Intensive training changes the heart. Just like skeletal muscles, the heart adapts to the demands placed on it, and in elite athletes this can result in a thicker heart muscle wall. Usually, this is a healthy response to years of training. But increased heart wall thickness can also be a sign of hypertrophic cardiomyopathy (HCM), an inherited heart condition. This creates an important diagnostic ‘grey zone’: when is a thicker heart simply the result of training, and when could it indicate disease?

One of the measurements doctors use is the maximum thickness of the heart wall. Traditionally, fixed thresholds of 13 and 15 millimetres are used to determine whether someone falls within the range that could indicate HCM. Yet hearts differ between people. This is particularly relevant for women, who generally have thinner heart walls and therefore rarely exceed the traditional thresholds.

Recently, researchers in the United Kingdom developed new reference values that take sex, age and body size into account. Their study, however, did not include athletes. Researchers from the Sports Cardiology Team (Including first author Maarten van Diepen and research group leader Harald Jorstad) at Amsterdam UMC therefore wanted to know what would happen when these more personalised thresholds were applied to elite athletes.

Using cardiac MRI scans from 493 elite athletes in the ELITE cohort, the researchers used the AI tool 1CMR Pro to measure heart wall thickness and apply the new personalised reference values. The results differed between men and women. Among men, fewer athletes were flagged as having an unusually thick heart muscle: this dropped from 7.2% with the traditional threshold to 4.8% with the new values. Among women, the new values identified a small group that the traditional threshold missed: from none to 2.5%.

The findings suggest that taking individual characteristics into account could reduce some of the male bias created by fixed thresholds. But they also raise an important question: what does exceeding these new reference values actually mean in an elite athlete?

After all, none of the athletes in the study showed other features of HCM. Their thicker heart muscle could therefore simply reflect a healthy adaptation to intensive training. The researchers stress that being above a reference value is not the same as having HCM.

The research group, led by sports cardiologist Harald Thune Jørstad, therefore sees the new thresholds not as a final answer, but as another step towards more individualised assessment of the athlete’s heart.

Genetic testing and long-term follow-up could provide another piece of the puzzle. By following athletes over time, researchers hope to better distinguish between heart muscle thickening that is a healthy consequence of training and thickening that may be genetically associated with heart muscle disease and a higher risk of cardiac events.

That international collaboration will be particularly important because only a small proportion of athletes fall above the new reference values. Ultimately, studying more athletes, including athletes with confirmed HCM, and following them over time will be necessary to determine whether personalised thresholds can help doctors more accurately navigate the diagnostic ‘grey zone’ between a healthy athlete’s heart and heart muscle disease.

Read the full publication in the European Journal of Preventive Cardiology: Sex-specific redistribution of the hypertrophic cardiomyopathy grey zone in elite athletes using demographic-based wall thickness thresholds | European Journal of Preventive Cardiology | Oxford Academic

Funders of the ELITE cohort: NOC*NSF, Heart to Handle and AMS

Written in collaboration with Amsterdam hartcentrum