Physical Activity and Cardiac Morphologic Adaptations

Abstract

Chronic and intense exercise programs lead to cardiac adaptations, followed by increased left ventricular wall thickness and cavity diameter, at times meeting the criteria for left ventricular hypertrophy (LVH), commonly referred to as "athlete's heart". Recent studies have also reported that extremely vigorous exercise practices have been associated with heightened left ventricular trabeculation extent, fulfilling noncompaction cardiomyopathy criteria, as part of exercise-induced structural adaptation. These changes are specific to the exercise type, intensity, duration, and volume and workload demands imposed on the myocardium. They are considered physiologic adaptations not associated with a negative prognosis. Conversely, hypertrophic cardiac adaptations resulting from chronic elevations in blood pressure (BP) or chronic volume overload due to valvular regurgitation, lead to compromised cardiac function, increased cardiovascular events, and even death. In younger athletes, hypertrophic cardiomyopathy (HCM) is the usual cause of non-traumatic, exercise-triggered sudden cardiac death. Thus, an extended cardiac examination should be performed, to differentiate between HCM and non-pathological exercise-related LVH or athlete's heart. The exercise-related cardiac structural and functional adaptations are normal physiologic responses designed to accommodate the increased workload imposed by exercise. Thus, we propose that such adaptations are defined as "eutrophic" hypertrophy and that LVH is reserved for pathologic cardiac adaptations. Systolic BP during daily activities may be the strongest predictor of cardiac adaptations. The metabolic demand of most daily activities is approximately 3-5 metabolic equivalents (METs) (1 MET = 3.5 mL of $O_2$ kg of body weight per minute). This is similar to the metabolic demand of treadmill exercise at the first stage of the Bruce protocol. Some evidence supports that an exercise systolic BP response $\ge$ 150 mmHg at the end of that stage is a strong predictor of left ventricular hypertrophy, as this BP reflects the hemodynamic burden of most daily physical tasks. Aerobic training of moderate intensity lowers resting and exercise systolic BP at absolute workloads, leading to a lower hemodynamic burden during daily activities, and ultimately reducing the stimulus for LVH. This mechanism explains the significant LVH regression addressed by aerobic exercise intervention clinical studies.

Keywords: arrhythmias; athletes; cardiac function; cardiac structure; exercise; left ventricular mass; physical activity.

Fig. 1.

Classification of all left ventricular hypertrophy patterns, based on calculated relative wall thickness and left ventricular mass index (LVMI). LVH, left ventricular hypertrophy; LVMI, left ventricular mass index.

Fig. 2.

Cardiac structural changes of select sports that represent aerobic, resistance and the combination of the two exercise types [27]. LV, left ventricular.

Fig. 3.

Proposed pathophysiologic mechanisms of cardiomyopathy and arrhythmias in endurance athletes. LVH, left ventricular hypertrophy; LV, left ventricular; CK-MB, creatine kinase-myocardial band; BNP, B-Type natriuretic peptide; RA/RV, right atrium/right ventricle; SCD, sudden cardiac death.