P wave shows atrial depolarization.

 
Ta wave shows atrial repolarization.

  During normal sinus rhythm, the Ta wave is not seen since it coincides with the QRS complex.

  Ta wave may be observed in the presence of the following:

                  o   Prolonged PR interval:
1st degree AV block

                  o  
2:1 AV block

                  o  
Complete AV block

                  o  
When P wave is tall in COPD (best seen in lead II)


  Ta wave is usually seen
like a saucer following the P wave.

  Ta wave axis
opposes P wave axis by approximately 180 degrees.

  As heart rate increases during treadmill exercise test, the Ta wave may falsely give the impression of

      ST segment depression.

  In patients with
atrial infarction, Ta wave depression is seen more often than its elevation.

  The voltage of a Ta wave produced by a retrograde P wave is generally more than that of a sinus P wave.




References

  Journal of Electrocardiology 2011;44:635-640.

  J Am Coll Cardiol 1991;18:127.

  Am Heart J 1976;91:689.





ECG 1. The ECG above belongs to a 57 years-old woman with heart failure. Her left ventricular ejection fraction is 30%. Left
bundle branch block and 1st degree AV block is seen. PR interval is about 220 msec.
P waves are followed by Ta waves .

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ECG 2. The ECG above belongs to a woman with coronary artery disease, aotic stenosis and aortic regurgitation.
There is AV block.
P waves are followed by saucer-like Ta waves . Since the axis of Ta wave is opposite to that of the P wave,
the negative P wave in lead aVR
is followed by positive Ta wave .


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ECG 3. The ECG above shows 3:1 AV block.
P waves are followed by saucer-like Ta waves .


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ECG 4. Atrial tachycardia and complete AV block is seen in the ECG above.
P waves are followed by saucer-like Ta waves .
Since the axis of Ta wave is opposite to that of the P wave,
the negative P wave in lead aVR is followed by positive Ta wave .


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ECG 5. The ECG above shows atrial tachycardia (155/min.) with 3:1 AV block.
P waves are followed by saucer-like Ta waves .
Since the axis of Ta wave is opposite to that of the P wave,
the negative P wave in lead aVR is followed by positive Ta wave .
Atrial tachycardia does not obscure the observation of Ta waves.


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ECG 6a. The ECG above belongs to a 73 years-old man with coronary artery disease, old myocardial infarction,
mild left ventricular systolic dysfunction and chronic renal failure. Several coronary stents had been implanted in the past.
It was recorded at a
calibration of 20 mm/mV to depict PR depression (Ta depression) clearly.
The
initial part of the P wave is positive and the terminal part of the P wave is negative in precordial leads.
However, the terminal negativity of the P wave is not solely responsible for the observed PR depression.
The PR segment after termination of the P wave is still depressed. This finding suggests that the patient had
infarction of atrial myocardium in the past.
He does not have chest pain or dyspnea at the moment.
He also does not have clinical or laboratory evidence of acute pericarditis.

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ECG 6b. Above is a zoomed view from a section of the ECG 6a showing
PR depression (Ta depression) clearly.