The Vectorcardiographic Study of the P Loop in Adults with Ostium Secundurn Atrial Septal Defect

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Frank vectorcardiographic P loops with satisfactory signal-to-noise ratio were obtained from 44 patients with ostium secundum atrial septal defect (OSASD), confirmed at operation, by using computer-averaging technique of 8 successive beats. Morphological and quantitative analyses of the P loop were made in order to reveal those characteristics of the P loop in OSASD which seemed most typically to show volumetric or diastolic overloading of the right atrium. Twenty-three automatically measured parameters of the P loop were compared with hemodynamic variables such as the systolic right ventricular pressure (s-RVP) and the left-to-right shunt ratio.A majority of the maximal P-vector directions in 3 projection planes and the P duration were within normal 95 percentile ranges. The magnitude of the maximal horizontal, the magnitude of mean polar and the magnitude of the maximal spatial P-vector increased above the 97.5 percentile values considered as the upper limit of normality in 66%, 55%, and 50% of the cases, respectively. These findings seem to suggest that the vectorcardiographic analysis of the P loop with computer-averaging technology is a valuable screening tool of right atrial diastolic overloading.Although the horizontal P loop of normal subjects showed many different patterns, the horizontal P loop of OSASD could be divided morphologically into 3 groups (Type A, Type B, and Type C). Thirteen cases (30%) out of 44 were of Type A, 22 cases (50%) Type B, and 9 cases (20%) Type C. There was a significant age difference between the individual mean values in the 3 groups (p<0.01), and there was a significant difference between the mean values in the shunt ratio of groups Type A and Type B and group Type C (p<0.01). The horizontal P loop pattern seems to be very important in the vectorcardiographic diagnosis of the presence and degree of the right atrial diastolic overloading.There was a significant correlation between 5 P-loop parameters and s-RVP, and between 3 of the parameters and the shunt ratio. The correlation between magnitude of the maximal horizontal P vector (XmV) and the shunt ratio (Y%) was the highest of all (r=0.426, p<0.01), the regression equation being Y=130.7X+49.8 (SEE=11.5%). These findings seem to suggest that the horizontal P loop can provide valuable information for the vectorcardiographic diagnosis of the presence of right atrial diastolic overloading and for estimating the degree of its severity.
International Heart Journal刊行会の論文

The Vectorcardiographic Study of the P Loop in Adults with Ostium Secundurn Atrial Septal Defect

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