Interatrial Block (IAB)

1. Interatrial Block (IAB)
ANWER GHANI
FIBMS
IRAQ

2. .
It has been considered that an interatrial block exists when there is
a delay of conduction in some part of the Bachmann’s bundle zone.

3. .
The interatrial blocks are the most frequent and well-known blocks
at atrial level.

4. .
Partial IAB (P-IAB) : P wave duration that equals or exceeds 120
milliseconds and a bimodal morphology, especially in leads I, II, VL
or inferior leads.

5. .
advanced interatrial block (A-IAB): P wave morphology ± in II, III,
and VF with duration ≥120 ms.

6. .
The prolonged P wave duration (P-wave duration ≥120
milliseconds) may be present in the elderly but can also be a
consequence of acute illness, such as pericarditis or acute
myocardial infarction.

7. .
The combination of LAE with advanced interatrial block (A-IAB) is
very common but isolated cases of A-IAB may be seen.

8. .
Cutting the Bachmann’s bundle at either the right or left atrial side
results in a typical ECG pattern with wide P wave with biphasic
morphology in inferior leads.

9. .
The interatrial blocks may be of first (partial), second (transient
interatrial block is part of atrial aberrancy), or third degree
(advanced).

10. .First-degree (Partial) Interatrial Block
-The electrical impulse is conducted from the right to the LA
through the normal propagation route but with a delay.
-The ECG shows that a P wave of 120 milliseconds or more, usually
bimodal, is especially visible in leads I, II, or III.

11. Second-degree Interatrial Block
Interatrial block occurs transiently on a beatby- beat basis or may
be recorded momentarily.
The morphology of the P wave may change in the same recording
from interatrial block pattern (first or third degree) to normal
pattern, usually transiently in relation to the preceding premature
beats.
These changes may be considered as atrial aberrancy.
Atrial aberrancy may also present a transient bizarre P wave
without the morphology of interatrial block. In these cases, the
location of the block is usually the right atrium.

12. Third-degree (advanced) Interatrial Block
The electrical impulse is blocked especially in the upper and middle
part of the interatrial septum, in the Bachmann’s bundle zone,
and/or in the upper part of LA.
Retrograde left atrial activation occurs mainly via muscular
connections in the vicinity of coronary sinus.
In rare occasions, the right atrium and LA can demonstrate
dissociated electrical activity.

13. Third-degree (advanced) Interatrial Block
The ECG shows that
(a) P wave duration of 120 milliseconds or more.
(b) the morphology of P wave is usually biphasic [±] in leads II, III,
and VF ( and also often in V1 to V3)
The electrophysiological mechanism underlying this ECG pattern has been explained using deductive ECG-VCG data.

14. Third-degree (advanced) Interatrial Block
In dogs, the same biphasic morphology appears after cutting the
Bachmann’s bundle at the right and left sides of the septum.
Atrial fibrosis is considered the anatomic substrate of A-IAB, which
does not necessarily mean that the LA is enlarged.
P wave (biphasic in inferior leads) that pinpoints that there is a
retrograde activation of the LA.
This type of block is very frequently accompanied by paroxysmal
atrial arrhythmia.

15. .
.

16. Inter-Atrial Block degrees
1st
d: pIAB: prolonged P-wave duration>120 ms.
2nd
d: tIAB: transient IAB, ( a, p)
3rd d: aIAB : prolonged P-wave duration>120ms + biphasic P-wave
morphology.
- Bayés syndrome: The association of A-IAB and AF.

17. .
The prevalence of partial (P) and advanced A–IAB is rare before
the age of 50.
The prevalence is much higher with advancing age.
In patients with heart failure a prevalence of A-IAB of 10 %.

18. .
The advanced IAB group presented a higher incidence of atrial
flutter/fibrillation during a 30-month follow-up compared with
partial IAB.
At one year of follow-up, the incidence of arrhythmias was 80 %
and 20 % of AIAB and PIAB respectively.
The prevalence of frequent premature atrial contractions (more
than 60/h by Holter) was much more frequent in advanced (75 %)
than in partial (25 %) IAB.

19. Bayés syndrome
The association of A-IAB and AF has been called Bayés syndrome.

20. .
The strong relationship between advanced IAB and atrial flutter/
fibrillation suggests the possible role of preventing atrial
arrhythmias using antiarrhythmic drugs.
A small comparative trial of patients with advanced IAB received
either an antiarrhythmic drug or a placebo.
A significant reduction of AF recurrences was observed at follow-up
in the group receiving prophylactic antiarrhythmic medication.

21. BAYÉS SYNDROME
Bayés syndrome is a new
clinical entity, characterized
by the association of
advanced interatrial block
(IAB) on surface

22. .
.

23. BAYÉS SYNDROME
In 1988, Bayés de Luna et al.1 reported that patients with advanced interatrial
block (IAB) presented with supraventricular arrhythmia more often than
patients with partial IAB. However, until a consensus article was published
on IAB in 2012,2 only a few authors had shown interest in the subject,
mainly the groups led by Spodick,3 García-Cosío,4 and Platonov,5 as well
as our own group.6,7 Since this consensus article was published, there has
been growing interest, and Conde and Baranchuk8 named this
combination “Bayés syndrome,” a term quickly accepted by the scientific
community.

24. THANKS
The reference: Antoni Bayés de Luna,Albert Massó-van Roessel,Luis Alberto Escobar Robledo;
The Diagnosis and Clinical Implications of Interatrial Block.European Cardiology Review
2015;10(1):54–9