NONINVASIVE IDENTIFICATION OF SIGNIFICANT NARROWING OF THE LEFT MAIN CORONARY-ARTERY BY DIPYRIDAMOLE THALLIUM SCINTIGRAPHY

To evaluate the usefulness of dipyridamole thallium scintigraphy with low-level exercise for the identification of left main (LM) coronary artery disease (CAD), 466 consecutive patients with CAD were studied. Thirty-eight patients (8%) had LM stenosis (diameter narrowing greater-than-or-equal-to 50%). The LM scintigraphic pattern was present in 9 of 38 patients with LMCAD and 38 of 428 CAD patients without LMCAD (24 vs 9%; p < 0.005). This pattern was present in 6 of 9 patients with LMCAD without right CAD and in only 3 of 29 patients with LM and right CAD (67 vs 10%; p = 0.0005). Patients with LMCAD had a higher incidence of premature cessation of low-level exercise (53 vs 21%; p < 0.0001), chest pain (68 vs 48%; p < 0.02), blood pressure decrease of greater-than-or-equal-to 20 mm Hg (44 vs 16%; p < 0.002) and greater ST depression (0.17 +/- 0.13 vs 0.06 +/- 0.10 mV; p < 0.001) during dipyridamole loading than patients without LMCAD. Stepwise discriminant analysis revealed that the LM scintigraphic pattern and markers of ischemia during dipyridamole loading best identified (p < 0.0001) patients with LMCAD without right CAD (sensitivity 67%, specificity 91%) but this predictability is no better than the LM scintigraphic pattern alone. The combination of clinical markers of ischemia during dipyridamole loading and scintigraphic findings of diffuse slow washout, extensive fixed defects and the LM pattern best identified (p < 0.0001) patients with LM and right CAD (sensitivity 72%, specificity 80%). These results indicate that the LM scintigraphic pattern is specific and sensitive for LMCAD without right CAD. In LM and right CAD, the predictability of this finding is low, but the addition of clinical markers of ischemia during dipyridamole loading facilitates better identification.