Left atrial volume and function assessed by cardiac magnetic resonance imaging are markers of subclinical atrial fibrillation as detected by continuous monitoring

We aimed to investigate whether left atrial (LA) markers from cardiovascular magnetic resonance (CMR) were able to predict atrial fibrillation (AF) in elderly patients with risk factors for stroke.

At baseline, 203 participants with stroke risk factors but without history of AF underwent advanced CMR and received an implantable loop recorder. During a median of 40 (37–42) months of continuous monitoring, incident AF was detected in 79 patients (39%). With regards to CMR markers, a steep increase in incidence rate of AF was seen with LA maximum volume (LA_max) above 55 mL/m², LA minimum volume (LA_min) above 30 mL/m², LA total emptying fraction (LA TEF) below 45%, LA active emptying fraction (LA AEF) below 37%, LA strain S below 25%, LA strain A below 17%, and LA strain rate A above −1.7 s⁻¹. After multivariate adjustment, the above-mentioned CMR markers remained associated with AF incidence: hazard ratio (95% confidence interval) 1.25 (1.06–1.48) and 1.51 (1.22–1.87) per 10 mL/m² increase of LA_max and LA_min, respectively, 1.49 (1.26–1.76) and 1.46 CI (1.25–1.71) per 5% decrease in LA TEF and LA AEF, respectively, 1.23 (1.05–1.44) and 1.56 (1.18–2.06) per 5% decrease in LA strain S and A, respectively, and 2.06 (1.31–3.23) per s⁻¹ increase in LA strain rate A. In prediction analyses, LA functional indices increased area under the receiver operating characteristic curve significantly.

The risk of AF, including asymptomatic AF, increases significantly with increasing LA volumes and worsening LA function.