Call it endurance cardiology: at a time when obesity spirals out of control, more Americans are actively—often very actively—pursuing their own peak performance. Over the last decade, US athletic participation has doubled or nearly doubled in all major demographic groups; 7.7 million students now participate in high school programs (2012-2013);¹ and running/jogging participation has increased to a record of nearly 42,000,000.² Endurance sports draws older athletes: marathon finishers have increased from 353,000 in 2000 to 541,000 in 2013, with a record 47% categorized as "masters," defined as 40 years of age or older.³ At the end of 1999, USA Triathlon membership stood at 127,824, doubling to 262,703 by 2005 and then nearly doubling again, topping out at a record high 510,859 in 2012.⁴

Add in patients with heart disease who want to regain, maintain, or accelerate their activity levels and it's important that the heart team not drop the ball.

The Teeter-Totter of Exercise and the Heart

This is all good, because the cardiovascular (CV) benefits of regular exercise are firmly established; individuals exercising consistently boast an average life expectancy 7 years longer than their sedentary counterparts. Such benefits are achievable with relatively modest doses of exercise amounting to 60-70 MET (metabolic equivalents) minutes per day (or 10 minutes at about 7 METS daily), yet a growing number of people are getting a lot more exercise than that. However, despite its favorable effects on well-being and survival, some studies have shown that exercise acutely increases the risk of myocardial infarction, aortic dissection, arrhythmias, and sudden cardiac arrest (SCA) and/or death (SCD).

Complicating the situation: exercise may have a typical dose-response curve with toxicity at more extreme levels. The evidence of chronic exercise having a detrimental effect in individuals with normal hearts includes a growing number of athletes exhibiting cardiac changes who are now showing up in routine clinical practice. Given the growing number of children and adults with established heart disease who are living longer and want to participate in sports and exercise, and clearly there's a need to understand all the issues coming together at the crossroads where exercise and sports intersect with cardiovascular medicine.

Given all this, it probably should have surprised no one that health professionals who take care of these individuals—and likely participate themselves—want to learn more about caring for the active patient. In 2011, the American College of Cardiology (ACC) launched its Section of Sports and Exercise Cardiology. Membership soared from 150 to more than 2,000 members in just 2 short years, indicating intense interest from the CV community to advance the integration of sports and exercise cardiology into mainstream CV care. (To access the section, go to cardiosource.org/en/ACC/ACC-Membership/Sections-Segments-Councils/Sports-and-Exercise-Cardiology.aspx)

Recently, Christine E. Lawless, MD, and colleagues published a state-of-the-art paper in JACC on sports and exercise cardiology in the United States.⁵ Contrary to expectation, when considering exercise as a trigger for SCD, the contemporary incidence of sudden death is actually similar or lower in young athletes (11 to 19 years) compared with nonathletes: 0.44 per 100,000 person-years versus 6.37 per 100,000 person-years, respectively. However, the data do suggest variable risk according to age, sex, ethnicity, level of play, and sport. (Another recent state-of-the-art paper in JACC covered Sudden Cardiac Death in Young Athletes: Practical Challenges and Diagnostic Dilemmas.⁶)

In broader terms of risk, Michael S. Emery, MD, medical director of the sports cardiology program at Greenville Health System said overall risk increases with the intensity of the competitive sport and the intensity of the participant's effort. When considering an exercise prescription for athletes with coronary heart disease, he said risk of exercise-related events increases with:

• extent of disease,
• left ventricular dysfunction,
• inducible ischemia, and
• electrical instability.

Just how risky are public events, like marathons? In looking at 12 years of experience with the Twin Cities marathon,⁷ William O. Roberts, MD, a professor of family medicine and community health at the University of Minnesota Medical School in St. Paul, reported that the number of medical encounters have ranged from 19 to 24 per 1,000 participants with <2/1,000 serious events, including one death among the 81,277 entrants. In an unpublished update covering 1995 to 2013, Dr. Roberts reports six cardiac arrests (four survived), two severe and three mild cases of hyponatremia (all survived), and 25+ severe cases of heat stroke (all survived, but four required hospitalization for up to 5 days).

