Dr Larry Creswell
In my column today at the Endurance Corner website, I share part 2 in a series about endurance athletes and heart rate variability (HRV). Today, I talk about measuring HRV and how athletes might use HRV to help guide their training. Stay tuned for part 3, where I’ll talk about the available hardware and software options and summarize my thoughts on the subject.
Every so often, a scientific report about runners and heart disease really captures the attention of the media. About a week ago, a report in the March/April edition of Missouri Medicine entitled “Increased Coronary Artery Plaque Volume Among Male Marathon Runners” generated quite a bit of interest and discussion. I’ve written previously here at the blog about the general issue of the “heart healthiness” of long-distance running in a post entitled “Don’t Stop Running Yet!” I still feel that way. But let’s take a look, though, at this new article about marathoners and coronary plaque.
The report is written by a large group of very credible investigators from the Minneapolis Heart Institute, Integra Group, University of Colorado, Medtronic Inc., University of Minnesota, and the Mid America Heart Institute. Included in the group of authors is Kevin Harris, MD, who authored an important 2010 report on triathlon-related fatalities, William Roberts, the Runners World “Sports Doc” and medical director of the Twin Cities Marathon, and James O’Keefe, MD, a one-time triathlete who has been an outspoken critic in recent years of excess exercise.
The investigators report on a group of 50 male participants in the Twin Cities Marathon who had run at least 1 marathon per year for 25 years in a row. The average age was 59 years. None of these subjects had any history of heart disease or any current symptoms suggestive of heart disease. The runners underwent testing that included measurement of the height and weight, blood pressure, and resting heart rate; a 12-lead EKG; and blood tests for serum lipids and creatinine. The subjects also completed a questionnaire about historical lifestyle and risk factors. Each of the athletes underwent a high-resolution coronary computed tomographic angiography (CCTA) study. A control group of 23 sedentary men were identified from a contemporaneous group who were undergoing a CCTA study for some clinically-necessary reason and also underwent the other tests just like the runners did. The subjects and controls were similar in terms of: age, resting blood pressure, height, smoking history, serum creatinine, total cholesterol, and low density lipoprotein (LDL) levels.
Coronary artery plaque “lesions” were identified in both the runners and the controls: 95 lesions in 30 of the 50 runners, and 46 lesions in 12 of the 23 controls. The total volume of plaque was greater among the runners and this was also true for the amount of calcified or non-calcified plaque, as well. There was no difference in the lesion area, lesion diameter, or lesion length between the runners and controls.
Why is this all important? Because coronary plaque is generally associated with problems like heart attack. In clinical practice, we ordinarily discover coronary plaque when we search for a cause of a patient’s heart attack. Or, in recent years, we discover the plaque when an individual undergoes a screening test like a coronary calcium scoring CT scan. And we know from studies of individuals (not necessarily runners) who’ve undergone coronary calcium scoring CT scans that those with high calcium scores, indicating plaques, there is a greater risk of future heart attack. So it’s somewhat surprising that seemingly healthy long-time runners would have more coronary plaque than the sedentary controls.
On the bright side, despite being nearly 5 years older on average than the controls, the runners had significantly lower resting heart rate, weight, and body-mass index (BMI), less hypertension (high blood pressure), less diabetes, and an increased level of high density lipoprotein (HDL), the “good” cholesterol.
All of this news isn’t really new, though. These investigators first reported their findings at the 2011 meeting of the American Heart Association. It’s just now making its way into print, and into a rather unlikely and somewhat obscure medical journal for some reason. Missouri Medicine, the journal of the Missouri State Medical Association, even sent out a press release with advance copies of the article and accompanying editorials to a wide distribution list, all to take advantage of the lead-up to this year’s Boston Marathon. All pretty sensational, really. I can’t recall anything quite like this for research that was already more than 2 years old.
Given their findings, the authors conclude that “chronic excessive high intensity exercise” is the cause for the plaque build-up in the runners. They hypothesize that the mechanism is related to metabolic or mechanical stresses placed on the heart and coronary arteries during running that may be mediated by inflammation. The authors suggest, then, that “some runners” ought to “choose shorter, less exhausting challenges” in order to avoid this problem. On the face of it, this is a neat narrative, but….
