Wolff-Parkinson-White Syndrome ECG vs Normal ECG

Wolff-Parkinson-White syndrome is a condition present at birth. WPW syndrome is fairly rare and has another name, pre-excitation syndrome. Cardiac pre-excitation syndrome arises from abnormal cardiac electrical conduction through an accessory pathway. It results in asymptomatic and life-threatening arrhythmias.

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The characteristic ECG findings of the WPW pattern of pre-excitation consist:

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• Short PR interval.

• Prolonged QRS complex with the initial upstroke-delta wave in the presence of sinus rhythm.

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An extra electrical pathway allows signals to bypass the conduction route between the atria and the ventricles, leading to abnormally fast heartbeats. These irregular rhythms reduce the heart's efficiency, making it hard for it to pump blood effectively. WPW Syndrome has clinical symptoms, including tachycardia such as palpitations, lightheadedness, presyncope, syncope and even cardiac arrest.

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What is WPW Syndrome?

Many people are born with single or multiple accessory electrical pathways between the atria and ventricles. The accessory pathway rarely causes problems. Some people show abnormalities on surface electrocardiography.

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The Wolff Parkinson White syndrome pattern and a few of those with the WPW pattern experience WPW syndrome. The latter has the potential to lead to malignant tachyarrhythmias and even sudden cardiac death, so diagnosing the WPW electric cardiographic pattern is important.

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Important facts

• WPW syndrome occurs in 1 to 3 per 1000 people worldwide.

• Most individuals with the WPW pattern have no symptoms.

• The most frequent arrhythmia in WPW is atrioventricular reentrant tachycardia AVRT.

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How do tachyarrhythmias occur in WPW syndrome?

WPW syndrome is passed down through families. It is associated with the thickened heart muscle called hypertrophic cardiomyopathy.

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The heart has four chambers

• Two upper chambers are called the atria.

• Two lower chambers are called the ventricles.

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The upper right heart chamber has a SA node from where the heart begins to beat. The signals move from the upper heart chambers to the atrioventricular node, where they usually slow down and reach low heart chambers. The signaling process continues smoothly, with a resting rate of 60-100 beats per minute.

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In WPW syndrome, an extra electrical pathway, Bundle of Kent, connects the upper and lower heart chambers, allowing heart signals to bypass the AV node. Consequently, the heart signals don't slow down; the signals get excited, and the heart rate increases. The extra pathway can also cause heart signals to travel backward, resulting in an uncoordinated heart rhythm.

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Symptoms

The most common symptom of Wolf Parkinson White Syndrome is a heart rate greater than 100 beats per minute tachycardia. The fast heartbeat begins suddenly and lasts a few seconds to several hours. Episodes occur during exercise or while at rest.

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Symptoms depend upon the

• speed of the heartbeat and,

• the underlying heart rhythm disorder.

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The most common irregular heartbeat seen with the WPW syndrome is supraventricular tachycardia. During an episode of SVT, the heart beats around 150 to 200 times a minute, and occasionally, it can beat faster or slower. WPW syndrome often has a fast and chaotic heart rhythm disorder called atrial fibrillation.

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 Some common symptoms are

• Rapid fluttering or pounding of the heart.

• Chest pain.

• Difficulty breathing.

• Dizziness or Lightheadedness.

• Venting.

• Fatigue.

• Shortness of breath.

• Anxiety.

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WPW is often discovered by chance during a heart test.

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Characteristics of a Normal ECG

A normal ECG reflects heart electrical activity through a well-organized pattern of waves and intervals. In a healthy ECG, the heart rhythm is regular, and the beat originates from the sinoatrial node. No extra waves or regularities and intervals are present between the beats, and the blood is pumped regularly, reflecting normal cardiac function.

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1. P wave

It represents atrial depolarization. When atrial contraction occurs in a normal ECG, its duration is less than 120 milliseconds. It is a smooth, rounded morphology, and leads I, II, and aVF must have a positive P wave.

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2. PR Interval

It is the time interval the electric impulse takes to travel from the atria to the ventricles. Normal PR interval ranges from 120 to. 200 milliseconds. The duration contributes to efficient heart function and a coordinated blood flow.

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3. QRS complex

The QRS complex indicates the contraction of the ventricles (ventricular depolarization). A normal QRS duration is less than 120 milliseconds. Its morphology features initial download deflection (Q Wave), Prominent upward deflection R wave, and a subsequent downward deflection S wave representing ventricular electrical activity.

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4. T wave

A T wave represents ventricle repolarization; it is smooth, has asymmetrical morphology, and points upwards in leads I, II, and aVF. If the T wave is tall or pointed, it indicates abnormalities in heart recovery or electrolyte imbalances.

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5. QT interval 

It is the time the heart takes to contract and relax. Normal QT interval ranges from 320 to 440 milliseconds. Life-threatening arrhythmias occur if the length of the interval increases or decreases.

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WPW Syndrome ECG Characteristics

The ECG displays distinct features due to the presence of an accessory conduction pathway through the Bundle of Kent. It is characterized by.

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• Short PR interval, less than 120 milliseconds.

• The presence of a delta wave is an upstroke at the beginning of the QRS complex.

•  It is present at the beginning of a QRS complex and reflects ventricular depolarization.

• QRS complex is prolonged, exceeding 100 milliseconds.

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1. Delta wave

It is a distinctive feature of WPW syndrome.

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• A characteristic upstroke at the beginning of the QRS complex.

