Right atrial enlargement

The left panel shows the normal pattern of atrial activation as it would appear on lead II of the electrocardiogram: activation of the right atrium (RA) occurs first, followed by left atrial (LA) activation. The right panel shows the pattern in a patient with right atrial enlargement: prolonged activation of the right atrium, due to dilatation, hypertrophy, scarring, or a conduction abnormality, results in simultaneous activation of the right and left atria. The synchronous electrical activity has an additive effect upon the surface ECG, resulting in a relatively narrow P wave which is of increased amplitude (P pulmonale). The amplitude of the P wave may become significantly increased in the presence of right atrial hypertrophy; it also becomes peaked due to the increase in amount of depolarized tissue.