1. Although the plaque volume (the total amount of plaque) was greater in the runners than the controls, the percentage of affected individuals in the running and control groups was not significantly different. Remember that 30 out of 50 (60%) runners had plaque identified and so did 12 out of 23 (52.2%) controls. In the statistical sense, those percentages are not significantly different. In terms of the most obvious, and perhaps most important, endpoint–the number of affected individuals with coronary plaque, the prevalence of coronary plaque–the study is essentially a negative study. Negative studies are hard to get published and I suspect this is why this report was published 2+ years after the study was completed.
2. If running was the cause of the plaque build-up, then why did only 60% of the long-time runners have this problem? And why did 52.2% of the controls have this problem, assuming that they were truly sedentary? Obviously the “cause” of plaque build-up in the coronary arteries is multifactorial. The authors can’t have it both ways: running cannot be responsible in the runners yet not responsible in the controls. For the runners, the real question is: what unmeasured variables might account for the finding of coronary plaque. We simply don’t know.
3. What is the consequence of having asymptomatic coronary plaque in a long-time runner? We don’t know. The current study doesn’t address this issue and to my knowledge, no study has. I’ve certainly heard from long-time endurance athletes who’ve been found to have coronary plaque, or elevated score on a coronary calcium scoring CT scan, who ask about the significance of the finding. We obviously need studies to find out what happens to such athletes.
4. What about….other endurance sports? And women? And younger athletes? There are just many, many questions left to be answered.
So, what’s the runner to do? I would still suggest that you not stop running. There’s every reason to believe that exercise is a healthy pursuit and there’s every reason to believe that exercise leads to better longevity, even for long-time endurance athletes. But stay informed. The general issue about the possibility of too much exercise is receiving a lot of attention. More studies are sure to come. And little by little, we’ll piece together the information that will help us determine if there is some sort of “sweet spot” in terms of the amount of exercise that is most heart-healthy.
Two articles on this topic caught my eye this week. Both are good reading. Amby Burfoot, the long-time editor at Running World and winner of the 1968 Boston Marathon, wrote an online piece for his magazine entitled “Heart Risk? Marathoners Have Increased Artery Plaque.” Interestingly, Amby learned last spring that he falls into the category of long-time runners with an (asymptomatic) high coronary calcium score. The second article was by Kevin Helliker in the Wall Street Journal, entitled “Why Runners Can’t Eat Whatever They Want.”
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This year’s annual meeting of the American College of Cardiology was held in Washington, D.C. last week. I wasn’t able to attend the meeting, but the results of several studies related to sports cardiology caught my attention. Here are my Top 8:
1. Prodromal symptoms, exercise, and sudden cardiac arrest (SCA). In a study reported by Lawless CE et al., questionnaires were distributed to known survivors of SCA. Prodromal, or warning, symptoms surveyed included chest pain, shortness of breath, and evidence of arrhythmia (syncope, dizziness, palpitations). Such prodromal symptoms were present in 31% during the month preceding the SCA episode. Half of the prodromal symptoms occurred at rest and half occurred during exercise. We’ve known about the importance of recognizing exercise-related arrhythmias, but the important new finding here is the importance of arrhythmic symptoms at rest as a potential warning sign for later SCA.
2. Exercise blood pressure in Olympic athletes. Little is currently known about blood pressure during exercise for elite athletes. In a study reported by Caselli S et al., 1,140 Olympic athletes from the 2008 or 2012 Games were divided into 4 groups depending upon their sport: skill disciplines, power disciplines, mixed disciplines, or endurance disciplines. These athletes underwent a battery of cardiovascular testing that included measurement of the blood pressure during a maximal bicycle exercise test. For the entire group, the peak systolic blood pressure (SBP) and diastolic blood pressure (DBP) were 190+/-21 mm Hg and 76 +/- 7 mm Hg, respectively. Interestingly, there were no differences between athletes of the 4 sporting groups. A total of 102 athletes had either SBP or DBP above the 95th percentile for the group (220 mmHg and 85 mmHg, respectively). This new information may allow for better identification of elite caliber athletes with hypertension that should be treated.
3. Maximal heart rate in men and women. We often use the calculation of 220 minus age to give an estimate of an individual’s maximal heart rate. This number has bearing in clinical cardiology testing as well as for setting up training zones for endurance athletes. Based on the observations in more than 25,000 individuals undergoing exercise stress tests, Sydo N. et al. reported that more accurate estimates for individuals older than 40 years may come from these equations: Men, 216 minus 93% of age; Women, 200 minus 67% of age. These new equations may provide better estimates for athletes who want to establish appropriate training zones.
