[Vectorcardiographic findings in atrial enlargement].

Rational interpretation of changes of the P loop, due to atrial enlargements, must be based on the magnitude and spatial orientation of the main resulting vectors of the atrial activation phenomenon. Under normal conditions, these ones give origin to a mean vector oriented to the left, downward and slightly forward. Right atrial enlargement can be recognized by P loops of more than 100 mcv. The main axis of the elongated PF is comprised between + 60 degrees and + 90 degrees; that of the open PH between + 70 degrees and + 80 degrees and that of PS is located around + 135 degrees. Left atrial enlargement can be diagnosed by a characteristic box glove configuration of the PF loop as well as by an eight-shaped PH. In some cases, the PS loop also becomes eight-shaped. Biatrial enlargement gives rise to slurrings and notchings of the distal portion of the PF loop, a diphasic aspect and frequently an eight-shaped configuration of the PH loop and a triangular morphology of PS, whose base lasts 30 msec. or more.