Reevaluation of the criterion for interatrial block.

The importance of the interatrial block has often been overshadowed by the debate on the appropriate cutoff to define its excessively wide P waves. However, by far, most publications have accepted P waves of >or=110 ms to represent abnormal interatrial conduction on the electrocardiogram. These "guidelines" have been structured on anachronistic electrocardiographic standards mostly determined from references to earlier textbooks and other publications that often did not involve original work. As such, reevaluation of the top normal value for the P-wave duration in adults is probably long overdue. We reevaluated the prevalence of interatrial block in our previously published series of 500 outpatients using existing standards for normal P-wave values and compared these results with the previous known prevalence of interatrial block to generate this present report. In conclusion, the frequency of the mode duration for P waves (120 ms) suggests electrophysiologic reevaluation of the normal range.