In this March issue of BJSM, Wilson and colleagues investigate sudden cardiac death:

[Abstract]
[Full Text]
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This emotional and very important area of sports medicine always raises the issue of how many children how have cardiac abnormalities may need to be disqualified from sport to save one life.

Editorial Board member Jon Drezner posted the following comments relating to this paper (originally posted to the AMSSM listserve):

The studies on ECG screening are mounting fast with improved and more specific ECG criteria that lower the total positive (and thus false positive) rate. Pelliccia et al (Euro Heart J 2007) recently described their experience reviewing 32,652 screening ECGs primarily in young amateur athletes (median age 17). Distinct ECG abnormalities suggesting cardiac disease were present in only 4.8%. This lower total positive rate was after acknowledging that a prolonged PR, incomplete RBBB, and early repolarization patterns are essentially normal/common findings in athletes and not indicative of cardiac disease. Other refinements to the definition of “abnormal” for a screening ECG are also being recognized. A recent study presented at the 2007 AHA Scientific Sessions by Melacini et al (Marginal overlap between ECG abnormalities in patients with HCM and trained athletes: implications for preparticipation screening) found that voltage criteria alone for LVH (without ST depression, T wave inversion, or pathologic Q waves) is a common finding in trained athletes and unlikely to be indicative of cardiac disease.

Two recent studies have used modifications of the Corrado criteria and found a substantially lower (about 2%) total positive rate. In a recent study by Wilson et al. (BJSM 2007) out of the U.K., 2,720 national/international athletes and physically active school children (mean age 16) were screened using personal & family history, exam, and ECG. They found a total ECG positive rate of only 1.5%. Nine athletes (0.3%) were identified with cardiac disease known to cause SCD (WPW, LQT1, ARVC, RVOT), and none of these 9 cases were symptomatic or would have been identified by personal or famhx. (see abstract below). I found it interesting that the true positive rate found was consistent with the AHA estimate regarding the prevalence of cardiac disease known to cause SCD in young athletes ( 0.3% or 3 in 1,000).

Also recently, Joseph Marek from the Midwest Heart Foundation presented at the 2007 AHA Scientific Sessions their findings of screening over 12,500 high school aged individuals with ECG. They also used modified Corrado criteria for defining abnormal ECGs. Their total positive rate was only 2%. This is the largest study in the U.S. and the first I am aware of to apply the Italian criteria to a U.S. population.

Another way to look at the numbers is to model a screening program for 50,000 high school freshman athletes: (1) Incidence of SCD is approx 1:50,000 (based on current data from the U.S. Sudden Death in Young Athletes Registry by Barry Maron); (2) Prevalence for any cardiac disease known to cause SCD in young athletes is estimated to be 0.3% or 3 in 1,000 (from the 2007 AHA Scientific Statement on preparticipation screening); (3) A screening ECG will suggest about 60% of silent CV dz known to cause SCD.

Assume 2-5% total positive rate (based on studies above using updated ECG criteria) = 1,000 to 2,500 total positives. 150 potential true positives (prevalence 0.3%), but only 100 (about 60%) true positives with CV dz suggested by ECG (0.2%). That leaves 900 to 2,400 false positives (1.8% to 4.8%).

In other words, we would need to temporarily disqualify/work-up 9 to 24 kids with false positives to identify 1 kid at risk for SCA, or we would need to disqualify 99 kids with CV diagnosis to potentially prevent 1 death (in the first year of screening). However, each year it is possible that an additional SCD event will be prevented through disqualification (this is shown in Corrado’s study from Italy). Assuming high school participation for 4 years (200,000 person years of athletic participation in this model), we might expect 4 cases of SCD (incidence 1:50,000 per year). Since ECG did not capture all of the silent CV dz (only about 60%), then screening 50,000 high school freshmen with ECG would likely prevent 2-3 deaths (of the predicted 4) through disqualification of 100 kids with identified cardiac dz. In other words, we would need to disqualify 30-50 kids with identified CV dz from high school athletics to prevent 1 death.

I recognize these calculations are rough, but I’m trying to pull from the most recent studies and apply to our setting.

Anyway, new studies, more accurate and rigorous ECG criteria, and lower total positive rates. Over time with confirmatory studies and a better understanding of disease prevalence, this will change our calculations on false positives, disqualifications, cost, and lives saved, and quite possibly compel us to revisit our recommendations on the role of ECG in the screening process.

