PACING IN CHILDREN

236 CHRONIC SECOND-DEGREE ATRIOVENTRICULAR BLOCK IN INFANTS AND CHILDREN. Robert Stanton, Arno Hohn. Childrens Hospital Los Angeles, University of Southern California, Los Angeles, California, U.S.A. Chronic second-degree atrioventricular (A-V) block is uncommon in children. Our purpose is to describe the course of 6 children with such block in order to better assess the natural history of the process and to establish methods of management. The age when first seen was 5 months to 6 years with a mean of 3 yrs. Four children had no heart disease; 2 had congenital heart disease with 1 developing Mobitz type II A-V block 3 yrs. after surgery for a septal defect, and the other with L-transposition of great arteries and type II A-V block. Seconddegree A-V block progressed to' complete heart block in 3 pts., and there was a gradual reduction of ventricular rates with symptomatic changes in the other 3 pts. All were treated with a permanent pacemaker with no further problems in a follow-up of 600 pt. months. Chronic second-degree A-V block is not a benign condition, but it may require yrs. for children to develop symptoms. Management should include permanent pacing in the symptomatic pt., those with surgical complete heart block and those with heart rates below 40 beats/minute in order to avoid the risk of sudden death. 238 INITIAL HISTOLOGIC COMPARISONS BETWEEN APICAL AND A NEW SEPTAL VENTRICULAR PACING METHOD IN IMMATURE CANINES Peter P Karpawich, Chung-Ho Chang, Lawrence R Kuhns, Cheryl D Justice. Children's Hospital of Michigan, Wayne State University, Detroit, USA Ventricular (V) pacing (WI) from an apical (A) implanted electrode (E) alters V depolarization (Dp) producing myofibrillar disarray (MD). To determine if MD can be avoided in the paced V by more normal V Dp, 10 beagle puppies (age 3 mos) underwent atrioventricular block followed by W I pacing. In 5 a Medtronic model 6917-35T E was attached to the right ventricular apex and in 5 a modified model 4951 E was inserted into the aortoatrial groove and positioned in the proximal septum (S). V Dp patterns were confirmed using multigated nuclear imaging and epicardial electrograms. After 4 mos pacing, matched tissue samples were obtained from both paced groups and 3 agematched controls. The A paced group showed bundle branch Dp, MD, calcium deposits (CD) and mitochondrlal changes (MC). The S paced group showed nearly normal surface QRS and V Dp patterns; normal myofibrillar arrangements and absence of CD and MC. Conclusion: Abnormal cellular development in the paced immature myocardium may be prevented by more normal paced V Dp achievable with a new septal pacing method.