Heat stroke, and its impact on participants, is no small matter: Dr. Roberts emphasizes that "heat attack" requires an emergency response like a "heart attack." (See the sidebar on recent key papers in sports cardiology and Is it the Heart or the Heat?) There is a "golden half-hour" for heat stroke, meaning recognition is critical (TABLE 1) and demands immediate, rapid cooling. That requires helping participants to understand that cardiac and noncardiac medical issues and emergencies arising during a race should not be "toughed out" but cause for concern – or the "finish line" could be just that.

Getting to Know You...

Whether caring for patients who want to participate in races or just volunteering to be part of the medical team at large public events, Aaron L. Baggish, MD, associate director of the cardiovascular performance program at Massachusetts General Hospital in Boston, emphasizes the importance of better understanding the participants. In September at the 2014 ACC Sports Cardiology Summit in Indianapolis, Dr. Baggish told of his experience this past summer as a participant in New Hampshire's popular 7.6-mile Mount Washington Road Race that starts at the mountain's base and finishes near the summit (6,288 feet). The most interesting part of the experience, he said, was standing in line for the porta potty.

Standing behind four fit, middle-aged endurance athletes, Dr. Baggish summarized their conversation:

• "Man, I am not sure that second chili dog and extra couple of beers last night was a good idea. Oh well, they always say don't change your routine prior to races."
  
  
• "Just wish my old man could see me now; he died at 45 of a massive heart attack."
  
  
• "Regardless of what happens, I gotta be better off than I was 20 years ago when I was smoking a pack a day and got short of breath driving up this damn hill."
  
  
• His favorite: "Cough, cough, hack. If this race weren't just once a year I would be home in bed, I feel like shit. Oh well, this little climb will help me clear out the junk."
  
  
• Dr. Baggish said, "We cannot know what does or does not cause disease unless we know who these people are."

The participants themselves are just one important variable of large events like a marathon, according to Dr. Roberts. On-site medical oversight must be well-planned and staffed to speed emergency care and relieve the community burden should something untoward affect a number of participants. This 'planned disaster' approach becomes necessary due to the myriad of unpredictable variables, such as these, that have all affected events in recent years:

• condition of participants
• weather conditions (including post hurricane)
• course conditions
• uncontrolled traffic
• volcano eruptions
• terrorist bomb

The events themselves are rarely dull and there's always a chance for real excitement. Also, anytime you have such an active field in medicine, there are sure to be controversies.

Controversies in Sports Cardiology

While the risk of dropping dead during a marathon or triathalon is remote (0.5 to 1 per 100,000 participants), the occasional exercise-related mortality may be the canary in the coal mine, according to James O'Keefe, MD, and Chip Lavie, MD. In a recent paper, they wrote: "Chronic extreme exercise appears to cause excessive wear-and-tear on the heart, inducing adverse structural and electrical remodeling, which offsets some of the CV benefits and longevity improvements conferred by moderate physical activity.⁸ Even if chronic extreme exercise does not kill you, they wrote, "It may erase many of the health advantages of regular moderate exercise."

At the Sports Cardiology Summit, Dr. Baggish looked at three current controversies.

Do endurance sports cause arrhythmia?
There have been about a dozen cross-sectional studies with a consistent finding: compared to sedentary controls, aging master athletes are more likely to develop atrial fibrillation. Both the number of races run and the speed at which they are run contribute to this excess risk. The atrium is susceptible to remodeling and this may be one reason for this increased AF risk. Other possible mechanisms: persistent vagotonia, sympathetic surges, chronic inflammation, intermittent left atrial hypertension, genes, caffeine, and even psychological stress. And how much of this increased risk is due to lifestyle choices, like those expressed at the porta potty, is unknown.

