Radiology: Cardiac MR details response to triathlon training
3D whole heart MR angiography Image source: Toshiba Medical Systems
Cardiac MRI revealed cardiac adaptations, including a balanced increase in left ventricular (LV) and right ventricular (RV) myocardial mass, wall thickness, ventricular dilation and diastolic function, among  elite triathletes, according to a study published in the October edition of Radiology.

The athlete’s heart adapts to long-term, frequent training and is differentiated into two morphologic types, wrote Michael M. Lell, MD, of the University of Erlangen-Nuremberg in Erlangen, Germany. Endurance training leads to thickening of the ventricular wall and cavity dilation, while resistance training results in increased myocardial mass and wall thickness without subsequent changes in cavity size, he noted. Triathlon training differs from pure endurance and resistance sports, and the impact of training has not been previously investigated.

Lell and colleagues sought to assess cardiac morphologic and functional adaptation in the elite triathletes with an MRI and to compare findings to recreationally active subjects.

The researchers recruited 26 elite male triathletes (mean age, 27.9 years) with more than six years of continuous training and 27 males controls (mean age, 27.3 years) recreationally active three or fewer hours weekly for at least five years to undergo an MRI to measure indexed LV function and RV myocardial mass, end-diastolic and end-systolic volumes, stroke volume, ejection fraction (EF) and cardiac index at rest.

Two experienced readers blinded to the identity of the subject performed LV and RV functional analysis in consensus. Radiologists found that indexed LV and RV myocardial masses at end diastole were significantly greater in athletes than in control subjects, wrote Lell.

The range of triathletes’ LV and RV myocardial mass of 70-113g/m2 and 16-36g/m2, respectively, were within the normal ranges. LV and RV myocardial mass were 31 percent and 30 percent, respectively, larger than in control subjects; however, myocardial mass was within clinical limits for all triathletes.

LV wall thickness was significantly thicker in athletes than in control subjects at ranges of 8.2 mm to 11.6 mm and 7mm to 10.5 mm, respectively, added Lell and colleagues.

The researchers found that triathletes showed greater stroke volume, despite a larger end-systolic volume and also reported strong positive correlations between LV and RV end-diastolic volume and myocardial mass. Triathletes had larger LV and RV-end diastolic volumes than reported among other athletes, which is likely attributable to the selection of elite triathletes, suggested Lell.

Triathletes showed a balanced 27 percent increase in LV and 28 percent increase in RV end-diastolic volume, and both triathletes and control subjects had similar LV and RV remodeling  indexes, indicating balanced adaptation of the heart in triathletes, according to researchers.

The researchers found a much higher percentage of left atrium enlargement (62 percent) among triathletes than previously reported among athletes in other disciplines, which indicates that a combination of endurance and resistance training has a greater effect on LA remodeling, wrote Lell.

Lell and colleagues did not find arrhythmias among triathletes despite the association between an enlarged left atrium and arrhythmia and noted that cardiac adaptations in elite triathletes are not associated with ventricular arrhythmias. However, they cautioned that the short duration of the study and small sample size warrants careful interpretation.

“The findings suggest that the specific type of training involved with triathlon results in myocardial adaptations that combine features of eccentric and concentric remodeling,” concluded Lell and colleagues. “The pattern of myocardial remodeling in elite triathletes reflects the nature of the underlying training which combines both endurance and resistance components.”