Background Left atrial (LA) size is a marker of diastolic function and is associated with atrial fibrillation and cardiovascular outcomes. However, there are no large population studies measuring LA structure. The relationship of demographics and cardiovascular risk factors to LA size is largely unknown. This study aimed to determine associations of LA size with demographic factors, cardiac structure and function, and cardiovascular risk factors. Methods and Results LA volume indexed to body surface area was measured by cardiovascular magnetic resonance SSFP and FGRE cine long- and short-axis images in 2576 asymptomatic participants of the Multi-Ethnic Study of Atherosclerosis (68.7 years, 53.0% women, white 42.2%, Chinese-American 12.0%, black 24.5% and Hispanic 21.2%) using biplane and short-axis images. The mean LA volume index was 36.5±11.4 ml/m2 in the entire cohort and 35.5±10.1 ml/m2 in subjects free of cardiovascular risk factors (n=283). Multivariable analysis included adjustment for demographics, ethnicity, cardiovascular risk factors, serologic studies, socioeconomic status, left ventricular structure and medications. In the adjusted analysis, age (β=0.2 ml/m2 per year, p<0.0001), male gender (β=-4.2 ml/m2, p<0.0001), obesity (β=1.3 ml/m2, p<0.01),end-diastolic volume index (β=0.4 ml/m2, p<0.0001), Chinese-American (β=-2.6 ml/m2, p<0.0001) and Hispanic (β=1.1 ml/m2, p<0.05) ethnicities were associated with LA volume index. Diabetes and smoking were not associated with LA volume index. LA volumes measured by SSFP were 3% larger than by fGRE cine CMR (p <0.001). Conclusions Age, gender, ethnicity and left ventricular structural parameters were associated with LA size. Importantly, the study provides reference values of normal LA volume index.

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Right ventricular (RV) function has prognostic significance in patients with pulmonary hypertension (PH). We evaluated whether cardiac magnetic resonance (CMR)-derived strain and strain rate (SR) parameters could reliably reflect RV systolic and diastolic function in precapillary PH. End-systolic elastance (Ees) and the time constant of RV relaxation tau, both derived from invasive high-fidelity micromanometer catheter measurements, were used as gold standards for assessing systolic and diastolic RV function, respectively. Nineteen consecutive precapillary PH patients underwent CMR and right heart catheterization prospectively. CMR data were compared with those of 19 control subjects. In PH patients, associations between strain- and SR-related parameters and invasive hemodynamic parameters were evaluated. Longitudinal peak systolic strain, SR, and early diastolic SR were lower in PAH patients than in controls; peak atrial-diastolic SR was higher in PH patients. Similarly, circumferential peak systolic SR was lower and peak atrial-diastolic SR was higher in PH. In PH, no correlations existed between CMR-derived and hemodynamically-derived measures of systolic RV function. Regarding diastolic parameters, tau was significantly correlated with peak longitudinal atrial-diastolic SR (r = -0.61), deceleration time (r = 0.75), longitudinal systolic to diastolic time ratio (r = 0.59), early diastolic SR (r = -0.5), circumferential peak atrial-diastolic SR (r = -0.52), and deceleration time (r = 0.62). Strain analysis of the RV diastolic phase is a reliable non-invasive method for detecting RV diastolic dysfunction in PAH.