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Pre-excitation Syndrome - ECG

Pre-excitation syndrome, Wolff-Parkinson-White syndrome, Lown-Ganong-Levine syndrome, Mahaim-type

Accessory Pathways
Pre-excitation Syndrome
ECG and Pre-excitation Syndrome
Wolff-Parkinson-White (WPW) Syndrome
Lown-Ganong-Levine (LGL) Syndrome
Mahaim Syndrome
Malignant Accessory Pathway
Benign Accessory Pathway

12-lead ECG

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Accessory Pathways

Pre-excitation syndrome, conduction pathway: Bundle of Kent, James bundle, Mahaim fibers

Physiologically, the atria are electrically isolated from the ventricles

The only electrical connection is the AV junction
If the AV junction is interrupted, AV block III degree (electrical isolation of the atria from the ventricles) occurs

0.5% of the population have an additional accessory pathway in addition to the AV junction

The atria and ventricles are electrically connected through 2 pathways:

AV junction
Accessory pathway

10% of patients with an accessory pathway also have an additional secondary accessory pathway

which is often inactive

Based on localization, there are 3 main accessory pathways:

Kent bundle

Connects the atria and ventricles
(Atrio-Ventricular bypass)
Creates the WPW syndrome

James bundle

Connects the atria with the His bundle
(Atrio-Hisian bypass)
Creates the LGL syndrome

Mahaim fibers

Connects the AV junction and ventricles
(Nodo-Ventricular bypass)
Creates the Mahaim syndrome

Pre-excitation Syndrome

Pre-excitation, Wolff-Parkinson-White (WPW) syndrome, bundle of Kent (Atrio-Ventricular bypass)

Physiologically, the ventricles are activated via

the AV junction and conduction system

Pre-excitation syndrome means

that the ventricles are activated earlier
The ventricles are pre-excited via an accessory pathway

The most common accessory pathway is the Kent bundle

Thus, WPW syndrome is often referred to as

Pre-excitation syndrome (which is not entirely accurate)

There are 3 pre-excitation syndromes:

Wolff-Parkinson-White (WPW) syndrome - Kent bundle
Lown-Ganong-Levine (LGL) syndrome - James bundle
Mahaim pre-excitation syndrome - Mahaim fibers

ECG and Pre-excitation Syndrome

Accessory Pathways
- Conduct impulses to the ventricles without delay (non-decremental conduction)
- The ventricles are activated earlier through the accessory pathway
Pre-excitation syndromes produce:

Wolff-Parkinson-White (WPW) Syndrome

Accessory pathway, bundle of Kent, Atrio-Ventricular bypass

Kent Bundle and WPW Syndrome

WPW Syndrome features the Kent bundle

It connects the atria and ventricles, bypassing the AV junction (Atrio-Ventricular bypass)

Delta Wave

The impulse through the Kent bundle activates the ventricles earlier and widens the lower part of the QRS complex

Shortened PR Interval < 0.12s

The broadened base of the QRS complex shifts towards the P wave

Lown-Ganong-Levine (LGL) Syndrome

LGL syndrome, short PR interval, normal QRS interval, No delta wave

James Bundle and LGL Syndrome

LGL Syndrome features the James bundle

It connects the atria to the His bundle, bypassing the AV node (Atrio-Hisian bypass)

Absence of Delta Wave

The delta wave is absent because the ventricles are activated through the conduction system

Shortened PR Interval < 0.12s

The impulse bypasses the AV node and reaches the ventricles more quickly

Mahaim Syndrome

ECG Mahaim delta wave, normal PR interval

Mahaim Bundle and Mahaim Syndrome

Mahaim Syndrome features the Mahaim bundle

It connects the AV junction to the ventricles, bypassing the Tawar branches (Nodo-Ventricular bypass)

Delta Wave

The ventricles are activated earlier through the Mahaim bundle, resulting in a delta wave

Normal PR Interval (0.12s-0.20s)

The impulse reaches the AV junction, where it physiologically slows down
and then continues through the Mahaim bundle to the ventricles

Malignant Accessory Pathway

It has a short refractory period, which allows it to conduct impulses at high frequencies
Malignant accessory pathway in supraventricular tachycardia

Conducts impulses to the ventricles at a frequency of 200-300/min.
Progressively leads to ventricular fibrillation and the heart ceases to function as a pump

Patients with WPW syndrome are at risk from any supraventricular tachycardia, most commonly

malignant accessory pathway, WPW syndrome, atrial fibrillation

Atrial Fibrillation and WPW

Impulses pass to the ventricles through the accessory pathway (without slowing down)
Results in irregular wide-complex tachycardia (QRS > 0.12s)

with a frequency of 200-300/min.

