Assessment of left ventricular enlargement from planar thallium-201 images

Although a subjective assessment of left ventricular (LV) size can be made from planar thallium images, the validity of this practice had not been critically assessed. The objective of this study was to determine the accuracy of planar thallium imaging in the assessment of LV size by using two-dimensional guided M-mode echocardiographic measurements as the standard. Consecutive patients (n = 100) who had clinically indicated stress thallium and echocardiography done within a time interval of 1 month were selected. LV size was classified as dilated or normal on immediate and 4-hour-delayed thallium scans by the consensus of two blinded observers. When present, perfusion defects were noted. LV end-diastolic internal diameter (LVIDd) was measured on M-mode images. The mean LVIDd was 5.7 cm in patients with dilated LVs compared with 5.0 cm in those with normal LVs (p < 0.01). By using an LVIDd of 5.6 cm as the upper limit of normal, the sensitivity and specificity of planar thallium imaging for detection of left ventricle enlargement were 87% and 86%, respectively. Corresponding positive and negative predictive accuracies in this population were 65% and 96%, respectively. There was a higher incidence of fixed defects in group 1 (p < 0.01). We conclude that LV enlargement can be easily and reliably determined from routine planar thallium images.