The premature atrial stimulus technique was used to evaluate sinoatrial conduction (SAC) in 50 children (age range 6 months to 21 years; median 6.5 years) to obtain normal values of sinoatrial conduction time (SACT) and to determine the usefulness of the technique in evaluation of sinoatrial node (SAN) dysfunction in children. The results in the normal group (n= 20) were compared with those of patients with documented SAN dysfunction (group 1, n= 20) or at risk todevelop SAN dysfunction because of a previous intracardiac operation (group 2, n= 10). Among the 30 patients in groups 1 and 2, 23 had undergone an intra-cardiac operation 13 Mustard operations and five closures of an atrial septal defect. In group 1, the mean value of total SACT was 172 msec±42 (SD) compared with 124 msec±38 in the nor-mal group (p< 0.001). Each of the 20 patients in group 1 had abnormal SAN automaticity (prolonged cor-rected sinus node recovery time, CSNRT) and 13 of the 20 had abnormal SAC. While each of the 10 patients in group 2 had normal CSNRT, two of them had abnormal SAC. We conclude that the evaluation of SAC should be included in the assessment of children with suspected SAN dysfunction.

CORRECTED SINUS NODE RECOVERY TIME (CSNRT) isan indicator of the automaticity of the sinoatrial node (SAN) and has been useful in confirming known or suspected SAN dysfunction.'7 Some patients, however, have clinical manifestations of SAN dysfunction but have normal CSNRT. 5-1'The presence of prolonged sinoatrial conduction time (SACT) invalidates the reliability of CSNRT, since the rapidly paced atrial impulses may not reach the SAN in sufficient number to suppress the SAN. Normal recovery of the unstressed SAN could then occur at the termination of the pacing despite SAN dysfunction. The recent introduction by Strauss et al. 1" of an indirect method to calculate SACT in man has been valuable in identifying previously unrecognized SAN dysfunction in adult patients. 6'-'Based on preliminary reports, 16'17 the technique also may be valuable in assessing SAN function in children. This study was undertaken to 1) obtain normal values of SACT in children without SAN dysfunction; 2) determine SACT in children with abnormal SAN automaticity; 3) determine SACT in patients with normal CSNRT but who have had an intracar-diac operation, with emphasis on children who have had operations involving the right atrium.