• Early ventricular depolarization due to the accessory conduction pathway indicates abnormal electrical activity.

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2. Short PR interval

• It is less than 120 milliseconds.

• The reduction occurs because of electrical impulses bypassing the normal conduction pathway through the atrioventricular node causing rapid ventricular activation.

• A short PR interval is a diagnostic marker for identifying WPW syndrome on ECG.

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3. Wide QRS complex

• It is more than 120 milliseconds.

• The widening is due to the simultaneous activation of ventricles by conduction systems and accessory pathways.

• A wide QRS complex indicates impaired conduction and is essential for differentiating WPW from other arrhythmias.

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4. Pseudo RB pattern

Sometimes, WPW syndrome resembles the right bundle branch block on the ECG. It occurs due to ventricular activation through an accessory pathway. Identifying this pattern helps in the diagnosis of WPW syndrome.

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5. Left Lateral Accessory Pathway

Left lateral accessory pathways are most common in WPW syndrome.

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• Signals skip the AV node, causing short PR intervals and delta waves on the ECG.

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Key Differences Between the WPW ECG and a Normal ECG

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1. PR interval length

• In WPW syndrome, the PR interval is less than 120 milliseconds and is due to the rapid conduction of electrical impulses by the accessory pathways.

• This short interval distinguishes it from a normal ECG, where the PR interval is between 120 and 200 milliseconds.

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2. QRS, complex duration and morphology

• WPW syndrome has a broad QRS complex exceeding 100 milliseconds. The widening is due to the activation of both natural and accessory pathways in the conduction system.

• In a normal ECG, the QRS complex is narrow and less than 100 milliseconds.

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3. Presence of Delta wave

• A delta wave is present at the start of the QRS complex in WPW ECG. The delta wave results from early ventricle depolarization due to the accessory conduction pathway.

• A normal ECG does not have a delta wave.

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4. T wave changes

• In WPW syndrome, T waves invert or flatten in the leads where the delta wave is present. These changes indicate underlying myocardial strain.

• A normal ECG displays upright, well-defined T waves, indicating normal ventricular repolarization.

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Types of SVT in WPW Syndrome 

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1. Orthodromic

• Orthodromic tachycardia has a narrow QRS complex and is the most common of the SVT.

• The impulse travels down from the normal AV pathway into the ventricle and then back into the atrium through the accessory pathway.

• Delta waves do not form during tachycardia.

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2. Antidromic

• It occurs in the remaining 10% of the population.

• It has a wide QRS complex.

• The signals move down the accessory pathway and return through the A V node.

• Antidromic tachycardia is often mistaken for ventricular tachycardia due to the wide QRS complex.

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3. Confirming the diagnosis of WPW syndrome

It cannot be confirmed during the tachycardia.

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• ECG during tachycardia shows an absent delta wave.

• Post-tachycardia ECG confirms WPW syndrome due to the presence of delta waves.

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Pre Excitation in WPW Syndrome

Preexcitation happens when ventricles are activated early as the electrical signals bypass the AV node through the accessory pathways called bypass tracts, which are formed during heart development and are found in many locations. The accessory pathway is the Bundle of Kent.

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Conduction through accessory pathways

 Accessory pathways can conduct signals in the following directions.

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• Both directions: Most common when the signals travel both to and fro from the ventricles.

• Retrograde only: (15%): Signals move from the ventricles towards the atria.

• Anterograde only: (rare): The signal moves towards the ventricles.

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ECG features based on accessory pathway location

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Left-sided accessory pathway

• Positive delta wave in all chess leads.

• R/S Ratio > 1 in V1.

• Also known as Type A WPW.

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Right-sided accessory pathway

• Negative delta wave in leads V1 and V2.

• Also known as type B WPW pattern.

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Concealed pathway

It is in an accessory pathway that conducts signals backward from the ventricles to the atria. All signals pass forward through the normal AV node. So, there is no preexcitation and no signs of WPW on the ECG in normal rhythm. These pathways can still cause tachyarrhythmias by participating in re-entry circuits.

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Treatment for WPW

Treatment options for WPW syndrome depend on.

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• Symptoms of the patient.

• Frequency of arrhythmias.

• Risk of severe complications.

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Asymptomatic individuals require regular monitoring. Wild symptomatic patients require medications.

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Catheter ablation

• It is a minimally invasive procedure used to treat the WPW syndrome.

• It identifies and destroys the accessory pathway responsible for abnormal electrical conduction.

• This technique involves inserting a catheter into the heart and using radio frequency to eliminate the path.

• It offers long-term relief.

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Medications

• Beta-blockers and anti-arrhythmic medications are prescribed to manage WPW syndrome.

• Beta Blockers slow down the heart rate and reduce the frequency of arrhythmias.

• Anti-arrhythmic drugs reduce the heart's electrical activity.

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Pacemakers

They provide electrical signals, creating a consistent heart rate. They are given to patients with severe symptoms or those with a risk of life-threatening arrhythmias. 

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Lifestyle modifications

Avoid excessive caffeine, alcohol, and stress. Do regular exercises and take a healthy diet with an adequate amount of water contribute to overall health.

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Conclusion

Special ECG features, such as delta waves, short PR intervals and wide QR complexes, characterize WPW. These features help to distinguish it from normal cardiac rhythms. Early detection and appropriate management are vital in preventing potential complications associated with it.

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These help to improve patient outcomes and quality of life. Gauze helps you identify distinctive features of the ECG that affect the lives of individuals. Early detection contributes to improved outcomes.