Associations of Cardiac Mechanics With Exercise Capacity: The Multi-Ethnic Study of Atherosclerosis

Abstract

Background: Lower exercise capacity, as measured by 6-minute walk distance (6MWD), is associated with incident heart failure (HF). Among those without HF, the associations of measures of cardiac function with 6MWD are unclear, and may provide insight regarding the risk of incident HF.

Objectives: The purpose of this study was to understand the relationships between cardiac function and exercise capacity.

Methods: This study evaluated the associations of cardiac mechanics with 6MWD in the sixth examination of the Multi-Ethnic Study of Atherosclerosis. Echocardiography (2-dimensional, Doppler, and speckle-tracking) was performed at rest and after passive leg raise to evaluate functional reserve after intravascular volume challenge.

Results: Of 2,096 participants without HF (mean age 73 years, 48% men, 58% non-White), individuals with lower (worse) left atrial (LA) reservoir strain were older and had higher blood pressure. Lower resting LA reservoir strain (β coefficient per SD decrease: -5.0; 95% confidence interval [CI]: -8.8 to -1.3 m; p = 0.009), inability to augment LA reservoir strain after passive leg raise (β coefficient per SD decrease: -5.8; 95% CI: -9.1 to -2.5 m; p < 0.001), and lower right atrial reservoir strain (β coefficient per SD decrease: -4.4; 95% CI: -7.8 to -1.1 m; p = 0.01) were associated with shorter 6MWD. Worse left ventricular (LV) diastolic function was also associated with lower 6MWD. There were no independent associations of measures of LV systolic function (global longitudinal strain, circumferential strain, ejection fraction) with 6MWD.

Conclusions: Among individuals without HF, worse biatrial function, lack of LA functional reserve, and worse LV diastolic function were associated with reduced submaximal exercise capacity. Therapies aimed to improve these functional domains may increase exercise capacity and prevent HF.

Keywords: 6-min walk test; cardiac structure and function; echocardiography; heart failure; subclinical.

Figure 1.. Association of LA Reservoir Strain with 6MWD by AF Status.

Shown are linear models of resting LA reservoir strain and 6MWD by AF status. The rug plot shows distribution of LA reservoir strain. 6MWD = 6-minute walk distance; AF = atrial fibrillation; LA = left atrial

Figure 2.. Association of Change in LA Reservoir Strain with 6MWD.

Shown are linear models of change in LA reservoir strain after passive leg raise (intravascular volume challenge) and 6MWD by AF status. The rug plot shows distribution of change in LA reservoir strain. 6MWD = 6-minute walk distance; AF = atrial fibrillation; LA = left atrial

Figure 3.. Mediation Analysis of Risk Factors, Cardiac Mechanics, and 6MWD.

The path models and mediation analyses describing mediation by LA reservoir strain or e’ lateral velocity on the associations between demographics and 6MWD are displayed. Red arrows display the indirect (mediation) effect. Blue arrows display the direct effect.

Central Illustration:. LA Function, LA Functional Reserve, and 6MWD.

Reduced resting LA reservoir strain and lack of augmentation of LA reservoir strain after passive leg raise (i.e. intravascular hemodynamic challenge) were independently associated with reduced exercise capacity. Additionally, reduced resting RA reservoir strain was associated with lower 6MWD.