The presence of subclinical atrial fibrillation (SCAF) is relevant to issues such as the risk of stroke and the necessity of anticoagulant use in patients with cardiac resynchronization therapy (CRT). Our study aimed to investigate SCAF frequency and associated parameters in patients with CRT.

One hundred ninety-one patients with CRT (77 females, 114 males, mean age 65.9 ± 9.8) were included in the study. Atrial high-rate episodes detected by the device, atrial electrode impedance, P-wave sense amplitude, and atrial lead threshold values were measured during pacemaker controls. SCAF was defined as asymptomatic atrial high-rate episodes (AHRE) longer than 6 min and shorter than 24 h. Patients were divided into two groups as with and without SCAF.

SCAF was detected in 44 (23.2%) of 191 patients with CRT. Age, sex, weight, aortic end-systolic diameter, left atrium (LA) diameter, left bundle branch block morphology, CHA₂DS₂-VASc score, and right atrium thresholds were associated with SCAF. In multivariate regression analysis, CHA₂DS₂-VASc score, LA diameter, and atrial threshold values were found to be independent predictors of SCAF occurrence. According to this analysis, every 1 point increase in CHA₂DS₂-VASc score, every 1 mm increase in LA diameter, and every 0.1 V increase in atrial threshold increased the risk of SCAF by 32.5, 59.6, and 14.6%, respectively. In the ROC analysis, the area under the curve (AUC) was 0.870, 0.638, and 0,652 for LA diameter, CHA2DS2-VASc score, and atrial lead threshold, respectively (p < 0.05, for all). The cut-off values were 34 mm, 3, and 0.6 V for LA diameter, CHA2DS2-VASc score, and atrial lead threshold, respectively.

Patients with CRT have significantly higher frequency of SCAF than the normal population. CHA₂DS₂-VASc score, LA diameter, and atrial threshold values were considered to be useful and easily applicable parameters in identifying the patients to develop SCAF.