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 IAB development.

  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 and in patients older than 60 years.



Types of interatrial block

  Type 1:
- Only 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 widening, inferior leads show biphasic +- P waves.
- Also called as complete interatrial block.
- Rare type.



For the detection of IAB

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

  The offset of 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 diagnose 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 and 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.

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

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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.

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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.

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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.

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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.

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

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

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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.

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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.

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ECG 9. The ECG above is from a 82 years-old man who was admitted late to hospital for acute anterior myocardial infarction.
He had also experienced acute inferior wall myocardial infarction 4 months ago.
The wide and notched P waves in leads V3, V4 and V5 show interatrial block.

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ECG 10. The ECG above was recorded from a 59 years-old man during acute inferior wall myocardial infarction.
Urgent coronary angiography showed proximal and total occlusion of the Right Coronary Artery (RCA).
The Left Anterior Descending (LAD) and Circumflex (Cx) coronary arteries had significant stenoses, too.
P waves in inferior leads have terminal negativity (Type 3 interatrial block)

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ECG 11a. A 66 years-old woman had been implanted a pacemaker for sick sinus syndrome 4 months ago.
Because of syncope and self-limited polymorphic ventricular tachycardia (VT) attack,
her pacemaker was later upgraded to a dual-chamber ICD.
The above ECG was recorded at the time of ICD implantation. The QT interval is normal.
There is no interatrial delay.

The ECG above has been used with the permission of Texas Heart Institute Journal.

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Click here to go to the relevant article of the Texas Heart Institute Journal



ECG 11b. The above ECG belongs to the same patient. It was recorded one month after the ECG 1a.
Her ICD was delivering shocks for VT attacks.
Atrial pacing at an interval of 60/minute, prolonged QT interval (QTc 550 ms), low voltage in limb leads and
a pseudoinfarct pattern (QS waves in anteroseptal leads) are seen in the above ECG.
Prolonged P wave duration after atrial spikes denotes interatrial block (which is not rare during atrial pacing).

The ECG above has been used with the permission of Texas Heart Institute Journal.

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Click here to go to the relevant article of the Texas Heart Institute Journal



ECG 11c. The above ECG belongs to the same patient.
A ventricular ectopy occurring during the vulnerable period of the preceding T wave starts a polymorphic VT attack.
The basic rhythm is atrial pacing at a rate of 60/minute.
Prolonged P wave duration after atrial spikes denotes interatrial block.
Interatrial block is not rare during atrial pacing.

The ECG above has been used with the permission of Texas Heart Institute Journal.

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Click here to go to the relevant article of the Texas Heart Institute Journal




ECG 12a. The above ECG is from a 52 years-old man. He was diagnosed as having severe mitral stenosis just 2 weeks ago.
(with a mitral valve area of 0.7 cm2). The wide and fragmented P waves denote interatrial block.
The duration of the P wave is more than 4 small squares (>160msec).
The initial portion of the P wave and the second part of it are easily discernible.



ECG 12b. The above ECG belongs to the same man. It was recorded 1 week after ECG 12a when he complained of palpitations.
Interatrial block is associated with the development of atrial fibrillation.

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ECG 13. The ECG above is from a 78 years-old man. It was recorded 24 hours after acute inferior myocardial infarction.
He had undergone coronary artery bypass graft surgery 20 years ago.
Lead III shows wide and biphasic P waves: type 3 interatrial block.

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ECG 14a. The above ECG shows both interatrial block and complete (3rd degree) AV block.
It was recorded during acute inferior wall myocardial infarction.
P waves are not related to the QRS complexes. Therefore, some P waves are buried in QRS complexes.
The P wave width is slightly more than 120 milliseconds: interatrial block.
This ECG was recorded at a calibration of 20 mm/mV to show interatrial block.

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ECG 14b. Above is his ECG at a standard 10 mm/mV calibration.
It is difficult to see interatrial block and complete AV block, at first glance.

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ECG 15. The ECG above is from a 85 years-old man with a VVI pacemaker and normal coronary arteries.
Interatrial block is clearly seen at a calibration of 20 mm/mV.
In this patient, the time interval between the onset and the end of the P wave is 200 msec.
Pacemaker spikes can be seen only in some leads.

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ECG 16. The compact ECG above is from a 41 years-old man with significant mitral valve stenosis (mitral valve area 0.7 cm2).
Type 3 interatrial block is seen: widened and biphasic P wave in lead III.




ECG 17. The ECG above is from a 52 years-old woman with hypertension.
ECHOcardiography showed hypertrophy of the interventricular septum.
At first glance, P waves in leads V2 and V3 may seem like interatrial block (widened P wave).
However, this appearance is due to fusion of the U wave with the P wave.
P waves in other leads are not wide. This also supports that there is U-P wave fusion in leads V2 and V3.
It is well-known that U waves are best seen in leads V2 and V3.
Therefore, U-P wave fusion is most frequently seen in leads V2 and V3.

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ECG 18. The ECG above belongs to a 39 years-old man with mitral valve stenosis.
Type 1 interatrial block (widened P wave) is best seen in lead II. PR interval is prolonged.
ECHOcardiography showed severe mitral valve stenosis, left atrial dilation and moderate pulmonary hypertension.

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