Athletic Cardiac Adaptation in Males Is a Consequence of Elevated Myocyte Mass

Abstract

Background: Cardiac remodeling occurs in response to regular athletic training, and the degree of remodeling is associated with fitness. Understanding the myocardial structural changes in athlete's heart is important to develop tools that differentiate athletic from cardiomyopathic change. We hypothesized that athletic left ventricular hypertrophy is a consequence of increased myocardial cellular rather than extracellular mass as measured by cardiovascular magnetic resonance.

Methods and results: Forty-five males (30 athletes and 15 sedentary age-matched healthy controls) underwent comprehensive cardiovascular magnetic resonance studies, including native and postcontrast T1 mapping for extracellular volume calculation. In addition, the 30 athletes performed a maximal exercise test to assess aerobic capacity and anaerobic threshold. Participants were grouped by athleticism: untrained, low performance, and high performance (O2max <60 or>60 mL/kg per min, respectively). In athletes, indexed cellular mass was greater in high- than low-performance athletes 60.7±7.5 versus 48.6±6.3 g/m(2); P<0.001), whereas extracellular mass was constant (16.3±2.2 versus 15.3±2.2 g/m(2); P=0.20). Indexed left ventricular end-diastolic volume and mass correlated with O2max (r=0.45, P=0.01; r=0.55, P=0.002) and differed significantly by group (P=0.01; P<0.001, respectively). Extracellular volume had an inverse correlation with O2max (r=-0.53, P=0.003 and left ventricular mass index (r=-0.44, P=0.02).

Conclusions: Increasing left ventricular mass in athlete's heart occurs because of an expansion of the cellular compartment while the extracellular volume becomes relatively smaller: a difference which becomes more marked as left ventricular mass increases. Athletic remodeling, both on a macroscopic and cellular level, is associated with the degree of an individual's fitness. Cardiovascular magnetic resonance ECV quantification may have a future role in differentiating athlete's heart from change secondary to cardiomyopathy.

Keywords: ECV; T1 mapping; athlete’s heart; cardiovascular magnetic resonance imaging; exercise physiology; hypertrophy/remodeling.

Figure 1.

Myocardial remodeling by performance group. A, Cellular mass increases out of proportion to increase in extracellular mass. B, Indexed left ventricular end-diastolic volume (LVEDV) and left ventricular (LV) mass increases stepwise as athletic grouping changes (P<0.001 for both).

Figure 2.

Typical cardiac magnetic resonance (CMR) appearances in low-performance and high-performance athletes. Left column shows an athlete with a O_2max of 50 mL/kg per in, and right column shows a high-performance athlete with a O_2max of 75 mL/kg per min. A and D, Short-axis images of left and right ventricle. B and E, extracellular volume (ECV) color maps showing lower ECV in the high performance athletes throughout the myocardium. C and F, Pie charts scaled to overall indexed LV mass displaying the relative indexed masses of the cellular and extracellular compartments (not short axis images). ECMI indicates indexed extracellular mass; and ICMI, indexed intracellular mass.

Figure 3.

Relationship between exercise capacity and left ventricular (LV) remodeling and remodeling and tissue composition (R and P values determined with Spearman correlation coefficient for all). A, LVEDVi and VO_2max, r=0.45, P=0.01; B, LVMi and VO_2max, r=0.55, P=0.002; C, extracellular volume and VO_2max, r=−0.53, P=0.003; D, significant inverse relationship between extracellular volume (ECV) and indexed LV mass (r=−0.44, P=0.02). LVEDVi indicates LV end-diastolic volume index; and LVMi, left ventricular mass index.