Background and Aim

Sedentary
behaviour is associated with increased risk of cardiovascular diseases, but its
effects on cardiac structure and function are unknown.

The purpose of
this study was to study the cross-sectional associations of TV viewing
time during a 10-year follow-up (as an indicator of sedentary behaviour) with
ultrasonographically assessed cardiac structure and function in midlife.

Methods

1,994 adults of the population-based
Cardiovascular Risk in Young Finns study (914 men and 1080 women, mean age 41.9+5.0 years, range 34–49 years) had echocardiography
performed in 2011. Cardiac volumes and dimensions (20), indices adjusted for
body surface area (16), and ventricular systolic (8) and diastolic functions
(9) were evaluated in subjects with constantly low (<1h/d),
moderate (1-3h/d), or high (>3h/d) daily TV time, and in groups with
>1 hour in-/decrease in daily TV time between
2001 and 2011.

Transthoracic echocardiographic examinations were
performed at 2011 follow-up according to American and European guidelines with
Acuson Sequoia 512 (Acuson, Mountain View, CA, USA) ultrasonography, using 3.5
MHz scanning frequency phased-array transducer. The sonographers from different
locations were trained by a cardiac imaging specialist. Analysis of the echo
images was carried out by one observer blinded to the clinical details using
ComPACS 10.7.8 (MediMatic Solutions, Italy) analysis program. Also the offline
echocardiographic measurements and analyses were produced and reported in
accordance with guidelines.

In model 1, the
multivariable, linear regression analyses were adjusted for age, sex,
socioeconomic status, occupational physical activity (PA), energy intake,
alcohol consumption, smoking, sleep duration, region of living, and thereafter,
to detect possible mediators, by adding leisure-time PA, BMI, heart rate,
systolic (SBP), and diastolic blood pressure (DBP), one by one in the model.

Key Results

Of the diastolic
parameters, constantly high TV time was independently associated with decreased
early lateral velocity of the mitral annulus (e’) (p<0.02) indicating lower diastolic
function by reduced myocardial relaxation. The association of constantly high
TV time with decreased ratio of transmitral flow velocities
(E/A-ratio) indicating left ventricle wall stiffening was diluted only after
adjustment for DBP. Decreased ratio of early diastolic mitral
annular and early myocardial relaxation velocity (e’/a’)
remained statistically significant after adjustment with PA (p=0.034). Increased
end-diastolic mitral flow velocity (A) turned borderline significant after
adjustment for PA or BMI (p=0.052 or 0.057).

Conclusions

In this adult population, constantly high TV viewing
time is inversely associated with markers of

subclinical left ventricle diastolic function. This
relationship is partly explained by PA, BMI, heart rate and blood pressure.