Superior Defect on 45 Degree Left Anterior Oblique Radiothallium Image: Is it a Normal Variation?
Superior defects involving approximately a proximal third of the septum and a proximal third of the posterolateral wall (basilar region) of the left ventricular myocardium on the 45 degree left anterior oblique (LAO) images are frequently encountered. Clinicians may presume the presence of coronary artery disease or normalcy but the exact statistical significance of such defects has never been established. In 45 patients who underwent radiothallium imaging and coronary arteriography, the presence or absence of superior defect was correlated with the presence of coronary artery disease (CAD) in the left anterior descending (LAD) and/or circumflex arteries (CA). Presence of superior defect on the 45 degree LAO image was not associated with increased frequency of CAD. Superior defects are observed in approximately one-third of patients undergoing radiothallium myocardial perfusion studies. In most cases the defects are fixed; reveal no redistribution on delayed imaging and represent normal variations. In a rare patient the defect may be reversible and presence of redistribution may be indicative of ischemia.
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