Abstract
Although a superior frontal plane ORS axis SA is considered pathognomonic of a left anterior hemiblock (LAH), the latter has not been proven to be the basis for the SA in ostium primum defects(OP). To elucidate the mechanism of SA in OP, the influence of abnormal hemodynamics(AH), ventricular hypertrophy (VH) and right bundle branch block (RBBB) on the SA was studied pre and postoperatively in 29 patients with OP. A mean SA of -75 was found with right ventricular pressure ≥40mmHg or left to right shunts > 3:1 and -50 with lower values. Preoperatively mean SA was -70 in presence of VH and -30 in its absence. Postoperative resolution of VH resulted in a shift of mean SA from -70 to -30 with 3 returning to normal. With persistence of VH there was no change in the SA. Surgically induced RBBB shifted the SA more superiorly and rightward. The dependence of SA on AH, VH and RBBB suggest that LAH is not the basis for SA. In OP early activation of the posterobasal region of the left ventricle through an abnormal posterior fascicle results in minimal SA and is then exaggerated with AH, VH and RBBB. Thus SA in OP with RBBB does not represent a true bifascicular block and has a different natural, history and clinical significance.
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Borkon, A., Varghese, P., Pieroni, D. et al. AN ALTERNATE EXPLANTION FOR SUPERIOR AXIS IN OSTIUM PRIMUM ASD OTHER THAN LEFT ANTERIOR HEMIBLOCK. Pediatr Res 8, 347 (1974). https://doi.org/10.1203/00006450-197404000-00045
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DOI: https://doi.org/10.1203/00006450-197404000-00045