Long–Term Effect of VVI Pacing on Atrial and Ventricular Function in Patients with Sick Sinus Syndrome

We conducted a prospective, 6–month echocardiographic study on the effect of WI pacing on left atrial and ventricular function and dimensions in patients with sick sinus syndrome. Thirty nine patients (23 women and 16 men, aged 71.7 ± 9.2 years; 30 in sinus rhythm and 9 in atrial fibrillation) who had a WI pacemaker implanted because of sick sinus syndrome were recruited in the study. In 26 patients who presented with and remained in sinus rhythm, paced left ventricular ejection fraction and stroke volume were significantly decreased (71.4%± 11.8% to 67.0%± 13.6%, and 73.9 ± 29.0 cm3 to 66.3 ±21.1 cm3, respectively, P < 0.001 for both), whereas the paced diastolic dimension of the left atrium was significantly increased (3.2 ± 0.7 cm to 3.7 ± 0.9 cm, P < 0.001) at 6 months as compared with preimplantation. In nine patients with atrial fibrillation at implantation, paced left ventricular ejection fraction at follow–up was significantly decreased (67.7%±10.1% to 64.2%± 10.6%, P = 0.003), but paced stroke volume and left atrial diastolic dimension were not significantly changed (75.1 ± 25.6 cm3 to 79.0 ± 22.7 cm3, and 4.3 ±1.2 cm to 4.6 ±1.5 cm, P = NS for both) at follow–up. Cessation of pacing and restoration of sinus rhythm in 21 patients at follow–up did not result in any significant change of ejection fraction (67.5%± 10.2% to 67.6%± 9.7%, P = NS) whereas stroke volume was increased (59.1 ± 19.6 cm3 to 69.1 ± 22.3 cm3, P < 0.0001) in comparison with paced values. However, compared with preimplantation values, ejection fraction was significantly decreased (70.4%± 10.0% to 67.6%± 9.7%, P = 0.001), whereas stroke volume was not significantly changed (68.4 ± 22.3 cm3 to 69.1 ± 22.3 cm3, P = NS) during sinus rhythm at follow–up. In 14 of those patients, discontinuation of pacing resulted in a significant increase of left atrial fractional shortening (8.1 %± 1.7% to 20.1 %± 4.3%, P < 0.001) and significant increase of left atrial diastolic dimension compared with paced and preimplantation levels (3.8 ± 0.7 cm vs 3.6 ± 0.7 cm and 3.0 ± 0.5 cm, respectively, P < 0.001). Long–term WI pacing in patients with sick sinus syndrome results in increase of the left ventricular end–systolic dimension and permanent reduction of the left ventricular ejection fraction. In the left atrium, WI pacing causes an immediate reduction of the fractional shortening as well as long–term increase of the diastolic dimension.