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Article: Wolff-Parkinson-White Syndrome and the Risk of Sudden Cardiac Death Back to article | View all comments

Author: John Kenyon, CNA | October 07, 2010

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October 17, 2010 12:55 AM
M. Aroon Kamath, M.D.'s avatar

Dear Sir,
You would agree that the vast majority of published work on WPW invariably tends to have a profusion of statistics(percentages)- perhaps underlying the fact that there are still lots of uncertainties. There seems to be no way to discuss WPW without referring to the statistics! It has so happened that your interesting anecdotal reference to a ‘0.6% chance of a bomb going off in a major metropolitan center’ seems to have set off a bombshell after all!

I must admit that I have not been able to access any review article which has conclusively determined the mortality (the WPW statistic is for death only) and morbidity of iatotrogenesis. Due to the relatively small number of cases and long durations of follow-up involved, there appears to be an inevitable paucity of reports. One study (2001) in which the natural history of Wolff Parkinson-White syndrome was studied in 228 military aviators over a period of 22 years,  reports a sudden cardiac death risk of 0.02%/patient/year and the SVT incidence was 1%/ patient/year [1].

There are a number of serious procedure-related complications which include, coronary artery injuries, permanent damage to the AV node [resulting in need for a permanent pace maker (ICD)], septal perforations, cardiac tamponade, stroke etc. In advanced centers, these are managed promptly and become success stories. However, it may be worth remembering that in facilities where these complications can not be managed promptly or adequately, they will become parts of the mortality statistics. 

Reference
[1]. Fitzsimmons PJ, McWhirter PD, Peterson DW, et al. The natural history of Wolff Parkinson-White syndrome in 228 military aviators: a long-term follow-up of 22 years. Am Heart J. 2001;142:530–536.

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October 16, 2010 05:10 PM
John Kenyon, CNA's avatar

Dear Doctors Tamer and Aroon,
Thank you both for your fascinating and extensive discussion of statistically-driven medicine. This is what I had hoped might happen and it opens up the topic and new thoughts and facts are added. I appreciate in particular the referral to the article by Dr. Gould and will be reading it promptly. I was aware of his unusual survival and had followed his situation informally for years. The assessment of the meaning of this and other outlier cases does, indeed upen up the discourse and that can only be a positive.

Dr. Aroon, your acess to statistics is, in itself, a huge help as well, and so is your pointing out the closeness between mortality from WPW (in this instance) and iatrogenic injuries sustained during catheter ablation attempts. The one thing I wonder about (and perhaps you have access to this information) is the comparison between mortality (the WPW statistic is for death only) and morbidity of iatotrogenesis. Having had a personal experience with catheter-related (during angiogram)near-catastrophic event followed two years later by an uneventful AVNRT ablation in one of my children makes this of great personal interest, as does the still later sudden death of a first cousin of my daughter due to known WPW without prior reported symptoms. It is all only food for thought, but it is thought that recurs from time to time.

To both of you, again, my thanks for the extended and very erudite discussion, and I will be reading Dr. Gould’s article ASAP.

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October 12, 2010 10:44 AM
Tamer M. Fouad, M.D.'s avatar

Dear Dr. Aroon. Thank you very much for your effort in obtaining this data. It certainly makes things clearer. I think they will be a valuable addition to the original article.

Today I noticed that Dr. Stephen Jay Gould’s article “The Median isn’t the Message” is actually an intelligent play on Marshall McLuhan’s famous expression “the medium is the message”. McLuhan is a Canadian philosopher who is a cornerstone in modern day media theory.

On another note, not only did Dr. Gould’s article help explain the limits of statistically driven data. I believe that by outliving the median survival of his disease he has also demonstrated how the median is designed to lose information. As an outlier Dr. Gould’s 20 year survival would not have affected the disease median survival of 8 months. If this had been a simple arithmetic mean (average), however, Dr. Gould’s 20 years would have skewed the results dramatically. In this case the overall survival rate would, like the simple mean, be affected by an outlier. But even in this situation outliers are usually ‘corrected’ and ‘normalized’ before the results are calculated. It is assumed that outliers are ‘rare’ and therefore distracting. They contaminate the point estimate which is designed to give us a single ‘average’ without the ‘exceptions’.

However, this is very concerning as the fact that he survived with peritoneal mesothelioma for 20 years is indeed very important. It’s these examples that warrant further study and the hope for cure. At the very least a median should also be mentioned in association with its range (as a measure of dispersion) and its confidence interval.

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October 11, 2010 01:01 PM
M. Aroon Kamath, M.D.'s avatar

Dear Dr.Tamer,
Thank you for your very interesting and valid comments. I take this opportunity to quote some of the very crucial figures (percentages) which seem to be responsible for causing all the controversy and hesitation on the part of some experts in this field in advocating routine radio frequency ablation (RFA) for individuals with asymptomatic WPW findings.

The risk of sudden death in WPW is approximately 0.1% per year overall and may be as high as 0.6% per year in “high risk” patients [1, 2].