4. Cardiovascular health and marathon training. Zilinski JL et al. reported on a group of 45 male recreational runners who undertook a relatively short 18-week, structured training program leading up to the 2013 Boston Marathon. Each of the runners had at least one known cardiovascular risk factor at the outset. They underwent clinical evaluation, echocardiography, VO2max testing, and laboratory evaluation before and again after the training period. There were significant improvement in: peak oxygen consumption, body-mass index (BMI), serum triglyceride level, serum low density lipoprotein (LDL) level, serum total cholesterol, and one particular index of ventricular function based on echocardiography. The results suggest, perhaps not surprisingly, that marathon training may be a useful strategy for improving conventional cardiovascular risk factors.
5. Running and longevity. A couple recent studies have documented a so-called “U-shaped” relationship between the amount of running and longevity among long-time runners, where individuals with moderate amounts of running enjoyed better longevity compared to those with larger (>20 miles per week) amounts of running. These previous studies have suggested some sort of “sweet spot” with respect to healthy amounts of exercise. The reasons and potential mechanisms for this observation remain unclear, though. In a study reported by Bell AC et al., an update was provided for the ongoing MASTERS Athletic Study, a longitudinal study of runners aged 35 and older. The investigators tested the hypothesis that perhaps decreased longevity among the highest-volume runners might be due to adverse cardiovascular risk factors (eg, family history of heart disease, high blood pressure, abnormal serum lipid levels, diabetes, smoking) rather than to the amount of running. It turns out, though, that these factors did not account for the difference in mortality for the 2 groups. So the reason(s) behind the U-shaped longevity curve (if it’s not due simply to the amount of running) remain unclear.
6. Pre-participation screening. There have been several guidelines about the utility of pre-participation cardiovascular screening for athletes, including the 4th PreParticipation Physical Evaluation monograph in 2010, the 2007 American Heart Association (AHA) reparticipation screening recommendations, and the Proceedings of the 36th Bethesda Conference in 2005. In a study reported by Lawless CE et al., 190 Nebraska primary care providers (PCPs) were surveyed about their use of these guidelines in the evaluation of athletes. The percentage of PCPs who “consistently used” the guidelines were only 7.9%, 11.4%, and 3.2%, respectively. The percentage of PCPs who were unaware of the guidelines were surprisingly 73.0%, 48.0%, and 76.4%, respectively. The results suggest that the guidelines are under-utilized and the investigators recognize a potential opportunity for improved screening with better education about the available guidelines.
7. Smartphone apps and silent arrhythmias. A variety of smartphone apps related to heart rhythm monitoring have become available in recent years. In a study reported by Sawant AC et al., 103 patients being treated in an outpatient setting used a smartphone app to record their EKG and then also underwent conventional EKG recording in the doctor’s office. The smartphone app correctly identified atrial fibrillation in almost 90% of cases where the arrhythmia was silent (did not produce symptoms). This technology will undoubtedly continue to evolve and may enable recording of both silent and symptomatic arrhythmias in the outpatient setting in a much easier and less costly fashion that traditional Holter monitoring.
8. Endurance exercise and cardiac remodeling. Many different sports qualify for being “endurance” activities, but each has its own unique make-up of so-called dynamic and static exercise components. In a study reported by Wasfy MM et al., 38 long distance runners were compared to 33 rowers in terms of their cardiac structure and function. The investigators found that runners had larger left ventricular (LV) volumes but lower LV muscle wall thickness than the rowers. The function of the LV was similar for the 2 groups. It’s important to keep in mind that, as far as the heart is concerned, all endurance sports are not created equal!
We can expect more detailed reporting on these studies as they make their way into print form in a scientific journal over the next year or so. Stay tuned.
In my column this month at Endurance Corner, I’m writing about heart rate variability (HRV). In Part 1, I offer an introduction to the topic and develop the basic concepts and terminology. In an upcoming Part 2, I’ll write about the application of HRV to endurance training and share some information about the currently available hardware and software tools that athletes might find helpful.
At my column this month at Endurance Corner, I wrote about age group triathletes and doping. Based on athlete questionnaires, a recent study found that about 15% of age group triathletes at three long course events in 2013 reported some form of doping in the preceeding year. I shared some information about the study and its findings as well as some of the cardiovascular concerns with the common doping agents.
Looking at the Tweets and comments today, some are surprised the rate is so high….and others are surprised it’s so low. I’m not surprised.