INTRODUCTION: The precise clinical utility of lung 201Tl uptake in exercise SPECT myocardial perfusion imaging remains open to research. This study validates an optimal index for lung 201Tl uptake measurement and assesses its value in the prediction of higher-risk coronary artery disease (CAD).
METHOD: Three hundred and ninety-eight patients underwent exercise SPECT myocardial perfusion imaging. They were separated into derivation (n = 217) and validation (n = 186) groups, both including sub-populations of lower- and higher-risk CAD, according to coronary angiography. Another 56 individuals with a low probability of CAD comprised the control group. From a planar, anterior, post-exercise acquisition, the lung (L) to heart (H) maximal (L/H(max)), total (L/H(mean)) and background-subtracted total (L/H(net)) ratios were calculated. These were also adjusted for confounding variables, as assessed from the control group. ROC analysis was used to compare the L/H ratios and define thresholds of abnormality. The performance of the optimal index was assessed in the derivation group and was then tested in the validation population. Subsequently, it was compared with other scintigraphic, exercise electrocardiography and clinical variables.
RESULTS: In the derivation group L/H(net) was a better discriminator for higher-risk CAD than both L/H(max) and L/H(mean). Similarly, the adjusted L/H(net) was a better discriminator than both the adjusted L/H(max) and the adjusted L/H(mean). No significant difference was attained between L/H(net) and the adjusted L/H(net). At the upper defined threshold of abnormality, sensitivity and specificity of L/H(net) in the detection of higher-risk CAD in the derivation and the validation cohorts were 52% and 92% versus 47% and 94%, respectively (p = ns). The results were similar at other defined thresholds. Moreover, L/H(net) was found to be a significant predictor of higher-risk CAD, superior to myocardial perfusion images, transient ventricular dilation measurements, and clinical and exercise testing variables (ROC analysis and logistic regression). By raising the threshold of abnormality of L/H(net), specificity and positive predictive value increased, whereas sensitivity and negative predictive value decreased.
CONCLUSION: Lung 201Tl assessment assists substantially in the identification of higher-risk CAD in exercise SPECT myocardial perfusion imaging and this is best achieved by L/H(net). This index is a significant predictor of higher-risk CAD, superior to myocardial perfusion images, and its value is associated with the probability of a disease state.