Relationship of the P Loop Measurements to Pulmonary Artery Wedge Pressure and Left Atrial Volume in Pure Mitral Stenosis

Frank vectorcardiographic P loops with satisfactory signal to noise ratio were obtained from 28 patients with pure mitral stenosis by using computer-averaging technique of eight successive beats. Twenty-three parameters of the P loop automatically measured were compared with the mean pulmonary artery wedge pressure (mPAW) and the maximal left atrial volume (max. LAV) calculated from biplane angiocardiogram by the area-length method. There was a significant correlation between the m PAW and four P loop measurements. The positive amplitude in lead Z (the posterior component) showed the highest correlation with the mPAW (r=0.54, p less than 0.01). In the multiple regression analysis, the predicted m PAW using eight P loop measurements and the measured m PAW showed a high significant correlation (r=0.86, p less than 0.01). There were significant correlations between the max. LAV and fourteen P loop measurements. The magnitude of spatial maximal P-vector showed the highest correlation with the max. LAV (r=0.86, P less than 0.01). In the multiple regression analysis, the predicted max. LAV using four P loop measurements out of 23 showed the best correlation with the measured max. LAV (r=0.94, P less than 0.01).