Article by Dr Claire Roche, Clinical Fellow in Emergency Medicine, Countess of Chester Hospital.

The setting for this year’s polar medicine course was Alta, a small settlement, 72 degrees north and well within the Arctic Circle. A place with a deserted high street where you would be lucky to see one other passer by every 15 minutes, easily explained by a temperature at least ten degrees below freezing and a good foot of snow on the ground.

Base camp was a 40 km drive along icy roads to a picturesque mountain lodge by the name of Ongajoksetra. At the higher altitude the temperature was that much lower and if a wind was blowing, temperatures as low as minus fifty could be achieved. We were introduced to the Scandinavian team who would teach us methods of navigation across such tough terrain in harsh conditions and also to the Expedition Medicine team who would teach us polar medicine in a series of lectures and practical sessions both in the classroom and in the field. One more group I must not forget to mention is the team of fifty sled dogs who would provide another mode of transport across the snow.

My first day involved skidooing up a mountain demonstrating the importance of protective clothing, navigation aids and preparation for travel in severe blizzards with visibility of approximately two metres, sudden drops in temperature and rapid weather changes. I realised that without our trustworthy guide, Espen Ottem, we could become hopelessly lost in such conditions where you would be unable to survive more than a couple of hours at most. Our dog sledding guide, Pre-Thore was the perfect example of this as he told us of the time where inadequate preparation resulted in frostbite, blackening of his fingertips but fortunately no amputation. This story made me somewhat paranoid about the daily pain and numbness in my hands and feet when outside in the cold for prolonged periods. A “buddy system” was paramount to preventing frostnip. Simply by having that small exposed area of skin, pointed out to you to cover up.

Dr Leslie Thomson, a consultant anaesthetist who had first - hand experience of polar medicine after spending several years in Antarctica taking part in the British Antarctic Survey gave an excellent lecture on hypothermia, bringing home how hypothermia is not just a condition seen near the poles but also in the Saturday night party goer who collapses under the stars, the homeless and the elderly. We were taught how to treat by various re-warming methods and when to commence C.P.R in the hypothermic patient sending home the message of not pronouncing death until warm and dead in certain individuals. This information was demonstrated by the story of Dr Anna Bagenholm , a 29 year old doctor who fell into icy water whilst skiing in Northern Sweden, immersed for approximately an hour, her body temperature was 13.7 degrees centigrade. C.P.R continued for three and a half hours alongside re-warming techniques such as bypass, bladder / stomach / peritoneal lavage and warm intravenous fluids. She survived to become the person with the lowest body temperature ever to survive.

Expedition Medicine obviously feel that first- hand experience is the best way of teaching and as a result each member of the group had to undergo cold water immersion. Prior to undertaking this challenge we were kindly taught about the cardiac arrhythmias that can be induced by the shock of entering the water, the short term cold water gasp reflex increasing the chance of aspiration and swimmers failure! One by one we stepped up to an ice hole in our thermal underwear and in the more daring members of the group a little less! to swim across icy water. I can confidently say that was the coldest I had ever been. As if several knives had been plunged into my body, breath taking and inducing chest pain, I swam across water of ridiculously low temperature to attempt getting out of the hole using my ski poles.

Of our nights spent in the field we were taught how to construct snow holes. Five hours later our own little home with two double beds, stove, cupboards and shelves for our candles was constructed. It was as comfortable as it could be on a mountain side with winds blowing outside dropping the temperature to twenty below. I was amazed that the snow hole was so warm at five degrees compared to the outside however a slight air of nervousness was in the back of my mind as my avalanche detector slowly flashed in the corner and a rope attached to a spade inside connected our holes to other holes in case of us having to be dug out. The course perfectly demonstrated how to survive in such conditions.

In summary the course prepared 25 everyday doctors to be able to traverse the polar landscape, recognise and competently treat local cold injury and hypothermia as well as to be safe expedition medics capable of caring for their groups and evacuating when required. To spend a week in such a location gave me the upmost respect for those who live in these regions and cross the landscape as part of everyday life, as well as a great respect for the land. In a day and age of global warming and melting of the polar ice caps it becomes paramount to look after our environment, to take only photographs and to leave only footprints.

The next expedition medicine course will be in Desert Medicine which will be held in Namibia, August 17th – 23rd 2008. For more details go to: www.expeditionmedicine.co.uk.

Click here to see a great slideshow video from the last Polar Expedition Medical Course.