Intra-observer repeatability of 2D Simpson atrial volumes within a single transthoracic echocardiography session

Diagnostic and monitoring decisions often rely on a single measured atrial volume compared with a fixed threshold or a prior visit’s value. Many treatment plans rely on this single echocardiographic measurement, and we sought to determine whether a single 2D Simpson measurement obtained by an experienced operator is sufficiently repeatable within a single session. In this single-center cross-sectional study, we included adults with sinus rhythm who underwent routine TTE. Four experienced echocardiographers each measured left and right atrial volumes (LAV4, LAV2, RAV4) across three consecutive cardiac cycles within one imaging session. Repeatability was quantified using intraclass correlation coefficient (ICC), coefficient of variation (CV), repeatability coefficient (RC), standard error of measurement (SEM), minimal detectable change (MDC), precision, and least significant change (LSC). An exploratory post hoc subgroup analysis stratified patients into quartiles of atrial volume. Among 351 patients assessed by four observers, intra-observer repeatability was high overall (ICC 0.866–0.994), strongest for Observers 2 and 3 (CV 3.2–6.0%) and weakest for Observer 4’s RAV4 (ICC 0.866; CV 10.3%). LAV was consistently more repeatable than RAV (CV 3.2–8.5% vs. 3.9–10.3%). MDC ranged from 5.1 to 12.7 mL, defining the smallest change distinguishable from tracing noise. Within a single session, intra-observer repeatability of 2D Simpson atrial volumes was high among experienced operators in sinus rhythm. These findings apply to expert interpreters in a tertiary referral setting and should not be extrapolated to atrial fibrillation, less-experienced operators, inter-observer agreement, between-session reproducibility, or measurement accuracy against a reference standard.