Congenital complete heart block (CCHB) has been associated to the dilation of the ascending aorta (AsAo). Several mechanisms, such as increased stroke volume, have been proposed. We hypothesized that pacemaker (PM) implantation, known to reduce stroke volume in complete heart block, would help the regression of AsAo dilation in CCHB.

We aim to describe our experience on the effects of chronic PM on aortic dilation in CCHB with structural normal hearts.

METHODS
Retrospective review of echocardiograms was performed for patients with CCHB and structural normal heart in whom PM was implanted in the last 24 years at our institution. Z-scores of aortic segments were analyzed. Relative AsAo dilation was defined as AsAo/aortic annulus ratio >2SD based on normal values from 250 controls.

RESULTS
Twenty-five patients met inclusion criteria. Average age at PM was 4,0±3,8 years with mean follow-up of 7,8±5,6 years. Z-score of the aortic valve annulus was similar before and after PM (0,32±0,76 vs 0,49±1,23, p=0,21). Increased AsAo/aortc valve ratio was observed in 29,4% of the patients without significant dilation of aortic root ratio. Relative AsAo Z-score regressed from 1,82±2,89 to 1,65±1,64 (p=0,001). While within normal limits, the Z-score of ortic root ratio regressed from 0,12±0,89 to 0,005±0,51 (p=0,001).

CONCLUSION
Ascending aorta dilation is present in a large proportion of patients with CCHB. Our observations of relative AsAo regression following chronic dual chamber pacing support our hypothesis that large stroke volume in non-paced CCHB is the primum-movens of AsAo dilation.