The vectorcardiographic estimation of left ventricular filling pressure following acute myocardial infarction.

High gain vectorcardiograms, in the "timed" mode, have been recorded in 50 patients hospitalized with noncardiac complaints, and in 32 previously well patients following acute myocardial infarction. The terminal component of the atrial vector loop has been analysed in the horizontal, frontal and sagittal planes in all the cases. A technique is described by which the three variables, magnitude, direction and depolarization time of the terminal atrial vector in each plane can be summated to give a numerical value for the total displacement of left atrial activity. This figure is referred to as the "total vector value". In the 32 postinfarction patients the "P-terminal force" was also measured from lead V1 of the scalar electrocardiogram. In these patients both the total vector value and the "P-terminal force" was correlated with the pulmonary diastolic pressure, as an indirect assessment of left ventricular filling pressure. In the immediate postinfarction period the correlation between the total vector value and the pulmonary diastolic pressure was good (r = 0.92), but that between the "P-terminal force" and the pulmonary diastolic pressure was poor (r = 0.11). Alterations in atrial electrical activity recorded by either method correlated poorly with changes in the pulmonary arterial pressure occurring more than 36 h after acute infarction. The "total vector value" provides an accurate noninvasive method for the detection of a rise in the left ventricular enddiastolic pressure within the first 36 h following an acute myocardial infarction. It is superior in this respect to the "P-terminal force" measured from the standard scalar electrocardiogram.