BACKGROUND: Left atrial reservoir strain (LASr) is an established marker of left atrial (LA) mechanical dysfunction and may identify early remodeling preceding HFpEF in patients undergoing conventional right ventricular (RV) pacing. OBJECTIVE: To identify early determinants of impaired LASr at 12 month follow-up after conventional right ventricular pacing. METHODS: Fifty-two patients undergoing conventional right ventricular pacing were prospectively enrolled. TTE was performed at baseline, 3 months, and 12 months. Left ventricular (LV) mechanical dispersion (LVMD), global longitudinal strain (LVGLS), diastolic function indices, and LA strain parameters were assessed. Patients were stratified according to 12-month LASr, with values <25% defining impaired LA mechanics. RESULTS: Nineteen patients (36.5%) developed impaired LA mechanics. Baseline clinical and echocardiographic parameters were comparable between groups. At 3 months, patients who subsequently developed impaired LA mechanics exhibited significantly greater LVMD (56 ± 11 vs. 42 ± 9 ms, p < 0.001), reduced LVGLS (-17.2 ± 2.1% vs. -18.4 ± 1.9%, p = 0.03), and higher E/e' ratio (12.3 ± 2.5 vs. 10.9 ± 2.2, p = 0.04), while LASr remained similar between groups. On multivariable analysis, 3-month LVMD independently predicted impaired LASr at 12 months (OR 2.04, 95% CI 1.18-3.52, p = 0.01). ROC analysis demonstrated that LVMD had the highest discriminatory performance (AUC 0.84, 95% CI 0.75-0.93). CONCLUSIONS: Early LVMD develops before overt atrial dysfunction following conventional right ventricular pacing. LVMD is an independent predictor of subsequent impairment in LA mechanics and may identify patients at risk for adverse atrial remodeling before the onset of clinically apparent heart failure.