Reduced EF Evident in Some Elite Endurance Athletes

Some elite endurance athletes have evidence of impaired cardiac function, which, along with other findings, may raise suspicions of early dilated cardiomyopathy, according to results of a new study.

Overall, one in six elite endurance athletes had a reduction in left or right ventricular ejection fraction at rest and this reduction appeared to be partly related to an underlying genetic predisposition, report researchers.  

“We also assessed the athletes during exercise, and we see function picks up,” lead investigator Guido Claessen, MD, PhD (University of Hasselt/Limburg Clinical Research Center, Diepenbeek, Belgium), told TCTMD. “So, in the short term, we don't see that their heart muscles are damaged—they function well during exercise. They have the same VO₂max, for example. But it is a phenotype that is distinct from the other group [with preserved EF].”

The athletes with reduced EF share some of the genes seen in patients with heart failure—a finding based on a polygenic risk score—and have a higher burden of ventricular ectopic beats.

“Again, this isn’t harmful, but it’s different,” said Claessen. “These are little features that kind of tick the boxes so that we have to follow-up these individuals in the future to see whether the long-term outcome is still benign, which we do not know at this point.”

Cardiac changes resulting from intense endurance exercise have long been known as the “athlete’s heart,” with structural and functional adaptations including increased chamber size, wall thickness, and mass. These changes can mimic the pathological structural changes associated with inherited and acquired cardiac disease, including dilated cardiomyopathy, which can make screening a challenge for physicians. More recently, it’s been recognized that intense endurance exercise can lead to electrical remodeling and a predisposition to various arrhythmias, including atrial fibrillation.

Prashant Rao, MD (Beth Israel Deaconess Medical Center, Boston, MA), who wasn’t involved in the study, said past research also has shown reduced EF in endurance athletes. An older study of Tour de France cyclists, for example, found that 7% of riders participating in the 1995 and 1998 event had reduced EF.

Rao explained that the ability to augment a low EF during endurance exercise—seen in the 44 athletes with reduced EF at baseline—is an important discriminator that helps differentiate athletic remodeling and the more-common heart failure phenotype.

“It’s always a bit of a conundrum to be able to recognize what's largely athletic remodeling and what could be an early manifestation of dilated cardiomyopathy,” he said.

“Kudos to the investigators because they recruited the crème de la crème of endurance athletes,” Rao continued. “Their VO₂max alone won’t make them immune to cardiovascular disease, but it’s certainly going to helpful and will reduce their risk of having adverse outcomes.” 

To TCTMD, Claessen said their study, which includes athletes enrolled in the Pro@Heart and ProAFHeart studies, is an attempt to prospectively understand what drives the physiological adaptation to endurance exercise, noting that there are degrees of remodeling seen in athletes. “It’s not black-and-white, but really like different shades of grey,” he said. The authors are also planning long-term follow-up—at least 20 years—to understand if these athletes with unique phenotypes, such as reduced EF, later develop clinical problems.

The paper was published online December 18, 2023, ahead of print in Circulation.

Cyclists, Runners, Skiers, and More

The study included 281 athletes (mean age 19 years; 80% male) competing at the national and international level in triathlon, cycling, rowing, cross-country skiing, distance running (≥ 1500 m), and swimming (≥ 400 m), and exercising, on average, 15 to 16 hours per week. All underwent a battery of tests, including MRI, echocardiography, ECG and 24-hour Holter monitoring, stress testing, and genetic analyses.

In all, 15.7% had reduced EF (LVEF < 50% or RVEF < 45%) on cardiac MRI. Twelve athletes had isolated LVEF, 14 had isolated RVEF, and 18 had a combination. Age, sex, body mass index, blood pressure, sport, and training load were similar between the athletes with and without reduced EF. At rest, the LV end-diastolic volume was comparable between the groups, but athletes with reduced EF had higher RV end-diastolic volumes.

Compared with athletes with preserved EF, those with reduced EFs had lower LV global longitudinal strain, which is considered a more-accurate reflection of the heart’s contractility. They also were more likely than those with preserved EF to meet clinical criteria for reduced LV global longitudinal strain. Late gadolinium enhancement (LGE), which is a marker of myocardial fibrosis, was present in 15.7% of athletes, with no difference seen between those with and without reduced EF.

During exercise testing, heart rates and power outputs were similar irrespective of EF. While the EF remained lower in the athletes with reduced EF at baseline during peak exercise, these athletes had an overall larger increase in EF in response to physical activity. Athletes with reduced EF had a marginally longer QRS duration than those with preserved EF, but other measures were similar. As noted, this group did have a higher burden of ventricular premature beats than athletes with preserved EF, however. 

Finally, the researchers assessed whether genetics played a role in reduced EF in the endurance athletes. They calculated a polygenic risk score (PRS) associated with the left ventricular end-systolic volume index (LVESVi) and incident dilated cardiomyopathy. This score, they found, was significantly higher in athletes with reduced EF than those with preserved EF (0.57 versus 0.51; P = 0.009). Male sex and a higher PRS for LVESVi were significant predictors of reduced EF in a multivariate analysis that also adjusted for age and fitness.

To TCTMD, Rao explained that if the reduced EF was entirely due to adaptations from training, then you wouldn’t necessarily expect to see a decrease on global longitudinal strain. “Now, the clinical significance of that is unclear, just like the clinical significance of the increased ventricular premature beat burden is also unclear,” said Rao. “You might not expect to see all of that from beneficial physiological remodeling.”

For Rao, the genetic data “is a little bit paradigm-shifting” because it also suggests that reduced EF is not solely the result of athletic remodeling. “I think that's where it will really enhance our understanding of these individuals, that genetics does play a role here, and it contributes to some of the individual variability in ejection fraction we see in endurance athletes,” he said.

The Athletic Heart or Dilated Cardiomyopathy?

These data suggest, Rao said, that attention is warranted when caring for these elite athletes with reduced EF, even if the implications of the findings are as yet unclear.

The athletes were followed for 4.4 years, but none developed symptomatic heart failure or documented sustained atrial or ventricular arrhythmias. There was one athlete with reduced RVEF and low-normal LVEF who died of sudden cardiac death, with postmortem data showing evidence of patchy myocardial fibrosis, “raising the possibility of a cardiomyopathic process,” say investigators. 

“I think it does raise some kind of caution with these athletes, but it's also important to put this in the context that we really have no idea what the prognostic significance of this means in this particular cohort of individuals,” said Rao. “They did follow them for five years, and I know there was one sudden cardiac death, but there were no overall differences in follow-up.”

Claessen agreed, saying that if physicians detect a low EF in a young athlete, this shouldn’t be cause for alarm. “It’s a relatively common finding and shouldn’t be a disturbing finding,” he said. “But I would tend to follow them up a bit closer than those in whom all findings were normal.”

At their clinic, Claessen said they’ll assess EF during exercise in those athletes with reduced EF to determine how the heart responds. “If the EF goes up smoothly, then that’s reassuring. We also do rhythm monitoring and if there is nothing there, then we don’t treat them any different than all of the other athletes.”