Do endurance sports cause coronary disease?
In general, people who exercise drive their cardiac risk factors in the right direction, reducing their CV risk profile. However, in the long run, does the long run become too much exercise that's just not heart healthy? Investigators have reported increased calcified and noncalcified coronary plaque in marathoners over sedentary controls. While excess exercise may drive atherosclerosis, we also should consider whether runners have more established risk factors that were simply unappreciated in the reported data. It is certainly not uncommon to find former smokers among marathon participants (one-half of marathoners in one study) as well as individuals with a history of hypertension or obesity. After conducting a close analysis of marathon runners, one group of investigators detected "higher than anticipated coronary risk," including more risk factors among those experiencing events during follow-up.9 However, they also found advanced coronary artery calcium scores that "seem to contribute to increased myocardial damage and appear to impair outcome" in the runners studied. Finally, given the caloric burn of endurance activities, there are marathoners who have far from ideal diets. "There is a huge difference between being fit and being healthy," they noted. Without controlling for all these variables, Dr. Baggish said, there is no proof of causality.

Do endurance sports cause cardiomyopathy?
A body of evidence suggests that high-intensity, high-volume training, in the predisposed individual, may end up causing a myopathic condition. Post-event, participants demonstrate detectable changes in size and function, particularly function; researchers have found a relative ventricular fatigue that occurs after long periods of endurance exercise. This manifests as a preponderance of right ventricular volume at the end of exercise, an overloading of the right ventricle relative to the left ventricle, and the right ventricle is more likely to be 'fatigued.' With repetition over a period of years or decades, this could lead to scarring and fibrosis.

Exercise-Induced Cardiac Remodeling

These activity-related cardiovascular changes, termed exercise-induced cardiac remodeling, are characterized by structural changes that appear to be sport-specific: strength-trained athletes tend to demonstrate concentric left ventricular (LV) hypertrophy, whereas endurance-trained athletes tend to demonstrate eccentric LV hypertrophy.

The previously mentioned 2014 State-of-the-Art paper by Lawless et al.⁵ (co-authors include Dr. Baggish and our CSWN editor-in-chief, Alfred A. Bove, MD, PhD), summarized 35 years of research on cardiac structural athletic adaptations:

• Increases in LV and right ventricular (RV) dimension and volume are common and more apt to occur in endurance sports such as cycling, rowing, and cross country skiing.
  
  
• Conversely, increases in LV wall thickness >1.3 cm are unusual, but can occur in up to 1.7% of elite athletes and 0.4% of junior elite athletes.
  
  
• Degree of adaptation varies according to sex, age, body size and mass, type of sport, and ethnicity, especially for athletes of African descent.
  
  
• A small number of healthy athletes can show 1.3 to 1.5 cm LV wall thickness; athletes of African descent can demonstrate LV wall thickness up to 1.6 cm.
  
  
• Strength sports (weightlifting or wrestling) are associated with usually normal thickness (<1.2 cm) but disproportionate increase in relation to cavity size.
  
  
• Although uncommon among athletes in general, up to 11% of healthy long-distance cyclists may have mildly reduced LV ejection fraction.
  
  
• Newer techniques such as tissue Doppler and speckle tracking radial strain echocardiography assist in differentiating physiological from pathological remodeling.

Despite all of that, Dr. Baggish said, it is good to circle back and consider those in line prior to the Mt. Washington Road Race. "We have to be careful to not ascribe causality to endurance activities and cardiovascular disease. While there may be some increased risk, we cannot forget the low-hanging fruit that we do not always associate with athletes: poor diet, bad choices early in life, obsessive habits that do not include breaks in exercise routines, and family history. If we think that their problem is associated with their activity, we may logically suggest they stop such activity, but I would submit that this is likely to cause more harm than good."

He added, "If we think of exercise as showing efficacy curves and toxicity curves, the vast majority of participants fall in the sweet spot where they are getting more benefit from their participation than harm."

