Advanced interatrial block: a well-defined electrocardiographic pattern with clinical arrhythmological implications

We read with interest Hinojar et al.1 case recently published in the journal. Their case wisely demonstrated the presence of P-wave with +/− morphology in leads II, III, and aVF as a pattern of advanced interatrial block (IAB). This pattern has been also called ‘block in the Bachmann bundle zone’ since Waldo obtained this electrocardiogram (ECG) pattern by cutting the Bachmann bundle at both sides of the septum [right and left atrium (LA)].2 The electroanatomical mapping (CARTO) showed by Hinojar et al. in sinus rhythm clearly shows that the atrial activation starts normally, but its propagation is blocked along the LA roof and the high lateral activation is delayed and directed caudocraneally starting at the posteroinferior LA region. Therefore, this type of atrial activation may be explained by two vectors: the first positive component of the P-wave in a craneocaudal direction, and the second negative component of the P-wave due to caudocraneal activation. This ECG pattern was reported several decades ago.2,3 Later, our group redefined the concept and also determined the ECG–vectocardiography diagnostic criteria.4 A very frequent association with supraventricular tachyarrhythmias (atypical flutter and atrial fibrillation) was also reported.5,6 The presence of atrial tachyarrhythmias in a 2-year follow-up occurs in 94% of patients with advanced IAB, being atrial flutter the most frequent presentation (69% of cases), and only in 28% of the control group. This led different authors7–9 to consider that the association of advanced IAB (long P-wave duration + ECG pattern consisting in P-waves in leads II, III, and aVF with +/− morphology) with atrial arrhythmias constitutes an arrhythmological syndrome. Therefore, the case of Hinojar et al., is a clear example of the association mentioned above, and reintroduces the idea of considering antiarrhythmic treatment when this type of interatrial block is detected. Indeed, we suggested this idea in a small series presented more than two decades ago.9 However, whether antiarrhythmic treatment should be used to prevent arrhythmias in asymptomatic patients with advanced IAB needs to be tested in a large prospective trial. We would like to offer our view on the title of Hinoja's paper ‘Bachmann block pattern resulting from inexcitable areas peripheral to the Bachmann's bundle: controversial name or concept?’. A consensus paper on IAB was recently published.10 In this manuscript, the terminology and classification was established and an analogy to other blocks in the human electrical system was made to classify IABs. In that sense, it was proposed that partial or advanced IAB should be used to define a P-wave duration ≥120 ms (first degree or partial) or a P-wave duration ≥120 ms plus +/− morphology in leads II, III, and aVF (third degree or advanced). This purely ECG classification is independent of the location of block along the Bachmann region. As we have already commented, Waldo demonstrated11 that the section of the Bachmann in dogs at the right or left atrium level always produced the same ECG pattern (P-wave with +/− morphology in leads II, III, and aVF). Therefore, there is no doubt about what causes the ECG morphology during advanced IAB. To us, this resolves the rhetorical question of the Hinojar's manuscript's title. The long-lasting existence of this ECG phenomenon (IAB) has followed the historical rules to accept and ECG pattern due to a block:11–13 In conclusion, Hinojar et al.1 should be congratulated to demonstrate another case of advanced IAB associated to atypical atrial flutter using CARTO. Given the mounting evidence that led to a consensus paper recently published,10 we believe that both the name and the concept are not controversial. It has been experimentally reproduced; Clinical reproducibility (‘transient or reversible’ phenomenon) has been demonstrated; It has been detected as an isolated electrical finding (rare). Conflict of interest: none declared.