Objective:To investigate the predictive value of intrinsic QRS duration(IQRSd) for left ventricular function deterioration in patients dependent on right ventricular apical(RVA) pacing. Methods:In this study,42 patients with third degree atrioventricular block who underwent pacemaker implantation were included. Twenty-two patients with absolute reduction value of left ventricular ejection fraction(ΔLVEF)≥5% after pacing (group with ΔLVEF≥5%) and 20 patients with ΔLVEF<5% after pacing(group with ΔLVEF<5%) were enrolled to investigate the possible reasons or predictors for the cardiac function deterioration. The examination results of 12-lead electrocardiography and echocardiography,and clinical conditions were recorded for every patient before the implantation and during the follow-up. The cumulative pacing rate of pateints were also obtained at each follow-up visit. Results:After 77.3 months of follow-up,left ventricular ejection fraction(LVEF) decreased significantly from (64.20 ± 6.30)% to (40.60 ± 10.00)%(P < 0.001) while left atrial diameter (LAD) and left ventricular end-diastolic dimension(LVEDD) enlarged significantly in group with ΔLVEF≥5%[LAD:(34.77 ± 6.42)mm vs. (41.00 ± 7.45)mm;LVEDD:(49.82 ± 4.86)mm vs. (55.59 ± 8.44)mm;P < 0.001)]. However,the average LVEF,LAD and LVEDD levels in group with ΔLVEF<5% after pacing were not statistically different from those before pacing[LVEF:(65.40 ± 3.25)% vs. (64.94 ± 3.00)%;LAD:(37.40 ± 4.84)mm vs. (38.15 ± 5.83)mm;LVEDD:(48.30 ± 3.95)mm vs.(49.00 ± 3.87)mm]. Kaplan-Meier analysis revealed that LVEF diminution after pacing appeared significantly earlier in patients with IQRSd≥110 ms than that in patients with IQRS<110 ms. Chi Square Test showed the rate of LVEF diminution was significantly higher in patients with IQRSd≥110 ms than that in patients with IQRSd<110 ms(P < 0.05). COX regression analysis indicated that IQRSd≥110 ms was the independent predictor of left ventricular systolic function decrease (P < 0.05). Conclusion:Long-term RVA pacing leads to deterioration of left ventricular systolic function and cardiac remodeling. In patients with IQRSd≥110 ms,deterioration of left ventricular systolic function occured earlier and more serious than in those with IQRSd<110 ms. IQRSd≥110 ms is the independent predictor of LVEF reduction in patients dependent on right ventricular pacing.