Wolff-Parkinson-White syndrome


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Wolff-Parkinson-White syndrome


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Wolff-Parkinson-White syndrome


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USMLE® Step 1 questions

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Wolff-Parkinson-White syndrome

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USMLE® Step 1 style questions USMLE

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A 32-year-old male presents to the emergency department with palpitations. The patient was in the park jogging when he suddenly felt lightheaded, dizzy, and noted a pounding sensation in his chest. The symptoms resolved prior to arrival, and he now feels back to his baseline. Medical history is otherwise noncontributory, and he does not consume alcohol, tobacco, or illicit substances. Temperature is 37.0°C (98.6°F), pulse is 88/min, respirations are 14/min, and blood pressure is 124/72 mmHg. The electrocardiogram from triage is demonstrated below:  

Image reproduced from Wikimedia Commons  

Which of the following is the most likely etiology of this patient’s clinical presentation?  

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Wolff-Parkinson-White syndrome p. 314

Wolff-Parkinson-White syndrome p. 314


Content Reviewers

Rishi Desai, MD, MPH

Tanner Marshall, MS


Tanner Marshall, MS

Wolff-Parkinson-White pattern, or WPW, is a type of heart arrhythmia caused by an accessory pathway, or an extra electrical conduction pathway, connecting the atria and ventricles, or the upper and lower chambers of the heart.

Normally, an electrical signal starts at the sinoatrial node, or SA node, in the right atrium. It then propagates out through both atria, including bachmann’s bundle in the left atrium, and contracts both atria. Then, it’s delayed just a little bit as it goes through the atrioventricular node, or AV node, before it passes through the Bundle of His and to the Purkinje fibers of the left and right ventricles, causing them to contract as well.

On an electrocardiogram, the P-wave corresponds to atrial contraction, the PR interval corresponds to the slight delay through the AV node, and the QRS complex corresponds to ventricular contraction.

Now, in a normal electrical conduction system, the AV node is the only place where the signal can get through to the ventricles from the atria. It’s kind of like there’s a gatekeeper that has to stop the signal and make sure everything’s good before letting it pass, so there’s always a slight delay here. People with WPW essentially have a secret, backdoor entrance. Because this entrance is secret, it doesn’t have a gatekeeper; therefore, there’s no delay as the signal moves through it. This secret backdoor entrance is a tiny bundle of cardiac tissue that conducts electrical signals really well, called the Bundle of Kent. Using the Bundle of Kent means the ventricles start to contract a little bit early, which is called pre-excitation. If the Bundle is on the left side of the heart, it’s called “type A pre-excitation.” If it’s on the right side, it’s called “type B pre-excitation.” Type A, on the left side, is a lot more common.

All right, even though one signal sneaks through early, the other signal waiting at the AV node eventually makes its way through, and the two signals essentially combine to contract the ventricles. So, on an ECG, people with WPW have a short PR interval with a delta wave, as well as QRS prolongation, which makes sense because the signal’s taking the shortcut and contracting the ventricles early. This means the PR interval is shorter, and the overall QRS complex is longer. People with WPW usually have a PR interval less than 120 ms and a QRS complex greater than 110 ms. Also, the ST segment and T wave, which represent repolarization, will often be directly opposite the QRS complex. This WPW pattern doesn’t typically cause any symptoms and is relatively benign.


Wolff-Parkinson-White pattern (WPW) is a congenital disorder, in which there is heart arrhythmia caused by an extra electrical conduction pathway, called the Bundle of Kent, connecting the atria and ventricles. This can cause the ventricles to contract earlier, leading to pre-excitation, a short PR interval with a delta wave, and QRS prolongation on an electrocardiogram. While WPW is usually benign, it can lead to dangerous arrhythmias, such as atrioventricular reentrant tachycardia (AVRT), which can cause sudden cardiac death.


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