P13.04: Echo AV interval overestimates MCG PR interval in SSA+ pregnancies: evidence for new criteria for 1° AV block

Abstract

We compared simultaneous fetal echo AV intervals (E-AV) and magentocardiogram (fMCG) PR intervals (M-PR) in SSA+ and control pregnancies to determine if an AV interval of + 2 z-scores correlated with a prolonged M-PR interval and 1° AV block. We searched the database of the University of Wisconsin Biomagnetism laboratory for pregnant women referred for fMCG with SSA antibodies. Maternal and pregnancy data were obtained from the mother's medical record. Fetal MCGs were performed using a 37-channel biomagnetometer (Magnes, 4D Neuroimaging, Inc). During the same session, we measured and averaged PR and cardiac RR intervals from 5 rhythm tracings and compared results to Echo Doppler AV interval (mitral inflow/aortic outflow) and RR intervals. Results were normalised for RR interval and compared by paired t-test. Regression analysis was used to test associations between gestational age (GA) and cardiac intervals. The mean M-PR was 23.3 ms less than the mean E-AV (95% CI: 20.1,26.5, p<0.001); this statistically significant difference persisted when normalised for RR interval. There were no significant differences between SSA and controls for RR, PR, or AV intervals. Neither E-RR interval or GA were associated with predicting E-AV; nor were M-RR or GA associated with predicting M-PR. However, the interaction between E-AV interval and GA were significantly associated with the AV-PR difference of 23.3 ms. Our results suggests that E-AV overestimates M-PR in both SSA and controls. Using the previous definition of 1° AVB (an AV interval of 150 ms) may result in unnecessary treatment of SSA+ normal fetuses. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.