Comparison of exercise radionuclide angiography with thallium SPECT imaging for detection of significant narrowing of the left circumflex coronary artery

Although quantitation of exercise thallium tomograms has enhanced the noninvasive diagnosis and localization of coronary artery disease, the detection of stenosis of the left circumflex coronary artery remains suboptimal. Because posterolateral regional wall motion during exercise is well assessed by radionuclide angiography, this study determined whether regional dysfunction of the posterolateral wall during exercise radionuclide angiography is more sensitive in identifying left circumflex disease than thallium perfusion abnormalities assessed by single-photon emission computed tomography (SPECT). One hundred ten consecutive patients with CAD were studied, of whom 70 had a significant stenosis of the left circumflex coronary artery or a major obtuse marginal branch. Both regional function and segmental thallium activity of the posterolateral wall were assessed using visual and quantitative analysis. Left ventricular regional function was assessed objectively by dividing the left ventricular region of interest into 20 sectors; the 8 sectors corresponding to the posterolateral free wall were used to assess function in the left circumflex artery distribution. Similarly, using circumferential profile analysis of short-axis thallium tomograms, left ventricular myocardial activity was subdivided into 64 sectors; the 16 sectors corresponding to the posterolateral region were used to assess thallium perfusion abnormalities in the left circumflex artery territory. Qualitative posterolateral wall motion analysis detected 76% of patients with left circumflex coronary artery stenosis, with a specificity of 83%, compared with only 44% by qualitative thallium tomography (p < 0.001) and a specificity of 92%. Whereas quantitation of thallium activity increased the sensitivity for detecting left circumflex coronary artery stenosis to 80% with a specificity of 55%, it did not achieve statistical significance when compared with qualitative wall motion analysis. Similarly, quantitation of the posterolateral regional function did not improve the sensitivity for detecting left circumflex coronary artery stenosis (74%) when compared with qualitative regional function. A similar analysis applied to the interventricular septum revealed a higher predictive accuracy for detecting left anterior descending coronary artery stenosis by qualitative thallium SPECT, with a sensitivity of 80% and a specificity of 71%, compared with a sensitivity of 68% and a specificity of 57% by qualitative radionuclide angiography. Quantitation of thallium activity in both septal and anterior regions provided no additional insight for detection of left anterior descending artery stenosis. Thus, for noninvasive detection of left circumflex coronary artery disease, the data suggest that qualitative exercise radionuclide angiography is preferable to qualitative thallium SPECT and provides comparable information to quantitative thallium analysis.