Optical mapping of activation patterns in an animal model of congenital heart block

Congenital heart block (CHB) is associated with high mortality and affects children of mothers with autoantibodies (IgG) to ribonucleoproteins SSB/La and SSA/Ro. IgG from mothers of children with CHB (positive IgG) was used t o assess activation patterns in both the right atrium (RA) and right ventri cle (RV) of Langendorff-perfused young rabbit hearts. Optical action potent ials (AP) were obtained by using a 124-site photodiode array with 4-[-[2-(d i-n-butylamino)-6-naphthyl] vinyl] pyridinium. Optical APs were recorded to simultaneously image activation patterns from the RA and RV. Perfusion of positive IgG (800-1,200 mug/ml) resulted in sinus bradycardia and varying d egrees of heart block. Activation maps revealed marked conduction delay at the sinoatrial junction but only minor changes in overall atrial and ventri cular activation patterns. No conduction disturbances were seen in the pres ence of IgG from mothers with healthy children. In conclusion, besides atri oventricular (AV) block, positive IgG induces sinus bradycardia. These resu lts establish that the sequelae of CHB are associated with impaired intrasi nus and/or sinoatrial conduction. The findings raise the possibility that s inus bradycardia in the developing heart may indicate the potential for AV conduction disturbances.