[Myocardial scintigraphy with technetium 99m MIBI in patients with left bundle branch block]

Myocardial perfusion scintigraphy is a non-invasive method helpful for evaluating the coronary heart disease. Its use may be particularly indicated in cases of inconclusive ECG (i.e. in left bundle branch block, LBBB). On the other hand there are observations indicating the decreased accumulation of the radiotracer in the septal segments of myocardium in patients with left bundle branch block (LBBB). This phenomenon previously described for the thallium-201, recently was also reported in the MIBI 99mTc studies. Purpose of the present study were: (1) to check the frequency of the diminished uptake of the radiotracer (MIBI 99mTc) in the LBBB patients, and (2) to test its interference with the evaluation of the coronary heart disease.

Our observation material included 42 patients in mean age 49 +/- 7 yr (26 women) divided into 3 groups: Group I--12 patients without intraventricular conduction disorders and with normal coronarography (the reference group), Group II--15 patients with LBBB and no signs of coronary artery disease in angiography and Group III--15 patients with LBBB and coronary artery disease confirmed by angiography. All patients underwent stress-rest perfusion scintigraphy according to a 2-days protocol. Submaximal bicycle exercise test was performed using the Bruce protocol. A single-head SPECT scintillation camera (DIACAM-Siemens) was used to acquire 64 views over 180 degrees. Acquisition was started 60-90 minutes after injection of MIBI 99mTc (800 MBq). After generating tomographic images their reorientation towards the left ventricle axes and creating the bull's eye polar maps were carried out with the aid of manufacturer's programs.

The mean decrease of the radiotracer accumulation in the septal segment was similar in both groups of patients with LBBB (32.7 +/- 9.5 vs 28.5 +/- 8.6 in stress and 27.6 +/- 9.5 vs 27.5 +/- 7.9 in rest in groups II and III, respectively). It was, however, significantly less pronounced in the reference (I) group (the mean decrease being 17.7 +/- 4.7 or 16.9 +/- 5.5 in stress and rest studies, respectively). Distribution of MIBI 99mTc in the myocardium was more homogeneous in the reference group (the maximal differences of the radiotracer accumulation never exceeded 45%) than in the LBBB groups. In the group II defects of the maximal depth over 46% were observed in 9 patients (60%), and in the group C in 12 patients (80%). In 6 patients of the latter group maximal depth of decets exceeded 56% (value never found in group II).

The diminished uptake of MIBI 99mTc in the septal segment of the left ventricle is a common phenomenon. In some cases it may interfere with the evaluation of the perfusion scintigraphic studies. The more pronounced defects, however, may be significant for the coronary artery disease.