Effect of long-term atrial-demand ventricular pacing on cardiac sympathetic activity

It has been shown that either dual-chamber or atrial pacing may be better t han ventricular single-chamber pacing, but the long term effect of dual-cha mber pacing on cardiac sympathetic activity is unclear. The aim of this stu dy was to assess the effect of long-term dual-chamber pacing on cardiac sym pathetic activity, compared with atrial pacing and unpaced individuals. We studied 11 patients with dual-chamber pacemakers (Group D), nine with atria l single-chamber pacemakers (Group A) over the long term (mean 44+/-36 mont hs) and 10 normal individuals without cardiac pacing. All underwent myocard ial I-123-metaiodobenzylguanidine (MIBG) imaging to assess cardiac sympathe tic activity. The heart-to-mediastinum (H/M) MIBG uptake ratio and the MIBG washout rate from the myocardium were calculated. Echocardiography was per formed in all patients with cardiac pacing to assess left ventricular funct ion. In Group D, the H/M ratio on delayed images was significantly lower th an that of Group A (1.82+/-0.51 vs 2.56+/-0.50, P<0.001) and normal individ uals (2.65+/-0.35, P<0.05). The myocardial MIBG washout rate of Group D was significantly higher than that of either Group A (52+/-13% vs 36+/-8%, P<0 .01) or normal individuals (31+/-7%, P<0.05). Neither the H/M ratio nor MIB G washout rate differed significantly between patients in Group A and norma l individuals. Furthermore, the echocardiographic parameters did not differ significantly between the two pacing groups. We conclude that long-term ve ntricular pacing, even in the presence of atrioventricular synchrony, accel erates cardiac sympathetic activity without deteriorating left ventricular function. ((C) 2000 Lippincott Williams & Wilkins).