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WPW Syndrome (Wolff-Parkinson-White)

Pre-excitation syndrome, WPW syndrome, Atrioventricular bypass, Auriculoventricular accessory pathway syndrome

Wolff Parkinson White (WPW) Syndrome

• WPW syndrome was described once in 1930 by cardiologists Wolff, Parkinson, and White
• They observed that patients with an enlarged QRS complex and a shortened PQ interval have paroxysmal AVRT
• Kent bundle
• It is an accessory connection in WPW syndrome, linking the atria and ventricles (Atrio-Ventricular bypass)
• About 0.5% of the population has it (it is a congenital anomaly)
• 10% of patients with Kent bundle also have an additional secondary accessory pathway
• which is often inactive
• Does not slow down impulse conduction like the AV node
• The impulse from the Kent bundle creates a Delta wave on the ECG
• Kent bundle (and any accessory pathway) can have
  • Only Antegrade conduction (from atria to ventricles)
  • Only Retrograde conduction (from ventricles to atria)
  • Or conduction in both directions

ECG and WPW Syndrome

• Shortened PQ interval < 0.12s
• Delta wave (Arises due to early activation of part of the ventricle via the Kent bundle)
• Widened QRS complex > 0.11s (QRS complex is widened due to the delta wave)
• Pathological Q wave in the inferior leads (II, III, aVF)
  • 70% of patients with WPW syndrome have a pathological Q wave, which may not indicate an inferior myocardial infarction
• High R wave in the precordial leads
  
  
• ECG signs of WPW syndrome are present
  • Only if the anterograde conduction through the Kent bundle is faster than conduction through the AV junction

Localization of Kent's Bundle

• Kent's bundle is most commonly found in:
• Left atrium: 46-60%
• Right atrium: 13-21%
• Postero-septal: 25%
• Anterior-septal: 2%
  
  
• d'Avila algorithm
• Can localize Kent's bundle with 90% accuracy
• Into 8 anatomical sites
  
  
• For localizing Kent's bundle in the left and right atrium
• Leads V1 and V6 are used
• WPW syndrome type A (left atrium)
• Kent's bundle connects the left atrium - left ventricle
• WPW syndrome type B (right atrium)
• Kent's bundle connects the right atrium - right ventricle

WPW Syndrome Type B (Right Atrial Pathway)

• The Kent bundle connects the right atrium + right ventricle
• The impulse pre-excites the right ventricle, then spreads to the entire myocardium
• The QRS complex resembles Left Bundle Branch Block
• The QRS complex is negative in V1

Manifest Kent Bundle

• Anterograde conduction through the Kent bundle is faster than conduction through the AV node
• A Delta wave appears on the ECG
• 25% of patients with anterograde conduction have blocked retrograde conduction
• Antidromic AVRT may occur
• Orthodromic AVRT cannot occur
• 10% of patients with the Kent bundle have an additional secondary accessory pathway
• Which is often inactive
• Degree of preexcitation
• The wider the QRS complex (Delta wave), the larger part of the ventricles is pre-excited
• Preexcitation (QRS width) depends on heart rate
• With increasing heart rate, conduction through the AV junction speeds up and the QRS complex narrows

ECG (Delta Wave)

• The ECG shows a Delta wave
• Because the impulse through the Kent bundle begins to activate the ventricles earlier
• Than the impulse through the AV junction

Concealed Conduction through the Kent Bundle

• The Kent bundle can conduct impulses both anterogradely and retrogradely, but they are blocked
• Because the Kent bundle has a long refractory period
• The Kent bundle blocks the middle 2 impulses that reset
• The ECG shows a sinus rhythm with a narrow QRS complex
• This is concealed conduction (Concealed conduction), because it is not visible on the ECG under normal circumstances
• Retrograde conduction is unmasked during orthodromic AVRT
• Antegrade conduction is unmasked during atrial fibrillation
• Benign Accessory Pathway
• The Kent bundle with a long refractory period is referred to as a benign accessory pathway
• Because during supraventricular tachycardia (most commonly atrial fibrillation), it acts as a filter for impulses

ECG (Narrow QRS without Delta Wave)

• The ECG shows a narrow QRS complex without a Delta wave
• Because the ventricles are activated only through the AV junction
• The impulse through the Kent bundle is blocked, and the Delta wave does not appear
• The ECG appearance is the same as with a latent Kent bundle

Antidromic AVRT

• Antidromic AVRT (5% of all AVRT)
• The circulating impulse in the re-entry circuit can trigger ventricular or atrial extrasystoles
• The impulse circulates:
• Anterogradely through the Kent bundle
• The ventricles are activated through the Kent bundle, resulting in wide QRS complexes (Delta wave is present)
• Retrogradely through the AV junction
• The atria are activated through the AV junction. P waves are before the QRS complex (often hidden in the T wave)

ECG (Wide QRS and Delta wave)

• Antidromic AVRT
• Wide QRS complexes, with Delta wave
• The ventricles are activated through the Kent bundle
• The atria are activated through the AV junction
• P waves are before the QRS complex (often hidden in the T wave)

Malignant Accessory Pathway

• Has a short refractory period, allowing it to conduct impulses at high frequencies
• Malignant accessory pathway in supraventricular tachycardia
• Conducts impulses to the ventricles at a rate of 200-300/min.
• Progressively leads to ventricular fibrillation and the heart stops functioning as a pump
• A patient with WPW syndrome is at risk from any supraventricular tachycardia, most commonly
• Atrial Fibrillation
• Atrial Flutter

WPW Syndrome (Type A)

• Sinus rhythm
• Heart rate 75/min.
• Shortened PQ interval < 0.12s
• Delta wave and wide QRS approximately 0.18s
• The QRS complex resembles the Greek letter delta
• Dominant QRS and Delta wave (V1)
• This indicates that the Kent bundle is in the left atrium
• Dominant R wave (V1-V3)
• This is not right ventricular hypertrophy
• Dominant R (V4-6)
• This is not left ventricular hypertrophy
• Pathological Q (aVL)
• This is not a previous lateral infarction

WPW Syndrome (Type A)

• Shortened PQ interval < 0.12s
• Delta wave and widened QRS about 0.15s
• Dominant QRS and Delta wave (V1)
• This indicates that the Kent bundle is in the left atrium
• Dominant R wave in V1-V3
• This is not right ventricular hypertrophy

WPW Syndrome (Type B)

• Shortened PQ interval < 0.12s
• Delta wave and widened QRS about 0.15s
• Negative QRS (V1)
• This indicates that the Kent bundle is in the right atrium
• Dominant R wave in V4-V6, not due to:
• left ventricular hypertrophy
• left Tawar's bundle branch block
• Pathological Q wave (III and aVF)
• Not due to a inferior wall infarction

Intermittent WPW Syndrome (Type B)

• On the ECG, there is a alternation between WPW syndrome and sinus rhythm
• Mainly, we see widened QRS complexes with delta wave (WPW syndrome)
• The Kent bundle is in the right atrium
• Widened QRS complexes with Delta wave are negative in the V1 lead

WPW Syndrome and Atrial Fibrillation

• Widened QRS complexes with Delta wave
• The heart rate is irregular with a frequency of approximately 300/min.
• The morphology of the QRS complexes changes
• In the center of the ECG, a capture beat appears to be present
• The ventricles were activated only through the AV junction
• We see 2 different QRS complexes with Delta wave (lead II)
• The patient has 2 accessory pathways (2 Kent bundles)
• Through which impulses alternately pass to the ventricles