Short-term repeatability of electrocardiographic P wave indices and PR interval

Abstract Background P wave indices and PR interval from 12-lead electrocardiograms (ECGs) are predictors of cardiovascular morbidity and mortality, but their repeatability has not been examined. Objectives Determine the short-term repeatability of P wave indices (P axis, maximum P area and duration, P dispersion and P terminal force in V1) and PR interval. Methods Participants (n = 63) underwent two standard ECGs at each of two visits, two weeks apart. We calculated the intra-class correlation coefficient (ICC), weighted kappa, and minimal detectable change and difference. Results ICCs were 0.93 for PR interval, 0.78 for P axis, 0.77 for maximum P area, and 0.58 for maximum P duration. Within- and between-visit Kappa were 0.30 and 0.11 for P dispersion, and 0.68 and 0.46 for P terminal force. Conclusion Repeatability of PR duration was excellent, that of P wave axis and maximum area was fair, and maximum P wave duration and terminal force was poor. Repeatability of P wave dispersion was fair within visit, yet poor between visits. These results illustrate potential biases when measurement error of some P wave indices is ignored in clinical and epidemiologic studies.