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Medical Definition of Atrial echo
1. Electrical reactivation of the atrium by a retrograde impulse returning from the A-V node while the antegrade impulse continues to the ventricle; characterised electrocardiographically, by a pair of P waves enclosing a QRS complex, the second P wave being inverted, indicating that it is the reverse (the retrograde pathway) of the pathway of the first P wave (the antegrade pathway). (05 Mar 2000)