundle will produce wide complex that are difficult to differentiate from VT(Antidromic conduction).

 LGL Syndrome/James FIbres

• Renterant SVT assosciated with james fibers is termed Lown- Ganog-Levine syndrome . James fibres are a continuation of the posterior internodal tract and connect the atrium and proximal His bundles .

• Atrial impulse completely bypasses the AV node to activate ventricles thus bypassing the usual delay in the AV node ; this is because the james fibres are directly inserted into ventricles in septal region. The ventricles are activated normally.

• ECG : Short PR interval, Normal QRS complex

Mahiam Bundles

• They are composed of myogenic tissue that originates from the AV node,HIS bundle or bundle branches and insert into ventricles at septal region.

• Here atrial impulse passes through AV node but all or part of the impulse bypasses the infranodal conducting system to activate the ventricles.

• The initial depolarisation starts at the ventricular insertion of bypass tract and is spread slowly by cell to cell transmission of the impulse. Subsequently the impulse from normal conducting system takes over the initial depolarisation and activates the bulk of ventricular myocardium.

• ECG: this leads to distortion of initial QRS complex producing delta wave the rest are normal.



WPW Syndrome/ Kent Bundles

• They are composed of myogenic tissue and directly link the atria to ventricles, completely bypassing the AV node and infranodal system. They are most common source for preexcitation and the anatomic basis for WPW syndrome.

WPW Pre Excitation Pattern

• In individuals with WPW syndrome the ventricles are activated early via the bypass tract resulting in short PR interval.

• Slow conduction through the ventricles from the bypass tract insertion site results in initial QRS slurring. (delta wave)

• Once the normal conduction system catches up with the prexcitation wave and activates the remaining ventricles in the usual way resulting in a hybrid or fusion waves.

• Resulting ECG:

  • Shortened PR interval

  • Delta wave.

  • Wide QRS Complex



Fig1 :Conduction during sinus rhythm spreads from SA Node to AV node and then down the bundle branches resulting in a narrow QRS. Fig 2: WPW Syndrome: AN abnormal bypass tract (BT) conncects the atria and ventricles. WPW syndome in sinus rhythm the impulse is quickly conducted down the bypass tract, preexciting the ventricles before the impulse arrives via the AV node.Consequently the PR interval is short and QRS is wide with a delta wave. Fig 3: WPW predisposes patients to develop an AVRT in which a premature atrial beat may spread down the normal pathway to the ventricles, and travels back up through bypass tract, and reciculate down the AV Node again. This reenetrant loop can repeat itself over and over, resulting in a tachycardia, resulting in a normal QRS complex and often a negative p wave in lead II.

Clinical Significance

• Those individuals with WPW Preexcitation Pattern is more prone to arrythmias, especially PSVT .

• It may be mistaken for an bundle branch block or an MI.

• Orthodromic AVRT:

  • It is the commonest form of tachycardia in WPW. When individuals with WPW develops PSVT the reentry circuit passes anterogradely through AV node and retrograde through accessory pathway therefore the ventricles are depolarised in a normal way producing narrow complex tachycardia that is indistinguishable from other forms of SVT. (Normally during sinus rhythm the impulse passes concomitantly via both AV Node and bypass tract producing fusion beat)

• Antidromic AVRT :

• It is a much less common finding, here the signal goes down the bypass tract and up the AV node resulting in a wide QRS.

 WPW in sinus rhythm : Note the slurring of QRS (Delta waves) during sinus rhythm, the delta waves are absent during an episode of orthodromic tachycardia.

Management

• Vagal Maneuvers

• Pharmacological Management

  • Adenosine

  • Calcium Channel / Beta Blockers

• Electrophysiological studies should be carried on.

• RF Ablation therapy.

• In any patient with wide complex tachycardia AV nodal blocking agents should not be used. It is because blocking the AV node will result in conduction via bypass tract and produce VF.

• Any patient with wide complex tachycardia should be treated as VT unless proven.



Updated on 5/9/2015

Reference

• Goldberger

• Tintinalli

• ECG Made Easy by John Hampton