Introduction: Atrial fibrillation (AF), the most com-mon cardiac arrythmia, is one of the major cardiovas-cular morbidity and mortality factors worldwide. Left atrial (LA) structural remodeling is one of the pathoge-nic mechanisms involved in the occurrence and persis-tency of AF. It is known that the degree of LA dilatation, as a structural remodeling marker, is highly associated with AF. The determination of the LA dilatation degree by measuring the LA diameters and volumes (even normalized to the body surface area – BSA) is impor-tant to compare data from different studies.

Objective: In this pilot study, we compared LA para-meters determined by magnetic resonance imaging (MRI – gold standard) with echocardiography results of healthy volunteers and patients with atrial fibrillation (w/o LA fibrosis at MRI).

Methods: The study imATFIB is an observational, sin-gle center study run at the County Clinical Emergency Hospital of Cluj-Napoca (NCT03584126). The study was approved by the local ethics committee. Healthy volunteers and patients with AF underwent clinical examinations by electrocardiography, echocardiogra-phy and cardiac MRI. We compared LA parameters determined by echocardiography (area-length method, biplane A4c and A2c) with those determined by MRI for 25 healthy volunteers and 25 patients with AF. For patients with AF, a subgroup analysis of the LA volume based on the presence and absence of fibrosis at MRI was conducted, too. For the statistical analysis, we used the non-parametric Mann-Whitney t-test (p<0.05 was considered significant). Values reported are medians with confidence intervals.

Results: T he median age of the analyzed 50 subjects was 53 [49–63] years (51[45.5–54] for healthy volunte-ers and 60 [51.5–68] for patients with AF, respectively). The sex distribution was identic in the two groups (8W/17M). The median value of LA volume determi-ned by cardiac MRI (VASIRM) was 81.0 [62.3–105.9] cm³ (n=50). Similar value, VASeco=76.9 [54.1–111.3] cm³ (n=50), was obtained by echocardiography, too. There were no statistical differences between the two groups present (p=0.328). Neither at the subgroup analysis were differences present: for healthy volunte-ers – VASIRM_M =63.1 [49.8-76.9] cm³ vs. VASeco_ M=57.3 [44.7-69.1] cm³ (pM=0.07, nM=25); whereas for patients with AF – VASIRM_P=101.9 [82.0–125.4] cm³ vs. VASeco_P=110.9 [86.2–140.4] cm³ (pP=0.812, nP=25). Moreover, neither at patients with fibrosis, nor without fibrosis, were differences observed: VASIRM_ fibr=111.3 [100.3–140.2] cm³ vs. VASeco_fibr=132.3 [108.3–160.1] cm³ (pfibr=0.769, nfibr=10); VASIRM_ nofibr=98.6 [77.4–118.1] cm³ vs. VASeco_nofibr=89.6 [66.9–131.9] cm³ (pnofibr=0.999, nnofibr=15). The si-milarities were confirmed for all cases when analyzing LA volumes normalized to the BSA as well.

Conclusions: In this pilot study on healthy volunteers and patients with atrial fibrillation, no significant diffe-rences were observed in the LA volume determined by echocardiography as compared with the gold standard (magnetic resonance imaging). Although the num-ber of subjects included in the study is relatively low (n=50), they were well characterized by a full clinical evaluation. We consider the LA volume determination by echocardiography validated and propose a clinical study for validation of this diagnostic parameter in a large cohort of patients with different etiologies.