P wave abnormalities with myocardial infarction: an aid to the diagnosis of left ventricular failure.

An investigation during a prospective study of myocardial infarction has confirmed previous observations of P wave changes in association with left ventricular failure. Although an indicator of pre-existing left ventricular disease as well as acute left atrial distension, a negative deflection of 1 mm or more in the P wave of lead V1 should raise strong suspicions about the presence of this serious complication.