Definition

  IAB is the delay of left atrial depolarization.

  P wave duration must be
> 120 msec ( >3 mm or >3 small squares on standard ECG ).

  P wave is frequently
notched.



Interatrial block

  Generally, it is due to the delay of conduction in the Bachmann bundle zone,

      between right and left atria.

  IAB
may appear transiently.

  Atrial enlargement is NOT necessary for the development of IAB.

  However, left atrial abnormality (LAA)
frequently coexists with IAB (88%).

  Patients with IAB are reported to have a sluggish, poorly contractile left atrium.

  IAB is seen more frequently

            - in men

            - over the age of 60 years




Types of interatrial block

  Type 1: Only the P wave duration is >120 ms.

                Also called as
partial interatrial block.

               
The most common type.

                P wave axis is normal.

  Type 2: Transiently seen Type 1 or Type 3.

  Type 3: In addition to the widening, the inferior leads show biphasic +- P waves.

                Also called as
complete interatrial block.

               
Rare type.



For the detection of IAB

  The onset of the P wave is defined as the junction between the TP isoelectric line and

      the beginning of P deflection.

  The offset of the P wave is defined as the junction between the end of the P deflection and

      the PR segment.

 
NOT PR interval, but only the duration of P wave is measured to decide for IAB.

  Observation of widened P wave may be difficult in the presence of low voltage.

  In case of low voltage, re-recording the ECG at
20 mm/mV may help to detect the onset and

      termination of P waves more clearly.






Prognostic significance

  IAB is associated with the development of

            - atrial fibrillation

            - atrial flutter

            - increased global and cardiovascular mortality




References

  Journal of Electrocardiology 2012;45:445-451.

  Am J Cardiol 2006;98:936-937.

  Am J Cardiol 2003;91:882.

  Ann Noninvasive Electrocardiol 2006;11:259-262.

  Journal of Electrocardiology 2009;42:687-692.

  Journal of Electrocardiology 2006;39:177-179.

  Journal of Electrocardiology 2006;39:380-384.

  Journal of Electrocardiology 2005;38:324-326

  Circulation 1978;57:213-216.

  Europace 1999;1:43-46.





ECG 1a. The ECG above is from a 74 years-old woman with mitral stenosis and severe mitral regurgitation.
This ECG was recorded before her hospitalization for heart failure.
Wide P waves denote
interatrial block.

Click here for a more detailed ECG




ECG 1b. Above is her ECG after one week of intensive diuretic treatment.
Wide P waves and interatrial block are not seen now.

Click here for a more detailed ECG





ECG 2a. The ECG above is from a 58 years-old man with paroxysmal atrial fibrillation.
P waves are not easily discernible because of low voltage in the limb leads.
However, leads V3 and V4 show
wide P waves suggesting interatrial block.

Click here for a more detailed ECG




ECG 2b. The ECG above was recorded from the same patient at a calibration of 20 mm/mV.
Wide P waves and interatrial block is overtly seen now.

Click here for a more detailed ECG





ECG 3. Type 2 interatrial block:
Transient widening of the P wave ( atrial aberration ).
Aberration of the atrial premature contraction.
The ECG above is from a 46 years-old woman.

Click here for a more detailed ECG





ECG 4. Type 1 interatrial block: The ECG above is from a 70 years-old hypertensive man.
He had previously undergone aortic valve replacement and coronary artery bypass grafting surgery.
Now, he has significant left ventricular systolic dysfunction.
The
wide P waves in lead II denote Type 1 interatrial block.

Click here for a more detailed ECG





ECG 5. Type 2 interatrial block:
Transient widening of the P wave ( atrial aberration ).

Click here for a more detailed ECG





ECG 6. When measuring P wave duration,
the widest P waves are noted.

Click here for a more detailed ECG





ECG 7. The ECG above is from an old man with hypertension, chronic renal failure and left ventricular hypertrophy.
In subjects with prominent
U waves , the T, U and P waves must be discerned.

Click here for a more detailed ECG





ECG 8. The ECG above is from a 64 years-old man with mild mitral valve stenosis.
Wide P waves denote interatrial block.
The P waves in V3 are
notched.

Click here for a more detailed ECG




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