Incidence of Sudden Cardiac Death in Athletes

Podcast Transcript

Announcer:

Welcome to Cleveland Clinic Cardiac Consult, brought to you by the Sydell and Arnold Miller Family Heart, Vascular and Thoracic Institute at Cleveland Clinic.

Thomas Callahan, MD:

My name's Tom Callahan. I'm one of the cardiac electrophysiologists here at Cleveland Clinic, co-director of our Lead Extraction Program. And I'll be talking about the incidence of sudden cardiac death in athletic populations. We'll talk about how often, when, their survival, the etiology, so really kind of talking about the scope of this problem. And as we'll see, these questions can actually be very challenging to answer if you just take the question of how often, what's the cause of this problem? It really depends on how you define both the numerator and the denominator. So, what are we calling an event and what populations are we looking at? For instance, are we capturing sudden cardiac death, or do we capture sudden cardiac arrests that were rescued? Some of the older studies they used tools and mechanisms that really just captures sudden cardiac death and may have missed some of the arrests that were rescued. So that makes a difference.

Are we talking about sudden cardiac death in athletes at any time of the day or are we talking about death within an hour of activity? And so again, how we try and answer these questions, how we design these studies will really affect the answers that we get. So that just kind of highlights some of the challenges that we'll see in trying to answer these questions and some of the differences that we see in the studies that do try and address these questions. Again, defining the denominator can be a challenge as well. Are we talking about young athletes? Are we talking about older athletes? And then what are we talking about in terms of competition, and do we want to include recreational versus just really competitive? So, all of these things will affect the numbers. And we'll also see, we have studies that really have a broad range of ages, for instance, then what we'll see is the etiology and the incidence may be vastly different compared to focusing on specific age ranges.

So, we'll start with some US studies that kind of go after these questions and then once we kind of go through the US studies, we'll talk about some studies from other areas of the world that I think also shed some light on these problems. If we're just looking at the incidence of sudden cardiac death in younger athletes, that sort of generally accepted number would be somewhere around one sudden cardiac death in about 200 to 300 athlete years. That's sort of the generally accepted number. But these numbers come from some older studies, younger athletes, and do have some issues. For instance, a lot of these older studies relied on media reports, insurance claims to capture events and acknowledged that those may not capture all the events. So, these numbers may under-represent reality.

There are some other studies that have sort of captive audiences, as it were. So, you have studies of military personnel. These studies would look at age ranges around 18 to 35, and they found an incidence of sudden cardiac death about one in 25,000 subjects per year, so much higher. But again, this is a different age range, a different way of capturing, and these personnel may be engaged in a higher level of activity or different types of activity compared to what we think of as our general athlete. NCAA studies showed sudden cardiac death with a frequency of about one in 53-54,000 athlete years. And then if you dial down on higher intensity activities such as basketball, you see some real differences and also some gender and race related differences as well. So again, we'll start with some of the US studies.

This is an older study looking at a specific group of high school athletes from Minnesota. And they looked at about 650,000 students over a course of about 12 years and these students were participating in about 27 different sports. And this study found a rate of sudden cardiac death in these young athletes, so about one in 200,000 athlete years. There were three deaths in this group and so this started to give us some information about the general etiologies. An anomalous coronary artery was found in one of the deaths, a bicuspid aortic valve with aortic valve stenosis in another, and myocarditis in the third.

Another US study, and this looked at a much broader group, this included young athletes but up to an age of about 40, so these were competitive athletes up to about age of 40 and they've identified about 1,860 sudden deaths in this group. And this included both sudden cardiac death as well as those that were rescued from an arrest. And then they kind of focused on the cardiac events. So, they eliminated things like heat stroke and drugs and then unresolved cases and found about 56 percent of these events were thought to be cardiovascular in etiology. About a third of those didn't find any specific diagnosis. But about two thirds were able to sort of come up with a likely etiology. And in this US population, again a relatively broad but young age group up to about 40, hypertrophic cardiomyopathy represented the largest percentage of cases followed by coronary anomalies. And then less frequently were things like channelopathies and ARVC.

