Wolff-Parkinson-White Syndrome: Symptom-Free Is Not Risk-Free

Bernard J Gersh, MBChB, DPhil; Bryan C Cannon, MD


March 31, 2014

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More Patients With Wolff-Parkinson-White

Bernard J Gersh, MBChB, DPhil: This is Bernard Gersh from the Mayo Clinic, and with me today is Dr Bryan Cannon, who is associate professor of pediatrics and director of pediatric and congenital heart electrophysiology. Welcome, Bryan. I know it's a very complex area that you work in, but I want to focus today on the patient with Wolff-Parkinson-White (WPW) syndrome. Thanks to you pediatricians, we don't see these patients as adults anymore. You seem to be cherry-picking a population of patients for whom so much can be done. It's such a satisfying group to treat.

Bryan C Cannon, MD: It's good for us and hopefully good for patients. WPW is relatively common in the population. We used to think that the incidence was about one in 1000, but as we do more screening and more evaluation (athletic screening and other screening for attention-deficit/hyperactivity-disorder medications), ECG screening has become much more prevalent. Many patients who would not normally have an ECG are now having an ECG, so we are finding a lot more patients who have WPW syndrome.

Dr Gersh: Let's focus on the asymptomatic patient. WPW with palpitations, syncope, or atrial fibrillation is clear-cut. But you identify it as an incidental finding. Can you take us through your evaluation of that patient? Say it's a 10-year-old.

Dr Cannon: If you take a look at those patients, we do care whether they have asymptomatic WPW, because a very small percentage of patients will present with sudden cardiac death as their initial finding.

Dr Gersh: When you say very small, how many is it? Among 1000 patients with WPW, most of the sudden deaths will be in people who have palpitations, right?

Dr Cannon: Correct, although up to 50% of the deaths are in patients with no palpitations at all.

Dr Gersh: Really? It's as high as that?

Dr Cannon: In the initial study by George Klein, three out of the 25 patients who presented with ventricular fibrillation and sudden death were in the pediatric population.[1] Of interest, none of those three had previous symptoms. So younger patients can present like that.

Dr Gersh: That study was done when he was a Duke many years back.

Dr Cannon: Correct. In 1979.

Dr Gersh: So it is a concern. Take us step by step through it.

Evaluating the Patient With WPW

Dr Cannon: First of all, you are going to carefully elucidate a history of symptoms. If the patient is old enough to perform an exercise treadmill test, we look for loss of preexcitation in a single beat, not the gradual loss of preexcitation that we see as the AV node improves conduction, but you see an abrupt loss of preexcitation. If you see that on a treadmill test or on a Holter monitor, it suggests that it's a low-risk pathway.

Dr Gersh: That's an important point. A gradual loss of preexcitation could be because the AV node is speeding up, secondary to catecholamines and, therefore, you have less preexcitation and more conduction down the AV node.

Dr Cannon: Absolutely, and especially with the left-sided pathway that may be further away from the sinus node. Sometimes it's hard to tell.

Dr Gersh: So it's the sudden loss of preexcitation.

Dr Cannon: Correct. You want to see that abrupt loss, preferably in a single beat. And if you do that, you can rest assured that it's almost certainly a low-risk pathway.

Dr Gersh: This is a pathway that can't conduct very fast.

Dr Cannon: Correct, and if you can't tell on the basis of the exercise treadmill test, it's reasonable to do a more invasive evaluation.

Dr Gersh: What is the role of the Holter monitor?

Dr Cannon: If you see intermittent preexcitation either on an ECG or a Holter monitor, it suggests that it's a low-risk pathway. It's not quite as good as losing it in a single beat on a treadmill, but it also suggests that it is probably a low-risk pathway.

Dr Gersh: You say that it "suggests." What will take you to an electrophysiology study?

Dr Cannon: If you see intermittent preexcitation in a patient who is truly asymptomatic, it would be reasonable to follow that patient.

Dr Gersh: Even if it's just on a Holter monitor?

Dr Cannon: Correct. Even if it's just on a Holter. However, if you don't see loss of preexcitation or you can't be sure, particularly in somebody who wants to play competitive sports, it would be reasonable to perform a risk stratification in the catheterization lab. There are a couple different ways you can do that. You can either do it with a transesophageal study or invasively through the femoral vessels.

Dr Gersh: The purpose of the study is to assess the refractory period and conduction times down the bypass tract. And the ability to induce atrial fibrillation and the speed of atrial fibrillation.

Dr Cannon: Correct.

Dr Gersh: How do you do that transesophageally?

Dr Cannon: We induce atrial fibrillation. Actually, if a patient presents clinically in atrial fibrillation, which about 10% of pediatric patients do, or if you can induce it with a transesophageal study or invasively, we look for the shortest preexcited RR interval—which is when two beats are preexcited in a row—and then you measure the distance. If that is less than 250 ms, particularly less than 220 ms, that is a patient who is potentially at risk.

Dr Gersh: If the distance is a little longer than that, it suggests that they are not at high risk—we do the studies at rest and we don't know what is going to happen on the sports field when they have catecholamines—is there a role for isoproterenol in that study?

Dr Cannon: Yes, if you look at the studies, it increases the conduction in a lot of these pathways.[2] The question is whether that is a clinically significant increase. Most people would say that isoproterenol would be a reasonable option, particularly for the septal pathways that tend to be catecholamine insensitive.

Dr Gersh: Particularly for competitive athletes?

Dr Cannon: Absolutely.

Treat Now, or Wait?

Dr Gersh: You have determined that this 10-year-old has a pathway that places him or her at risk. Do you go in and ablate it right then and there?

Dr Cannon: I think so. With the modern technology and the incidence of complications with ablations being < 2%, it allows us to be a bit more aggressive with techniques such as cryoablation and also mapping without using any radiation exposure. We can do this with a very low incidence and potentially remove the risk altogether.

Dr Gersh: It seems very logical. In adult cardiology, it's accepted that for high-risk or certain occupations such as airline pilots with symptomatic WPW or even asymptomatic WPW that you can ablate. Why not do the ablation in an asymptomatic child? It's probably the closest we will ever get to cures in cardiology.

Dr Cannon: And we can have a success rate around 95% with a less than 1% to 2% incidence of complications.[3,4] If we have a very high success rate with a very low complication rate in something that can be potentially permanently cured, I have been in favor of being a bit more aggressive about ablating those.

Dr Gersh: Thank you very much, Bryan. That was a very helpful discussion on a rather satisfying disease in that we can treat it so well.


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