TC-99M HEXAKIS 2-METHOXY-2-ISOBUTYLISONITRILE MYOCARDIAL SCINTIGRAPHYFOR THE NONINVASIVE DIAGNOSIS OF CORONARY-ARTERY DISEASE IN PATIENTS WITH COMPLETE LEFT-BUNDLE-BRANCH BLOCK

Thallium-201 mycardial scintigraphy is usually indeterminate for left anterior descending (LAD) coronary disease in the presence of left bun dle branch block (LBBB). To determine whether Tc-99m-hexakis 2-methoxy -2-isobutylisonitrile (Tc-MIBI) myocardial scintigraphy could improve the diagnostic accuracy in LBBB for the detection of LAD coronary arte ry disease (CAD) 96 patients with LBBB and anginal pain and without ev idence of dilated cardiomyopathy at the time of the study (group 1: 53 patients without CAD; group 2: 25 with isolated LAD stenosis without infarction; group 3: 18 with isolated LAD stenosis with infarction) we re evaluated. All individuals underwent Tc-MIBI scintigraphy at exerci se and at rest after exercise. The results were compared with the Tl-2 01 findings of the same patients and with their coronary angiograms wh ich were blinded or unknown at the time of the nuclear studies. Patien ts in group 3 had persistent pronounced septal defects comparable to t hat in Tl-201 studies. Patients in group 2 revealed reversible septal defects. The reversibility of Tc-MIBI defects was, however, significan tly lower than that of Tl-201. Surprisingly, patients in group 1 had p ersistent septal defects in Tc-MIBI after an exercise rest study but r eversible septal defects in Tl-201 studies. In order to elucidate this discrepancy, an additional Tc-MIBI preexercise rest study (in 10 pati ents of each group) and an additional Tl-201 rest study (in 10 patient s of group 1) were carried out. In an additional Tc-MIBI preexercise r est study, patients in group 3 had septal defects, in group 2 and in g roup 1 had normal septal uptake which is comparable to that in Tl-201 delayed or in an additional Tl-201 rest study. These results indicate; (1) that Tc-MIBI myocardial scintigraphy could improve the diagnostic accuracy in LBBB for the detection of LAD disease; (2) that in patien ts with LBBB, Tc-MIBI uptake at preexercise rest reflects myocardial p erfusion at rest, whereas Tc-MIBI uptake at postexercise rest seems to be not determined solely by restperfusion, but it may reflect prolong ed exercise-induced metabolic alterations which lead to a reduced Tc-M IBI net uptake in the postexercise rest study.