TC-99M HEXAKIS 2-METHOXY-2-ISOBUTYLISONITRILE MYOCARDIAL SCINTIGRAPHY FOR 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 bundle 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 artery disease (CAD) 96 patients with LBBB and anginal pain and without evidence 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) were evaluated. All individuals underwent Tc-MIBI scintigraphy at exercise and at rest after exercise. The results were compared with the Tl-201 findings of the same patients and with their coronary angiograms which were blinded or unknown at the time of the nuclear studies. Patients in group 3 had persistent pronounced septal defects comparable to that in Tl-201 studies. Patients in group 2 revealed reversible septal defects. The reversibility of Tc-MIBI defects was, however, significantly lower than that of Tl-201. Surprisingly, patients in group 1 had persistent septal defects in Tc-MIBI after an exercise rest study but reversible septal defects in Tl-201 studies. In order to elucidate this discrepancy, an additional Tc-MIBI preexercise rest study (in 10 patients of each group) and an additional Tl-201 rest study (in 10 patients of group 1) were carried out. In an additional Tc-MIBI preexercise rest study, patients in group 3 had septal defects, in group 2 and in group 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 patients with LBBB, Tc-MIBI uptake at preexercise rest reflects myocardial perfusion at rest, whereas Tc-MIBI uptake at postexercise rest seems to be not determined solely by restperfusion, but it may reflect prolonged exercise-induced metabolic alterations which lead to a reduced Tc-MIBI net uptake in the postexercise rest study.