New pattern of atypical advanced interatrial block

Interatrial block (IAB) is defined as prolonged P-wave duration (≥ 120 ms) due to delayed conduction in the Bachmann bundle. This is readily identifiable using surface electrocardiogram (ECG). Advanced IAB can be classified as typical and atypical. Atypical IAB can be further categorized by (i) duration or (ii) morphology. In this report, we have identified a new pattern of atypical IAB with triphasic morphology of the P-wave in the inferior leads.Two clinical cases were evaluated including surface ECGs. P-wave durations and amplitudes were measured with digital calipers using ECG analysis software (MUSE, GE HealthCare). Comparisons were made using prior data to evaluate IAB and P-wave duration and morphology.A new pattern of atypical advanced IAB shows prolonged P-wave duration (P wave >160 ms) and triphasic morphology in all inferior leads with P +/+/- and P +/-/+, respectively. We speculate that triphasic P-waves in the inferior leads represent three moments of atrial depolarization; from right to left.This study describes a novel pattern of atypical advanced IAB. Further investigation regarding the increased risk of atrial fibrillation and stroke associated with this new pattern is warranted in the future.