So again, hypertrophic cardiomyopathy causes about one third of the deaths. And this study actually had many of the same patients in that larger study that I was just discussing but limited to participants of about 35 years old. And again, hypertrophic cardiomyopathy, the most frequent cause of sudden cardiac death in this population, followed by coronary anomalies of about 17 percent and then much less common myocarditis, ARVC and aortopathies. The study also highlighted some differences in race, so non-white and particularly African American athletes were more likely to have structural disorders, hypertrophic cardiomyopathy and coronary anomalies. And then white athletes had higher percentages of ARVC and channelopathies compared to their non-white athletes. This is a much more recent study from 2019 but I thought shed some light on survival. And so, looking at population of middle school through college athletes, the survival for sudden cardiac death in this study was between 40 and 75 percent. Now, while those numbers are discouraging, they're actually much better than what you see in the world in general population, and it's likely because of the design of this study. Looking at this age group, most of these events occurred either on the athletic field or during training where they were witnessed and often trainers were involved. And you see the study also found 83 percent survival, so much improved survival if there was an athletic trainer involved in the resuscitation, 89 percent if an AED was available and used.

So now kind of moving outside of the US studies, we'll look at this study from Canada from 2017. This looked at a broader population, ages 12 to 45, and found an event rate, sudden cardiac death, about 0.76 per 100,000 athlete years. The survival was 44 percent, so better than what we get in sudden cardiac death reports from sort of non-athletes in the general population. Another nice feature of the study is they sort of break it down for us by age group. In the younger age group 12 to 17, the underlying etiology was much more likely to be primary arrhythmia or structural. And when we get to our older athletes, 35, 45, you start to see ischemic events really predominating. They also gave us some information about what these athletes were doing at the time of the arrest, race events and soccer, so high intensity activities are more likely to be the sport that these people were engaged in during the events, basketball, even though there weren't a lot of participants with sort of the next most common activity. This British study is sort of interesting in that it's done by a pathology center. So, this pathology center was receiving hearts from cases of sudden cardiac death across the UK, and this is over about a 20-year period, and they identified 357 athletes with sudden cardiac death. And so, it's interesting in that the events aren't necessarily happening just with sport. These were people that died from sudden cardiac death at any time of the day, but they were sort of defined as an athlete if they engaged in more than three hours of organized physical training per week. As with other studies, there was a male predominance and high intensity sport was more likely to be involved. 69 percent were engaged in some sort of competitive activity, 25 percent in running and 25 percent in football aka soccer. So, the time of the event is much more likely to die during exertion, 61 percent die during exertion. ARVC was more represented in this population as well. And then they break this down for us also by age group, and again the younger population more likely to have anomalous coronary arteries. When we get to the over 35 population, we're starting to see ischemic events become more common. A study from France over a five-year period, and this one really broadens it out, the group here from 10 to 75 years of age, and they captured events by finding people who had expired within an hour of activity or during activity. They included those that survived with CPR, and they defined a really broad range, so this works out to about 0.5 to almost two cases of sports related sudden death per hundred thousand per year. And most of these occurred in healthy males, a lot in public areas. What was really sort of sobering about this study was that CPR, bystander CPR, occurred only in about a third of the cases, and survival here was really poor. Only 16 percent survived discharge. They sort of break things down by the activity and time. We have our young and sort of athletic population, so engaged in competitive athletics and we see that's a relatively small portion of the sudden cardiac death related to activity in sport in this population. They highlight the female sudden cardiac death events with strong male predominance and again a lot of very vigorous activity involved in these events. Young competitive athletes differed from the general population, more ischemia in the general population, more hypertrophic cardiomyopathy, structural disease and so forth in the younger competitive athletes.

So, in summary, the general accepted rates of one in 200,000, one in 300,000, come from some older studies and may under-represent even the younger population that that was sort of was describing. Male gender is a risk factor, as is race or non-whites, that increased risk for these events compared to Caucasian counterparts. Basketball and high intensity sports are risk factors. Vigorous activity does increase the risk of sudden cardiac death by five-fold for those with underlying CV disorders. And survival, there's a lot of room for improvement in some of the studies with the highest survival rates, 40 to 75 percent, in these supervised settings, and the France study with a survival rate just 16 percent. And finally, etiologies really differ greatly based on the age group. In the adult age group think about ischemia, as opposed to the younger age groups who think about hypertrophic cardiomyopathy, anomalous coronary arteries, channelopathy. Thank you.

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