Changes in heart dipole moment after surgical correction of atrial septal defect.

Spatial dipole moment of the heart (M) was measured in patients before and 1 to 2 weeks after repair of atrial septal defect. In normals three peaks of M were found, corresponding to excitation of the septum (M1), ventricular walls (M2), and basal portion of ventricles (M3). Most of the patients also had an M2a peak at 52 to 56 per cent of QRS duration. The patients with secundum defects were divided into two groups, A and B, depending on whether right ventricular pressure was less than or greater than 30 mm. Hg. M1 was smaller for the Group B patients than for the normals for Group A and decreased slightly after surgery. M2 was about half normal for Group A and one third normal for Group B. After surgery M2 increased for both Groups but was still below normal. There were small mean clockwise rotations of the M2 vector in the horizontal plane PO. The M2a vector pointed to the right anterior or posterior and generally downward. In three Group A patients the M2a peak disappeared PO but in two others it increased in magnitude with a counterclockwise rotation in the horizontal plane. In the Group B patients, M2a increased in all cases. The M3 vectors generally increased slightly in magnitude postoperatively. M3 pointed posteriorly in the normals but to the right in the patients, with little change in direction after surgery. Both P and T curves dropped in magnitude after surgery. The changes observed may be due in part to restoration of right ventricular blood volume towards normal after surgery. The remaining VCG abnormalities should be due to right ventricular hypertrophy.