Left atrial enlargement is typically characterized by an increase in the terminal portion of the P wave. Best seen in lead II, this terminal deflection is often demonstrated as a distinct second peak within the P wave (arrow below). In some leads, this second peak gives the P wave an "m-like" shape. This deflection does not usually affect the amplitude of the P wave, but may increase its duration to greater than 0.12 seconds. In addition to this increased P wave deflection in lead II, LAE results in a terminal negative deflection within the P wave best seen in lead V1 (see below). With extreme LAE, the amplitude of the P wave may be increased, and terminal negativity may be demonstrated in leads II, III and aVF (see below). Left atrial enlargement may result from left atrial dilatation, pressure overload (ie. from mitral valve disease) or abnormal intra-atrial conduction. Other terms frequently used to describe LAE include left atrial hypertrophy, left atrial overload and left atrial abnormality.