---

REFERENCES:

• [No authors] Participation Statistics. National Federation of State High School Associations. Available at: http://www.nfhs.org/ParticipationStatics/ParticipationStatics.aspx Accessed: November 1, 2014.
• [No authors] 2014 State of the Sport - Part II: Running Industry Report. Source: Running USA; June 15, 2014. http://www.runningusa.org/2014-running-industry-report Accessed: November 1, 2014.
• [No authors] Running USA. 2013 annual marathon report. Available at: http://www.runningusa.org/ marathon-report-2014 Accessed: November 1, 2014.
• [No authors] 2013 USA Triathlon Membership Report — updated June 2014. Available at http://www.usatriathlon.org/about-multisport/demographics.aspx Accessed: November 1, 2014
• Lawless CE, Olshansky B, Washington RL, et al. Sports and Exercise Cardiology in the United States: Cardiovascular Specialists as Members of the Athlete Healthcare Team. J Am Coll Cardiol. 2014;63:1461-72. http://content.onlinejacc.org/article.aspx?articleID=1831424
• Chandra N, Bastiaenen R, Papadakis M, Sharma S. Sudden Cardiac Death in Young Athletes: Practical Challenges and Diagnostic Dilemmas. J Am Coll Cardiol. 2013;61:1027-40. http://content.onlinejacc.org/article.aspx?articleID=1659758
• Roberts WO. A 12-yr profile of medical injury and illness for the Twin Cities Marathon. Med Sci Sports Exerc. 2000;32:1549-55.
• O'Keefe JH, Lavie CJ. Run for your life ... at a comfortable speed and not too far. Heart. 2013;99:516-9.
• Möhlenkamp S, Lehmann N, Breuckmann F, et al. Running: the risk of coronary events: Prevalence and prognostic relevance of coronary atherosclerosis in marathon runners. Eur Heart J. 2008;29:1903-10.

---

In Training to Be a Sports Cardiologist

We mentioned Christine Lawless, MD, near the top of this cover story. Currently, she is the only physician in the United States dual certified in cardiology and sports medicine. Young doctors regularly email or approach Dr. Lawless asking, "How can I be a sports cardiologist?" While work is continuing on the development of a set of core competencies, Dr. Lawless is first author of a conference report soon to appear in JACC that offers a great deal of information on "Protecting the Heart of the American Athlete."¹

The document derives from a think tank assembled by the American College of Cardiology Sports and Exercise Cardiology Section. When convened in October of 2012, the group's participants represented athletic trainers; primary care professional societies; cardiovascular specialty, subspecialty, and imaging societies; government agencies; industry; sports governing bodies; and patient advocacy groups. They identified 92 quality gaps, and the resulting document, available online and linked in the references below, includes an action plan to address the most urgent of these gaps, a look at the American athlete and risks of participation, suspected etiologies and suggested work-up for specific symptoms in athletes, and pitfalls in interpreting cardiac testing in athletes.

As for working as a sports cardiologist (TABLE 2), Dr. Lawless said it starts with an athlete-centered approach that requires knowledge of the patient and, importantly, the sport itself. Athletes are "different" from the general population from a physiologic and/or medical perspective that includes the appearance of cardiac tests, risk perspective, and the team requirements relating to drug testing. Moreover, athletes are "different" from each other, with clear physiological differences seen among basketball, football, and soccer players, for example. Sometimes, even within a single sport, the variation is striking. In football, for example, player weight varies from 150 to 400 pounds. In the 2014 National Football League Scouting Combine of players considered for drafting, 20% weighed more than 300 pounds.

The physiologic demands can vary greatly, too. During a 90-minute soccer match, field players cover 10-12 kilometers or 6.2 -7.5 miles. Even goalkeepers cover about 4 kilometers (2.5 miles). The game also includes sprints of 2 to 4 seconds in length and occur about every 90 seconds.

Christine Lawless, MD, Sports Cardiology Consultants LLC and the University of Chicago, is the only physician in the U.S. who holds dual certification in cardiology and sports medicine. Here she discusses a recent State-of-the-Art Paper in JACC on Sports and Exercise Cardiology in the United States: Cardiovascular Specialists as Members of the Athlete Healthcare Team.

REFERENCE:
1. Lawless CE, Asplund C, Asif IM, et al. Protecting the Heart of the American Athlete: Proceedings of the American College of Cardiology Sports and Exercise Cardiology Think Tank October 18, 2012, Washington, DC. J Am Coll Cardiol. 2014;2146-71. http://content.onlinejacc.org/article.aspx?articleid=1915071

---

Key Studies in Sports and Exercise Cardiology

Exercise Testing and Training

Whether exercise testing should be performed in asymptomatic adults prior to beginning vigorous exercise has been controversial—even more so for routine screening of young people before engaging in athletics.

