Advanced Interatrial Block: A Classic Electrocardiogram

Abstract

Interatrial block (IAB; P wave ≧110 ms) indicates conduction delay between the right and left atria. IAB can present as partial or advanced and is denoted on the electrocardiogram (ECG) by bifid or biphasic P waves, respectively, the latter in inferior leads. The importance of IAB cannot be overemphasized due to high prevalence, especially at ages 60 and over, and due to grave associations with atrial flutter and fibrillation as well as congestive heart failure. Thus, we present a classic ECG of the much less common form of IAB, namely advanced IAB, as it serves as an excellent yardstick and teaching tool to help clinicians understand this medical entity thoroughly and to easily recognize this often missed type of block.

Variable Interatrial Conduction Illustrated in a Hypertrophic Cardiomyopathy Population

“…It has previously been suggested that biphasic P waves in inferior leads (12‐lead ECG) or in Lead Y (orthogonal lead configuration) are most likely due to Bachmann's bundle block producing an advanced intraatrial block 23,30 . Unexpectedly, 14% of the HCM patients in the present study were found to have biphasic P waves in Lead Y, compatible with Bachmann's bundle block (Type 3).…”

“…This should be compared with 2% of the control subjects and a prevalence in the general population of 1%, according to previous studies 30 . As shown in Figure 2C, the presence of a biphasic Lead Y was always accompanied by a biphasic Lead Z; hence the activation direction was not only characterized by the superior–inferior–superior route but also a posterior–anterior–posterior propagation, indicating not only a Bachmann's bundle block 23 but also a block or a delayed conduction in the posterior route 7,8…”

“…Nine (14%) HCM patients and one (2%) control subject exhibited a pattern of advanced interatrial block, compatible with sinus rhythm and Bachmann's bundle block (positive Lead X, biphasic Lead Y (negative mode > 40 ms) and biphasic Lead Z; illustrated in Figure 2C 23 . These subjects were included in the subsequent analyses and the morphology pattern was labeled Type 3.…”

“…Type 3 P‐wave morphology (C) was identified in 11 patients (10 HCM patients and 1 control subject). The pattern is compatible with Bachmann's bundle block 23 . Two patients from the HCM population were excluded from subsequent analysis because of P‐wave morphology noncompatible with sinus rhythm (i.e., predominantly negative Lead Y).…”

P-wave dispersion: an update

“…This P-wave morphology is uncommon in healthy subjects. Electrical impulse is blocked/delayed in Bachmann's muscular interatrial bundle (BB), but retrograde left atrial activation usually occurs [55]. Note the existence of an open angle between the vector of the first portion of the P-wave (RA) and the last portion (LA).…”