As for coronary injuries due to RFA, the reported incidences of injury were 0.03% in children [3], and 0.06-0.1% in adults [4]. Solomon et al have reported a 1.3% incidence of coronary artery injury in 70 patients following RFA for accessory pathway-mediated tachycardias [5].

The percentage figures for these major complications are indeed alarmingly too close to the 0.1% risk of sudden death due to WPW. This is the crucial reason why the actual rates of sudden death due to WPW syndrome and that due to RFA need to be ascertained. It is likely to be a difficult task given the relative rarity of the condition and the length of follow up needed.At the present time, the cardiologists may have to decide only on a case-to-case basis.


References
1. Andrew D Blaufox, MD. Catheter Ablation of Tachyarrhythmias in Small Children. Indian Pacing Electrophysiol J. 2005 Jan–Mar; 5(1): 51–62.
2. Klein GJ, Bashere TM, Sellers TD. Ventricular fibrillation in the Wolff-Parkinson-White syndrome. NEJM. 1979;301:1080–1085.
3. Kugle JD, Danford DA, Houston K, et al. Radiofrequency catheter ablation for paroxysmal supraventricular tachycardia in children and adolescents without structural heart disease. Pediatric EP Society, Radiofrequency Catheter Ablation Registry. Am J Cardiol. 1997;804:1438–1443.
4. Calkins H, Langberg J, Sousa J, et al. Radiofrequency catheter ablation of accessory atrioventricular connections in 250 patients. Abbreviated therapeutic approach to Wolff-Parkinson-White syndrome. Circulation. 1992;85:1337–1346.
5. Solomon AJ, Tracy CM, Swartz JF, et al. Effect on Coronary Artery Anatomy of Radiofrequency Catheter Ablation of Atrial Insertion Sites of Accessory Pathways. J Am Coll Cardiol. 1993;21:1440–1444.

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October 11, 2010 11:01 AM
Tamer M. Fouad, M.D.'s avatar

Thank you John for your inspiring article and thank you Dr. Kamath for your input. The real controversy behind this article and countless others is what inferential statistics tell us about the individual at risk. So we know that, as in this example, there is a 0.6% risk of sudden death in a certain population of WPW patients at risk. But how does that number add up to the single patient that is sitting right in front of us now? Sadly, as with all random samples there is no certain answer. It would be akin to spinning a dice once and knowing that the probability of getting a six is 1/6. We would still be unable to tell with any certainty what the result will be.

I would like to refer you to a classic essay by Dr. Stephen Jay Gould an evolutionary biologist who taught at Harvard University and who was unfortunately diagnosed with peritoneal mesothelioma and was faced with gloomy survival statistics about his disease. Dr. Gould lived for 20 very productive years after his diagnosis, thus exceeding his 8 month median survival by a factor of thirty. Although he died of cancer, it wasn’t mesothelioma, but a second primary cancer.[1]

REFERENCE:
=========
1. Stephen Jay Gould, Steve Dunn. The Median Isn’t the Message. Cancer Guide Website. Available at http://cancerguide.org/median_not_msg.html. Accessed October 11 2010.

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October 08, 2010 09:27 PM
John Kenyon, CNA's avatar

Dear Dr. Aroon,
Thank you for your comments. There is most certainly a learning curve gap between various practices, and this does of course need to be considered in assessing management especially of asymptomatic or seemingly benign WPW. Same holds true for AVNRT, which while almost never life-threatening can certainly pose a threat to life quality. It is also related in some genetically-related cases, to WPW.

Defining the markers for high risk in WPW patients is the biggest challenge, I believe, but the decision, I would contend, should at least be left to the specialists. The calculation of risk of sudden death in patients with non-serious arrhythmias remains uncertain, and when placed alongside the native .1% complication rate for almost any cateter introduction does make the decision all the more difficult.

I greatly appreciate your remarks and your own tact in citing the reasons this will continue to be a difficult choice for some time to come.

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October 08, 2010 01:53 AM
M. Aroon Kamath, M.D.'s avatar

Dear Sir,
Radiofrequency ablation for individuals with ‘WPW findings’ on an EKG is an ongoing, hotly debated topic. You have very tactfully left out the heat and managed to bring out the importance of recognizing WPW and taking it seriously. The first clinical use of radiofrequency (RF) energy for catheter ablation of an accessory pathway (AP) was reported in 1987. The procedure began to be used in the more common forms of dysrrhythmias in the 1990s. Thus, it is a fairly young and constantly evolving procedure. Some teams have undoubtedly gained more experience and perhaps have lower complication rates but several others are more likely to be in the steeper part of the learning curve. There seems to be a growing general acceptance of this procedure in symptomatic WPW individuals (WPW syndrome). However, there is controversy surrounding its use in the asymptomatic group. The central difficulties seem to be in defining the markers of high risk, the actual rates of sudden death in these individuals (not the serious arrhythmias) and the quoted risk of death due to ablation (approximately 0.1%) [1].

1. Lerman BB, Basson CT. High-risk patients with ventricular preexcitation—A pendulum in motion [perspective]. N Engl J Med. 2003;349:1787-1789.

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