New exercise standard for testing and training do not recommend routine screening of asymptomatic low-risk younger individuals, but the guidelines do recommend exercise testing before starting a vigorous exercise program in asymptomatic people:

with diabetes mellitus
in men >45 and women >55 years of age
in individuals with "major coronary risk factors"

Fletcher GF, Ades PA, Kligfield P, et al. Exercise standards for testing and training: a scientific statement from the American Heart Association. Circulation. 2013;128:873-934.

---

Incidence of Sudden Death in Athletes

In a review of the literature, investigators evaluated the incidence of sudden cardiac death (SCD) in athletes.

There is a large range of SCD rates reported, ranging from 1:917,000 to 1:3,000.

However, studies with higher methodological quality consistently yielded incidence rates in the range of 1:40,000 to 1:80,000.

Some athlete subgroups, specifically men, African-American/black athletes, and basketball players, appear to be at higher risk.

The incidence of SCD in athletes is likely higher than traditional estimates, which may impact the development of more effective prevention strategies.

Harmon KG, Drezner JA, Wilson MG, Sharma S. Incidence of sudden cardiac death in athletes: a state-of-the-art review. Br J Sports Med. 2014;48:1185-92.

---

Is it the Heart or the Heat?

Dr. Thompson said, "I always beg cardiology fellows to be more than just cardiologists." This has applicability for those who work with athletes because a recent paper in JACC suggests that in analyzing life-threatening events during endurance sports, heat stroke is more prevalent than arrhythmic death.

In a cohort of 137,580 runners participating in popular long-distance races (10Ks, half-marathons, and marathons), for every serious cardiac adverse event, there were 10 serious events related to heat stroke.

Yankelson L, Sadeh B, Gershovitz L, et al. Life-Threatening Events During Endurance Sports: Is Heat Stroke More Prevalent Than Arrhythmic Death? J Am Coll Cardiol. 2014;64:463-9.

---

Can Exercise Training Alter Gene Expression?

James and colleagues interviewed 87 carriers of arrhythmogenic right ventricular dysplasia / cardiomyopathy (ARVD/C) mutations for information about their regular physical activity from 10 years of age.

Dr. Thompson thinks this paper is "probably the most important 'concept-changing article' of the last 2 years." In terms of these mutations linked to ARVD/C, "Penetrance is variable, so why do some people have the same gene but not the same disease? Could that be due to environmental factors and could one of those factors be vigorous exercise?"

In this study, endurance athletes developed symptoms at a younger age (30 years vs. 41 years), were more likely to meet ARVD/C criteria at last follow-up (82% vs. 35%), and had a lower lifetime survival free from ventricular tachycardia/fibrillation and heart failure.

James CA, Bhonsale A, Tichnell C, et al. Exercise Increases Age-Related Penetrance and Arrhythmic Risk in Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy–Associated Desmosomal Mutation Carriers. J Am Coll Cardiol. 2013;62:1290-7.

---

Good News: Leisure Running Lowers Mortality

Investigators examined the associations of running with all-cause and cardiovascular mortality risks in 55,137 adults (mean age: 44 years). Over a 15-year period, running even 5 to 10 minutes per day and at slow speeds, is associated with markedly reduced risks of death from all causes and cardiovascular disease. Although below the current minimum guidelines of vigorous-intensity aerobic activity, this level and length of activity remained sufficient for substantial mortality benefits.

Said Dr. Thompson, "Even very slow runners got some benefit; even if they did not spend a lot of time running, they got some benefit in terms of mortality."

Lee D, Pate RR, Lavie CJ, Sui X, Church TS, Blair SN. Leisure-Time Running Reduces All-Cause and Cardiovascular Mortality Risk. J Am Coll Cardiol. 2014;64:472-81.

Keywords: ACC Publications, CardioSource WorldNews

< Back to Listings