Quantification of atrial dynamics using cardiovascular magnetic resonance: inter-study reproducibility

Abstract

Background: Cardiovascular magnetic resonance (CMR) offers quantification of phasic atrial functions based on volumetric assessment and more recently, on CMR feature tracking (CMR-FT) quantitative strain and strain rate (SR) deformation imaging. Inter-study reproducibility is a key requirement for longitudinal studies but has not been defined for CMR-based quantification of left atrial (LA) and right atrial (RA) dynamics.

Methods: Long-axis 2- and 4-chamber cine images were acquired at 9:00 (Exam A), 9:30 (Exam B) and 14:00 (Exam C) in 16 healthy volunteers. LA and RA reservoir, conduit and contractile booster pump functions were quantified by volumetric indexes as derived from fractional volume changes and by strain and SR as derived from CMR-FT. Exam A and B were compared to assess the inter-study reproducibility. Morning and afternoon scans were compared to address possible diurnal variation of atrial function.

Results: Inter-study reproducibility was within acceptable limits for all LA and RA volumetric, strain and SR parameters. Inter-study reproducibility was better for volumetric indexes and strain than for SR parameters and better for LA than for RA dynamics. For the LA, reservoir function showed the best reproducibility (intraclass correlation coefficient (ICC) 0.94-0.97, coefficient of variation (CoV) 4.5-8.2%), followed by conduit (ICC 0.78-0.97, CoV 8.2-18.5%) and booster pump function (ICC 0.71-0.95, CoV 18.3-22.7). Similarly, for the RA, reproducibility was best for reservoir function (ICC 0.76-0.96, CoV 7.5-24.0%) followed by conduit (ICC 0.67-0.91, CoV 13.9-35.9) and booster pump function (ICC 0.73-0.90, CoV 19.4-32.3). Atrial dynamics were not measurably affected by diurnal variation between morning and afternoon scans.

Conclusions: Inter-study reproducibility for CMR-based derivation of LA and RA functions is acceptable using either volumetric, strain or SR parameters with LA function showing higher reproducibility than RA function assessment. Amongst the different functional components, reservoir function is most reproducibly assessed by either technique followed by conduit and booster pump function, which needs to be considered in future longitudinal research studies.

Fig. 1

Quantification of atrial function as derived from volumetric analysis and CMR-FT derived strain and strain rate (SR) parameters. Atrial analysis comprised reservoir, conduit and booster pump function. For the calculation of fractional volume changes, atrial volumes were measured in three time frames according to the maximum (Vmax), minimum (Vmin) and atrial volume prior to atrial contraction (Vpac) resulting in ‘EF Total’ corresponding to reservoir function and global atrial function, ‘EF Passive’ corresponding to conduit function and ‘EF Booster’ corresponding to atrial contractile booster pump function (please see equations in the methods section under volumetric analysis). Total strain (ε_s) and peak positive strain rate (SRs) correspond to reservoir function. Passive strain (ε_e) and peak early negative strain rate (SRe) correspond to conduit function. Active strain (ε_a) and peak late negative strain rate (SRa) correspond to contractile booster pump function

Fig. 2

Atrial strain and strain rate profiles. Left and right atrial strain and strain rate profiles are displayed for all three Exams A-C. The three curves displayed for each parameter represent an average of the whole study group for the first, the second and the third CMR examination (Exams A-C) respectively (please see colour codes)