May result in

Fusion beat (Fusion beat)
Capture beat (Capture beat)

Benign Accessory Pathway

It has a long refractory period, so it cannot conduct impulses to the ventricles at high frequencies
In sinus rhythm, this pathway is inactive

It is concealed conduction, because in the accessory pathway, the middle 2 impulses during the refractory period are blocked
There is no sign of pre-excitation on the ECG

The accessory pathway becomes unmasked during tachycardia

When atrioventricular reentry tachycardia occurs

In sinus rhythm, delta wave may intermittently appear (if it is WPW syndrome)

When a supraventricular impulse passes to the ventricles through the accessory pathway outside the refractory period

$concealed accessory pathway, WPW syndrome, retrograde accessory pathway refractory block$

Sinus Rhythm

The ECG shows a narrow QRS complex without delta waves
Because the ventricles are activated only through the AV junction
Impulses in the accessory pathway

Are blocked during the refractory period

The ECG shows sinus rhythm without pre-excitation
The accessory pathway becomes unmasked during AVRT

Bundle of Kent, Atrio-Ventricular bypass

WPW Syndrome

Shortened PQ interval < 0.12s
Delta wave
Extended QRS complex (>0.12s)
Dominant R waves in V1-3

It is not right ventricular hypertrophy
It is a sign of WPW Syndrome

LGL Syndrome

Shortened PQ interval < 0.12s
Absent Delta wave
The same ECG pattern is seen in:

LGL Syndrome
Accelerated AV conduction
To differentiate, electrophysiological testing is used

ECG Mahaim type preexcitation syndrome, normal PR interval, Long QRS, Delta Wave

Mahaim Syndrome

Normal PQ interval (0.16s)
Delta wave
Wide QRS complex (>0.12s)
Mahaim pathway confirmed by electrophysiological examination
ECG resembles left bundle branch block

Because the Mahaim pathway is in the right ventricle

Sources

ECG from Basics to Essentials Step by Step
litfl.com
ecgwaves.com
metealpaslan.com
medmastery.com
uptodate.com
ecgpedia.org
wikipedia.org
Strong Medicine
Understanding Pacemakers

Home /

Pre-excitation Syndrome - ECG

Pre-excitation syndrome, Wolff-Parkinson-White syndrome, Lown-Ganong-Levine syndrome, Mahaim-type

Accessory Pathways
Pre-excitation Syndrome
ECG and Pre-excitation Syndrome
Wolff-Parkinson-White (WPW) Syndrome
Lown-Ganong-Levine (LGL) Syndrome
Mahaim Syndrome
Malignant Accessory Pathway
Benign Accessory Pathway

12-lead ECG

Smartwatch ECG

Have a doctor’s or smartwatch ECG?

Upload your 12-lead, smartwatch or smart device ECG.
Get a physician’s report within 24 hours.

Get my ECG reviewed →

Reviewed by a physician · Your questions answered · Not AI

Accessory Pathways

Physiologically, the atria are electrically isolated from the ventricles

The only electrical connection is the AV junction
If the AV junction is interrupted, AV block III degree (electrical isolation of the atria from the ventricles) occurs

0.5% of the population have an additional accessory pathway in addition to the AV junction

The atria and ventricles are electrically connected through 2 pathways:

AV junction
Accessory pathway

10% of patients with an accessory pathway also have an additional secondary accessory pathway

which is often inactive

Based on localization, there are 3 main accessory pathways:

Kent bundle

Connects the atria and ventricles
(Atrio-Ventricular bypass)
Creates the WPW syndrome

James bundle

Connects the atria with the His bundle
(Atrio-Hisian bypass)
Creates the LGL syndrome

Mahaim fibers

Connects the AV junction and ventricles
(Nodo-Ventricular bypass)
Creates the Mahaim syndrome

Pre-excitation Syndrome

Physiologically, the ventricles are activated via

the AV junction and conduction system

Pre-excitation syndrome means

that the ventricles are activated earlier
The ventricles are pre-excited via an accessory pathway

The most common accessory pathway is the Kent bundle

Thus, WPW syndrome is often referred to as

Pre-excitation syndrome (which is not entirely accurate)

There are 3 pre-excitation syndromes:

Wolff-Parkinson-White (WPW) syndrome - Kent bundle
Lown-Ganong-Levine (LGL) syndrome - James bundle
Mahaim pre-excitation syndrome - Mahaim fibers

ECG and Pre-excitation Syndrome

Accessory Pathways
- Conduct impulses to the ventricles without delay (non-decremental conduction)
- The ventricles are activated earlier through the accessory pathway
Pre-excitation syndromes produce:

Wolff-Parkinson-White (WPW) Syndrome

Kent Bundle and WPW Syndrome

WPW Syndrome features the Kent bundle

It connects the atria and ventricles, bypassing the AV junction (Atrio-Ventricular bypass)

Delta Wave

The impulse through the Kent bundle activates the ventricles earlier and widens the lower part of the QRS complex

Shortened PR Interval < 0.12s

The broadened base of the QRS complex shifts towards the P wave

Lown-Ganong-Levine (LGL) Syndrome

James Bundle and LGL Syndrome

LGL Syndrome features the James bundle

It connects the atria to the His bundle, bypassing the AV node (Atrio-Hisian bypass)

Absence of Delta Wave

The delta wave is absent because the ventricles are activated through the conduction system

Shortened PR Interval < 0.12s

The impulse bypasses the AV node and reaches the ventricles more quickly

Mahaim Syndrome

Mahaim Bundle and Mahaim Syndrome

Mahaim Syndrome features the Mahaim bundle

It connects the AV junction to the ventricles, bypassing the Tawar branches (Nodo-Ventricular bypass)

Delta Wave

The ventricles are activated earlier through the Mahaim bundle, resulting in a delta wave

Normal PR Interval (0.12s-0.20s)

The impulse reaches the AV junction, where it physiologically slows down
and then continues through the Mahaim bundle to the ventricles

Malignant Accessory Pathway

It has a short refractory period, which allows it to conduct impulses at high frequencies
Malignant accessory pathway in supraventricular tachycardia

Conducts impulses to the ventricles at a frequency of 200-300/min.
Progressively leads to ventricular fibrillation and the heart ceases to function as a pump

Patients with WPW syndrome are at risk from any supraventricular tachycardia, most commonly

Atrial Fibrillation and WPW

Impulses pass to the ventricles through the accessory pathway (without slowing down)
Results in irregular wide-complex tachycardia (QRS > 0.12s)

with a frequency of 200-300/min.

May result in

Fusion beat (Fusion beat)
Capture beat (Capture beat)

Benign Accessory Pathway

It has a long refractory period, so it cannot conduct impulses to the ventricles at high frequencies
In sinus rhythm, this pathway is inactive

It is concealed conduction, because in the accessory pathway, the middle 2 impulses during the refractory period are blocked
There is no sign of pre-excitation on the ECG

The accessory pathway becomes unmasked during tachycardia

When atrioventricular reentry tachycardia occurs

In sinus rhythm, delta wave may intermittently appear (if it is WPW syndrome)

When a supraventricular impulse passes to the ventricles through the accessory pathway outside the refractory period

$concealed accessory pathway, WPW syndrome, retrograde accessory pathway refractory block$

Sinus Rhythm

The ECG shows a narrow QRS complex without delta waves
Because the ventricles are activated only through the AV junction
Impulses in the accessory pathway

Are blocked during the refractory period

The ECG shows sinus rhythm without pre-excitation
The accessory pathway becomes unmasked during AVRT

WPW Syndrome

Shortened PQ interval < 0.12s
Delta wave
Extended QRS complex (>0.12s)
Dominant R waves in V1-3

It is not right ventricular hypertrophy
It is a sign of WPW Syndrome

LGL Syndrome

Shortened PQ interval < 0.12s
Absent Delta wave
The same ECG pattern is seen in:

LGL Syndrome
Accelerated AV conduction
To differentiate, electrophysiological testing is used

Mahaim Syndrome

Normal PQ interval (0.16s)
Delta wave
Wide QRS complex (>0.12s)
Mahaim pathway confirmed by electrophysiological examination
ECG resembles left bundle branch block

Because the Mahaim pathway is in the right ventricle

Sources

ECG from Basics to Essentials Step by Step
litfl.com
ecgwaves.com
metealpaslan.com
medmastery.com
uptodate.com
ecgpedia.org
wikipedia.org
Strong Medicine
Understanding Pacemakers